A facile and preferential synthesis of the complexes, cis-trans-cis-Ru II [NC 5H 4NNC 6H 4(R)] 2 (R = H, o-Me/Cl, m-Me/Cl, p-Me/Cl) Synthesis, spectroscopic characterization and electron-transfer properties

Abstract

A group of seven complexes of the type ctc-Ru IIL 2Cl 2 ( 2a− 2g) (L = NC 5H 4-NN-C 6H 5(R), R = H, o-Me/Cl, m-Me/Cl, p-Me/Cl and ctc = cic-traps-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 1H NMR spectroscopy. They exhibit a strong metal to ligand charge-transfer band in the range 582–603 nm and intra ligand π-π ∗ transition near 320 nm. In acetonitrile solution the complexes display reversible ruthenium (II) 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 to the corresponding trivalent species ( 3a and 3e) by using HNO 3 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 π-π ∗ transition near 370 nm. In glassy condition (77 K) complexes display rhombic EPR spectra corresponding to the distorted octahedral geometry.