Alkyl group dependence on structure and magnetic properties in layered cobalt coordination polymers containing substituted glutarate ligands and 4,4′-bipyridine

Five two-dimensional divalent cobalt coordination polymers containing 4,4′-bipyridine (bpy) and substituted or unsubstituted glutarate ligands have been prepared hydrothermally and structurally characterized by single-crystal X-ray diffraction. [Co(mg)(bpy)]n (1, mg=3-methylglutarate) forms a (4,4) rhomboid grid structure based on the connection of {Co2(CO2)2} dimeric units. Using the more sterically encumbered ligands 3,3-dimethylglutarate (dmg) and 3-ethyl, 3-methylglutarate (emg) generated {[Co(dmg)(bpy)(H2O)]·2H2O}n (2) and {[Co(emg)(bpy)(H2O)]·H2O}n (3), respectively. These complexes manifest {Co(CO2)}n chains linked into 2-D by aliphatic dicarboxylate and bpy ligands. The “tied-back” substituted glutarate ligand 1,1-cyclopentanediacetate (cda) afforded [Co(cda)(bpy)]n (4), and the unsubstituted glutarate (glu) generated [Co(glu)(bpy)]n (5), both of which exhibit a topology similar to that of 1. The magnetic properties of complexes 1–4 were analyzed successfully with a recently developed phenomenological chain model accounting for both magnetic coupling (J) and zero-field splitting effects (D), even though 1 and 4 contain isolated, discrete {Co2(CO2)2} dimers. The D parameter in this series varied between 21.8(8) and 48.0(9) cm−1. However weak antiferromagnetic coupling was observed in 1 (J=–2.43(4) cm−1) and 4 (J=−0.89(2) cm−1), while weak ferromagnetic coupling appears to be operative in both 2 (J=0.324(5) cm−1) and 3 (J=0.24(1) cm−1).