SYNTHESIS, REACTIVITY AND STRUCTURES OF HAFNIUM-CONTAINING HOMO-BI-METALLIC AND HETERO-BI-METALLIC AND HOMO-TRI-METALLIC AND HETERO-TRI-METALLIC ALKOXIDES BASED ON EDGE-SHARING AND FACE-SHARING BIOCTAHEDRAL ALKOXOMETALATE LIGANDS

Using [{Hf(OPr1)(4)((PrOH)-O-1}(2)] as a building-block precursor, a s eries of home- and hetero-metallic alkoxides of hafnium has been prepa red and characterised using elemental analyses, infrared, multinuclear ((1)Hi Li-7, C-13 and Cd-113) NMR and single-crystal X-ray diffractio n studies. The solid-state structure of [Hf-2(OPr1)(8)((PrOH)-O-1)(2)] 1 reveals an edge-shared bioctahedral structure with the co-ordinated alcohol forming a hydrogen bridge across the dinuclear unit. The reac tions of I with other nitrogen- or,oxygen-containing donors gave monos ubstituted products of the general formula [Hf-2(OPr1)(8)((PrOH)-O-1)L ] (L = C5H5N 2 or C4H8O2 3) which retain the dinuclear edge-sharing bi octahedral structure as determined for 2 by X-ray crystallography. Com pound 1 reacted (1 :2) with 1 LiBun or LiOPr1 to afford dimeric [{LiHf (OPr1)(5)}(2)] 4. The molecular structure of 4 can be conceived as a d ianionic [Hf-2(OPr1)(10)](2-) unit that binds two Li+ one on each side of the Hf-Hf vector which are additionally co-ordinated by the bridgi ng OPr1 groups to display a trigonal-pyramidal geometry at the lithium atoms. The Hf2O6Li2 core in 4 comprises two analogous seconorcubane s ubunits sharing a common face defined by a Hf2O2 ring. Equimolar react ion of CuCl2 and [KHf2(OPr1)(9)] afforded the monomeric halide heterob imetallic derivative [CuHf2Cl(OPr1)(9)] 5. Compound 5 is paramagnetic and follows Curie law behaviour as inferred by a variable-temperature H-1 NMR. study. In the solid state its molecular geometry could be for mally seen as a tetradentate interaction of the distorted confacial bi octahedron [Hf-2(OPr1)(9)](-) with a CuCl+ fragment. Each Hf is six-ed -ordinated; Cu is five-co-ordinated and displays a distorted trigonal- bipyramidal geometry. The reaction (1:1) of [CdHf2I(OPr1)(9)] with RSr (OPr1)(3) produced a new heterotermetallic derivative [{[Cd(OPr1)(3)]S r[Hf-2(OPr1)(9)]}(2)] 6. This involves the switching of central metal atoms between the two precursors and the Hf-2(OPr1)(9) unit in 6 binds to Sr rather than Cd as anticipated. The centrosymmetric dimeric form of 6 is made up of a [Sr(mu-OPr1)(2)Cd(mu-OPr1)(2)Cd(mu-OPr1)(2)Sr](2 +) spirocyclic unit capped at both the ends by [Hf-2(OPr1)(9)](-) moie ties.