One-Dimensional Collective Electronic Effects in the Helically Stacked Cs2[NI(CN)4]-H20 and Cs2[Pt(CN)4]-H2(): X-ray Structure, Polarized Specular Reflectance, and ZINDO Calculations

The X-ray structure of Cs2[Ni(CN)4)*H20 and the polarized single-crystal UV absorbance spectra of Cs2[Ni(CN)4)HgO and Cs2[Pt(CN)4]*H20 are presented. The two complexes are isostructural, with helical arrangements of M(CN)4 ions in which there is moderate metal-metal electronic perturbation resulting in a spectral red shift from solution in the UV absorbance spectra. In addition, we have modeled the nickel system with a ZINDO calculation of a three-molecule segment of the helix and have found remarkably good agreement with experiment, including excellent reproduction of the red shift. Crystal data are as follows: Cs2[Ni(CN)4]-H20, hexagonal, space group P61, a = 9.5260(10) A, c = 19.043(2) A, V = 1496.5(3) A T = 100 K, Z = 6, 4335 observed data, R = 0.016, = 0.034.