Importance of π-π interactions in the solid state structures of two cobalt complexes derived from N,O donor reduced Schiff base ligands

This study explores the utilization of two structurally similar 'reduced Schiff base' ligands. [H2L1r=(1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol) and H2L2r=(1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol)] for the synthesis of two cobalt complexes, [CoL1r(μ-O2CR1)2Co(NCS)(CH3OH)] (1) and [(μ1,3-N3){Co(L2r)(μ-O2CR2)Co(N3)}2]PF6 (2) {R1CO2H = 4-methyl-3-nitrobenzoic acid; R2CO2H = benzoic acid}. The structures of both complexes have been confirmed through single crystal X-ray diffraction analysis. The compartmental ligands, H2L1r and H2L2r, consist of an inner N2O2 compartment and an outer O2O′2 compartment. In each compound, one cobalt center is situated in the inner N2O2 compartment with octahedral geometry, while the other cobalt center adopts an octahedral geometry in complex 2 and a square pyramidal geometry in complex 1. Notably, there is intermolecular π-π stacking in the solid-state structure of complex 2, which is absent in complex 1. This additional π-π stacking enhances complex 2, leading to dimer formation. Conversely, in complex 1, intra-molecular π-π stacking provides extra stability, which is absent in complex 2.