Homoleptic Tetranuclear Complexes of Divalent Tin and Lead Tetraolates

Homoleptic tetranuclear complexes of divalent tin and lead tetraolates, M4(hfpt)2 [M = Sn (1) and Pb (2); hfpt4– is an anion of 1,1,1,5,5,5-hexafluoropentane-2,2,4,4-tetraol], have been obtained in high yield from the corresponding (trimethylsilyl)amides. The solid-state structures of 1 and 2 contain discrete molecules in which a butterfly tetrahedron of metal atoms is sandwiched between two tetraolate ligands acting in tetradentate mode. The lone-pair Sn2+ and Pb2+ cations exhibit pyramidal coordination of four ligand oxygen atoms. A multinuclear NMR study unambiguously confirmed that metal tetraolates retain their polynuclear structure in solution of even coordinating solvents. An interesting example of the strong through-space coupling between 19F of the tetraolate trifluoromethyl groups and 117/119Sn or 207Pb nuclei was found. Both compounds were shown to have clean, low-temperature decomposition that results in crystalline oxides SnO2 and PbO, respectively, for 1 and 2. This work demonstrates the remarkable coordination properties of the tetraolate ligand that can be utilized for the preparation of a wide variety of poly- and heterometallic complexes. Decomposition studies revealed a great potential of metal tetraolate complexes as prospective molecular precursors for the soft chemistry approach to oxide materials.