TETRANUCLEAR COMPLEXES OF 1,3,5,9,11,13-HEXAKETONATES .1. SYNTHESIS AND STRUCTURE OF BIS[1,3-BIS(2-METHYL-4,6,8-OCTANETRION-8-YL)BENZENATO(4-)]TETRAKIS(PYRIDINE)TETRACOPPER-(II), CU4(MOB)2(PY)4 - OBSERVATION OF 4-ELECTRON-TRANSFER ELECTROCHEMISTRY

A new hexaketone ligand has been prepared, 1,3-bis(2-methyl-4,6,8-octanetrion-8-yl)benzene, abbreviated H4MOB, that is capable of binding four metal ions. Two deprotonated ligand molecules and four divalent metal ions form neutral, molecular complexes. A crystal structure is reported for the tetranuclear copper(II) complex. Recrystallization from pyridine yields single crystals of Cu4(MOB)2(py)4·2py. Crystal data: P21/c, a = 19.33 (2) Å, b = 19.831 (6) Å, c = 9.809 (8) Å, β = 97.64 (8)°, Z = 2, V = 3727 (5) Å3, R1 = 0.078, R2 = 0.090. The Cu4(MOB)2(py)4 molecules consist of two binuclear copper(II) triketonate type moieties linked through 1,3-substitutions on phenyl rings. The Cu-Cu separation within a binuclear unit is 3.021 (1) Å. The closest Cu-Cu distance between the binuclear units is 6.9 Å. Each copper is bound to four ketonate oxygens and one pyridine nitrogen in typical square-pyramidal geometry. Strong magnetic superexchange between Cu(II)'s in the binuclear units renders the molecule diamagnetic at room temperature. Cyclic voltammetry in pyridine in the range 0 to −1.2 V yields one quasi-reversible wave with E1/2 ≅ −0.8 V. Chronoamperometric results show that this wave is due to a four-electron-transfer process. © 1990, American Chemical Society. All rights reserved.