R. Bhattacharya et A. Ghosh, Thermal analysis of pyridinium tetrachloronickelate(II); tetrahedral reversible arrow octahedral structural transformation, J CHEM R-S, (8), 2001, pp. 332-333
Pyridinium tetrachloronickelate(II), which is green and tetrahedral in the
anhydrous state but yellow and octahedral when aquated, undergoes dehydroha
logenation upon heating in the solid state to yield [NiCl2Py2].