The structural and spectroscopic characterisation of three actinyl complexes with coordinated and uncoordinated perrhenate: [UO_2(ReO_4)_2(TPPO)_3], [{(UO_2)(TPPO)_3}_2(μ_2-O_2)][ReO_4]_2 and [NpO_2(TPPO)_4][ReO_4]

摘要

The first structural characterization of an actinide complex with coordinated perrhenate is reported, [UO_2(ReO_4)_2(TPPO)_3] (1). In this {UO_2}~(2+) complex two [ReO_4]– anions and three TPPO (triphenylphosphine oxide) PO donor ligands are coordinated in the equatorial plane in a cisoid arrangement. This bonding arrangement, and apparent strain observed in the equatorially bonded ligands, is attributed to the solid state packing in adjacent molecules in which hydrophobic TPPO ligands form an effective shell around a hydrophilic core of two UO_2(ReO_4)_2 moieties. Solid state vibrational spectroscopy (infrared and Raman), ~(31)P CP MAS NMR and elemental analysis are also consistent with the formula of 1. Solution state vibrational spectroscopy and ~(31)P NMR measurements in EtOH indicate the lability of the TPPO and [ReO_4]– groups. The photolytic generation of peroxide in EtOH solutions of 1 leads to the formation of trace quantities of [{(UO_2)(TPPO)_3}_2(μ_2-O_2)][ReO_4]_2, 2, in which the coordinated [ReO_4]– groups of 1 have been displaced by bridging O_2~(2–), derived from atmospheric O_2. Finally, attempts to synthesise a {NpO_2}~+ analogue of 1 have resulted only in the formation of [NpO_2(TPPO)_4][ReO_4], 3, in which [ReO_4]~– acts solely as a counter anion. From these results it can be concluded that [ReO_4]~– will bond to {UO_2}~(2+), but will be readily displaced by a more strongly coordinating ligand (e.g. peroxide) and will not coordinate to an actinyl cation with a lower charge, {NpO_2}~+, under the same reaction conditions.