Electronic Structures of Molecules XIII. Diborane and Related Molecules

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Abstract
The electronic structure of diborane (B2H6), which is known to have a nuclear arrangement similar to that of ethane but which has two less electrons, is determined. It is shown that there must be eleven low energy electron states (some singlet, some triplet), belonging to three electron configurations. To account for the colorless diamagnetic character of B2H6, it must be that all or most of these eleven states fall within an energy range of 1.5 volts or less, with the lowest state, somewhat accidentally, probably of 1A1 type. Derivatives of B2H6 have similar structures. According to the present method there is nothing particularly anomalous about these structures. The structures here arrived at are in general agreement with the suggestions of Sidgwick and Pauling that the three H atoms in each BH3 in B2H6 are held by two electron‐pair bonds and one one‐electron bond, although according to the present method one would say that the H atoms are held by two [s] and three [π] bonding electrons, a total of five, shared equally by the three H's. The present method shows clearly that in, e.g., B2H2(CH3)4, there is no reason to suppose that the B–H bonds have fewer electrons per bond than the B–C bonds, the number being 5/3 in each case. Equal energy for B2R6 and 2 BR3 would mean equal effective strength of B–R and B–B bonds. It is noted that the B–B bond is a remarkably strong one. Reasons why BCl3 does not form B2Cl6 are discussed. The desirability of magnetic susceptibility and perhaps molecular weight determinations, if possible at elevated temperatures, for some of the types BR3 and B2R6 is pointed out.