Reversible Penta- and Hexacoordination Motifs in [Co(TMPP)] Resulting in Interchange of 1D and 2D Supramolecular Designs

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.