NOVEL REDOX PROPERTIES OF THE PARAMAGNETIC HEXANUCLEAR NIOBIUM CLUSTER HALIDE NB6CL18(3-) AND THE PREPARATION, STRUCTURES, AND CONDUCTING AND MAGNETIC-PROPERTIES OF ITS ONE-DIMENSIONAL MIXED-VALENCE TETRAMETHYLTETRA(SELENA AND THIA)FULVALENIUM SALTS - [TMTSF AND TMTTF]5[NB6CL18].(CH2CL2)0.5

A cyclic voltammetry study in acetonitrile of [(C2H5)4N]3Nb6Cl18 is presented that gives the first evidence for the existence at 1.72 V vs SCE of the 13-electron cluster core Nb6Cl125+, a novel powerful inorganic oxidant. The title compounds have been prepared by electrocrystallization and characterized by single-crystal X-ray diffraction, ESR, and magnetic susceptibility and transport experiments. [(D)43+(D0)]Nb6Cl183−(CH2Cl2)0.5 [D = 2,3,6,7-tetramethyl-1,4,5,8-selena- and thiafulvalene (TMTSF and TMTTF) in 1 and 2, respectively] are semiconducting (σ300K = 0.5 Ω−1 cm−1 for 1; activation energies of 0.16 and 0.20 eV for 1 and 2, respectively) and the triclinic (space group [formula omitted]) unit-cell parameters are a = 13.176 (5), b = 13.847 (7), c = 14.581 (9) Å, α = 113.79 (3), β = 96.47 (3), γ = 99.94 (3)°, V = 2348.1 (2) Å3 for 1 and a = 12.933 (7), b = 13.669 (8), c = 14.334 (11) Å, α = 114.40 (3), β = 96.97 (4), γ = 99.21 (4)°, V = 2227.8 (3) Å3 for 2. Both salts are isostructural and present stacks of the organic radical cations with one-dimensional electronic properties. The electronic structure of these salts has been studied by means of tight-binding band structure calculations. A unique magnetic interaction between the organic spins and the localized inorganic cluster spins is presented and discussed. © 1990, American Chemical Society. All rights reserved.