IODINE-DOPED POLYAZINES - EVIDENCE AGAINST BIPOLARONS AND NITRENIUM IONS

The recent claim of the first isolation and N-15 NMR observation of the long-sought nitrenium ion has been revisited through extensive molecular-orbital calculations at the AM1, RHF/6-31G*, and MP2/6-31G* levels on neutral and cationic polyazine model systems. These data as well as a careful analysis of the available spectroscopic and conductivity data lead to the conclusion that no such nitrenium ions (bipolarons) are present. Oxidative doping of polyazines leads to irreversible reaction or structural rearrangement of the polymer through nearly collinear diazoalkane-like -C=N+=N- moieties. Formation of the latter, in which all atoms have complete octets, is energetically favored over a six-electron nitrenium ion. However, experimental evidence suggests this species undergoes further reaction or rearrangement. Calculations suggest that a dicationic nitrenium charge carrier, as originally proposed, would cause fragmentation of the polymer to nitrogen and acetylene, disfavoring this conductivity mechanism. Other possibilities are explored.