BIS(PORPHYRIN)ACTINIDE COMPLEXES AND THEIR RADICAL CATIONS AND DICATIONS

The first bis(porphyrin)actinide complexes have been prepared by reaction of the diethylamide complexes M(NR2)4 (where M = Th, U and R = Mc, Et) with 5, 10, 15, 20-tetraphenylporphyrin (H-2TPP) or 2, 3, 7, 8, 12, 13, 17, 18-octacthylporphyrin (H2OEP). The coordination geometry of Th(TPP)2 is a distorted square-antiprism where the thorium center is displaced 1.47 angstrom from each of the porphyrin N4 planes; the porphyrin N4 planes are threrefore separated by 2.94 angstrom. In Th(OEP)2, the two porphyrin N4 planes are separated by 2.89 angstrom in a nearly perfect square-antiprismatic coordination geometry around the thorium center. The porphyrin macrocycles, held in such close proximity, interact electronically as shown by a blue-shift in the porphyrin Soret band and by unusually low oxidation potentials relative to related monoporphyrin species. Chemical oxidations of M(TPP)2 and of Th(OEP)(TPP) yield porphyrin-based radical cation complexes [M(porph)2+][SbCl6-] and dicationic complexes [M(porPh)22+][SbCl6-]2. The solid-state structure of [Th(TPP)2+][SbCl6-] is nearly identical to that of Th(TPP)2, but the separation between the N4 planes decreases to 2.89 angstrom. The EPR spectra of [Th(TPP)2+] and [Th(OEP)(TPP)+] are characteristic of simple organic radicals, while [U(TPP)2+] shows unusual signals at g(parallel-to) = 3.175 and g(perpendicular-to) 1.353. The magnetic susceptibility of the paramagnetic (S = 1/2) complex [Th(TPP)2+][SbCl6-] suggests that above 70 K there are thermally populated excited state(s) with f-orbital character. The uranium cation [U(TPP)2+] apparently adopts an S = 1/2 ground state, in which the porphyrin radical is antiferromagnetically coupled to the f2 U(IV) center; at higher temperatures, the magnetic moment increases due to thermal population of S = 3/2 states. The thorium dicationic complexes are essentially diamagnetic. These results support the suggestion that direct porphyrin-porphyrin interactions yield new molecular orbitals that are composed of atomic orbitals from both porphyrin ligands; some contribution from metal f-orbitals is also possible. All of the oxidized complexes have near-IR absorptions due to transitions between these supermolecular'' orbitals. Crystal data for Th(TPP)2.C7H8 at -25-degrees-C: orthorhombic, space group Fddd with a = 21.635(5) angstrom, b = 21.859(5) angstrom, c = 31.119(6) angstrom, beta = 90.59(2)-degrees, V = 14716(5) angstrom3, Z = 8, R(F) = 0.054, and R(wF) = 0.069 for 333 variables and 3646 data with I>2.58 sigma(I). Crystal data for Th(OEP)2 at 28-degrees-C: monoclinic, space group P2(1)/n with a = 15.699(1) angstrom, b = 15.474(1) angstrom, c = 26.318(2) angstrom, beta = 91.97(1)-degrees, V = 6389(2) angstrom3, Z = 4, R(F) = 0.031, and R(wF) = 0.038 for 734 variables and 6059 data with I>2.58 sigma(I). Crystal data for [Th(TPP)2+][SbCl6-].2C7H8.CH2Cl2 at 26-degrees-C: tetragonal, space group P4/nnc with a = 19.104(3) angstrom, b = 19.104(3) angstrom, c = 26.335(3) angstrom, V = 9612(5) angstrom3, Z = 4, R(F) = 0.065, and R(wf) = 0.106 for 248 variables and 1894 data with 1>2.58 sigma(I).