Poly[aquahexabenzimidazoleocta-μ-cyanido-octacyanidotricopper(II)ditungstate(V)]

In the polymeric title compound, [Cu3W2(CN)16(C7H6N2)6(H2O)]n, the coordination geometry of the W(V) atom is eight-coordinate dodecahedral, where four CN groups of [W(CN)8] are bridged to CuII ions, and the other four CN groups are not bridged. The coordination geometries of the CuII ions are five-coordinate pseudo-square-based pyramidal. There are two distinct Cu sites, which build and link the cyanido-bridged Cu—W ladder chains. Successive connections lead to the formation of a two-dimensional network. The H atoms of a coordinated water molecule and the imino groups form hydrogen bonds to the N atoms of non-bridged CN groups.

In the polymeric title compound, [Cu 3 W 2 (CN) 16 (C 7 H 6 N 2 ) 6 -(H 2 O)] n , the coordination geometry of the W(V) atom is eight-coordinate dodecahedral, where four CN groups of [W(CN) 8 ] are bridged to Cu II ions, and the other four CN groups are not bridged. The coordination geometries of the Cu II ions are five-coordinate pseudo-square-based pyramidal. There are two distinct Cu sites, which build and link the cyanido-bridged Cu-W ladder chains. Successive connections lead to the formation of a two-dimensional network. The H atoms of a coordinated water molecule and the imino groups form hydrogen bonds to the N atoms of non-bridged CN groups.

Comment
In molecule-based magnets, preparing compounds with a high Curie temperature (T C ) is a challenging issue. From this view point, octacyanometalate [M(CN) 8 ] (M = Mo, W, Nb)-based magnets have been aggressively studied due to their high T C (Garde et al., 1999;Zhong et al., 2000;Herrera et al., 2008;Sieklucka et al., 2009;Kosaka et al., 2009) and properties such as photomagnetism (Herrera et al., 2004;Catala et al., 2005;Ohkoshi et al., 2006;Ohkoshi et al., 2008) and chemically sensitive magnetism (Ohkoshi et al., 2007). Octacyanometalates, [M(CN) 8 ] (M = Mo, W, Nb), a versatile class of building blocks, can adopt different spatial configurations depending on their chemical environment, e.g., square antiprism (D 4d ), dodecahedron (D 2d ), and bicapped trigonal prism (C 2v ) (Leipoldt et al., 1994) (Fig. 1). The coordination geometry of W is an 8-coordinated dodecahedron, where four CN groups of [W(CN) 8 ] are bridged to Cu ions (three Cu1 and one Cu2), and other four CN groups are not bridged. The coordination geometries of the two types of Cu II ions (Cu1 and Cu2) are 5-coordinated pseudo-square pyramidal. The Cu1 atom is coordinated to three nitrogen atoms of CN groups and two nitrogen atoms of benzimidazole molecules. The Cu2 atom is coordinated to two nitrogen atoms of CN groups, two nitrogen atoms of benzimidazole molecules, and an oxygen atom of an H 2 O molecule. The cyano-bridged-Cu1-W ladder chains are linked by Cu2 pillar units ( Fig. 2). The benzimidazole molecules coordinated to Cu1 are aligned alternately between the layers with the intermolecular shortest distance of 3.452 (7) Å.
The field-cooled magnetization (FCM) curve at 10 Oe showed that the magnetization value gradually increased below 10 K and then drastically dropped below 7.5 K with decreasing temperature. The magnetization vs. external magnetic field (M-H) curve at 2 K showed a spin-flip transition with the critical magnetic field of 900 Oe and the saturation magnetization (M s ) value of 5.2 µ B . This M s value is close to the expected value of 5.0 µ B for the ferromagnetic ordering of W V (S = 1/2) ions and Cu II (S = 1/2) ions. These FCM and M-H curves indicate that this compound is a metamagnet.

Refinement
The H atoms of the benzimidazole molecules were placed in calculated positions, with C-H = 0.95 Å, and refined using a riding model, with U iso (H) = 1.2 U eq (C). The maximum and minimum residual electron density peaks were located 0.83 and 0.93 Å, respectively from the W1 atom. A plausible water hydrogen was found in a difference map, and was refined freely.
The second water hydrogen is a symmetry equivalent of the first, because the water oxygen O1 lies on the crystallographic 2-fold. Fig. 1. Thermal ellipsoid plots (50% probability level) of Cu 3 [W(CN) 8 ] 2 (C 7 H 6 N 2 ) 6 (H 2 O). Magenta, Green, gray, light blue, red, and white circle represent W, Cu, C, N, O, and H atoms, respectively. The asterisks indicate the atoms generated by symmetry operations.  (C 7 H 6 N 2 ) 6 (H 2 O). Magenta, Green, gray, light blue, and red represent W, Cu, C, N, and O atoms, respectively. Hydrogen atoms are omitted for clarity.