Crystal and molecular structure by neutron diffraction of potassium tetracyanoplatinate(II) trihydrate, the starting product for partially oxidized conducting cyanoplatinate salts

Potassium tetracyanoplatinate(II) trihydrate, K/sub 2/Pt(CN)/sub 4/.3H/sub 2/O, crystallizes in the orthorhombic space group Pbcn, with a = 13.426 (5), b = 11.848 (4), and c = 6.956 (2) A with Z = 4. The strongly efflorescent crystals grown from aqueous solution were sealed in capillaries for three-dimensional neutron data collection. The structure was deduced from the neutron Patterson map and was refined by Fourier and full-matrix least-squares techniques to R/sub F/sup 2// = 0.061 (R/sub F/ = 0.056) for 587 reflections with F/sup 2/ > sigma(F/sup 2/). The structure consists of planar Pt(CN)/sub 4//sup 2 -/ groups stacked parallel to c forming linear Pt chains with a Pt-Pt separation of 3.478 (1) A. Alternate Pt(CN)/sub 4//sup 2 -/ groups are rotated giving an eclipsed configuration with C-Pt-Pt-C torsion angles of 15.7 (1) and 16.7 (1)/sup 0/. The Pt(CN)/sub 4//sup 2 -/ plane is also tilted with respect to c by approx.3/sup 0/. The two types of water molecules serve to link Cn/sup -/ groups within a Pt(CN)/sub 4//sup 2 -/ stack and to cross-link adjacent Pt(CN)/sub 4//sup 2 -/ stacks. Comparisons are made with the structure of the mixed-valence compound K/sub 2/Pt(CN)/sub 4/Bro.3.3H/sub 2/O, KCP(Br). (auth)