LIGAND ISOMERISM AND STACKING IN SQUARE-PLANAR PLATINUM(II) COMPLEXES

The structure and bonding in two forms of the bisthiocyanate complex of Pt(II), Pt[(bpy)(X)2] (where bpy is 2,2'-bipyridyl and X is the pseudohalide), have been studied by solution and solid-state NMR, FTIR, and EXAFS spectroscopies. The yellow complex, which is soluble in a variety of organic solvents, contains two cis S-bonded SCN ligands and is the kinetically favored form. On heating, either in solution or as a solid, this complex transforms to a red insoluble complex, in which the SCN ligands have "flipped" to become N-bonded and which appears to be the thermodynamically stable form at room temperature. Conversion of the solid does not involve loss of a solvent molecule. EXAFS experiments involving the Pt-L3 edge show the presence of two Pt-Pt distances in the red solid, one of which is indicative of the formation of stacked square planar Pt moieties, in which the 18-electron rule is satisfied.