Thermal studies of N,N′-diethylethane-1,2-diamine complexes of nickel (II) in the solid state

Abstract

NiL₂X₂•nH₂O (where L = N,N′-diethylethane-1,2-diamine; n = 2 when X is Cl⁻, Br⁻, I⁻, NO₃⁻,0.5SO₄²⁻ or CF₃SO₃⁻; n = 0 when X is CF₃CO₂⁻ or CCl₃CO₂⁻) have been synthesised from solution and investigated by TG-DTA and DSC in the solid state. All the hydrated complexes have trans octahedral geometry and on heating undergo dehydrationanation reactions. The dehydrated complexes are also trans octahedral, except NiL₂X₂ (X is NO₃⁻,0.5SO₄²⁻ or 0.5SeO₄²⁻) for which cis octahedral geometry is proposed. [NiL₂(H₂O)₂]X₂ (X is Br⁻ or CF₃SO₃⁻) shows thermochromism (blue→green) upon dehydration. NiL₂X₂ (X is Cl⁻, Br⁻, 0.5SO₄²⁻ or 0.5SeO₄²⁻) yield mono-diamine species in the solid state on heating. NiL₂SO₄ undergoes a reversible phase transition (heating cycle, 178–193°C, ΔH = −4.0 kJ mol⁻¹; cooling cycle, 186-172°C; Δ = 4.0 kJ mol⁻¹) without a visual colour change.