Bis{2-[2,5-bis(pyridin-2-yl)-1H-imidazol-4-yl]pyridinium} tetracyanidoplatinate(II) tetrahydrate

The asymmetric unit of the title hydrated complex salt, (C18H14N5)2[Pt(CN)4]·4H2O, consists of one 2-[2,5-bis(pyridin-2-yl)-1H-imidazol-4-yl]pyridinium cation, half a tetracyanidoplatinate(II) dianion, which is located about a crystallographic inversion center, and two water molecules of crystallization. The PtII atom has a square-planar coordination environment, with Pt—CCN distances of 1.992 (4) and 2.000 (4) Å. In the cation, there is an N—H⋯N hydrogen bond linking adjacent pyridinium and pyridine rings in positions 4 and 5. Despite this, the organic component is non-planar, as shown by the dihedral angles of 10.3 (2), 6.60 (19) and 15.66 (18)° between the planes of the central imidazole ring and the pyridine/pyridinium substituents in the 2-, 4- and 5-positions. In the crystal, cations and anions are linked via O—H⋯O, O—H⋯N and N—H⋯O hydrogen bonds, forming a three-dimensional network. Additional π–π, C—H⋯O and C—H⋯N contacts provide stabilization to the crystal lattice.


Experimental
Crystal data (C 18

Campos-Gaxiola Comment
Hydrogen bond based inorganic-organic hybrid materials are receiving continuous interest because of their structural, magnetic, optical and electrical properties (Sanchez et al., 2005;Yao et al., 2010;Wang et al., 2010;Lebeau et al., 2011;Pardo et al., 2011;Du et al., 2013). An interesting approach for the preparation of such materials consists in the utilization of supramolecular synthons capable of forming O-H···O, O-H···N and N-H···O hydrogen bonds, through which organic cations and anionic metal complexes are linked to form crystalline inorganic-organic hybrid solids (Crawford et al., 2004;Dechambenoit et al., 2006;Maynard & Sykora, 2008). As a further contribution to this filed of research we report herein on the synthesis and crystal structure of the title compound.
The asymmetric unit of the title compound consists of one organic cation of the composition [(C 18 H 14 N 5 )] + , which is located in a general position, half of an independent [Pt(CN) 4 ] 2anion, which is located on a crystallographic inversion center, and two water molecules of crystallization (Fig. 1). The Pt atom has a square-planar coordination environment with Pt-C(cyanido) distances ranging from 1.992 (4) to 2.000 (4) Å. Although two of the three pyridine substituents are linked by an intramolecular N5 + -H5′···N4 hydrogen bond (Table 1) (Table 1 and Fig. 2). Within the network, the organic cations are stacked through a series of π-π interactions involving the imidazole and pyridinium rings [Cg1···Cg1 i distance = 3.359 (2) Additionally, there are a number of C-H···O and C-H···N contacts present, thus providing additional stabilization to the crystal lattice (Table 1 and Fig. 2).

Refinement
The C-bound H atoms were positioned geometrically and refined as riding atoms [aryl C-H = 0.95 Å and U iso (H) = 1.2U eq (C)]. The pyridinium N-H + and water H atoms were located in difference Fourier maps. They were refined with distance restraints of 0.840 (1)Å, with U iso (H) = 1.5U eq (O, N). For the refinement of the water molecules a constraint has also been employed for the H-O-H bond angles (DANG = 1.35 (1) Å). In the final difference Fourier map a large residual density peak, 3.10 eÅ -3 , and hole, -2.26 eÅ -3 , were found near the Pt atom.

Bis{2-[2,5-bis(pyridin-2-yl)-1H-imidazol-4-yl]pyridinium} tetracyanidoplatinate(II) tetrahydrate
Crystal data (C 18   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 > σ(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.