Purposeful construction versusself-assembly in approaches to single source precursors of spinel materials. Synthesis, structure and stability studies of MiiAl2(acac)3(OiPr)4(OAc), Mii = Mn, Co, Zn – a new class of heterometallic heteroleptic alkoxide complexes

Abstract

The reaction of Mn(acac)₃ with 3 eq. of Al(OⁱPr)₃ in toluene at reflux provided with minor yield single crystals of MnAl₂(acac)₃(OⁱPr)₄(OAc)(C₇H₈)_0.5 (1), incorporating into the molecular structure the acetate ligand originating from oxidation of the OⁱPr-groups. 1 was obtained with high yield (76%) via the reaction of Mn(acac)₃ with 2.2 eq. of Al(OⁱPr)₃ with subsequent addition of 1 eq. of HOAc to the reaction mixture cooled to room temperature. The analogs of 1, CoAl₂(acac)₃(OⁱPr)₄(OAc)(C₇H₈)_0.5 (2), and ZnAl₂(acac)₃(OⁱPr)₄(OAc)(C₇H₈)_0.5 (3), were obtained with almost quantitative yields by reaction of the corresponding M^II(acac)₂ with 2 eq. of Al(OⁱPr)₃ in toluene at reflux with subsequent addition of 1 eq. of Hacac and 1 eq. of HOAc after cooling the reaction mixture to the room temperature. In the molecules 1–3 the late transition metal atom is tetrahedrally coordinated (η²-acac plus 2 bonds to μ-OⁱPr-groups), and the Al atoms have a slightly distorted octahedral coordination (hexacoordinated) (η²-acac plus 3 bonds to μ-OⁱPr-groups plus one bond to μ-OAc-group). 1–3 are stable to solvolysis in toluene and are volatile under reduced pressure. Thermal decomposition of CoAl₂(acac)₃(OⁱPr)₄(OAc)(C₇H₈)_0.5 leads to nanoparticles of CoAl₂O₄, while homogeneous coatings of the spinel can be easily obtained using MOCVD.