Thermally-induced phase transition of zinc (II) diamine complexes in the solid state

Abstract

ZnLCl₂•0.5H₂O and ZnL₂X₂•nH₂O (L = N-2(hydroxyethyl)-1,2-ethanediamine: X = Br, 0.5SO₄, 0.5SeO₄ and n = 0.5–2) have been synthesized and thermal investigations have been carried out in the solid state. ZnLCl₂•0.5H₂O and ZnL₂Br₂•0.5H₂O show endothermic reversible phase transitions (135.0–152.0° C; ΔH = 1.6 kJ mol⁻¹ and 127.0–144.5 ° C; ΔH = 10.4 kJ mol⁻¹, respectively) after dehydration. ZnL₂SO₄•2H₂O becomes dehydrated at 100° C and on further heating undergoes an exothermic irreversible phase transition (109.5–146.0° C; ΔH = −9.5 kJ mol⁻¹), whereas ZnL₂SeO₄• H₂O first undergoes dehydration at 134° C and then an endothermic irreversible phase transition occurs (141.5–171.5° C; ΔH = 14.2 kJ mol⁻¹).