Metal-nitroxyl interactions. 25. Exchange interactions via saturated linkages in spin-labeled porphyrins

Article abstract of DOI:10.1139/v82-204

A series of spin-labeled copper porphyrins has been prepared in which nitroxyl radicals are attached to a porphyrin pyrrole ring by propionamide and propionate ester linkages.The solution epr spectra at room temperature indicate that the values of the electron spin - electron spin coupling constant, J, for these compounds are in the range 4 to 18 G, depending on the solvent and the size of the nitroxyl ring.Below -45 deg C two isomers with different values of J were observed in the epr spectra of two of the compounds.Variable temperature epr spectra were also analyzed for analogous spin-labeled copper porphyrins which have cis and trans acrylic ester and acrylamide linkages between the porphyrin and the nitroxyl ring.Comparison of the values of J for the complexes with saturated and unsaturated linkages suggest that ?-bonding pathways dominate the copper-nitroxyl interaction in these compounds.