MIXED-VALENCE DINUCLEAR MOLYBDENUM COMPLEXES WITH BENZENEDIAMIDO AND DIANILIDO BRIDGES - COMPARISON WITH RELATED PHENOLATE AND DIPYRIDYL SPECIES, AND WITH THEIR PENTAMMINERUTHENIUM ANALOGS

The monoanionic mixed-valence benzenediamido complexes ortho- and ara- [({Mo(NO)[HB(dmpz)(3)]X}(2-)(Z(2)C(6)H(4))](-) A [HB(dmpz)(3) = tris(3 ,5-dimethylpyrazolyl)hydroborate; Z = NH; X = Cl, Br or I] have been c haracterised by electronic, EPR and IR spectroscopic and electrochemic al techniques. They are delocalised at room temperature on the EPR tim e-scale but valence-trapped on the IR time-scale, whereas the meta iso mer exhibits valence-trapped behaviour according to both techniques. T he electrochemical properties of these species and of related dianilid o complexes [{Mo(NO)[HB(dmpz)(3)]X}(2)(ZC(6)H(4)EC(6)H(4)Z)] B [Z = NH ; E = CH2, O, SO2, CO or OC6H4(SO2)C6H4O] are dependent on X and E. Th ese results are compared with those obtained from related diphenolato species A (Z = 0) and B (Z = 0) and dipyridyl analogues [{Mo(NO)[HB(dm pz)(3)]X}(2){(NC5H4)E'-(C5H4N)}] C (E' = nothing, CH2CH2, CH=CH or dim ethyldecapentene). Comproportionation constants and related data for t he redox equilibria A + A(2-) reversible arrow 2(A-), B + B2- reversib le arrow ; 2B(-) and C + C2- reversible arrow 2C(-) show that interact ion between the molybdenum-based redox centres increases significantly as the distance between them decreases and as a function of the group connecting the bridge to the molybdenum, in the order O < NH < N (pyr idine) The data are generally consistent with those obtained from rela ted dinuclear penatmmineruthenium complexes [{Ru(NH3)(5)}(2)Q](n+) (Q = bridging group) but the interaction between the metal centres is muc h greater in the molybdenum species than in the ruthenium complexes, a nd a simple explanation for this behaviour is given.