Synthesis, structure, redox, NLO and DNA interaction aspects of [{(L′–‴)2RuII}3(μ3-L)]3+ and [(L′)2RuII(NC5H4S−)]+ [L3− = 1,3,5-triazine-2,4,6-trithiolato, L′–‴ = arylazopyridine]

Abstract

The trinuclear complexes [{(L′^–‴)₂Ru^II}₃(μ₃-L)](ClO₄)₃, [1](ClO₄)₃–[3](ClO₄)₃ {L = trianionic form of 1,3,5-triazine-2,4,6-trithiol; N_pC₅H₄NN_a–C₆H₄(R), R = H (L′), m-Me (L″), p-Me (L‴)} and the analogous mononuclear complex [(L′)₂Ru^II(NC₅H₄S⁻)]ClO₄ [4]ClO₄ were synthesized. Crystal structures of [1](ClO₄)₃ and [4]ClO₄ were determined. [1]³⁺–[3]³⁺ exhibit three successive oxidative couples corresponding to Ru^IIRu^IIRu^III ⇌ Ru^IIRu^IIRu^II; Ru^IIRu^IIIRu^III ⇌ Ru^IIRu^IIRu^III; Ru^IIIRu^IIIRu^III ⇌ Ru^IIRu^IIIRu^III where the mixed valent states are moderately coupled. The complexes display multiple reductions associated with the azo functions of the ancillary ligands (L′^–‴). The energy of the Ru^II-based lowest energy MLCT transitions (533–558 nm) involving the π* level of azoimine chromophore of L′^–‴ varies depending on the nuclearity as well as substituents in the ligand framework and follows the order: [1]³⁺ > [2]³⁺ > [3]³⁺ > [4]⁺. The complexes exhibit reasonably high third-order non-linear optical properties with γ = (0.90–2.45) × 10⁻²⁹ esu. The interactions of the trinuclear complexes [{(L′)₂Ru^II}₃(μ₃-L)]³⁺ [1]³⁺, [{(bpy)₂Ru^II}₃(μ₃-L)]³⁺ [5]³⁺ and [{(phen)₂Ru^II}₃(μ₃-L)]³⁺ [6]³⁺ (bpy = 2,2′-bipyridine and phen = 1,10-phenanthroline) with the circular and linear forms of p-Bluescript DNA show reduced ethidium bromide fluorescence on gel electrophoresis.