Synthesis, structure and characterisation of magnesium and calcium beta-diketonate complexes [Ca-3(tmhd)(6)] and [Ca-2(tmhd)(4)(EtOH)(2)] (Htmhd=2,2,6,6-tetramethylheptane-3,5-dione)

The reaction of the oligomeric Group 2 metal ethoxide complexes [{Mg(OEt)(2)}(n)] and [{Ca(OEt)(2)(EtOH)(4)}(n)] with 2 equivalents of 2,2,6,6-tetramethylheptane-3,5-dione (Htmhd) yielded the homoleptic beta-diketonate compounds [{M(tmhd)(2)}(n)] (M = Mg 1 or Ca 2). An intermediate en route to complex 2 is the ethanol-solvated species [Ca-2(tmhd)(4)(EtOH)(2)] 3. The reaction of 1 with triglyme (2,5,8,11-tetraoxadodecane, C8H18O4) yielded the air- and moisture-stable derivative [{[Mg(tmhd)(2)](2)(C8H18O4)}(n)] 4. The calcium complexes 2 and 3 were characterised structurally by X-ray crystallography: 2 is the first structurally characterised homoleptic beta-diketonate of calcium and has a novel triangular core, with all the calcium ions six-co-ordinate and held together by tmhd ligands in a wide range of co-ordinating modes; 3 has a dimeric structure with both chelating and bridging tmhd ligands and two terminal ethanol molecules.