ABSTRACT: The redox-active ligand 5,7,12,14-tetraazapentacene-6,13-quinone (L) forms a series of dimeric (linkage isomer 1 and 2), trimeric (3) and tetrameric(4) complexes on reacting with two, three and four equivalents of [Ru(acac)2(CH3CN)2] metal precursors. All of the structurally characterized complexes form five membered chelate rings around central Ru atom (rac-1, rac-2, rac-3, meso-4) via N and O atoms of the bridging ligand. The ambiguity in valence and spin distribution of the synthesized metal-ligand assemblies have been addressed by means of cyclic voltammetry, spectroelectrochemical responses, EPR and theoretical calculations (DFT and TD-DFT). The collective experimental and theoretical investigation reveals that the one electron oxidized moiety of complex 1 and 2 preferably exists in electronic configurations {RuIII(μ-L0)RuII} and {RuIII(μ-L−)RuIII} respectively. Moreover, one electron oxidized variety of complex 2 exhibits three spin situations with negative spin density at one metal site having lower energy than 1+ as suggested by DFT. Further, successive electron transfer at metal-ligand interface in case of all of the complexes has been investigated thoroughly by spectroelectrochemistry and TD-DFT analysis. In contrast to the two isomeric dinuclear species 1 and 2, the quinone oxygen centres in 3 and 4 serves as atomic bridges (ca. 4 Å) between two metals. The systems appear electronically delocalised with reduced ligand and partially oxidised metals. Thus, pairs of mixed-valent entities [Ru2.5-(C-O-)-Ru2.5] are connected in spin-coupled fashion via the tetraazapentacene p system.

Di, tri and tertanuclear ruthenium complexes of a heterocyclic and quinonoid bridging ligand: Valence and spin alternatives for the metal/Ligand/ metal arrangement, non-innocence and mixed valency

256th National Meeting (2018)

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