New modifications (denoted as beta-) of the compounds H2SeO3, NaHSeO4, and Na5H3(SeO4)(4)(H2O)(2) were isolated from aqueous solutions and their crystal structures determined from single crystal data. beta-H2SeO3 crystallizes in the space group P1 with lattice parameters of a = 4.6794(4) angstrom, b = 5.0988(4) angstrom, c = 5.7743(5) angstrom, a = 102.252(6)degrees, beta = 91.594(6)degrees, gamma = 98.054(6)degrees, and consists of two unique trigonal-pyramidal SeO(OH)(2) units that are held together by O-H center dot center dot center dot O hydrogen bonds. beta-NaHSeO4 crystallizes in the space group P (1) over bar with lattice parameters of a = 5.0814(2) angstrom, b = 5.6345(3) angstrom, c = 6.5125(3) degrees, a = 88.352(3)degrees, beta = 73.163(3)degrees, gamma = 82.027(3)degrees, and is made up of distorted NaO6 octahedra and tetrahedral SeO3(OH)(-) anions, with the hydrogen atom statistically disordered between two positions. beta-Na5H3(SeO4)(4)(H2O)(2) crystallizes in the space group I-2/c with lattice parameters of a = 7.0472(15) angstrom, b = 13.194(3) angstrom, c = 17.845(4) angstrom, beta = 101.345(9)degrees. The asymmetric unit contains three Na+ sites (one situated on a twofold rotation axis and each with a distorted octahedral coordination by oxygen atoms), one water molecule, one SeO3(OH)(-) anion, and half of an [SeO4 center dot center dot center dot H center dot center dot center dot O4Se] unit with a very short interpolyhedral O center dot center dot center dot O distance of 2.447 (4) angstrom. The crystal structures of the beta-modifications are comparatively discussed with those of the corresponding known a-modifications. Moreover, the crystal structure of Te2O4(OH)(2) was reinvestigated [Pna2(1), a = 12.0512(8) angstrom, b = 8.0267(5) angstrom, c = 4.7268(3) angstrom], allowing the localization of the hydrogen atoms and hence a more detailed view of the hydrogen bonding system.
