Torsional profiles of protonated and metal-coordinated 2,2′-bipyridine

The rotational profiles of both the mono and di-protonated 2,2'-bipyridinium cations were calculated with ab initio Hartree Fock and density functional theoretical methods. The most stable form of the singly protonated bipyridine is the planar cisoid conformation with a weak, bent and strongly asymmetric NHN hydrogen brigde. The transoid conformer is predicted to exhibit the maximal charge delocalization in the coplanar arrangement, however, it is twisted due to sterical hindrance. The di-protonated species is most stable in a twisted (about 40degrees) transoid conformation with a very shallow potential minimum of the twisted cisoid form. Rotational profiles of transition metal complexes [bipyZn(H2O)(n)](2+) with n=2-4 and [bipyRu(CO)(4)](2+) leading from the monodentate transoid to the stable bidentate bipy complex are also calculated with density functional theory methods. There is no potential energy barrier between the coordinated cisoid and transoid bipy complexes with [bipyZn(H2O)n](2+) and a small barrier is found for [bipyRu(CO)(4)](2+). (C) 2004 Elsevier B.V. All rights reserved.