Cobalt(ii), nickel(ii), manganese(ii) and zinc(ii) metal–organic frameworks constructed with the newly designed 2-(pyridin-4-yl)-4,6-pyrimidine dicarboxylic acidligand: syntheses, crystal structures and properties

Abstract

Four new coordination polymers, [Co(ppmdc)(H₂O)₂]_n (1), [Ni(ppmdc)(H₂O)₂]_n (2), [Mn(ppmdc)(H₂O)]_n (3) and {[Zn(ppmdc)(H₂O)₂]·H₂O}_n (4) (H₂ppmdc = 2-(pyridin-4-yl)-4,6-pyrimidine dicarboxylic acid), have been synthesized by self-assembly of the newly designed H₂ppmdc ligand and corresponding metal salts under hydrothermal conditions. The four complexes exhibit versatile frameworks with different topologies due to the different metal ions and especially the diverse coordination modes of the H₂ppmdc ligand. Complexes 1 and 2 exhibit 2-D layered structures with (4·8²)₂ and (8²)₂ topology, respectively, which are constructed from the self-assembly of the L- and R-type single chain helixes, in which the ppmdc²⁻ ligand adopts a μ₃-kN,O:kN′:kO′ mode to link metal ions. Complex 3 features a 3-D metal–organic framework with 5-connected (4⁵·6⁵)₂ topology, in which the metal ions are bridged by μ₅-ppmdc²⁻ ligands. Complex 4 possesses a 2-D sheet structure with 3-connected (6³)₂ topology, in which the ppmdc²⁻ ligand adopts a μ₃-kN:kO:kO′ mode to link Zn(II) ions. The thermal properties of complexes 1–4, and the magnetic property of 3 have been investigated and discussed in detail.