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Title:Actinide porphyrin complexes
Author(s):Milam, Stanley Nemec
Doctoral Committee Chair(s):Suslick, Kenneth S.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Chemistry, Nuclear
Abstract:The first bis(porphyrin)actinide complexes have been prepared by reaction of M(NEt$\sb2$)$\sb4$ (where M = Th, U) with H$\sb2$TPP or H$\sb2$OEP. The coordination geometry of (TPP)$\sb2$Th is a distorted square-prism where the thorium center is displaced 1.47 A from each of the porphyrin N$\sb4$ planes; the porphyrin planes are separated by 2.94 A. The porphyrin macrocycles, held in such close proximity, interact electronically as shown by a shift in the porphyrin Soret band to higher energy and unusually facile oxidation processes relative to related monoporphyrin complexes.
Oxidation of (TPP)$\sb2$M yields porphyrin-based radical cation complexes ((TPP)$\sb2$M$\sp+$) (SbCl$\sb6\sp-$) and dicationic complexes, ((TPP)$\sb2$M$\sp{2+}$) (SbCl$\sb6\sp-$) $\sb2$. The porphyrin planes of ((TPP)$\sb2$Th$\sp+$) (SbCl$\sb6\sp-$) are separated by 2.89 A, this separation is slightly less than that of (TPP)$\sb2$Th.
The EPR spectrum of ((TPP)$\sb2$Th$\sp+$) (SbCl$\sb6\sp-$) is that of a simple organic radical (g = 2.0016) while the uranium complex shows unusual signals at g$\sb{\rm para}$ = 3.175 and g$\sb{\rm perp}$ = 1.343. SQUID measurements on ((TPP)$\sb2$Th$\sp+$) (SbCl$\sb6\sp-$) suggest that above 70 K there are thermally populated excited state(s) with f-orbital character. Above 200 K, ((TPP)$\sb2$U$\sp+$) (SbCl$\sb6\sp-$) apparently adopts S = 3/2 spin state(s), but below 70 K the spin state appears to be S = 1/2. This behavior may be due to antiferromagnetic coupling of the porphyrin radical to the f$\sp2$ U$\sp{\rm IV}$ center.
The dicationic complex ((TPP)$\sb2$Th$\sp{2+}$) (SbCl$\sb6\sp-$) $\sb2$ is essentially diamagnetic. This suggests that there is a direct porphyrin-porphyrin interaction that results in a new set of molecular orbitals composed of both porphyrin ligands and perhaps some metal contribution. All of the oxidized complexes have near-IR absorptions due to transitions between these molecular orbitals.
Mono(porphyrin)actinide complexes may be prepared directly from UCl$\sb4$ or ThCl$\sb4$. The uranium center of (TPP)UCl$\sb2$(thf) is displaced 1.29 A from the porphyrin macrocycle. Reaction of Na (OCH(CF$\sb3$)$\sb2$) with (TPP)UCl$\sb2$ in 1,2-dimethoxyethane (dme) yields $\{$Na(dme)$\sb3\sp+\}\{$(TPP)U (OCH(CF$\sb3$)$\sb2$) $\sb3\sp-\}$. The uranium center of this complex is displaced 1.43 A from the porphyrin macrocycle plane. Reaction of KOC$\sb6$H$\sb3$Cl$\sb2$ with (TPP)UCl$\sb2$ yields (TPP)U(OC$\sb6$H$\sb3$Cl$\sb2$)$\sb2$, which has an available coordination site and binds Lewis bases. (TPP)U(OC$\sb6$H$\sb3$Cl$\sb2$)$\sb2$ reacts with O$\sb2$ to form the first U$\sp{\rm VI}$ porphyrin complex (TPP)U(O)(OC$\sb6$H$\sb3$Cl$\sb2$)$\sb2$. This oxo complex cannot oxidize PPh$\sb3$ to OPPh$\sb3$.
Issue Date:1989
Rights Information:Copyright 1989 Milam, Stanley Nemec
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9010958
OCLC Identifier:(UMI)AAI9010958

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