Abstract:
The ruthenium-iminoquinone complexes, [Ru(tpm)(Cl)(Q)](+) [tpm = tris(1-pyrazolyl)methane, Q = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, where aryl = C(6)H(5), [1](+); m-(OCH(3))(2)C(6)H(3), [2](+); m-(Cl)(2)C(6)H(3), [3](+)] have been synthesized. The sensitive bond distances of "Q" in [1](ClO(4)) and [2](ClO(4)), C-O: 1.294(8), 1.281(2) angstrom; C-N: 1.352(8), 1.335(2) angstrom; and C-C(meta): 1.366(10)/1.367(9) angstrom, 1.364(2)/1.353(2) angstrom, respectively, and other analytical as well as theoretical (DFT) events suggest the valence configuration of [Ru(III)(tpm)(Cl)(Q(Sq)(.) )](+) for [1](+)-[3](+). The paramagnetic [1](+)-[3](+) show sharp (1)H NMR spectra with strikingly small J of 1.8-3.0 Hz. The DFT calculations on [1](+) predict that the triplet (S = 1) state exists above (1004 cm (1)) the singlet (S = 0) ground state. [1](+) exhibits mu equivalent to 2.2 BM at 300 K which diminishes to 0.3 BM near 2 K due to the steady decrease in the ratio of triplet to singlet population with the lowering of temperature. [1](+)-[3](+) exhibit one oxidation and two successive reductions each in CH(3)CN. Experimental and DFT analyses collectively establish the valence configurations at the non-innocent {Ru-Q} interface along the redox chain as [(tpm)(Cl)Ru(III)(Q(Q)(o))](2+) ([1](2+)-[3](2+)) -> [(tpm)(Cl) Ru(III)(Q(Sq)(.))](+) ([1](+)-[3](+)) -> [(tpm)(Cl) Ru(II)(QSq(.))] -> [(tpm)(Cl) Ru(III)(Q(Cat))] (1-3) -> [(tpm)(Cl)-Ru(II)(Q(Cat))] ([1] -[3] ). The spectral features of [1](n)-[3](n) (n = +2, +1, 0) have been addressed based on the TD-DFT calculations on [1](n). (C) 2011 Elsevier B.V. All rights reserved.