Dirhenium heptaoxide dissolves in donor solvents such as 1,2-dimethoxyethane, thf, and CH3CN to form adducts of the general formula O3ReOReO3 . 2L (L = monodentate ligand site). A strong reactivity enhancement of Re2O7 for alkylation, arylation, and similar reactions follows from this unsymmetric Lewis-base coordination. The terminal and bridging oxygens equilibrate in solution (O-17 NMR). These adducts exhibit unsymmetrical bent oxygen bridges in their solid state structures, e.g. O3ReOReO3 . dme (X-ray diffraction study; crystal data : space group P2(1)/c, a = 12.162(2) Angstrom, b = 10:830(1) Angstrom, c = 8.195(1) Angstrom, beta = 90.80(1)degrees, Z = 4). With stronger, chelating N-donors L(2) such as 2,2’-bipyridine, N,N’-dicyclohexyl-1,4-diazabuta-1,3-dien, and 2,2’-bis(pyrazolyl)propane the Re2O7 . 2L complexes have rigid asymmetric bridges even in solution (O-17 NMR). Thermal decomposition liberates Re2O7 (EI-MS) and the respective ligand (EI-MS, TG-MS). With tridentate ligands L(3) like tris(pyrazolyl)-methane, 1,4,7-triazacyclononane (tacn), N,N’,N"-trimethyl-1,4,7-triazacyclononane (tacn*), 1,4,7-trithiacyclononane (ttcn), the Re-O-Re bridge breaks with formation of the ionic perrhenates [ReO(3)L(3)](+)[ReO4](-). An example is the ionic [ReO3(tacn*)](+)[ReO4](-), the structure of which compound has been determined by X-ray diffraction (crystal data : space group P $($) over bar$$ 1, a = 7.389(2) Angstrom, b = 9.143(2) Angstrom, c = 1.2294(3) Angstrom, alpha = 83.68(2)degrees, beta = 77.99(2)degrees, gamma = 89.29(2)degrees, Z = 2). Intermolecular hydrogen bridging plays a major role in the crystal packing of the ionic perrhenates.