Ab Initio Study of Hydrogen Cyanide Borane(1) Polymer and Its Dehydrogenated Analog

Electronic structure of the polymers constructed from 1-λ 2 -2-azonia-1-borata-2-propyne (HCNBH) and 2-azonia-1-λ 1 -borata-2-propynyl radical (HCNB) have been studied ab initio by the use of finite periodic cluster approximation within the second-order many-body perturbation theory [MBPT(2)] with the Hartree-Fock reference. Results are compared with molecular calculations of corresponding oligomers. It is shown that though oligomers can be used for initial guess of the geometry, it is not appropriate to extrapolate some basic features of the polymer band structure from the results of increasing oligomers. (HCNB) n polymer has all of the atoms in plane, which allows for conjugation of π-electrons. The band gap of ∼2.8 eV at MBPT(2) level for (HCNB) n puts this species among semiconductors, with a possibility of further improvements of its properties by doping. (HCNBH) n polymer has a nonplanar staggered structure, and it is an insulator.