Hydrothermal reaction of 3-(3-pyridyl)acrylic acid (pyaraH) with NiCl₂ and NaOH results in formation of different polymorphs at different temperatures. α-Ni(pyara)₂(H₂O)₂ forms at 180 °C, and has a 3D polymeric structure. The topology of the network is that of a self-penetrating, four-coordinate (8,4) network (Schläfli symbol 8⁶). This is the first uniform net to contain only planar four-coordinate nodes, and it is also the first four-coordinate uniform net not to have the Schläfli symbol 6⁶. This fundamental network topology has been previously unrecognized. The second polymorph, the β phase, forms from an analogous reaction at 150 °C, and contains 1D chains hydrogen bonded into a 3D network.