Metal complexes of sulphur-nitrogen chelating agents: Part 11 - Synthesis, characterisation, and thermodynamics of nucleophilic substitution reactions of monohalogeno nickel(II) complexes of tridentate ligands of the type SNN in solution and the solid state

Abstract

Square-planar nickel(II) complexes [NiLX](X = Cl, Br, I, or SCN) have been obtained through deprotonation of the ligands methyl 2-(β-aminoethylamino)cyclopent-1-enedithiocarboxylate (HL¹), methyl 2-(β-aminoisopropylamino)cyclopent-1-enedithiocarboxylate (HL²), and methyl 2-(β-diethylaminoethylamino)cyclopent-1-enedithiocarboxylate (HL³). Diamagnetic complexes of composition [NiL(MeCN)][ClO₄](L = L¹-L³) and [Ni₂L₂(HL)][ClO₄]₂(L = L¹ or L²) have also been synthesised. The equilibrium constants for the nucleophilic substitution reaction [NiL²X]+ B ⇌[NiL²(B)]⁺+ X^-(X = Cl, Br, or I; B = pyridine and its methyl-substituted derivatives) have been determined spectrophotometrically in the temperature range 25-50 ¯C. A linear correlation has been obtained between the ΔH⊖ and ΔS⊖ values. The enthalpy changes (ΔH₂) and activation energies (E_a*) for the thermal dissociation [NiL²(B)]X(s)→[NiL²X](s)+ B(g) have been determined. A linear correlation has been found between the (ΔS₂) and E_a* values.