Redox responsive bi/tri-nuclear complexes incorporating ferrocenyl unit: Synthesis, characterization, physicochemical studies and X-ray structure of [C₅H₅FeC₅H₄CH = CHC₅H₄N---CH₃]PF₆ with a mirror creating disorder

Abstract

(Trans-1(4-pyridyl)-ethylene) ferrocene, L reacts with K[Ru^III(edtaH)]Cl to form binuclear complex. K[Ru^III(edtaH)]Cl exist as RuIII(edtaH(H₂O) in aqueous solutions and substitution of the aqua molecule by L occurs within the stopped flow time scale. Rate constants for the reaction are 1620 ± 20, 2080 ± 35, 2690 ± 50 M^-1 s^-1 at 28, 34 and 39.9°C, respectively [ΔH^# is 30.3 ± 1.1 kJ mol^-1 and ΔS^# is - 124 ± 4 J K^-1 mol^-1]. R^II(2,2'-bipy)₂Cl₂ reacts with L to form bi/trinuclear complexes. [Ru^II(2,2'-bipy)₂LCl]PF₆ and [Ru^II(2,2'-bipy)₂L₂](PF₆)₂, depending on the reaction conditions. Luminescence of the Ru^II(2,2'-bipy)₂(py)₂²⁺ center in the trinuclear complexes is completely quenched presumably through energy transfer pathway. There exist a moderate to weak electrochemical interaction between the two redox centers either in N-methylated form of L or in the bi/trinuclear complexes derived from Ru(II) or Ru(III). All these new bi/trinuclear complexes are characterized by physicochemical methods. Single crystal X-ray structure of [L---CH₃]PF₀ is reported. A very low value of powder SHG efficiency observed earlier for this salt can now be well understood in terms of the centrosymmetric molecular arrangement created due to the disorder in the crystal.