Molecular Structure, UV/Vis Spectra, and Cyclic Voltammograms of Mn(II), Co(II), and Zn(II) 5,10,15,20-Tetraphenyl-21-oxaporphyrins

The 5,10,15,20-tetraphenyl-21-oxaporphyrin complexes
of Mn­(II),
Co­(II), and Zn­(II) have been crystallized and studied by X-ray diffraction,
NMR and UV/vis spectroscopy, and mass spectrometry as well as cyclic
voltammetry. The X-ray structure of the earlier described Cu­(II) complex
is also reported. All complex structures possess a five-coordinate,
approximately square-pyramidal geometry with a slight deviation of
the heteroaromatic moieties from planarity. The packing structures
are characterized by parallel strands of complex molecules interacting
by weak hydrogen bonds. In the case of Zn­(II) an octahedral complex
has also been isolated using a side-chain hydroxy functionalized oxaporphyrin
ligand; the structure was verified by NMR and EXAFS spectroscopy.
Cyclic voltammetry studies reveal that the reduction of the complex
bound Mn­(II), Co­(II), and Zn­(II) ions is a ligand-centered process
whereas the first oxidation step depends on the metal ion present.