From [RuX6] to [Ru(RCN)6]: synthesis of mixed halide–nitrile complexes of ruthenium, and their spectroelectrochemical characterization in multiple oxidation states

Publisher Website
Google Scholar
Abstract
A complete series of benzonitrile- and acetonitrile-substituted ruthenium halide complexes [RuX6-n(RCN)n]z(n= 0–6), ranging stepwise from [RuX6]2– to [Ru(RCN)6]2+, has been prepared and characterized. Three series were established, having RCN/X = PhCN/Cl, PhCN/Br, and MeCN/Cl. The strategy of reductive substitution has been developed to prepare [RuX5(RCN)]2–, trans-[RuX4(RCN)2]–, mer-[RuX3(RCN)3] and trans-[RuX2(RCN)4] in turn from [RuX6]2– by systematic electrosynthetic routes, through detailed management of potential, temperature and RCN concentration. The monosubstituted pentahalogeno complexes are unstable and their preparation is only practicable via electrode-induced (RuIV→ RuIII) halide displacement from [RuX6]2– at low temperature. At the divalent level, exhaustive substitution to form [RuX(RCN)5]+ and [Ru(RCN)6]2+ from [RuX2(RCN)4] required more forcing chemical conditions (Ag+ and CF3SO3H respectively). Voltammetric studies between –65 and 20 °C confirm that the family of mixed halide–nitrile monomeric complexes is rich in redox chemistry, spanning oxidation states V to II. Under reversible conditions, the various metal-based electrode potentials for [RuX6-n(RCN)n]z are a linear function of the stoichiometry parameter, n, increasing by 0.45 (Ruv–RuIV) or 0.6 V (RuIV–RuIII and RuIII–RuII) per halide replaced by nitrile. By use of spectroelectrogeneration techniques, the optical charge-transfer spectra for every available member of each family have been recorded in multiple oxidation levels, defining the states RuIV for n= 0–2, RuIII for n= 0–5 and RuII for n= 2–6. For the present complexes, there are unmistakable complementary progressions in the halide-to-metal (X→RuIII) and metal-to-ligand (RuII→RCN) bands, in accord with the underlying trend in E½(RuIII–RuII). These measurements present an unusual opprotunity to document and analyse the characteristic trends in appearance and location of both ligand-to-metal (RuIII) and metal-to-ligand (RuII) charge-transfer manifolds as a function of stoichiometry.

This publication has 22 references indexed in Scilit: