Thermal studies of N-propylethane-1,2-diamine and N-isopropylethane-1,2-diamine complexes of nickel(II) in the solid state

Article abstract of DOI:10.1016/0040-6031(96)02973-5

[NiL₃]X₂ · 2H₂O (X is Cl^-, Br^- and ClO^-₄; L is N-propylethane-1,2-diamine), [NiL₂(H₂O)₂](ClO₄)₂, [NiL₂X₂] (X is Cl^-, Br^-, 0.5SO^2-₄ and 0.5SeO^2-₄), [NiL¹₂(H₂O)₂](ClO₄) ₂ · 2H₂O (L¹ is N-isopropylethane-1,2-diamine), [NiL¹₂X₂] (X is Cl^-, Br^-, NCS^- and O.5SeO^2-₄) and [NiL¹₂SO₄] · 3H₂O have been synthesised from solution and their thermal studies have been carried out in the solid phase. [NiL₂X₂] (X is Cl^- and Br^-), NiLCl₂ and NiL¹SO₄ have been prepared pyrolytically from their respective parent species in the solid state. [NiL₂](ClO₄)₂ and [NiL¹₂](ClO₄)₂ were prepared pyrolytically from their parents species, and also by storing [NiL₂(H₂O)₂](ClO₄)₂ and [NiL¹₂(H₂O)₂](ClO₄) ₂ · 2H₂O in a CaCl2 desiccator, respectively; these transformations are accompanied by a pink to yellow colour change due to octahedral to square-planar configurational changes. All other bis(diamine) species have octahedral geometry. Among them, [NiL₂X₂] (X is Cl^- and Br^-) and [NiL¹₂X₂] (X is Cl^-, Br^- and NCS^-) possess trans-octahedral configuration, whereas [NiL₂X] (X is SO^2-₄ and SeO^2-₄), [NiL¹₂SO₄] · 3H₂O and [NiL¹₂SeO₄] have cis-configuration. On heating, trans-[NiL¹₂ Br₂] and trans-[NiL¹₂(NCS)₂] undergo reversible endothermic phase transitions (86-99°C, ΔH = 0.52 kJ mol^-1 for heating, and 92-81°C, ΔH = - 0.53 kJ mol^-1 for cooling for the former, and 162-224°C, ΔH = 0.27 kJ mol^- for heating and 208-150°C, ΔH = - 0.25 kJ mol^-1 for cooling for the latter), most likely due to conformational changes of the diamine chelate rings.