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)

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The triruthenium complexes [{(bpy)2RuII}3L]3+ [1]3+ and [{(phen)2RuII}3L]3+ [2]3+ have been synthesized via the reactions of [RuII(bpy)2(EtOH)2]2+ and [RuII(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 RuIIRuIIRuIII [1]4+ and RuIIRuIIIRuIII [1]5+, characteristic of class II behaviour. The calculated coupling constant (Vab), 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 RuIII 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+.