Tetranuclear Complexes of 1,3,5,9,11,13-Hexaketonates. 2. Synthesis and Electrochemistry of a Series of Heterotetranuclear Complexes, Bis{1,1′-(1,3-phenylene)bis[7-methyl-1,3,5-octanetrionato(4-)]}hexakis(pyridine)bis[dioxouranium(VI)]dimetal(II), M₂(UO₂)₂(MOB)₂(py)₆

A series of heterotetranuclear complexes was prepared by using a 1,3,5,9,11,13-hexaketone ligand. The specific ligand used in this study contains two 1,3,5-triketone groups substituted at the meta positions of a benzene ring. Neutral complexes are formed by binding four dicationic metal species to two tetraanionic ligands. The resulting tetranuclear complexes contain two binuclear moities separated by about 7 Å. A series of complexes with two uranyl ions and two metal ions, M²⁺, per molecule was prepared. Reaction of the ligand with UO₂²⁺ results in the selective coordination of the uranium to the “outside” (1,3 and 11,13) coordination sites of the hexaketonates. As a result, the UO₂²⁺ ions assemble the ligands so that the “interior” (3,5 and 9,11) coordination sites are available for binding the divalent metal ions M²⁺. The electrochemical properties of the resulting M₂(UO₂)₂(L)₂ complexes were investigated by cyclic voltammetry, chronoamperometry, and controlled-potential electrolysis. The nature of the multielectron-transfer processes observed is discussed on the basis of the results of these experiments.