An overview of published crystalline dimercury(I) hydrates, solvates, and complexes/compounds with O-donor ligands shows that there is virtually no correlation between the Hg—Hg bond distance and the overall Hg—O bonding conditions. Additionally, many structures feature different configurations for the individual mercury atoms in the dimercury(I) ion, Hg22+. To supplement these findings, the crystal structures of the perchlorate salts of hydrated and dimethylsulfoxide (dmso) solvated mercury(I), [Hg2(OH2)2](ClO4)2(1) and [Hg10(OS(CH3)2)16](ClO4)10(2), respectively, have been determined by single crystal X-ray diffraction. In compound 1, the perchlorate ions act as bridges between the almost linear [Hg2(OH2)2]2+ units forming infinite chains. The Hg—Hg bond distance is 2.500(1) Å and the Hg—O distance to the water molecule is 2.231(19) Å. Additional much weaker Hg—O bonds to the bridging perchlorate oxygens lie in the range 2.78–3.15 Å. Compound 2 consists of five crystallographically independent [Hg—Hg]2+ units solvated and bridged by dmso oxygens. These larger entities form chains through much weaker bridging perchlorate ions at longer distances, 3.0–3.3 Å, with a few remaining perchlorate ions isolated in the lattice. The mean Hg—Hg bond distance is 2.500(1) Å, while the Hg—Odmso bond distances are in the range of 2.15–2.92 Å. The dmso molecules are grouped into three types of coordination, strong κO-terminal, medium μ2O-bridging, or medium/weak μ3O-bridging, depending on which dimercury(I) ion(s) in the entity they coordinate to.
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