Ru(iv)–Ru(iv), Ru(iii)–Ru(iv), and Ru(iii)–Ru(iii) complexes having a sulfato bridging ligand on the doubly oxido-/hydroxido-bridged core, and their crystallographic and electronic structures

Abstract

The Ru₂(IV,IV), Ru₂(III,IV), and Ru₂(III,III) complexes with the doubly oxido- and/or hydroxido-bridged diamond core {Ru₂(μ-O(H))₂}, bridged by an η¹:η¹:μ²-type bidentate sulfato ligand, [{Ru(L)}₂(μ-O)₂(μ-O₂SO₂)]^m+ (m = 1: [III,IV]⁺; m = 2: [IV,IV]²⁺), [{Ru^III,IV(L)}₂(μ-O)(μ-OH)(μ-O₂SO₂)]²⁺ ([III,IV_1H]²⁺), and [{Ru^III,III(L)}₂(μ-OH)₂(μ-O₂SO₂)]²⁺ ([III,III_2H]²⁺) (L = ethylbis(2-pyridylmethyl)amine), were synthesised as ClO₄⁻-salts, and their crystal and electronic structures investigated. The corresponding hydrogencarbonato-bridged Ru₂(III,III) complex, [{Ru^III,III(L)}₂(μ-OH)₂(μ-O₂COH)]³⁺ ([III,III(HCO₃)_2H]³⁺), was also prepared and its crystallographic and electronic structures compared to those of the sulfato-bridged system, [III,III_2H]²⁺. All the sulfato-bridged complexes isolated were confirmed in the Pourbaix diagram, wherein the redox potential was plotted as a function of pH. The pK_as were determined using UV-vis-NIR spectroscopic measurements and incorporated into the Pourbaix diagram. This is the first sequential study, both experimentally and theoretically, on the various oxidation states of Ru centres and the number of protons on the {Ru₂(μ-O(H))₂} core in the same tridentate ligand system for complexes with the {Ru₂(μ-O(H))₂(μ-O₂XY)}-type dinuclear framework, which are analogous to the intermediate structures of the diiron-containing soluble methane monooxygenase.