Genuine supramolecular isomers based on Y-shaped pyridinedicarboxylate ligands with distinct topology: 2D 63 layer, kgd layer to 3D rtl net

Abstract

Three genuine supramolecular isomers with an identical formula of [Co(cpna)(H₂O)₂] (1a, 1b and 1c) [H₂cpna = 5-(4′-carboxyl-phenyl) nicotinic acid] have been synthesized by adjusting the relative molar ratio of Y-shaped ligand H₂cpna : CoCl₂ under solvothermal conditions. Isomer 1a possesses a two-dimensional (2D) 6³-hcb layer, in which the central Co(II) adopts trigonal bipyramidal geometry. 1b and 1c contain the same edge-shared dimeric SBUs, which are further ligated by cpna²⁻ ligands to form 2D (3,6)-connected (43)₂(4⁶·6⁶·8³)-kgd layers and a 3D (3,6)-connected (4·6²)₂(4²·6¹⁰·8³)-rtl net, respectively. The coordination modes of the cpna²⁻ ligand in 1b and 1c are the same, indicating that only the difference in the dihedral angles of the pyridine and phenyl rings contributes to different isomers. Magnetic investigation indicates ferromagnetic interactions between Co(II) ions in edge-shared dimeric SBUs.