Crystal structure of the tetra-aqua-bis-(thio-cyanato-κN)cobalt(II)-caffeine-water (1/2/4) co-crystal.

In the structure of the title compound [systematic name: tetra-aqua-bis-(thio-cyanato-κN)cobalt(II)-1,3,7-trimethyl-1,2,3,6-tetra-hydro-7H-purine-2,6-dione-water (1/2/4)], [Co(NCS)2(H2O)4]·2C8H10N4O2·4H2O, the cobalt(II) cation lies on an inversion centre and is coordinated in a slightly distorted octa-hedral geometry by the oxygen atoms of four water mol-ecules and two N atoms of two trans-arranged thio-cyanate anions. In the crystal, the complex mol-ecules inter-act with the caffeine mol-ecules through O-H⋯N, O-H⋯O and C-H⋯S hydrogen bonds and π-π inter-actions [centroid-to-centroid distance = 3.4715 (5) Å], forming layers parallel to the ab plane, which are further connected into a three-dimensional network by O-H⋯O and O-H⋯S hydrogen bonds involving the non-coordinating water mol-ecules.

Chemical context

Compounds with supra­molecular metal–organic structures, which are diversified by their innovative applications, attract attention in various fields such as non-linear optical activity, catalysis, electrical conductivity, and cooperative magnetic behavior (Fan et al., 2016 ▸). In particular, the supra­molecular complexes of mixed metals and ligands that possess active pharmaceutical ingredients (APIs) offers an approach to generate crystalline materials that form pharmaceutical co-crystals to effect therapeutic parameters such as solubility and lipophilicity (Ma & Moulton, 2007 ▸). The properties of caffeine as a pharmaceutical compound exhibiting moisture instability with the formation of a non-stoichiometric crystalline hydrate have been widely studied. Caffeine is a stimulant of the central nervous system and a smooth muscle relaxant, and is used as a formulation additive to analgesic remedies (Trask et al., 2005 ▸). Caffeine has attractive effects on various biological systems, including cardiovascular, gastrointestinal, respiratory and muscle systems (Taşdemir et al., 2016 ▸), and forms complexes with transition metals having different coordination and biological properties such as anti-inflammatory and anti­bacterial (Taşdemir et al., 2016 ▸). Thio­cyanate is a commonly used ligand because of its numerous bonding modes to one or more transition metal ions, and provides useful precursors for numerous coordination complexes. Usually, the thio­cyanate anion bonds terminally through the nitro­gen atom with first-row transition metals, and can act as a hydrogen-bond acceptor through the nitro­gen or sulfur atom (Bie et al., 2005 ▸).

Structural commentary

The asymmetric unit of the title compound (Fig. 1 ▸) contains half a complex mol­ecule of formula [Co(NCS)2(H2O)4], a caffeine mol­ecule and two free water mol­ecules. The cobalt(II) cation lies on an inversion centre and displays a trans-arranged octa­hedral coordination geometry provided by the N atoms of two thio­cyanate anions and four O atoms of coordinating water mol­ecules. The Co1—N15 [2.0981 (8) Å] and Co1—O18 [2.0981 (7) Å] bond lengths are equal within standard uncertainties and significantly longer than the Co1–O19 bond length [2.0732 (7) Å], and therefore the CoN2O4 octa­hedron is slightly axially compressed. This structural feature is typical for related compounds (Shylin et al., 2013 ▸, 2015 ▸). The thio­cyanato ligands are bound through the nitro­gen atoms and are nearly linear [N15—C16—S17 = 177.81 (8)°], while the Co–NCS linkage is bent [C16—N15—Co1 = 167.35 (8)°]. Previously reported complexes with an N-bound NCS group possess similar structural features (Petrusenko et al., 1997 ▸). The caffeine mol­ecule is nearly planar (r.m.s. deviation = 0.0346 Å), with a maximum deviation from the mean plane of 0.0404 (7) Å for atom N5.

Figure 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 + 2, −y + 1, −z + 1] of the title compound, with displacement ellipsoids drawn at the 50% probability level

Supra­molecular features

In the crystal, each complex mol­ecule inter­acts with four neighboring caffeine mol­ecules through classical O—H⋯N and O—H⋯O hydrogen bonds (Table 1 ▸) involving the coordinating water mol­ecules as H-atom donors to form layers parallel to the ab plane. These planes are further enforced by C—H⋯S hydrogen bonds and π–π inter­actions occurring between centrosymmetrically related six-membered rings of the purine ring system [Cg⋯Cg i = 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 non-coordinating water mol­ecules linked through O—H⋯O and O—H⋯S hydrogen bonds (Fig. 3 ▸), leading to the formation of a three-dimensional network (Fig. 3 ▸).

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2—H21⋯S17i	0.97	2.83	3.7622 (9)	160.6
O20—H202⋯O21ii	0.86	1.98	2.8119 (11)	161.6
O19—H191⋯O21	0.86	1.91	2.7634 (10)	174.9
O18—H182⋯N3iii	0.85	2.01	2.8671 (11)	178.4
O21—H211⋯S17iv	0.88	2.38	3.2481 (7)	173.3
O21—H212⋯O20iv	0.87	1.97	2.8157 (11)	164.8
O20—H201⋯O12	0.85	2.02	2.8531 (10)	166.8
O19—H192⋯O14v	0.85	1.89	2.7460 (10)	178.5

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) .

Figure 2

Partial packing diagram of the title compound, showing the network of hydrogen bonds (orange dotted lines) and π–π inter­actions (purple dotted lines) linking complexes and caffeine mol­ecules into layers parallel to the ab plane.

Figure 3

Crystal packing of the title compound viewed down the a axis.

Synthesis and crystallization

In a glass tube, a solution of CoCl2·6H2O (129 mg, 1 mmol) in 5 ml of water and caffeine (194.19 mg, 1 mmol) in 10 ml of ethanol was added to a solution of potassium thio­cyanate (190 mg, 2 mmol) in 5 ml of water. Single crystals of the title compound suitable for X-ray analysis were grown after several months by slow evaporation of the solvent at room temperature.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. All H atoms could be located in a difference-Fourier 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 = 0.98, O—H = 0.82 Å) and with U iso(H) set at 1.2–1.5 times of the U eq of the parent atom, after which the positions were refined with riding constraints (Cooper et al., 2010 ▸).

Table 2

Experimental details

Crystal data
Chemical formula	[Co(NCS)2(H2O)4]·2C8H10N4O2·4H2O
M r	707.61
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	120
a, b, c (Å)	10.65854 (19), 8.16642 (14), 18.0595 (3)
β (°)	96.4701 (15)
V (Å3)	1561.93 (3)
Z	2
Radiation type	Mo Kα
μ (mm−1)	0.75
Crystal size (mm)	0.25 × 0.20 × 0.20
Data collection
Diffractometer	Oxford Diffraction Gemini
Absorption correction	Multi-scan (CrysAlis PRO; Agilent, 2011 ▸)
T min, T max	0.78, 0.86
No. of measured, independent and observed [I > 2.0σ(I)] reflections	62568, 4002, 3693
R int	0.023
(sin θ/λ)max (Å−1)	0.689
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.023, 0.022, 1.13
No. of reflections	3586
No. of parameters	196
H-atom treatment	H-atom parameters not refined
Δρmax, Δρmin (e Å−3)	0.36, −0.24

Computer programs: GEMINI (Oxford Diffraction, 2006 ▸), CrysAlis PRO (Agilent, 2011 ▸), SIR92 (Altomare et al., 1994 ▸), CRYSTALS (Betteridge et al., 2003 ▸) and CAMERON (Watkin et al., 1996 ▸). Weighting scheme: Chebychev polynomial, (Watkin, 1994 ▸; Prince, 1982 ▸).

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S2056989017008180/rz5216sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989017008180/rz5216Isup2.hkl

CCDC reference: 1553654

Additional supporting information: crystallographic information; 3D view; checkCIF report

[Co(NCS)2(H2O)4]·2C8H10N4O2·4H2O	F(000) = 738
Mr = 707.61	Dx = 1.504 Mg m−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 26895 reflections
a = 10.65854 (19) Å	θ = 4–29°
b = 8.16642 (14) Å	µ = 0.75 mm−1
c = 18.0595 (3) Å	T = 120 K
β = 96.4701 (15)°	Block, orange
V = 1561.93 (3) Å3	0.25 × 0.20 × 0.20 mm
Z = 2

Oxford Diffraction Gemini diffractometer	3693 reflections with I > 2.0σ(I)
Graphite monochromator	Rint = 0.023
φ & ω scans	θmax = 29.3°, θmin = 3.1°
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2011)	h = −14→13
Tmin = 0.78, Tmax = 0.86	k = −10→10
62568 measured reflections	l = −24→24
4002 independent reflections

Refinement on F	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.023	H-atom parameters not refined
wR(F2) = 0.022	Method, part 1, Chebychev polynomial, (Watkin, 1994, Prince, 1982) [weight] = 1.0/[A0*T0(x) + A1*T1(x) ··· + An-1]*Tn-1(x)] where Ai are the Chebychev coefficients listed below and x = F /Fmax Method = Robust Weighting (Prince, 1982) W = [weight] * [1-(deltaF/6*sigmaF)2]2 Ai are: 4.58 -1.83 2.76
S = 1.13	(Δ/σ)max = 0.001
3586 reflections	Δρmax = 0.36 e Å−3
196 parameters	Δρmin = −0.24 e Å−3
0 restraints

Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems open-flow nitrogen cryostat (Cosier & Glazer, 1986) with a nominal stability of 0.1K. Cosier, J. & Glazer, A.M., 1986. J. Appl. Cryst. 105-107.

	x	y	z	Uiso*/Ueq
N1	0.52963 (7)	0.70159 (10)	0.44118 (4)	0.0159
N3	0.39238 (7)	0.69668 (10)	0.52732 (4)	0.0165
N5	0.50891 (7)	0.88202 (9)	0.61607 (4)	0.0138
N7	0.70166 (7)	0.97981 (10)	0.57845 (4)	0.0148
N15	0.87722 (7)	0.56972 (10)	0.57738 (4)	0.0177
C2	0.42006 (9)	0.64292 (12)	0.46092 (5)	0.0177
C4	0.49202 (8)	0.79469 (11)	0.55076 (5)	0.0134
C6	0.61761 (8)	0.97269 (11)	0.63265 (5)	0.0145
C8	0.68939 (8)	0.89801 (11)	0.50972 (5)	0.0140
C9	0.57826 (8)	0.80031 (11)	0.49965 (5)	0.0138
C10	0.58693 (10)	0.66144 (13)	0.37365 (5)	0.0214
C11	0.41902 (9)	0.86319 (12)	0.67132 (5)	0.0187
C13	0.81636 (9)	1.07902 (13)	0.59652 (6)	0.0212
C16	0.82097 (8)	0.58619 (11)	0.62832 (5)	0.0146
O12	0.63887 (6)	1.04807 (9)	0.69164 (4)	0.0199
O14	0.76700 (6)	0.91542 (9)	0.46473 (4)	0.0191
O18	1.14207 (7)	0.63274 (10)	0.56379 (4)	0.0243
O19	1.04404 (7)	0.29467 (9)	0.56531 (4)	0.0202
O20	0.85940 (7)	1.15725 (10)	0.78244 (4)	0.0218
O21	1.04346 (7)	0.33657 (9)	0.71711 (4)	0.0227
S17	0.73704 (2)	0.60472 (3)	0.699098 (13)	0.0206
Co1	1.0000	0.5000	0.5000	0.0133
H21	0.3674	0.5683	0.4293	0.0226*
H103	0.6697	0.6105	0.3874	0.0339*
H102	0.5958	0.7614	0.3446	0.0343*
H101	0.5302	0.5835	0.3448	0.0347*
H111	0.4397	0.9420	0.7112	0.0299*
H112	0.3339	0.8828	0.6471	0.0298*
H113	0.4258	0.7533	0.6921	0.0310*
H131	0.8546	1.0964	0.5513	0.0326*
H132	0.7942	1.1847	0.6172	0.0322*
H133	0.8741	1.0211	0.6328	0.0327*
H181	1.1398	0.6463	0.6098	0.0378*
H202	0.9034	1.2295	0.7618	0.0364*
H191	1.0428	0.3014	0.6127	0.0336*
H182	1.2164	0.6538	0.5531	0.0384*
H211	1.1073	0.2809	0.7394	0.0376*
H212	1.0591	0.4409	0.7176	0.0382*
H201	0.7920	1.1412	0.7538	0.0355*
H192	1.1020	0.2292	0.5552	0.0330*

	U11	U22	U33	U12	U13	U23
N1	0.0180 (4)	0.0155 (4)	0.0136 (3)	0.0004 (3)	0.0001 (3)	−0.0018 (3)
N3	0.0150 (3)	0.0163 (4)	0.0178 (4)	−0.0018 (3)	0.0000 (3)	−0.0004 (3)
N5	0.0130 (3)	0.0168 (4)	0.0119 (3)	−0.0009 (3)	0.0028 (3)	−0.0008 (3)
N7	0.0127 (3)	0.0175 (4)	0.0140 (3)	−0.0031 (3)	0.0010 (3)	0.0002 (3)
N15	0.0152 (3)	0.0229 (4)	0.0155 (3)	−0.0010 (3)	0.0039 (3)	−0.0018 (3)
C2	0.0164 (4)	0.0178 (4)	0.0185 (4)	−0.0015 (3)	−0.0005 (3)	−0.0012 (3)
C4	0.0133 (4)	0.0136 (4)	0.0132 (4)	0.0012 (3)	0.0007 (3)	0.0012 (3)
C6	0.0140 (4)	0.0156 (4)	0.0135 (4)	0.0007 (3)	0.0002 (3)	0.0007 (3)
C8	0.0137 (4)	0.0141 (4)	0.0140 (4)	0.0024 (3)	0.0012 (3)	0.0023 (3)
C9	0.0149 (4)	0.0146 (4)	0.0120 (4)	0.0011 (3)	0.0011 (3)	0.0000 (3)
C10	0.0269 (5)	0.0228 (5)	0.0152 (4)	0.0007 (4)	0.0058 (4)	−0.0028 (4)
C11	0.0177 (4)	0.0244 (5)	0.0152 (4)	−0.0010 (4)	0.0067 (3)	−0.0006 (3)
C13	0.0154 (4)	0.0269 (5)	0.0208 (4)	−0.0084 (4)	0.0000 (3)	−0.0009 (4)
C16	0.0139 (4)	0.0147 (4)	0.0146 (4)	−0.0021 (3)	−0.0005 (3)	−0.0003 (3)
O12	0.0199 (3)	0.0232 (3)	0.0163 (3)	−0.0028 (3)	0.0006 (2)	−0.0052 (3)
O14	0.0172 (3)	0.0224 (3)	0.0190 (3)	0.0006 (3)	0.0071 (2)	0.0021 (3)
O18	0.0175 (3)	0.0413 (4)	0.0147 (3)	−0.0121 (3)	0.0044 (2)	−0.0074 (3)
O19	0.0212 (3)	0.0232 (3)	0.0173 (3)	0.0041 (3)	0.0063 (2)	0.0018 (3)
O20	0.0203 (3)	0.0300 (4)	0.0146 (3)	−0.0021 (3)	−0.0004 (2)	0.0011 (3)
O21	0.0241 (3)	0.0246 (4)	0.0195 (3)	0.0044 (3)	0.0020 (3)	0.0047 (3)
S17	0.01944 (11)	0.02902 (12)	0.01456 (10)	−0.00462 (9)	0.00757 (8)	−0.00446 (9)
Co1	0.01068 (8)	0.01859 (9)	0.01093 (8)	−0.00186 (6)	0.00259 (5)	−0.00104 (6)

N1—C2	1.3469 (12)	C10—H102	0.980
N1—C9	1.3820 (11)	C10—H101	0.985
N1—C10	1.4616 (12)	C11—H111	0.972
N3—C2	1.3407 (12)	C11—H112	0.975
N3—C4	1.3588 (12)	C11—H113	0.972
N5—C4	1.3727 (11)	C13—H131	0.963
N5—C6	1.3792 (11)	C13—H132	0.980
N5—C11	1.4672 (11)	C13—H133	0.969
N7—C6	1.4006 (11)	C16—S17	1.6476 (9)
N7—C8	1.4027 (11)	O18—Co1	2.0981 (7)
N7—C13	1.4723 (11)	O18—H181	0.842
N15—C16	1.1610 (12)	O18—H182	0.853
N15—Co1	2.0981 (8)	O19—Co1	2.0732 (7)
C2—H21	0.969	O19—H191	0.860
C4—C9	1.3749 (12)	O19—H192	0.853
C6—O12	1.2291 (11)	O20—H202	0.864
C8—C9	1.4226 (12)	O20—H201	0.846
C8—O14	1.2314 (11)	O21—H211	0.877
C10—H103	0.982	O21—H212	0.868
C2—N1—C9	105.49 (7)	H111—C11—H112	110.1
C2—N1—C10	126.68 (8)	N5—C11—H113	109.5
C9—N1—C10	127.76 (8)	H111—C11—H113	109.0
C2—N3—C4	103.21 (8)	H112—C11—H113	110.5
C4—N5—C6	119.42 (7)	N7—C13—H131	108.3
C4—N5—C11	119.83 (7)	N7—C13—H132	109.8
C6—N5—C11	120.37 (7)	H131—C13—H132	109.6
C6—N7—C8	126.55 (7)	N7—C13—H133	109.2
C6—N7—C13	116.65 (7)	H131—C13—H133	110.3
C8—N7—C13	116.77 (7)	H132—C13—H133	109.6
C16—N15—Co1	167.35 (8)	N15—C16—S17	177.81 (8)
N1—C2—N3	113.89 (8)	Co1—O18—H181	120.7
N1—C2—H21	122.0	Co1—O18—H182	127.7
N3—C2—H21	124.1	H181—O18—H182	109.1
N5—C4—N3	126.58 (8)	Co1—O19—H191	119.2
N5—C4—C9	121.78 (8)	Co1—O19—H192	120.6
N3—C4—C9	111.64 (8)	H191—O19—H192	110.2
N7—C6—N5	117.28 (8)	H202—O20—H201	107.9
N7—C6—O12	120.99 (8)	H211—O21—H212	111.4
N5—C6—O12	121.70 (8)	O18i—Co1—O18	179.995
N7—C8—C9	111.93 (7)	O18i—Co1—N15i	87.69 (3)
N7—C8—O14	121.76 (8)	O18—Co1—N15i	92.31 (3)
C9—C8—O14	126.29 (8)	O18i—Co1—N15	92.31 (3)
C8—C9—N1	131.30 (8)	O18—Co1—N15	87.69 (3)
C8—C9—C4	122.88 (8)	N15i—Co1—N15	179.995
N1—C9—C4	105.77 (8)	O18i—Co1—O19	89.86 (3)
N1—C10—H103	109.4	O18—Co1—O19	90.14 (3)
N1—C10—H102	109.5	N15i—Co1—O19	92.36 (3)
H103—C10—H102	110.5	N15—Co1—O19	87.64 (3)
N1—C10—H101	107.3	O18i—Co1—O19i	90.14 (3)
H103—C10—H101	109.9	O18—Co1—O19i	89.86 (3)
H102—C10—H101	110.2	N15i—Co1—O19i	87.64 (3)
N5—C11—H111	108.8	N15—Co1—O19i	92.36 (3)
N5—C11—H112	108.9	O19—Co1—O19i	179.994

D—H···A	D—H	H···A	D···A	D—H···A
C2—H21···S17ii	0.97	2.83	3.7622 (9)	160.6
O20—H202···O21iii	0.86	1.98	2.8119 (11)	161.6
O19—H191···O21	0.86	1.91	2.7634 (10)	174.9
O18—H182···N3iv	0.85	2.01	2.8671 (11)	178.4
O21—H211···S17v	0.88	2.38	3.2481 (7)	173.3
O21—H212···O20v	0.87	1.97	2.8157 (11)	164.8
O20—H201···O12	0.85	2.02	2.8531 (10)	166.8
O19—H192···O14i	0.85	1.89	2.7460 (10)	178.5