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Synthesis, structure, spectral characterization and thermal analysis of the tetraaquabis (isothiocyanato-κN) cobalt (II)-bis(caffeine)-tetrahydrate complex
Journal of Molecular Structure 1157 (2018) 1e7
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, structure, spectral characterization and thermal analysis of the tetraaquabis (isothiocyanato-kN) cobalt (II)-bis(caffeine)tetrahydrate complex H. EL Hamdani a, M. EL Amane a, *, C. Duhayon b, c Equipe M etallation, Complexes Mol eculaires et Applications, Universit e Moulay Ismail, Facult e des Sciences, Mekn es, Morocco Laboratoire de Chimie de Coordination du CNRS, 205, Route de Narbonne, BP 44099, F-31077, Toulouse Cedex 4, France c Universit e de Toulouse, UPS, INPT, F-31077, Toulouse Cedex 4, France a
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The complex 2(C8H10N4O2).[Co(H2O)4(NCS)2].4H2O was prepared in the water-ethanol solution at room temperature and characterized by the single crystal X-ray diffraction analysis, 1H, 13C NMR, TGA/DTA and IR spectroscopy. This complex was crystallized in the monoclinic system (P 21/c). The unit cell parameters are a ¼ 10.65854 (19) A , b ¼ 8.16642 (14) A , c ¼ 18.0595 (3) A with b ¼ 96.4701 (15). The cobalt (II) cation is coordinated by four oxygen atoms of the water molecules and two nitrogen in isothiocyanato a trans octahedral geometry, stabilized by hydrogen bonds with caffeine molecule and free water molecule, The intermolecular hydrogen bonds: OeH/N, OeH/O, CeH/S, p$$$p interactions are together playing a vital role in the stabilization of the crystal packing. © 2017 Elsevier B.V. All rights reserved.
Keywords: Crystal structure Caffeine Hydrogen bonds Single-crystal X-ray diffraction analysis 1 H 13 C NMR TGA/DTA IR spectroscopy
1. Introduction In recent years, metal-organic supramolecular complexes are known for their diversity and structural applications [1e7]. These complexes are characterized by much weaker intermolecular interactions than the covalent bonds in their formation. The principal interactions between the organic structures and inorganic components are established through hydrogen bonding and Van Der Waals forces, which are significantly weaker if compared to the covalent or ionic bonds, these interactions are sufficient to provide the building and stabilization of frameworks in these materials [8]. Moreover, mode sensitivity of thiocyanate ion such as a bidentate chelate ligand has attained great interest. The linear triatomic pseudo halide, SCN, is an ambidentate ligand with two donor atoms, which may coordinate through either S or N atom or both. In coordination polymers, a thiocyanate ion must take action as a rigid bridging ligand and link a pair of metal centers [9,10]. The thiocyanate moiety was reported to possess an capacity to modify the biochemical behaviour when present in mixed ligand coordination complexes [9,11].
* Corresponding author. E-mail address: [email protected] (M. EL Amane). https://doi.org/10.1016/j.molstruc.2017.12.033 0022-2860/© 2017 Elsevier B.V. All rights reserved.
Caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) has been known to have attractive effects on diverse biological systems such as gastrointestinal, cardiovascular, respiratory and muscle systems [12,13]. Its complexes have different coordination with transition metals, moreover, the biological properties such as antibacterial and anti-inflammatory. In this study, a new complex was synthesized and the interaction of caffeine with tetraaquabis (Isothiocyanato-kN)cobalt (II) was studied. The prepared complex was characterized by spectral studies (IR, 1H, 13C NMR and UVevis). The thermal stabilities of the complex were discussed. The structure of the complex was determined by single-crystal XRD method (Fig. 1). 2. Materials and methods 2.1. Materials The initial products were analytical grade chemicals and used without any purification. Fourier transform infrared spectroscopy (FT-IR) spectra were obtained by using the FT/IR-4100 Fourier transform infrared spectrophotometer (JASCO Corporation, Tokyo, Japan) over a range of 400e4000 cm1. Before each measurement, the sample was finely ground, mixed with KBr by using a mortar and pressed into pellets.
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H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7 Table 1 Experimental details. Crystal data Chemical formula Mr Crystal system, space group Temperature (K) a, b, c (Å) b ( ) V (Å3) Z Radiation type m (mm1) Crystal size (mm) Data collection Diffractometer
Fig. 1. The asymmetric unit [expanded for the cobalt (II) cation to show the full coordination sphere; primed atoms are related to the non-primed atoms by the symmetry operation -x þ 2, -y þ 1, -z þ 1] of the title compound, with displacement ellipsoids drawn at the 50% probability level.
The 1H, 13C NMR spectra of complex were recorded with the Bruker AVANCE 300 at 25 C. All chemical shifts 1H and 13C are given in ppm using tetramethylsilane (TMS) as internal reference and DMSO as solvent. The thermal decomposition process of complex was studied by TGA and DTA (DTG-60H, Shimadzu).
2.2. Crystallographic data collection and structure determination X-ray diffraction data for the complex were collected at 120 K on a Oxford Diffraction Gemini diffractometer using a graphite monochromated Mo-Ka radiation source (k ¼ 0.71073 Å). Data collection: Apex2 (Bruker AXS, 2006); cell refinement: Apex2 (Bruker AXS, 2006); data reduction: Apex2 (Bruker AXS, 2006); program(s) used to solve structure: Superflip (Palatinus & Chapuis, 2007); program(s) used to refine structure: CRYSTALS [14]; molecular graphics: CAMERON [15]. Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms could be located in a difference Foutier map, but those attached to carbon atoms were repositioned geometrically. The H atoms were initially refined based on the bonds lengths and angles to regularize their geometry (CeH ¼ 0.98 Å, OeH ¼ 0.82 Å) and Uiso(H) set at 1.2e1.5 times of the Ueq of the parent atom, after which the positions were refined with riding constraints [16].
2.3. Preparation of complex Caffeine (194.19 mg, 1 mmol) was dissolved in ethanol (10 ml). An aqueous solution (5 ml) of CoCl2,6H2O (237 mg, 1 mmol) was added slowly. Then, the potassium thiocyanate (190 mg, 2 mmol) in water solution (5 ml) was added. The crystals of the complex suitable for X-ray analysis were crystallized after some months by slow evaporation of the solvent at room temperature. The most important details of the structure are summarized in Table 1.
2(C8H10N4O2).[Co(H2O)4(NCS)2].4H2O 707.61 Monoclinic, P21/c 120 10.65854 (19), 8.16642 (14), 18.0595 (3) 96.4701 (15) 1561.93 (3) 2 Mo Ka 0.75 0.25 0.20 0.20
Absorption correction Tmin, Tmax No. of measured, independent and observed [I > 2.0s(I)] reflections Rint (sin q/l)max (Å1) Refinement R [F2> 2s(F2)], wR (F2), S No. of reflections No. of parameters H-atom treatment Drmax, Drmin (e Å3)
Oxford Diffraction Gemini diffractometer Multi-scan CrysAlis PRO [17] 0.78, 0.86 62568, 4002, 3693
0.023 0.689 0.023, 0.022, 1.13 3586 196 H-atom parameters not refined 0.36, 0.24
3. Results and discussion 3.1. Structural description The X-ray structural determination of complex confirmed the assignments of the structure from spectroscopic data. The bond lengths, angles and Hydrogen bonds are represented in Tables 2 and 3 respectively. The molecular structure with atom-numbering Table 2 Geometric parameters (Å, º). N1eC2 N1eC9 N1eC10 N3eC2 N3eC4 N5eC4 N5eC6 N5eC11 N7eC6 N7eC8 C2eN1eC9 C2eN1eC10 C9eN1eC10 C2eN3eC4 C4eN5eC6 C4eN5eC11 C6eN5eC11 C6eN7eC8 C6eN7eC13 C8eN7eC13 C16eN15eCo1 N1eC2eN3 N5eC4eN3 N5eC4eC9 N3eC4eC9 N7eC6eN5 N7eC6eO12 N5eC6eO12 N7eC8eC9 N7eC8eO14
1.3469 1.3820 1.4616 1.3407 1.3588 1.3727 1.3792 1.4672 1.4006 1.4027 105.49 126.68 127.76 103.21 119.42 119.83 120.37 126.55 116.65 116.77 167.35 113.89 126.58 121.78 111.64 117.28 120.99 121.70 111.93 121.76
(12) (11) (12) (12) (12) (11) (11) (11) (11) (11) (7) (8) (8) (8) (7) (7) (7) (7) (7) (7) (8) (8) (8) (8) (8) (8) (8) (8) (7) (8)
Symmetry code: (i) xþ2, yþ1, zþ1.
N7eC13 N15eC16 N15eCo1 C4eC9 C6eO12 C8eC9 C8eO14 C16eS17 O18eCo1 O19eCo1 C9eC8eO14 C8eC9eN1 C8eC9eC4 N1eC9eC4 N15eC16eS17 O18idCo1dO18 O18idCo1dN15i O18eCo1eN15i O18idCo1dN15 O18eCo1eN15 N15idCo1dN15 O18idCo1dO19 O18eCo1eO19 N15idCo1dO19 N15eCo1eO19 O18idCo1dO19i O18eCo1eO19i N15idCo1dO19i N15eCo1eO19i O19eCo1eO19i
1.4723 (11) 1.1610 (12) 2.0981 (8) 1.3749 (12) 1.2291 (11) 1.4226 (12) 1.2314 (11) 1.6476 (9) 2.0981 (7) 2.0732 (7) 126.29 (8) 131.30 (8) 122.88 (8) 105.77 (8) 177.81 (8) 179.995 87.69 (3) 92.31 (3) 92.31 (3) 87.69 (3) 179.995 89.86 (3) 90.14 (3) 92.36 (3) 87.64 (3) 90.14 (3) 89.86 (3) 87.64 (3) 92.36 (3) 179.994
H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7 Table 3 Hydrogen-bond geometry (Å, º). DdH$$$A
DdH
H$$$A
D$$$A
C2eH21/S17b O18eH181/O20c O20eH202/O21d O19eH191/O21 O18eH182/N3e O21eH212/O20c O20eH201/O12 O19eH192/O14a O21eH211/S17c
0.97 0.84 0.86 0.86 0.85 0.87 0.85 0.85 0.88
2.83 1.95 1.98 1.91 2.01 1.97 2.02 1.89 2.38
3.7622 2.7860 2.8119 2.7634 2.8671 2.8157 2.8531 2.7460 3.2481
DdH$$$A (9) (10) (11) (10) (11) (11) (10) (10) (7)
160.6 174.72 161.61 174.87 178.34 164.85 166.79 178.50 173.26
Symmetry codes. a xþ2, yþ1, zþ1. b xþ1, yþ1, zþ1. c xþ2, y1/2, zþ3/2. d x, yþ1, z. e xþ1, y, z.
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The cobalt (II) located an inversion center and gives a trans-arranged octahedral coordination geometry provided by the N atoms of two isothiocyanate (eNCS) anions and four O atoms of coordinated water (H2O) molecules. The bond lengths (Co1eN15 (2.0981 (8) Å) and (Co1eO18 (2.0981 (7) Å) are equal, based standard uncertainties and significantly longer than the Co1eO19 bond length (2.0732 (7) Å) and therefore the CoN2O4 octahedron is slightly axially compressed. This structural feature is typical for related compounds [18,19]. The isothiocyanato ligands are bound through the nitrogen atoms and are nearly linear (N1eC1eS1 ¼177.81 (9) ), while the CoeNCS bound is bent (C16eN15eCo1 ¼ 167.34 (8) ). Previously reported complexes with an N-bound NCS group possess similar structural proprieties [20]. The caffeine is almost planar (r.m.s. deviation ¼ 0.0346 Å), with a maximum deviation from the mean plane of 0.0404 (7) Å for atom N5. In the crystal structure, each complex molecule [Co(H2O)4(NCS)2] interact with four neighboring caffeine molecules through classical OeH/N and OeH/O hydrogen bonds (Table 3) involving the coordinated water molecules as H-donors to form layers parallel to the ab plane (see Scheme 1). These planes are enforced by CeH/S hydrogen bonds and p$$$p interactions occurring between centrosymmetrically related six-membered rings of the purine ring system (Cg$$$Cgi ¼ 3.4715 (5) Å; Cg is the centroid of the N3/N7/C4/C6/C8/C9 ring; symmetry code: (i) 1. x, 2 y, 1. z; Fig. 2), and are alternated by layers of uncoordinated water molecules linked through OeH/O and OeH/S hydrogen bonds, leading to the formation of the three-dimensional network (Fig. 3). 3.2. FT-IR spectral analysis
Fig. 2. Partial packing diagram of the complex showing the network of hydrogen bonds.
is shown in Fig. 1, besides A partial packing diagrams are given in Figs. 2 and 3. The complex crystallized in the centrosymmetric space group P21/c, where the asymmetric unit contain half a [Co(H2O)4(NCS)2], a caffeine molecule and two free water molecules (see Fig. 1).
Infrared (IR) spectroscopy is helpful to identify the characteristics of vibrational modes of a molecule resulting from changes in the physical state of samples, also differences in hydrogen bonding and molecular conformations. The FT-IR spectra of free caffeine and complex are shown in Fig. 4. The presence of a broad band at 3466 cm1, this band could be attributed to the water molecules of hydration and coordination [21]. The very strong band observed at
Fig. 3. Partial packing diagram of the complex showing the network of hydrogen bonds (orange dotted lines) and p$$$p interactions (purple dotted lines) linking complex and caffeine molecules into layers parallel to the ab plane.
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H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7
Scheme 1. The structure of complex.
Table 4 Experimental FT-IR frequencies (cm1) with assignment for complex and free caffeine. Caffeine
3111 m 2952 m
Fig. 4. FTIR spectra of the complex and free caffeine (KBr disk).
2091 cm1 in the spectrum of complex is attributed to the isothiocyanato stretching frequency. In the region 700-800 cm1, a new peak was observed at 765 cm1, it is more intense compared to the peak of caffeine to 759 cm1, this result indicates the existence n (CeS) of the isothiocyanato ligand [22]. The comparison of infrared spectrum bands of the free caffeine with infrared spectrum of the complex showed the following: The carbonyl C ¼ O stretching vibration appearing at 1700 cm1 in infrared spectrum of the free caffeine is shifted to lower frequency at 1695 cm1 in frared spectrum of the complex. A peak at 1655 cm1 of ns (C]O) þ n (C]C) in free caffeine is shifted to lower frequency at 1644 cm1 [23]. These results confirm the formation of hydrogen bonds (C]O/H) between two carbonyl C]O with the hydration and coordination water. The Quadratal CeN stretching in imidazole ring appearing at 1403 cm1 of the caffeine is shifted to lower frequency at 1399 cm1 of the complex, that indicate the formation of hydrogen bonds (N/H) [23]. The vibrations of free caffeine appearing at 3111, 1548, 1483, 1456, 1430, 1402, 1358, 1325, 1284, 973, 925, 860, 643 and 481 cm1, are shifted to higher frequency at 3122, 1555, 1496, 1459, 1436, 1418, 1364, 1331, 1291, 980, 931 and 488 cm1 in the complex respectively [23] (see Table 4). New sharp bands are observed at 562 cm1 and 453 cm1, which assigned to the y (M - N) and y (M - O) stretching vibration [24].
1700 vs 1655 vs 1600 w 1548 s 1483 s 1456 s 1430 s 1402 w 1358 m 1325 vw 1284 m 1237 s 1212 vw 1189 w 1131 vw 1071 w 1026 m 973 m 925 vw 860 m 800 vw 759 w 744 s 699 vw 643 vw 612 m e 481 m 443 m 425 m
Complex
Assignement
3466 s 3398 s 3242 m 3122 m 2952 m 2886 w 2091 vs 1695 vs 1644 vs 1602 w 1555 s 1496 s 1459 s 1436 s 1418 m 1399 m 1364 s 1331 m 1291 s 1236 s 1218 w 1184 s 1131 vw 1070 vw 1032 s 980 m 931 m 875 m 841 w 805 vw 765 s 743 s
n (OeH) in water of hydration and coordination n (OeH) n (OeH)
699 vw 653 w 611 m 562 m 488 s 473 vw 453 s 425 m 395 w 383w
C2eH21 str Sym CH3 str Asym CH3 str SCN str nas (C]O) ns (C]O) þ n (C]C) C¼C str. þ C]N str. Imid ring str. þ CN str. þ C]C str. þ CH bend Sym CH3 bend, CN str in Imid ring Sym CH3 bend Sym CH3 bend þ C10eN1 str þ CN str þ CH bend d(OH)H2O-Coordination Quadratal CeN str in imid ring N7eCH3 str.þ CN str þ CH3 bend Trigonal CeN str. in imid ring, N7eCH3 str.þ CeN str N5eCH3 str., C6eN5 str., CeN & CeC str. in both rings C2eH21 bend, CH3 rock, CeN str. CH bend (in plane deformation), CH3 rock,N7eCH3 str. C2eH21 bend., CN str., CH3 rock Out of plane CH3 rocking CH3 rocking (in plane) CH3 rocking (in plane) In plane pyrimid ring deformation, CH3 rocking In plane pyrimid ring deformation, CH3 rocking C2eH21 wagg. rH2O N7eC8eC9 torsion N7eC6eN5 torsion þ (CeS) str N1eCH3 str.þ In plane imid ring deformation þ CH3 rocking CC & CN torsion, C]O wagg. In plane pyrimid ring deformation Out of plane imid ring deformation (NCN torsion) CoeN str þ Breathing in pyrimid ring þ N1eCH3 bend In plane pyrimid ring bend., C10eN1eC2 bend dNCS M - O str þ In plane pyrimid ring deformation C2¼O12 bend. C6¼O14 bend. N7eCH3 (in plane) bend
Abbreviations useds: strong; m: medium; w: weak; very weak: vw; very strong: vs; Bend: bending; str: stretching; r: roking; sym: symmetric; asym: asymmetric; wagg: wagging; pyramid: pyrimidine; imid: imidazole; ns: Symetrical stretching; nas: Asymetrical stretching.
H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7
3.3.
1
5
H NMR-13C NMR analysis
The proton NMR spectrum of complex was measured in dimethyl sulfoxide (DMSO) solution using Bruker Advance 300 NMR spectrometer. The chemical shifts (d) of complex are listed in Table 5 and given in Fig. 5. Some changes were observed in the chemical shift values of complex in 1H NMR spectrum. These changes are affected by the interaction between [Co(II) (H2O)4(NCS)2] as an electrons donor with p acceptor caffeine. The spectrum display five signals indicating five different proton environments. The 1H NMR spectrum of caffeine in dimethyl sulfoxide (DMSO) solution showed four relatively low intensive peaks at 3.141 ppm (S, 3H, H131,132,133), 3.266 ppm (S, 3H, H111,112,113), 3.853 ppm (S, 3H, H101,102,103) and 7.973 ppm (S, 1H, H21) corresponding to the three CH3-groups and CH, respectively. The analogous spectrum of complex is characterized by peaks at 2.869 ppm (S, 3H, H131,132,133), 3.057 ppm (S, 3H, H111,112, 113), 3.480 ppm (S, 3H, H101,102,103) and 7.556 ppm (S, 1H, H21) [25]. These shifts in caffeine peaks referring to the formation of intermolecular hydrogen bonds: OeH/N, OeH/O, CeH/S. The new signal at 4.646 ppm is attributed to hydration water and water of coordination. 13 C NMR spectrum of the complex is presented in Fig. 6. This figure shows proton signals at 27,78; 29,68; 33,40; 106,85; 143; 148,37; 151,31 and 154,79 due to C13, C11, C110, C9, C2, C4, C6 and C8 respectively. The new signal at 142 ppm is attributed to carbon of the isothiocyanato coordinated in [Co(II) (H2O)4(NCS)2] [25] (see Table 6).
Fig. 6.
13
C NMR spectrum of the complex in DMSO. TMS was used as the standard.
Table 6 13 C NMR spectral data of the free caffeine and complex in DMSO. Position
13C NMR data free caffeine
13C NMR data co-crystal
13 11 10 9 2 C-NSC 4 6 8
27.88 29.7 33.57 107.51 141.57 e 148.67 151.66 155.32
27.78 29.68 33.40 106.85 143 142 148.37 151.31 154.79
3.4. Electronic absorption spectral study The interaction of caffeine with [Co(II) (H2O)4(NCS)2] is characterized by UVeVisible absorption technique. The UVeVisible Table 5 1 H NMR spectral data of the free caffeine and complex. Compound
1
Free caffeine
3141 3266 3853 7973 2869 3057 3480 4646 7556
Complex
H NMR chemical Shift (d ppm)
Assignement S, S, S, S, S, S, S, S, S,
3H, H131,132,133 3H, H111,112,113 3H, H101,102,103 1H, H21 3H, H111,112,113 3H, H131,132,133 3H, H101,102,103 12H, HH2O 1H, H21
Fig. 7. UVevisible spectra of the free caffeine and their co-crystal dissolved in acetonitril.
electronic spectra for all compounds are recorded in acetonitrile (see Fig. 7). The electronic spectra of these compounds are very similar in the UV region and show characteristic bands at 205, 230 and 273 nm for free caffeine in acetonitril, which is corresponds to Table 7 UVevisible data of the free ligands and their co-crystal dissolved in acetonitril. Compound
lmax (nm)
Assignement
KSCN
276 360 205 230 273 208 271 331 561 637
p/p* n/p* s/s* p/p* p/p* s/s* p/p* n/p* 4 T1g(F) / 4T1g [27] 4 T1g(F) / 4T1g [27]
caffeine
Co-crystal
Fig. 5. 1H NMR spectrum of the complex in DMSO. TMS was used as the standard.
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H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7
DTA uV
TGA mg 20.00
100.00
15.00
-0.00 10.00
5.00 DTA TGA
100.00
200.00
300.00 400.00 Temp [C]
500.00
600.00
Fig. 8. The TGA-DTA of the co-crystal.
s/s*, p/p* transitions, at 208, 271, 331 nm for the complex; these bands are attributed to s/s*, p/p*, n/p* (see Table 7). The electronic spectrum recorded in water solution for potassium thiocyanate exhibited that, the absorption bands in UV region can be annotated as p/p* and n/p* transitions, these bands are less intense compared to the free caffeine bands [26]. Another bands appeared at the visible region at 561 nm and 637 nm assigned to 4 T1g (F) / 4T1g (P) transition. These rules are accepted for octahedral geometry around the Cobalt (II) center [26]. 3.5. DTA and TGA analysis The thermal properties of complex are investigated by TGA and DTA methods in the temperature range (50e600) C (Fig. 8). A systematic analysis of the presented TGA curve was showed that caffeine decomposes at 290 C [27]. The thermal stability of the complex differed, with the decomposition temperatures at 80 C, 122 C, 224 C, 430 C shown in Fig. 8. These results indicate that caffeine usual thermal properties are changed due to associate with a metal complex and water of the hydration. For the DTA curve of free caffeine shows the endothermic peak at 315.82 C corresponding to its melting point [27]. The DTA curve of complex shows endothermic peaks at about 82.43 C and 125 C corresponds to the loss of water (Hydration, coordination); another endothermic peak is present at about 336.57 C, this endothermic peak of melting point of caffeine in the complex. The endothermic peak appeared at 495.36 C corresponds to the loss of isothiocyanato groups [28]. The exothermic peak at 560 C is observed corresponding to the formation of Co3O4 [29]. The thermal stability of the caffeine molecule is significantly increased in terms of melting point. Hence, the melting point of caffeine in complex is increased around 20 C than that of pure caffeine. With these results we confirmed the strong interaction between the caffeine molecule and water of (Hydration and coordination). Supplementary material Crystallographic data for of the complex [Co(H2O)4(NCS)2]-2 (cafeine),4H2O have been deposited at the Cambridge
Crystallographic Data Center as supplementary publication under the registration number CCDC 1542060. 4. Conclusion Supramolecular complex of Co (II) with isothiocyanato and caffeine has been synthesized and their structure determined from FTIR, UVevisible, DTA, TGA, 1H, 13C NMR and single crystal XRD studies. The Co (II) ions are octahedrally coordinated by two isothiocyanato ligands, four water molecules leading to an overall CoN2O4 coordination environment. The asymmetric unit of the mononuclear complex comprises half of [Co(II) (NCS)2(H2O)4] compound, one caffeine and two water molecules. The co-crystal packing is mainly stabilized by hydrogen bonds and p$$$p interactions. Therefore, the Cobalt complex is directly linked to four molecules of caffeine by OeH/N and OeH/O classical hydrogen bonds. Acknowledgements The authors would like to thank the LCC CNRS (Laboratory of Chemistry of Coordination) for their help. References [1] P.A. Gale, Supramolecular chemistry anniversary, Chem. Soc. Rev. 36 (2) (2007) 141e142. [2] N. Goel, N. Kumar, Study of supramolecular frameworks having aliphatic dicarboxylic acids, N,N0-bis(salicyl)ethylenediamine and N,N0-bis(salicyl) butylenediamine, J. Mol. Struct. 1071 (2014) 60e70. [3] N.M.H. Salem, A.R. Rashad, L. El Sayed, S. Foro, W. Haase, M.F. Iskander, Synthesis, characterization, molecular structure and supramolecular architectures of some copper (II) complexes derived from salicylaldehyde semicarbazone, Inorg. Chim. Acta. 432 (1) (2015) 231e242. [4] R. Chakrabarty, P. Sarathi Mukherjee, P.J. Stang, Supramolecular coordination: self-assembly of finite two- and three-dimensional ensembles, Chem. Rev. 111 (11) (2011) 6810e6918. [5] Q. Liu, Y.Z. Li, Y. Song, H. Liu, Z. Xu, Three-dimensional five-connected coordination polymer [M2(C3H2O4)2(H2O)2(m2-hmt)]n with 4466 topologies (M ¼ Zn, Cu; Hmt ¼ hexamethylenetetramine, Solid State Commun. 177 (12) (2004) 4701e4705. [6] S. Hazra, S. Biswas, A.M. Kirillov, A. Ghosh, Nickel(II) complexes selfassembled from hexamethylenetetramine and isomeric nitrobenzoates: structural diversity and supramolecular features, Polyhedron 79 (2014) 66e71. [7] W.J. Shi, L. Hou, D. Li, Y.G. Yin, Supramolecular assembly driven by hydrogenbonding and pep stacking interactions based on copper(II)- terpyridyl complexes, Inorg. Chim. Acta. 360 (2) (2007) 588e598.
H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7 [8] T.J. Bednarchuk, V. Kinzhybalo, O. Bednarchuk, A. Pietraszko, Synthesis, structural characterization, IR- and Raman spectroscopy, magnetic properties of new organically templated metal sulfates with 4-aminopyridinium, J. Mol. Struct. 1120 (2016) 138e149. [9] N. Upadhayay, Synthesis, characterization and biological studies of some thiocyanato-bridged bimetallic complexes containing Co(II), Cd(II), Hg(II) and N, N'-Bis(benzylidene)- 1,2-phenylene-diamine schiff base, Chem. Sci. Trans 2 (2) (2013) 455e460. ski, Bimetallic complexes with macrocyclic [10] A. Tomkiewicz, J. Kłak, J. Mrozin ligands. Variation of magnetic exchange interactions in some heteronuclear thiocyanatobridged compounds, Mater. Sci. Poland 22 (3) (2004) 253e263. [11] S. Suckert, L.S. Germann, R.E. Dinnebier, J. Werner, C. N€ ather, Synthesis, structures and properties of cobalt thiocyanate coordination compounds with 4-(hydroxymethyl)pyridine as Co-ligand, Crystals 6 (38) (2016) 1e17. [12] F. Valach, B. Koren, M. Tokarcík, M. Melník, Structure of l,3,7-Trimethyl-2,6dioxopurine Copper(II) o-Iodobenzoate, Chem. Pap. 52 (3) (1998) 140e146. [13] (a) M.J. Arnaud, B. Caballero, Guide to Nutritional Supplements, Elsevier Ltd., Oxford, 2009, pp. 65e71; (b) M. Melník, M. Kohútov, Complex view on biomedical activity of caffeine, Acta Fac. Pharm. Univ. Comen. 56 (2009) 5e7. [14] W. Betteridge, J.R. Carruthers, R.I. Cooper, K. Prout, D.J. Watkin, CRYSTALS version 12: software for guided crystal structure analysis, J. Appl. Cryst. 36 (2003) 1487. [15] D.J. Watkin, C.K. Prout, L.J. Pearce, CAMERON, Chemical Crystallography Laboratory, Oxford, England, 1996. [16] I. Cooper, A.L. Thompson, D.J. Watkin, CRYSTALS enhancements: dealing with hydrogen atoms in refinement, J. Appl. Cryst. 43 (2010) 1100e1107. [17] Agilent, CrysAlis PRO, Agilent Technologies, Yarnton, England, 2011. [18] S.I. Shylin, I.A. Gural'skiy, D. Bykov, S. Demeshko, S. Dechert, F. Meyer, M. Hauka, I.O. Fritsky, Iron (II) isothiocyanate complexes with substituted pyrazines: Experimental and theoretical views on their electronic structure, Polyhedron 87 (2015) 147e155. [19] S.I. Shylin, I.A. Guralskiy, M. Haukka, I.A. Golenya, Pyridinium bis(pyridine-kN) tetrakis(thiocyanato-kN)ferrate(III), Acta Crystallogr. E69 (2013), 280e280. [20] S.R. Petrusenko, V.N. Kokozay, I.O. Fritsky, Direct synthesis and crystal structure of zinc thiocyanate complexes with 1,4diazabicyclo(2,2,2)octane, Polyhedron 16 (1997) 267e274.
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_ [21] H. Ilkimen, C. Yenikaya, A. Gülbandılar, M. Sarı, Synthesis and characterization of a novel proton salt of 2-amino-6-nitrobenzothiazole with 2,6pyridinedicarboxylic acid and its metal complexes and their antimicrobial and antifungal activity studies, J. Mol. Struct. 1120 (2016) 25e33. [22] (a) S. Endrit, E.M. Curtis, A.L. Rheingold, S.H. Lapidus, P.W. Stephens, A.M. Arif, J.S. Miller, First row transition metal(II) thiocyanate complexes, and formation of 1-, 2-;, and 3-dimensional extended network structures of m(NCS)2(solvent)2 (M ¼ Cr, Mn, Co) composition, Inorg. Chem. 52 (18) (2013) 10583e10594; (b) J.L. Burmeister, Linkage isomerism in metal complexes, Coord. Chem. Rev. 3 (1968) 225e245. [23] S.K. Srivastava, V.B. Singh, Ab initio and DFT studies of the structure and vibrational spectra of anhydrous caffeine, Spectrochim. Acta Mol. Biomol. Spectrosc. 115 (2013) 45e50. [24] V.T. Yilmaz, O. Andac, T.K. Yazicilar, H. Kutuk, Y. Bekdemir, W.T.A. Harrison, The first metal complex of p-nitrobenzoxasulfamate. Synthesis, spectral and structural characterization of triaquabis(p-nitrobenzoxasulfamato)copper(II) monohydrate, J. Mol. Struct. 608 (2002) 71e76. Physique et De sordre Orientationnel dans [25] (a) D. d'Anne-Amandine, Stabilite Usage The rapeutique : La Cafe ine, Lille 1 (2009) 108e109; un Cristal a (b) M.O. Okuom, M.V. Wilson, A. Jackson, A.E. Holmes, Intermolecular interactions between eosin Y and caffeine using 1H-NMR spectroscopy, Int. J. Spectrosc. (2013) (2013) 1e6. € € lu, [26] E. Taʂdemir, F.E. Ozbek, M. Sertçelik, T. HOkelek, R. Çatak Çelik, H. Necefog Supramolecular complexes of Co(II), Ni(II) and Zn(II) phydroxybenzoates with caffeine: synthesis, spectral characterization and crystal structure, J. Mol. Struct. 1119 (2016) 472e478. [27] S. Prabu, M. Swaminathan, K. Sivakumar, R. Rajamohan, Preparation, Characterization and molecular modeling studies of the inclusion complex of Caffeine with Beta-cyclodextrin, J. Mol. Struct. 1099 (2015) 616e624. [28] S.C. Mojumdar, M. Melnık, E. Jona, Thermoanalytical investigation of Mg (II) compounds containing SCN and heterocyclic N-donor ligands, J. Anal. Appl. Pyrol. 48 (1999) 111e120. [29] S. Prasad, Cobalt(II) complexes of various thiosemicarbazones of 4-aminoantipyrine: syntheses, spectral, thermal and antimicrobial studies, Transit. Met. Chem. 32 (2007) 143e149.
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, structure, spectral characterization and thermal analysis of the tetraaquabis (isothiocyanato-kN) cobalt (II)-bis(caffeine)tetrahydrate complex H. EL Hamdani a, M. EL Amane a, *, C. Duhayon b, c Equipe M etallation, Complexes Mol eculaires et Applications, Universit e Moulay Ismail, Facult e des Sciences, Mekn es, Morocco Laboratoire de Chimie de Coordination du CNRS, 205, Route de Narbonne, BP 44099, F-31077, Toulouse Cedex 4, France c Universit e de Toulouse, UPS, INPT, F-31077, Toulouse Cedex 4, France a
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The complex 2(C8H10N4O2).[Co(H2O)4(NCS)2].4H2O was prepared in the water-ethanol solution at room temperature and characterized by the single crystal X-ray diffraction analysis, 1H, 13C NMR, TGA/DTA and IR spectroscopy. This complex was crystallized in the monoclinic system (P 21/c). The unit cell parameters are a ¼ 10.65854 (19) A , b ¼ 8.16642 (14) A , c ¼ 18.0595 (3) A with b ¼ 96.4701 (15). The cobalt (II) cation is coordinated by four oxygen atoms of the water molecules and two nitrogen in isothiocyanato a trans octahedral geometry, stabilized by hydrogen bonds with caffeine molecule and free water molecule, The intermolecular hydrogen bonds: OeH/N, OeH/O, CeH/S, p$$$p interactions are together playing a vital role in the stabilization of the crystal packing. © 2017 Elsevier B.V. All rights reserved.
Keywords: Crystal structure Caffeine Hydrogen bonds Single-crystal X-ray diffraction analysis 1 H 13 C NMR TGA/DTA IR spectroscopy
1. Introduction In recent years, metal-organic supramolecular complexes are known for their diversity and structural applications [1e7]. These complexes are characterized by much weaker intermolecular interactions than the covalent bonds in their formation. The principal interactions between the organic structures and inorganic components are established through hydrogen bonding and Van Der Waals forces, which are significantly weaker if compared to the covalent or ionic bonds, these interactions are sufficient to provide the building and stabilization of frameworks in these materials [8]. Moreover, mode sensitivity of thiocyanate ion such as a bidentate chelate ligand has attained great interest. The linear triatomic pseudo halide, SCN, is an ambidentate ligand with two donor atoms, which may coordinate through either S or N atom or both. In coordination polymers, a thiocyanate ion must take action as a rigid bridging ligand and link a pair of metal centers [9,10]. The thiocyanate moiety was reported to possess an capacity to modify the biochemical behaviour when present in mixed ligand coordination complexes [9,11].
* Corresponding author. E-mail address: [email protected] (M. EL Amane). https://doi.org/10.1016/j.molstruc.2017.12.033 0022-2860/© 2017 Elsevier B.V. All rights reserved.
Caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) has been known to have attractive effects on diverse biological systems such as gastrointestinal, cardiovascular, respiratory and muscle systems [12,13]. Its complexes have different coordination with transition metals, moreover, the biological properties such as antibacterial and anti-inflammatory. In this study, a new complex was synthesized and the interaction of caffeine with tetraaquabis (Isothiocyanato-kN)cobalt (II) was studied. The prepared complex was characterized by spectral studies (IR, 1H, 13C NMR and UVevis). The thermal stabilities of the complex were discussed. The structure of the complex was determined by single-crystal XRD method (Fig. 1). 2. Materials and methods 2.1. Materials The initial products were analytical grade chemicals and used without any purification. Fourier transform infrared spectroscopy (FT-IR) spectra were obtained by using the FT/IR-4100 Fourier transform infrared spectrophotometer (JASCO Corporation, Tokyo, Japan) over a range of 400e4000 cm1. Before each measurement, the sample was finely ground, mixed with KBr by using a mortar and pressed into pellets.
2
H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7 Table 1 Experimental details. Crystal data Chemical formula Mr Crystal system, space group Temperature (K) a, b, c (Å) b ( ) V (Å3) Z Radiation type m (mm1) Crystal size (mm) Data collection Diffractometer
Fig. 1. The asymmetric unit [expanded for the cobalt (II) cation to show the full coordination sphere; primed atoms are related to the non-primed atoms by the symmetry operation -x þ 2, -y þ 1, -z þ 1] of the title compound, with displacement ellipsoids drawn at the 50% probability level.
The 1H, 13C NMR spectra of complex were recorded with the Bruker AVANCE 300 at 25 C. All chemical shifts 1H and 13C are given in ppm using tetramethylsilane (TMS) as internal reference and DMSO as solvent. The thermal decomposition process of complex was studied by TGA and DTA (DTG-60H, Shimadzu).
2.2. Crystallographic data collection and structure determination X-ray diffraction data for the complex were collected at 120 K on a Oxford Diffraction Gemini diffractometer using a graphite monochromated Mo-Ka radiation source (k ¼ 0.71073 Å). Data collection: Apex2 (Bruker AXS, 2006); cell refinement: Apex2 (Bruker AXS, 2006); data reduction: Apex2 (Bruker AXS, 2006); program(s) used to solve structure: Superflip (Palatinus & Chapuis, 2007); program(s) used to refine structure: CRYSTALS [14]; molecular graphics: CAMERON [15]. Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms could be located in a difference Foutier map, but those attached to carbon atoms were repositioned geometrically. The H atoms were initially refined based on the bonds lengths and angles to regularize their geometry (CeH ¼ 0.98 Å, OeH ¼ 0.82 Å) and Uiso(H) set at 1.2e1.5 times of the Ueq of the parent atom, after which the positions were refined with riding constraints [16].
2.3. Preparation of complex Caffeine (194.19 mg, 1 mmol) was dissolved in ethanol (10 ml). An aqueous solution (5 ml) of CoCl2,6H2O (237 mg, 1 mmol) was added slowly. Then, the potassium thiocyanate (190 mg, 2 mmol) in water solution (5 ml) was added. The crystals of the complex suitable for X-ray analysis were crystallized after some months by slow evaporation of the solvent at room temperature. The most important details of the structure are summarized in Table 1.
2(C8H10N4O2).[Co(H2O)4(NCS)2].4H2O 707.61 Monoclinic, P21/c 120 10.65854 (19), 8.16642 (14), 18.0595 (3) 96.4701 (15) 1561.93 (3) 2 Mo Ka 0.75 0.25 0.20 0.20
Absorption correction Tmin, Tmax No. of measured, independent and observed [I > 2.0s(I)] reflections Rint (sin q/l)max (Å1) Refinement R [F2> 2s(F2)], wR (F2), S No. of reflections No. of parameters H-atom treatment Drmax, Drmin (e Å3)
Oxford Diffraction Gemini diffractometer Multi-scan CrysAlis PRO [17] 0.78, 0.86 62568, 4002, 3693
0.023 0.689 0.023, 0.022, 1.13 3586 196 H-atom parameters not refined 0.36, 0.24
3. Results and discussion 3.1. Structural description The X-ray structural determination of complex confirmed the assignments of the structure from spectroscopic data. The bond lengths, angles and Hydrogen bonds are represented in Tables 2 and 3 respectively. The molecular structure with atom-numbering Table 2 Geometric parameters (Å, º). N1eC2 N1eC9 N1eC10 N3eC2 N3eC4 N5eC4 N5eC6 N5eC11 N7eC6 N7eC8 C2eN1eC9 C2eN1eC10 C9eN1eC10 C2eN3eC4 C4eN5eC6 C4eN5eC11 C6eN5eC11 C6eN7eC8 C6eN7eC13 C8eN7eC13 C16eN15eCo1 N1eC2eN3 N5eC4eN3 N5eC4eC9 N3eC4eC9 N7eC6eN5 N7eC6eO12 N5eC6eO12 N7eC8eC9 N7eC8eO14
1.3469 1.3820 1.4616 1.3407 1.3588 1.3727 1.3792 1.4672 1.4006 1.4027 105.49 126.68 127.76 103.21 119.42 119.83 120.37 126.55 116.65 116.77 167.35 113.89 126.58 121.78 111.64 117.28 120.99 121.70 111.93 121.76
(12) (11) (12) (12) (12) (11) (11) (11) (11) (11) (7) (8) (8) (8) (7) (7) (7) (7) (7) (7) (8) (8) (8) (8) (8) (8) (8) (8) (7) (8)
Symmetry code: (i) xþ2, yþ1, zþ1.
N7eC13 N15eC16 N15eCo1 C4eC9 C6eO12 C8eC9 C8eO14 C16eS17 O18eCo1 O19eCo1 C9eC8eO14 C8eC9eN1 C8eC9eC4 N1eC9eC4 N15eC16eS17 O18idCo1dO18 O18idCo1dN15i O18eCo1eN15i O18idCo1dN15 O18eCo1eN15 N15idCo1dN15 O18idCo1dO19 O18eCo1eO19 N15idCo1dO19 N15eCo1eO19 O18idCo1dO19i O18eCo1eO19i N15idCo1dO19i N15eCo1eO19i O19eCo1eO19i
1.4723 (11) 1.1610 (12) 2.0981 (8) 1.3749 (12) 1.2291 (11) 1.4226 (12) 1.2314 (11) 1.6476 (9) 2.0981 (7) 2.0732 (7) 126.29 (8) 131.30 (8) 122.88 (8) 105.77 (8) 177.81 (8) 179.995 87.69 (3) 92.31 (3) 92.31 (3) 87.69 (3) 179.995 89.86 (3) 90.14 (3) 92.36 (3) 87.64 (3) 90.14 (3) 89.86 (3) 87.64 (3) 92.36 (3) 179.994
H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7 Table 3 Hydrogen-bond geometry (Å, º). DdH$$$A
DdH
H$$$A
D$$$A
C2eH21/S17b O18eH181/O20c O20eH202/O21d O19eH191/O21 O18eH182/N3e O21eH212/O20c O20eH201/O12 O19eH192/O14a O21eH211/S17c
0.97 0.84 0.86 0.86 0.85 0.87 0.85 0.85 0.88
2.83 1.95 1.98 1.91 2.01 1.97 2.02 1.89 2.38
3.7622 2.7860 2.8119 2.7634 2.8671 2.8157 2.8531 2.7460 3.2481
DdH$$$A (9) (10) (11) (10) (11) (11) (10) (10) (7)
160.6 174.72 161.61 174.87 178.34 164.85 166.79 178.50 173.26
Symmetry codes. a xþ2, yþ1, zþ1. b xþ1, yþ1, zþ1. c xþ2, y1/2, zþ3/2. d x, yþ1, z. e xþ1, y, z.
3
The cobalt (II) located an inversion center and gives a trans-arranged octahedral coordination geometry provided by the N atoms of two isothiocyanate (eNCS) anions and four O atoms of coordinated water (H2O) molecules. The bond lengths (Co1eN15 (2.0981 (8) Å) and (Co1eO18 (2.0981 (7) Å) are equal, based standard uncertainties and significantly longer than the Co1eO19 bond length (2.0732 (7) Å) and therefore the CoN2O4 octahedron is slightly axially compressed. This structural feature is typical for related compounds [18,19]. The isothiocyanato ligands are bound through the nitrogen atoms and are nearly linear (N1eC1eS1 ¼177.81 (9) ), while the CoeNCS bound is bent (C16eN15eCo1 ¼ 167.34 (8) ). Previously reported complexes with an N-bound NCS group possess similar structural proprieties [20]. The caffeine is almost planar (r.m.s. deviation ¼ 0.0346 Å), with a maximum deviation from the mean plane of 0.0404 (7) Å for atom N5. In the crystal structure, each complex molecule [Co(H2O)4(NCS)2] interact with four neighboring caffeine molecules through classical OeH/N and OeH/O hydrogen bonds (Table 3) involving the coordinated water molecules as H-donors to form layers parallel to the ab plane (see Scheme 1). These planes are enforced by CeH/S hydrogen bonds and p$$$p interactions occurring between centrosymmetrically related six-membered rings of the purine ring system (Cg$$$Cgi ¼ 3.4715 (5) Å; Cg is the centroid of the N3/N7/C4/C6/C8/C9 ring; symmetry code: (i) 1. x, 2 y, 1. z; Fig. 2), and are alternated by layers of uncoordinated water molecules linked through OeH/O and OeH/S hydrogen bonds, leading to the formation of the three-dimensional network (Fig. 3). 3.2. FT-IR spectral analysis
Fig. 2. Partial packing diagram of the complex showing the network of hydrogen bonds.
is shown in Fig. 1, besides A partial packing diagrams are given in Figs. 2 and 3. The complex crystallized in the centrosymmetric space group P21/c, where the asymmetric unit contain half a [Co(H2O)4(NCS)2], a caffeine molecule and two free water molecules (see Fig. 1).
Infrared (IR) spectroscopy is helpful to identify the characteristics of vibrational modes of a molecule resulting from changes in the physical state of samples, also differences in hydrogen bonding and molecular conformations. The FT-IR spectra of free caffeine and complex are shown in Fig. 4. The presence of a broad band at 3466 cm1, this band could be attributed to the water molecules of hydration and coordination [21]. The very strong band observed at
Fig. 3. Partial packing diagram of the complex showing the network of hydrogen bonds (orange dotted lines) and p$$$p interactions (purple dotted lines) linking complex and caffeine molecules into layers parallel to the ab plane.
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H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7
Scheme 1. The structure of complex.
Table 4 Experimental FT-IR frequencies (cm1) with assignment for complex and free caffeine. Caffeine
3111 m 2952 m
Fig. 4. FTIR spectra of the complex and free caffeine (KBr disk).
2091 cm1 in the spectrum of complex is attributed to the isothiocyanato stretching frequency. In the region 700-800 cm1, a new peak was observed at 765 cm1, it is more intense compared to the peak of caffeine to 759 cm1, this result indicates the existence n (CeS) of the isothiocyanato ligand [22]. The comparison of infrared spectrum bands of the free caffeine with infrared spectrum of the complex showed the following: The carbonyl C ¼ O stretching vibration appearing at 1700 cm1 in infrared spectrum of the free caffeine is shifted to lower frequency at 1695 cm1 in frared spectrum of the complex. A peak at 1655 cm1 of ns (C]O) þ n (C]C) in free caffeine is shifted to lower frequency at 1644 cm1 [23]. These results confirm the formation of hydrogen bonds (C]O/H) between two carbonyl C]O with the hydration and coordination water. The Quadratal CeN stretching in imidazole ring appearing at 1403 cm1 of the caffeine is shifted to lower frequency at 1399 cm1 of the complex, that indicate the formation of hydrogen bonds (N/H) [23]. The vibrations of free caffeine appearing at 3111, 1548, 1483, 1456, 1430, 1402, 1358, 1325, 1284, 973, 925, 860, 643 and 481 cm1, are shifted to higher frequency at 3122, 1555, 1496, 1459, 1436, 1418, 1364, 1331, 1291, 980, 931 and 488 cm1 in the complex respectively [23] (see Table 4). New sharp bands are observed at 562 cm1 and 453 cm1, which assigned to the y (M - N) and y (M - O) stretching vibration [24].
1700 vs 1655 vs 1600 w 1548 s 1483 s 1456 s 1430 s 1402 w 1358 m 1325 vw 1284 m 1237 s 1212 vw 1189 w 1131 vw 1071 w 1026 m 973 m 925 vw 860 m 800 vw 759 w 744 s 699 vw 643 vw 612 m e 481 m 443 m 425 m
Complex
Assignement
3466 s 3398 s 3242 m 3122 m 2952 m 2886 w 2091 vs 1695 vs 1644 vs 1602 w 1555 s 1496 s 1459 s 1436 s 1418 m 1399 m 1364 s 1331 m 1291 s 1236 s 1218 w 1184 s 1131 vw 1070 vw 1032 s 980 m 931 m 875 m 841 w 805 vw 765 s 743 s
n (OeH) in water of hydration and coordination n (OeH) n (OeH)
699 vw 653 w 611 m 562 m 488 s 473 vw 453 s 425 m 395 w 383w
C2eH21 str Sym CH3 str Asym CH3 str SCN str nas (C]O) ns (C]O) þ n (C]C) C¼C str. þ C]N str. Imid ring str. þ CN str. þ C]C str. þ CH bend Sym CH3 bend, CN str in Imid ring Sym CH3 bend Sym CH3 bend þ C10eN1 str þ CN str þ CH bend d(OH)H2O-Coordination Quadratal CeN str in imid ring N7eCH3 str.þ CN str þ CH3 bend Trigonal CeN str. in imid ring, N7eCH3 str.þ CeN str N5eCH3 str., C6eN5 str., CeN & CeC str. in both rings C2eH21 bend, CH3 rock, CeN str. CH bend (in plane deformation), CH3 rock,N7eCH3 str. C2eH21 bend., CN str., CH3 rock Out of plane CH3 rocking CH3 rocking (in plane) CH3 rocking (in plane) In plane pyrimid ring deformation, CH3 rocking In plane pyrimid ring deformation, CH3 rocking C2eH21 wagg. rH2O N7eC8eC9 torsion N7eC6eN5 torsion þ (CeS) str N1eCH3 str.þ In plane imid ring deformation þ CH3 rocking CC & CN torsion, C]O wagg. In plane pyrimid ring deformation Out of plane imid ring deformation (NCN torsion) CoeN str þ Breathing in pyrimid ring þ N1eCH3 bend In plane pyrimid ring bend., C10eN1eC2 bend dNCS M - O str þ In plane pyrimid ring deformation C2¼O12 bend. C6¼O14 bend. N7eCH3 (in plane) bend
Abbreviations useds: strong; m: medium; w: weak; very weak: vw; very strong: vs; Bend: bending; str: stretching; r: roking; sym: symmetric; asym: asymmetric; wagg: wagging; pyramid: pyrimidine; imid: imidazole; ns: Symetrical stretching; nas: Asymetrical stretching.
H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7
3.3.
1
5
H NMR-13C NMR analysis
The proton NMR spectrum of complex was measured in dimethyl sulfoxide (DMSO) solution using Bruker Advance 300 NMR spectrometer. The chemical shifts (d) of complex are listed in Table 5 and given in Fig. 5. Some changes were observed in the chemical shift values of complex in 1H NMR spectrum. These changes are affected by the interaction between [Co(II) (H2O)4(NCS)2] as an electrons donor with p acceptor caffeine. The spectrum display five signals indicating five different proton environments. The 1H NMR spectrum of caffeine in dimethyl sulfoxide (DMSO) solution showed four relatively low intensive peaks at 3.141 ppm (S, 3H, H131,132,133), 3.266 ppm (S, 3H, H111,112,113), 3.853 ppm (S, 3H, H101,102,103) and 7.973 ppm (S, 1H, H21) corresponding to the three CH3-groups and CH, respectively. The analogous spectrum of complex is characterized by peaks at 2.869 ppm (S, 3H, H131,132,133), 3.057 ppm (S, 3H, H111,112, 113), 3.480 ppm (S, 3H, H101,102,103) and 7.556 ppm (S, 1H, H21) [25]. These shifts in caffeine peaks referring to the formation of intermolecular hydrogen bonds: OeH/N, OeH/O, CeH/S. The new signal at 4.646 ppm is attributed to hydration water and water of coordination. 13 C NMR spectrum of the complex is presented in Fig. 6. This figure shows proton signals at 27,78; 29,68; 33,40; 106,85; 143; 148,37; 151,31 and 154,79 due to C13, C11, C110, C9, C2, C4, C6 and C8 respectively. The new signal at 142 ppm is attributed to carbon of the isothiocyanato coordinated in [Co(II) (H2O)4(NCS)2] [25] (see Table 6).
Fig. 6.
13
C NMR spectrum of the complex in DMSO. TMS was used as the standard.
Table 6 13 C NMR spectral data of the free caffeine and complex in DMSO. Position
13C NMR data free caffeine
13C NMR data co-crystal
13 11 10 9 2 C-NSC 4 6 8
27.88 29.7 33.57 107.51 141.57 e 148.67 151.66 155.32
27.78 29.68 33.40 106.85 143 142 148.37 151.31 154.79
3.4. Electronic absorption spectral study The interaction of caffeine with [Co(II) (H2O)4(NCS)2] is characterized by UVeVisible absorption technique. The UVeVisible Table 5 1 H NMR spectral data of the free caffeine and complex. Compound
1
Free caffeine
3141 3266 3853 7973 2869 3057 3480 4646 7556
Complex
H NMR chemical Shift (d ppm)
Assignement S, S, S, S, S, S, S, S, S,
3H, H131,132,133 3H, H111,112,113 3H, H101,102,103 1H, H21 3H, H111,112,113 3H, H131,132,133 3H, H101,102,103 12H, HH2O 1H, H21
Fig. 7. UVevisible spectra of the free caffeine and their co-crystal dissolved in acetonitril.
electronic spectra for all compounds are recorded in acetonitrile (see Fig. 7). The electronic spectra of these compounds are very similar in the UV region and show characteristic bands at 205, 230 and 273 nm for free caffeine in acetonitril, which is corresponds to Table 7 UVevisible data of the free ligands and their co-crystal dissolved in acetonitril. Compound
lmax (nm)
Assignement
KSCN
276 360 205 230 273 208 271 331 561 637
p/p* n/p* s/s* p/p* p/p* s/s* p/p* n/p* 4 T1g(F) / 4T1g [27] 4 T1g(F) / 4T1g [27]
caffeine
Co-crystal
Fig. 5. 1H NMR spectrum of the complex in DMSO. TMS was used as the standard.
6
H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7
DTA uV
TGA mg 20.00
100.00
15.00
-0.00 10.00
5.00 DTA TGA
100.00
200.00
300.00 400.00 Temp [C]
500.00
600.00
Fig. 8. The TGA-DTA of the co-crystal.
s/s*, p/p* transitions, at 208, 271, 331 nm for the complex; these bands are attributed to s/s*, p/p*, n/p* (see Table 7). The electronic spectrum recorded in water solution for potassium thiocyanate exhibited that, the absorption bands in UV region can be annotated as p/p* and n/p* transitions, these bands are less intense compared to the free caffeine bands [26]. Another bands appeared at the visible region at 561 nm and 637 nm assigned to 4 T1g (F) / 4T1g (P) transition. These rules are accepted for octahedral geometry around the Cobalt (II) center [26]. 3.5. DTA and TGA analysis The thermal properties of complex are investigated by TGA and DTA methods in the temperature range (50e600) C (Fig. 8). A systematic analysis of the presented TGA curve was showed that caffeine decomposes at 290 C [27]. The thermal stability of the complex differed, with the decomposition temperatures at 80 C, 122 C, 224 C, 430 C shown in Fig. 8. These results indicate that caffeine usual thermal properties are changed due to associate with a metal complex and water of the hydration. For the DTA curve of free caffeine shows the endothermic peak at 315.82 C corresponding to its melting point [27]. The DTA curve of complex shows endothermic peaks at about 82.43 C and 125 C corresponds to the loss of water (Hydration, coordination); another endothermic peak is present at about 336.57 C, this endothermic peak of melting point of caffeine in the complex. The endothermic peak appeared at 495.36 C corresponds to the loss of isothiocyanato groups [28]. The exothermic peak at 560 C is observed corresponding to the formation of Co3O4 [29]. The thermal stability of the caffeine molecule is significantly increased in terms of melting point. Hence, the melting point of caffeine in complex is increased around 20 C than that of pure caffeine. With these results we confirmed the strong interaction between the caffeine molecule and water of (Hydration and coordination). Supplementary material Crystallographic data for of the complex [Co(H2O)4(NCS)2]-2 (cafeine),4H2O have been deposited at the Cambridge
Crystallographic Data Center as supplementary publication under the registration number CCDC 1542060. 4. Conclusion Supramolecular complex of Co (II) with isothiocyanato and caffeine has been synthesized and their structure determined from FTIR, UVevisible, DTA, TGA, 1H, 13C NMR and single crystal XRD studies. The Co (II) ions are octahedrally coordinated by two isothiocyanato ligands, four water molecules leading to an overall CoN2O4 coordination environment. The asymmetric unit of the mononuclear complex comprises half of [Co(II) (NCS)2(H2O)4] compound, one caffeine and two water molecules. The co-crystal packing is mainly stabilized by hydrogen bonds and p$$$p interactions. Therefore, the Cobalt complex is directly linked to four molecules of caffeine by OeH/N and OeH/O classical hydrogen bonds. Acknowledgements The authors would like to thank the LCC CNRS (Laboratory of Chemistry of Coordination) for their help. References [1] P.A. Gale, Supramolecular chemistry anniversary, Chem. Soc. Rev. 36 (2) (2007) 141e142. [2] N. Goel, N. Kumar, Study of supramolecular frameworks having aliphatic dicarboxylic acids, N,N0-bis(salicyl)ethylenediamine and N,N0-bis(salicyl) butylenediamine, J. Mol. Struct. 1071 (2014) 60e70. [3] N.M.H. Salem, A.R. Rashad, L. El Sayed, S. Foro, W. Haase, M.F. Iskander, Synthesis, characterization, molecular structure and supramolecular architectures of some copper (II) complexes derived from salicylaldehyde semicarbazone, Inorg. Chim. Acta. 432 (1) (2015) 231e242. [4] R. Chakrabarty, P. Sarathi Mukherjee, P.J. Stang, Supramolecular coordination: self-assembly of finite two- and three-dimensional ensembles, Chem. Rev. 111 (11) (2011) 6810e6918. [5] Q. Liu, Y.Z. Li, Y. Song, H. Liu, Z. Xu, Three-dimensional five-connected coordination polymer [M2(C3H2O4)2(H2O)2(m2-hmt)]n with 4466 topologies (M ¼ Zn, Cu; Hmt ¼ hexamethylenetetramine, Solid State Commun. 177 (12) (2004) 4701e4705. [6] S. Hazra, S. Biswas, A.M. Kirillov, A. Ghosh, Nickel(II) complexes selfassembled from hexamethylenetetramine and isomeric nitrobenzoates: structural diversity and supramolecular features, Polyhedron 79 (2014) 66e71. [7] W.J. Shi, L. Hou, D. Li, Y.G. Yin, Supramolecular assembly driven by hydrogenbonding and pep stacking interactions based on copper(II)- terpyridyl complexes, Inorg. Chim. Acta. 360 (2) (2007) 588e598.
H. EL Hamdani et al. / Journal of Molecular Structure 1157 (2018) 1e7 [8] T.J. Bednarchuk, V. Kinzhybalo, O. Bednarchuk, A. Pietraszko, Synthesis, structural characterization, IR- and Raman spectroscopy, magnetic properties of new organically templated metal sulfates with 4-aminopyridinium, J. Mol. Struct. 1120 (2016) 138e149. [9] N. Upadhayay, Synthesis, characterization and biological studies of some thiocyanato-bridged bimetallic complexes containing Co(II), Cd(II), Hg(II) and N, N'-Bis(benzylidene)- 1,2-phenylene-diamine schiff base, Chem. Sci. Trans 2 (2) (2013) 455e460. ski, Bimetallic complexes with macrocyclic [10] A. Tomkiewicz, J. Kłak, J. Mrozin ligands. Variation of magnetic exchange interactions in some heteronuclear thiocyanatobridged compounds, Mater. Sci. Poland 22 (3) (2004) 253e263. [11] S. Suckert, L.S. Germann, R.E. Dinnebier, J. Werner, C. N€ ather, Synthesis, structures and properties of cobalt thiocyanate coordination compounds with 4-(hydroxymethyl)pyridine as Co-ligand, Crystals 6 (38) (2016) 1e17. [12] F. Valach, B. Koren, M. Tokarcík, M. Melník, Structure of l,3,7-Trimethyl-2,6dioxopurine Copper(II) o-Iodobenzoate, Chem. Pap. 52 (3) (1998) 140e146. [13] (a) M.J. Arnaud, B. Caballero, Guide to Nutritional Supplements, Elsevier Ltd., Oxford, 2009, pp. 65e71; (b) M. Melník, M. Kohútov, Complex view on biomedical activity of caffeine, Acta Fac. Pharm. Univ. Comen. 56 (2009) 5e7. [14] W. Betteridge, J.R. Carruthers, R.I. Cooper, K. Prout, D.J. Watkin, CRYSTALS version 12: software for guided crystal structure analysis, J. Appl. Cryst. 36 (2003) 1487. [15] D.J. Watkin, C.K. Prout, L.J. Pearce, CAMERON, Chemical Crystallography Laboratory, Oxford, England, 1996. [16] I. Cooper, A.L. Thompson, D.J. Watkin, CRYSTALS enhancements: dealing with hydrogen atoms in refinement, J. Appl. Cryst. 43 (2010) 1100e1107. [17] Agilent, CrysAlis PRO, Agilent Technologies, Yarnton, England, 2011. [18] S.I. Shylin, I.A. Gural'skiy, D. Bykov, S. Demeshko, S. Dechert, F. Meyer, M. Hauka, I.O. Fritsky, Iron (II) isothiocyanate complexes with substituted pyrazines: Experimental and theoretical views on their electronic structure, Polyhedron 87 (2015) 147e155. [19] S.I. Shylin, I.A. Guralskiy, M. Haukka, I.A. Golenya, Pyridinium bis(pyridine-kN) tetrakis(thiocyanato-kN)ferrate(III), Acta Crystallogr. E69 (2013), 280e280. [20] S.R. Petrusenko, V.N. Kokozay, I.O. Fritsky, Direct synthesis and crystal structure of zinc thiocyanate complexes with 1,4diazabicyclo(2,2,2)octane, Polyhedron 16 (1997) 267e274.
7
_ [21] H. Ilkimen, C. Yenikaya, A. Gülbandılar, M. Sarı, Synthesis and characterization of a novel proton salt of 2-amino-6-nitrobenzothiazole with 2,6pyridinedicarboxylic acid and its metal complexes and their antimicrobial and antifungal activity studies, J. Mol. Struct. 1120 (2016) 25e33. [22] (a) S. Endrit, E.M. Curtis, A.L. Rheingold, S.H. Lapidus, P.W. Stephens, A.M. Arif, J.S. Miller, First row transition metal(II) thiocyanate complexes, and formation of 1-, 2-;, and 3-dimensional extended network structures of m(NCS)2(solvent)2 (M ¼ Cr, Mn, Co) composition, Inorg. Chem. 52 (18) (2013) 10583e10594; (b) J.L. Burmeister, Linkage isomerism in metal complexes, Coord. Chem. Rev. 3 (1968) 225e245. [23] S.K. Srivastava, V.B. Singh, Ab initio and DFT studies of the structure and vibrational spectra of anhydrous caffeine, Spectrochim. Acta Mol. Biomol. Spectrosc. 115 (2013) 45e50. [24] V.T. Yilmaz, O. Andac, T.K. Yazicilar, H. Kutuk, Y. Bekdemir, W.T.A. Harrison, The first metal complex of p-nitrobenzoxasulfamate. Synthesis, spectral and structural characterization of triaquabis(p-nitrobenzoxasulfamato)copper(II) monohydrate, J. Mol. Struct. 608 (2002) 71e76. Physique et De sordre Orientationnel dans [25] (a) D. d'Anne-Amandine, Stabilite Usage The rapeutique : La Cafe ine, Lille 1 (2009) 108e109; un Cristal a (b) M.O. Okuom, M.V. Wilson, A. Jackson, A.E. Holmes, Intermolecular interactions between eosin Y and caffeine using 1H-NMR spectroscopy, Int. J. Spectrosc. (2013) (2013) 1e6. € € lu, [26] E. Taʂdemir, F.E. Ozbek, M. Sertçelik, T. HOkelek, R. Çatak Çelik, H. Necefog Supramolecular complexes of Co(II), Ni(II) and Zn(II) phydroxybenzoates with caffeine: synthesis, spectral characterization and crystal structure, J. Mol. Struct. 1119 (2016) 472e478. [27] S. Prabu, M. Swaminathan, K. Sivakumar, R. Rajamohan, Preparation, Characterization and molecular modeling studies of the inclusion complex of Caffeine with Beta-cyclodextrin, J. Mol. Struct. 1099 (2015) 616e624. [28] S.C. Mojumdar, M. Melnık, E. Jona, Thermoanalytical investigation of Mg (II) compounds containing SCN and heterocyclic N-donor ligands, J. Anal. Appl. Pyrol. 48 (1999) 111e120. [29] S. Prasad, Cobalt(II) complexes of various thiosemicarbazones of 4-aminoantipyrine: syntheses, spectral, thermal and antimicrobial studies, Transit. Met. Chem. 32 (2007) 143e149.