Determination of the Metal-Metal ~istance in the Mixed Valence Complex K2Pt[CN]4Brom3~3H20 Diana L. S e d n e y Williams College, Williamstown. MA 01267 Martin Tanner Ciba-Geigy. Fribourg, Switzerland The potassium tetracyanoplatinate complex of the title ( I ) , hereafter designated KCP, is a fascinating choice for investigation in the advanced inorganic laboratory. This unusual compound is a one-dimensional metal that exhibits all of the major types of chemical bonding: covalent, ionic, metallic, and hydrogen. The electrochemical synthesis and properties of KCP, which crystallizes as lustrous copper-colored needles, have been recently described in THIS JOURNAL (2). The non-integral formula of KCP indicates the mixed valence nature of the nlatinum atoms in this comolex. The platinum atoms align in infinite chains along the molecular axis where all P t - P t distances are eauivalent. Thus, the oxidation state of all of the platinum atoms is 72.9 and is not a ieauenceof PttII) and Pt\l\'J aulms.The ~ r o ~ e r t i e s KCI' uf are quite distinct from its p l a t i n u h ( I ~ ) precursor, K2Pt(CN)q3H20 (KCP(II)), and the fully oxidized platinum(IV) complex, KzPt(CN)dBrz (KCP(IV)) (3).Because the Pt-Pt distance in KCP is sufficiently short, metallic interaction occurs along the platinum chain hut does not occur in either KCP(I1) or KCP(1V). I n this experiment, the Pt-Pt distance of KCP is determined from its x-ray diffraction pattern. Experimental Synthesis of KCP (4) The electrochemicalsynthesis of KCP followed here is outlined in (2). (An alternative synthesis is given in (3),and the mechanism far this svnthesis is detailed in (41.1 A solution of 700 me K?Pt(CN)a 3 ~ 2 0 " ( ~ l f a - ~ e n t rdissol"ed'in on) 6 ml of 1 M potassium bromide solution is placed in an electrochemical cell containing a platinum anode and cathode. Application of a 1.5-V source (e.g., a dry cell battery) causes the oxidation of platinum, and the evolution of Hz is observed at the cathode. Electrolysis is continued for 24 h. At the end of this period, the large needle crystals which form at the anode are recovered by vacuum filtration, washed with a minimal amount of ice cold distilled water 1
