Crystal structure of poly[(2,2′-bi­pyridine-κ² N,N′)tetra­kis­(μ-cyanido-κ² N:C)dinickel(II)]

The binuclear coordination polymer consists of two nickel cations with different coordination environments. One has a square-planar environment whereas the other has an octa­hedral environment. Cyanide ligands bridge the cations into a polymeric layer structure.

Abstract

The polymeric title complex, [Ni₂(CN)₄(C₁₀H₈N₂)]_n, was obtained serendipitously under hydro­thermal conditions. The asymmetric unit consists of one half of an [Ni(CN)₄]²⁻ anion with the Ni²⁺ cation situated on an inversion centre, and one half of an [Ni(2,2′-bpy)]²⁺ cation (2,2′-bpy is 2,2′-bi­pyridine), with the second Ni²⁺ cation situated on a twofold rotation axis. The two Ni²⁺ cations exhibit different coordination spheres. Whereas the coordination of the metal in the anion is that of a slightly distorted square defined by four C-bound cyanide ligands, the coordination in the cation is that of a distorted octa­hedron defined by four N-bound cyanide ligands and two N atoms from the chelating 2,2′-bpy ligand. The two different Ni²⁺ cations are alternately bridged by the cyanide ligands, resulting in a two-dimensional structure extending parallel to (010). Within the sheets, π–π inter­actions between pyridine rings of neighbouring 2,2′-bpy ligands, with a centroid-to-centroid distance of 3.687 (3) Å, are present. The crystal packing is dominated by van der Waals forces. A weak C—H⋯N inter­action between adjacent sheets is also observed.

Chemical context  

Coordination metal complexes have been the subject of intensive investigation not only due to their potential application to material science as catalytic, conductive, luminescent, magnetic, porous, chiral or non-linear optical materials (Janiak et al., 2003 ▸), but also because of their intriguing structural diversity (Kong et al., 2008 ▸). The assembly of functional mol­ecular building blocks into crystalline polymeric materials through coordination bonds or other weak inter­actions has many advantages over traditional stepwise syntheses and was demonstrated to be an effective approach to fabricating new materials (Kopotkov et al., 2014 ▸). Using this approach, numerous materials with inter­esting structures and properties have been prepared through the reactions of cyanidometallate building blocks (Cui et al., 2011 ▸; Zhang & Lachgar, 2015 ▸). These compounds show novel functionalities due to strong inter­actions mediated by the linear cyanide bridges. The probably oldest and most inter­esting example is the Prussian blue framework, Fe₄[Fe(CN)₆]₃·14H₂O, and its analogues derived from the assembly of hexa­cyanidometalate anions [M(CN)₆]_n and transition-metal ions (Li et al., 2008 ▸). For instance, cyanide-bridged bimetallic assemblies were obtained from K₃[Fe(CN)₆] as a source of cyanidometalate anions, metal cations, and aromatic nitro­gen-containing ligands. These compounds show inter­esting magnetic and other properties that can be affected through the careful choice of the building-block components (Shen et al., 2014 ▸).

Our own efforts are focused to assemble metallic complexes and the achievement of tuning their properties by crystal engineering of the terminal/bridging ligands. However, the hydro­thermal reaction of Ni(acetate)₂, 2,2′-bi­pyridine and K₃[Fe(CN)₆] did not yield the expected bimetallic system analogous to coordinated iron ions which were reported in literature (Colacio et al., 2003 ▸), but to the serendipitous formation of the polymeric complex (I), [Ni₂(CN)₄(C₁₀H₈N₂)]_n, the crystal structure of which is reported here.

Structural commentary  

The asymmetric unit of the structure of (I) contains formally one half of an [Ni(CN)₄]²⁻ (Ni1) anion, and one half of an [Ni(2,2′-bpy)]²⁺ (Ni2) cation (2,2′-bpy is 2,2′-bi­pyridine). The anion is completed by inversion symmetry, whereas the cation is completed by a twofold rotation axis (Fig. 1 ▸). The Ni1 atom shows a slightly distorted square-planar geometry through coordination by four C atoms (C6 and C6ⁱ, C7 and C7ⁱ) [symmetry code: (i)x + 2, −y, −z + 1] from four cyanide groups, bridging Ni1 to four adjacent Ni2 atoms. The latter exhibits an overall distorted octa­hedral environment, being defined by four N atoms (N3, N3ⁱⁱ, N2ⁱⁱ, N2ⁱⁱⁱ) [symmetry codes: (ii) −x + 1, y, −z + ; (iii) x − 1, y, z] from four [Ni(CN)₄]²⁻ groups, and two N atoms (N1 and N1ⁱⁱ) of one 2,2′-bpy ligand. The corresponding N1—Ni2—N1 bite angle is 77.32 (13)°. Relevant bond lengths involving the two metal cations are compiled in Table 1 ▸. As depicted in Fig. 2 ▸, the cyanide groups bridge nickel cations, forming undulating sheets of composition [Ni₂(CN)₄(2,2′-bpy)₂] parallel to (010), constituted by alternation of Ni1 and Ni2 ions.

Figure 1.

The principal building units of complex (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms have been omitted for clarity. For symmetry codes, see text.

Table 1. Selected bond lengths ().

Ni1C6	1.863(3)	Ni2N1	2.102(2)
Ni1C7	1.871(3)	Ni2N2i	2.116(2)
Ni2N3	2.071(2)

Symmetry code: (i) .

Figure 2.

A view of the polymeric sheet of complex (I). Ni atoms are represented by hatched green spheres, C atoms are grey, N atoms blue and H atoms green.

Supra­molecular features  

Within a sheet, π–π inter­actions between pyridine rings with a centroid-to-centroid distance of 3.687 (3) Å are present. The adhesion of the sheets in the crystal packing is dominated by van der Waals forces. However, a weak non-classical C—H⋯N inter­action (Table 2 ▸) between neighbouring sheets may participate in the stabilization of the crystal packing.

Table 2. Hydrogen-bond geometry (, ).

DHA	DH	HA	D A	DHA
C1H1N3	0.96(3)	2.54(3)	3.129(3)	120(2)

Synthesis and crystallization  

Ni(acetate)₂ (0.159 g, 0.64 mmol), 2,2′-bi­pyridine (0.047 g, 0.3 mmol) and K₃[Fe(CN)₆] (0.21 g, 0.64 mmol) dissolved in aqueous solution of 1M NaCl (8 ml) were added to a 15 ml Teflon-lined autoclave and heated at 433 K for 3 d. The autoclave was then cooled to room temperature. Green block-shaped crystals of (I) deposited on the wall of the container and were collected and air-dried.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. Hydrogen atoms bound to carbon were found in a difference map and were refined with U _iso(H) = 1.2U _eq(C).

Table 3. Experimental details.

Crystal data
Chemical formula	[Ni2(CN)4(C10H8N2)]
M r	377.68
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	293
a, b, c ()	6.519(5), 16.698(5), 12.019(5)
()	90.852(5)
V (3)	1308.2(12)
Z	4
Radiation type	Mo K
(mm1)	2.88
Crystal size (mm)	0.40 0.10 0.06
Data collection
Diffractometer	Siemens SMART CCD
No. of measured, independent and observed [I > 2(I)] reflections	3858, 1156, 1039
R int	0.032
(sin /)max (1)	0.594
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.028, 0.074, 1.10
No. of reflections	1156
No. of parameters	118
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
max, min (e 3)	0.71, 0.40

Computer programs: SMART and SAINT (Bruker, 2007 ▸), SHELXS97, SHELXL97and XP in SHELXTL (Sheldrick, 2008 ▸).

Supplementary Material

CCDC reference: 1058383

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

supplementary crystallographic information

Crystal data

[Ni2(CN)4(C10H8N2)]	F(000) = 760
Mr = 377.68	Dx = 1.918 Mg m−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: -C 2yc	Cell parameters from 3858 reflections
a = 6.519 (5) Å	θ = 1.0–25.0°
b = 16.698 (5) Å	µ = 2.88 mm−1
c = 12.019 (5) Å	T = 293 K
β = 90.852 (5)°	Block, green
V = 1308.2 (12) Å3	0.40 × 0.10 × 0.06 mm
Z = 4

Data collection

Siemens SMART CCD diffractometer	1039 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.032
Graphite monochromator	θmax = 25.0°, θmin = 3.4°
Detector resolution: 9 pixels mm-1	h = −7→7
ω scans	k = −19→16
3858 measured reflections	l = −14→10
1156 independent reflections

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.074	H atoms treated by a mixture of independent and constrained refinement
S = 1.10	w = 1/[σ2(Fo2) + (0.0374P)2 + 0.9543P] where P = (Fo2 + 2Fc2)/3
1156 reflections	(Δ/σ)max < 0.001
118 parameters	Δρmax = 0.71 e Å−3
0 restraints	Δρmin = −0.40 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
Ni1	1.0000	0.0000	0.5000	0.01983 (19)
Ni2	0.5000	0.12867 (3)	0.7500	0.01682 (18)
C6	0.8027 (4)	0.02639 (16)	0.6043 (2)	0.0207 (6)
C1	0.8426 (4)	0.22353 (19)	0.6347 (3)	0.0275 (7)
N3	0.6828 (3)	0.04836 (14)	0.6654 (2)	0.0242 (5)
N1	0.6675 (3)	0.22697 (13)	0.6906 (2)	0.0198 (5)
C5	0.5950 (4)	0.29952 (16)	0.7170 (2)	0.0207 (6)
C7	1.1817 (4)	0.07283 (17)	0.5669 (2)	0.0220 (6)
C4	0.6937 (5)	0.36889 (18)	0.6855 (3)	0.0305 (7)
N2	1.2931 (3)	0.11329 (14)	0.6143 (2)	0.0240 (5)
C3	0.8723 (5)	0.3640 (2)	0.6262 (3)	0.0343 (8)
C2	0.9471 (5)	0.29004 (19)	0.6008 (3)	0.0317 (7)
H2	1.062 (5)	0.284 (2)	0.562 (3)	0.043 (10)*
H4	0.636 (4)	0.4223 (19)	0.711 (3)	0.031 (8)*
H1	0.892 (5)	0.171 (2)	0.616 (3)	0.033 (9)*
H3	0.940 (5)	0.409 (2)	0.608 (3)	0.038 (9)*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Ni1	0.0146 (3)	0.0249 (3)	0.0202 (3)	−0.00164 (17)	0.0062 (2)	−0.0069 (2)
Ni2	0.0146 (3)	0.0183 (3)	0.0177 (3)	0.000	0.0058 (2)	0.000
C6	0.0184 (13)	0.0189 (14)	0.0248 (16)	−0.0028 (11)	0.0033 (12)	−0.0031 (12)
C1	0.0244 (15)	0.0288 (17)	0.0297 (18)	−0.0016 (12)	0.0091 (13)	−0.0005 (13)
N3	0.0212 (12)	0.0240 (13)	0.0275 (15)	0.0002 (9)	0.0066 (11)	−0.0042 (11)
N1	0.0186 (11)	0.0217 (12)	0.0192 (13)	−0.0020 (9)	0.0026 (9)	0.0021 (10)
C5	0.0217 (14)	0.0197 (15)	0.0208 (16)	−0.0016 (10)	−0.0013 (12)	0.0022 (11)
C7	0.0176 (13)	0.0254 (15)	0.0233 (16)	0.0018 (11)	0.0084 (12)	−0.0024 (12)
C4	0.0314 (17)	0.0264 (17)	0.034 (2)	−0.0035 (12)	0.0005 (14)	0.0030 (13)
N2	0.0187 (12)	0.0289 (13)	0.0245 (15)	−0.0021 (10)	0.0054 (10)	−0.0033 (11)
C3	0.0331 (18)	0.0323 (19)	0.037 (2)	−0.0125 (14)	0.0004 (15)	0.0098 (15)
C2	0.0241 (16)	0.0390 (19)	0.0323 (19)	−0.0083 (13)	0.0084 (14)	0.0054 (15)

Geometric parameters (Å, º)

Ni1—C6i	1.863 (3)	C1—C2	1.368 (4)
Ni1—C6	1.863 (3)	C1—H1	0.95 (3)
Ni1—C7i	1.871 (3)	N1—C5	1.340 (3)
Ni1—C7	1.871 (3)	C5—C4	1.381 (4)
Ni2—N3ii	2.071 (2)	C5—C5ii	1.480 (5)
Ni2—N3	2.071 (2)	C7—N2	1.139 (4)
Ni2—N1	2.102 (2)	C4—C3	1.377 (5)
Ni2—N1ii	2.102 (2)	C4—H4	1.02 (3)
Ni2—N2iii	2.116 (2)	N2—Ni2v	2.116 (2)
Ni2—N2iv	2.116 (2)	C3—C2	1.364 (5)
C6—N3	1.140 (4)	C3—H3	0.90 (4)
C1—N1	1.335 (4)	C2—H2	0.89 (4)
C6i—Ni1—C6	180.0	N1—C1—C2	123.3 (3)
C6i—Ni1—C7i	89.76 (12)	N1—C1—H1	117 (2)
C6—Ni1—C7i	90.24 (12)	C2—C1—H1	120 (2)
C6i—Ni1—C7	90.24 (12)	C6—N3—Ni2	158.3 (2)
C6—Ni1—C7	89.76 (12)	C1—N1—C5	117.7 (2)
C7i—Ni1—C7	180.00 (13)	C1—N1—Ni2	126.15 (19)
N3ii—Ni2—N3	99.29 (14)	C5—N1—Ni2	116.02 (18)
N3ii—Ni2—N1	167.94 (10)	N1—C5—C4	121.7 (3)
N3—Ni2—N1	91.91 (10)	N1—C5—C5ii	115.32 (15)
N3ii—Ni2—N1ii	91.91 (10)	C4—C5—C5ii	122.95 (18)
N3—Ni2—N1ii	167.94 (10)	N2—C7—Ni1	174.8 (3)
N1—Ni2—N1ii	77.32 (13)	C3—C4—C5	119.6 (3)
N3ii—Ni2—N2iii	86.28 (10)	C3—C4—H4	122.1 (18)
N3—Ni2—N2iii	84.71 (10)	C5—C4—H4	118.2 (18)
N1—Ni2—N2iii	99.29 (9)	C7—N2—Ni2v	148.4 (2)
N1ii—Ni2—N2iii	91.61 (9)	C2—C3—C4	118.5 (3)
N3ii—Ni2—N2iv	84.71 (10)	C2—C3—H3	122 (2)
N3—Ni2—N2iv	86.28 (10)	C4—C3—H3	120 (2)
N1—Ni2—N2iv	91.61 (9)	C3—C2—C1	119.1 (3)
N1ii—Ni2—N2iv	99.29 (9)	C3—C2—H2	122 (2)
N2iii—Ni2—N2iv	166.06 (13)	C1—C2—H2	119 (2)
N3—C6—Ni1	174.8 (2)
N3ii—Ni2—N3—C6	173.2 (7)	N3—Ni2—N1—C5	174.8 (2)
N1—Ni2—N3—C6	−11.3 (6)	N1ii—Ni2—N1—C5	0.33 (14)
N1ii—Ni2—N3—C6	15.2 (9)	N2iii—Ni2—N1—C5	89.9 (2)
N2iii—Ni2—N3—C6	87.8 (6)	N2iv—Ni2—N1—C5	−98.8 (2)
N2iv—Ni2—N3—C6	−102.8 (6)	C1—N1—C5—C4	1.7 (4)
C2—C1—N1—C5	−1.9 (5)	Ni2—N1—C5—C4	178.3 (2)
C2—C1—N1—Ni2	−178.2 (2)	C1—N1—C5—C5ii	−177.6 (3)
N3ii—Ni2—N1—C1	149.5 (4)	Ni2—N1—C5—C5ii	−0.9 (4)
N3—Ni2—N1—C1	−8.8 (2)	N1—C5—C4—C3	−0.6 (5)
N1ii—Ni2—N1—C1	176.7 (3)	C5ii—C5—C4—C3	178.6 (3)
N2iii—Ni2—N1—C1	−93.7 (2)	C5—C4—C3—C2	−0.3 (5)
N2iv—Ni2—N1—C1	77.5 (2)	C4—C3—C2—C1	0.1 (5)
N3ii—Ni2—N1—C5	−26.9 (5)	N1—C1—C2—C3	1.0 (5)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1···N3	0.96 (3)	2.54 (3)	3.129 (3)	120 (2)