A facile and preferential synthesis of the complexes, cis-trans-cis-RuII[NC5H4-N=N-C6H4(R)]2 (R = H, o-Me/Cl, m-Me/Cl, p-Me/Cl).: Synthesis, spectroscopic characterization and electron-transfer properties

A group of seven complexes of the type ctc-(RuL2Cl2)-L-II (2a-2g) (L = NC5H4-N=N-C6H5(R), R = H, o-Me/Cl, m-Me/Cl, p-Me/Cl and ctc = cic-trans-cis with respect to chlorides, pyridine and azo nitrogens, respectively) have been synthesized and characterized. The complexes are diamagnetic (Ru-II, t(2g)(6), S = 0) and electrically neutral. The molecular geometry of the complexes (2) in solution has been established by H-1 NMR spectroscopy. They exhibit a strong metal to ligand charge-transfer band in the range 582-603 nm and intra ligand pi-pi* transition near 320 nm. In acetonitrile solution the complexes display reversible ruthenium(II) reversible arrow ruthenium(III) oxidation couples in the range 1.02 --> 1.36 V vs SCE. Two successive quasi-reversible ligand reductions are observed for each complex in the ranges -0.42 --> -0.60 V and -0.68 --> -0.85 V vs SCE, respectively. The complexes 2a and 2e have been oxidized tb the corresponding trivalent species (3a and 3e) by using HNO3 as oxidizing agent and isolated in solid state as perchlorate salts. Complexes are one-electron paramagnets (Ru-III, t(2g)(5), S = 1/2) and show 1:1 conductivity in acetonitrile solution. The presence of perchlorate counter ion in the complexes has been evidenced by the strong infrared bands near 1100 and 600 cm(-1). Complexes exhibit a strong ligand to metal charge-transfer band near 530 nm and intra ligand pi-pi* transition near 370 nm. In glassy condition (77 K) complexes display rhombic EPR spectra corresponding to the distorted octahedral geometry. (C) 1998 Elsevier Science Ltd. All rights reserved.