Quantum mechanical studies of distortions and polymerization of borate polyhedra

Ab initio self-consistent-field (SCF) molecular orbital (MO) theory has been used to calculate energy optimized B-O bond lengths (R(B-O)) for BO3- and optimized R(B-O) and zB-o-B for B(oH)r (D $ and C3, symmetry), H2BOBH2, (OH)2BOB (OH)2, H2BOHBH}, B:Ol-, B3O6H3 and AIO2BO. At the STO-3G minimum basis set level calculated R(B-O) for the neutral clusters differ from experiment by no more than 0.04A. STO-3GcalculationsonH2BOBH2and(OH)zBOB(OH)2predict LB-O-Bof 126 ' and 130", respectively, with the predicted value for H2BOBH2 being in good agreement with values predicted using larger basis sets and with values for both molecules being near the range of values (128-133") observed in crystalline B2O3. Protonation of the oxygen in H2BOBH2 causes almost no change in calculated ZB-G-B but does produce a calculated increase in R(B-O) which is in agreement with observed bond length-bond strength sum systematics. For the (OH)3BOS(OH) | cluster the calculated STO-3G value of ZB-O-Si is 125', in good agreement with average observed values of 125-128 " for such angles. STO-3G calculations on the B3O6H3 ring reproduce the ordering of R(B-O) observed in K3B3O6, with distances internal to the ring larger than those external, and give a LB-O-B in good agreement with the experimental value af 122.7'. The (OH)zBOB(OH)2 results also indicate that smaller valence electron charge buildup occurs in bridging than in nonbridging B-O bonds