Crystalline assemblies of a functionalized terphenyl ligand

With the aim of producing an extended bridging ligand for the assembly of coordination polymers, a terphenyl ligand incorporating carboxyl and phenol functionalities, namely, 4''-hydroxy-1,1':4',1''-terphenyl-4-carboxylic acid (H₂htpa, C₁₉H₁₄O₃, 1), was prepared. Within the structure, complementary hydrogen bonding between carboxylic acid groups leads to dimer formation with additional hydrogen bonding between phenolic groups, resulting in the formation of a 2D network. Following the addition of Na₂CO₃, mono- and dianionic forms of the ligand are generated within a compound of composition Na₃(Hhtpa)(htpa)·hydrate or {[Na₃(C₁₉H₁₃O₃)(H₂O)₉](C₁₉H₁₂O₃)}_n (2). The addition of tetraethylammonium hydroxide (NEt₄OH) solution to the acid leads to the formation of (Et₄N)Hhtpa·2(dioxane) or C₈H₂₀N⁺·C₁₉H₁₃O₃^-·2C₄H₈O₂ (3) and (Et₄N)₅(Hhtpa)₂(H_0.5htpa)₂·hydrate or 5C₈H₂₀N⁺·[H(C₁₉H₁₂O₃)₂]^3-·2C₁₉H₁₃O₃^-·17.522H₂O (4), with hydrogen-bonded chains a feature of both. Compound 4 contains both the Hhtpa^- anion, and pairs of htpa^2- dianions linked by a single proton between phenolate O atoms to generate a trianionic unit, [H(htpa)₂]^3-. A ladder-shaped anionic coordination polymer of composition (NEt₄)₄[Zn₄(htpa)₃Cl₆] or {(C₈H₂₀N)₄[Zn₄(C₁₉H₁₂O₃)₃Cl₆]}_n (5) was obtained when Zn^II was combined with htpa^2- in the presence of NEt₄⁺ and chloride. Finally, an anionic coordination polymer with the formulation (Et₄N)[Zn(htpa)(OAc)]·1.5(dioxane) or {(C₈H₂₀N)[Zn(C₃H₃O₂)(C₁₉H₁₂O₃)]·1.5C₄H₈O₂}}_n (6) was generated with both OAc^- (acetate) and htpa^2- serving as bridging ligands between Zn^II centres in a 2D network.