Ruthenium coordination preferences in imidazole ‐containing systems revealed by electrospray ionization mass spectrometry and molecular modeling: possible cues for the surprising stability of the Ru (III)/tris (hydroxymethyl)‐aminomethane/imidazole complexes

AbstractRuthenium is a platinoid that exhibits a range of unique chemical properties in solution, which are exploited in a variety of applications, including luminescent probes, anticancer therapies and artificial photosynthesis. This paper focuses on a recently demonstrated ability of this metal in its +3 oxidation state to form highly stable complexes with tris (hydroxymethyl)aminomethane (H2NC(CH2OH)3, Tris ‐base or T) and imidazole (Im) ligands, where a single RuIII cation is coordinated by two molecules of each T and Im ‐. High‐resolution electrospray ionization mass spectrometry (ESI MS) is used to characterize RuIII complexes formed by placing a RuII complex [(NH3)5RuIICl]Cl in a Tris buffer under aerobic conditions. The most abundant ionic species in ESI MS represent mononuclear complexes containing an oxidized form of the metal,i.e. [XnRuIIIT2– 2H]+, where X could be an additional T (n = 1) or NH3 (n = 0 ‐2). Di‐ and tri‐metal complexes also give rise to a series of abundant ions, with the highest mass ion representing a metal complex with an empirical formula Ru3C24O21N6H66 (interpreted ascyclo(T2RuO)3, a cyclic oxo ‐bridged structure, where the coordination sphere of each metal is completed by two T ligands). The empirical formulae of the binuclear species are consistent with the structures representing acyclic fragments ofcyclo(T2RuO)3 with addition of various combinations of ammonia and dioxygen as ligands. Addition of histidine in large molar exc...

Source: Journal of Mass Spectrometry - September 10, 2019 Category: Chemistry Authors: Igor A. Kaltashov, Anton El ‐Khoury, Chengfeng Ren, Sergey N. Savinov Tags: SPECIAL ISSUE ‐ RESEARCH ARTICLE Source Type: research