Solid state thermal isomerisation of diethylenetriamine complexes of NiX2 (X=NO3, ClO4, BF4 and CF3SO3)

Summary Ni(dien)₂]X₂·nH₂O (dien=diethylenetriamine; n=0, X=NO₃ or CF₃SO₃; n=0.5, X=ClO₄ or BF₄ and n=2, X=CF₃SO₃) complexes have been prepared and investigated thermally in the solid state. Ni(dien)₂](NO₃)₂ (1) and Ni(dien)₂](CF₃SO₃)₂ (2) undergo endothermic irreversible phase transitions (209–247°C and 184–205°C; H=5.6 kJ mol^–1 and 7.7 kJ mol^–1 for (1) and (2), respectively). Ni(dien)₂](ClO₄)₂·0.5H₂O (3) shows an endothermic irreversible phase transition after deaquation (201–216°C; H=7.7 kJ mol^–1). Ni(dien)₂](BF₄)₂·0.5H₂O also shows an endothermic irreversible phase transition after deaquation, accompanied by partial decomposition. All the complexes possess octahedral geometry with the ligands arranged meridionally. The phase transitions are explained in terms of conformational changes of the triamine chelate rings.Author to whom all correspondence should be directed. Supplementary data available: i.r. spectra (Table 4) and x-ray diffraction patterns (Table 5).