Ruthenium(II) octa-beta-halotetrakis(pentafluorophenyl)porphyrins (RuTFPPX(8)(CO), RuTFPPCl8(py)(2); X = Cl, Br) have been synthesized, and the crystal structure of RuTFPPCl8(CO)H2O has been determined : C57H28Cl8F20N(4)O(5)-Ru, monoclinic, space group P2(1)/c, a = 14.364(3) Angstrom, b = 16.012(4) Angstrom, c = 26.679(8)Angstrom; beta = 90.29(2)degrees, V = 6136(3) Angstrom(3), Z = 4, R(w) = 0.028 on F-2 for 8005 reflections, R(F) = 0.067 for 5378 reflections with F-o(2) > 3 sigma(F-o(2)); the porphyrin is highly distorted, with 0.68 and 1.11 Angstrom average displacements of the beta-chlorine atoms from the mean porphyrin plane. The reduction potentials of RuTFPPX(8) complexes are much more positive (> 0.5 V) than those of unhalogenated analogues, owing to the influence of the electron-withdrawing X atoms. The relatively high energies of the Soret bands in the RuTFPPX(8) electronic spectra are consistent with an electronic structural model involving Run back-bonding to the porphyrin e pi* orbitals.