The effects of unconventional modifications of iron tetraarylporphyrins on their electronic structure and chemical properties were examined. The alterations included the β(meso)-substitution or an oxygen atom insertion into an iron-nitrogen bond. The profound transformation of porphyrin to 2-pyridiniumylporphyrin, isoporphyrin or porphodimethene occurred in reactions involving iron porphyrin in highly-oxidized states and pyridine. Addition of 2,4,6-collidine generated iron porphyrin N-oxides. The 2-hydroxy substituted tetraphenylporphyrin (a hybrid-type ligand) coordinates using a tetranitrogen macrocyclic center and an ionized hydroxy group of the periphery to form the cyclic trimer [(2-O-TPP)Fe(III)] 3 . The seven pyrrole protons of (2-X-TPP)Fe(III)Cl and [(2-X-TPP)Fe(III)(CN) 2 ] provided the direct probe of the spin density distribution around the porphyrin macrocycle as determined by 1 H-NMR. Studies on the controlled modification of the tetraarylporphyrin periphery also included a symmetrical modification of a single pyrrole ring to obtain iron(III) quinoxalinoporphyrin characterized by the less common (d x z d y z ) 4 (d x y ) 1 low-spin ground electronic state of the bis-cyanide derivative [(QTPP)Fe(III)(CN) 2 ] - .