13 Chromium, molybdenum, and tungsten

Abstract

The following provides a selected highlight for each element of the chromium triad in 2003. Chromium: A series of remarkably stable chromium(IV) alkyl and chromium-(III) and -(IV) hydride complexes have been prepared using the triamidoamine tetradentate ligand L1H3. This ligand has also been employed to prepare the first trigonal monopyramidal chromium(II) complex. Molybdenum: Molybdenum(V) coordination complexes have been extensively studied to provide further insights into the active sites found within many molybdoenzymes. A nice example of a model complex that contains the heteroscorpionate ligand L2SH, [(L2S)MoO(bdt)2], has been reported. The complex was structurally characterised and is only the second known model compound that closely approximates the active site structure of reduced forms of sulfite oxidase. Tungsten: The field of molecular magnetism has exploited the use of the [W(CN)8]3− building block in preparing a range of 2-D and 3-D bimetallic assemblies. For example, [Cu(tn)]3[W(CN)8]2·3H2O and [Cu(pn)]3[W(CN)8]2·3H2O have a 2-D layer structure and the magnetic properties of the compounds show typical metamagnetic behaviour. The critical field at which the interlayer antiferromagnetic ground-state switches to a ferromagnetic state is approximately 1.25 T for [Cu(tn)]3[W(CN)8]2·3H2O and 0.35 T for [Cu(pn)]3[W(CN)8]2·3H2O at 1.8 K.