Semi-empirical LCAO MO theory for infinite systems. Part 3.—Regular boron—nitrogen polymers

Abstract

LCAO MO SCF solid-state calculations on the “covalent” boron nitrogen polymer polyiminoborane [BHNH]_n, the “coordination” polymer polyaminoborane [BH₂—NH₂]_n and their B-chloro- and N-chloro-derivatives have been performed. The calculated band structures of these materials are compared with those of the isoelectronic carbon systems, polyacetylene [CH—CH]_n, polyethylene [CH₂—CH₂]_n and poly(vinyl chloride)[CHCl—CH₂]_n. Whilst the band structures of the two “unsaturated” polymers are different from their carbon analogues polyacetylene and polychloroacetylene respectively, the band structures of the saturated polymers polyaminoborane and poly-B-chloroaminoborane are strikingly similar to those of polyethylene and poly(vinyl chloride). The relative energies of the “saturated” and “unsaturated” chloro-substituted boron–nitrogen polymers suggests, as expected, that the B-chloro-systems should be more stable than their N-chloro-counterparts. Electron removal from polyiminoborane, poly-B-chloroiminoborane and polychloroacetylene, involves the σ-frameworks of the polymers. Finally, the optical properties of polyiminoborane and poly-B-chloroiminoborane are predicted to be sensitive to a π^* orbital centred mainly on boron.