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) rhornboid grid structure based on the connection of {Co-2(CO2)(2)} dimeric units. Using the more sterically encumbered ligands 3,3-dimethylglutarate (ding) and 3-ethyl, 3-rnethylglutarate (emg) generated {[Co(dmg)(bpy)(H2O)] center dot 2H(2)O}(n), (2) and {[Co(emg)(bpy)(H2O)] center dot 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)], (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)). (C) 2009 Elsevier Inc. All rights reserved