W0130

Doubling Oxidation States in Paddlewheel Compounds: Molecules That Ionize More Readily Than Cesium. Carlos A. Murillo, Dept. of Chemistry, Texas A&M Univ., P.O. Box 30012, College Station, TX 77842-3012 USA.

Nearly forty years ago the field of multiply-bonded dimetal compounds in tetragonal coordination environments, a,b, began with the correct identification of the stoichiometry, as well as the geometric and electronic structure of the Re₂Cl₈^2- ion. The field has grown to embrace nearly three thousand compounds. As numerous as these compounds are, the formal oxidation for the M₂ cores have been limited however, to the range from +4 to +6. Here we will review some of this chemistry but especially our recent results which have expanded the range of oxidation states for the M₂ units of structurally characterized compounds from +3 to +7 and provide evidence of the existence of M₂⁸⁺ cores. We will examine the influence of a few selected types of ligands on metal-metal distances, and electrochemical and electronic properties. Special attention will focus on the anion of the guanidinate-type compound 1,3,4,6,7,8-hexahydro-2H-pyrimido-[1,2a]pyrimidine (hpp), c, which is capable of producing stable compounds with ionization potentials less than that of the cesium atom.