DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, Page 3 3 Synthesis and characterisation of tetramethylammonium selenosulfate(VI) tetrahydrate, (NMe4)2SeSO3?4H2O Alexander J. Blake, Victoria Consterdine, Michael F. A. Dove,* Scott Lammas and Linda H. Thompson Department of Chemistry, University of Nottingham, Nottingham, UK NG7 2RD Tetramethylammonium selenosulfate tetrahydrate has been synthesised and characterised; a single-crystal X-ray structure determination shows the presence of the dianion SeSO3 22, in which the central sulfur atom is bonded to three oxygens and one selenium atom [S]Se distance 2.1746(7) Å].The solubility of elemental selenium in aqueous solutions of the sulfites of the more electropositive elements has been known since the middle of the nineteenth century.1 Indeed, the dissolution in and subsequent precipitation of selenium from aqueous sulfite has been described as a means of separating selenium from tellurium.2 In 1995 Ball and Milne 3 reported on their studies of the synthesis and spectroscopy of the selenosulfate anion; their data are fully consistent with the expected structure of this species and, like our earlier work,4 refute the possible existence of both the isomeric thioselenate(VI) and the selenoselenate(VI) dianions.2 Brunner et al.5 had previously shown that a selenium-bridged dirhodium complex, [(C5Me5)- Rh(CO)]2Se could be converted by the action of SO3 into the related m-SeSO3 complex, which they characterised by a singlecrystal X-ray diffraction study.As part of our study of the chemistry of selenosulfates we attempted to isolate single crystals of a salt containing the free anion, searches of the October 1996 release of the Cambridge Structural Database 6 and of the latest Inorganic Crystal Structure Database having revealed the bridged dirhodium complex and the earlier study of a copper complex, Cu(en)2SeSO3 (en = ethane-1,2-diamine),7 as the only relevant structures. Crystallographic studies of M(en)3SeSO3 compounds, MII = Cd,8a Mn, Fe, Co, Ni, Zn or Cd,8b had shown them to have disordered O and Se sites in the selenosulfate anion.We have now succeeded in preparing crystals of the colourless tetrahydrate of tetramethylammonium selenosulfate. The compound was made from excess selenium, aqueous tetramethylammonium hydroxide (2 equivalents) and sulfur dioxide (1 equivalent) and isolated from the concentrated solution.It is stable in air at room temperature for more than a month in the dark; it may be partially dehydrated in vacuo and decomposes at 200 8C to a brown solid, which turns red with further heating. The hydrate was isolated in ca. 50% yield and gave satisfactory elemental analyses, 77Se NMR (in aqueous sulfite), infrared and Raman spectra fully consistent with the formulation.† Its crystal structure has been determined by single-crystal X-ray methods‡ and shows the presence of the tetramethylammonium ions and † Spectroscopic data for the selenosulfate anion.Raman (solid state) 1144(E), 991(A1), 637(A1), 518(E), 303(A1), 279 (sh)(E) cm21; 77Se NMR in aqueous sulfite, a singlet at d 650 relative to Me2Se. ‡ Crystal data for: C8H32N2O7SSe, M = 379.38, monoclinic, a = 8.2902(9), b = 15.551(3), c = 14.198(3) Å, b = 94.924(15)8, U = 1823.7(6) Å3, space group P21/n, Z = 4, Dx = 1.382 g cm23, Mo-Ka radiation, m = 2.198 mm21, T =150 K, w–q scans, 2q < 508, 4499 total data, 3195 unique, Rint = 0.024 after a numerical absorption correction (Tmax = 0.758, Tmin = 0.535), 301 variables refined in full-matrix least squares against 3188 F2 data to R[F > 4s(F )] = 0.0285, wR(F2) = 0.0622, S = 0.99, Drmax = 0.56 e Å23.CCDC reference number 186/793. the free selenosulfate ion interacting via two of its oxygen atoms (O2 and O3) with a network of H-bonded water molecules, Fig. 1. There is also a long selenium–hydrogen interaction, Se1 ? ? ? H3W1 2.58 Å, with a hydrogen bond angle of 1738.The S]Se bond length of 2.1746(7) Å in the anion is shorter than that reported earlier 7 for Cu(en)2SeSO3 in which selenium was said to complete the octahedral co-ordination of copper(II). The length of the S]Se bond in the dirhodium complex is significantly greater, 2.301 Å, consistent with it being a single bond; indeed, it is quite comparable with the related single bond in OnS]Se (n = 2 or 3) fragments listed in the Database,6 for which the average value is 2.26 (±0.03) Å.Acknowledgements Financial support from the EPSRC in the form of a studentship (to L. H. T.) and of funding for the purchase of the X-ray diffractometer is gratefully recorded. References 1 Gmelin’s Handbuch der Anorganische Chemie, Selen, B, Gmelin- Verlag GmbH, Clausthal-Zellerfeld, 1949. 2 K. W. Bagnall, Comprehensive Inorganic Chemistry, eds. J. C. Bailar, H. J. Emeléus, R. Nyholm and A. F. Trotman-Dickenson, Pergamon Press, 1973, vol. 2, p. 938. 3 S. Ball and J. Milne, Can. J. Chem., 1995, 73, 716. 4 L. H. Thompson, Ph.D. Thesis, University of Nottingham, 1993. 5 H. Brunner, N. Janietz, J. Wachter, H.-P. Neumann, B. Nuber and M. L. Ziegler, J. Organomet. Chem., 1990, 388, 203. 6 F. H. Allen and O. Kennard, Chem. Design Automation News, 1993, 8, 1; 31. 7 N. V. Podbereskaya, S. V. Borisov and V. V. Bakakin, Zh. Strukt. Khim., 1971, 12, 840. 8 (a) N. V. Podbereskaya and S. V. Borisov, Zh. Strukt. Khim., 1971, 12, 1114; (b) V. L. Varand, N. V. Podbereskaya, V. M. Shulman, V. V. Bakakin and E. D. Ruchkin, Izv. Akad. Nauk SSSR, Ser. Khim., 1967, 44. Received 10th October 1997; Communication 7/07328C Fig. 1 The asymmetric unit in the structure of tetramethylammonium selenosulfate tetrahydrate. Selected bond distances (Å) and angles (8): Se1]S1 2.1746(7), S1]O1 1.452(2), S1]O2 1.464(2), S1]O3 1.462(2); O1]S1]O3 110.90(13), O1]S1]O2 111.86(12), O3]S1]O2 108.79(12), Se1]S1]O1 108.57(8), Se1]S1]O2 108.35(8), Se1]S1]O3 108.28(9)