Thermal studies of 2-aminoethanol complexes of nickel (II) in the solid state

Abstract

[NiL₃]X₂ (where L = 2-aminoethanol and X is Cl⁻, Br⁻, I⁻, NO₃⁻, 0.5SO₄²⁻ or 0.5SeO₄²⁻ and [NiL₂X₂] (X is Cl⁻, Br⁻ or SCN⁻) have been synthesised from solution and their thermal study has been carried out in the solid phase. [NiL₃]I₂ and [NiL₃]SeO₄ undergo reversible endothermic phase transitions upon heating (63–93°C and 94–113°C, respectively, for heating and 94-65°C and 110–190°C, respectively, for cooling), whereas [NiL₃](NO₃)² exhibits two successive reversible endothermic phase transitions (10–38°C and 50–62°C for heating and 56-48°C and 19–(−8)°C for cooling). On the other hand, [NiL₃]SO₄ undergoes irreversible endothermic phase transition (99–112°C) in the solid state. All these transformations are assumed to be associated with the conformational changes of 2-aminoethanol chelate rings. [NiL₂(NCS)₂] melts at ≈ 168°C and remains supercooled for a few days at ambient temperature. The initial temperatures of decomposition (T_i) of these complexes have been compared with those of the corresponding ethane-1, 2-diamine complexes of nickel (II).