Structural studies of precursor and partially oxidized conducting complexes. XIII. A neutron diffraction and x-ray diffuse scattering study of the dimerized platinum chain in rubidium tetracyanoplatinate chloride (2:1:0.3) trihydrate, Rb2[Pt(CN)4]Cl03.3.0H2O

The crystal structure and molecular formula of the one-dimensional conductor Rb2[Pt(CN)4]Cl0.30 . 3.0H2O, RbCP(Cl), have been fully characterized using single-crystal neutron diffraction, x-ray diffuse scattering data, and thermogravimetric analysis. RbCP(Cl) is isostructural with KCP(Cl) and KCP(Br) except that only one halide site can be identified. From thermogravimetric analyses RbCP(Cl) is a 3.0 hydrate as is KCP(Br). RbCP(Cl) crystallizes in the tetragonal space group P4mm, with unit cell dimensions a = 10.142 (6) A, c = 5.801 (4) A, V/sub c/ = 596.7 A3, and Z = 2. Using x-ray diffuse scattering techniques we have established the Pt oxidation as +2.31 (2) from which the molecular formula Rb2[Pt(CN)4]Cl/sub 0.31(2)/ . 3.0H2O is obtained. The structure consists of nearly planar Pt(CN)4 moieties stacked along the c axis forming a perfectly linear Pt-Pt chain. The crystal asymmetric unit contains two independent Pt(CN)41.7- groups, two H2O sites, one Rb+ site, and one Cl- site. The asymmetric ordering of the Rb+ ion and the H2O molecules constitutes the main source of crystal asymmetry. The two-independent Pt-Pt chain distances are definitely unequal (2.877 (8) and 2.924 (8) A) with the average intrachain separation (2.90 A) being slightly longer than in KCP(Br) (2.88 A) and KCP(Cl) (2.87 A). The replacement of K+ by Rb+ results in lattice expansion along c, which produces larger Pt-Pt intrachain separations. Thus the unequal and slightly longer Pt-Pt separations in RbCP(Cl), apparently result in increased electron localization along the Pt-atom chain and a concomitant decrease in the electrical conductivity. 10 figures, 3 tables