Poly[tetra­amminecopper(II) bis­[tris­([mu]₂-cyanido-[kappa]²C,N)dicuprate(I)]]: a unique Cu^I-Cu^II mixed-valence complex containing anionic cuprous cyanide layers and [Cu(NH₃)₄]²⁺ cations

The title compound, {[Cu(NH₃)₄][Cu(CN)₃]₂}_n, features a Cu^I-Cu^II mixed-valence CuCN framework based on {[Cu₂(CN)₃]^-}_n anionic layers and [Cu(NH₃)₄]²⁺ cations. The asymmetric unit contains two different Cu^I ions and one Cu^II ion which lies on a centre of inversion. Each Cu^I ion is coordinated to three cyanide ligands with a distorted trigonal-planar geometry, while the Cu^II ion is ligated by four ammine ligands, with a distorted square-planar coordination geometry. The inter­linkage between Cu^I ions and cyanide bridges produces a honeycomb-like {[Cu₂(CN)₃]^-}_n anionic layer containing 18-membered planar [Cu(CN)]₆ metallocycles. A [Cu(NH₃)₄]²⁺ cation fills each metallocyclic cavity within pairs of exactly superimposed {[Cu₂(CN)₃]^-}_n anionic layers, but there are no cations between the layers of adjacent pairs, which are offset. Pairs of N-H...N hydrogen-bonding interactions link the N-H groups of the ammine ligands to the N atoms of cyanide ligands.

S1. Comment

Cuprous cyanide (CuCN) has attracted much attention in chemistry and in industry for its applications in electroplating, metal abstraction, ceramic superconductor preparation and as potential catalysts in organic synthesis (Fehlhammer & Fritz, 1993; Lancashire, 1987; Ondono-Castillo et al., 1995). In particular, metal–organic frameworks (MOFs) based on CuCN have been widely developed in crystal engineering because of the strong binding ability of cyanide anion toward the Cu^I ion. It has been found that a single cyanide anion can bridge two, three or even four Cu^I ions, and the one Cu^I ion can be coordinated by two, three or four cyanide anions, giving rise to linear Cu(CN)₂, trigonal Cu(CN)₃ and tetrahedral Cu(CN)₄ geometries (Hibble & Chippindale, 2005; Pretsch et al., 2004; Pretsch & Hartl, 2004; Qin et al., 2011; Zhang et al., 2011), respectively, which results in a remarkable diversity of structures of CuCN frameworks, such as chain, layer and three-dimensional patterns (Hou et al., 2010; Pretsch & Hartl, 2004; Su et al., 2011). Much research interest has been focused on the construction of CuCN–amine complexes with abundant structual diversity, some of which exhibit excellent luminescent properties in the visible region (Ley et al., 2010; Pike et al., 2007; Tronic et al., 2007, Xia et al., 2010). However, there has been relatively little work carried out on Cu^I–Cu^II mixed-valence cyanide systems because of the high resistance to oxidation of Cu^I ions in the presence of cyanide anions (Colacio et al., 2002; Song et al., 2006), which leads to difficulties in the preparation of Cu^I–Cu^II mixed-valence complexes. To obtain Cu^I–Cu^II mixed-valence cyanide framework, we reacted a mixture of CuCN and 3,5-diethyl-4-(4-pyridin-4-yl)pyrazole in aqueous ammonia media, because the Cu^II ion is more stable than Cu^I ion in aqueous ammonia. As excepted, partial oxidation of Cu^I to Cu^II occurred, and a new Cu^I–Cu^II mixed-valence cyanide framework {[Cu(NH₃)₄][Cu₂(CN)₃]₂}_n, (I), was successfully synthesized.

The structure of (I) consists of a honeycomb-like {[Cu₂(CN)₃]^-}_n anionic layer and [Cu(NH₃)₄]²⁺ cation, as shown in Fig. 1. The asymmetric unit contains three Cu atoms, three cyanide ligands and two ammine ligands. Atoms Cu1 and Cu2 are monovalent and display distorted trigonal planar geometries through the coordination of three cyanide ligands with two C and one N atom and one C and two N atoms, respectively. The C/N—Cu—N/C bond angles are in the ranges 107.7 (1)–132.1 (1) and 106.5 (1)–130.6 (1)° around Cu1 and Cu2, respectively (Table 1). The Cu—C distances [in the range 1.897 (3)–1.907 (3) Å for Cu1 and Cu2] are slightly shorter than the Cu—N distances [1.949 (3)—1.992 (3) Å] and are in reasonable agreement with those found in other CuCN frameworks (Pretsch et al., 2004; Yun et al., 2004). In contrast to the Cu1 and Cu2 atoms, the Cu3 atom is divalent and involved in the formation of the [Cu(NH₃)₄]²⁺ counter-cation, in which the Cu^II ion lies on an inversion centre and is ligated by four ammine ligands to give a distorted square-planar geometry, with Cu—N distances of 2.008 (3)–2.028 (3) Å.

In complex (I), each cyanide anion bridges two Cu^I ions, and each Cu^I ion links three cyanide ligands to form a honeycomb-like {[Cu₂(CN)₃]^-}_n anionic layer, as shown in Fig. 2. The layer contains 18-atom {Cu(CN)}₆ rings, with the longest Cu···Cu separation being 11.596 (3) Å, which is longer than that of 9.97 Å in the recently reported guanidinium cyanocuprate {[C(NH₂)₃][Cu₂(CN)₃]}_n framework (Lin et al., 2008). In the crystal packing, two adjacent layers are eclipsed to form a pair of superimposed anionic layers, while the adjacent pairs are offset along the c axis. It is interesting that the two AA packed layers generate a hexagonal cavity with large enough window sizes (about 6.05 × 3.58 Å, excluding van der Walls radii of the atoms) so that the [Cu(NH₃)₄]²⁺ cation is adducted to form a Cu^I–Cu^II mixed bilayer system, which is further stabilized by an N4—H4A···N3 hydrogen-bonding interaction (Table 2) between ammine ligands and cyanide anions (Fig. 3). However, no [Cu(NH₃)₄]²⁺ cation is deposited between the two AB-packed layers because their staggered stack leads to the decrease of the hexagonal window sizes. A similar {[Cu₂(CN)₃]^-}_n layer has been observed in some CuCN–amine complexes, however, the difference is that the hexagonal cavities are filled by di- and tetraammonium cations, forming different adducts from the case in (I) (Colacio et al., 2002; Pretsch et al., 2004).

A Cu^I–Cu^II mixed-valence cyanide framework based on a {[Cu₂(CN)₃]^-}_n anionic layer has only previously been observed in the framework {[Cu(pn)₂][Cu₂(CN)₃]₂}_n (pn is 1,3-diaminopropane; Benmansour et al., 2009), however, in this structure, the layers stack in a AAA fashion to form infinite hexagonal channels, resulting in the [Cu(pn)₂]²⁺ cations being arranged in line along the channels, which contrasts with complex (I).

It should be noted that the presence of 3,5-diethyl-4-(pyridin-4-yl)pyrazole is essential for the generation of complex (I) because in its absence only a blue solution was obtained under the same reaction conditions; therefore, 3,5-diethyl-4-(pyridin-4-yl)pyrazole appears to act as a directing or templating agent during the generation of complex (I), although, the mechanism for its involvement is presently not clear.

Related literature

For related literature, see: Benmansour et al. (2009); Colacio et al. (2002); Fehlhammer & Fritz (1993); Hibble & Chippindale (2005); Hou et al. (2010); Lancashire (1987); Ley et al. (2010); Lin et al. (2008); Ondono-Castillo, Fuertes, Perez, Gomez-Romero & Casan-Pastor (1995); Pike et al. (2007); Pretsch & Hartl (2004); Pretsch et al. (2004); Qin et al. (2011); Song et al. (2006); Su et al. (2011); Tronic et al. (2007); Xia et al. (2010); Yun et al. (2004); Zhang et al. (2011).

S2. Experimental

A mixture of CuCN (0.036 g, 0.4 mmol), 3,5-diethyl-4-(pyridin-4-yl)pyrazole, ethanol (8 ml) and aqueous ammonia (25%, 1 ml) was sealed in a 15 ml Teflon-lined stainless steel container, which is heated to 413 K and held at that temperature for 72 h. After cooling to room temperature at a rate of 0.1 K min^-1, purple block-shaped crystals of the title compound were obtained in 55% yield (yield 0.020 g, based on CuCN). Analysis calculated for C₆H₁₂Cu₅N₁₀: C 13.30, H 2.23, N 25.84%; found: C 13.34, H 2.18, N 25.87%.

S3. Refinement

H atoms on N atoms were placed at calculated positions (N—H = 0.89 Å) and refined as riding, with U_iso(H) = 1.5U_eq(N).

Computing details

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2005); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. The molecular structure of (I), with displacement ellipsoids drawn at the 30% probability level, and with the H atoms shown as spheres of arbitrary radii. [Symmetry codes: (i) x-1, -y+1/2, z-1/2; (ii) x-1, -y+3/2, z-1/2; (iii) -x+1, -y+2, -z.]
	Fig. 2. A view of the honeycomb-like {[Cu2(CN)3]^-}n anionic layer in the title compound.
	Fig. 3. The stacking along the c axis, showing the adduction between the two AA-packed {[Cu2(CN)3]^-}n layers and [Cu(NH3)4]^2+ cations through N—H···N hydrogen-bonding interactions.

Poly[tetraamminecopper(II) bis[tris(µ₂-cyanido- κ²C,N)dicuprate(I)]]

Crystal data

[Cu(NH3)4][Cu(CN)3]	F(000) = 526
Mr = 541.96	Dx = 2.379 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1643 reflections
a = 7.6501 (9) Å	θ = 2.9–27.3°
b = 8.9083 (10) Å	µ = 6.92 mm^−1
c = 13.2509 (12) Å	T = 295 K
β = 123.086 (5)°	Block, purple
V = 756.61 (14) Å^3	0.19 × 0.17 × 0.11 mm
Z = 2

Data collection

Bruker SMART APEX area-detector diffractometer	1479 independent reflections
Radiation source: fine-focus sealed tube	1261 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.020
ϕ and ω scans	θmax = 26.0°, θmin = 2.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −8→9
Tmin = 0.353, Tmax = 0.517	k = −10→10
3397 measured reflections	l = −14→16

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.033	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.094	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0493P)^2 + 0.5775P] where P = (Fo^2 + 2Fc^2)/3
1479 reflections	(Δ/σ)max = 0.001
97 parameters	Δρmax = 0.75 e Å^−3
0 restraints	Δρmin = −0.44 e Å^−3

Special details

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cu1	0.86771 (7)	0.59343 (5)	0.31346 (4)	0.04692 (19)
Cu2	0.17894 (8)	0.40406 (5)	−0.02790 (5)	0.0523 (2)
N1	0.4450 (5)	0.4664 (4)	0.1178 (3)	0.0550 (9)
N2	1.0584 (5)	0.4212 (3)	0.3998 (3)	0.0463 (8)
N3	1.0300 (5)	0.9123 (4)	0.3907 (3)	0.0488 (8)
C1	0.6004 (5)	0.5134 (4)	0.1958 (3)	0.0424 (8)
C2	1.1100 (5)	0.3001 (4)	0.4260 (3)	0.0403 (8)
C3	0.9665 (5)	0.7933 (4)	0.3571 (3)	0.0363 (7)
Cu3	0.5000	1.0000	0.0000	0.0386 (2)
N4	0.6351 (5)	1.1244 (4)	0.1529 (3)	0.0471 (7)
H4C	0.6854	1.2088	0.1423	0.071*
H4A	0.7387	1.0723	0.2134	0.071*
H4B	0.5405	1.1465	0.1700	0.071*
N5	0.4292 (6)	0.8440 (4)	0.0816 (3)	0.0523 (8)
H5A	0.3624	0.7682	0.0311	0.078*
H5B	0.3478	0.8845	0.1031	0.078*
H5C	0.5460	0.8103	0.1468	0.078*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0417 (3)	0.0332 (3)	0.0571 (3)	−0.00224 (18)	0.0214 (2)	0.00163 (18)
Cu2	0.0525 (3)	0.0308 (3)	0.0587 (3)	−0.00176 (19)	0.0208 (3)	−0.00400 (19)
N1	0.051 (2)	0.0374 (18)	0.066 (2)	0.0028 (15)	0.0255 (18)	0.0005 (16)
N2	0.0498 (18)	0.0308 (18)	0.0485 (18)	−0.0006 (13)	0.0205 (15)	0.0007 (12)
N3	0.0478 (18)	0.043 (2)	0.0460 (18)	0.0027 (15)	0.0196 (15)	0.0039 (14)
C1	0.0325 (17)	0.0275 (18)	0.052 (2)	−0.0023 (14)	0.0136 (16)	−0.0009 (14)
C2	0.0402 (17)	0.032 (2)	0.0385 (17)	−0.0023 (15)	0.0148 (15)	−0.0002 (14)
C3	0.0341 (16)	0.0276 (18)	0.0378 (17)	−0.0019 (14)	0.0135 (14)	0.0012 (13)
Cu3	0.0439 (4)	0.0256 (3)	0.0384 (3)	0.0009 (2)	0.0174 (3)	0.0017 (2)
N4	0.0500 (18)	0.0392 (17)	0.0450 (17)	−0.0062 (14)	0.0215 (14)	−0.0055 (14)
N5	0.063 (2)	0.0354 (17)	0.0466 (17)	−0.0035 (15)	0.0219 (15)	0.0080 (14)

Geometric parameters (Å, º)

Cu1—C3	1.897 (3)	Cu3—N5	2.008 (3)
Cu1—C1	1.907 (3)	Cu3—N5^v	2.008 (3)
Cu1—N2	1.992 (3)	Cu3—N4	2.028 (3)
Cu2—C2^i	1.899 (4)	Cu3—N4^v	2.028 (3)
Cu2—N3^ii	1.949 (3)	N4—H4C	0.8900
Cu2—N1	1.972 (4)	N4—H4A	0.8900
N1—C1	1.147 (5)	N4—H4B	0.8900
N2—C2	1.136 (4)	N5—H5A	0.8900
N3—C3	1.149 (4)	N5—H5B	0.8900
N3—Cu2^iii	1.949 (3)	N5—H5C	0.8900
C2—Cu2^iv	1.899 (4)
C3—Cu1—C1	132.12 (14)	N5—Cu3—N4^v	91.13 (14)
C3—Cu1—N2	120.18 (13)	N5^v—Cu3—N4^v	88.87 (14)
C1—Cu1—N2	107.69 (14)	N4—Cu3—N4^v	180.0
C2^i—Cu2—N3^ii	130.57 (13)	Cu3—N4—H4C	109.5
C2^i—Cu2—N1	122.80 (14)	Cu3—N4—H4A	109.5
N3^ii—Cu2—N1	106.52 (13)	H4C—N4—H4A	109.5
C1—N1—Cu2	173.4 (4)	Cu3—N4—H4B	109.5
C2—N2—Cu1	158.4 (3)	H4C—N4—H4B	109.5
C3—N3—Cu2^iii	169.9 (3)	H4A—N4—H4B	109.5
N1—C1—Cu1	173.8 (4)	Cu3—N5—H5A	109.5
N2—C2—Cu2^iv	175.5 (4)	Cu3—N5—H5B	109.5
N3—C3—Cu1	175.7 (3)	H5A—N5—H5B	109.5
N5—Cu3—N5^v	180.000 (1)	Cu3—N5—H5C	109.5
N5—Cu3—N4	88.87 (14)	H5A—N5—H5C	109.5
N5^v—Cu3—N4	91.13 (14)	H5B—N5—H5C	109.5
C2^i—Cu2—N1—C1	136 (3)	N2—Cu1—C1—N1	−95 (3)
N3^ii—Cu2—N1—C1	−40 (3)	Cu1—N2—C2—Cu2^iv	−54 (5)
C3—Cu1—N2—C2	175.4 (9)	Cu2^iii—N3—C3—Cu1	43 (6)
C1—Cu1—N2—C2	−3.7 (10)	C1—Cu1—C3—N3	123 (4)
Cu2—N1—C1—Cu1	−42 (6)	N2—Cu1—C3—N3	−56 (5)
C3—Cu1—C1—N1	86 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N4—H4A···N3	0.89	2.61	3.498 (5)	178