Influence of the Ionic Radius of Alkali Metals on the Structures of Polymeric 3,5-Dinitro-2-pyridonates

Abstract

New ionic polymeric compounds are synthesized by the reactions of alkali metal carbonates with 3,5-dinitro-2-pyridone (Hdnhp) in an aqueous-alcohol solution: [Li(dnhp)(H₂O)]_n (I), [Na(dnhp)(H₂O)]_n (II), [K(dnhp)(H₂O)]_n (III), and [K(dnhp)(Hdnhp)]_n (IV). Their structures are determined by single-crystal X-ray diffraction analysis. Analysis of the structures of the synthesized compounds shows that an increase in the ionic radius of the alkali metal cation (Li−Na−K) results in a regular increase in the coordination number (5, 6, and 7/8, respectively) and a change in the polymeric architecture type: from one-dimensional polymeric chains in compounds I and II to framework structures in compounds III and IV. The stereochemically rigid 2-pyridonate ligand plays a key role in structure formation exhibiting a variable denticity and different coordination modes. Hydrogen bonds and π−π-stacking interactions provide an additional stabilization of the crystal packings in compounds I and II. The structures are compared with the earlier described rubidium and cesium polymers to trace the coordination behavior of the dnhp^– anion in the alkali metal series.