We report the synthesis, structural, and spectroscopic characterization of a series of uranium(IV)-perrhenato complexes. Three isostructural complexes with general formula [U(ReO4)(4)(L)(4)] (where L = tri-n-butylphosphine oxide/TBPO (2), triethyl phosphate/TEP (3), or tri-iso-butyl phosphate/(TBP)-B-i (4)), have been synthesized, both through the photoreduction of ethanolic {UO2}(2+) Solutions and also via a novel U-IV starting material, U(ReO4)(4)center dot 5H(2)O (1). Compound 1 has also been used in the preparation of [U(ReO4)(4)(TPPO)(3)(CH3CN)]center dot 2CH(3)CN (5) and [U(ReO4)(DPPMO2)(3)(OH)][ReO4](2)center dot 2CH(3)CN (6), where TPPO represents triphenylphosphine oxide and DPPMO2 represents bis(diphenylphosphino)methane dioxide. All six complexes have been spectroscopically characterized using NMR, UV-vis-NIR, and IR techniques, with 2, 3, 5, and 6 also fully structurally characterized. The U atoms in compounds 2-6 all exhibit eight-coordinate geometry with up to four perrhenate groups in addition to three (DPPMO2 and TPPO) or four (TEP, (TBP)-B-i, TBPO) coordinated organic ligands. In the case of compounds 5 and 6, the coordination of eight ligands to the U-IV center is completed by the binding of a solvent molecule (CH3CN) and OH-, respectively. Solid-state physical analysis (elemental and thermogravimetric) and infrared spectroscopy are in agreement with the structural studies, The crystallographic data suggest that the strength of the U-IV-O-donor ligand bonds decreases across the series R3PO > [ReO4](-)> (RO)(3)PO. Solution-state IR and P-31 NMR spectroscopy appear to be in agreement with these solid-state results.