Formation of Strong OH₂···^-O₂C Hydrogen Bonds in a Trinuclear Core-Based Nickel 1,3,5-Benzenetricarboxylate Coordination Polymer

The nickel 1,3,5-benzenetricarboxylate (1,3,5-btc^3-) coordination polymer, [Ni₆(μ-OH₂)₄(1,3,5-btc)₄(H₂O)₁₂]_n (1), has been synthesized using a hydrothermal reaction. Trinuclear nickel cores constructed from the μ-OH₂ and carboxylate bridges are linked by the 1,3,5-btc^3- ligands, forming a two-dimensional network. The μ-OH₂ molecules form strong hydrogen bonds with the free oxygens of the carboxylate groups in the trinuclear clusters. A structural phase transition occurs around 373 K and is categorized as a second-order phase transition.