A series of three-dimensional lanthanide(iii) coordination polymers of 2,5-dihydroxy-1,4-benzenedicarboxylic acid based on dinuclear lanthanide units

Abstract

The reactions of Ln(NO₃)₃ with 2,5-dihydroxy-1,4-benzenedicarboxylic acid (H₂-DHBDC) under solvothermal conditions produce a series of isomorphous lanthanide coordination polymers with the empirical formula {[Ln₂(DHBDC)₃(DMF)₄](DMF)₂}_n (Ln = La(1), Nd(2), Sm(3), Gd(4), and Er(5)). Compound {[Ln₂(DHBDC)₃(DMF)₄](DMF)₂}_n contains dinuclear Ln₂(COO)₆ units, which are linked by the –C₆H₂(OH)₂– spacers to form a three-dimensional framework exhibiting α-Po topology (pcu-(4¹²·6³) net) based on dinuclear Ln₂(COO)₆ nodes. The three-dimensional framework shows one-dimensional open channels that accommodate the coordinated and guest DMF molecules. Gas adsorption measurements on compound 4 indicate that the desolvated solid of 4 adsorbs CO₂ and shows nonporous behavior toward N₂. The adsorption favoring CO₂ over N₂ may arise from the chemical environments of the host framework, which contains the polar –OH groups of the phenyl and the π-electrons of the ligands. Magnetic measurements on compound 4 indicate that there is an antiferromagnetic interaction between Gd³⁺ ions.