Thermal studies N-(2-aminoethyl)-1,3-propanediamine and N-(3-aminopropyl)-1,3-propanediamine complexes of cadmium(II)

Abstract

[Cd(aepn)₂]X₂•nH₂O (where aepn is N-(2-aminoethyl)-1,3-propanediamine, and n = 1 when X is Cl⁻ and Br⁻, n = 0 when X is 0.5SO²⁻₄, 0.5SeO²⁻₄, NO⁻₃ and I⁻), Cd(aepn)X₂ (where X is Cl⁻, Br⁻, I⁻, 0.5SeO²⁻₄, 0.5SO²⁻₄ and SCN⁻) and Cd(dpt)X₂•nH₂O (where dpt is N-(3-aminopropyl)-1,3-propanediamine, and n = 1 when X is 0.5SO²⁻₄ and 0.5SeO²⁻₄, n = 0 when X is Cl⁻, Br⁻, I⁻ and SCN⁻) have been synthesised and investigated thermally in the solid state. The species Cd(aepn)Cl₂, Cd(aepn)SO₄ and Cd(aepn)SeO₄ have also been synthesised pyrolytically in the solid state from the corresponding parent bis-complexes. Cd(aepn) (SCN) ₂ and Cd(dpt) (SCN) ₂ melt on heating and exist as supercooled liquids at ambient temperature. On heating and after deaquation, Cd(dpt)SO₂•H₂O shows two endothermic phase transitions (172–190°C, ΔH = 8.0 kJ mol⁻¹ and 210–245°C, ΔH = 3.5 kJ mol⁻¹ and the low-temperature transition is reversible (182–165°C, ΔH = −7.8 kJ mol⁻¹). Conversely, the selenate analogue undergoes an irreversible endothermic phase transition (240–257°C, ΔH = 13.2 kJ mol⁻¹). [Cd(aepn) ₂] (NO₃)₂ and Cd(aepn)I₂ show irreversible endothermic phase transitions (198–218°C, ΔH = 5.9 kJ mol⁻¹ for nitrate, and 195–202°C, ΔH = 8.3 kJ mol⁻¹ for iodide). The transitions are assumed to be due to the conformational changes in the triamine chelate rings. The thermal stabilities are rationalized with respect to the carbon chain lengths of the triamine ligands.