Bis(porphyrin)actinide complexes and their radical cations and dications

Gregory S. Girolami, Philip A. Gorlin, Stanley N. Milam, Kenneth S Suslick, Scott R. Wilson

Research output: Contribution to journalArticlepeer-review

Abstract

The first bis(porphyrin)actinide complexes have been prepared by reaction of the diethylamide complexes M(NR2)4 (where M = Th, U and R = Me, Et) with 5, 10, 15, 20-tetraphenylporphyrin (H2TPP) or 2, 3, 7, 8, 12, 13, 17, 18-octaethylporphyrin (H2OEP). The coordination geometry of Th(TPP)2 is a distorted square-antiprism where the thorium center is displaced 1, 47 A from each of the porphyrin N4planes; the porphyrin N4planes are threrefore separated by 2.94 A. In Th(OEP)2, the two porphyrin N4planes are separated by 2.89 A 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 N4planes decreases to 2.89 A. 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 gj = 3.175 and g= 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 UIV 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°C: orthorhombic, space group Fddd with a = 21.635(5) A, b = 21.859(5) A, c = 31.119(6) Å, β = 90.59(2)0, V= 14716(5) Å3, Z= 8, RF= 0.054, and RwF = 0.069 for 333 variables and 3646 data with I>2.58σ(I). Crystal data for Th(OEP)2 at 28°C: monocinic, space group P21/n with a = 15.699(1) Å, b= 15.474(1) Å, c = 26.318(2) Å, β = 91.97(1)°, V= 6389(2) Å3, Z = 4, RF = 0.031, and RwF = 0.038 for 734 variables and 6059 data with I>2.58 σ(I). Crystal data for [Th(TPP)2+][SbCl6-].2C7H8.CH2C12 at 26°C: tetragonal, space group P4/nnc with a = 19.104(3) Å, b= 19.104(3) A, c = 26.335(3) Å, V=9612(5) Å3, Z = 4, RF =0.065, and RwF=0.106 for 248 variables and 1894 data with I>2.58 σ(I).

Original languageEnglish (US)
Pages (from-to)173-212
Number of pages40
JournalJournal of Coordination Chemistry
Volume32
Issue number1-3
DOIs
StatePublished - Jun 1 1994

Keywords

  • Special Pair
  • actinide
  • metalloporphyrin
  • porphyrin
  • sandwich complexes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Materials Chemistry

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