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DOI: 10.1039/A700833C (Paper) Reference Section for: J. Chem. Soc., Dalton Trans., 1997, 2101-2108

Synthesis, reactivity and structures of hafnium-containing homo- and hetero- (bi- and tri-) metallic alkoxides based on edge- and face-sharing bioctahedral alkoxometalate ligands[hair space]

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Michael Veith, Sanjay Mathur, Charu Mathur and Volker Huch

Abstract

Using [{Hf(OPri)4(PriOH)}2 ] as a building-block precursor, a series of homo- and hetero-metallic alkoxides of hafnium has been prepared and characterised using elemental analyses, infrared, multinuclear (1H, 7Li, 13C and 113Cd) NMR and single-crystal X-ray diffraction studies. The solid-state structure of [Hf2(OPri)8(PriOH)2 ] 1 reveals an edge-shared bioctahedral structure with the co-ordinated alcohol forming a hydrogen bridge across the dinuclear unit. The reactions of 1 with other nitrogen- or oxygen-containing donors gave monosubstituted products of the general formula [Hf2(OPri)8(PriOH)L] (L = C5H5N 2 or C4H8O2 3) which retain the dinuclear edge-sharing bioctahedral structure as determined for 2 by X-ray crystallography. Compound 1 reacted (1[hair space]:[hair space]2) with LiBun or LiOPri to afford dimeric [{LiHf(OPri)5}2] 4. The molecular structure of 4 can be conceived as a dianionic [Hf2(OPri)10]2- unit that binds two Li+ one on each side of the Hf–Hf vector which are additionally co-ordinated by the bridging OPri groups to display a trigonal-pyramidal geometry at the lithium atoms. The Hf2O6Li2 core in 4 comprises two analogous seconorcubane subunits sharing a common face defined by a Hf2O2 ring. Equimolar reaction of CuCl2 and [KHf2(OPri)9] afforded the monomeric halide heterobimetallic derivative [CuHf2Cl(OPri)9] 5. Compound 5 is paramagnetic and follows Curie law behaviour as inferred by a variable-temperature 1H NMR study. In the solid state its molecular geometry could be formally seen as a tetradentate interaction of the distorted confacial bioctahedron [Hf2(OPri)9]- with a CuCl+ fragment. Each Hf is six-co-ordinated; Cu is five-co-ordinated and displays a distorted trigonal-bipyramidal geometry. The reaction (1[hair space]:[hair space]1) of [CdHf2I(OPri)9] with KSr(OPri)3 produced a new heterotermetallic derivative [{[Cd(OPri)3]Sr[Hf2(OPri )9]}2] 6. This involves the switching of central metal atoms between the two precursors and the Hf2(OPri)9 unit in 6 binds to Sr rather than Cd as anticipated. The centrosymmetric dimeric form of 6 is made up of a [Sr(µ-OPri)2Cd(µ-OPri)2 Cd(µ-OPri)2Sr]2+ spirocyclic unit capped at both the ends by [Hf2(OPri)9]- moieties.

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