Remarkable structures of lithium compounds

Abstract

The geometries of lithium compounds do not follow classical structural considerations. Lithium bonds have a high degree of ionic character, but also engage in multicenter covalent bonding. Replacement of a hydrogen in a molecule by lithium almost always results in some fundamental change in geometry or electronic structure. Triplet ground states and anti van't Hoff forms may be favored. Lithium also can participate in stoichiometries which violate the octet rule, e.g., CLi’ and CLi’. The extra electrons in these hypermetallated species are not associated with the central atom, but contribute to metal-metal bonding. Lithium often prefers bridging positions; symmetrical multiple bridging is also quite common. Association energies of lithium compounds are quite large and double bridging within a molecule can be considered to be the intramolecular equivalent of association. X-ray determinations and theoretical calculations provide the best information concerning structural details. Results from both these areas will be described and compared. Formerly, bits and pieces of information were available. These are now fitting together so that patterns and regularities are becoming apparent. © 1984 IUPAC