Crystal structure of the tetra­aqua­bis­(thio­cyanato-κN)cobalt(II)–caffeine–water (1/2/4) co-crystal

El Hamdani, H.; El Amane, M.; Duhayon, C.

doi:10.1107/S2056989017008180

research communications

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 73| Part 7| July 2017| Pages 980-982

https://doi.org/10.1107/S2056989017008180

Open

access

Crystal structure of the tetraaquabis(thiocyanato-κN)cobalt(II)–caffeine–water (1/2/4) co-crystal

H. El Hamdani,^a ^* M. El Amane ^a and C. Duhayon ^b,^c

^aEquipe Métallation, Complexes Moléculaires et Applications, Université Moulay Ismail, Faculté des Sciences, BP 11201 Zitoune, 50000 Meknès, Morocco, ^bCNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, F-31077 Toulouse, France, and ^cUniversité de Toulouse, UPS, INPT, LCC, F-31077 Toulouse, France
^*Correspondence e-mail: elhamdanihicham41@gmail.com

Edited by C. Rizzoli, Universita degli Studi di Parma, Italy (Received 30 May 2017; accepted 1 June 2017; online 7 June 2017)

In the structure of the title compound [systematic name: tetraaquabis(thiocyanato-κN)cobalt(II)–1,3,7-trimethyl-1,2,3,6-tetrahydro-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 octahedral geometry by the oxygen atoms of four water molecules and two N atoms of two trans-arranged thiocyanate anions. In the crystal, the complex molecules interact with the caffeine molecules through O—H⋯N, O—H⋯O and C—H⋯S hydrogen bonds and π–π interactions [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 molecules.

Keywords: crystal structure; caffeine; hydrogen bonding; single-crystal X-ray diffraction analysis.

CCDC reference: 1553654

1. 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 ).

2. 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

3. 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⋯Cgⁱ = 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⋯S17^iv	0.88	2.38	3.2481 (7)	173.3
O21—H212⋯O20^iv	0.87	1.97	2.8157 (11)	164.8
O20—H201⋯O12	0.85	2.02	2.8531 (10)	166.8
O19—H192⋯O14^v	0.85	1.89	2.7460 (10)	178.5
Symmetry codes: (i) -x+1, -y+1, -z+1; (ii) x, y+1, z; (iii) x+1, y, z; (iv) $[-x+2, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (v) -x+2, -y+1, -z+1.

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.

4. 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.

5. 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[F² > 2σ(F²)], wR(F²), S	0.023, 0.022, 1.13
No. of reflections	3586
No. of parameters	196
H-atom treatment	H-atom parameters not refined
Δρ_max, Δρ_min (e Å⁻³)	0.36, −0.24
Computer programs: GEMINI (Oxford Diffraction, 2006 $[Oxford Diffraction (2006). Gemini User Manual. Oxford Diffraction, Abingdon, England.]$ ), 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 ).

Supporting information

CCDC reference: 1553654

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2056989017008180/rz5216sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989017008180/rz5216Isup2.hkl

checkCIF report

Computing details top

Data collection: Gemini (Oxford Diffraction, 2006); cell refinement: CrysAlis PRO (Agilent, 2011); data reduction: CrysAlis PRO (Agilent, 2011); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS (Betteridge et al., 2003).

(I) top

Crystal data top

[Co(NCS)₂(H₂O)₄]·2C₈H₁₀N₄O₂·4H₂O	F(000) = 738
M_r = 707.61	D_x = 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

Data collection top

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

Refinement top

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/[A₀T₀(x) + A₁T₁(x) ··· + A_n-1]T_n-1(x)] where A_i are the Chebychev coefficients listed below and x = F /Fmax Method = Robust Weighting (Prince, 1982) W = [weight] [1-(deltaF/6*sigmaF)²]² A_i are: 4.58 -1.83 2.76
S = 1.13	(Δ/σ)_max = 0.001
3586 reflections	Δρ_max = 0.36 e Å⁻³
196 parameters	Δρ_min = −0.24 e Å⁻³
0 restraints

Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
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*

Atomic displacement parameters (Å²) top

	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)

Geometric parameters (Å, º) top

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

Symmetry code: (i) −x+2, −y+1, −z+1.

Hydrogen-bond geometry (Å, º) top

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···N3^iv	0.85	2.01	2.8671 (11)	178.4
O21—H211···S17^v	0.88	2.38	3.2481 (7)	173.3
O21—H212···O20^v	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

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

Acknowledgements

The authors would like to thank the LCC CNRS (Laboratory of Chemistry of Coordination) for their help.

References

Agilent (2011). CrysAlis PRO. Agilent Technologies, Yarnton, England. Google Scholar
Altomare, A., Cascarano, G., Giacovazzo, C., Guagliardi, A., Burla, M. C., Polidori, G. & Camalli, M. (1994). J. Appl. Cryst. 27, 435. CrossRef Web of Science IUCr Journals Google Scholar
Betteridge, P. W., Carruthers, J. R., Cooper, R. I., Prout, K. & Watkin, D. J. (2003). J. Appl. Cryst. 36, 1487. Web of Science CrossRef IUCr Journals Google Scholar
Bie, H. Y., Lu, J., Yu, J. H., Xu, J., Zhao, K. & Zhang, X. (2005). J. Solid State Chem. 178, 1445–1451. Web of Science CSD CrossRef CAS Google Scholar
Cooper, R. I., Thompson, A. L. & Watkin, D. J. (2010). J. Appl. Cryst. 43, 1100–1107. Web of Science CrossRef CAS IUCr Journals Google Scholar
Fan, G., Deng, L.-J., Ma, Z.-Y., Li, X.-B., Zhang, Y.-L. & Sun, J.-J. (2016). Chin. J. Struct. Chem. 35, 100–106. CAS Google Scholar
Ma, Z. & Moulton, B. (2007). Mol. Pharm. 4, 373–385. Web of Science CSD CrossRef PubMed CAS Google Scholar
Oxford Diffraction (2006). Gemini User Manual. Oxford Diffraction, Abingdon, England. Google Scholar
Petrusenko, S. R., Kokozay, V. N. & Fritsky, I. O. (1997). Polyhedron, 16, 267–274. CSD CrossRef CAS Web of Science Google Scholar
Prince, E. (1982). In Mathematical Techniques in Crystallography and Materials Science. New York: Springer-Verlag. Google Scholar
Shylin, S. I., Gural'skiy, I. A., Bykov, D., Demeshko, S., Dechert, S., Meyer, F., Hauka, M. & Fritsky, I. O. (2015). Polyhedron, 87, 147–155. Web of Science CSD CrossRef CAS Google Scholar
Shylin, S. I., Gural'skiy, I. A., Haukka, M. & Golenya, I. A. (2013). Acta Cryst. E69, m280. CSD CrossRef IUCr Journals Google Scholar
Taşdemir, E., Özbek, F. E., Sertçelik, M., Hökelek, T., Çelik, R. Ç., & Necefoğlu, H. (2016). J. Mol. Struct. 1119, 472–478. Google Scholar
Trask, A. V., Motherwell, W. D. S. & Jones, W. (2005). Cryst. Growth Des. 5, 1013–1021. Web of Science CSD CrossRef CAS Google Scholar
Watkin, D. (1994). Acta Cryst. A50, 411–437. CrossRef CAS Web of Science IUCr Journals Google Scholar
Watkin, D. J., Prout, C. K. & Pearce, L. J. (1996). CAMERON. Chemical Crystallography Laboratory, Oxford, England. Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.