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(NR 2 ) 4 (where M = Th, U and R = Me, Et) with 5, 10, 15, 20-tetraphenylporphyrin (H 2 TPP) or 2, 3, 7, 8, 12, 13, 17, 18-octaethylporphyrin (H 2 OEP). The coordination geometry of Th(TPP) 2 is a distorted square-antiprism where the thorium center is displaced 1.47 Å from each of the porphyrin N 4 planes; the porphyrin N 4 planes are threrefore separated by 2.94 Å. In Th(OEP) 2 , the two porphyrin N 4 planes are separated by 2.89 Å 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 + ][SbCl 6 − ] and dicationic complexes [M(porph) 2 2+ ][SbCl 6 − ] 2 . The solid-state structure of [Th(TPP) 2 + ][SbCl 6 − ] is nearly identical to that of Th(TPP) 2 , but the separation between the N 4 planes decreases to 2.89 Å. 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 ∥ = 3.175 and g ⊤ = 1.353. The magnetic susceptibility of the paramagnetic (S = 1/2) complex [Th(TPP) 2 + ][SbCl 6 − ] 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 f 2 U 1v 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 °C 7 H 8 at −25°C: orthorhombic, space group Fddd with a = 21.635(5) Å, b = 21.859(5) Å, c = 31.119(6) Å, β = 90.59(2)°, V = 14716(5) Å 3 , Z = 8, R F = 0.054, and R wF = 0.069 for 333 variables and 3646 data with I>2.58 σ(I). Crystal d