Mechanisms of ligand substitution reactions in ternary dioxouranium(VI) complexes

Journal Article · Mon Nov 30 04:00:00 EST 1998 · Inorganic Chemistry

DOI:https://doi.org/10.1021/ic9804364· OSTI ID:316219

Szabo, Z; Grenthe, I ^[1]

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1. Royal Inst. of Tech., Stockholm (Sweden)

The activation parameters of various inter- and intramolecular ligand exchange reactions in ternary complexes of the type UO{sub 2}LF{sub 3} (where L is one of the bidentate ligands picolinate, 4-nitropicolinate, 4-(3-pentyl)picolinate, oxalate, or carbonate) and UO{sub 2}L{sub 2}F (where L = picolinate or oxalate) have been determined by different NMR techniques. The activation entropies for the reactions have been used to discuss their intimate mechanism, particularly the solvent participation. Additional mechanistic information has been obtained from studies of H{sup +}/D{sup +} catalysis of the various reactions. Through the use of the proton-catalyzed pathway, the rate of carbonate exchange in UO{sub 2}CO{sub 3}F{sub 3}{sup 3{minus}} was varied by a factor of ca. 10. The fact that the rate of fluoride exchange remained constant clearly indicates that the exchanges of carbonate and fluoride follow parallel pathways. The activation entropies of most of the fluoride exchange reactions in UO{sub 2}LF{sub 3} have values close to 10 J/K mol, indicating dissociative (D) or dissociative interchange (I{sub D}) mechanisms. The exchange of L takes place in two steps: The first is a chelate ring opening/closing, resulting in a ligand rotation. The second is bond breaking at the carboxylate end and exchange; hence, the activation entropies for the exchange vary with L.

• OSTI ID: 316219
• Journal Information: Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 24 Vol. 37; ISSN 0020-1669; ISSN INOCAJ
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ACTIVATION ENERGY
CARBONATES
DEUTERIUM
DISSOCIATION
FLUORIDES
ION EXCHANGE
ISOTOPE EFFECTS
PICOLINES
URANYL COMPLEXES