Specific sequestering agents for the actinides. 7. Synthesis and structural chemistry of tetrakis(thiohydroxamato)hafnium(IV) in Hf(CH3C6H4(S)N(O)CH3)4.C2H5OH

Abstract

A continuing project in this laboratory has been the design and synthesis of specific sequestering agents for the actinide IV ions. The degree of success so far achieved in this goal has been reviewed recently. The approach used relies on the similar coordination chemistry of high-spin Fe/sup 3 +/ and Pu and the molecular architecture of the siderophores (ferric ion specific chelating agents of microbial origin). While hydroxamate and catecholate chealating groups are the primary functional groups in siderophores, the thiohydroxamate chelating unit also occurs in at least one compound of natural origin. The tetrakis(catecholato)metalate(IV) complexes of Th(IV), U(IV), and Hf(IV) have all been prepared and structurally characterized. They are isostructural, with the D/sub 2d/ coordination symmetry of the trigonal-faced dodecahedron. Both the hydroxamate complexes tetrakis(N-isoproply-3,3-dimethylbutanehydroxamato)hafnium(IV)/sup 2/ and tetrakis(N-phenylbenzohydroxamato)hafnium(IV)/sup 9/ have this same D/sub 2d/ geometry. In contrast, the more sterically hindered complex, tetrakis(N-isopropyl-2,3-dimethylpropanehydroxamato)thorium(IV), is distorted substantially toward a cubic coordination polyhedron. No tetrakis(thiohydroxamate) complexes have been structurally characterized to date. Determination of the coordination geometry of the unconstrained tetrakis(bidentate)metalate(IV) complexes are a fundamental component in the design of an octadentate chelating agent that incorporates four such functionalities to form an optimum metal coordination environment. While we have prepared thiohydroxamatemore » complexes of Th(IV), no crystals suitable for structural analysis have been obtained. Instead, we report the synthesis and structural characterization of the hafnium complex, the title compound.« less