A cyanide-bridged heterometallic coordination polymer constructed from square-planar [Ni(CN)₄]^2-: synthesis, crystal structure, thermal decomposition, electron paramagnetic resonance (EPR) spectrum and magnetic properties

Square-planar complexes are commonly formed by transition metal ions having a d⁸ electron configuration. Planar cyano­metallate anions have been used extensively as design elements in supra­molecular coordination systems. In particular, square-planar tetra­cyano­metallate(II) ions, i.e. [M(CN)₄]^2- (M^II = Ni, Pd or Pt), are used as good building blocks for bimetallic Hofmann-type assemblies and their analogues. Square-planar tetra­cyano­nickellate(II) com­plexes have been extensively developed with N-donor groups as additional co-ligands, but studies of these systems using O-donor ligands are scarce. A new cyanide-bridged Cu^II-Ni^II heterometallic compound, poly[[di­aqua­tetra-[mu]₂-cyanido-[kappa]⁸C:N-nickel(II)copper(II)] monohydrate], {[Cu^IINi^II(CN)₄(H₂O)₂]·H₂O}_n, has been synthesized and characterized by X-ray single-crystal diffraction analyses, vibrational spectroscopy (FT-IR), thermal analysis, electron paramagnetic resonance (EPR) and magnetic moment measurements. The structural analysis revealed that it has a two-dimensional grid-like structure built up of cationic [Cu(H₂O)₂]²⁺ and anionic [Ni(CN)₄]^2- units connected through bridging cyanide ligands. The overall three-dimensional supra­molecular network is expanded by a combination of inter­layer O-H...N and intra­layer O-H...O hydrogen-bond inter­actions. The first decomposition reactions take place at 335 K under a static air atmosphere, which illustrates the existence of guest water mol­ecules in the inter­layer spaces. The electron paramagnetic resonance (EPR) spectrum confirms that the Cu^II cation has an axial coordination symmetry and that the unpaired electrons occupy the d orbital. In addition, magnetic investigations showed that anti­ferromagnetic inter­actions exist in the Cu^II atoms through the diamagnetic [Ni(CN)₄]^2- ion.

Computing details

Data collection: SMART (Bruker, 2002); cell refinement: SMART (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg,2005); software used to prepare material for publication: publCIF (Westrip, 2010) and PLATON (Spek, 2009).

Poly[[diaquatetra-µ₂-cyanido-κ⁸C:N-copper(II)nickel(II)] monohydrate]

Crystal data

[CuNi(CN)4(H2O)2]·H2O	Dx = 2.089 Mg m^−3
Mr = 280.38	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Imma	Cell parameters from 1022 reflections
a = 14.1746 (7) Å	θ = 2.7–25.9°
b = 7.0724 (4) Å	µ = 4.48 mm^−1
c = 8.8940 (13) Å	T = 293 K
V = 891.61 (15) Å^3	Block, blue
Z = 4	0.28 × 0.27 × 0.25 mm
F(000) = 556

Data collection

Bruker APEX CCD diffractometer	451 reflections with I > 2σ(I)
φ and ω scans	Rint = 0.020
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θmax = 26.4°, θmin = 2.7°
Tmin = 0.124, Tmax = 0.213	h = −17→9
1152 measured reflections	k = −5→8
520 independent reflections	l = −11→5

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)] = 0.034	Hydrogen site location: difference Fourier map
wR(F^2) = 0.102	H-atom parameters constrained
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0609P)^2 + 3.4486P] where P = (Fo^2 + 2Fc^2)/3
520 reflections	(Δ/σ)max < 0.001
40 parameters	Δρmax = 0.77 e Å^−3
0 restraints	Δρmin = −0.46 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
Ni1	0.5000	0.2500	0.68692 (12)	0.0217 (3)
Cu1	0.2500	0.7500	0.7500	0.0247 (3)
C1	0.4065 (3)	0.4353 (5)	0.6935 (5)	0.0265 (8)
N1	0.3484 (2)	0.5458 (5)	0.7075 (4)	0.0328 (8)
O1W	0.2928 (3)	0.7500	0.9799 (6)	0.0517 (13)
H1WA	0.2557	0.8403	1.0346	0.078*
O2W	0.5000	0.7500	0.9706 (10)	0.098 (4)
H2WA	0.5447	0.7500	0.9070	0.147*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni1	0.0089 (5)	0.0142 (5)	0.0418 (7)	0.000	0.000	0.000
Cu1	0.0131 (5)	0.0181 (5)	0.0430 (7)	0.000	0.0009 (4)	0.000
C1	0.0174 (16)	0.0199 (17)	0.042 (2)	−0.0013 (15)	0.0025 (15)	0.0013 (17)
N1	0.0186 (15)	0.0232 (16)	0.057 (2)	0.0043 (14)	0.0025 (15)	0.0006 (17)
O1W	0.031 (2)	0.084 (4)	0.040 (3)	0.000	−0.003 (2)	0.000
O2W	0.038 (4)	0.200 (12)	0.056 (6)	0.000	0.000	0.000

Geometric parameters (Å, º)

Ni1—C1^i	1.865 (4)	Cu1—N1^vi	2.043 (3)
Ni1—C1^ii	1.865 (4)	Cu1—O1W	2.133 (5)
Ni1—C1^iii	1.865 (4)	Cu1—O1W^vi	2.133 (5)
Ni1—C1	1.865 (4)	C1—N1	1.142 (6)
Cu1—N1	2.043 (3)	O1W—H1WA	0.9599
Cu1—N1^iv	2.043 (3)	O2W—H2WA	0.8500
Cu1—N1^v	2.043 (3)
C1^i—Ni1—C1^ii	176.4 (3)	N1—Cu1—O1W	89.04 (14)
C1^i—Ni1—C1^iii	89.3 (2)	N1^iv—Cu1—O1W	89.04 (14)
C1^ii—Ni1—C1^iii	90.6 (2)	N1^v—Cu1—O1W	90.96 (14)
C1^i—Ni1—C1	90.6 (2)	N1^vi—Cu1—O1W	90.96 (14)
C1^ii—Ni1—C1	89.3 (2)	N1—Cu1—O1W^vi	90.96 (14)
C1^iii—Ni1—C1	176.4 (3)	N1^iv—Cu1—O1W^vi	90.96 (14)
N1—Cu1—N1^iv	89.98 (19)	N1^v—Cu1—O1W^vi	89.04 (14)
N1—Cu1—N1^v	90.02 (19)	N1^vi—Cu1—O1W^vi	89.04 (14)
N1^iv—Cu1—N1^v	180.0	O1W—Cu1—O1W^vi	180.0
N1—Cu1—N1^vi	180.00 (19)	N1—C1—Ni1	175.4 (4)
N1^iv—Cu1—N1^vi	90.02 (19)	C1—N1—Cu1	174.9 (4)
N1^v—Cu1—N1^vi	89.98 (19)	Cu1—O1W—H1WA	109.2

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2W—H2WA···O1W^vii	0.85	2.39	2.938 (4)	123
O1W—H1WA···N1^viii	0.96	2.58	3.532 (5)	172

Symmetry codes: (vii) −x+1, −y+3/2, z; (viii) −x+1/2, y+1/2, z+1/2.