Structural diversity of alkali metal coordination polymers driven by flexible biphenyl-4,4′-dioxydiacetic acid

Abstract

A new series of four coordination polymers of alkali metals (Li, Na, and K) was assembled from a poorly explored building block, biphenyl-4,4′-dioxydiacetic acid (H2L), and characterized by FTIR-ATR, TG-DSC, elemental analysis, and single crystal X-ray diffraction methods. The obtained structures range from 2D coordination polymers [Li2(µ-L)(µ-H2O)2(H2O)2] (1) and [Na2(µ4-L)(µ-H2O)2(H2O)2] (2) to 3D metal-organic frameworks [Na2(µ6-L)(µ-H2O)2] (3) and [K2(µ10-L)] (4). The influence of metal ionic radii on the crystal structures of the coordination polymers and conformation of the flexible biphenyl-4,4′-dioxydiacetate ligand was analyzed. Structural complexity increases within the series of products 1–4 following the Li<Na<K trend, accompanied by the evolution of the coordination modes of biphenyl-4,4′-dioxydiacetate ligand from the µ2-L2- (1) and µ4-L2- (2) to µ5-L2- (3) and µ10-L2- (4). Topological classification of the simplified underlying metal-organic networks in 1–4 was performed, disclosing the hcb (1), 3,4L13 (2), and fit (4) topological networks, whereas a topologically unique framework was identified in 3. The obtained coordination polymers are thermally stable and decompose in one (4) or several stages (1–3) forming metal carbonates and/or oxides as final decomposition products. The obtained products 1–4 represent the first examples of alkali metal coordination compounds derived from biphenyl-4,4′-dioxydiacetic acid.