Structural, Magnetic, and Charge-Transport Properties of Stacked Metal Chelate Complexes

Intense effort devoted to the synthesis and physical characterization of crystals containing stacked, planar, transition-metal chelate complexes has yielded many materials of widely divergent properties. Some are primarily of structural interest. Others have unusual magnetic properties; for example, the first well-documented instance of a spin Peierls transition (a solid state analogue of the Jahn-Teller effect) was observed in such a material.1 Yet others exhibit high or unusual electrical conductivities, and the greatest effort is currently being expended toward the understanding and control of charge-transport properties in molecular crystals. Here compounds prepared from metallomacrocycles are of particular interest and challenge. For example, with phthalocyaninatonickel iodide, Ni(pc)I,† a high, metallike conductivity along the stacking axis is achieved,2,3 whereas bis(diphenylglyoximato)nickel iodide, Ni(dpg)I,4 has the same structural motif but exhibits much lower conductivity. To understand and control such divergent physical properties in related solid state structures has engendered considerable research, particularly since the possibility exists of tailor-making compounds with specific transport properties through well-defined chemical modifications.