The reaction of [PPh4](3)[Re7C(CO)(21)] (1) with 1 or more equiv of Hg(OAc)(2) in dichloromethane provides the monomercury derivative [PPh4](2)[Re7C(CO)(21)HgOAC] (2) in high yield. However, in the presence of methanol the reaction of 1 with 2 equiv of Hg(OAc)(2) yields the dimercury hexarhenium cluster compound [PPh4](2)[Re6C(CO)(18)(HgOAc)(2)] (3) together with the dirhenium complex [PPh4][Re-2(CO)(6)(mu-OMe)(2)(mu-OAc)] (4). The dimercury compound 3 reacts with various thiols HS-Z to form thiolate-substituted derivatives [PPh4](2)[Re6C(CO)(18)(HgSZ)(2)] [Z = C6H4Br (5); C5H4N (6); C2H4COOH (7)]. All new compounds have been characterized by a combination of analytical and spectroscopic data, and the molecular structures of compounds 3-6 have been determined by X-ray crystallography.