Synthesis, structure and bonding in Nb-2(eta(6)-mesitylene)(2)(mu-I)(4) and a new intermediate-valent dinuclear niobium complex, [Nb-2(eta(6)-mesitylene)(2)(mu-I)(4)]I

Nb-2(eta(6)-mesitylene)(2)(mu-1)(4)(mesitylene = 1,3,5-C6H3(CH3)(3) = mes) (2) has been synthesized from the reaction of Nb(eta(6)-mes)(2) (1) with iodine in THF and characterized by NMR, IR, UV-vis spectroscopy, and single crystal X-ray diffraction. The mesitylene ligands in 2 show nonplanar boat conformations, indicating localization of pi-electron density in a 1,4-diene fashion, which is supported by a molecular orbital calculation. NMR spectra, however, indicate that 2 undergoes rapid interconversion of boat conformations as well as ring rotation in solution even at - 62 degrees C. A cyclic voltammogram of complex 2 exhibits two redox waves. A new intermediate-valent dinuclear complex [Nb-2(eta(6)-mes)(2)(mu-I)(4)]I(3) was prepared from oxidation of 2 with iodine. The powder EPR spectrum of 3 is discussed, while magnetic studies of 3 exhibit Curie-Weiss paramagnetic behavior at temperatures above 100 K with mu(eff) = 1.77 BM. Crystal data: 2, C18H24I4Nb2, monoclinic, P21/n (No. 14), a = 10.186(2) Angstrom, b = 8.837(2) Angstrom, c = 12.797(3) Angstrom, beta = 96.95(2)degrees, V = 1143.3 Angstrom(3) , Z = 2, and d(calcd) = 2.71 g cm(-3); 3, C18H24I5Nb2, monoclinic, C2/c, a = 8.348(2) Angstrom, b = 15.038(3) Angstrom, c = 20.373(4) Angstrom, beta = 97.25(3)degrees,V = 2537.1(9) Angstrom(3), Z = 4, and d(calcd), = 2.78 g cm(-3).