Virginia Polytechnic lnstitute and State Uniuersity

The geometries of a variety of borate polyanions extracted from borate crystals and proto-nated to achieve quasi-neutral or neutral molecules have been optimized using quantum mechanical molecular orbital methods. The calculated bond lengths and angles for the neutral molecules are in good agreement with those in borate minerals. However, calculations on molecules with negative charges as large as two electrostatic units yield bridging angles that depart by as much as 15 ' and BO bond lengths that depart by as much as 0.03A from observed values. Even in this case, when these molecules can be neutralized by further protonation, the calculated angles agree with observed values. A regression analysis of bond strength and calculated BO bond lengths yield bond strength-bond length parameters that are identical with those obtained for crystals. Deformation electron density maps calculated for various borate molecules mimic experimental maps of comparable units in crystals; how-ever, they fail to provide evidence for the bonding of discrete OBO units into endless chains as recently proposed for LiBOr. A reaction involving a monomer, a dimer and a 6-membered ring of triangles is examined