Controlling Cation-Cation Interactions in Uranyl Coordination Dimers by Varying the Length of the Dicarboxylate Linker
Résumé
The chemistry of linear uranyl(V/VI) dioxo cations, [Oyl-U-Oyl] +/2+ , is dominated by coordination of uranium in the equatorial plane. Effects of this constraint were evaluated by experiment and theory for gas-phase mixed-valence U V/VI coordination dimers in which uranyl moieties are linked by alkyl dicarboxylates, [(UO2 +)(UO2 2+)(OOC-(CH2)n-2-COO 2-)2]-(n = 3-12). Faster O2-addition to dimers with short linkers n = 3 and 4, versus n ≥ 5, suggests a structural difference. Computed structures with the shortest linkers have bridging dicarboxylates and nearly parallel, noninteracting uranyls. Longer linkers, n = 5-7, accommodate uranyl orientations with distinct U V-U VI end-on cation-cation interactions (CCIs), whereby Lewis base Oyl from U V coordinates to the acid U VI , denoted as U V Oyl … U VI. The dimer structure for n = 8 has a U V-U VI side-on diamondshape CCI, with U V Oyl … U VI and U VI Oyl … U V interactions. Addition of O2 to the n = 4 and 5 dimers yields [(UO2 2+)2(OOC-(CH2)n-2-COO 2-)2(O2-)]-, with U V oxidized to U VI and O2 reduced to O2-. Whereas O2 can associate to and oxidize the exposed U V center for dimers with n = 3 and 4, the more crowded U V site in the CCI structures inhibits O2 addition. The results demonstrate rational structural control of uranyl-uranyl bonding and reactivity in small coordination complexes.
Domaines
Chimie théorique et/ou physiqueOrigine | Fichiers produits par l'(les) auteur(s) |
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