Gs. Girolami et al., BIS(PORPHYRIN)ACTINIDE COMPLEXES AND THEIR RADICAL CATIONS AND DICATIONS, Journal of coordination chemistry, 32(1-3), 1994, pp. 173-212
The first bis(porphyrin)actinide complexes have been prepared by react
ion 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, 1
2, 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 porp
hyrin 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 near
ly perfect square-antiprismatic coordination geometry around the thori
um center. The porphyrin macrocycles, held in such close proximity, in
teract electronically as shown by a blue-shift in the porphyrin Soret
band and by unusually low oxidation potentials relative to related mon
oporphyrin species. Chemical oxidations of M(TPP)2 and of Th(OEP)(TPP)
yield porphyrin-based radical cation complexes [M(porph)2+][SbCl6-] a
nd dicationic complexes [M(porPh)22+][SbCl6-]2. The solid-state struct
ure of [Th(TPP)2+][SbCl6-] is nearly identical to that of Th(TPP)2, bu
t 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(p
arallel-to) = 3.175 and g(perpendicular-to) 1.353. The magnetic suscep
tibility of the paramagnetic (S = 1/2) complex [Th(TPP)2+][SbCl6-] sug
gests that above 70 K there are thermally populated excited state(s) w
ith f-orbital character. The uranium cation [U(TPP)2+] apparently adop
ts an S = 1/2 ground state, in which the porphyrin radical is antiferr
omagnetically coupled to the f2 U(IV) center; at higher temperatures,
the magnetic moment increases due to thermal population of S = 3/2 sta
tes. The thorium dicationic complexes are essentially diamagnetic. The
se results support the suggestion that direct porphyrin-porphyrin inte
ractions yield new molecular orbitals that are composed of atomic orbi
tals from both porphyrin ligands; some contribution from metal f-orbit
als is also possible. All of the oxidized complexes have near-IR absor
ptions due to transitions between these supermolecular'' orbitals. Cry
stal data for Th(TPP)2.C7H8 at -25-degrees-C: orthorhombic, space grou
p 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) angstr
om, c = 26.318(2) angstrom, beta = 91.97(1)-degrees, V = 6389(2) angst
rom3, Z = 4, R(F) = 0.031, and R(wF) = 0.038 for 734 variables and 605
9 data with I>2.58 sigma(I). Crystal data for [Th(TPP)2+][SbCl6-].2C7H
8.CH2Cl2 at 26-degrees-C: tetragonal, space group P4/nnc with a = 19.1
04(3) angstrom, b = 19.104(3) angstrom, c = 26.335(3) angstrom, V = 96
12(5) angstrom3, Z = 4, R(F) = 0.065, and R(wf) = 0.106 for 248 variab
les and 1894 data with 1>2.58 sigma(I).