Synthesis, structure, topology and magnetic properties of new coordination polymers based on 5(–Br/–COOH)-substituted nicotinic acid

Abstract

Nine new coordination polymers of 5-substituted nicotinic acid (with either –Br, HBNA, or –COOH, 3,5-H₂PDC) with d-transition (Co, Ni, Zn and Cd) and f-lanthanoid (La, Ce, Sm and Tb) metal ions have been synthesized. The two metal complexes [Co₂(BNA)₄(H₂O)]_n·H₂O (1a) and [Cd(BNA)₂]_n (1b) have polymorphic/isomeric structures to those of metal–organic-frameworks (MOFs) with similar structural building units (SBUs) reported earlier. Modified reaction conditions yielded new isomeric metal complexes in the present case. Reactions of the 3,5-H₂PDC linker with different metal ions led to the formation of polymeric complexes [Mn₃(3,5-PDC)₃(DMA)₃]_n·DMA (2a), [Zn(3,5-PDC)(DMA)]_n·DMA (2b) and [Cd₂(3,5-PDC)₂(DMA)₄]_n (2c), as well as lanthanoid MOFs [Sm(3,5-PDC)_1.5(DMF)]_n·DMF (2d, as well as isomorphous products with La (2f) and Ce (2g) ions) and [Tb₂(3,5-PDC)₃(DMF)₂]_n·DMF (2e). Networking diversity observed in these coordination polymers with the conformationally rigid 5-substituted nicotinic acid ligand is discussed. The magnetic properties of 2a, 2d and 2e have been studied as well.