An ordering phase transition, short hydrogen bonds and high Z' in the structure of Ni(Hpydc) 2 ·3H 2 O

The structure of Ni(Hpydc) ·3H O (H pydc = pyridine-2,6-dicarboxylic acid, also known as dipicolinic acid) has been reinvestigated at variable temperatures. At room temperature, it matches the known structure in the space group P2 /c, but at 180 K it undergoes a phase transformation to a twinned structure in Cc. By 120 K, the structure is ordered and twinned with Z' = 4, and shows interesting short hydrogen-bonding interactions that include the formation of hydroxonium species.