Supramolecular architecture of organotin(IV) N-methyl ferrocenyl N-ethanol dithiocarbamates: Crystallographic and computational studies

Supramolecular architecture of organotin(IV) N-methyl ferrocenyl N-ethanol dithiocarbamates: Crystallographic and computational studies

Inorganica Chimica Acta 471 (2018) 234–243 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/loca...

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Inorganica Chimica Acta 471 (2018) 234–243

Contents lists available at ScienceDirect

Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica

Research paper

Supramolecular architecture of organotin(IV) N-methyl ferrocenyl N-ethanol dithiocarbamates: Crystallographic and computational studies Abhinav Kumar a,⇑, Amita Singh a, Reena Yadav a, Suryabhan Singh b, Gabriele Kociok-Köhn c, Manoj Trivedi d,⇑ a

Department of Chemistry, University of Lucknow, Lucknow 226 007, India Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India c Chemical Characterisation and Analysis Facility (CCAF), University of Bath, Bath BA2 7AY, UK d Department of Chemistry, University of Delhi, Delhi, India b

a r t i c l e

i n f o

Article history: Received 13 June 2017 Received in revised form 30 October 2017 Accepted 10 November 2017 Available online 13 November 2017 Keywords: Organotin X-ray Supramolecular MP2 AIM

a b s t r a c t Four new organotin(IV) ferrocenyl dithiocarbamate complexes viz. [(FcCH2EtOHdtc)2SnR2] (R = Me (1), nBu (2) and Ph (3)) and [(FcCH2EtOHdtc)SnPh3] (4) have been synthesized and characterized by electronic absorption, IR, 1H, 13C and 119Sn NMR spectroscopy. The molecular structures of 1 and 2 have been confirmed by single crystal X-ray diffraction technique. The X-ray analyses for 1 and 2 reveal a skew trapezoidal bipyramid geometry around Sn(IV) which is being satisfied by the two sulfur atoms of the two dithiocarbamate ligands in anisobidentate fashion. In the crystal structure of 1, an interesting one dimensional chain held by OAH  O intermolecular interactions and also display weak CAH  p and CAH  S interactions. The crystal structure of 2 exhibit the formation of one dimensional chain held by weak OAH  S, (Cp)CAH  O and p  p interactions. Additionally 2 also display the formation of one dimensional chain because of the (Cp)CAH  S and (Cp)CAH  p interactions. These interactions have been addressed by ab initio and atoms-in-molecules analyses. Ó 2017 Elsevier B.V. All rights reserved.

1. Introduction In the recent years, amongst dithiolates, the dithiocarbamates have received substantial extent of consideration as prospective ligand systems for main group, transition metal and organometallic building blocks [1–5]. This is because of its easy methodology of syntheses, strong coordination ability and its capability to produce coordination-driven self-assembly. Also, this class finds utility in a variety of research areas viz. materials science and supramolecular chemistry and has shown imperative biological activities [1–5]. During the last few years the dithiocarbamate chemistry is concentrated upon the functionalization of the ancillary region of the dithiocarbamate which can develop fascinating supramolecules through non-covalent interactions viz. O  H, N  H, p  p and CAH  p (chelate, CS2M) in solid state [1–8]. These different interactions are capable of giving rise to physical properties which can be tuned by changing the nature of the substituents [1–8]. ⇑ Corresponding authors. E-mail addresses: [email protected] (A. Kumar), [email protected] (M. Trivedi). https://doi.org/10.1016/j.ica.2017.11.016 0020-1693/Ó 2017 Elsevier B.V. All rights reserved.

The inherent Lewis acidity of organotin(IV) halides makes them an ideal candidate for synthesizing complexes with dithiocarbamates and the resulting products shows substantial tendency to generate self-assembled supramolecular architecture [9] and can also offer a platform for the formation of macrocycles [3h,i]. Additionally, organotin(IV) dithiocarbamates have shown application in the area of medicinal chemistry because of the unique stereo-electronic properties of organotin(IV) centers bonded to the sulfur of dithiocarbamate ligands [10]. Also, they find applications in the field of material chemistry as the single source precursors for tin sulfide which is IV–VI semiconductor [11]. Molecular recognition studies with organotin(IV) dithiocarbamates indicated that they can function as receptors for neutral and anionic substrates particularly for the carboxylate anionic derivatives [12]. The interest in organometallic chemists for this class of organometallic system have been develop because of the capability of organotin(IV) derivatives to form complexes with dtc ligands through self-assembly and, hence offering the possibility to form macrocyclic assemblies in one-pot synthetic procedures [13]. Although organotin(IV) compounds of the type comprising of aromatic or aliphatic substituents at the

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dithiocarbamate fragment are abundant [1–13] but those featuring a ferrocenyl pendant on the dithiocarbamate entity are scarce [14]. We expect that exploration of the synthetic routes and as well as investigation of new types of secondary interactions viz. intermolecular O  H, (Cp)CAH  O and p  p interactions in organotin(IV) dithiocarbamates bearing ferrocenyl pendants would be interesting. With these views, we herein report the synthesis, characterization and molecular and supramolecular structures of new organotin(IV) dithiocarbamates comprising of ferrocenyl pendant and also having an AOH group at the periphery of the ligand. The nature of interaction in supramolecular motifs and their energies have been addressed using MP2 calculations and further these interactions have been validated using the Atoms in Molecules (AIM) theory. 2. Experimental 2.1. Materials and methods All chemical reagents are commercially available and were used without further purification. Infrared spectra were recorded as KBr pellets on a Shimadzu IR Affinity IS FTIR spectrophotometer. 1H, 13 C and 119Sn NMR spectra were recorded on Bruker Avance IIIHD 300 MHz spectrophotometers. Chemical shifts were reported in parts per million using TMS as internal standard for 1H and 13C NMR and tetramethyltin for 119Sn NMR. The potassium salt of Nmethylferrocenyl N-ethanol dithiocarbamate (KFcCH2EtOHdtc) had been synthesized in accordance with our previously reported method [5g]. 2.2. Syntheses 2.2.1. Synthesis of [(FcCH2EtOHdtc)2SnR2] (R = Me (1), Bu (2) and Ph (3)) The dithiocarbamate KFcCH2EtOHdtc (0.373 g, 1 mmol) was dissolved into the methanol and to this dimethyl tin(IV)dichloride (0.110 g, 0.5 mmol)/di-n-butyl tin(IV)dichloride (0.152 g, 0.5 mmol)/diphenyl tin(IV) dichloride (0.172 g, 0.5 mmol) dissolved in dichloromethane was added dropwise under nitrogen atmosphere. The reaction mixtures were stirred for 2 h and then evaporated up to dryness. The dried product was dissolved in dichloromethane and filtered through Celite, concentrated and finally precipitated with petroleum ether. 2.2.1.1. Characterization data. 1: yield (0.680 g, 83.02%); m. p. 125 °C; IR (KBr): m = 3376 (OAH), 1468 (C@N), 1077 (CAS), cm1; 1H NMR (300.13 MHz, CDCl3): d = 4.86 (s, 4H, FcACH2), 4.33 (s, 4H, FcAH), 4.16 (s, 14H, Fc), 3.89 (d, J = 4.5, 4H, CH2CH2OH), 3.83 (d, J = 4.2, 4H, CH2CH2OH), 1.18 (s, 6H, CH3) ppm; 13C NMR (75.50 MHz, CDCl3): d = 200.8 (CS2), 81.6 (FcCC), 70.1 (FcCH), 68.8 (FcCH), 60.6 (FcCH2), 55.1 (CH2CH2OH), 54.7 (CH2CH2OH), 29.8 (CH3); 119 Sn NMR (111.90 MHz, CDCl3): d = 331.2. 2: yield (0.540 g, 59.80%); m. p. 174 °C; IR (KBr): m = 3399 (OAH), 1466 (C@N), 1049 (CAS), cm1; 1H NMR (300.13 MHz, CDCl3): d = 4.96 (s, 4H, FcACH2), 4.41 (s, 4H, FcAH), 4.18 (s, 14H, Fc), 3.99 (t, J = 5.1, 4H, CH2CH2OH), 3.91 (t, J = 4.8, 4H, CH2CH2OH), 2.11 (t, J = 6.9, 4H, CH2), 1.95 (m, 4H, CH2), 1.51 (m, 4H, CH2), 0.94 (t, J = 7.2, 6H, CH3) ppm; 13C NMR (75.50 MHz, CDCl3): d = 200.1 (CS2), 81.8 (FcCC), 70.1 (FcCH), 68.7 (FcCH), 60.8 (FcCH2), 54.9 (CH2CH2OH), 54.6 (CH2CH2OH), 34.8 (CH2), 28.7 (CH2), 26.6 (CH2), 14.1 (CH3); 119Sn NMR (111.90 MHz, CDCl3): d = 334.6. 3: yield (0.592 g, 62.74%), m. p. 90 °C; IR (KBr): m = 3403 (OAH), 1487 (C@N), 1081 (CAS) cm1; 1H NMR (300.13 MHz, CDCl3): d = 7.99 (d, J = 6.0, 4H, C6H5), 7.83 (d, J = 6.6, 4H, C6H5), 7.41 (m, 2H,

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C6H5) 4.80 (s, 4H, Fc-CH2), 4.32 (s, 4H, FcAH), 4.13 (s, 4H, FcAH), 4.09 (S, 10H, FcAH), 3.79 (S, 8H, CH2CH2OH), ppm; 13C NMR (75.45 MHz, CDCl3): d = 200.2 (CS2), 150, 135.9, 134.4, 128.4 (C6H5), 81.4 (FcCC), 70.1 (FcCH), 69.6 (FcCH), 65.6 (FcCH), 60.3 (FcCH2), 55.6 (CH2CH2OH), 48.1 (CH2CH2OH); 119Sn NMR (111.90 MHz, CDCl3): d = 491.6. 2.2.2. Synthesis of [(FcCH2EtOHdtc)SnPh3] (4) The dithiocarbamate KFcCH2EtOHdtc (0.373 g, 1 mmol) was dissolved in methanol and to this triphenyl tin(IV)chloride (0.385 g, 1 mmol) dissolved in dichloromethane was added dropwise under nitrogen atmosphere. The reaction mixture was stirred for 2 h and the evaporated to dryness. The dried product was dissolved in dichloromethane and filtered through Celite, concentrated and finally precipitated with petroleum ether. 4: yield (0.392 g, 57.20%), m.p.110 °C; IR (KBr): m = 3425 (OAH), 1496 (C@N), 1063 (CAS) cm1; 1H NMR (300.13 MHz, CDCl3): d = 8.06 (d, J = 5.7, 6H, C6H5), 7.91 (d, J = 6.3, 6H, C6H5), 7.47 (m, 3H, C6H5), 4.93 (s, 2H, FcACH2), 4.40 (s, 2H, FcAH), 4.20 (s, 2H, Fc), 4.16 (s, 5H, Fc), 3.85 (t, J = 16.5, 8H, CH2CH2OH), ppm; 13C NMR (75.45 MHz, CDCl3): d = 200.8 (CS2), 142.1, 135.9, 134.4, 129.1 (C6H5), 81.4 (FcCC), 70.1 (FcCH), 68.8 (FcCH), 64.8 (FcCH) 60.4 (FcCH2), 56.5 (CH2CH2OH), 55.7 (CH2CH2OH); 119Sn NMR (111.90 MHz, CDCl3): d = 491.2, 321.3. 2.3. X-ray crystallography Intensity data for 1 and 2 were collected at 150(2) K on a Rigaku Xcalibur, EosS2 single crystal diffractometer using graphite monochromated Mo-Ka radiation (k = 0.71073 Å). Unit cell determination, data collection and data reduction were performed using the CrysAlisPro software [15]. A symmetry-related (multiscan) absorption correction had been applied. The structures were solved with SHELXT [16] and refined by a full-matrix leastsquares procedure based on F2 (Shelxl-2014) [17]. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed onto calculated positions and refined using a riding model except for the OH hydrogen atoms which have been located in the difference Fourier map and were refined with bond lengths restraints. In 1 both EtOH groups are disordered over two sites in the ratio 1:1 as they are connected to each other through intermolecular hydrogen bonding. However, the OH hydrogen atoms could only be refined using geometric constraints. Atoms C13 and C13A had to be refined with ADP restraints because of their proximity to each other. Additional programs used for analysing data and their graphical manipulation included: SHELXle [18] and ORTEP 3 for windows [19]. The pertinent crystallographic data and refinement parameters for 1 and 2 are presented in Table 1. 2.4. Computational details Molecular geometries were optimized at the level of density functional theory (DFT) using the B3LYP functional [20]. The split valence basis sets, 6-31G⁄⁄ were used for all C, N, O, S, and H atom centers. LANL2DZ basis set was used for the Sn and Fe atom centers. The intermolecular interaction energies have been estimated at the MP2 level of theory [21]. For the interaction energy calculations, the interaction distances have been fixed for the dimer or trimer while all other degrees of freedom were relaxed in the geometry optimization. The stabilization energies (DEdimer and DEtrimer) for dimeric and trimeric motifs involving the 2 and 3 molecules, respectively were calculated using the formula DEdimer = Edimer(2  Emonomer) and DEtrimer = Etrimer(3  Emonomer) where Emonomer, Edimer, Etrimer are the energies of the monomer, dimer

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Table 1 Crystallographic data and structure refinements for 1 and 2.

CCDC No. Empirical formula Formula weight/g mol1 Crystal System Space group a/Å b/Å c/Å a/° b/° c/° V/Å3 Z Dcalc/g cm3 F(0 0 0) Crystal size (mm3) Reflections collected Independent reflections Final R indices [I > 2r(I)] R indices (all data) Goodness-of-fit on F2 Largest difference peak and hole/e Å3 R1 = R||F0|  ||Fc||/R|F0|. where P = (F20 + 2F2c )/3.

3. Results and discussion 3.1. Synthesis and spectroscopic characterization

1

2

1527939 C30H38Fe2N2O2S4Sn 817.25 Monoclinic P21/n 19.4569(5) 7.2594(2) 23.0324(6) 90 96.230(3) 90 3234.01(15) 4 1.679 1656 0.40  0.40  0.20 45846 8844 [R(int) = 0.0331] R1 = 0.026 wR2 = 0.051 R1 = 0.035, wR2 = 0.055 1.04 0.47 and 0.45

1555524 C36H50Fe2N2O2S4Sn 901.41 Monoclinic I2/a 26.980(5) 7.3014(8) 20.406(3) 90 109.894(19) 90 3780.0(11) 4 1.584 1848 0.10  0.03  0.01 7012 3323 [R(int) = 0.0740] R1 = 0.062 wR2 = 0.079 R1 = 0.099, wR2 = 0.092 1.02 0.84 and 0.54 w = 1/[r2(F20) + (xP)2],

R2 = {[Rw(F20  F2c )/Rw(F20)2]}1/2,

and trimer motifs. Emonomer was calculated by optimizing a single molecule at the same level of theory. The intermolecular interaction strengths are significantly weaker than either ionic or covalent bonding, therefore it was essential to do basis set superposition error (BSSE) corrections. The BSSE corrections in the interaction energies were done using Boys-Bernardi scheme. In this paper all the interaction energies have been reported after BSSE correction [22]. All computational experiments have been performed using the Gaussian 09 programme [23].

S

Fe

SK OH

N

The addition of dichloromethane solution of triorganotin(IV) monohalide/diorganotin(IV)dihalides in appropriate stoichiometric ratio to the methanol solution of the dithiocarbamate ligand gave a yellow coloured solid (Scheme 1). All synthesized compounds were air stable and have been characterized by spectroscopic techniques and in two cases by single crystal X-ray diffraction. The electronic absorption spectra for all the four compounds were recorded in dichloromethane solution and are presented in Fig. 1. The electronic absorption spectra for all four compounds display two major prominent bands. The first at ca. 275–300 nm can be attributed to localized p–p⁄ transition while the another band located at 440 nm (inset) is arising due to the d ? d (assigned 1 to the 1E1g A1g) transition [5g]. IR spectra for the four compounds display bands in the region 1500–1484 and 1050–1048 cm1 corresponding to mC@N and mCS2, respectively, a characteristic feature of dithiocarbamate ligand. Also, bands at 3400–3490 cm1 indicate the presence of a free AOH group in all the four compounds. The purity and composition of the complexes have been studied by 1H NMR spectroscopy. 1H NMR integrated well with the corresponding hydrogen atoms and display characteristic resonances of the ligand and there is no major changes in the chemical shift value of the 1H NMR spectra of complexes in comparison to the potassium salt of the ferrocenyl dithiocarbamate ligand. The 13C NMR spectra of all the complexes showed a single low field resonance associated with the thioureide NCS2 carbon of the dithiocarbamate moiety lying in the range of d 196.3–197.7 ppm and this value is relatively more shielded than that of the free ligand (d 213.8 ppm) because of the prevailing involvement of R2N+@CS2 2 resonance form in the uncoordinated dithiocarbamate ligand. The 119Sn NMR chemical shift values were found in the expected region for diphenyltin dithiocarbamates (d 491 ppm) and for dialkylltin dithiocarbamates (d 331.6 ppm) indicating the typical six coordination of the tin atom [24]. In

OH

1/2 R2SnCl2

Fe

N

MeOH:DCM HO

MeOH:DCM Ph3SnCl

S S

Sn R

S S R

N

R = Me (1); nBu (2); Ph (3)

Fe S

N

S

Ph Sn

Fe

Ph Ph

HO

4 Scheme 1. Synthetic routes for the organotin(IV) ferrocenyl dithiocarbamate complexes.

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Fig. 1. Electronic absorption spectra for compounds 1–4 recorded in 105 M dichloromethane solution (inset: Electronic absorption spectra recorded at 103 M concentration).

organotin(IV) compounds the chemical shift values in the 119Sn NMR spectra moves upfield as the coordination number of tin increases from four to seven [24a]. In tetrahedral compounds the 119 Sn signal is usually observed between +200 and 60 ppm while the same for penta-coordinate and hexa-coordinate tin appears in the ranges 90 to 190 ppm and 210 to 400 ppm, respectively [24b]. The 119Sn signal in the NMR spectrum of compounds 1 and 2 clearly indicates the existence of six coordinated tin. The signal observed for 3 and 4 suggests the presence of five coordinate tin (cf. 46.5 ppm for Ph3SnCl) [24c]. From the NMR spectral features one would conclude a bidentate bonding of dithiocarbamate ligands in all of these complexes, which is not in consistence with the X-ray structural features (vide infra) and hence the possibility of structural differences in solution and solid state cannot be ruled out.

3.2. Crystal structure description 3.2.1. Crystal structure of 1 Single crystals of compound 1 were obtained by slow evaporation of a solution of the compounds in a dichloromethane/methanol mixture (2:1). The X-ray structure for compound 1 is depicted in Fig. 2 along with the atom numbering scheme. The crystal struc-

Fig. 2. ORTEP view of the molecular structure of 1. Atoms are drawn at 30% probability. H-atoms except those located at oxygen are removed for clarity.

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ture indicates that 1 adopts a skew trapezoidal bipyramidal structure with the Sn atom at the center and four S atoms at the corners of the trapezoid and the two methyl groups occupy the axial positions to complete the six coordination of the tin center. The two dithiocarbamate ligands binds to tin center in an anisobidentate fashion. The asymmetry in bonding of the ligand is also reflected in carbon–sulfur bond distances for both the ligand moieties which are not equal (C14AS2 = 1.7064(18) Å; C17AS4 = 1.6992(19) Å; C14AS1 = 1.7459(19) and C9AS4 = 1.742(2) Å). The two methyl groups occupy the axial sites subtending an angle of 134.2(2)° resembling the cis–trans pathway which starts forming at about a C15ASnAC16 angle of 137.98(8)°. The thiocarbonyl sulfur atoms of the ligands interact unsymmetrically with the metal leading to a distorted structure. There are two strong SnAS bonds with shorter bond lengths with distances SnAS1 2.5142(5) and SnAS3 2.5123 (5) Å and two weak SnAS bonds with longer bond lengths (SnAS2 3.0119(5) and SnAS4 3.0166(6) Å). The two strong Sn-S bonds are cis to each other subtending an acute angle S1ASnAS3 of 80.512 (16)°. These bond distance/angle parameters are in good agreement with the previously reported dimethyl tin(IV) dithiocarbamates [25]. The weaker SnAS bonds with S2ASnAS4 angle of 150.401(14)° lie 30° less from being co-linear to each other. These two SnAS bond lengths are longer than the sum of the covalent radii of the tin and sulfur (2.42 Å) but significantly below the sum of the van der Waals radii of these atoms (3.97 Å). The C15ASnAC16 angle (137.98(8)°) is far from ideal angles of both tetrahedron and octahedron. In skew trapezoidal bipyramidal molecules the CASnAC angles in cis-diorganotin complexes are in the range of 102–110° while the same range between 180° and 145° in the case of trans-isomers. The C1ASnAC5 bond angle may be considered to resemble the transition state of the cis–trans pathway which starts forming at about 134 for a CASnAC angle. In 1 the solid state structure is stabilized by inter-molecular hydrogen bonds present in between a free AOH groups present at the N-methyl ferrocenyl N-ethanol dithiocarbamate ligands with a O1aAH1a  O2a hydrogen bonding distance of 1.91 Å. It is noteworthy here that these intermolecular interaction lead to the formation of one dimensional chain (Fig. 3a). Additionally, chains of dimers held by OAH  O intermolecular interactions have been formed in which O1aAH1a  O2a and O2aAH2a  O1a interaction distances are 1.91 Å and 2.16 Å, respectively (Fig. 3b). Additionally, the disorder associated with the AOH functional does not appear to have significant impact on the molecular packing. Apart from the OH  O hydrogen bonding, 1 display significant CAH  S and CAH  p(Cp ring) intermolecular interactions with distances between 2.96 and 2.87 Å, respectively (Fig. 4). 3.2.2. Crystal structure of 2 Single crystals of the compound 2 were obtained by slow evaporation of a solution of the compounds in a dichloromethane/ methanol mixture (2:1). The molecular structure and numbering scheme is shown in Fig. 5. The coordination sphere around the tin atom in the compound can be described as bicapped tetrahedron or a skew trapezoidal bipyramid. The four sulfur atoms constitute a trapezoid and the two n-butyl groups occupy the axial positions to complete the six coordination of the tin atom. This model is based on the presumption that the dithiocarbamate ligand chelates the tin center in an asymmetric manner. The anisobidentate mode of coordination in this compound is accompanied by unequal SnAS bond distances. The asymmetry in bonding of the ligand is also reflected in carbon–sulfur bond distances for both the ligand moieties which are not equal (C14AS2 = 1.702(6) Å; C14AS1 = 1.758(6) Å). The two strong SnAS1 (2.5560(10) Å) and SnAS3 bonds (2.5477(11) Å) are cis to each other with a very acute angle S1ASnAS3 (79.99(3)°). The weaker SnAS2 (2.9335(10) Å) and SnAS4 (3.0078(11) Å) bonds are also cis with respect to each

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Fig. 3. (a) One dimensional chain of 1 held by intermolecular OAH  O interactions; (b) One dimensional dimer chain of 1 held by intermolecular OAH  O interactions.

Fig. 4. (Cp)CAH  p and CAH  S interactions in 1.

other S2ASnAS4 angle of 151.69(3)° deviate only by 28° from being linear. These bond distance/angle parameters are in good agreement with the previously reported di-n-butyl tin(IV) dithiocarbamates [25b,26]. The weak SnAS2 and SnAS4 distances are quite longer than the sum of covalent radii of Sn and S atoms (2.42 Å) but significantly less than the sum of van der waals radii of these atoms (3.97 Å). The C15iASnAC15 angle (137.9(3)°) is far from ideal angles of both tetrahedron and octahedron. In skew trapezoidal bipyramidal molecules the CASnAC angles in cis-

diorganotin complexes are in the range of 102–110° while the same range between 180° and 145° in the case of trans-isomers. The C15iASnAC15 bond angle may be considered to resemble the transition state of the cis–trans pathway which starts forming at about 134° for a CASnAC angle. In case of the crystal structure of compound 2, inter-molecular hydrogen bonds are present in between AOH groups and the more weakly coordinated S of the CS2 group with a distance of 2.42 Å along with CH(Cp)  O (2.55 Å) and pp interactions (3.34 Å)

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Fig. 5. ORTEP view of the molecular structure of 2 with atoms drawn at 30% probability. H-atoms except those located at oxygen are removed for clarity.

and are forming a one dimensional chain along the c-axis (Fig. 6). Additionally, 2 also exhibits relatively weaker (Cp)CAH  S and (Cp)CAH  p interactions (Fig. 7) with dimensions of 2.97 and 2.89 Å, respectively. It is interesting to note here that although AOH groups are present in 2 they still do not display strong OAH  O intermolecular interactions. The absence of OAH  O interactions in 2 may be attributed to the inherent bulkiness of the n-butyl fragment. Hence, both the compounds 1 and 2 displayed interesting interplay between O  H and S  H intermolecular interactions which mainly depends upon the bulkiness of the alkyl fragments attached to the Sn(IV) center. Similar phenomenon have been observed in the previous reports [3g,5d,14a,27] where the bulkiness associated with the functionalized pendants on dithiocarbamate ligand as well as the size of the aliphatic and aromatic moieties attached at the Sn (IV) center play pivotal role in the interplay weak interactions. 3.3. DFT and AIM results regarding non-covalent interactions The crystal structures of compounds 1 and 2 are good examples of the interplay of different molecular interactions that lead to interesting supramolecular aggregates in solid state (Figs. 3, 4, 6 and 7). It is obvious that OAH  O, OAH  S, pp, CAH  O, CAH  S and (Cp)CAH  p non-covalent interactions play

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an important role if the structure is to be rationalized in terms of interactions between the molecular fragments. However, it needs to be investigated to what kind of intermolecular interaction(s) contributes to the binding energy between molecules and dimers in the structure. In order to analyse the various interactions that lead to the crystal structure, interaction energies have been calculated for dimers and trimers held by the aforementioned interactions. The analysis of the interaction energies in the crystal structure of 1 by means of dimer unit at the BSSE-corrected MP2 level of theory yields an interaction energy of 10.06 kJ/mol (Fig. 3); the interaction energy of the p(Cp)  p(Cp) and CAH  S (Fig. 4) is calculated to be 4.36 kJ/mol. In order to gain insight into the cooperative effect between both OAH  O and CAS  H interactions energy calculations were performed for the motifs displaying both type of interactions and for this type of trimer the interaction energy was calculated to be 8.98 kJ/mol. This indicates that both the interactions are not involved in the cooperative effect. The analysis of the interaction energies calculated at the same level theory for the dimers and trimer in the crystal structure of 2 yields an interaction energy of 10.60 kcal/mol and 21.33 kcal/mol for the dimers and trimers held by OAH  S, (Cp)CAH  O and p  p interactions. The interaction energies of the dimer and trimer held by CAH  S and CAH  p interactions are relatively on the lower energy scale of 3.05 and 5.79 kcal/mol. These interaction energy calculations indicates that OAH  S, (Cp) CAH  O and p  p interactions offers significant stability to the solid state structure of 2. In order to gain further insight into the nature of these interactions, bond critical points (bcp) were calculated for dimers (Figs. 8 and 9) by using the Atoms in Molecules (AIM) theory [28]. The bond critical points observed between the pertinent atoms in all the dimers confirms the presence of intermolecular OAH  O, OAH  S, p  p, CAH  O, CAH  S and (Cp)CAH  p non-covalent interactions. The interactions have further been corroborated by calculating the interatomic surfaces between the atoms of interest which bisects at the corresponding bond critical points (Figs. 8, 9). The values of electron density (q); Laplacian (r2qbcp); bond ellipticity (e), Hamiltonian form of the Kinetic Energy (K), Potential Energy density (V), Lagrangian form of Kinetic Energy (G) at the

Fig. 6. One dimensional chain formed due to the OAH  S, (Cp)CAH  O and p  p interactions.

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Fig. 7. One dimensional chain formed due to the (Cp)CAH  S and (Cp)CAH  p interactions.

Fig. 8. Molecular graph for the OAH  O dimer (upper) and dimer held by CAH  S and CAH  p interactions for 1 (interatomic surfaces between the atoms of interest for the monomer are also presented).

bond critical points between pertinent atoms are presented in Table 2. The Table 2 indicates that the electron density for all types of interactions at bond critical point (qbcp) are less than +0.10 au which indicates a closed shell hydrogen bonding interaction [29]. Additionally, the Laplacian of the electron density r2qbcp in all the cases are greater than zero which indicates the depletion of electron density in the region of contact between the O  H and

S  H atoms. The bond ellipticity (e) measures the extent to which the density is preferentially accumulated in a given plane containing the bond path [29]. The e values for all the interactions indicate that these are not cylindrically symmetrical in nature [29]. The total electron energy density (Hb = G + V) associated with these interactions indicates that they are not associated with the significant sharing of electrons and hence confirming the weak noncovalent interaction nature for the two atomic centers.

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Fig. 9. Molecular graph for the dimer of 2 held by OAH  S, (Cp)CAH  O and p  p interactions (upper) and dimer held by (Cp)CAH  S and (Cp)CAH  p for 2 (interatomic surfaces between the atoms of interest for the monomer are also presented).

Table 2 Selected topographical features viz. Electron density (qbcp), Laplacian of electron density (r2qbcp), ellipticity (e), Hamiltonian form of the Kinetic Energy (K), Potential Energy density (V), Lagrangian form of Kinetic Energy (G) at the bond critical points of inter-molecular interactions computed at MP2/6-31G**/LANL2DZ level of theory for dimers of 1 and 2. Interaction

qbcp

r2qbcp

(e)

K

V

G

1 OAH  O CAH  p CAH  S CAH  S

+0.0240 +0.0044 +0.0066 +0.0033

+0.0737 +0.0166 +0.0210 +0.0103

+0.0950 +2.0722 +0.0979 +0.1093

+0.0006 0.0011 0.0011 0.0007

0.0195 0.0020 0.0031 0.0012

+0.0190 +0.0031 +0.0042 +0.0019

2 OAH  S (Cp)CAH  O p  p (Cp)CAH  S CAH  p

+0.0176 +0.0035 +0.0053 +0.0045 +0.0019

+0.0461 +0.0269 +0.0168 +0.0137 +0.0062

+0.0689 +0.0284 +0.0962 +0.0467 +1.0716

0.0008 0.0006 0.0009 0.0008 0.0004

0.0114 0.0056 0.0024 0.0018 0.0008

+0.0114 +0.0006 +0.0033 +0.0026 +0.0012

qbcp, r2qbcp, e, K, V, G, in a.u.

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4. Conclusions The crystallographic studies of the reported compounds demonstrated various supramolecular structural diversities as a function of AOH group present on the dithiocarbamate ligands and the bulkiness of the organic fragments attached to the Sn(IV) center. Attempts were made to address the nature of weak interand intra-molecular interactions in the newly synthesized compounds using DFT and AIM theory calculations. Based on our findings it can be concluded that by judiciously choosing the functional group at the dithiocarbamate ligand and by tuning the bulkiness associated with the aliphatic and aromatic fragments bonded to the Sn(IV) center one can observe the interesting interplay between weak interactions especially between O  H and S  H interactions. Acknowledgement

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