Preparation, spectral characterization, crystal structure, thermal analysis and Hirshfeld surface analysis of the complex [Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2),1.25H2O

Journal Pre-proofs Preparation, spectral characterization, crystal structure, thermal analysis and Hirshfeld surface analysis of the complex [Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2),1.25H2O H. EL Hamdani, M. EL Amane, C. Duhayon PII: DOI: Reference:

S1387-7003(19)30260-6 https://doi.org/10.1016/j.inoche.2019.107663 INOCHE 107663

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Inorganic Chemistry Communications

Received Date: Revised Date: Accepted Date:

16 March 2019 25 October 2019 4 November 2019

Please cite this article as: H. EL Hamdani, M. EL Amane, C. Duhayon, Preparation, spectral characterization, crystal structure, thermal analysis and Hirshfeld surface analysis of the complex [Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2),1.25H2O, Inorganic Chemistry Communications (2019), doi: https:// doi.org/10.1016/j.inoche.2019.107663

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Preparation, spectral characterization, crystal structure, thermal analysis and Hirshfeld surface analysis of the complex [Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2),1.25H2O H. EL Hamdani a, M. EL Amane a*, C. Duhayon bc a

Equipe Métallation, complexes moléculaires et applications, School of sciences, Meknes, Moulay

Ismail University, BP 11201 Zitoune, 50000 Meknes, Morocco b

CNRS ; LCC (Laboratoire de Chimie de Coordination) ; 205, route de Narbonne, F-31077 Toulouse,

France. c Université de Toulouse ; UPS, INPT ; LCC ; F-31077 Toulouse, France * Corresponding author : [email protected]

Abstract: The complex of the [Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2),1.25H2O has been prepared in the water-ethanol solution at room temperature and characterized by single crystal and powder X-ray diffraction analysis, UV-Visible, Infrared spectroscopies and thermal analysis (TGA and DTA). This complex is crystallized in the monoclinic system with C 2/c space group. The unit cell parameters are a = 27.6240(11) Å, b = 17.6694(7) Å, c = 16.6504(6) Å and β = 92.5713(15)°,. The Co(II) ion is octahedral coordinated by three oxygen atoms of the coordinated water molecules, three nitrogen of thiocyanato ligands and one molecule of 2-Aminopyridine leading to an overall CoO3N3 coordination. Beside π-π interactions, the intermolecular hydrogen bonds (O—H···N, O—H···O, N—H···O, C—H···S and N—H···S) together play a vital role in stabilizing of the crystal packing. Hirshfeld surface analysis and two-dimensional fingerprint plots have been used to determine the percentage of interactions involved in the formation of the crystal packing. Keywords: X-ray diffraction, Single crystal, Inorganic compounds, Infrared devices, Caffeine, thiocyanate, 2-aminopyridine, Supramolecular complex 1. Introduction Intermolecular interactions, that is to be much weaker than the covalent bonds, take part an important role in the formation of the complexes. Metal-organic supramolecular complexes are of considerable interest for their structural diversity and their applications [1-7]. In the last years, pyridine and its derivatives have been investigated by several studies because of their involvement in bioactivities and applications in pharmaceutical, agro- chemical and many other industries [8-10]. In particular it has been mentioned that 2-amino pyridine derivatives have

paying attention considerable because they are useful precursors for the synthesis of a diversity of heterocyclic compounds possessing a medicinal value [11-14]. Caffeine (1,3,7-Trimethyl-3,7-dihydro-1H-purine-2,6-dione) has been known to have attractive effects on various biological systems such as cardiovascular, gastrointestinal, respiratory and muscle systems [15-17]. Its complexes with transition metals have different coordination and biological properties such as antibacterial and anti-inflammatory [17-20]. In this work we have synthesized

a

new

Metal-organic

supramolecular

complex

[Co(NCS)2(C5H6N2)(H2O)3].3C8H10N4O2.1,25H2O. 2. Experimental 2.1. Materials All chemicals were analytical grade products and used without any purification. Infrared spectra were fitted using the FT/IR-4100 FT-IR Spectrometer. Before each measurement, the sample was finely ground, mixed with KBr using a mortar and pestle, and pressed into pellets. UV-Visible spectra were measured in acetonitrile using Shimadzu UV-Visible recorder spectrophotometer UV-1800. 2.2. Single Crystal X-Ray Diffraction (SCXRD) Data collection: Apex2 (Bruker AXS, 2006); cell refinement: Apex2 (Bruker AXS, 2006); data reduction: Apex2 (Bruker AXS, 2006); program used to solve structure: Superflip [21]; program used to refine structure: CRYSTALS [22]; molecular graphics: MERCURY [23]; software used to prepare material for publication: CRYSTALS. Crystal data, data collection and structure refinement details are summarized in table 1. In the absence of significant anomalous scattering, Friedel pairs were merged. Atomic scattering factors were taken from the International Tables for X-ray Crystallography. All non-hydrogen atoms were refined anisotropically. The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically. The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C—H in the range 0.93– 0.98, N—H in the range 0.86–0.89 N—H to 0.86 O—H = 0.82 Å) and Uiso(H) (in the range 1.2– 1.5 times Ueq of the parent atom), after which the positions were refined with riding constraints [24].

2.3. Synthesis of complex The single crystal of the [triaquabis(thiocyanato-κN)(2-aminopyridine-κN)Cobalt(II)]3caffeine-1,25H2O was prepared by slow evaporation of the concentrated aqueous solution at room temperature (Sheme 1). The typical experimental process is as follows: 237 mg (1 mmol) of CoCl2.6H2O was dissolved in water solution, 188,24 mg (2 mmol) of 2-aminopyridine was dissolved in 5 ml of ethanol solution and 388,38 mg (2 mmol) of caffeine was dissolved in 10 ml of ethanol solution. In other hand we have dissolved 190 mg of potassium thiocyanate (2 mmol) in 5 ml of water solution. The mixture between these solutions was carried out at room temperature. Red crystals were obtained after two months by slow evaporation at room temperature. The details of the crystal structure determination are summarized in Table 1.

Scheme 1. Synthesis route to the complexes [Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2),1.25H2O

Table 1 Crystallographic data and structure refinement results for complex Chemical formula Mr Crystal system, space group Temperature (K) a, b, c (Å) β (°) V (Å3) Z Radiation type µ (mm−1) Crystal size (mm) Diffractometer Absorption correction Tmin, Tmax No. of measured, independent and observed [I > 3.0σ(I)] reflections Rint R[I > 3σ(I)], wR, S No. of parameters Δρmax, Δρmin (e Å−3)

Crystal data C7H12CoN4O3S2·3(C8H10N4O2)·1.25(H2O) 928.36 Monoclinic, C2/c 175 27.6240 (11), 17.6694 (7), 16.6504 (6) 92.5713 (15) 8118.9 (3) 8 Mo Kα 0.60 0.23 × 0.20 × 0.20 Nonius KappaCCD Multi-scan DENZO/SCALEPACK [25] 0.83, 0.91 206308, 7766, 7560 0.024 0.0301, 0.0311, 1.05 546 0.64, −0.27

3. Results and Discussion 3.1. Structural description The X-ray structural determination of compound confirms the assignments of the structure from spectroscopic data. Selected bond lengths (see Table 2) and angles are given in (Table 3). Selected hydrogen interactions parameters are given in (Table 4). The molecular structure along with the atom-numbering scheme is depicted in figure 1, while the packing diagram is given in figures 3, 4 and 5 respectively. Single-crystal X-ray diffraction reveals that the compound [triaquabis-(thiocyanato-κN)(2aminopyridine-κN)Cobalt(II)]-3caffeine-1,25H2O crystallizes in the monoclinic system with space group C 2/c. The unit cell parameters are a = 27.6240(11) Å, b = 17.6694(7) Å, c = 16.6504(6) Å with β = 92.5713(15) °, V = 8118. 87Å3.

Figure 1. The asymmetric unit of the title complex with displacement ellipsoids drawn at the 50% probability level. In the crystal structure of the title compound, the Co(II) cation is in an octahedral coordination environment formed by two N atoms of the thiocyanato anions, one nitrogen of 2-aminopyridine and three O atoms of coordination water molecules (Fig.2). The distance between the Co(II) ion with different ligands in complex is different, therefore the CoN3O3 octahedron is slightly distorted (see fig. 2). These structural features are typical for related compounds. The thiocyanato ligands are bound through nitrogen atoms and are quasi-linear [N8—C9—S10 = 178.8(2)°, N11—C12—S13 = 178.4(2)°], while the Co–NCS linkages are bent [C9—N8—Co1 = 161.1(1)°, [C12—N11—Co1= 173.8(2)°]. Our synthesized complex possess similar structural features with the complexes which are involved the N-bound NCS group [26]. The molecule of caffeine is involved in supramolecule structure by hydrogen bonded with the complex [triaquabis-(thiocyanato-κN)(2-aminopyridine-κN)Cobalt(II)] and free water molecules.

The molecules of water of crystallization are involved in the formation of three-dimensional networks through hydrogenated bonds with caffeine molecules and the complex (2).

Figure 2: Coordination environment of the Co(II) ion Table 2 : selected bond lengths (Å) for the complex C7H12CoN4O3S2·3(C8H10N4O2)·1.25(H2O) Co1 - N1 2.2237(11) Co1 - O16 2.1065(9) Co1 - N8

2.0736(12)

N8 - C9

1.1590(18)

Co1 - N11

2.0998(12)

C9 - S10

1.6310(14)

Co1 - O14

2.1427(9)

N11 - C12

1.1594(18)

Co1 - O15

2.0839(9)

C12 - S13

1.6435(13)

Table 3 : selected angles ( °) for the complex C7H12CoN4O3S2·3(C8H10N4O2)·1.25(H2O) Co1 -N1 - C2 115.51(8) O14 - Co1 - O15 86.96(4) Co1 - N1 - C6

126.75(8)

N1 - Co1 - O16

86.73(4)

N1 - Co1 - N8

93.76(4)

N8 - Co1 - O16

91.39(4)

N1 - Co1 - N11

172.78(4)

N11 - Co1 - O16

90.03(4)

N8 - Co1 - N11

92.76(5)

O14 - Co1 - O16

176.08(4)

N1 - Co1 - O14

89.64(4)

O15 - Co1 - O16

91.41(4)

N8 - Co1 - O14

90.33(4)

Co1 - N8 - C9

161.06(12)

N11 - Co1 - O14

93.40(4)

N8 - C9 - S10

178.77(12)

N1 - Co1 - O15

87.78(4)

Co1 - N11 - C12

173.84(11)

N8 - Co1 - O15

176.87(4)

N11 - C12 - S13

178.36(12)

N11 - Co1 - O15

85.84(4)

Figure 3: Partial packing diagram of the complex showing the network of hydrogen bonds. Hydrogen bonds are shown as dashed lines. In the crystal, each complex molecule interacts with five neighboring caffeine molecules through classical O—H···N and O—H···O hydrogen bonds involving the coordinating water molecules as H-atom donors to form layers parallel to the bc plane with a thickness of a/2. These planes are further enforced by C—H···S and N—H···S hydrogen bonds and are alternated with the half occupancy water molecule O60 (see Figure 3 and Figure 4).

Figure 4: Partial packing diagram of the title compound, showing the network of hydrogen bonds (orange dotted lines) linking complexes and caffeine/water molecules into layers parallel to the b c plane and with a thickness of a/2. Table 4: Selected hydrogen interactions (Å, °) parameters. D—H···A D—H H···A O16—H162···O58v 0.824 2.045 O15—H152···N19vi 0.814 1.929 N7—H71···O15 0.840 2.290 O16—H161···N47vii 0.823 1.985 O15—H151···O30 0.818 1.992 O14—H141···O59 0.796 1.998 O14—H142···O56i 0.810 2.006 N7—H72···S13vi 0.838 2.656 C32—H321···S13 0.945 2.735

D···A 2.862 (2) 2.743 (2) 2.890 (2) 2.800 (2) 2.770 (2) 2.769 (2) 2.808 (2) 3.482 (2) 3.626(2)

D—H···A 171 177 129 170 159 163 170 169 157.2

Symmetry codes: (i) x, −y+1, z+1/2; (ii) −x+1, −y+1, −z+1; (iii) x, −y+1, z−1/2; (iv) −x+1/2, y−1/2, −z+3/2; (v) −x+1/2, y+1/2, −z+3/2; (vi) x, −y+2, z+1/2; (vii) −x+1/2, −y+3/2, −z+1.

π—π interactions occur between complex and caffeine molecule and caffeine molecules themselves (see Figure 5), giving rise to columns along axis a ; hydrogen bonds and π—π interactions leading to the formation of a three-dimensional network (see Table 5).

Table 5: π—π interactions between rings Centroid-centroid distance (Å) 3.38

Plane to plane distance(Å) 3.30

C(34)/N(35)/C(36)/N(37)/C(38)/C(39) and [C(34)/N(35)/C(36)/N(37)/C(38)/C(39)]ii

3.37

3.36

N(1)/C(2)/C(3)/C(4)/C(5)/C(6) and [C(48)/N(49)/C(50)/N(51)/C(52)/C(53)]v

3.42

3.42

N(1)/C(2)/C(3)/C(4)/C(5)/C(6) and [N(17)/C(18)/N(19)/C(20)/C(25)]vi

3.62

3.37

π—π interactions between rings C(34)/N(35)/C(36)/N(37)/C(38)/C(39) and C(48)/N(49)/C(50)/N(51)/C(52)/C(53)

Symmetry codes: (i) x, −y+1, z+1/2; (ii) −x+1, −y+1, −z+1; (iii) x, −y+1, z−1/2; (iv) −x+1/2, y−1/2, −z+3/2; (v) −x+1/2, y+1/2, −z+3/2; (vi) x, −y+2, z+1/2; (vii) −x+1/2, −y+3/2, −z+1.

Figure 5: Crystal packing of the title compound viewed down the b axis (1) and a axis (2). Molecules interacting each other through π-π interactions are drawn with same style (“stick” or “ball and stick”).

3.2. X-Ray patterns property X-ray powder diffraction spectrum (XRPD) for finely ground powder of complex is carried out at room temperature. Figure 6 shows a comparison of the calculated XRPD pattern from the single-crystal structure of complex obtained from X-ray data with the XRPD pattern of the bulk sample. The overlay indicate that the supramolecular complex as single-phase which can be easily synthesized [26].

Figure 6: Experimental (a) simulated (b) and X-Ray diffraction patterns of complex. 3.3. Hirshfeld surface analysis Hirshfeld surface (HS) [27-28] analysis was carried out by using Crystal Explorer 17.5 [29] in order to visualize the inter-molecular inter-actions in the crystal of the supramolecular complex (Fig. 7). In the HS plotted over dnorm, the white surface indicates contacts with distances equal to the sum of van der Waals radii, and the red and blue colours indicate distances shorter (in close contact) or longer (distant contact) than the van der Waals radii, respectively [30]. The Hirshfeld surface presented by the dnorm surface of the complex [Co(H2O)3(SCN)2(C5H8N2)] (Fig. 8) shows red spots that correspond to strong interactions OH(coordinated OH(coordinated

water)...Ncaf,

OH(coordinated

water)...OH2O

water)...Ocaf,

and CH...S. The H...H interaction is the most

abundant contributor of the total Hirshfeld surface around the [Co(H2O)3(SCN)2(C5H8N2)] complex, it contributed by 29.3% (Tab. 6). We can also report the presence of H...S (26.1%), H...C (15.8%), H...O (10%) and H...N (9.5 %). In addition, very low percentages of interactions

C...C (3.2%), N...C (2.9%), S...S (1.2%), C...S (0.8%) ), N...S (0.3%), S...O (0.3%), N...N (0.2%) are recorded in the crystal lattice.

Figure 7. The asymmetric unit of the title complex

Figure 8. View of the three-dimensional Hirshfeld surface of [Co(H2O)3(SCN)2(C5H8N2)] complex plotted over d norm in the range −0.6757 to 1.2305 a.u. From the shape-index surface, it is also evident that the complexes [Co(H2O)3(SCN)2(C5H8N2)] are related to caffeine molecular by π-π stacking interactions, as can be inferred from the inspection of adjacent red and blue triangles (highlighted by blue circles) (Fig. 9). Indeed, the pattern of red and blue triangles in the same region of the shapeindex surface is characteristic of

stacking interactions. The blue triangles represent convex regions resulting from the presence of ring carbon atoms of the molecule inside the surface, while the red triangles represent concave regions caused by carbon atoms of the stacked molecule above it.

Figure 9. Three-dimensional shape-index surface of [Co(H2O)3(SCN)2(C5H8N2)] complex

Figure

10.

Two-dimensional

fingerprint

[Co(H2O)3(SCN)2(C5H8N2)] complex

plots

to

the

Hirshfeld

surface

of

The Hirshfeld dnorm surface, 2D fingerprint plots and shape index of the caffeine part in the complex are depicted in the Fig 11, 12 and 13. These analyses reveal the presence of different types of intermolecular interactions. It can be inferred that the dominant interactions are H…H. The second largest percentage can be attributed to the H…O interactions, which are responsible for the appearance of deep red spots in the norm scheme. They are identified by N–H…O, CH…O and O–H…O hydrogen bonds in the crystal lattice. The contribution of H…S/S…H, and H…N/N…H contacts to the total Hirshfeld surface is relatively small. The presence of the adjacent red and blue triangles on the shape index surface of caffeine parts, demonstrates the presence of π–π stacking interactions, which exist between two caffeine rings and between the caffeine with 2-aminopyridine rings. This result has been confirmed by X-ray crystal structural analysis (Fig. 5). The study of the water molecule environment by Hirshfeld surface analysis Intermolecular contacts were analyzed around the water molecule in the asymmetric unit. The Hirshfeld surface analysis of the water molecule is depicted in Fig. 14, which is mapped by dnorm and the 2D fingerprint plots. It is clear that H…H contacts are the most important interactions (53.1 %), which refer basically to the abundance of hydrogen on the molecular surface. The H…N interactions contribute to only 8.8 % of the Hirshfeld surface.

Figure 11. Shape index, Three-dimensional dnorm surface and fingerprint of caffeine (a) part

Figure 12. Shape index, Three-dimensional dnorm surface and fingerprint of caffeine (b) part

Figure 13. Shape index, Three-dimensional dnorm surface and fingerprint of caffeine (c) part

Figure 14. Three-dimensional dnorm surface and fingerprint of crystallization water part Table 6. Percentage contributions of interatomic contacts to the Hirshfeld surface Contacts N…N N…C N…S N…H C…C C…S C…H S…S S…O S…H O…H H…H C…O O…O N…O

[Co(H2O)3(SCN)2(C5H8N2)] 0,2 2,9 0,3 9,5 3,2 0,8 15 ,8 1,2 0,3 26,1 10 29,3 -

contribution % Caféine (a) Caféine (b) 1,4 0,8 5,2 7,5 0,4 7 8,7 3,7 4,5 1 6,9 4,6 0,2 3,1 4,4 24,5 27,1 45 39,7 0 ,4 0,7 1,9 0,9

Caféine (c) 0,9 5,8 12 5,7 0,1 10,1 4,3 17,6 43,2 0,3

H2O 8,8 38 ,1 53,1 -

3.4. FT-IR spectral analysis Infrared spectra of caffeine, 2-aminopyridine and their complex are show in (Fig.15). In infrared spectra of the free ligands

and the complex

[Co(H2O)3(SCN)2(C5H8N2)]-

3(C8H10N4O2),1.25H2O are discussed with tabulations and tentative assignments of the their characteristic bands . The peaks of various important vibrations of all modes observed in the spectrum of the complex are listed in (Tab. 7). The absorption bands are recorded in the range 3700-3500 cm-1 due to coordination and lattice water molecules [31]. The stretching frequencies of νas (NH2) and νs (NH2) are observed at 3465 and 3347 cm-1, respectively. This confirms that NH2 group is not involved in coordination [32-a]. The vibrations assigned to aromatic C-H stretching of free caffeine is showed in the region (3111-2956) cm-1 are shifted at (3121-2947) cm-1 for the complex. This shift is due to the formations of hydrogen bonds in the solid state [33]. Similarly the two intense ν(CO) asymmetric and symmetric stretching of carbonyl groups and δ(CO) deformation are observed at 1700, 1660 cm-1 and 425 cm-1 respectively, also shifted to (1704,1650) cm-1 and 420 cm-1 respectively [33]. These shifts suggested that the caffeine is involved in the formation of the threedimensional network by intermolecular hydrogen bond O-H···O between a water molecule and a carbonyl atom (Table 2). The band noticed in the free caffeine at 1548 cm-1 is attributed to the imidazole ring stretching + ν C=C + ν CN + δ CH is appeared for the complex at 1553 cm-1 [33]. These shifts are confirming that, the C-H aromatic in purine ring is involved in the formation of three-dimensional networks by hydrogen bonds. The absorption bands observed at 2096, 2077 and 465 cm-1 are due respectively to the ν NCS stretching vibration, and deformation δ NCS of isothiocyanato ligand. These results indicate the coordination of the isothiocyanato ligand in the complex. The presence of the two bands corresponding to the stretching vibrations of the isothiocyanato suggested that the complex is a cis position [34]. The IR spectrum of the complex (Fig. 15) showed the absorption band of (N-H) group at 2365 cm-1 [32-b]. The bands corresponding to δ(N-H) and ρ(N-H) appears at 1622 and 845 cm-1 respectively for free ligand, are shifted to higher frequency at 1627 and 875 cm-1 in spectrum of the complex [32]. These changes confirm that 2-aminopyridine involved in network formation by intermolecular interaction (O-H···N-H) and intermolecular interaction N-H···S. The νC-H and δ(C-H)

frequencies of 2-Aminopyridine free are observed, respectively at 3209, 3068, 3045, 3033 cm -1 and 1171, 1125 cm-1 are appearing for the complex at 3207, 3079, 3051 3018 cm-1 and 1153, 1113 cm-1 [32, 35]. The bands ρr (H2O) and ρw (H2O) in the spectrum of the complex are observed at 793, 780 and 540 cm-1, respectively, indicates the presence of coordinated water [36]. In the infrared spectrum of the complex, we observed new bands at 556 cm -1 and 500 cm-1. These bands assigned to the vibrations ν (Co-N) and ν (Co-O) respectively [37]. This observations are confirmed by the X-ray structure of the complex which shows that ligands (SCN-, OH2,caffeine, 2-Aminopyridine) is bonded to multiple hydrogen bonds in the solid-state.

Figure 15. Infrared spectra of caffeine, 2-aminopyridine and the complex

Table 7. The infrared spectral data of complex and free ligands 2-AP caffeine crystal Assignment 3692-3500 ν OH2 [31] 3446 3465 νas NH2 [32] 3415-3381 ν OH2 3345 3347 νs NH2 [32] 3209 3207 ν C-H str of 2AP 3111 3121 ν C-H str of caf 3068 3079 ν CH of 2AP [36] 3045 3051 ν CH of 2AP [36] 3033 3018 ν CH of 2AP [36] 2956 2947 νCHcaf 2916 2916 ν CH of 2AP 2857 2853 ν CH of 2AP 2096 ν SCN [35] 2077 ν SCN[35] 1701 1700 ν C=O str 1660 1650 ν CO + ν CN + δ (OH)H2O 1622 1627 δ (NH2)2AP [32] 1599 1607 ν CC + ν CN 1548 1553 Imid ring str + ν C=C + ν CN +CH bend 1483 1490 Sym CH3 bend + CN str* + CH3 bend 1456-1432 1445 Sym CH3 bend + CN str +CH bend 1403 1406 Quadratal C-N str in imid ring of caffeine 1358 1359 N-CH3 str + CN str + CH3 bend 1326 1325 Trigonal C-N str in imid ring + N-CH3 + C-N str 1286 1287 N-CH3 str + C-N,C-C str in both rings 1238 1236 C-Hcaf bend + CH3 rock + ν (C-N) CHcaf bend in plane deformation + CH3 rock +N-CH3 1210 1210 str 1190 1183 C-H bend + υ (C-N) + CH3 rock 1171 1153 δ C-H2AP [32] 1132 1127 Out of plane CH3 rocking 1125 1113 δ C-H2AP [32] 1095 1073 1074 CH3 rocking (in plane) 1055 1054 δring of 2AP [32] 1025 1027 CH3 rocking (in plane) + υ (CN) 998 997 Ring breathing of 2AP [32] 974 974 In plane pyrimidine ring deformation, CH3 rocking 927 927 CH3 rocking + υ (CN) 845 875 ρNH2 859 858 C-Hcaf wagg 818 832 γ C-H2AP out of plan [32] 800 801 N23-C24-C25 , N37-C38-C39, N51-C52-C53 torsion

-

759

793 780 763

-

745

743

-

700

-

702 682 641 611 556 540 500

-

481

478

644 611 554

439-

443 425

465 452 431 420

ρOH2 [35] ρOH2 [35] N49-C50-N51, N35-C36-N37, N21-C22-N23 torsion υ (N-CH3) In plane imidazole ring deformation + CH3 rock CC & CN torsion + C=O wagg δ(C3-C2-N1 + C5-C4-C3) + δ(C4-C5-C6) In plane pyrimidine ring deformation Out of plane imidazole ring deformation (NCN torsion) νM-N [37] ρw (H2O) [35] νM-O [37] In plane pyrimidine ring bend + (C54-N45-C46, C40-N31C32, C26-N17-C18 ) bend ẟNCS In plane pyrimidine ring deformation ω[NH2] + τ[C4-C3-C2-N1] C2-O11 bend.

*C-N for caffeine and aminopyridine, as- asymmetric stretching, νs – symmetric stretching, δ-in-plane bending vibration, τ- torsional, γ-out-plane vibration, ω- wagging, ρ- rocking, t- twisting, 2AP2aminopyridine, caf -caffeine

3.4. Electronic absorption spectral study The complex [Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2),1.25H2O is characterized by UV-Visible absorption technique. The UV-Visible electronic spectra are recorded in acetonitrile for concentration of 10-4 l/mol-1 (see Figure 16). The electronic spectrum for the complex, shows characteristic bands at 209, (225, 274), 344 nm (see Table 8) corresponds to σ→σ*, π→π*, n→π* transitions, another band observed at 464 nm attributed to charge transfer CT [35]. The bands appeared at the visible region at 564 nm and 629 nm assigned to 4T1g (F) → 4T1g transition. These rules are accepted for cobalt (II) regular Octahedral complex [35, 39].

Figure 16: UV–visible spectra of caffeine, 2-aminopyridine and the complex

Table 8: UV-visible data of free ligands and their complex dissolved in acetonitrile Compound λmax(nm)(abs) Assignement 276 π→π* kSCN 360 n→π*

caffeine

Complex

205 230 273

σ→σ* π→π* π→π*

209 225 274 344 464 561 637

σ→σ* π→π* n→π* CT 4 T1g(F) → 4T1g 4 T1g(F) → 4T1g

3.5. DTA and TGA analysis To study of the thermal decomposition proceeding of the compounds is useful to identify the structures of the compounds. The thermal stability of the complex was study by TGA and DTA. The thermal methods are shown in (Fig. 17) and the prospective pyrolysis reaction of the complex are summarized in Table 9. There are five endothermic peaks observed at 108 °C, 217 °C, 292 °C, 317°C and 435 °C in the DTA curve. The first mass loss of [Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2),1.25H2O occurs at about 108 °C, corresponding to the release of molecules of crystalline water. This is consistent with the single crystal structure. The second mass loss occurs at about 217 °C, which show loss of three water molecules from the complex. The mass loss of water at higher temperature indicate that the three water molecules should be coordinated water. The next step mass loss in the temperature range of 187–376 °C corresponds to the loss of 2-aminopyridine and three caffeine [39]. This is just why there is an appreciable endothermic peak at 292 and 317 °C in the DTA curve. The endothermic Peak appeared at 435 °C corresponds to the loss of two isothiocyanato groups in the complex [40]. The exothermic peak up at 544 °C corresponding to the formation of Co3O4 [41].

Table 9: Thermal decomposition data of the complex Reaction

DTA

DTG

peak

T(°C)

Mass loss

[Co(H2O)3(SCN)2(C5H8N2)]3(C8H10N4O2),1.25H2O

108(endo)

[Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2)

217(endo)

[Co(SCN)2(C5H8N2)]-3(C8H10N4O2)

81→126

H2 O water

187→376

3H2O coordinated water

2923Caffeine + 2-AP

317(endo) 376 →574

[Co(SCN)2] 435 (endo)

Co3O4

crystalline

544(exo)

Figure 17. The TGA-DTA of the complex

2(NCS)

4. Conclusion The complex [Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2),1.25H2O was synthesized and determined by Single Crystal X-Ray Diffraction and confirmed by FTIR, UV-visible, thermal analysis. The crystal structure of complex belongs to monoclinic system with C 2/c space group, with cell parameters are a = 27.6240(11) Å, b = 17.6694(7) Å, c = 16.6504(6) Å with β = 92.5713(15)°, V = 8118. 87Å3. The structure consists of mononuclear Co(II) to a octahedral geometry coordinated by three oxygen atoms of the aqua molecules, two nitrogen

of

isothiocyanato and one nitrogen atom of 2-aminopyridine ligand. The asymmetric unit of the compound comprises of [Co(H2O)3(SCN)2(C5H8N2)] complex, three caffeine and 1.25 water molecules. Therefore, the Cobalt complex is directly linked to five molecules of caffeine by OH···N and O-H···O classical hydrogen bonds. The crystal packing is mainly stabilized by hydrogen bonds and π···π interactions. Supplementary

Material:

Crystallographic

data

for

of

the

complex

[Co(H2O)3(SCN)2(C5H8N2)]-3(C8H10N4O2),1.25H2O have been deposited at the Cambridge Crystallographic Data Center as supplementary publication under the registration number CCDC:1810967. Acknowledgements : The authors would like to thank the LCC CNRS (Laboratory of Chemistry of Coordination) for their help.

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Graphical abstract

Highlights: - The new Supramolecular complex of general formula [Co(H2O)3(SCN)2(C5H8N2)]3(C8H10N4O2),1.25H2O was prepared. - The structure of the complex was determined by Single Crystal X-Ray Diffraction and confirmed by FTIR, UV-visible and thermal analysis. - The percentage of interactions involved in the formation of the crystal packing was determined by Hirshfeld surface analysis. - The thermal characterization of the complex was determined by thermal analysis methods ATD and ATG