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Neutron diffraction results for deuterated imidazolium hydrogen maleate are presented. The normal and

Introduetlon. Although potassium hydrogenperoxomonosulfate is sold in an impure form commercially, pure salts of peroxomonosulfate have not been previously available. We have developed a procedure involving hydrolysis of K2S208 that affords highly pure KHSOs.H20. This product yielded crystals suitable for the first determination of the structure of the HSO~-ion. An earlier X-ray study (Kyrki & Lappalainen, 1965) reported an orthorhombic unit cell but did not include a structure determination.Because of the difference in chemistry of oxidation- -(Kirfel & Will, 1980, 1981, and for $2032-(Elerman, Bats & Fuess, 1983).0108-2701/84/I 11781-05501.50Experimental. Concentrated solution of sodium peroxodisulfate was converted to the acid by passage through a column of Dowex 50X8 cation-exchange resin in the hydrogen form. The solution was concentrated in a rotary evaporator and hydrolyzed by heating at 323 K until no peroxodisulfate was detected. The solution was then neutralized to pH 3.5 by addition of KHCO 3 in an ice bath, filtered and freeze-dried. The residue was redissolved in a small quantity of water at room temperature and filtered. The filtrate was chilled in an ice bath and the crystals that formed were filtered, washed with a small quantity of absolute ethanol and dried between sheets of filter paper. Iodometric analysis indicated a bulk composition approximating KHSOs.-H20. Plate-like crystal; ~0.07 x 0.23 x 0.27 mm; Enraf-Nonius CAD-4 diffractometer; T maintained by constant flow of N 2 gas; 24 reflections, 0 = 9-15 °, used for cell dimensions; empirical ~,-scan absorption (range of transmission = 0.

Dichlorodihydridotetrakis(trimethylphosphine)tantalum(IV), TaCl2H2(PMe3)4, is reduced under argon by sodium amalgam in the presence of PMe3 to give green TaClH2(PMe3)4 (la) in 70% yield, la has been characterized by IR spectroscopy, variable-temperature and 31P('H) NMR spectroscopy, and low-temperature (50 K) neutron crystallography. In the solid state, la is a slightly distorted pentagonal bipyramid with two axial phosphines. The hydride ligands are coordinated in a cis configuration in the pentagonal plane with a H-Ta-H angle of 66.2 (6)°a nd Ta-H distances of 1.79 (1) and 1.80 (1) A. la reacts readily with Me2PCH2CH2PMe2 (dmpe) to give TaClH2(dmpe)2 (2) and with ethylene to give TaCl(C2H4)(PMe3)4 (3). It also reacts with dinitrogen to given the µ-dinitrogen complex [TaClH2(PMe3)3]2(M-N2) (4a) and with carbon monoxide to provide TaCl-(CO)3(PMe3)3 (5). The latter complex has been characterized by low-temperature (-160 °C) X-ray crystallography. In the solid state, 5 is a capped (by Cl) trigonal prism with three PMe3 ligands and one CO on the capped quadrilateral face and two CO ligands on the remaining edge. Crystal data are as follows: for la (at 50 K), monoclinic space group P2\/a, a = 18.436 (4) A, b = 9.139 (2) A, c = 12.376