Synthesis, structure and properties of coordination polymers formed from bridging 4-hydroxybenzoic acid anions

Abstract

The combination of 4-hydroxybenzoic acid (H₂hba) with Li⁺, Mg²⁺ and Cu²⁺ yields coordination polymers in which metal centres are bridged by an anion of the acid, either Hhba⁻ or hba²⁻. In the case of Li⁺, a 3D network of composition Li₂(hba)DMF was isolated in which parallel channels are occupied by coordinated DMF molecules. Mg²⁺ combines with H₂hba to form a 2D square grid network with the formula Mg(Hhba)₂(H₂O)₂. The alignment of parallel sheets results in the formation of channels filled with 1,4-dioxane molecules that hydrogen bond to coordinated water molecules. The compound Cu₃(hba)₂(OH)₂(1,4-dioxane)_1.5·0.5(1,4-dioxane) is a complex 3D network formed from the combination of Cu²⁺ with H₂hba under basic conditions. The crystal structure determination reveals bridging 1,4-dioxane molecules. A reversible phase change occurs in the temperature range 200–220 K. The investigation highlights the key role of the solvent molecules in the structures of this series of compounds.