Tetraethylammonium (2,2′-bipyridine)tetracyanidocobaltate(III) sesquihydrate acetonitrile solvate

The title complex, (C8H20N)[Co(CN)4(C10H8N2)]·CH3CN·1.5H2O, consists of tetraethyl ammonium cations, mononuclear [CoIIIbpy(CN)4]− anions and uncoordinated water and acetonitrile molecules. The CoIII atom is six-coordinated by two 2,2′-bipyridine (bpy) N atoms and four cyanide C atoms in a distorted octahedral geometry. The acute bite angle of the chelating bpy [82.28 (8)°] is the main factor accounting for this distortion. In addition, the tetraethylammonium cation is significantly disordered [occupancy ratio 0.611 (3):0.389 (3)]. The presence of water molecules, one of which is disordered over two positions about an inversion center, results in the formation of a network of O—H⋯N hydrogen bonds involving the cyanide N atoms.

GL gratefully acknowledges the College of Science and Technology, Southern Arkansas University, for financial support.
Tetraethylammonium (2,2'-bipyridine)tetracyanidocobaltate(III) sesquihydrate acetonitrile solvate G. Lyubartseva and S. Parkin Comment Self-assembly of cyano-linked metal complexes draws considerable interest as a strategy for developing new bimetallic clusters. Typically one needs a stable cyanometallate anion as a ligand for fully or partially solvated metal ions. Hexacyanometallate anion [M(CN) 6 ] 3is very useful but it often gives three dimensional Prussian Blue analogs. If the metal ions are partially blocked with a bidentate ligand it is possible to control the nuclearity of the bimetallic clusters which have potential application as catalysts, see Darensbourg et al. (2004); room temperature magnets, see Mallah et al. (1993), Garde et al. (2002 and Holmes & Girolami (1999); or single-molecule magnets, see Sokol et al. (2002). Here we report a new building block [(Co III bpy(CN) 4 ] --which can be applied to make new bimetallic clusters.
The structure consists of tetraethyl ammonium cations, mononuclear [Co III bpy(CN) 4 ]anions, uncoordinated water and acetonitrile molecules. The cobalt (III) atom is six-coordinate with two bpy-nitrogen atoms and four cyanide-carbon atoms in a distorted octahedral geometry (Fig.1). The acute bite angle of the chelating bpy [82.28 (8)°] is the main factor accounting for this distortion from the ideal geometry. The values of the Co III -nitrogen bond lengths are shorter than bond lengths in the similar chromium (III) anionic complex reported by Toma et al. (2004). The cobalt-carbon-nitrogen angles for the Experimental 2,2'-bipyridine and tetraethylammonium cyanide were purchased from Sigma-Aldrich and used as received. The starting complex [Co(bpy) 3 ]Cl 2 .2H 2 O.CH 3 CH 2 OH was synthesized according to the previously published procedure by Szalda et al.(1983). [Co(bpy) 3 ]Cl 2 .2H 2 0.CH 3 CH 2 OH (680 mg, 1 mmol) was dissolved in 20 ml 1:1 mixture of methanol and acetonitrile. Tetraethylammonium cyanide (468 mg, 3 mmol) was dissolved in 10 ml wet acetonitrile. The cyanide solution was added dropwise to metal solution with slow stirring. Once the addition was complete, the resulting solution was filtered and solvent was evaporated slowly. Yellow coloured, analytically pure monoclinic crystals were obtained after one week and found to be [tetraethylammonium] [(2-(pyridin-2-yl) 3496, 2997, 2133, 1578, 1557, 1453, 1412, 1313, 1250, 1185, 1083, 997, 791, 773,757,653, 620, 403. supplementary materials sup-2 Refinement H atoms on the anion, cation, and acetonitrile were found in difference Fourier maps and later placed in idealized positions with constrained distances of 0.98 Å (RCH 3 ), 0.99 Å (R 2 CH 2 ), and 0.95 Å (C Ar H), and with U iso (H) values set to either 1.2U eq or 1.5U eq (RCH 3 ) of the attached atom. The H atoms attached to O1w were found in a difference map. The partial occupancy O2w is within H-bonding distance of N3, so it was assumed that one of the hydrogen atoms of this water would be found between O2w and N3. Indeed, a pair of plausible hydrogen atoms were found in a difference map, with one of them between O2w and N3, in spite of the partial occupancy. The water hydrogens were constrained to distances of 0.84 Å and assigned U iso of 1.5U eq (O).
To ensure chemically sensible and physically reasonable structural parameters for the disordered cation, the SHELXL97 SAME and DELU restraints were used along with the EADP constraint. Water molecule geometry was restrained using the SHELXL97 DFIX command. Fig. 1. View of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

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.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.