Current Research

    The chemical and physical properties of metal-containing materials largely depend on the oxidation state of the metal. The ease with which different oxidation states are accessed depends on the metal environment. Research conducted in the laboratory of Adrian George led to the discovery of a series of stable complexes of Fe⁴⁺, a relatively rare oxidation state of iron. The reaction of FeCl₂ with one mol of the tripodal tetradentate tristhiolatophosphine proligand P(C₆H₃-3-Me₃Si-2-SH)₃ (abbreviated PS₃H₃), (see Fig.1) produced, after controlled oxidation, the purple, diamagnetic, trigonal bipyramidal iron(IV) complex, FeCl(PS₃) the structure of which is shown in Fig.2.

Fig. 1	Fig. 2

FeCl(PS3) can be reversible reduced to [FeIIICl(PS3)]1- at a potential more negative that the FeIII/FeII couple of ferrocenium/ferrocene. Fe4+ is an important oxidation state in many iron-containing enzymes. The reaction of FeCl2 with PS3H3 (2:1 mol ratio) gave only black FeIII2(PS3)2. The structure of FeIII2(PS3)2 is shown in Fig.3 with the six Me3Si groups omitted for clarity. The molecule is diamagnetic at room temperature suggesting antiferromagnetic coupling between the two irons, which are 271 pm apart. Each ligand intimately wraps around both iron atoms. This molecule can be oxidized to give a mixed valence FeIV/FeIII complex and reduced to a mixed valence FeIII/FeII complex.

Fig. 3

Future topics include using sulfur ligands to stabilize other metals in high oxidation states, preparing and using oxygen and nitrogen analogues of the sulfur ligand to prepare metal complexes, and preparing and investigating the optical and magnetic properties of mixed-valent, and mixed-metal clusters.

Recent Key Publications

Clark, K. A.; George, T. A.; Brett, T. J.; Ross, C. R., II; Shoemaker, R. K., “Synthesis, Characterization, Crystal Structures, and Reactions of Trigonal Bipyramidal Tin(IV) Complexes Containing a Tetradentate Tripodal Tristhiolatophosphine Ligand. Use in the One-Step Synthesis of an Iron(IV) Complex”, Inorg. Chem. 39, 2252-2253 (2000).

Niemoth-Anderson, J. D.; Clark, K. A.; George, T. A.; Ross, C. R., II, “Five-Coordinate Diamagnetic Iron(IV) Complexes With A Trigonal Planar Arrangement of Thiolate Ligand Atoms: Synthesis and Crystal Structure of [FeX(PS₃)] (X = Cl, Br or I; PS₃H₃ = [P(C₆H₃-3-Me₃Si-2-SH)₃])”, J. Am. Chem. Soc. 122, 3977-3978 (2000).

Hammud, H. H.; George, T. A.; Kurk, D. N.; Shoemaker, R. K., “Synthesis and Characterization of Arene, Mono- and Dihydrido-arene, Monohydrido-Cyclopentadienyl, and Phosphite Complexes of Molybdenum Containing the Tridentate Ligand PhP(CH₂CH₂PPh₂)₂”, Inorg. Chim. Acta 281, 153-159 (1998).

Recent Graduate Students and Current Affiliations

· Kerry A. Fusie-Clark, Ph.D., 2001, now with Indian Head Division of Naval Surface Warfare Center, Research & Technology Department, High Energy Materials Division, Indian Head, MD.
· Jodi D. Niemoth-Anderson, Ph. D., 1998, now an instructor, University of Nebraska, Lincoln.