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An insight into non-covalent interactions in the tetraphenylarsonium dithiophosphates: Synthesis, DFT and Hirshfeld surface analysis
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An insight into non-covalent interactions in the tetraphenylarsonium dithiophosphates: Synthesis, DFT and Hirshfeld Surface Analysis Anu Radha , Pretam Kumar , Tahira Firdoos , Puneet Sood , Namrata Rani , Vikas , Sushil Kumar Pandey PII: DOI: Reference:
S0022-2860(20)32042-1 https://doi.org/10.1016/j.molstruc.2020.129729 MOLSTR 129729
To appear in:
Journal of Molecular Structure
Received date: Revised date: Accepted date:
2 September 2020 29 November 2020 3 December 2020
Please cite this article as: Anu Radha , Pretam Kumar , Tahira Firdoos , Puneet Sood , Namrata Rani , Vikas , Sushil Kumar Pandey , An insight into non-covalent interactions in the tetraphenylarsonium dithiophosphates: Synthesis, DFT and Hirshfeld Surface Analysis, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/j.molstruc.2020.129729
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Highlights
Synthesis and characterization of tetraphenylarsonium dithiophosphate crystals. Non-covalent C—H···X, C—H···π (X= O, S) interactions play a significant role in enhancing the stability of the salts. H…H and C…H/H…C interactions contribute more towards the total Hirshfeld surface. DFT parameters are found to be in good agreement with that determined by single crystal X-ray analysis.
1
An insight into non-covalent interactions in the tetraphenylarsonium dithiophosphates: Synthesis, DFT and Hirshfeld Surface Analysis
Anu Radhaa, Pretam Kumara, Tahira Firdoosa, Puneet Soodb, Namrata Ranic, Vikasc and Sushil Kumar Pandey*,a
a
b
Department of Chemistry, University of Jammu, Jammu–180006, J&K, India
Advanced Materials Research Center, Block-A2 Building, Kamand Campus, Indian Institute of Technology, Mandi, Himachal Pradesh-175005, India c
Quantum Chemistry Group, Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh, India *Corresponding Author’s e-mail address: [email protected]
Abstract Three tetraphenylarsonium dithiophosphate salts [Ph4As]+[S2P(OAr)2]-, where Ar = 2,4(CH3)2C6H3 (1), 3,5-(CH3)2C6H3 (2), {4-(CH3)3C}C6H4 (3), were crystallized in the monoclinic space group P21 (1), triclinic space group P¯1 (2) and monoclinic space group P21/c (3), respectively. These salts are stabilized by various non-covalent interactions resulting in the extension of their molecular structure along different axis. The cationic and anionic species are interconnected by various C—H···X, C—H···π (X= O, S) interactions leading the molecules as one-dimensional and two-dimensional supramolecular structures. A thorough Hirshfeld surface analysis elegantly quantifies the various non-covalent interactions present within the molecules. This analysis reveals that the main contributions in all the three salts are because of H…H and C…H/H…C interactions that represent 82.1%, 82.9% and 84.1% of the total contribution to the Hirshfeld surface for 1, 2 and 3, respectively. Further, the coordinates were optimized by DFT calculations with B3LYP hybrid functional along with LANL2DZ basis set. Experimental values of bond lengths and bond angles are in good agreement with the optimized structural parameters. HOMO-LUMO of the molecules were calculated using corresponding methods with the same basis set. Other computational data pertaining to chemical reactivity have indicated potential sites for nucleophilic and eletrophilic attack in the molecules.
2
Keywords: Non-covalent, Hirshfeld surface analysis, finger print plots, DFT optimized structural parameters 1. Introduction Arsenic(As) is a chemical element in the group 15 of the periodic table. It generally forms compounds in which oxidation state of +3 and +5 is exhibited. The chemistry related to the dithiophosphate complexes of As(III) has been a significant subject of research during the past few years [1-6]. A number of organo antimony(V) complexes with E-O-R linkage (E = Sb; OR = alkoxy, phenoxy, oximate) have been reported in the literature [7-11]. In comparison to them, much less attention has been paid towards the corresponding dithiophosphate complexes of As(V). Wide applications of organoarsenic dithiophosphates [R2AsS2P(OR′)2] (R = Me, Et, Ph; R′ = Me, Et], dithiocarbamates [MeAs(S2CNR2)2] and xanthates [Me2As(S2COPri)], [RAs(S2COR2)2], [As(S2COR2)3] as agricultural bactericides, insecticides, nematocides, fungicides and herbicides have been depicted in the literature [12, 13]. The pentavalent state is dominated by antimony complexes for which both inorganic and organometallic derivatives have been reported [14]. In comparison to the antimony complexes, much less work has been reported on the corresponding pentavalent complexes of arsenic. Tetraorganoarsonium dithiophosphate complexes of the formula, [R4As][S2PR′2] (R = Me or Ph; R′ = Pri, OMe) were reported in the literature, wherein both the cation and anion exhibits tetrahedral geometry and the two P-S bond lengths are equal [15-17]. Solid state crystal structures are stabilized through various non-covalent interactions such as hydrogen bonding, π···π stacking, cation-π, anion-π and C—H···X (X= O, N, S, F, Cl, Br, I) interactions. These non-covalent interactions which play an important role in supramolecular chemistry, crystal design and other areas of the molecular science includes the strong, moderate and weak interactions. Weak interactions such as C—H···X, C—H···π, π···π, X···X, X···Y (X= O, N, S, F, Cl, Br, I) are also seminal in determining the stability of the complexes [18, 19]. These non-covalent interactions are now-a-days commonly used for the self assembly of large supramolecular molecules. So far, no supramolecular interactions have been discussed in the case of tetraphenylarsonium dithiophosphate complexes. In the present study, three tetraphenylarsonium dithiophosphate salts corresponding to the formula [Ph4As]+[{2,4-(CH3)2C6H3O}2PS2]-(1), [Ph4As]+[{3,5-(CH3)2C6H3O}2PS2]-(2), [Ph4As]+[{(4– (CH3)3C)C6H4O}2PS2]- (3) have been synthesized and structurally characterized. The single
3
crystal analysis of the synthesized salts 1, 2 and 3 revealed the presence of various weak noncovalent interactions in the molecules. Hirshfeld surface analysis proves to be a pivotal tool of exploring the various noncovalent intermolecular interactions present in a molecular system and offer a very facile way of obtaining information on crystal packing [20-25]. The size and shape of the Hirshfeld surface depends on the chemical environment surrounding the molecule. The associated finger print plots provide information about the percentage contribution made by the various non-covalent interactions towards the Hirshfeld surface. Investigation of the Hirshfeld surface analysis of the three tetraphenylarsonium complexes allows a detailed scrutiny of the comparison of the weak forces experienced by each of the three complexes and the quantitative comparison of these weak interactions in these three complexes has been reflected in the associated finger print plots. 2. EXPERIMENTAL 2.1. Materials and instrumentation Tetraphenylarsonium chloride and all substituted phenols were purchased from Sigma Aldrich and
were
used
without
further
purification.
Sodium
salts
of
O,O′-substituted
diphenyldithiophosphates were synthesized by the procedure as discussed in the literature [26, 27]. Arsenic was estimated iodometrically [28]. Elemental analyses (C, H, S) were conducted using the Elemental Analyser Vario EL-III (Indian Institute of Integrative Medicine, Jammu). The 1H and
13
C NMR spectra were recorded in CDCl3 using TMS as internal reference. The
31
P NMR spectra were recorded in CDCl3 using H3PO4 (85%) as external reference on a
Bruker Avance III 400 MHz (Department of Chemistry, University of Jammu, Jammu). Infrared spectra were recorded in the range of 4000–400 cm-1 on a Perkin Elmer FT-IR spectrophotometer (Department of Chemistry, University of Jammu, Jammu).
2.2. Synthesis 2.2.1. Synthesis of [Ph4As]+[{2,4-(CH3)2C6H3O}2PS2]- (1) To a stirred aqueous solution of Ph4As+Cl- (1.16g, 2.67 mmol) was added a stirred aqueous solution of {2,4-(CH3)2C6H3O}2PS2-Na+ (1.00g, 2.77 mmol) in 1:1 molar ratio followed by continuous stirring. A white solid precipitated out. After stirring for about 30 min, the reaction mixture was filtered to obtain the white precipitates of the product [Ph4As]+[{2,4(CH3)2C6H3O}2PS2]-. The precipitates thus obtained were then dissolved in acetone and the 4
reaction mixture was then kept undisturbed for about 2-3 days resulting in the formation of the white crystals of the synthesized salt. Yield: 93.09% (1.86 g); Anal. Calc. for C40H38O2PS2As: C, 66.66; H, 5.30; S, 8.90; As, 10.39%. Found: C, 66.64; H, 5.28; S, 8.87; As, 10.36%. IR (KBr, cm-1): 1105.44 s [v(P)-O-C], 812.44 s [vP-O-(C)], 611.81 s [vP=S], 494.71 m [vP-S]. 1H NMR (CDCl3, ppm): 2.23 (s, 6H, 2-CH3), 2.29 (s, 6H, 4-CH3), 6.84 (d, J = 8Hz, 2H, H5), 6.91 (s, 2H, H3), 7.21 (d, J = 8Hz, 2H, H6), 7.67 (d, J = 8Hz, 8H, H 7.80 (t, J = 8Hz, 8Hz, H , ), 7.86 (t, J = 8Hz, 4H, H );
,
),
13
C NMR(CDCl3, ppm): 15.92 (2-
CH3), 22.62 (4-CH3), 115.22 (C6), 120.58 (C1,), 123.58 (C2), 126.61 (C5), 129.24 (C4),130.21 (C3), 133.05 (C3,,5,), 134.59 (C2,,6,), 136.25 (C4,), 152.34 (C1);
31
P NMR(CDCl3, ppm):
109.70(s) (Figure 1a) 2.2.2. Synthesis of [Ph4As]+[{3,5-(CH3)2C6H3O}2PS2]- (2) The salt 2 was also prepared by the same procedure as that used for the salt 1 i.e. by reacting Ph4As+Cl- (1.16g, 2.67 mmol) and {3,5-(CH3)2C6H3O}2PS2-Na+ (1.00g, 2.77 mmol) in 1:1 ratio resulting in the formation of white crystals. Yield: 91.09% (1.82 g); Anal. Calc. for C40H38O2PS2As: C, 66.66; H, 5.31; S; 8.90; As, 10.39%. Found: C, 66.63; H, 5.28; S, 8.88; As, 10.36%. IR (KBr, cm-1.): 1151.63 s [v(P)-O-C], 937.94 s [vP-O-(C)], 682.73 s [vP=S], 599.22 m [vP-S]. 1H NMR (CDCl3, ppm): 2.21 [s, 12H, 3,5-(CH3)2], 6.63 (s, 2H, H4), 7.04 (s, 4H, H2,6), 7.66 (d, J = 8Hz, 8H, H
,
), 7.77 (t, J = 8Hz, 8H, H , ), 7.84 (t, J = 7.6Hz, 4H, H ),
13
C NMR (CDCl3, ppm): 21.08 {3,5-(CH3)2}, 120.35 (C1,), 122.52 (C2,6), 128.25 (C4), 131.50
(C4,), 134.98 (C3,,5,), 135.77 (C2,,6,),138.63 (C3,5), 153.35 (C1).
31
P NMR (CDCl3, ppm):
108.70(s) (Figure 1b). 2.2.3. Synthesis of [Ph4As]+ [{(4–(CH3)3C)C6H4O}2PS2]- (3) Same procedure was used for the synthesis of salt 3 as that for the salts 1 and 2 using Ph4As+Cl- (1.00g, 2.40 mmol) and {(4–(CH3)3C)C6H4O}2PS2-Na+ (1.00g, 2.40 mmol) resulting in the formation of white crystals. Yield: 94.59% (1.75 g); Anal. Calc. for C44H46O2PS2As: C, 68.03; H, 5.96; S, 8.25, As, 9.64%. Found: C, 68.00; H, 5.93; S, 8.22; As, 9.61%. IR (KBr, cm-1.): 1109.64 s [v(P)-O-C], 933.74 s [vP-O-(C)], 674.80 s [vP=S], 574.02 m [vP-S] cm-1. 1H NMR (CDCl3, ppm): 4.82 (s, 18H, CH3 of (CH3)3C), 7.22 (d, J = 8Hz, 4H, H2,6), 7.31 (d, J = 7.6Hz, 4H, H3,5), 7.64 (d, J = 8Hz, 8H, H
,
), 7.77 (t, J = 7.8Hz, 8H, H
,
),
7.85 (t, J = 7.8 Hz, 4H, H ) 13C NMR (CDCl3, ppm): 31.65 (CH3 of (CH3)3C), 51.01 (tert C
5
of (CH3)3C), 121.57 (C2,6), 128.27 (C3,5), 131.45 (C3,,5,), 133.03 (C4,), 134.86 (C2,,6,), 137.90 (C1,), 145.30 (C4), 151.30 (C1). 31P NMR (CDCl3, ppm): 109.23(s) (Figure 1c)
Figure 1: Molecular structures of the salts 1-3
2.3. X-ray data collection and structure determination Crystallization of all the salts 1, 2 and 3 was done by dissolving them in minimum amount of acetone. White crystals were obtained after keeping the reaction mixture for about 2-3 days. Single-crystal X-ray diffraction data of the salts were collected with a CCD Agilent SUPERNOVAE (Dual) diffractometer using monochromatic Cu Kα radiation (λ = 1.
1 Å).
Using the program Olex 2 [29], the structures for salts 1, 2 and 3 were solved by the SHELXS program [30] and refined by full matrix least squares on F2 with the SHELXL program [30].
Table 1: Summary of the crystal structure, data collection and refinement parameters for salts 1, 2 and 3
Crystal data
1
Mr
720.71
Crystal system, space group a, b, c (Å)
2 720.71
3 776.82
Monoclinic, P21
Triclinic, P¯1
Monoclinic, P21/c
12.9898(6), 9.8492(4),
10.0755(8), 13.0884(10),
22.2434(8), 9.4923(2),
6
α, β, γ (°)
V (Å3)
13.8693(8)
14.4673(10)
19.2583(5)
90, 100.622(4),
98.075, 110.119,
90, 102.045(3)
90
98.086(6)
90
1744.01 (15)
1736.6 (2)
3976.72 (19)
Z µ (mm−1) Crystal size (mm)
2 1.18 0.35 × 0.28 × 0.19
2
4
1.18
1.03
0.23 × 0.19 × 0.14
0.27 × 0.14 × 0.12
0.477, 1.000
0.546, 1.000
0.795, 1.000
5992, 5222, 4648
9746, 7491, 6144
13562, 8642, 7009
Data collection Tmin, Tmax No. of measured, independent and observed [I> σ(I)] reflections Rint
0.052
0.033
0.027
(sin θ/λ)max (Å−1)
0.664
0.668
0.667
Refinement R[F2 > σ(F2)], wR(F2), S
0.060, 0.168, 1.03
0.044, 0.112, 1.05
0.040, 0.092, 1.06
No. of reflections
5222
7491
8642
No. of parameters
419
419
457
1
0
0
No. of restraints Δρmax, Δρmin (e Å−3)
1.1 , −1. 0
0.78, −0.
0.
, −0. 1
2.4. Hirshfeld surface analysis In order to demonstrate the interactions in the crystal structures, the Hirshfeld surface analysis was conducted and their 2D fingerprint plots were established using Crystal Explorer 17.5 software [31]. These molecular Hirshfeld surfaces in the crystal structure are constructed considering the electron distribution calculated as the sum of spherical atom electron densities [20-25]. For a given crystal system and set of spherical electron densities, the Hirshfeld surface is unique. A Hirshfeld surface is the outer contour of the space which a molecule or an atom consumes in a crystalline environment. The normalized contact distance 7
denoted by dnorm given by the equation enable the identification of the regions of particular importance to intermolecular interactions [32, 33].
+
(1)
The mapping of dnorm on the Hirshfeld surface highlights the donor and acceptor equally and hence acts as a powerful tool for analyzing directional intermolecular interactions. The positive and negative values of the dnorm denote whether intermolecular interactions are larger or smaller than the Van der Waals (vdW) separation respectively.
2.5. Computational Methodology The density functional theory (DFT) computations to obtain the optimized structure of salts are performed using Gaussian 09 quantum-mechanical software package [34, 35]. For the DFT computations, Becke-3-parameterized-Lee-Yang-Parr (B3LYP) hybrid exchangecorrelation functional along with a default Las Alamos double zeta basis set, LANL2DZ [3638] are used. The chemical reactivity of all the salts is further predicted through DFT computed HOMO-LUMO energy gap. Besides this, molecular electrostatic potential diagrams obtained from the DFT calculations are also used to determine the site for electrophilic and nucleophilic attack in the salts.
3. RESULTS AND DISCUSSION 3.1. Synthesis of salts The salts 1, 2 and 3 of the general formula [Ph4As]+[S2P(OAr)2]- [Ar = 2,4-(CH3)2C6H3 (1), 3,5-(CH3)2C6H3 (2) and {4-(CH3)3C}C6H4 (3)] were synthesized by the similar procedure by adding an aqueous solution of tetraphenylarsonium chloride to the aqueous solution of the sodium salt of the corresponding substituted dithiophosphate in 1:1 ratio at room temperature. The white precipitates thus formed when dissolved in acetone and kept for 2-3 days resulting in the formation of white crystals (Scheme 1).
(ArO)2PS2-Na+ + Ph4As+Cl-
H2O stirring 30 min -NaCl
[Ph4As]+[S2P(OAr)2]-
[Ar = (2,4-CH3)2C6H3 (1), (3,5-CH3)2C6H3 (2), {4-(CH3)3C}C6H4 (3)] Scheme 1: Reaction scheme highlighting the formation of the salts 1-3 8
3.2. IR Spectroscopy Interpretation of the IR spectra of the corresponding tetraphenylarsonium dithiophosphate salts was made on the basis of the corresponding sodium and triethylammonium salt of the akin dithiophosphate complexes as no literature available specifically on tetraphenylarsonium dithiophosphates. The infrared spectra of the tetraphenylarsonium dithiophosphate salts are almost similar to the corresponding sodium and triethylammonium salt with a slight variation [39, 40]. For all the salts 1-3, [v(P)−O−C] and [vP−O−(C)] stretching vibrations were observed as sharp peaks in the region 1164.09–1105.44 cm-1 and 850.23–812.44cm-1, respectively. The sharp to medium intensity bands of [vP=S] stretching vibrations for all the salts were found in the region 689.58-611.81 cm-1. The medium intensity bands in the range 497.66-486.31cm-1 are assignable to [vP−S] vibrations.
3.3. NMR spectroscopy In the 1H NMR spectra, all the salts 1-3 exhibit the proton signals with the expected peak multiplicities. The –CH3 protons of the methyl substituent in case of salts 1 and 2 exhibit their singlet in the range 2.25-2.30 ppm. The –CH3 of the tert-butyl group exhibits its resonance at 1.27 ppm. The protons of the phenyl rings of the substituted dithiophosphate exhibit their resonance in the range 6.63-7.67 ppm. The protons of the phenyl ring of the tetraphenylarsonium exhibit their peaks in the range 7.64-7.86 ppm. The 13C NMR spectra consist of all the peaks expected for the carbon atoms present in the molecules. The carbon atoms of the phenyl rings of both the substituted dithiophosphate anion and tetraphenylarsonium cation shows their chemical shifts in the range 115.22-153.35 ppm. The chemical shifts of the methyl substituent attached to the phenyl rings in case of salts 1 and 2 appear in the range 15.92-22.62 ppm. The methyl groups of the tert-butyl substituent in case of salt 3 reveal their resonance at 31.65 ppm. A single resonance was observed in the
31
P NMR spectra (proton-decoupled) of all
the complexes. The chemical shift of all the salts 1-3 exhibits a singlet in each case in the range 108.70–109.76 ppm. The appearance of a single sharp peak in this range clearly indicates the ionic nature of the synthesized tetraphenylarsonium dithiophosphate salts.
9
3.4. Molecular and crystal structure of salts 1, 2 and 3 The salts 1, 2 and 3 crystallized in the monoclinic point group with space group P21, triclinic point group with space group P¯1 and monoclinic point group with space group P21/c, respectively. Molecular structure of all the three salts 1, 2 and 3 with partial atomic numbering is shown in the Figure 2. These salts exist in the cation anion form. The cationic part consists of tetraphenylarsonium moiety having central arsenic atom attached to four phenyl rings. The anionic part consists of a substituted dithiophosphate moiety having phosphorus atom attached to two sulfur and two oxygen atoms. Selected bond lengths and bond angles of all the three salts are mentioned in Table 2. All coordinate bond lengths and bond angles
are within
the range of values previously reported for
related
tetraphenylarsonium salts [16, 17]. A slight variation between the parameters of previously reported and the newly synthesized tetraphenylarsonium salts occur that may be due to the effect of the steric bulkiness of the alkyl moiety attached to the phenyl ring. A deviation from the standard tetrahedral parameters is observed in case of all the three salts. The maximum deviation is depicted in case of S—P—S {121.33(5) in case of salt 1, 121.33(5) in case of salt 2 and 121.21(5) in case of salt 3} which may be due to the steric bulkiness of the substituent moiety attached to the phenyl ring. The P—S bond lengths in all the three salts {1.956(2) and 1.960(2) in case of salt 1, 1.946(11) and 1.948(11) in case of salt 2, 1.952(9) and 1.946(9) in case of salt 3} are within the range of values previously observed for the tetraphenylarsonium salts{1.995(2) and 1.991(1) in case of tetraphenylarsonium diisopropyldithiophosphinate and 1.954(3) and 1.944(2) in case of tetraphenylarsonium O,O-dimethyldithiophosphate salts} [16, 17]. In all the three salts, P—S bond lengths are almost equivalent which indicates the delocalization of the negative charge over the whole S—P—S fragment. In all the three salts, the cationic and anionic moieties are interlinked through various non-covalent interactions such as C—H···O, C—H···S and C—H···π [41-45] interactions which enhance the stability of the salts as well as results in the extension of the monomer moieties towards different crystallographic axis. The non-covalent interactions present in the molecules are mentioned in the Tables 3 and 4. In case of salt 1, each anionic unit is attached to a cationic unit and two other adjacent anionic moieties through C—H···O interactions. The two oxygen atoms of the dithiophosphate anionic moiety exhibit O···H interaction with an adjacent cationic (C10— H10···O1) and anionic moiety (C39—H39B···O2) while the hydrogen of the methyl group
10
attached to the phenyl at para position undergoes this interaction with another adjacent anionic moiety (C39—H39B···O2) (Figure 3a). The carbon C10 of the tetraphenylarsonium at (x, y, z) acts as donor to the oxygen O1 of the substituted dithiophosphate anion at (x, y, z) through C10—H10···O1 interaction and the carbon C39 of the substituent methyl group attached to the phenyl ring at (x, y, z) acts as donor to the oxygen atom O2 of other anionic moiety at (-x+1, -y+1/2, -z+1) through C39—H39B···O2 interaction. These C—H···O interactions in the salt results in a 2D extension of the molecule showing different patterns when viewed along different crystallographic axis. Figure 3b shows C—H···O interactions in salt 1 when viewed along b axis. Another important interaction present in salt 1 is C—H···S interaction. Each anionic moiety is attached to the adjacent three cationic moieties through these C—H···S (C8—H8···S2, C20—H20···S1 and C22—H22···S1) interactions. The carbon atoms C8, C20 and C22 of three tetraphenyl arsonium moieties each at (x, y, z) acts as donor to the sulfur atoms S2, S1 and S1 at (-x+2, y+1/2, -z+1), (x, y, z+1) and (-x+1, y+1/2, z+1), respectively. These C—H···S interactions in salt 1 result in a 3D framework network of the molecule which when viewed along the b axis reflects the pattern as shown in the Figure S13. C11, C37 and C39 atoms of the molecule are linked with the π cloud of the phenyl rings (C33-C38), (C13-C18) and (C13-C18) respectively through weak C—H···π interaction with symmetric operations (-x+1, y+1/2, -z+1), (-x+1, y-1/2, -z+1) and (-x+1, y-1/2, -z+1), respectively, as shown in the Figure 4, which play an important role in enhancing the stability of the salt. In case of salt 2, C—H···O (C40—H40C···O2 and C3—H3···O2) interactions result in the linking of two monomer molecules leading to the formation of a cyclic ring motif as shown in the Figure S14. Carbon C40 at (x, y, z) gets interlinked through C40—H40C···O2 with the oxygen O2 of the substituted diphenyldithiophosphate with symmetric operation (−x+1, −y+ , −z+2). Similarly, the carbon C3 of the tetraphenylarsonium at (x, y, z) acts as donor to the oxygen O2 at (x-1, y-1, z) through (C3—H3···O2) interactions as shown in Figure S14. Carbon and sulfur of the salt 2 also gets interlinked through C—H···S, generating a 2D network of the molecule, which when viewed along b axis generate a network of cyclic rings as shown in Figure 5. Each anionic dithiophosphate moiety interlinks with two adjacent tetraphenylarsonium moieties through these C—H···S interactions. The three types of C—H···S interactions present in the complex resulting in the generation of a ring are C5—H5···S2, C12—H12···S2 and C22—H22···S1. The carbon C5, C12 and C22 each at (x, y, z) acts as donor to the sulfur atoms S2, S2 and S1 at (x, y, z), (-x+1, -y+1, -z+2) 11
and (x-1, y, z) respectively. The cationic and anionic moiety are also interlinked to each other through the C—H···π interaction [C21—H21···Cg] where Cg denotes the centroid of the phenyl ring (C33-C38) as shown in the Figure S15. However, in case of salt 3, having tert-butyl group attached to the phenyl ring, only one C—H···O interaction occurs between the cationic anionic species C17—H17···O1 and hence neither a dimer nor a 1D framework is possible in this case as illustrated in Figure 6a. C—H···S interactions in salt 3 results in a 3D extension of the molecule, generate a network when viewed along b axis shows the pattern as shown in the Figure S16. The two sulfur atoms undergo three types of C—H···S interactions with two adjacent cationic moieties. Sulfur S1 and S35 of the dithiophosphate group undergoes C2—H2···S1, C4—H4···S1, C5—H5···S1 and C11—H11···S35 with symmetric operations (x, y, z), (-x, y+1/2, -z+3/2), (-x, y+1/2, -z+3/2) and (x, -y+3/2, z-1/2) respectively as shown in Figure 6b and S16. The carbon C20 and C13 also acts as donor towards the centroid of the rings (C25-C30) denoted by Cg1 and (C13-C18) denoted by Cg2 with symmetric operations (x, -y+3/2, z-1/2) and (x, y+1/2, z-1/2), respectively. As a result of these C—H···π interactions, the various cationic and anionic moieties are interlinked to each other, hence generating a 1D framework network of the molecule as shown in Figure S17. Table 2: Selected bond lengths (Å) and bond angles (°) of salts 1, 2 and 3 Salt 1 As1—C6 As1—C24 As1—C18 As1—C12 O1—C33 O2—C25 P1—O1 P1—O2 S1—P1 S2—P1 O2—P1—S2 O2—P1—S1 O1—P1—S2 O1—P1—S1 O1—P1—O2 S1—P1—S2 C33—O1—P1
1.906 (6) 1.904 (6) 1.902(8) 1.915(7) 1.417 (7) 1.392 (8) 1.604 (5) 1.617 (5) 1.960 (2) 1.956(2) 109.91 (19) 110.0 (2) 106.37(18) 110.86 (18) 96.50 (3) 121.33 (5) 112.51 (12)
Salt 2 As1—C6 As1—C7 As1—C13 As1—C19 O1—C25 O2—C33 P1—O1 P1—O2 S1—P1 S2—P1 O2—P1—S2 O2—P1—S1 O1—P1—S1 O1—P1—S2 O2—P1—O1 S1—P1—S2 C25—O1—P1
1.898 (3) 1.907 (3) 1.900 (3) 1.906 (3) 1.381 (3) 1.389 (3) 1.6448 (19) 1.643 (2) 1.9463 (11) 1.9476 (11) 111.53 (8) 104.61 (8) 111.97 (8) 104.91 (8) 100.68 (10) 121.33 (5) 126.13 (17)
Salt 3 As1—C7 As1—C13 As1—C1 As1—C19 O1—C25 O2—C35 P1—O1 P1—O2 S1—P1 S35—P1 O2—P1—S35 O2—P1—S1 O1—P1—S35 O1—P1—S1 O2—P1—O1 S35—P1—S1 C25—O2—P1
1.902 (2) 1.906(2) 1.914 (2) 1.917 (2) 1.391 (3) 1.389 (3) 1.6448 (19) 1.638 (16) 1.952 (9) 1.946(9) 105.86 (7) 110.54 (7) 110.71 (7) 104.60(6) 102.41(9) 121.21 (5) 126.42 (14)
12
Figure 2: Displacement ellipsoid plot (50% probability level) of (a) salt 1 (b) salt 2 (c) salt 3
13
Figure 3: Illustration of (a) C39—H39B···O2 interactions between the anionic moieties in salt 1, generating this network structure when viewed along a axis. (b) C—H···O (C10—H10···O1, C39—H39B···O2) interactions in salt 1 generating a network like structure when viewed along b axis.
Figure 4: C11, C37 and C39 atoms of salt 1 interacting with the π cloud of the phenyl rings (C33-C38), (C13-C18) and (C13-C18) respectively through weak C—H···π interaction
14
Figure 5: (a) Illustration of C—H···S (C5—H5···S2, C12—H12···S2 and C22— H22···S1) interactions in salt 2. (b) C—H···S (C5—H5···S2, C12—H12···S2 and C22— H22···S1) interactions in salt 2 leading to a 2D framework of the molecule when viewed along b axis.
Figure 6: Illustration of (a) C17—H17···O1 interaction in salt 3. (b) C—H···S (C2— H2···S1, C4—H4···S1, C5—H5···S1 and C11—H11···S35) interactions in the salt 3.
15
Table 3: Relevant hydrogen bonding parameters in salts 1, 2 and 3 D—H···A Salt 1 C10—H10···O1
C39—H 9B…O C8—H8···S2 C20—H20···S1 C22—H22···S1 Salt 2 C40—H40C···O2 C3—H3···O2 C12—H12···S2 C5—H5···S2
C22—H22···S1
D—H (Å)
H···A (Å)
D···A (Å)
D—H···A (°)
Symmetric operation
0.93 0.96 0.93 0.93 0.93
2.61 2.98 2.87 2.99 2.95
3.33 (9) 3.39 3.76 (8) 3.91 (7) 3.61 (7)
134.6 117.6 161.1 169.0 129.1
-x+1, y-1/2, -z+1 -x+2, y+1/2, -z+1 x, y, z+1 -x+1, y-1/2, -z+1
0.96 0.93 0.93 0.93 0.93
2.93 2.66 2.99 2.92 2.93
3.55 (3) 3.51 (4) 3.80 (3) 3.80 (3) 3.47 (3)
123.8 151.9 146.2 158.2 120.1
−x+1, −y+ , −z+2 x-1, y-1, z -x+1, -y+1, -z+2 -x+1, -y+1, -z+2 x-1, y, z
0.93 0.93 0.93 0.93
2.58 2.98 2.94 2.90 2.93
3.25 (3) 3.61 (3) 3.58 (3) 3.81 (3) 3.57 (3)
129.6 125.7 127.7 166.1 127.0
...... −x, y+1/ , −z+3/2 −x, y+1/ , −z+3/2
x. y, z
Salt 3
C17—H17…O1 C4—H …S1 C5—H …S1 C11—H11…S C2—H …S1
0.93
x, -y+3/2, z-1/2 x, y, z
Table 4: Geometrical parameters for the C—H···π interactions in salts 1, 2 and 3 X—H···Cg Salt 1 C11—H11···Cg1 C37—H37···Cg2 C39—H39A··Cg2 Salt 2 C21—H21···Cg1 Salt 3 C20—H20···Cg1 C25—H25···Cg2
X—Cg(Å)
H···Cg (Å)
X—H···Cg (°)
Symmetric operation
3.64 3.62 3.73
2.96 2.93 2.75
131.6 106.4 165.4
-x+1, y+1/2, -z+1 -x+1, y-1/2, -z+1 1-x, -1/2+y, 1-z
3.74
2.84
162.0
x, y, z
3.92 3.59
3.31 2.75
125.5 150.1
x, -y+3/2, z-1/2 x, -y+1/2, z-1/2
For salt 1, Cg1 represents the centroid of the ring (C33-C38), Cg2 represents the centroid of ring (C13-C18). For salt 2, Cg1 represents the centroid of the ring (C33C38). For salt 3, Cg1 represents the centroid of the ring (C25-C30), Cg2 represents the centroid of the ring (C13-C18).
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3.5. Hirshfeld surface analysis The Hirshfeld surface analysis has become an invaluable tool for providing additional insight into weak intermolecular interactions influential in the packing of molecule in crystals [2022]. The Hirshfeld surfaces of the salts are illustrated in Figure 7 showing the surfaces that have been mapped over a dnorm range of -0.11 to 1.46Å. The surfaces are shown as transparent to allow visualization of the molecular moiety, in a similar orientation for all the structures, around which they were calculated. The pattern of the intra and intermolecular interactions of the solid state structures of all the salts prompted us to explore and quantify the contribution of the non-covalent interactions involved in the crystal packing. The individual hydrogen bonding interactions are strictly identified separately on the dnorm surfaces as in Figure 7. The large circular depression (deep red) on the dnorm surface, which is evident for strong hydrogen bonding contacts and other light-colored depressions on the dnorm surface are an indicator of weaker and longer contacts other than hydrogen bonds. The intermolecular interactions involved within the molecular structures are also visible on the two-dimensional fingerprint plots [33] and can be decomposed to analyze the individual contributions of molecular interactions related to each structure. Figure 8 represents the different contributions from various interaction types, which are overlapped in the full fingerprint plot. The combination of di and de in the form of two-dimensional fingerprint plot, provides a outline of intermolecular contacts in the crystals, where one molecule act as donor (de> di) and the other as an acceptor (de
(di + de)
2.65 Å, where C…H
interactions have a larger contribution (13.6%, 14.5%, 13.2% in complexes 1, 2, and 3, respectively) than their corresponding H…C counterparts (11.4%, 13.1%, 11.2% in salts 1, 2, 17
and 3 respectively). Thus, the sum of C…H/H…C interactions comprise 25.0%, 27.2%, 24.4% for salts 1, 2, and 3, respectively, of the total Hirshfeld surface area of the molecule. The C…H/H…C interactions represented by the spikes in the bottom right and left region (di + de) 2.65 Å in 1, (di + de)
2.63 Å in 2, and (di + de)
2.60 Å in 3. The S…H/H…S contacts are
evidenced by two distinct spikes in the bottom right and left region (di + de) + de)
2.78 Å in 2, and (di + de)
3.79 Å in 1, (di
2.73 Å in 3, where S…H contribute more (9.5%, 6.6% and
7.0% in salts 1, 2, and 3 respectively) compared to H…S counterpart (5.6%, 4.3% and 4.6% in salts 1, 2, and 3 respectively). The S…H/H…S contacts contribute 15%, 10.9% and 11.6% for salts 1, 2, and 3 respectively towards the total Hirshfeld surface area. The proportions of O…H/H…O interactions comprise 1.4%, 3.8% and 2.5% of the total Hirshfeld surface for each molecule of salts 1, 2, and 3 respectively. These are evidenced by the distinct spikes in the region of (di + de)
2.74 Å in 1, (di + de)
2.54 Å in 2, and (di + de)
2.06 Å in 3, where O…H contribute more (2.1% and 1.3% in salts 2 and 3 respectively) as compared to H…O counterpart (1.7% and 1.2% in salts 2 and 3 respectively), and in salt 1 equal contribution of O…H and H…O contacts i.e., 0.7% Å respectively. Moreover, the proportions of H…H contacts which contributes 57.1% in 1, 55.3% in 2, and 59.7% in 3 of the total Hirshfeld surface of the molecules and their fingerprint plots that are spread only upto di = de = 1.13 Å in 1, 1.06 Å in 2 and 1.05 Å in 3. The inspection of the other atom type contacts pointed out that there are also specific features of the C…C and C…S contacts which contribute 1.4% and 0.1% in 1, 0.8% and 1.5% in 2, 0.9% and 0.6% in 3 in the total Hirshfeld surface area included as other interactions in the relative contribution. Figure 9 contains the percentage of relative contributions made by different interactions towards the Hirshfeld surface for all the salts 1-3.
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Figure 7: Hirshfeld surface of salts (a) 1, (b) 2, (c) 3 mapped with dnorm (left), de (middle), and shape index (right). Regions of most important interactions in d norm are indicated with arrows.
Figure 8: Fingerprint plots of salts 1-3: Full (left) and resolved into H…H, C…H/H…C, S…H/H…S, O…H/H…O (right) interactions showing the percentages of contacts to the total Hirshfeld Surface area of molecules.
19
Figure 9: Relative contributions of various non-covalent interactions towards the Hirshfeld surface in case of salts 1, 2 and 3.
3.6. Computational Analysis The density functional theory (DFT) computations to obtain optimized molecular structures with minimum energies and its atom numbering obtained from quantum chemical calculations using DFT/B3LYP/LANL2DZ level of theory [34-39] are shown below in Figure 10. The optimized structures of all the salts are similar to that of the molecular structure of the salts consisting of a cationic and anionic part. A superposition of the molecular structure of the salts evaluated by quantum mechanical calculation and X-ray studies show almost perfect matching only with slight variation as represented in the supplementary information Table S1, S2 and S3. The small difference originates from the fact that the theoretical calculations are performed for the isolated molecules in the gas phase.
20
Figure 10: Optimized geometries of (a) salt 1 (b) salt 2 (c) salt 3 at DFT/B3LYP/LANL2DZ level of theory. 3.6.1. HOMO–LUMO energy gap Frontier molecular orbitals (FMO’s) i.e. HOMO and LUMO play a significant role in determining the chemical reactivity of the complexes. The electron transfer takes place from the HOMO which is the highest occupied molecular orbital towards the LUMO which is the lowest unoccupied molecular orbital. They help in determining the ability of the molecules to accept (in terms of LUMO) or to donate (in terms of HOMO) an electron. A small HOMOLUMO energy gap indicates small excitation to the manifold of excited state and hence lower stability and higher polarizibility. The energy gap calculated in case of all the salts is an important factor in determining the stability index of the salts. The HOMO-LUMO energy gap diagrams of the three salts is shown in the Figure 11. The HOMO-LUMO energy gap diagrams of all the three salts reveals that in all the three salts, the HOMO orbitals are mainly localized over the dithiophosphate anionic moiety while the LUMO orbitals are mainly
21
localized over the tetraphenyl cationic moiety indicating that electron transition in these molecules occur from the dithiophosphate anionic part towards the tetraphenyl cationic part. The energy gap calculated in all the three salts comes out to be in the range 2.53-2.68 eV. A small energy gap value indicates the chemical softness and polarizable nature of all the molecules. The energy gap between the HOMO and LUMO is the measure of the chemical stability of the molecules. From the HOMO-LUMO energy gap we come to the conclusion that the energy gap of the three salts lie in the pattern 2 > 3 > 1 which indicates that the salt 2 is somewhat more stable and less reactive as compared to the other two salts 1 and 3. From the HOMO-LUMO energy gap we come to the conclusion that the chemical reactivity of these three lie in the range 1 > 3 > 2.
Figure 11: Surface plots (Isovalue = 0.02) of HOMO-LUMO energy gap diagram of (a) salt 1 (b) salt 2 (c) salt 3 obtained at the DFT/B3LYP/LANL2DZ level of theory.
22
3.6.2. Molecular Electrostatic Potential Electrostatic potential maps are three dimensional diagrams of molecules which help us in visualizing the charge distributions and charge related properties of molecules. Knowledge of the charge distribution suggests how molecules interact with each other. The molecular electrostatic potential has been used to predict reactive sites for electrophilic and nucleophilic attack and hydrogen bonding interactions as well as their potential use in the biological recognition studies. Calculations regarding electrostatic potential require only scalar distances and are coordinate less. Different colors in the molecular electrostatic potential diagrams are used to indicate the regions of different electrostatic potentials. The potential increases in the order red ˂ yellow ˂ green ˂ blue. Red color is used to indicate the regions of lower electrostatic potential (higher electron density) while blue color indicates the regions of the higher electrostatic potential (lower electron density). Since oxygen is more electronegative, hence more electron density is found around the oxygen atom and is indicated by the red region in the molecular electrostatic potential diagrams indicating lower electrostatic potential in this region while the blue regions indicate the regions of the higher electrostatic potential and hence the region of lower electron density. The red regions in the molecules which is mostly located over the oxygen and the sulfur atoms in the molecules indicate the site for the electrophilic attack while the blue region which is mostly located over the phenyl rings of the tetraphenylarsonium moiety indicates the site for the nucleophilic attack. As a result of this, electrophilic and nucleophilic region develops within the molecules and hydrogen bonding interactions occur between an electrophilic region and a nucleophilic region in another, or the same, molecular entity.
Figure 12: Molecular Electrostatic diagrams of (a) salt 1 (b) salt 2 and (c) salt 3 23
Conclusion We have reported new tetraphenylarsonium salts of the composition [Ph4As]+[S2P(OAr)2]-, where Ar = (2,4-CH3)2C6H3(1), (3,5-CH3)2C6H3(2), {4-(CH3)3C}C6H4(3). The salts 1, 2 and 3 crystallized in the monoclinic point group with space group P21, triclinic point group with space group P¯1 and monoclinic point group with space group P21/c, respectively. Single Crystal X-ray analysis reveals that the salts are stabilized by various non-covalent interactions C—H···X, C—H···π (X = O, S) interactions. These non-covalent interactions in the molecules result in their extension along different crystallographic axis. In some cases, these interactions result in the 1D extension of the molecules while in some other cases, these lead to the 2D network framework of the molecules. Hirshfeld surface analysis has been carried out in order to check the fidelity of the various non-covalent interactions in the molecules that are reported by using the single crystal X-ray analysis of the salts. The Hirshfeld surface analysis and the finger print plots provide quantitative information of these non-covalent interactions present in the molecules. The decomposed finger print plots provide the percentage contribution made by various non-covalent interactions towards the total Hirshfeld surface. Finally, the HOMO-LUMO energy gap of the molecules calculated using theoretical computational analysis helps in comparing the chemical reactivity of the synthesized tetraphenylarsonium compounds 1, 2 and 3. Authors credit Anu Radha: Conceptualization, Methodology, Writing-Original draft preparation, Pretam Kumar: Visualization and Writing-Review and Editing, Tahira Firdoos: Formal analysis and Writing-Review and Editing, Puneet Sood: Collection of XRD data, Namrata Rani: Theoretical Studies, Vikas: Theoretical Studies, Sushil K. Pandey: Conceptualization, Writing-Review & Editing and Supervision. Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement This research was supported by UGC NET-JRF scholarship (UGC-Ref.No.:193/CSIR-UGC NET DEC.2018). Post Graduate Department of Chemistry, University of Jammu, is acknowledged for recording NMR and IR spectra of the complexes. 24
Supporting Information CCDC 1981469-1981471 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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Graphical abstract
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An insight into non-covalent interactions in the tetraphenylarsonium dithiophosphates: Synthesis, DFT and Hirshfeld Surface Analysis Anu Radha , Pretam Kumar , Tahira Firdoos , Puneet Sood , Namrata Rani , Vikas , Sushil Kumar Pandey PII: DOI: Reference:
S0022-2860(20)32042-1 https://doi.org/10.1016/j.molstruc.2020.129729 MOLSTR 129729
To appear in:
Journal of Molecular Structure
Received date: Revised date: Accepted date:
2 September 2020 29 November 2020 3 December 2020
Please cite this article as: Anu Radha , Pretam Kumar , Tahira Firdoos , Puneet Sood , Namrata Rani , Vikas , Sushil Kumar Pandey , An insight into non-covalent interactions in the tetraphenylarsonium dithiophosphates: Synthesis, DFT and Hirshfeld Surface Analysis, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/j.molstruc.2020.129729
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Highlights
Synthesis and characterization of tetraphenylarsonium dithiophosphate crystals. Non-covalent C—H···X, C—H···π (X= O, S) interactions play a significant role in enhancing the stability of the salts. H…H and C…H/H…C interactions contribute more towards the total Hirshfeld surface. DFT parameters are found to be in good agreement with that determined by single crystal X-ray analysis.
1
An insight into non-covalent interactions in the tetraphenylarsonium dithiophosphates: Synthesis, DFT and Hirshfeld Surface Analysis
Anu Radhaa, Pretam Kumara, Tahira Firdoosa, Puneet Soodb, Namrata Ranic, Vikasc and Sushil Kumar Pandey*,a
a
b
Department of Chemistry, University of Jammu, Jammu–180006, J&K, India
Advanced Materials Research Center, Block-A2 Building, Kamand Campus, Indian Institute of Technology, Mandi, Himachal Pradesh-175005, India c
Quantum Chemistry Group, Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh, India *Corresponding Author’s e-mail address: [email protected]
Abstract Three tetraphenylarsonium dithiophosphate salts [Ph4As]+[S2P(OAr)2]-, where Ar = 2,4(CH3)2C6H3 (1), 3,5-(CH3)2C6H3 (2), {4-(CH3)3C}C6H4 (3), were crystallized in the monoclinic space group P21 (1), triclinic space group P¯1 (2) and monoclinic space group P21/c (3), respectively. These salts are stabilized by various non-covalent interactions resulting in the extension of their molecular structure along different axis. The cationic and anionic species are interconnected by various C—H···X, C—H···π (X= O, S) interactions leading the molecules as one-dimensional and two-dimensional supramolecular structures. A thorough Hirshfeld surface analysis elegantly quantifies the various non-covalent interactions present within the molecules. This analysis reveals that the main contributions in all the three salts are because of H…H and C…H/H…C interactions that represent 82.1%, 82.9% and 84.1% of the total contribution to the Hirshfeld surface for 1, 2 and 3, respectively. Further, the coordinates were optimized by DFT calculations with B3LYP hybrid functional along with LANL2DZ basis set. Experimental values of bond lengths and bond angles are in good agreement with the optimized structural parameters. HOMO-LUMO of the molecules were calculated using corresponding methods with the same basis set. Other computational data pertaining to chemical reactivity have indicated potential sites for nucleophilic and eletrophilic attack in the molecules.
2
Keywords: Non-covalent, Hirshfeld surface analysis, finger print plots, DFT optimized structural parameters 1. Introduction Arsenic(As) is a chemical element in the group 15 of the periodic table. It generally forms compounds in which oxidation state of +3 and +5 is exhibited. The chemistry related to the dithiophosphate complexes of As(III) has been a significant subject of research during the past few years [1-6]. A number of organo antimony(V) complexes with E-O-R linkage (E = Sb; OR = alkoxy, phenoxy, oximate) have been reported in the literature [7-11]. In comparison to them, much less attention has been paid towards the corresponding dithiophosphate complexes of As(V). Wide applications of organoarsenic dithiophosphates [R2AsS2P(OR′)2] (R = Me, Et, Ph; R′ = Me, Et], dithiocarbamates [MeAs(S2CNR2)2] and xanthates [Me2As(S2COPri)], [RAs(S2COR2)2], [As(S2COR2)3] as agricultural bactericides, insecticides, nematocides, fungicides and herbicides have been depicted in the literature [12, 13]. The pentavalent state is dominated by antimony complexes for which both inorganic and organometallic derivatives have been reported [14]. In comparison to the antimony complexes, much less work has been reported on the corresponding pentavalent complexes of arsenic. Tetraorganoarsonium dithiophosphate complexes of the formula, [R4As][S2PR′2] (R = Me or Ph; R′ = Pri, OMe) were reported in the literature, wherein both the cation and anion exhibits tetrahedral geometry and the two P-S bond lengths are equal [15-17]. Solid state crystal structures are stabilized through various non-covalent interactions such as hydrogen bonding, π···π stacking, cation-π, anion-π and C—H···X (X= O, N, S, F, Cl, Br, I) interactions. These non-covalent interactions which play an important role in supramolecular chemistry, crystal design and other areas of the molecular science includes the strong, moderate and weak interactions. Weak interactions such as C—H···X, C—H···π, π···π, X···X, X···Y (X= O, N, S, F, Cl, Br, I) are also seminal in determining the stability of the complexes [18, 19]. These non-covalent interactions are now-a-days commonly used for the self assembly of large supramolecular molecules. So far, no supramolecular interactions have been discussed in the case of tetraphenylarsonium dithiophosphate complexes. In the present study, three tetraphenylarsonium dithiophosphate salts corresponding to the formula [Ph4As]+[{2,4-(CH3)2C6H3O}2PS2]-(1), [Ph4As]+[{3,5-(CH3)2C6H3O}2PS2]-(2), [Ph4As]+[{(4– (CH3)3C)C6H4O}2PS2]- (3) have been synthesized and structurally characterized. The single
3
crystal analysis of the synthesized salts 1, 2 and 3 revealed the presence of various weak noncovalent interactions in the molecules. Hirshfeld surface analysis proves to be a pivotal tool of exploring the various noncovalent intermolecular interactions present in a molecular system and offer a very facile way of obtaining information on crystal packing [20-25]. The size and shape of the Hirshfeld surface depends on the chemical environment surrounding the molecule. The associated finger print plots provide information about the percentage contribution made by the various non-covalent interactions towards the Hirshfeld surface. Investigation of the Hirshfeld surface analysis of the three tetraphenylarsonium complexes allows a detailed scrutiny of the comparison of the weak forces experienced by each of the three complexes and the quantitative comparison of these weak interactions in these three complexes has been reflected in the associated finger print plots. 2. EXPERIMENTAL 2.1. Materials and instrumentation Tetraphenylarsonium chloride and all substituted phenols were purchased from Sigma Aldrich and
were
used
without
further
purification.
Sodium
salts
of
O,O′-substituted
diphenyldithiophosphates were synthesized by the procedure as discussed in the literature [26, 27]. Arsenic was estimated iodometrically [28]. Elemental analyses (C, H, S) were conducted using the Elemental Analyser Vario EL-III (Indian Institute of Integrative Medicine, Jammu). The 1H and
13
C NMR spectra were recorded in CDCl3 using TMS as internal reference. The
31
P NMR spectra were recorded in CDCl3 using H3PO4 (85%) as external reference on a
Bruker Avance III 400 MHz (Department of Chemistry, University of Jammu, Jammu). Infrared spectra were recorded in the range of 4000–400 cm-1 on a Perkin Elmer FT-IR spectrophotometer (Department of Chemistry, University of Jammu, Jammu).
2.2. Synthesis 2.2.1. Synthesis of [Ph4As]+[{2,4-(CH3)2C6H3O}2PS2]- (1) To a stirred aqueous solution of Ph4As+Cl- (1.16g, 2.67 mmol) was added a stirred aqueous solution of {2,4-(CH3)2C6H3O}2PS2-Na+ (1.00g, 2.77 mmol) in 1:1 molar ratio followed by continuous stirring. A white solid precipitated out. After stirring for about 30 min, the reaction mixture was filtered to obtain the white precipitates of the product [Ph4As]+[{2,4(CH3)2C6H3O}2PS2]-. The precipitates thus obtained were then dissolved in acetone and the 4
reaction mixture was then kept undisturbed for about 2-3 days resulting in the formation of the white crystals of the synthesized salt. Yield: 93.09% (1.86 g); Anal. Calc. for C40H38O2PS2As: C, 66.66; H, 5.30; S, 8.90; As, 10.39%. Found: C, 66.64; H, 5.28; S, 8.87; As, 10.36%. IR (KBr, cm-1): 1105.44 s [v(P)-O-C], 812.44 s [vP-O-(C)], 611.81 s [vP=S], 494.71 m [vP-S]. 1H NMR (CDCl3, ppm): 2.23 (s, 6H, 2-CH3), 2.29 (s, 6H, 4-CH3), 6.84 (d, J = 8Hz, 2H, H5), 6.91 (s, 2H, H3), 7.21 (d, J = 8Hz, 2H, H6), 7.67 (d, J = 8Hz, 8H, H 7.80 (t, J = 8Hz, 8Hz, H , ), 7.86 (t, J = 8Hz, 4H, H );
,
),
13
C NMR(CDCl3, ppm): 15.92 (2-
CH3), 22.62 (4-CH3), 115.22 (C6), 120.58 (C1,), 123.58 (C2), 126.61 (C5), 129.24 (C4),130.21 (C3), 133.05 (C3,,5,), 134.59 (C2,,6,), 136.25 (C4,), 152.34 (C1);
31
P NMR(CDCl3, ppm):
109.70(s) (Figure 1a) 2.2.2. Synthesis of [Ph4As]+[{3,5-(CH3)2C6H3O}2PS2]- (2) The salt 2 was also prepared by the same procedure as that used for the salt 1 i.e. by reacting Ph4As+Cl- (1.16g, 2.67 mmol) and {3,5-(CH3)2C6H3O}2PS2-Na+ (1.00g, 2.77 mmol) in 1:1 ratio resulting in the formation of white crystals. Yield: 91.09% (1.82 g); Anal. Calc. for C40H38O2PS2As: C, 66.66; H, 5.31; S; 8.90; As, 10.39%. Found: C, 66.63; H, 5.28; S, 8.88; As, 10.36%. IR (KBr, cm-1.): 1151.63 s [v(P)-O-C], 937.94 s [vP-O-(C)], 682.73 s [vP=S], 599.22 m [vP-S]. 1H NMR (CDCl3, ppm): 2.21 [s, 12H, 3,5-(CH3)2], 6.63 (s, 2H, H4), 7.04 (s, 4H, H2,6), 7.66 (d, J = 8Hz, 8H, H
,
), 7.77 (t, J = 8Hz, 8H, H , ), 7.84 (t, J = 7.6Hz, 4H, H ),
13
C NMR (CDCl3, ppm): 21.08 {3,5-(CH3)2}, 120.35 (C1,), 122.52 (C2,6), 128.25 (C4), 131.50
(C4,), 134.98 (C3,,5,), 135.77 (C2,,6,),138.63 (C3,5), 153.35 (C1).
31
P NMR (CDCl3, ppm):
108.70(s) (Figure 1b). 2.2.3. Synthesis of [Ph4As]+ [{(4–(CH3)3C)C6H4O}2PS2]- (3) Same procedure was used for the synthesis of salt 3 as that for the salts 1 and 2 using Ph4As+Cl- (1.00g, 2.40 mmol) and {(4–(CH3)3C)C6H4O}2PS2-Na+ (1.00g, 2.40 mmol) resulting in the formation of white crystals. Yield: 94.59% (1.75 g); Anal. Calc. for C44H46O2PS2As: C, 68.03; H, 5.96; S, 8.25, As, 9.64%. Found: C, 68.00; H, 5.93; S, 8.22; As, 9.61%. IR (KBr, cm-1.): 1109.64 s [v(P)-O-C], 933.74 s [vP-O-(C)], 674.80 s [vP=S], 574.02 m [vP-S] cm-1. 1H NMR (CDCl3, ppm): 4.82 (s, 18H, CH3 of (CH3)3C), 7.22 (d, J = 8Hz, 4H, H2,6), 7.31 (d, J = 7.6Hz, 4H, H3,5), 7.64 (d, J = 8Hz, 8H, H
,
), 7.77 (t, J = 7.8Hz, 8H, H
,
),
7.85 (t, J = 7.8 Hz, 4H, H ) 13C NMR (CDCl3, ppm): 31.65 (CH3 of (CH3)3C), 51.01 (tert C
5
of (CH3)3C), 121.57 (C2,6), 128.27 (C3,5), 131.45 (C3,,5,), 133.03 (C4,), 134.86 (C2,,6,), 137.90 (C1,), 145.30 (C4), 151.30 (C1). 31P NMR (CDCl3, ppm): 109.23(s) (Figure 1c)
Figure 1: Molecular structures of the salts 1-3
2.3. X-ray data collection and structure determination Crystallization of all the salts 1, 2 and 3 was done by dissolving them in minimum amount of acetone. White crystals were obtained after keeping the reaction mixture for about 2-3 days. Single-crystal X-ray diffraction data of the salts were collected with a CCD Agilent SUPERNOVAE (Dual) diffractometer using monochromatic Cu Kα radiation (λ = 1.
1 Å).
Using the program Olex 2 [29], the structures for salts 1, 2 and 3 were solved by the SHELXS program [30] and refined by full matrix least squares on F2 with the SHELXL program [30].
Table 1: Summary of the crystal structure, data collection and refinement parameters for salts 1, 2 and 3
Crystal data
1
Mr
720.71
Crystal system, space group a, b, c (Å)
2 720.71
3 776.82
Monoclinic, P21
Triclinic, P¯1
Monoclinic, P21/c
12.9898(6), 9.8492(4),
10.0755(8), 13.0884(10),
22.2434(8), 9.4923(2),
6
α, β, γ (°)
V (Å3)
13.8693(8)
14.4673(10)
19.2583(5)
90, 100.622(4),
98.075, 110.119,
90, 102.045(3)
90
98.086(6)
90
1744.01 (15)
1736.6 (2)
3976.72 (19)
Z µ (mm−1) Crystal size (mm)
2 1.18 0.35 × 0.28 × 0.19
2
4
1.18
1.03
0.23 × 0.19 × 0.14
0.27 × 0.14 × 0.12
0.477, 1.000
0.546, 1.000
0.795, 1.000
5992, 5222, 4648
9746, 7491, 6144
13562, 8642, 7009
Data collection Tmin, Tmax No. of measured, independent and observed [I> σ(I)] reflections Rint
0.052
0.033
0.027
(sin θ/λ)max (Å−1)
0.664
0.668
0.667
Refinement R[F2 > σ(F2)], wR(F2), S
0.060, 0.168, 1.03
0.044, 0.112, 1.05
0.040, 0.092, 1.06
No. of reflections
5222
7491
8642
No. of parameters
419
419
457
1
0
0
No. of restraints Δρmax, Δρmin (e Å−3)
1.1 , −1. 0
0.78, −0.
0.
, −0. 1
2.4. Hirshfeld surface analysis In order to demonstrate the interactions in the crystal structures, the Hirshfeld surface analysis was conducted and their 2D fingerprint plots were established using Crystal Explorer 17.5 software [31]. These molecular Hirshfeld surfaces in the crystal structure are constructed considering the electron distribution calculated as the sum of spherical atom electron densities [20-25]. For a given crystal system and set of spherical electron densities, the Hirshfeld surface is unique. A Hirshfeld surface is the outer contour of the space which a molecule or an atom consumes in a crystalline environment. The normalized contact distance 7
denoted by dnorm given by the equation enable the identification of the regions of particular importance to intermolecular interactions [32, 33].
+
(1)
The mapping of dnorm on the Hirshfeld surface highlights the donor and acceptor equally and hence acts as a powerful tool for analyzing directional intermolecular interactions. The positive and negative values of the dnorm denote whether intermolecular interactions are larger or smaller than the Van der Waals (vdW) separation respectively.
2.5. Computational Methodology The density functional theory (DFT) computations to obtain the optimized structure of salts are performed using Gaussian 09 quantum-mechanical software package [34, 35]. For the DFT computations, Becke-3-parameterized-Lee-Yang-Parr (B3LYP) hybrid exchangecorrelation functional along with a default Las Alamos double zeta basis set, LANL2DZ [3638] are used. The chemical reactivity of all the salts is further predicted through DFT computed HOMO-LUMO energy gap. Besides this, molecular electrostatic potential diagrams obtained from the DFT calculations are also used to determine the site for electrophilic and nucleophilic attack in the salts.
3. RESULTS AND DISCUSSION 3.1. Synthesis of salts The salts 1, 2 and 3 of the general formula [Ph4As]+[S2P(OAr)2]- [Ar = 2,4-(CH3)2C6H3 (1), 3,5-(CH3)2C6H3 (2) and {4-(CH3)3C}C6H4 (3)] were synthesized by the similar procedure by adding an aqueous solution of tetraphenylarsonium chloride to the aqueous solution of the sodium salt of the corresponding substituted dithiophosphate in 1:1 ratio at room temperature. The white precipitates thus formed when dissolved in acetone and kept for 2-3 days resulting in the formation of white crystals (Scheme 1).
(ArO)2PS2-Na+ + Ph4As+Cl-
H2O stirring 30 min -NaCl
[Ph4As]+[S2P(OAr)2]-
[Ar = (2,4-CH3)2C6H3 (1), (3,5-CH3)2C6H3 (2), {4-(CH3)3C}C6H4 (3)] Scheme 1: Reaction scheme highlighting the formation of the salts 1-3 8
3.2. IR Spectroscopy Interpretation of the IR spectra of the corresponding tetraphenylarsonium dithiophosphate salts was made on the basis of the corresponding sodium and triethylammonium salt of the akin dithiophosphate complexes as no literature available specifically on tetraphenylarsonium dithiophosphates. The infrared spectra of the tetraphenylarsonium dithiophosphate salts are almost similar to the corresponding sodium and triethylammonium salt with a slight variation [39, 40]. For all the salts 1-3, [v(P)−O−C] and [vP−O−(C)] stretching vibrations were observed as sharp peaks in the region 1164.09–1105.44 cm-1 and 850.23–812.44cm-1, respectively. The sharp to medium intensity bands of [vP=S] stretching vibrations for all the salts were found in the region 689.58-611.81 cm-1. The medium intensity bands in the range 497.66-486.31cm-1 are assignable to [vP−S] vibrations.
3.3. NMR spectroscopy In the 1H NMR spectra, all the salts 1-3 exhibit the proton signals with the expected peak multiplicities. The –CH3 protons of the methyl substituent in case of salts 1 and 2 exhibit their singlet in the range 2.25-2.30 ppm. The –CH3 of the tert-butyl group exhibits its resonance at 1.27 ppm. The protons of the phenyl rings of the substituted dithiophosphate exhibit their resonance in the range 6.63-7.67 ppm. The protons of the phenyl ring of the tetraphenylarsonium exhibit their peaks in the range 7.64-7.86 ppm. The 13C NMR spectra consist of all the peaks expected for the carbon atoms present in the molecules. The carbon atoms of the phenyl rings of both the substituted dithiophosphate anion and tetraphenylarsonium cation shows their chemical shifts in the range 115.22-153.35 ppm. The chemical shifts of the methyl substituent attached to the phenyl rings in case of salts 1 and 2 appear in the range 15.92-22.62 ppm. The methyl groups of the tert-butyl substituent in case of salt 3 reveal their resonance at 31.65 ppm. A single resonance was observed in the
31
P NMR spectra (proton-decoupled) of all
the complexes. The chemical shift of all the salts 1-3 exhibits a singlet in each case in the range 108.70–109.76 ppm. The appearance of a single sharp peak in this range clearly indicates the ionic nature of the synthesized tetraphenylarsonium dithiophosphate salts.
9
3.4. Molecular and crystal structure of salts 1, 2 and 3 The salts 1, 2 and 3 crystallized in the monoclinic point group with space group P21, triclinic point group with space group P¯1 and monoclinic point group with space group P21/c, respectively. Molecular structure of all the three salts 1, 2 and 3 with partial atomic numbering is shown in the Figure 2. These salts exist in the cation anion form. The cationic part consists of tetraphenylarsonium moiety having central arsenic atom attached to four phenyl rings. The anionic part consists of a substituted dithiophosphate moiety having phosphorus atom attached to two sulfur and two oxygen atoms. Selected bond lengths and bond angles of all the three salts are mentioned in Table 2. All coordinate bond lengths and bond angles
are within
the range of values previously reported for
related
tetraphenylarsonium salts [16, 17]. A slight variation between the parameters of previously reported and the newly synthesized tetraphenylarsonium salts occur that may be due to the effect of the steric bulkiness of the alkyl moiety attached to the phenyl ring. A deviation from the standard tetrahedral parameters is observed in case of all the three salts. The maximum deviation is depicted in case of S—P—S {121.33(5) in case of salt 1, 121.33(5) in case of salt 2 and 121.21(5) in case of salt 3} which may be due to the steric bulkiness of the substituent moiety attached to the phenyl ring. The P—S bond lengths in all the three salts {1.956(2) and 1.960(2) in case of salt 1, 1.946(11) and 1.948(11) in case of salt 2, 1.952(9) and 1.946(9) in case of salt 3} are within the range of values previously observed for the tetraphenylarsonium salts{1.995(2) and 1.991(1) in case of tetraphenylarsonium diisopropyldithiophosphinate and 1.954(3) and 1.944(2) in case of tetraphenylarsonium O,O-dimethyldithiophosphate salts} [16, 17]. In all the three salts, P—S bond lengths are almost equivalent which indicates the delocalization of the negative charge over the whole S—P—S fragment. In all the three salts, the cationic and anionic moieties are interlinked through various non-covalent interactions such as C—H···O, C—H···S and C—H···π [41-45] interactions which enhance the stability of the salts as well as results in the extension of the monomer moieties towards different crystallographic axis. The non-covalent interactions present in the molecules are mentioned in the Tables 3 and 4. In case of salt 1, each anionic unit is attached to a cationic unit and two other adjacent anionic moieties through C—H···O interactions. The two oxygen atoms of the dithiophosphate anionic moiety exhibit O···H interaction with an adjacent cationic (C10— H10···O1) and anionic moiety (C39—H39B···O2) while the hydrogen of the methyl group
10
attached to the phenyl at para position undergoes this interaction with another adjacent anionic moiety (C39—H39B···O2) (Figure 3a). The carbon C10 of the tetraphenylarsonium at (x, y, z) acts as donor to the oxygen O1 of the substituted dithiophosphate anion at (x, y, z) through C10—H10···O1 interaction and the carbon C39 of the substituent methyl group attached to the phenyl ring at (x, y, z) acts as donor to the oxygen atom O2 of other anionic moiety at (-x+1, -y+1/2, -z+1) through C39—H39B···O2 interaction. These C—H···O interactions in the salt results in a 2D extension of the molecule showing different patterns when viewed along different crystallographic axis. Figure 3b shows C—H···O interactions in salt 1 when viewed along b axis. Another important interaction present in salt 1 is C—H···S interaction. Each anionic moiety is attached to the adjacent three cationic moieties through these C—H···S (C8—H8···S2, C20—H20···S1 and C22—H22···S1) interactions. The carbon atoms C8, C20 and C22 of three tetraphenyl arsonium moieties each at (x, y, z) acts as donor to the sulfur atoms S2, S1 and S1 at (-x+2, y+1/2, -z+1), (x, y, z+1) and (-x+1, y+1/2, z+1), respectively. These C—H···S interactions in salt 1 result in a 3D framework network of the molecule which when viewed along the b axis reflects the pattern as shown in the Figure S13. C11, C37 and C39 atoms of the molecule are linked with the π cloud of the phenyl rings (C33-C38), (C13-C18) and (C13-C18) respectively through weak C—H···π interaction with symmetric operations (-x+1, y+1/2, -z+1), (-x+1, y-1/2, -z+1) and (-x+1, y-1/2, -z+1), respectively, as shown in the Figure 4, which play an important role in enhancing the stability of the salt. In case of salt 2, C—H···O (C40—H40C···O2 and C3—H3···O2) interactions result in the linking of two monomer molecules leading to the formation of a cyclic ring motif as shown in the Figure S14. Carbon C40 at (x, y, z) gets interlinked through C40—H40C···O2 with the oxygen O2 of the substituted diphenyldithiophosphate with symmetric operation (−x+1, −y+ , −z+2). Similarly, the carbon C3 of the tetraphenylarsonium at (x, y, z) acts as donor to the oxygen O2 at (x-1, y-1, z) through (C3—H3···O2) interactions as shown in Figure S14. Carbon and sulfur of the salt 2 also gets interlinked through C—H···S, generating a 2D network of the molecule, which when viewed along b axis generate a network of cyclic rings as shown in Figure 5. Each anionic dithiophosphate moiety interlinks with two adjacent tetraphenylarsonium moieties through these C—H···S interactions. The three types of C—H···S interactions present in the complex resulting in the generation of a ring are C5—H5···S2, C12—H12···S2 and C22—H22···S1. The carbon C5, C12 and C22 each at (x, y, z) acts as donor to the sulfur atoms S2, S2 and S1 at (x, y, z), (-x+1, -y+1, -z+2) 11
and (x-1, y, z) respectively. The cationic and anionic moiety are also interlinked to each other through the C—H···π interaction [C21—H21···Cg] where Cg denotes the centroid of the phenyl ring (C33-C38) as shown in the Figure S15. However, in case of salt 3, having tert-butyl group attached to the phenyl ring, only one C—H···O interaction occurs between the cationic anionic species C17—H17···O1 and hence neither a dimer nor a 1D framework is possible in this case as illustrated in Figure 6a. C—H···S interactions in salt 3 results in a 3D extension of the molecule, generate a network when viewed along b axis shows the pattern as shown in the Figure S16. The two sulfur atoms undergo three types of C—H···S interactions with two adjacent cationic moieties. Sulfur S1 and S35 of the dithiophosphate group undergoes C2—H2···S1, C4—H4···S1, C5—H5···S1 and C11—H11···S35 with symmetric operations (x, y, z), (-x, y+1/2, -z+3/2), (-x, y+1/2, -z+3/2) and (x, -y+3/2, z-1/2) respectively as shown in Figure 6b and S16. The carbon C20 and C13 also acts as donor towards the centroid of the rings (C25-C30) denoted by Cg1 and (C13-C18) denoted by Cg2 with symmetric operations (x, -y+3/2, z-1/2) and (x, y+1/2, z-1/2), respectively. As a result of these C—H···π interactions, the various cationic and anionic moieties are interlinked to each other, hence generating a 1D framework network of the molecule as shown in Figure S17. Table 2: Selected bond lengths (Å) and bond angles (°) of salts 1, 2 and 3 Salt 1 As1—C6 As1—C24 As1—C18 As1—C12 O1—C33 O2—C25 P1—O1 P1—O2 S1—P1 S2—P1 O2—P1—S2 O2—P1—S1 O1—P1—S2 O1—P1—S1 O1—P1—O2 S1—P1—S2 C33—O1—P1
1.906 (6) 1.904 (6) 1.902(8) 1.915(7) 1.417 (7) 1.392 (8) 1.604 (5) 1.617 (5) 1.960 (2) 1.956(2) 109.91 (19) 110.0 (2) 106.37(18) 110.86 (18) 96.50 (3) 121.33 (5) 112.51 (12)
Salt 2 As1—C6 As1—C7 As1—C13 As1—C19 O1—C25 O2—C33 P1—O1 P1—O2 S1—P1 S2—P1 O2—P1—S2 O2—P1—S1 O1—P1—S1 O1—P1—S2 O2—P1—O1 S1—P1—S2 C25—O1—P1
1.898 (3) 1.907 (3) 1.900 (3) 1.906 (3) 1.381 (3) 1.389 (3) 1.6448 (19) 1.643 (2) 1.9463 (11) 1.9476 (11) 111.53 (8) 104.61 (8) 111.97 (8) 104.91 (8) 100.68 (10) 121.33 (5) 126.13 (17)
Salt 3 As1—C7 As1—C13 As1—C1 As1—C19 O1—C25 O2—C35 P1—O1 P1—O2 S1—P1 S35—P1 O2—P1—S35 O2—P1—S1 O1—P1—S35 O1—P1—S1 O2—P1—O1 S35—P1—S1 C25—O2—P1
1.902 (2) 1.906(2) 1.914 (2) 1.917 (2) 1.391 (3) 1.389 (3) 1.6448 (19) 1.638 (16) 1.952 (9) 1.946(9) 105.86 (7) 110.54 (7) 110.71 (7) 104.60(6) 102.41(9) 121.21 (5) 126.42 (14)
12
Figure 2: Displacement ellipsoid plot (50% probability level) of (a) salt 1 (b) salt 2 (c) salt 3
13
Figure 3: Illustration of (a) C39—H39B···O2 interactions between the anionic moieties in salt 1, generating this network structure when viewed along a axis. (b) C—H···O (C10—H10···O1, C39—H39B···O2) interactions in salt 1 generating a network like structure when viewed along b axis.
Figure 4: C11, C37 and C39 atoms of salt 1 interacting with the π cloud of the phenyl rings (C33-C38), (C13-C18) and (C13-C18) respectively through weak C—H···π interaction
14
Figure 5: (a) Illustration of C—H···S (C5—H5···S2, C12—H12···S2 and C22— H22···S1) interactions in salt 2. (b) C—H···S (C5—H5···S2, C12—H12···S2 and C22— H22···S1) interactions in salt 2 leading to a 2D framework of the molecule when viewed along b axis.
Figure 6: Illustration of (a) C17—H17···O1 interaction in salt 3. (b) C—H···S (C2— H2···S1, C4—H4···S1, C5—H5···S1 and C11—H11···S35) interactions in the salt 3.
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Table 3: Relevant hydrogen bonding parameters in salts 1, 2 and 3 D—H···A Salt 1 C10—H10···O1
C39—H 9B…O C8—H8···S2 C20—H20···S1 C22—H22···S1 Salt 2 C40—H40C···O2 C3—H3···O2 C12—H12···S2 C5—H5···S2
C22—H22···S1
D—H (Å)
H···A (Å)
D···A (Å)
D—H···A (°)
Symmetric operation
0.93 0.96 0.93 0.93 0.93
2.61 2.98 2.87 2.99 2.95
3.33 (9) 3.39 3.76 (8) 3.91 (7) 3.61 (7)
134.6 117.6 161.1 169.0 129.1
-x+1, y-1/2, -z+1 -x+2, y+1/2, -z+1 x, y, z+1 -x+1, y-1/2, -z+1
0.96 0.93 0.93 0.93 0.93
2.93 2.66 2.99 2.92 2.93
3.55 (3) 3.51 (4) 3.80 (3) 3.80 (3) 3.47 (3)
123.8 151.9 146.2 158.2 120.1
−x+1, −y+ , −z+2 x-1, y-1, z -x+1, -y+1, -z+2 -x+1, -y+1, -z+2 x-1, y, z
0.93 0.93 0.93 0.93
2.58 2.98 2.94 2.90 2.93
3.25 (3) 3.61 (3) 3.58 (3) 3.81 (3) 3.57 (3)
129.6 125.7 127.7 166.1 127.0
...... −x, y+1/ , −z+3/2 −x, y+1/ , −z+3/2
x. y, z
Salt 3
C17—H17…O1 C4—H …S1 C5—H …S1 C11—H11…S C2—H …S1
0.93
x, -y+3/2, z-1/2 x, y, z
Table 4: Geometrical parameters for the C—H···π interactions in salts 1, 2 and 3 X—H···Cg Salt 1 C11—H11···Cg1 C37—H37···Cg2 C39—H39A··Cg2 Salt 2 C21—H21···Cg1 Salt 3 C20—H20···Cg1 C25—H25···Cg2
X—Cg(Å)
H···Cg (Å)
X—H···Cg (°)
Symmetric operation
3.64 3.62 3.73
2.96 2.93 2.75
131.6 106.4 165.4
-x+1, y+1/2, -z+1 -x+1, y-1/2, -z+1 1-x, -1/2+y, 1-z
3.74
2.84
162.0
x, y, z
3.92 3.59
3.31 2.75
125.5 150.1
x, -y+3/2, z-1/2 x, -y+1/2, z-1/2
For salt 1, Cg1 represents the centroid of the ring (C33-C38), Cg2 represents the centroid of ring (C13-C18). For salt 2, Cg1 represents the centroid of the ring (C33C38). For salt 3, Cg1 represents the centroid of the ring (C25-C30), Cg2 represents the centroid of the ring (C13-C18).
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3.5. Hirshfeld surface analysis The Hirshfeld surface analysis has become an invaluable tool for providing additional insight into weak intermolecular interactions influential in the packing of molecule in crystals [2022]. The Hirshfeld surfaces of the salts are illustrated in Figure 7 showing the surfaces that have been mapped over a dnorm range of -0.11 to 1.46Å. The surfaces are shown as transparent to allow visualization of the molecular moiety, in a similar orientation for all the structures, around which they were calculated. The pattern of the intra and intermolecular interactions of the solid state structures of all the salts prompted us to explore and quantify the contribution of the non-covalent interactions involved in the crystal packing. The individual hydrogen bonding interactions are strictly identified separately on the dnorm surfaces as in Figure 7. The large circular depression (deep red) on the dnorm surface, which is evident for strong hydrogen bonding contacts and other light-colored depressions on the dnorm surface are an indicator of weaker and longer contacts other than hydrogen bonds. The intermolecular interactions involved within the molecular structures are also visible on the two-dimensional fingerprint plots [33] and can be decomposed to analyze the individual contributions of molecular interactions related to each structure. Figure 8 represents the different contributions from various interaction types, which are overlapped in the full fingerprint plot. The combination of di and de in the form of two-dimensional fingerprint plot, provides a outline of intermolecular contacts in the crystals, where one molecule act as donor (de> di) and the other as an acceptor (de
(di + de)
2.65 Å, where C…H
interactions have a larger contribution (13.6%, 14.5%, 13.2% in complexes 1, 2, and 3, respectively) than their corresponding H…C counterparts (11.4%, 13.1%, 11.2% in salts 1, 2, 17
and 3 respectively). Thus, the sum of C…H/H…C interactions comprise 25.0%, 27.2%, 24.4% for salts 1, 2, and 3, respectively, of the total Hirshfeld surface area of the molecule. The C…H/H…C interactions represented by the spikes in the bottom right and left region (di + de) 2.65 Å in 1, (di + de)
2.63 Å in 2, and (di + de)
2.60 Å in 3. The S…H/H…S contacts are
evidenced by two distinct spikes in the bottom right and left region (di + de) + de)
2.78 Å in 2, and (di + de)
3.79 Å in 1, (di
2.73 Å in 3, where S…H contribute more (9.5%, 6.6% and
7.0% in salts 1, 2, and 3 respectively) compared to H…S counterpart (5.6%, 4.3% and 4.6% in salts 1, 2, and 3 respectively). The S…H/H…S contacts contribute 15%, 10.9% and 11.6% for salts 1, 2, and 3 respectively towards the total Hirshfeld surface area. The proportions of O…H/H…O interactions comprise 1.4%, 3.8% and 2.5% of the total Hirshfeld surface for each molecule of salts 1, 2, and 3 respectively. These are evidenced by the distinct spikes in the region of (di + de)
2.74 Å in 1, (di + de)
2.54 Å in 2, and (di + de)
2.06 Å in 3, where O…H contribute more (2.1% and 1.3% in salts 2 and 3 respectively) as compared to H…O counterpart (1.7% and 1.2% in salts 2 and 3 respectively), and in salt 1 equal contribution of O…H and H…O contacts i.e., 0.7% Å respectively. Moreover, the proportions of H…H contacts which contributes 57.1% in 1, 55.3% in 2, and 59.7% in 3 of the total Hirshfeld surface of the molecules and their fingerprint plots that are spread only upto di = de = 1.13 Å in 1, 1.06 Å in 2 and 1.05 Å in 3. The inspection of the other atom type contacts pointed out that there are also specific features of the C…C and C…S contacts which contribute 1.4% and 0.1% in 1, 0.8% and 1.5% in 2, 0.9% and 0.6% in 3 in the total Hirshfeld surface area included as other interactions in the relative contribution. Figure 9 contains the percentage of relative contributions made by different interactions towards the Hirshfeld surface for all the salts 1-3.
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Figure 7: Hirshfeld surface of salts (a) 1, (b) 2, (c) 3 mapped with dnorm (left), de (middle), and shape index (right). Regions of most important interactions in d norm are indicated with arrows.
Figure 8: Fingerprint plots of salts 1-3: Full (left) and resolved into H…H, C…H/H…C, S…H/H…S, O…H/H…O (right) interactions showing the percentages of contacts to the total Hirshfeld Surface area of molecules.
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Figure 9: Relative contributions of various non-covalent interactions towards the Hirshfeld surface in case of salts 1, 2 and 3.
3.6. Computational Analysis The density functional theory (DFT) computations to obtain optimized molecular structures with minimum energies and its atom numbering obtained from quantum chemical calculations using DFT/B3LYP/LANL2DZ level of theory [34-39] are shown below in Figure 10. The optimized structures of all the salts are similar to that of the molecular structure of the salts consisting of a cationic and anionic part. A superposition of the molecular structure of the salts evaluated by quantum mechanical calculation and X-ray studies show almost perfect matching only with slight variation as represented in the supplementary information Table S1, S2 and S3. The small difference originates from the fact that the theoretical calculations are performed for the isolated molecules in the gas phase.
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Figure 10: Optimized geometries of (a) salt 1 (b) salt 2 (c) salt 3 at DFT/B3LYP/LANL2DZ level of theory. 3.6.1. HOMO–LUMO energy gap Frontier molecular orbitals (FMO’s) i.e. HOMO and LUMO play a significant role in determining the chemical reactivity of the complexes. The electron transfer takes place from the HOMO which is the highest occupied molecular orbital towards the LUMO which is the lowest unoccupied molecular orbital. They help in determining the ability of the molecules to accept (in terms of LUMO) or to donate (in terms of HOMO) an electron. A small HOMOLUMO energy gap indicates small excitation to the manifold of excited state and hence lower stability and higher polarizibility. The energy gap calculated in case of all the salts is an important factor in determining the stability index of the salts. The HOMO-LUMO energy gap diagrams of the three salts is shown in the Figure 11. The HOMO-LUMO energy gap diagrams of all the three salts reveals that in all the three salts, the HOMO orbitals are mainly localized over the dithiophosphate anionic moiety while the LUMO orbitals are mainly
21
localized over the tetraphenyl cationic moiety indicating that electron transition in these molecules occur from the dithiophosphate anionic part towards the tetraphenyl cationic part. The energy gap calculated in all the three salts comes out to be in the range 2.53-2.68 eV. A small energy gap value indicates the chemical softness and polarizable nature of all the molecules. The energy gap between the HOMO and LUMO is the measure of the chemical stability of the molecules. From the HOMO-LUMO energy gap we come to the conclusion that the energy gap of the three salts lie in the pattern 2 > 3 > 1 which indicates that the salt 2 is somewhat more stable and less reactive as compared to the other two salts 1 and 3. From the HOMO-LUMO energy gap we come to the conclusion that the chemical reactivity of these three lie in the range 1 > 3 > 2.
Figure 11: Surface plots (Isovalue = 0.02) of HOMO-LUMO energy gap diagram of (a) salt 1 (b) salt 2 (c) salt 3 obtained at the DFT/B3LYP/LANL2DZ level of theory.
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3.6.2. Molecular Electrostatic Potential Electrostatic potential maps are three dimensional diagrams of molecules which help us in visualizing the charge distributions and charge related properties of molecules. Knowledge of the charge distribution suggests how molecules interact with each other. The molecular electrostatic potential has been used to predict reactive sites for electrophilic and nucleophilic attack and hydrogen bonding interactions as well as their potential use in the biological recognition studies. Calculations regarding electrostatic potential require only scalar distances and are coordinate less. Different colors in the molecular electrostatic potential diagrams are used to indicate the regions of different electrostatic potentials. The potential increases in the order red ˂ yellow ˂ green ˂ blue. Red color is used to indicate the regions of lower electrostatic potential (higher electron density) while blue color indicates the regions of the higher electrostatic potential (lower electron density). Since oxygen is more electronegative, hence more electron density is found around the oxygen atom and is indicated by the red region in the molecular electrostatic potential diagrams indicating lower electrostatic potential in this region while the blue regions indicate the regions of the higher electrostatic potential and hence the region of lower electron density. The red regions in the molecules which is mostly located over the oxygen and the sulfur atoms in the molecules indicate the site for the electrophilic attack while the blue region which is mostly located over the phenyl rings of the tetraphenylarsonium moiety indicates the site for the nucleophilic attack. As a result of this, electrophilic and nucleophilic region develops within the molecules and hydrogen bonding interactions occur between an electrophilic region and a nucleophilic region in another, or the same, molecular entity.
Figure 12: Molecular Electrostatic diagrams of (a) salt 1 (b) salt 2 and (c) salt 3 23
Conclusion We have reported new tetraphenylarsonium salts of the composition [Ph4As]+[S2P(OAr)2]-, where Ar = (2,4-CH3)2C6H3(1), (3,5-CH3)2C6H3(2), {4-(CH3)3C}C6H4(3). The salts 1, 2 and 3 crystallized in the monoclinic point group with space group P21, triclinic point group with space group P¯1 and monoclinic point group with space group P21/c, respectively. Single Crystal X-ray analysis reveals that the salts are stabilized by various non-covalent interactions C—H···X, C—H···π (X = O, S) interactions. These non-covalent interactions in the molecules result in their extension along different crystallographic axis. In some cases, these interactions result in the 1D extension of the molecules while in some other cases, these lead to the 2D network framework of the molecules. Hirshfeld surface analysis has been carried out in order to check the fidelity of the various non-covalent interactions in the molecules that are reported by using the single crystal X-ray analysis of the salts. The Hirshfeld surface analysis and the finger print plots provide quantitative information of these non-covalent interactions present in the molecules. The decomposed finger print plots provide the percentage contribution made by various non-covalent interactions towards the total Hirshfeld surface. Finally, the HOMO-LUMO energy gap of the molecules calculated using theoretical computational analysis helps in comparing the chemical reactivity of the synthesized tetraphenylarsonium compounds 1, 2 and 3. Authors credit Anu Radha: Conceptualization, Methodology, Writing-Original draft preparation, Pretam Kumar: Visualization and Writing-Review and Editing, Tahira Firdoos: Formal analysis and Writing-Review and Editing, Puneet Sood: Collection of XRD data, Namrata Rani: Theoretical Studies, Vikas: Theoretical Studies, Sushil K. Pandey: Conceptualization, Writing-Review & Editing and Supervision. Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement This research was supported by UGC NET-JRF scholarship (UGC-Ref.No.:193/CSIR-UGC NET DEC.2018). Post Graduate Department of Chemistry, University of Jammu, is acknowledged for recording NMR and IR spectra of the complexes. 24
Supporting Information CCDC 1981469-1981471 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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Graphical abstract
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