Ni(bipy)₂Ni(CN)₄, a new type of one-dimensional square tetra­cyano complex

The one-dimensional structure of catena-poly­[[bis(2,2'-bi­pyri­dyl-1[kappa]²N,N')-[mu]-cyano-1:2[kappa]²N:C-di­cyano-2[kappa]²C-di­nickel(II)]-[mu]-cyano-C:N], [Ni₂(CN)₄(C₁₀H₈N₂)₂]_n, consists of infinite zigzag chains running parallel to the c axis. The chains are composed of paramagnetic [Ni(bipy)₂]²⁺ cations (bricks; nickel on a twofold axis) linked by diamagnetic [Ni(CN)₄]^2- anions (mortar; nickel on an inversion center) via bridging cyano groups. The bridging cyano groups occupy cis positions in the cation and trans positions in the anion, giving rise to a new previously unknown CT-type chain (i.e. cis-trans-type) among square tetra­cyano complexes. The coordination polyhedron of the paramagnetic Ni atom (twofold symmetry) is a slightly deformed octahedron with the two Ni-N(bipy) bonds in cis positions being somewhat longer [2.112 (3) Å] than the remaining four Ni-N bonds with a mean value of 2.065 (6) Å. The bond distances and angles in the anion have typical values.

S1. Comment

One-dimensional (one-dimensional) magnetic materials are of current interest due to their interesting magnetic properties [Dagotto, 1996; Chen & Suslick, 1993; Orendáč et al., 1995; Delhaes & Drillon, 1987). The synthetic strategy of such materials can be based on the use of the so-called `brick and mortar' method (Willett et al., 1993), where paramagnetic entities (bricks) are linked by suitable bridging units (mortar). Square-planar tetracyano complexes are suitable bridging units due to the possibility of using cyano groups to link metal atoms. Stereochemical considerations and literature data (Iwamoto, 1996) indicate that various types of one-dimensional structures may be formed. As examples of different types of one-dimensional structures, we can mention Ni(en)₂Ni(CN)₄ exhibiting a TT-type chain structure [two bridging cyano groups occupy trans (T) positions in both the cation and anion; Černák, Chomič et al., 1988], diamagnetic Cd(en)₂Ni(CN)₄ (two polymorphs) forming CC-type chains (Yuge et al., 1995), Ni(en)₂Ni(CN)₄.nH₂O with more complicated CCTC-type chains (periodicity doubled; Černák et al., 1990) and [Eu(dmf)₄Ni(CN)₄] exhibiting a ladder-like one-dimensional structure with three bridging cyano groups (Knoeppel & Shore, 1997). To date, no crystal structures with CT– or TC-type chains containing square-planar tetracyano complexes as bridging units have been reported.

The results of crystal structure analyses of the one-dimensional compounds [Ni(bipy)₂N₃]ClO₄ and [Ni(bipy)₂N₃]PF₆ (Urtiaga et al., 1994) have shown that the presence of two bulky 2,2'-bipyridine (bipy) ligands in the nickel octahedral coordination sphere leads to zigzag-type chains. CT-type chains were found in [Cu(bipy)₂Ag₂(CN)₄]·H₂O, a compound with linear dicyanoargentate anions (Černák et al., 1993). These results indicate that the Ni(bipy)₂Ni(CN)₄ compound, (I), initially described a long time ago (Feigl et al., 1945), may be a good candidate for a CT (or CC) type chain. The results of its crystal structure analysis are reported here and are discussed with respect to similar one-dimensional structures containing square-planar tetracyano complex anions.

The centrosymmetric structure of the title compound consists of zigzag-type chains. The chains are composed of paramagnetic [Ni(bipy)₂]²⁺ cations (bricks), which are linked by diamagnetic [Ni(CN)₄]²⁻ anions (mortar). The bridging cyano groups occupy cis positions in the cation, thereby completing the chromophore to NiN₄N₂. On the other hand, they occupy trans positions in the anion giving rise to a CT-type chain not yet found among square tetracyano complexes. Only van der Waals forces operate between the chains, so the packing of the chains is directed mainly by geometric requirements. The shortest distance between two atoms of neighbouring chains is 2.42 (1) Å [H11A···H4A(x − 0.5, y − 0.5, 0.5 − z)], which is in line with the sum of the van der Waals radii of H atoms (2.40 Å; Taylor & Kennard, 1982). The shortest distance between two paramagnetic Ni atoms is 8.681 (1) Å [e.g. Ni2···Ni2(x − 0.5, y − 0.5, 0.5 − z)], but there is no effective bridging between these atoms. Two paramagnetic Ni atoms (Ni2) within the chain are separated by 10.116 (2) Å and the –N—C—Ni—C—N– five-atom bridge may serve as an exchange path for the observed superexchange-type interaction (Orendáč et al., 2000). The bridge is quite linear, where the highest deviation from linearity is represented by the Ni2—-N2—C2—(Ni1) angle [171.1 (3)°]. Similar, but positively charged chains, were found in the [Cu(bipy)₂Ag₂(CN)₄]·H₂O compound with linear dicyanoargentate anions, where the positive charge of the chains is counterbalanced by the negative charge of free dicyanoargentate anions (Černák et al., 1993). The same type of five-atom bridges were found in many other tetracyanonickellates or dicyanoargentates (Iwamoto, 1996).

The Ni atom in the anion (Ni1) lies on a symmetry center, so the NiC₄ chromophore is exactly planar. The geometrical parameters (bond distances and angles) have typical values and are similar to those found in other tetracyanonickellates (Černák, Dunaj-Jurčo et al., 1988).

The central Ni atom in the cation exhibits a hexacoordination in the cis-NiN₄N₂ form and lies on a twofold symmetry. If we assign the coordination sites letters A to F, with A and D being axial sites, the bridging cyano groups occupy neighboring positions E and F. Geometrical considerations indicate two possible arrangements of the chelate bipy ligands: they can be bound in positions A–B and C–D, or in positions A–C and B–D, respectively. Both orientations in the form of disorder were found to a different extent in various crystals.

The shape of the nickel coordination sphere is significant in connection with the zero-field splitting of the ³A₂ ground state as an important parameter in the interpretation of the magnetic properties. In the present compound, the nickel coordination sphere exhibits rather unusual deformation from the ideal octahedral one; four Ni—N coordination bonds [two Ni—N(C) and two among four Ni—N(bipy)] exhibit the same value within experimental error (3σ) with a mean value of 2.065 (6) Å, the remaining two Ni—N(bipy) bonds (Ni2—N4) in the trans positions with respect to the bridging cyano groups are somewhat longer with a distance of 2.112 (3) Å. Similar elongation of the trans positioned Ni—N(bipy) bonds (2.114 and 2.091 Å) versus cis-positioned Ni—N(bipy) bonds (2.083 and 2.066 Å) was observed in the [Ni(bipy)₂(N₃)₂]·H₂O compound (Urtiaga et al., 1995). On the other hand, in the Ni(en)₂Ni(CN)₄.nH₂O compound with en as chelating ligands the Ni—N(en) bonds are almost the same within s.u. [2.11 (1) and 2.12 (1) Å] regardless to their positions to the bridging cyano groups (Černák et al., 1990). The normalized bite value (b = 1.272; Kepert, 1982), and the bond distances and angles in the bipy ligands have standard values (Wada et al., 1976).

S2. Experimental

Single crystals of the title compound in the form of violet prisms suitable for X-ray studies were crystallized from a solution formed by the following procedure. Ni(NO₃)₂ solution (10 ml of 0.1 M) (1 mmol), 500 ml of water and 10 ml of 0.1M K₂Ni(CN)₄ solution (1 mmol) were mixed and yielded a nickel cyanide precipitate, which was immediately dissolved by addition of a concentrated solution of ammonia (25%). To the resultant solution, 0.3124 g of bipy (2 mmol) in 20 ml of methanol was added. Finally, the solution was filtered and left for crystallization in an Erlenmayer flask at room temperature (291 K). At first big needles of Ni(bipy)₃][Ni(CN)₄]. 6H₂O.1/2bipy (Černák et al., 1996; Akyüz et al., 1996) appeared, and they dissolved after a short time. Small single crystals of the title compound suitable for X-ray work formed after one month.

The IR spectrum was measured on a Specord M40 spectrometer. ν(CH): 3112 (vw), 3080 (bvw); ν(CN): 2148 (versus), 2120 (versus); ρ(NH): 1600 (versus); \v(C═C): 1576 (m), 1568 (m); δ(Ni—CN): 428 (s), 418 (s).

S3. Refinement

The H atoms were placed in idealized positions and were refined riding on their parent atoms. A C—H distance of 0.95 Å was used for all Csp² atoms. The H-atom displacement parameters were set at 1.2U_eq of the parent C atom. Full data collection details are reported elsewhere (Abboud et al., 1997). Four data sets using four different crystals were collected for this structure and each solution revealed the presence of disorder in the position of the two bipyridine ligands. The data reported here has the least disorder (less than 5%) and it was not possible to resolve.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART (Bruke, 1998); data reduction: SAINT and SHELXTL (Bruker, 1998); program(s) used to solve structure: SHELXTL (Bruker, 1998); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. Displacement ellipsoids (30% probability) drawing of the title compound displaying its one-dimensional character along with atom-numbering scheme. [Symmetry codes: (i) −x, 2 − y, −z; (ii) −x, y, 1/2 − z; (iii) −x, y, −1/2 − z; (iv) −x, 2 − y, 1 − z.

catena-poly[[bis(2,2'-bipyridyl-1κ²N,N')-µ-cyano-1:2κ²N:C-dicyano- 2κ²C-dinickel(II)]-µ-cyano-C:N]

Crystal data

[Ni2(CN)4(C10H8N2)2]	Dx = 1.572 Mg m^−3
Mr = 533.87	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbcn	Cell parameters from 3962 reflections
a = 14.067 (1) Å	θ = 2.5–27.5°
b = 10.1759 (7) Å	µ = 1.70 mm^−1
c = 15.755 (1) Å	T = 173 K
V = 2255.2 (3) Å^3	Platelets, light violet
Z = 4	0.19 × 0.19 × 0.06 mm
F(000) = 1088

Data collection

SMART platform/CCD diffractometer	2591 independent reflections
Radiation source: normal-focus sealed tube	1498 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.056
ω scans	θmax = 27.5°, θmin = 2.5°
Absorption correction: face-indexed (gaussian) ?	h = −17→18
Tmin = 0.684, Tmax = 0.911	k = −13→6
13421 measured reflections	l = −20→20

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)] = 0.046	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.142	Riding
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0754P)^2 + 1.2512P] where P = (Fo^2 + 2Fc^2)/3
2591 reflections	(Δ/σ)max < 0.001
156 parameters	Δρmax = 1.19 e Å^−3
0 restraints	Δρmin = −0.39 e Å^−3

Special details

Experimental. A hemisphere of frames, 0.3° in ω, was collected. The first 50 frames were remeasured at the end of data collection to monitor instrument and crystal stability. Full data collection details are reported elsewhere (Abboud et al., 1997).

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	0.0000	1.0000	0.0000	0.0358 (2)
C1	−0.1310 (4)	0.9967 (4)	0.0161 (3)	0.0487 (12)
N1	−0.2120 (3)	0.9886 (4)	0.0280 (3)	0.0705 (13)
C2	0.0104 (3)	0.8965 (3)	0.0977 (2)	0.0374 (9)
N2	0.0122 (2)	0.8285 (3)	0.1555 (2)	0.0379 (8)
Ni2	0.0000	0.68814 (6)	0.2500	0.02755 (19)
N3	0.1456 (2)	0.6696 (3)	0.25754 (19)	0.0373 (7)
N4	0.0246 (3)	0.5378 (3)	0.1602 (2)	0.0392 (9)
C3	0.2020 (3)	0.7405 (5)	0.3074 (3)	0.0560 (12)
H3A	0.1748	0.8070	0.3420	0.067*
C4	0.3003 (4)	0.7203 (7)	0.3104 (4)	0.0808 (18)
H4A	0.3399	0.7714	0.3464	0.097*
C5	0.3382 (4)	0.6218 (7)	0.2584 (4)	0.0789 (18)
H5A	0.4046	0.6051	0.2591	0.095*
C6	0.2808 (4)	0.5501 (6)	0.2071 (4)	0.0706 (15)
H6A	0.3067	0.4844	0.1710	0.085*
C7	0.1838 (3)	0.5742 (4)	0.2079 (3)	0.0475 (11)
C8	0.1153 (3)	0.4985 (4)	0.1559 (3)	0.0477 (11)
C9	0.1415 (4)	0.3923 (5)	0.1049 (3)	0.0660 (15)
H9A	0.2056	0.3634	0.1021	0.079*
C10	0.0703 (5)	0.3299 (5)	0.0581 (3)	0.0773 (19)
H10A	0.0863	0.2574	0.0228	0.093*
C11	−0.0191 (4)	0.3704 (5)	0.0620 (3)	0.0686 (17)
H11A	−0.0672	0.3280	0.0297	0.082*
C12	−0.0412 (4)	0.4761 (5)	0.1144 (3)	0.0548 (13)
H12A	−0.1053	0.5052	0.1175	0.066*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni1	0.0625 (5)	0.0245 (3)	0.0203 (3)	−0.0033 (4)	−0.0065 (3)	0.0036 (2)
C1	0.070 (3)	0.037 (2)	0.038 (3)	0.002 (2)	−0.009 (2)	0.010 (2)
N1	0.066 (3)	0.084 (3)	0.061 (3)	0.010 (2)	−0.005 (2)	0.019 (2)
C2	0.062 (3)	0.0259 (17)	0.0243 (17)	−0.0039 (19)	−0.0022 (19)	−0.0006 (14)
N2	0.060 (2)	0.0297 (15)	0.0235 (15)	−0.0055 (15)	−0.0073 (15)	0.0013 (12)
Ni2	0.0443 (4)	0.0217 (3)	0.0167 (3)	0.000	0.0015 (3)	0.000
N3	0.0479 (19)	0.0328 (16)	0.0313 (17)	−0.0019 (13)	−0.0005 (16)	0.0049 (15)
N4	0.067 (3)	0.0285 (16)	0.0223 (15)	−0.0076 (15)	0.0136 (15)	−0.0003 (14)
C3	0.057 (3)	0.056 (3)	0.055 (3)	−0.006 (2)	−0.011 (2)	0.008 (2)
C4	0.061 (4)	0.097 (5)	0.085 (4)	−0.020 (3)	−0.022 (3)	0.025 (4)
C5	0.047 (3)	0.107 (5)	0.082 (4)	0.004 (3)	0.008 (3)	0.024 (4)
C6	0.057 (3)	0.075 (4)	0.079 (4)	0.007 (3)	0.024 (3)	0.013 (3)
C7	0.052 (3)	0.041 (2)	0.049 (3)	0.006 (2)	0.019 (2)	0.008 (2)
C8	0.070 (3)	0.034 (2)	0.039 (2)	0.000 (2)	0.021 (2)	0.0013 (18)
C9	0.086 (4)	0.057 (3)	0.055 (3)	0.004 (3)	0.037 (3)	−0.001 (3)
C10	0.133 (6)	0.047 (3)	0.052 (3)	−0.030 (3)	0.031 (4)	−0.022 (3)
C11	0.120 (6)	0.050 (3)	0.036 (2)	−0.021 (3)	0.024 (3)	−0.019 (2)
C12	0.089 (4)	0.044 (3)	0.031 (2)	−0.020 (2)	0.012 (2)	−0.006 (2)

Geometric parameters (Å, º)

Ni1—C1^i	1.860 (6)	C3—H3A	0.9500
Ni1—C1	1.860 (6)	C4—C5	1.400 (9)
Ni1—C2	1.871 (4)	C4—H4A	0.9500
Ni1—C2^i	1.871 (4)	C5—C6	1.355 (8)
C1—N1	1.159 (7)	C5—H5A	0.9500
C2—N2	1.144 (5)	C6—C7	1.386 (7)
Ni2—N2	2.070 (3)	C6—H6A	0.9500
Ni2—N3	2.060 (4)	C7—C8	1.481 (6)
Ni2—N3^ii	2.060 (4)	C8—C9	1.395 (6)
Ni2—N2^ii	2.070 (3)	C9—C10	1.396 (8)
Ni2—N4	2.112 (3)	C9—H9A	0.9500
Ni2—N4^ii	2.112 (3)	C10—C11	1.326 (8)
N3—C3	1.330 (5)	C10—H10A	0.9500
N3—C7	1.358 (5)	C11—C12	1.390 (6)
N4—C12	1.332 (6)	C11—H11A	0.9500
N4—C8	1.340 (5)	C12—H12A	0.9500
C3—C4	1.399 (7)
C1^i—Ni1—C1	180.0	N3—C3—C4	122.0 (5)
C1^i—Ni1—C2	92.6 (2)	N3—C3—H3A	119.0
C1—Ni1—C2	87.4 (2)	C4—C3—H3A	119.0
C1^i—Ni1—C2^i	87.4 (2)	C3—C4—C5	117.5 (6)
C1—Ni1—C2^i	92.6 (2)	C3—C4—H4A	121.3
C2—Ni1—C2^i	180.0 (2)	C5—C4—H4A	121.3
N1—C1—Ni1	176.6 (4)	C6—C5—C4	120.5 (5)
N2—C2—Ni1	175.7 (4)	C6—C5—H5A	119.7
C2—N2—Ni2	171.1 (3)	C4—C5—H5A	119.7
N3—Ni2—N3^ii	169.5 (2)	C5—C6—C7	119.1 (5)
N3—Ni2—N2^ii	96.0 (1)	C5—C6—H6A	120.5
N3^ii—Ni2—N2^ii	91.3 (1)	C7—C6—H6A	120.5
N3—Ni2—N2	91.3 (1)	N3—C7—C6	121.5 (5)
N3^ii—Ni2—N2	96.0 (1)	N3—C7—C8	115.6 (4)
N2^ii—Ni2—N2	92.7 (2)	C6—C7—C8	122.9 (5)
N3—Ni2—N4	79.0 (1)	N4—C8—C9	120.8 (5)
N3^ii—Ni2—N4	93.3 (1)	N4—C8—C7	115.8 (4)
N2^ii—Ni2—N4	174.2 (1)	C9—C8—C7	123.4 (5)
N2—Ni2—N4	90.3 (1)	C8—C9—C10	117.9 (5)
N3—Ni2—N4^ii	93.3 (1)	C8—C9—H9A	121.1
N3^ii—Ni2—N4^ii	79.0 (1)	C10—C9—H9A	121.1
N2^ii—Ni2—N4^ii	90.3 (1)	C11—C10—C9	120.9 (5)
N2—Ni2—N4^ii	174.2 (1)	C11—C10—H10A	119.5
N4—Ni2—N4^ii	87.2 (2)	C9—C10—H10A	119.5
C3—N3—C7	119.4 (4)	C10—C11—C12	118.7 (5)
C3—N3—Ni2	125.3 (3)	C10—C11—H11A	120.6
C7—N3—Ni2	115.2 (3)	C12—C11—H11A	120.6
C12—N4—C8	119.6 (4)	N4—C12—C11	122.1 (5)
C12—N4—Ni2	126.2 (3)	N4—C12—H12A	119.0
C8—N4—Ni2	114.0 (3)	C11—C12—H12A	119.0
C1^i—Ni1—C1—N1	124 (8)	N2^ii—Ni2—N4—C8	−25.7 (14)
C2—Ni1—C1—N1	−29 (8)	N2—Ni2—N4—C8	95.6 (3)
C2^i—Ni1—C1—N1	151 (8)	N4^ii—Ni2—N4—C8	−89.6 (3)
C1^i—Ni1—C2—N2	−135 (5)	C7—N3—C3—C4	0.1 (7)
C1—Ni1—C2—N2	45 (5)	Ni2—N3—C3—C4	178.6 (4)
C2^i—Ni1—C2—N2	−152 (100)	N3—C3—C4—C5	0.2 (8)
Ni1—C2—N2—Ni2	7 (7)	C3—C4—C5—C6	0.3 (9)
C2—N2—Ni2—N3	130 (2)	C4—C5—C6—C7	−1.1 (9)
C2—N2—Ni2—N3^ii	−42 (2)	C3—N3—C7—C6	−0.9 (6)
C2—N2—Ni2—N2^ii	−133 (2)	Ni2—N3—C7—C6	−179.6 (4)
C2—N2—Ni2—N4	51 (2)	C3—N3—C7—C8	178.8 (4)
C2—N2—Ni2—N4^ii	−12 (3)	Ni2—N3—C7—C8	0.2 (5)
N3^ii—Ni2—N3—C3	−137.2 (3)	C5—C6—C7—N3	1.5 (8)
N2^ii—Ni2—N3—C3	−3.7 (3)	C5—C6—C7—C8	−178.3 (5)
N2—Ni2—N3—C3	89.1 (3)	C12—N4—C8—C9	−1.0 (6)
N4—Ni2—N3—C3	179.2 (4)	Ni2—N4—C8—C9	174.5 (3)
N4^ii—Ni2—N3—C3	−94.4 (3)	C12—N4—C8—C7	179.0 (4)
N3^ii—Ni2—N3—C7	41.4 (3)	Ni2—N4—C8—C7	−5.5 (4)
N2^ii—Ni2—N3—C7	174.8 (3)	N3—C7—C8—N4	3.6 (6)
N2—Ni2—N3—C7	−92.3 (3)	C6—C7—C8—N4	−176.6 (4)
N4—Ni2—N3—C7	−2.3 (3)	N3—C7—C8—C9	−176.3 (4)
N4^ii—Ni2—N3—C7	84.2 (3)	C6—C7—C8—C9	3.4 (7)
N3—Ni2—N4—C12	179.4 (3)	N4—C8—C9—C10	0.8 (7)
N3^ii—Ni2—N4—C12	6.7 (3)	C7—C8—C9—C10	−179.3 (4)
N2^ii—Ni2—N4—C12	149.4 (12)	C8—C9—C10—C11	0.0 (8)
N2—Ni2—N4—C12	−89.3 (3)	C9—C10—C11—C12	−0.5 (8)
N4^ii—Ni2—N4—C12	85.5 (3)	C8—N4—C12—C11	0.5 (6)
N3—Ni2—N4—C8	4.3 (3)	Ni2—N4—C12—C11	−174.4 (3)
N3^ii—Ni2—N4—C8	−168.4 (3)	C10—C11—C12—N4	0.2 (7)

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