Reversible penta- and hexacoordination motifs in [Co(TMPP)] resulting in interchange of 1D and 2D supramolecular designs

Abstract

meso-Tetrakis(3,4,5-trimethoxyphenyl)cobalt(II) porphyrin [Co(TMPP)] (1) is synthesized by a new method. The X-ray structure of 1 grown in dichloromethane shows square-pyramidal coordination around the Co(II) ion, displaying a 1D polymeric network. When grown in chloroform, 1 displays an octahedral coordination around Co(II), resulting in a 2D coordination network. This solvent-dependent variation in ligation of the O-donor atom(s) of the 4-methoxy groups of the meso-phenyl rings in the axial position(s) of the central Co(II) is reversible, as shown by electronic spectroscopy. The magnetic and electron paramagnetic resonance (EPR) data of these two crystalline forms are dependent on the nature of the axial interaction. Increased axial coordination showed increased splitting between the e and a1 orbitals, resulting in further separation between ²A₁ and ²E. The EPR data are consistent with this result. The difference in energy levels in these two forms is in agreement with the magnetic and spectroscopic data.