The effect of the phenanthroline substituents on the structure and reactivity of platinum(II) and platinum(IV) complexes has been investigated. The X-ray crystal structures of the compounds [PtI2(4,7-Ph(2)phen)]. CHCl3 (1dz . CHCl3), [PtI4(4,7-Ph(2)phen)]. CHCl3 (2dz . CHCl3), [PtI2(2,9-Me(2)-4,7-Ph(2)phen)] (1fz), and [PtI4(2,9-Me(2)-4,7-Ph(2)phen)]. I-2 (2fz . I-2) have shown that complexes 1fz and 2fz, containing ortho-substituted phenanthrolines, exhibit a remarkable displacement of the equatorial iodine atoms from the N-Pt-N’ plane (average 0.477(2) and 0.199(2) Angstrom, respectively), a bending of the phenanthroline [angle between outer rings of 19.9(7) and 14.2(7)degrees, respectively] and a rotation of the N-C-C’-N’ plane with respect to the N-Pt-N’ plane [32.3(10) and 26.5(9)degrees, respectively]. Comparison between the structures of 1fz and 2fz, both having the phenanthroline with methyl substituents in the ortho position, indicates that, in the latter case, because of the presence of the two axial iodine ligands, the displacements of the ligands from the equatorial plane are smaller and find a compensation in a narrowing of the I(1)-Pt-I(1’) angle (5 degrees) and a lengthening of the Pt-N bonds (0.07 Angstrom).