Metal complexes of sulphur–nitrogen chelating agents. Part 11. Synthesis, characterisation, and thermodynamics of nucleophilic substitution reactions of monohalogeno nickel(<scp>II</scp>) 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 (Ea*) 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 Ea* values.