Diaquabis(1,10-phenanthroline)nickel(II) tetrakis(cyanido-κC)nickelate(II) tetrahydrofuran solvate monohydrate

The title complex, [Ni(C12H8N2)2(H2O)2][Ni(CN)4]·C4H8O·H2O, consists of a cationic [Ni(C12H8N2)2(H2O)2]2+ unit, an anionic [Ni(CN)4]2− unit, one uncoordinated water and one tetrahydrofuran molecule. In the cationic unit, the Ni2+ atom is coordinated by four N atoms and two O atoms from two 1,10-phenanthroline ligands and two water molecules in a distorted octahedral coordination environment. In the anionic unit, the Ni2+ atom is in a square-planar coordination by four C atoms from four monodentate terminal cyanide ligands. O—H⋯N and O—H⋯O hydrogen bonds link neighboring cationic and anionic units, forming a three-dimensional supramolecular network. The interstitial tetrahydrofuran molecule is independently disordered over two sites in a 1:1 ratio.


Comment
The study of cyanide-bridged complexes has gained great recognition over the last decade not only owing to their fascinating structural diversity and their intriguing topological networks, but also because of interesting magnetic properties, such as spin-crossover behaviour or the formation of single-molecular or single-chain magnets (Miyasaka et al., 2007;Shatruk et al., 2009). To date, much effort has been invested to construct cyanide-based complexes by the choice of versatile metal cyanide or cyanide-based building units (Kou et al., 2001;Yun et al., 2004;Yuge et al., 1996). In this context we have chosen nickel cyanide as a potential bridging building block, and 1,10-phenanthroline as an auxilary ligand to construct new structures. Reaction of the two building blocks yielded the title compound [Ni (C 12  [Ni(CN) 4 ] 2unit, and each one interstitial water and tetrahydrofuran molecule. Thus no cyano bridged complex with different nickel centers was formed but the nickel atoms are found in separate anionic and a cationic complex ions. In the cationic unit, the six-coordinate octahedral Ni 2+ center is surrounded by four N atoms and two O atoms from two 1,10-phenanthroline ligands and two water molecules. In the anionic unit, the square planar Ni 2+ center is coordinated by four C atoms from four mono-dentate terminal cyanide ligands. Similar structures containing Ni(CN) 4 units have been observed in other complexes (Paharova et al., 2003). O-H···N and O-H···O hydrogen bonds (Table 1) are formed between the cationic units, the anionic units and the uncoordinating water molecules which assemble them to form a three-dimensional supramolecular network ( Fig. 2). The network is also stabilized by π-π stacking interactions between the Ni(CN) 4 units and the 1,10-phenanthroline ligands. The interplanar distance between them is ca. 3.60 Å (symmetry operator for the 1,10-phenanthroline ligand: 0.5+x, 0.5-y, -0.5+z). The interstitial tetrahydrofuran molecule is independently disordered over two sites in a one to one ratio (see refinement section for details).

Experimental
Nickel cyanide (0.1107 g, 1 mmol) and 1,10-phenanthroline (0.1801 g, 1 mmol) were added to a mixture of water (10 mL) and tetrahydrofuran (5 mL). The resultant mixture was sealed in a 25 ml stainless steel reactor with a Teflon liner and kept under autogenous pressure at 413 K for 24 h, and then cooled to room temperature at a rate of 0.5 K/min. Green block shaped crystals of the title compound suitable for single-crystal X-ray diffraction analysis formed with a yield of approximately 56% based on 1,10-phenanthroline.

Refinement
The tetrahydrofuran molecules are arranged as symmetry related pairs around a center of inversion. In the original refinement the oxygen atoms of the tetrahydrofuran molecules showed significantly elongated thermal ellipsoids indicating disorder.
supplementary materials sup-2 The THF molecule was thus refined as being disordered over two sites in a one to one ratio. Due to the significant overlap of the disordered atoms the following restraints and constraints were applied: The adps of the disordered atoms were restrained to be close to isotropic and those of equivalent atoms were set to be identical.
All water H atoms were tentatively located in difference density Fourier maps and were refined with O-H distance restraints of 0.83 (1) Å and with U iso (H) = 1.5 U eq (O). In the last stage of the refinement, they were treated as riding on their parent O atoms. All H atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.93 Å (aromatic) or 0.97Å (tetrahydrofuran ring) and U iso (H) = 1.2U eq (C). Fig. 1. The structure of the title compound, showing the atomic numbering scheme. Non-H atoms are shown with 30% probability displacement ellipsoids. The disordered section is omitted for clarity.

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 > 2sigma(F 2 ) is used only for calculating R-factors(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.