Preparation and Thermal Square Planar–Octahedral Transformation of Nickel(II) Complexes Containing 1,2-Butanediamine or 3,3-Dimethyl-1,2-butanediamine in Solid Phase

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Abstract
Nickel(II) complexes of 1,2-butanediamine(1,2-bn) and 3,3-dimethyl-1,2-butanediamine(dmbn), were prepared, and their thermal behavior was investigated in solid phase. The original complexes were all violet, octahedral diaquabis(diamine) complexes([Ni(H2O)2(1,2-bn/dmbn)2]X2; X=Cl, Br, NO3, or ClO4). The 1,2-bn complexes with Cl− or Br− and the dmbn complex with NO3− showed a two-step thermochromism, violet→yellow→violet blue, upon heating. These steps correspond to structural changes to a square planar anhydride, and then to an octahedral dianiono complex. The complexes of both ligands with ClO4− underwent only thermal deaquation, changing into orange square planar anhydride. Other salts, the 1,2-bn complex with NO3− and the dmbn complexes with Cl− or Br−, were converted into octahedral dianiono complexes by thermal deaquation-anation which occurs in one step. The differences among the thermal reactivities of the complexes with different diamines can be understood on the basis of steric hindrance caused by the substituent groups on the diamine