Influence of ligand positional isomerism on the molecular and supramolecular structures of cobalt(II)-phenylimidazole complexes.

In a study to evaluate the impact of flexible positional isomeric ligands on the coordination geometry and self-assembly process of 3d metal complexes, the synthesis of eight new cobalt(II) complexes with the 2-phenylimidazole (LH) and 5-phenylimidazole (L'H) ligands has been carried out. A variety of parameters/conditions have been probed using the general CoII/X-/LH or L'H (X- = Cl-, Br-, I-, NO3-, NCS-, ClO4-, SO42-) reaction system. Interestingly, X-ray analyses reveal two distinct groups of complexes: reactions with LH only lead to tetrahedral or quasi-tetrahedral complexes {i.e. [CoCl2(LH)2] (1), [CoI2(LH)2] (2), [Co(NO3)2(LH)2] (3), [Co(NCS)2(LH)2] (4)}, whereas L'H favours octahedral coordination {i.e. [Co(L'H)4(MeCN)(H2O)]I2 (5), [Co(L'H)4(MeCN)(H2O)](NO3)2 (6) and [Co(NCS)2(L'H)4)]·2MeOH (7·2MeOH)}. A tetrahedral [Co(NCS)2(L'H)2)] (8) complex was also concurrently isolated with complex 7. The effects of the positional isomeric ligands LH and L'H and of the coordinated inorganic anions on the stoichiometry and packing arrangements of the complexes are thoroughly discussed. The supramolecular assembly is firmly directed, in all types of complexes, by robust N-H...X (X = Cl, I, O or S) motifs, leading to varying dimensionalities (1D, 2D or 3D) and packing arrangements. The formation of these motifs has been activated by choosing appropriate anions X, acting as terminal ligands or counterions. At a second level of organization, additional subordinate C-H...X (X = Cl, I, O or S), C-H...π and π...π intermolecular interactions complement the rigidity of the complexes' packing towards compact 3D assemblies. Hirshfeld surface analyses provided insight into the intermolecular interactions, allowed quantification of the individual contact types and comparison between the complexes.