Crystal Structure of Monomeric Octahedral Monooxo d2-Rhenium(V) Complexes [ReO()] with Oxygen-Containing Pentadentate-Chelate Ligands

The structural features of eleven mononuclear octahedral monooxo [ d 2 -Re(V)] complexes with pentadentate chelate ligands (3О, 2N), (2O, 3N), (2O, 2N, P), (2O, 2N, S), and (O, 2N, 2S) have been discussed. The О atoms are always located in trans positions to multiply bonded O(oxo) ligands. It has been found that in nine compounds with negatively charged oxygen atoms of ligands in trans positions to multiply bonded O(oxo) ligands, the Re–O(L) trans bonds (1.960–2.065 Å) are comparable in length, somewhat longer or noticeably shorter than Re–O(L) cis (1.952–2.140 Å). These Re–O(L) bonds in trans positions to oxo ligands can be considered as having an increased multiplicity, since they are comparable in length (rather than elongated because of the structural manifestation of the trans -effect of the oxo ligand) with the Re–O(L) cis distances. In this case, we can speak of pseudodioxo complexes containing two ligands (O(oxo) and O(L trans )) with an increased order of the Re–O bonds (~2.5 and ~1.5 Å, respectively). In the other two complexes, the Re–O(L penta ) trans bonds (2.200 and 2.252 Å) are significantly elongated. In these two cases, we should talk about the structural manifestation of the trans -effect of the multiply linked oxo ligand.