Unusual solid-state reaction of [{CrL(acac)}2(µ-H3O2)][PF6]3. Isolation and crystal structures of [CrL(acac)F]PF6 and [CrL(acac)(O2PF2)]PF6(L = 1,4,7-trimethyl-1,4,7-triazacyclononane, acac = pentane-2,4-dionate)

Abstract

From a concentrated aqueous solution of the mononuclear complexes [CrL(acac)(OH)]PF₆·H₂O and [CrL(acac)(OH₂)][ClO₄]₂ at pH ≈ 6 the dinuclear H₃O₂^–-bridged species [{CrL(acac)}₂(µ-H₃O₂)][PF₆]₃ was isolated as a crystalline red solid (L = 1,4,7-trimethyl-1,4,7-triazacyclononane, acac = pentane-2,4-dionate). The dinuclear complex reacted at 145 °C in the solid state with evolution of 3 equivalents of HF, yielding quantitatively the mononuclear complexes [CrL(acac)F]PF₆ and [CrL(acac)(O₂PF₂)]PF₆ in equal amounts. Thus an unco-ordinated PF₆^– anion is thermally converted into a co-ordinated fluoride and a monodentate O₂PF₂^– ligand. The crystal structures of [CrL(acac)(OH₂)][ClO₄]₂, [CrL(acac)F]PF₆ and [CrL(acac)(O₂PF₂)]PF₆ have been determined by X-ray crystallography. The cobalt(III) complex [{CoL(acac)}₂(µ-H₃O₂)][PF₆]₃ has also been prepared and structurally characterized. It is isostructural with the chromium analogue. Heating to its melting point at 190 °C did not induce solid-state transformation to mononuclear cobalt(III) species analogous to [CrL(acac)F]PF₆ and [CrL(acac)(O₂PF₂)]PF₆.