Synthesis, mixed valence aspects and non-linear optical properties of the triruthenium complexes [{(bpy)2RuII}3(L)]3+ and [{(phen)2RuII}3(L)]3+ (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline and L3− = 1,3,5-triazine-2,4,6-trithiol)

Abstract

The triruthenium complexes [{(bpy)₂Ru^II}₃L]³⁺ [1]³⁺ and [{(phen)₂Ru^II}₃L]³⁺ [2]³⁺ have been synthesized via the reactions of [Ru^II(bpy)₂(EtOH)₂]²⁺ and [Ru^II(phen)₂(EtOH)₂]²⁺ with the trisodium salt of 1,3,5-triazine-2,4,6 trithiol (Na₃L) respectively. In CH₃CN, the complexes [1]³⁺ and [2]³⁺exhibit three reversible one-electron redox processes corresponding to successive Ru(II)/Ru(III) couples. The 190–250 mV separation in potential between the successive Ru(II)/Ru(III) couples is indicative of moderate intermetallic electronic coupling in the mixed valence states. The bipyridine and phenanthroline based reductions are observed at −1.58, −1.86 V and −1.77, −2.01, −2.43 V versus SCE respectively. The spectroelectrochemical study on the bipyridine derivative [1]ⁿ⁺ (n = 3–6) in acetonitrile medium at 243 K shows a broad and relatively weak intervalence charge-transfer transition (IVCT) near 1900 nm for both the mixed valence states Ru^IIRu^IIRu^III [1]⁴⁺ and Ru^IIRu^IIIRu^III [1]⁵⁺, characteristic of class II behaviour. The calculated coupling constant (V_ab), 560 cm⁻¹ is also supportive of class II mixed-valence states. The electrochemically generated one-electron oxidised species [1]⁴⁺ or [2]⁴⁺ exhibits an EPR spectrum characteristic of low-spin Ru^III ion in a distorted octahedral environment (g₁ = 2.246, g₂ = 1.993 for [1]⁴⁺ and g₁ = 2.469, g₂ = 2.191 for [2]⁴⁺). The complexes are moderately strongly luminescent at 77 K. Both the complexes have also shown third order non-linear optical properties with γ = −4.5 × 10⁻²⁹ esu for [1]³⁺ and −5.09 × 10⁻²⁹ esu for [2]³⁺.