Synthesis and characterization of chromium(III) octaphenylporphyrin complexes with various axial ligands: An insight into porphyrin distortion

Influence of axial ligands, MeCN, H2O, py, and piperidine (pip), on distortion of (2,3,5,10,12,13,15,20-octaphenylporphinato)chromium(III), [Cr(OPP)]+, was investigated by X-ray crystallography and UV–vis and ESR spectroscopies. In crystal structures of [Cr(OPP)(MeCN)(H2O)]ClO4 · MeCN and [Cr(OPP)(H2O)2]ClO4 · 3THF, the OPP2− ligand had a planar structure. On the other hand, crystal structures of [Cr(OPP)(pip)2]ClO4 · 2CH2Cl2 and [Cr(OPP)(py)2]ClO4 exhibited a waved structure and a saddle-shaped structure with ruffling, respectively. In the UV–vis spectrum of [Cr(OPP)(py)2]ClO4 in CH2Cl2, the large red shift of the Soret band was observed. Furthermore, the small D value of 0.10 cm−1 was obtained for [Cr(OPP)(py)2]ClO4 from the ESR spectrum in frozen 1,2-dichloroethane solution at 5 K. These results suggest that the OPP2− ligand is distorted both in solid and in solution, and that the axial ligand would exert some effects on the porphyrin distortion.