Abstract
The monoclinic crystal structure of Na(2)SO(3)(H(2)O)(7) is characterized by an alternating stacking of (100) cationic sodium-water layers and anionic sulfite layers along [100]. The cationic layers are made up from two types of [Na(H(2)O)(6)] octahedra that form linear (1)(∞)[Na(H(2)O)(4/2)(H(2)O)(2/1)] chains linked by dimeric [Na(H(2)O)(2/2)(H(2)O)(4/1)](2) units on both sides of the chains. The isolated trigonal-pyramidal sulfite anions are connected to the cationic layers through an intricate network of O-H...O hydrogen bonds, together with a remarkable O-H...S hydrogen bond, with an O...S donor-acceptor distance of 3.2582 (6) Å, which is about 0.05 Å shorter than the average for O-H...S hydrogen bonds in thiosalt hydrates and organic sulfur compounds of the type Y-S-Z (Y/Z = C, N, O or S). Structural relationships between monoclinic Na(2)SO(3)(H(2)O)(7) and orthorhombic Na(2)CO(3)(H(2)O)(7) are discussed in detail.