Crystal structure of bis-(N,N,N',N'-tetra-methyl-guanidinium) tetra-chlorido-cuprate(II).

In the structure of the title salt, (C5H14N3)2[CuCl4], the Cu(II) atom in the anion lies on a twofold rotation axis. The tetra-chlorido-cuprate(II) anion adopts a flattened tetra-hedral coordination environment and inter-acts electrostatically with the tetra-methyl-guanidinium cation. The crystal packing is additionally consolidated through N-H⋯Cl and C-H⋯Cl hydrogen bonds, resulting in a three-dimensional network structure.

Chemical context

The title compound belongs to the series of hybrid organic–inorganic materials of general formula A 2[MX 4] where A is an organic cation, M a divalent transition metal and X a halide. The copper representatives of these families have been extensively studied for their magnetic, dielectric and fluorescent properties in relation to their solid-state structures (Halvorson et al., 1990 ▸). Recent studies include examination of polymorphism in relation to electrostatic properties (Awwadi & Haddad, 2012 ▸) or thermochroism (Aldrich et al., 2016 ▸), sometimes in relation to phase transitions (Kelley et al., 2015 ▸).

Following our report on the crystal structure of bis-tetra­methyl­guanidinium tri­chlorido­cadmate (Ndiaye et al., 2016 ▸), we have investigated the inter­actions between tetra­methyl­guanidine and CuCl2·2H2O which has yielded the title salt, (C5H14N3)2[CuCl4], (I).

Structural commentary

The asymmetric unit of (I) contains a complete N,N,N′,N′-tetra­methyl­guanidinium cation and half of a [CuCl4]2− anion held together by an N—H⋯Cl hydrogen bond (Fig. 1 ▸). In the anion, the Cu—Cl distances range from 2.2396 (4) Å to 2.2557 (4) Å. They are shorter than those usually found in tetra­chlorido­cuprate(II) anions with a square-planar configuration (Guo et al., 2015 ▸). The distortion of the flattened tetra­chlorido­cuprate(II) anion in (I) from the ideal tetra­hedral configuration can be asserted by the values of the two trans Cl—Cu—Cl angles, 135.62 (3)° and 133.31 (3)°. These two angles can also be used to calculate the τ 4 geometry index developed by Yang et al. (2007 ▸) for complexes with coordination number four to qu­antify such a distortion. The τ 4 parameter is defined as [360 - (α+β)] / 141 where α and β are the two largest Cl—Cu—Cl angles. A τ 4 index value of 1 corresponds to an ideal tetra­hedral configuration while a value of 0 is for a perfect square-planar configuration. Here the value obtained (0.65) indicates a ‘see-saw’ (bis­phenoidal) configuration with point group symmetry 2.

Figure 1

The structures of the mol­ecular entities in (I), drawn with displacement parameters at the 50% probability level. The N—H⋯Cl hydrogen bond is indicated by a dashed line. [Symmetry code: (i) −x + 1, y, −z + .]

In the organic cation, the C—N distances in the central CN3 unit [1.332 (2), 1.335 (2) and 1.342 (2) Å] are consistent with a partial double-bond character and a positive charge delocalization, as usually found in structures involving tetra­methyl­guanidinium cations. The central core of the cation has an almost planar–trigonal geometry, as reflected by the values for the three N—C—N angles close to 120° and the r.m.s deviation from the least-squares plane calculated for atoms C1, N1, N2 and N3 that is only 0.0006 Å. The di­methyl­ammonium groups are twisted by 29.38 (16)° (C2, C3) and 25.08 (16)° (C4, C5) with respect to this plane.

Supra­molecular features

Anions and cations are connected through electrostatic inter­actions and via classical N—H⋯Cl hydrogen bonds involving atom Cl1 whereby only one of the H atoms of the amine group is involved; the remaining H atom has no acceptor atom (Fig. 1 ▸, Table 1 ▸). In addition, each Cl atom of the anion is engaged in three C—H⋯Cl hydrogen bonds, leading to the formation of a three-dimensional network structure (Fig. 2 ▸, Table 1 ▸).

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C4—H4B⋯Cl2i	0.95 (2)	2.77 (2)	3.5902 (19)	145.3 (18)
C2—H2C⋯Cl1ii	0.98 (3)	2.90 (3)	3.745 (2)	144.5 (18)
C2—H2D⋯Cl1iii	0.91 (2)	2.91 (2)	3.818 (2)	173.3 (19)
C3—H3B⋯Cl2iv	0.99 (3)	2.82 (3)	3.793 (2)	168 (2)
C5—H5C⋯Cl2v	0.93 (3)	2.80 (3)	3.5992 (18)	144.9 (19)
C2—H2E⋯Cl2vi	0.96 (3)	2.85 (3)	3.6491 (18)	140.5 (19)
N2—H2B⋯Cl1	0.86 (3)	2.53 (3)	3.3417 (16)	157 (2)

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

Figure 2

Packing diagram of (I) viewed along [001].

Database survey

A search in the Cambridge Structural Database (Version 5.37 with two updates; Groom et al., 2016 ▸) for isolated tetra­chlorido­cuprate(II) anions without disorder returned 342 hits for a total of 389 fragments. The configurations of these fragments were analysed using the τ 4 index as described above. Around 60 of these (15%) have a τ 4 index value less than 0.1, including 29 that have a τ 4 index of 0 (ideal square-planar configuration). Only four were found to have a configuration close to the ideal tetra­hedral one with a τ 4 index value larger than 0.9. A large number of fragments (72%) has a geometry index τ 4 value in the 0.6–0.8 range and feature a bis­phenoidal configuration as found for (I). An analysis with the modified version of the τ 4 index [τ 4′, as defined by Okuniewski et al. (2015 ▸)] gives a similar distribution with only minor variation.

The title compound is isostructural with bis­(N,n class="Chemical">N,N′,N′-tetra­methyl­guanidinium) tetra­bromido­nickelate(II) (Jones & Thonnessen, 2006 ▸) and shows similarities in terms of the space-group and cell parameters with tetra­methyl­guanidinium bis­ulfite (Heldebrant et al., 2009 ▸).

Synthesis and crystallization

Yellowish-green crystals were obtained by mixing in stoichiometric amounts n class="Species">tetra­methyl­guanidine with CuCl2·2H2O in ethanol.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. All hydrogen atoms were located from a Fourier difference map and were refined freely.

Table 2

Experimental details

Crystal data
Chemical formula	(C5H14N3)2[CuCl4]
M r	437.72
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	100
a, b, c (Å)	18.9274 (5), 8.2441 (2), 14.8654 (4)
β (°)	124.165 (1)
V (Å3)	1919.28 (9)
Z	4
Radiation type	Ga Kα, λ = 1.34139 Å
μ (mm−1)	9.51
Crystal size (mm)	0.16 × 0.10 × 0.06
Data collection
Diffractometer	Bruker Venture Metaljet
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 ▸)
T min, T max	0.449, 0.752
No. of measured, independent and observed [I > 2σ(I)] reflections	14222, 2208, 2178
R int	0.036
(sin θ/λ)max (Å−1)	0.650
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.028, 0.071, 1.11
No. of reflections	2208
No. of parameters	152
H-atom treatment	All H-atom parameters refined
Δρmax, Δρmin (e Å−3)	0.84, −0.35

Computer programs: APEX2 and SAINT (Bruker, 2014 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL2014 (Sheldrick, 2015b ▸), OLEX2 (Dolomanov et al., 2009 ▸), Mercury (Macrae et al., 2008 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989016010161/wm5303sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016010161/wm5303Isup2.hkl

CCDC reference: 1486986

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

(C5H14N3)2[CuCl4]	F(000) = 908
Mr = 437.72	Dx = 1.515 Mg m−3
Monoclinic, C2/c	Ga Kα radiation, λ = 1.34139 Å
a = 18.9274 (5) Å	Cell parameters from 9968 reflections
b = 8.2441 (2) Å	θ = 4.9–60.7°
c = 14.8654 (4) Å	µ = 9.51 mm−1
β = 124.165 (1)°	T = 100 K
V = 1919.28 (9) Å3	Block, clear yellowish green
Z = 4	0.16 × 0.10 × 0.06 mm

Bruker Venture Metaljet diffractometer	2208 independent reflections
Radiation source: Metal Jet, Gallium Liquid Metal Jet Source	2178 reflections with I > 2σ(I)
Helios MX Mirror Optics monochromator	Rint = 0.036
Detector resolution: 10.24 pixels mm-1	θmax = 60.7°, θmin = 4.9°
ω and φ scans	h = −24→24
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	k = −10→10
Tmin = 0.449, Tmax = 0.752	l = −16→19
14222 measured reflections

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.028	All H-atom parameters refined
wR(F2) = 0.071	w = 1/[σ2(Fo2) + (0.0315P)2 + 2.7253P] where P = (Fo2 + 2Fc2)/3
S = 1.11	(Δ/σ)max = 0.001
2208 reflections	Δρmax = 0.84 e Å−3
152 parameters	Δρmin = −0.35 e Å−3
0 restraints

Experimental. X-ray crystallographic data for I were collected from a single crystal sample, which was mounted on a loop fiber. Data were collected using a Bruker Venture diffractometer equipped with a Photon 100 CMOS Detector, a Helios MX optics and a Kappa goniometer. The crystal-to-detector distance was 4.0 cm, and the data collection was carried out in 1024 x 1024 pixel mode.

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

	x	y	z	Uiso*/Ueq
N1	0.18244 (9)	0.33219 (19)	0.30111 (11)	0.0202 (3)
N2	0.24981 (11)	0.5129 (2)	0.44495 (13)	0.0277 (4)
N3	0.32977 (9)	0.32615 (17)	0.42260 (11)	0.0164 (3)
C1	0.25428 (10)	0.3903 (2)	0.38962 (13)	0.0173 (3)
C2	0.17917 (12)	0.2676 (2)	0.20725 (14)	0.0215 (3)
C3	0.09950 (12)	0.3500 (3)	0.28512 (17)	0.0314 (4)
C4	0.40978 (11)	0.4132 (2)	0.49381 (15)	0.0235 (4)
C5	0.33922 (12)	0.1564 (2)	0.40153 (15)	0.0208 (3)
Cu1	0.5000	0.71829 (4)	0.7500	0.01698 (11)
Cl1	0.37443 (3)	0.61496 (7)	0.70754 (4)	0.03106 (13)
Cl2	0.54835 (3)	0.82595 (5)	0.91317 (3)	0.02989 (13)
H4A	0.4363 (15)	0.380 (3)	0.569 (2)	0.030 (6)*
H5A	0.2894 (16)	0.099 (3)	0.3780 (19)	0.029 (6)*
H4B	0.4000 (14)	0.526 (3)	0.4851 (18)	0.024 (5)*
H2C	0.1702 (16)	0.150 (3)	0.2047 (19)	0.030 (6)*
H2D	0.2285 (15)	0.291 (3)	0.2132 (18)	0.022 (5)*
H3A	0.0693 (18)	0.248 (4)	0.260 (2)	0.040 (7)*
H2A	0.2102 (18)	0.568 (4)	0.418 (2)	0.037 (7)*
H3B	0.0655 (19)	0.432 (4)	0.228 (2)	0.050 (8)*
H5B	0.3539 (15)	0.147 (3)	0.349 (2)	0.028 (6)*
H5C	0.3857 (16)	0.111 (3)	0.465 (2)	0.028 (6)*
H2E	0.1316 (16)	0.319 (3)	0.143 (2)	0.028 (6)*
H4C	0.4454 (16)	0.389 (3)	0.468 (2)	0.033 (6)*
H2B	0.2934 (17)	0.536 (3)	0.509 (2)	0.035 (6)*
H3C	0.1050 (17)	0.373 (3)	0.352 (2)	0.040 (7)*

	U11	U22	U33	U12	U13	U23
N1	0.0176 (6)	0.0242 (7)	0.0155 (6)	0.0023 (6)	0.0072 (5)	−0.0054 (6)
N2	0.0225 (7)	0.0289 (8)	0.0186 (7)	0.0092 (7)	0.0036 (6)	−0.0097 (6)
N3	0.0174 (6)	0.0135 (6)	0.0163 (6)	−0.0003 (5)	0.0083 (5)	−0.0008 (5)
C1	0.0196 (7)	0.0167 (7)	0.0130 (7)	0.0028 (6)	0.0075 (6)	−0.0001 (6)
C2	0.0273 (9)	0.0215 (9)	0.0134 (8)	−0.0026 (7)	0.0102 (7)	−0.0044 (6)
C3	0.0182 (8)	0.0432 (12)	0.0264 (9)	0.0061 (8)	0.0086 (7)	−0.0100 (9)
C4	0.0194 (8)	0.0228 (9)	0.0223 (8)	−0.0040 (7)	0.0079 (7)	−0.0029 (7)
C5	0.0234 (8)	0.0132 (7)	0.0253 (9)	0.0028 (7)	0.0135 (7)	0.0000 (7)
Cu1	0.01872 (18)	0.01483 (18)	0.01209 (17)	0.000	0.00542 (14)	0.000
Cl1	0.0201 (2)	0.0510 (3)	0.0243 (2)	−0.00970 (18)	0.01383 (17)	−0.01532 (19)
Cl2	0.0501 (3)	0.0180 (2)	0.01273 (19)	−0.00519 (18)	0.01222 (18)	−0.00224 (14)

N1—C1	1.342 (2)	C3—H3B	0.99 (3)
N1—C2	1.462 (2)	C3—H3C	0.96 (3)
N1—C3	1.457 (2)	C4—H4A	0.97 (3)
N2—C1	1.335 (2)	C4—H4B	0.95 (2)
N2—H2A	0.77 (3)	C4—H4C	0.97 (3)
N2—H2B	0.86 (3)	C5—H5A	0.93 (3)
N3—C1	1.332 (2)	C5—H5B	0.96 (2)
N3—C4	1.459 (2)	C5—H5C	0.93 (3)
N3—C5	1.467 (2)	Cu1—Cl1i	2.2557 (4)
C2—H2C	0.98 (3)	Cu1—Cl1	2.2557 (4)
C2—H2D	0.91 (2)	Cu1—Cl2i	2.2396 (4)
C2—H2E	0.96 (3)	Cu1—Cl2	2.2396 (4)
C3—H3A	0.96 (3)
C1—N1—C2	122.85 (14)	H3A—C3—H3B	108 (2)
C1—N1—C3	121.97 (14)	H3A—C3—H3C	105 (2)
C3—N1—C2	114.63 (14)	H3B—C3—H3C	113 (2)
C1—N2—H2A	120 (2)	N3—C4—H4A	110.4 (14)
C1—N2—H2B	119.9 (17)	N3—C4—H4B	110.0 (14)
H2A—N2—H2B	120 (3)	N3—C4—H4C	106.3 (15)
C1—N3—C4	122.24 (14)	H4A—C4—H4B	112 (2)
C1—N3—C5	122.31 (14)	H4A—C4—H4C	112 (2)
C4—N3—C5	115.01 (14)	H4B—C4—H4C	106 (2)
N2—C1—N1	119.64 (15)	N3—C5—H5A	110.2 (15)
N3—C1—N1	120.38 (15)	N3—C5—H5B	111.8 (15)
N3—C1—N2	119.98 (15)	N3—C5—H5C	109.2 (15)
N1—C2—H2C	108.1 (14)	H5A—C5—H5B	110 (2)
N1—C2—H2D	109.8 (14)	H5A—C5—H5C	111 (2)
N1—C2—H2E	107.2 (15)	H5B—C5—H5C	104 (2)
H2C—C2—H2D	111 (2)	Cl1—Cu1—Cl1i	135.62 (3)
H2C—C2—H2E	110 (2)	Cl2—Cu1—Cl1	100.265 (17)
H2D—C2—H2E	110 (2)	Cl2i—Cu1—Cl1	96.958 (19)
N1—C3—H3A	109.1 (16)	Cl2—Cu1—Cl1i	96.959 (19)
N1—C3—H3B	109.1 (17)	Cl2i—Cu1—Cl1i	100.264 (17)
N1—C3—H3C	111.8 (16)	Cl2—Cu1—Cl2i	133.31 (3)
C2—N1—C1—N2	146.94 (18)	C4—N3—C1—N1	159.80 (16)
C2—N1—C1—N3	−33.3 (3)	C4—N3—C1—N2	−20.4 (2)
C3—N1—C1—N2	−24.1 (3)	C5—N3—C1—N1	−28.2 (2)
C3—N1—C1—N3	155.67 (18)	C5—N3—C1—N2	151.61 (17)

D—H···A	D—H	H···A	D···A	D—H···A
C4—H4B···Cl2i	0.95 (2)	2.77 (2)	3.5902 (19)	145.3 (18)
C2—H2C···Cl1ii	0.98 (3)	2.90 (3)	3.745 (2)	144.5 (18)
C2—H2D···Cl1iii	0.91 (2)	2.91 (2)	3.818 (2)	173.3 (19)
C3—H3B···Cl2iv	0.99 (3)	2.82 (3)	3.793 (2)	168 (2)
C5—H5C···Cl2v	0.93 (3)	2.80 (3)	3.5992 (18)	144.9 (19)
C2—H2E···Cl2vi	0.96 (3)	2.85 (3)	3.6491 (18)	140.5 (19)
N2—H2B···Cl1	0.86 (3)	2.53 (3)	3.3417 (16)	157 (2)