Sensitivity of the Valence Structure in Diruthenium Complexes As a Function of Terminal and Bridging Ligands

Abstract

The compounds [(acac)2Ru(III)(μ-H2L(2-))Ru(III)(acac)2] (rac, 1, and meso, 1') and [(bpy)2Ru(II)(μ-H2L(•-))Ru(II)(bpy)2](ClO4)3 (meso, [2](ClO4)3) have been structurally, magnetically, spectroelectrochemically, and computationally characterized (acac(-) = acetylacetonate, bpy = 2,2'-bipyridine, and H4L = 1,4-diamino-9,10-anthraquinone). The N,O;N',O'-coordinated μ-H2L(n-) forms two β-ketiminato-type chelate rings, and 1 or 1' are connected via NH···O hydrogen bridges in the crystals. 1 exhibits a complex magnetic behavior, while [2](ClO4)3 is a radical species with mixed ligand/metal-based spin. The combination of redox noninnocent bridge (H2L(0) → → → →H2L(4-)) and {(acac)2Ru(II)} → →{(acac)2Ru(IV)} or {(bpy)2Ru(II)} → {(bpy)2Ru(III)} in 1/1' or 2 generates alternatives regarding the oxidation state formulations for the accessible redox states (1(n) and 2(n)), which have been assessed by UV-vis-NIR, EPR, and DFT/TD-DFT calculations. The experimental and theoretical studies suggest variable mixing of the frontier orbitals of the metals and the bridge, leading to the following most appropriate oxidation state combinations: [(acac)2Ru(III)(μ-H2L(•-))Ru(III)(acac)2](+) (1(+)) → [(acac)2Ru(III)(μ-H2L(2-))Ru(III)(acac)2] (1) → [(acac)2Ru(III)(μ-H2L(•3-))Ru(III)(acac)2](-)/[(acac)2Ru(III)(μ-H2L(2-))Ru(II)(acac)2](-) (1(-)) → [(acac)2Ru(III)(μ-H2L(4-))Ru(III)(acac)2](2-)/[(acac)2Ru(II)(μ-H2L(2-))Ru(II)(acac)2](2-) (1(2-)) and [(bpy)2Ru(III)(μ-H2L(•-))Ru(II)(bpy)2](4+) (2(4+)) → [(bpy)2Ru(II)(μ-H2L(•-))Ru(II)(bpy)2](3+)/[(bpy)2Ru(II)(μ-H2L(2-))Ru(III)(bpy)2](3+) (2(3+)) → [(bpy)2Ru(II)(μ-H2L(2-))Ru(II)(bpy)2](2+) (2(2+)). The favoring of Ru(III) by σ-donating acac(-) and of Ru(II) by the π-accepting bpy coligands shifts the conceivable valence alternatives accordingly. Similarly, the introduction of the NH donor function in H2L(n) as compared to O causes a cathodic shift of redox potentials with corresponding consequences for the valence structure.

Recognition of fractional non-innocent feature of osmium coordinated 2,2′-biimidazole or 2,2′-bis(4,5-dimethylimidazole) and their interactions with anions

“…3, Table 5) collectively suggest the significant involvement of L based orbitals in the first oxidation process (Ox1 in Fig. 1f,g An appreciable involvement of the bridge in the redox processes due to its non-innocent feature, 11a,20,21 leading to the mixed electronic structural form, has also been recognised recently for the analogous diosmium and diruthenium frameworks of {(μ-HL 2− )[Os(bpy) 2 ] 2 } n (H 3 L: 5-(1H-benzo [d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid) 6a and {(μ-H 2 L)[Ru(AL) 2 ] 2 } n (AL = acac − (acetylacetonate), bpy and H 2 L = 1,4-diimino-9,10-anthraquinone) 22 7a respectively. This indeed implies that the electronic structural forms of the one-electron oxidised 3 3+ and 4 3+ can be better described as the resonating form of {Os II (µ-L 2− )Os III } ↔ {Os II (µ-L •− )Os II } (Scheme 2), instead of a simple mixed valent situation {Os II (µ-L 2− )-Os III }, 18b,19 as was presumed earlier for the reported L 2− bridged analogous diruthenium [{(bpy) 2 Ru} 2 (µ-L 2− )] 3+ / [{( pap) 2 Ru} 2 (µ-L 2− )] 3+ and diosmium [{( pap) 2 Os} 2 (µ-L 2− )] 3+ complexes (Table 3).…”

A Diruthenium Complex of an N‐Pyridyl‐o‐aminophenol Derivative: A Route to Mixed Valency

“…[2] Mixed-valencem olecular systems are equally important in materials and chemical science, as well as metallo-protein chemistry. [3] In this regard, the first mixed-valence ion, [(NH 3 ) 5 Ru(pz)Ru(NH 3 ) 5 ] 5 + (pz = ab ridging pyrazine ligand),r eported by Creutz and Ta ube was considered as the leader of this research area. [4] In this complex ion, the sum of the oxidation numbers of two metal ions is an odd integer.…”

“…Lahiri et al reported several type Bc omplexes that contained redox-activeb ridging ligands. [5] Lahiri et al also reported am ixed-valencet ype Bc omplex, in which L NI was unsymmetrical. [5g] However,n ot ype Cc omplexes have been documented, so far.T he electronic environments of the two metal ions in type Cc omplexes are not similar and elucidation of the electronic states of the members of the redox series with an unsymmetrical Ru 2 core is worthyo fi nvestigation.…”

Design of Ruthenium Biimidazole-Anthraquinone Dyads to Demonstrate Photoinduced Electron Transfer: Combined Experimental and DFT/TD-DFT Investigations

“…[21–56] To this end, a variety of electron‐acceptor groups such as viologens and amines have been covalently linked to Ru(bpy) 3 2+ unit, although in combination with 9,10‐anthraquinone acceptor unit is relatively sparse in the literature . Despite of their important roles as good electron acceptors with desirable thermal and electrochemical stability, relatively little attention has been paid in connection with the construction of suitable donor‐acceptor systems connected with remarkably efficient photosensitizing Ru(bpy) 3 2+ unit …”