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The reaction of 1?:?4.4?M proportion ofcis-[ReO2I(PPh3)2] and 4-aminopyridine (ampy) in acetone–water givestrans-[ReO2(ampy)4]I·2H2O (1a) in 85% yield.1ahas been characterized by C, H, and N microanalyses, FT-IR, UV–vis,1H NMR spectroscopy, and molar conductivity. The X-ray crystal structure of1areveals an octahedraltransdioxorhenium(V) complex with a “N4O2” coordination for rhenium.1ahas an orthorhombic space groupC2221witha?=?17.576(4),b?=?19.370(4),c?=?15.730(4) Å,V?=?5355(2) Å3, andZ?=?8. Geometry optimization of thetrans-O,Ocomplex,1aand itscis-O,Oanalog,1bperformed at the level of density functional theory reveal that1ais more stable than1bby 25?kcal M–1in the gas phase. The electronic spectrum of1awas also analyzed at the level of time-dependent density functional theory. Excitation of1ain methanol at 450?nm leads to a fluorescent emission at 505?nm with a quantum yield (?) of 0.04. Electrochemical studies of1ain acetonitrile show a quasi-reversible Re(V) to Re(VI) oxidation at 0.618?VversusAg/AgCl. This redox potential matches with the calculated redox potential of 0.621?VversusAg/AgCl. [ABSTRACT FROM AUTHOR]