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H
YH Fig. 1.-Proposed structure of the B l ~ H I ~ ion - 2 viewed approximately along the S axis.
The molecular structure (Fig. I) has only two kinds of boron atoms in the ratio of 2 (apex) to S (approximately equatorial) in a polyhedron of symmetry D i d . The valence orbitals of the apical boron atoms are slightly less symmetrical than those of the equatorial boron atoms, and hence the temperature-independent paramagnetism should be slightly greater for the apical boron atoms. This explanation, based upon a choice of origin a t the boron nucleus, forms a more satisfactory basis for understanding B" resonance shifts than t h a t based strictly on formal charge and diamagnetism. Thus the n.m.r. results are well satisfied . The valence orbitals can best be described by recognition of the two B5Hj groups, like those in BjHg molecules, with almost equatorial boron atoms replacing bridge hydrogens. Of t.he twentyone electron pairs, ten are used for B H single bonds, and three for each of the framework B j groups like those3 in RjHq, and five for bonding among the sixteen remaining sp3 orbitals of the eight almost equatorial B atoms. In D.ld these sixteen orbitals have the representation XI -t A? B1 f B? 2E1 2E2 2Ea. Assuming all close interactions as the same, we find3 Alla t I-Io 28, E?,at Ho (2 2'ir)'/?,B and Fd l at. Ho %'/2/3 as strongly bonding orbitals to be occupied by these five electron pairs. The very weakly bonding E2 a t Ho + (2 - .)'/?)'/'$ and non-bonding R1 and B?, as well as all of the antibonding orbitals are unfilled. Thus AI0 theory in its simplest form leads to a closed shell electronic structure for BloHlc-'.
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tional w0rk.l Other methods, catalytic and chemical, of reductive C-S cleavage have had limited utility. Hydrazine with or without alkali has been found to desulfurize cyclic or acylic dithioketals. Xlthough the full scope and mechanism of this reaction has not as yet been established, preliminary results indicate satisfactory yields (60EW?
