First structural characterization of an eight-coordinate cobalt(II) complex containing five-membered chelate rings: evidence for d-orbital ς-stabilization energy favoring eight- over six-coordination at cobalt(II) ions

Abstract

For the first time, an eight-coordinate cobalt(II) complex is presented where only five-membered chelate rings are formed with the coordinated ligand; evidence is put forward that in addition to reasons of the tetraazamacrocyclic nature of the ligand 2,11-diaza-[3.3](2,6)pyridinophane (L), eight-coordination at cobalt(II) ions is, to some extent, favored with respect to six-coordination by the presence of d-orbital ς-stabilization energy as calculated by angular overlap methods.