| Abstract: | The characteristic feature of the structure of the title compound, dipotassium bis(sulfito‐κS)mercurate(II) 2.25‐hydrate, is a layered arrangement parallel to (001) where each of the two independent Hg(SO3)2]2? anions are grouped into centrosymmetric pairs and are surrounded by two K+ cations to give the overall layer composition {K2Hg(SO3)2]2}2?. The remaining cations and the uncoordinated water molecules are situated between these layers. Within the Hg(SO3)2]2? anions, the central Hg atoms are twofold coordinated by S atoms, with a mean Hg—S bond length of 2.384 (2) Å. The anions are slightly bent 174.26 (3) and 176.99 (3)°] due to intermolecular O...Hg interactions greater than 2.8 Å. All coordination polyhedra around the K+ cations are considerably distorted, with coordination numbers ranging from six to nine. Although the H atoms of the five water molecules (one with symmetry 2) could not be located, O...O separations between 2.80 and 2.95 Å suggest a system of medium to weak O—H...O hydrogen bonds which help to consolidate the structural set‐up. Differences and similarities between the bis(sulfito‐κS)mercurate(II) anions in the title compound and those in the related salts (NH4)2Hg(SO3)2] and Na2Hg(SO3)2]·H2O are discussed. |
