The tendency of sulfuric acid to form polysulfates as condensation products is not as pronounced as for the less acidic neighbors in the periodic table, H 3 PO 4 and H 4 SiO 4 , for which numerous polyphosphates and polysilicates are known. Therefore, it is not surprising that the number of structurally characterized polysulfates is rather low. Only the alkaline metals Na, K, Cs, [1][2][3] the main-group elements Se, Sb, Te, [4][5][6] and the transition-metal Cd form simple "binary" (hydrogen) disulfates, [7] and their crystal structures have been established. The disulfates of Na, K, Cs, and Cd are doubtless true ionic compounds, while Se 4 (HS 2 O 7 ) 2 and (IO 2 ) 2 (S 2 O 7 ) contain the polyatomic cations Se 4 2+ and IO 2 + exhibiting covalent bonds. [4,8] At first glance the disulfates Sb 2 (S 2 O 7 ) 3 and Te-(S 2 O 7 ) 2 seem to consist of discrete Sb 4 (S 2 O 7 ) 6 and Te(S 2 O 7 ) 2 molecules, respectively. But if weaker Sb À O (> 240 pm) and Te À O (> 270 pm) contacts are considered, which are clearly within bonding distance, the chain structures of the compounds are revealed. Thus, the only crystallographically characterized molecular disulfate is disulfuric acid, H 2 S 2 O 7 . [9] Although molecular derivates of H 2 S 2 O 7 such as the methyl or trimethylsilylester have been prepared, their solid-state structures remain unknown. [10,11] An unambiguous molecular metal disulfate has not been reported to date. During our investigations of refractory metal compounds containing complex oxo anions, [12][13][14] we also studied the reactions of rhenium metal and rhenium compounds with sulfuric acid/SO 3 mixtures. It turned out that rhenium metal is oxidized by sulfuric acid containing 65 % SO 3 to give the Re VII sulfate Re 2 O 5 (SO 4 ) 2 , which adopts two modifications. [12] The compound can be obtained even more conveniently when Re 2 O 7 (H 2 O) 2 is used as starting material instead of the metal. Herein, we present the oxide chloride disulfate ReO 2 Cl-(S 2 O 7 ), which forms in the reaction of ReCl 5 with SO 3 -rich (65 %) oleum in sealed glass ampoules at 150 8C, that is, by the oxidation of Re V , most probably according to Equation (1).