A novel three-dimensional copper(I) cyanide coordination polymer constructed from various bridging ligands: synthesis, crystal structure and characterization

The cyanide ligand can act as a strong σ-donor and an effective π-electron acceptor that exhibits versatile bridging abilities, such as terminal, μ₂-C:N, μ₃-C:C:N and μ₄-C:C:N:N modes. These ligands play a key role in the formation of various copper(I) cyanide systems, including one-dimensional (1D) chains, two-dimensional (2D) layers and three-dimensional (3D) frameworks. According to the literature, numerous coordination polymers based on terminal, μ₂-C:N and μ₃-C,C,N bridging modes have been documented so far. However, systems based on the μ₄-C:C:N:N bridging mode are relatively rare. In this work, a novel cyanide-bridged 3D Cu^I coordination framework, namely poly[(μ₂-2,2′-bi­imidazole-κ²N³:N^3′)(μ₄-cyanido-κ⁴C:C:N:N)(μ₂-cyanido-κ²C:N)dicopper(I)], [Cu₂(CN)₂(C₆H₆N₄)]_n, (I), was synthesized hydro­thermally by reaction of environmentally friendly K₃[Fe(CN)₆], CuCl₂·2H₂O and 2,2′-bi­imidazole (H₂biim). It should be noted that cyanide ligands may act as reducing agents to reduce Cu^II to Cu^I under hydrothermal conditions. Compound (I) contains diverse types of bridging ligands, such as μ₄-C:C:N:N-cyanide, μ₂-C:N-cyanide and μ₂-bi­imidazole. Inter­estingly, the [Cu₂] dimers are bridged by rare μ₄-C:C:N:N-mode cyanide ligands giving rise to the first example of a 1D dimeric {[Cu₂(μ₄-C:C:N:N)]ⁿ⁺}_n infinite chain. Furthermore, adjacent dimer-based chains are linked by μ₂-C:N bridging cyanide ligands, generating a neutral 2D wave-like (4,4) layer structure. Finally, the 2D layers are joined together via bidentate bridging H₂biim to create a 3D cuprous cyanide network. This arrangement leads to a systematic variation in dimensionality from 1D chain→2D sheet→3D framework by different types of bridging ligands. Compound (I) was further characterized by thermal analysis, solid-state UV–Vis diffuse-reflectance and photoluminescence studies. The solid-state UV–Vis diffuse-reflectance spectra show that com­pound (I) is a wide-gap semiconductor with band gaps of 3.18 eV. The photoluminescence study shows a strong blue–green photoluminescence at room temperature, which may be associated with metal-to-ligand charge transfer.

Computing details

Data collection: SMART (Bruker, 2003); cell refinement: SMART (Bruker, 2003); data reduction: SAINT (Bruker, 2003); program(s) used to solve structure: SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2001); software used to prepare material for publication: SHELXL (Sheldrick, 2008) and publCIF (Westrip,2010).

Poly[(µ₂-2,2'-biimidazole-κ²N³:N^3')(µ₄-cyanido-κ⁴C:C:N:N)(µ₂-cyanido-κ²C:N)dicopper(I)]

Crystal data

[Cu2(CN)2(C6H6N4)]	F(000) = 616
Mr = 313.28	Dx = 2.177 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 16.687 (4) Å	Cell parameters from 1115 reflections
b = 4.5071 (8) Å	θ = 2.5–25.3°
c = 13.933 (3) Å	µ = 4.43 mm^−1
β = 114.21 (3)°	T = 293 K
V = 955.7 (4) Å^3	Block, red
Z = 4	0.18 × 0.10 × 0.07 mm

Data collection

Bruker APEXII CCD area-detector diffractometer	801 reflections with I > 2σ(I)
φ and ω scans	Rint = 0.022
Absorption correction: multi-scan (SADABS; Bruker, 2003)	θmax = 26.4°, θmin = 2.7°
Tmin = 0.5, Tmax = 0.78	h = −20→19
1719 measured reflections	k = −5→4
980 independent reflections	l = −17→15

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.057	H-atom parameters constrained
wR(F^2) = 0.164	w = 1/[σ^2(Fo^2) + (0.0579P)^2 + 9.5332P] where P = (Fo^2 + 2Fc^2)/3
S = 1.21	(Δ/σ)max < 0.001
980 reflections	Δρmax = 1.09 e Å^−3
74 parameters	Δρmin = −0.61 e Å^−3

Special details

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.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
N3	0.5098 (4)	0.4906 (15)	0.4665 (6)	0.0371 (17)	0.5
C2	0.5000	1.101 (2)	0.2500	0.038 (2)	0.5
N2	0.5000	1.101 (2)	0.2500	0.038 (2)	0.5
C1	0.5000	0.850 (2)	0.2500	0.037 (2)	0.5
N1	0.5000	0.850 (2)	0.2500	0.037 (2)	0.5
C3	0.5098 (4)	0.4906 (15)	0.4665 (6)	0.0371 (17)	0.5
C4	0.7974 (5)	0.6431 (18)	0.3683 (6)	0.0358 (16)
H4	0.8341	0.7396	0.3431	0.043*
C5	0.7488 (4)	0.3561 (15)	0.4597 (5)	0.0277 (14)
C6	0.7094 (5)	0.6690 (18)	0.3310 (6)	0.0359 (16)
H6	0.6748	0.7900	0.2753	0.043*
N4	0.6784 (4)	0.4872 (12)	0.3885 (4)	0.0269 (13)
N5	0.8224 (4)	0.4459 (14)	0.4511 (5)	0.0356 (14)
H5	0.8752	0.3907	0.4899	0.043*
Cu1	0.54642 (6)	0.4733 (2)	0.35116 (7)	0.0379 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N3	0.027 (3)	0.052 (4)	0.030 (3)	0.000 (3)	0.009 (3)	−0.003 (3)
C2	0.030 (5)	0.037 (5)	0.047 (6)	0.000	0.017 (5)	0.000
N2	0.030 (5)	0.037 (5)	0.047 (6)	0.000	0.017 (5)	0.000
C1	0.032 (5)	0.026 (5)	0.055 (6)	0.000	0.020 (5)	0.000
N1	0.032 (5)	0.026 (5)	0.055 (6)	0.000	0.020 (5)	0.000
C3	0.027 (3)	0.052 (4)	0.030 (3)	0.000 (3)	0.009 (3)	−0.003 (3)
C4	0.034 (4)	0.040 (4)	0.035 (4)	−0.005 (3)	0.015 (3)	0.003 (3)
C5	0.030 (3)	0.032 (4)	0.022 (3)	0.002 (3)	0.012 (3)	−0.002 (3)
C6	0.040 (4)	0.042 (4)	0.026 (3)	0.006 (3)	0.013 (3)	0.004 (3)
N4	0.021 (3)	0.037 (3)	0.022 (3)	0.000 (2)	0.007 (2)	0.000 (2)
N5	0.023 (3)	0.047 (4)	0.036 (3)	0.002 (3)	0.011 (3)	0.006 (3)
Cu1	0.0311 (6)	0.0486 (7)	0.0342 (6)	0.0022 (4)	0.0134 (4)	0.0039 (4)

Geometric parameters (Å, º)

N3—Cu1	1.940 (7)	C5—N5	1.345 (9)
C2—C1	1.135 (14)	C5—C5^iv	1.463 (13)
C2—Cu1^i	2.121 (8)	C6—N4	1.386 (9)
C2—Cu1^ii	2.121 (8)	C6—H6	0.9300
C1—Cu1^iii	2.138 (8)	N4—Cu1	2.046 (6)
C1—Cu1	2.138 (8)	N5—H5	0.8600
C4—C6	1.347 (10)	Cu1—N2^v	2.121 (8)
C4—N5	1.378 (10)	Cu1—C2^v	2.121 (8)
C4—H4	0.9300	Cu1—Cu1^iii	2.601 (2)
C5—N4	1.326 (9)
C1—C2—Cu1^i	142.19 (17)	C5—N5—C4	107.1 (6)
C1—C2—Cu1^ii	142.19 (17)	C5—N5—H5	126.4
Cu1^i—C2—Cu1^ii	75.6 (3)	C4—N5—H5	126.4
C2—C1—Cu1^iii	142.53 (16)	N3—Cu1—N4	117.4 (3)
C2—C1—Cu1	142.53 (16)	N3—Cu1—N2^v	115.4 (2)
Cu1^iii—C1—Cu1	74.9 (3)	N4—Cu1—N2^v	104.78 (17)
C6—C4—N5	106.7 (6)	N3—Cu1—C2^v	115.4 (2)
C6—C4—H4	126.6	N4—Cu1—C2^v	104.78 (17)
N5—C4—H4	126.6	N2^v—Cu1—C2^v	0.0 (3)
N4—C5—N5	111.1 (6)	N3—Cu1—C1	111.2 (2)
N4—C5—C5^iv	127.0 (8)	N4—Cu1—C1	101.80 (17)
N5—C5—C5^iv	121.8 (8)	N2^v—Cu1—C1	104.7 (2)
C4—C6—N4	109.4 (7)	C2^v—Cu1—C1	104.7 (2)
C4—C6—H6	125.3	N3—Cu1—Cu1^iii	130.4 (2)
N4—C6—H6	125.3	N4—Cu1—Cu1^iii	112.11 (17)
C5—N4—C6	105.7 (6)	N2^v—Cu1—Cu1^iii	52.19 (17)
C5—N4—Cu1	135.1 (5)	C2^v—Cu1—Cu1^iii	52.19 (17)
C6—N4—Cu1	119.3 (5)	C1—Cu1—Cu1^iii	52.53 (16)
Cu1^i—C2—C1—Cu1^iii	180.000 (4)	N5—C5—N4—Cu1	−179.6 (5)
Cu1^ii—C2—C1—Cu1^iii	0.000 (9)	C5^iv—C5—N4—Cu1	−0.6 (13)
Cu1^i—C2—C1—Cu1	−0.001 (9)	C4—C6—N4—C5	0.2 (8)
Cu1^ii—C2—C1—Cu1	179.999 (3)	C4—C6—N4—Cu1	−179.7 (5)
N5—C4—C6—N4	−0.7 (9)	N4—C5—N5—C4	−0.9 (8)
N5—C5—N4—C6	0.5 (8)	C5^iv—C5—N5—C4	180.0 (8)
C5^iv—C5—N4—C6	179.5 (9)	C6—C4—N5—C5	1.0 (8)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N5—H5···N3^iv	0.86	2.46	3.223 (9)	148

Symmetry code: (iv) −x+3/2, −y+1/2, −z+1.