This paper reports fundamental vibration frequencies for molecular OS03Fz and o s o 4 isolated in argon matrices at low temperatures. Os03Fz is shown to have D3h symmetry on the basis of Raman and IR selection rules, and this conclusion is confirmed by the results of ' 8 0 enrichment studies which demonstrate the presence of an oso3 unit containing three equivalent oxygens. The argon matrix frequencies are 946.5 ( A ; ) , 928.5 (E'), 646 (A;), 619 ( A ; ) 348 (E"), 316.5 (E') 258 ( A ; ) and 206 (E') cm-l. High resolution spectra are also reported for matrix isolated oS1604 (~1963, vz 332, v3 956, and v4 327 cm-I) and for ' 8 0 enriched oso4 species.

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SO9 5NHThe title compound has been examined by single-crystal X-ray diffraction and crystallises in the space group P2Jc with Z = 4 in a unit cell of dimensions a = 6-1 2, b = 13.72, c = 13.38 8, and p = 100,4". The molecules of SnCI4,2MeCN are cis-octahedral. The i.r. and Raman spectrum of the adducts and its deuterio-analogue are reported and the vibrational assignment discussed.ADDUCTS of various stoicheiometry formed between tin tetrachloride and acetonitrile have been the subject of many studies since 1858 when SnC14,2MeCN was first rep0rted.l SnCl,,MeCN 2-7 SnC14,2MeCN,213*7-15 and more recently SnC1,,3MeCN I69l7 have been characterised. The vibrational spectrum of the 1 : 2 adduct has been interpreted in terms of a cis-octahedral model and both cis-(e.g. SnCl4,2POC1,1*) and trans-(e.g. SnC14,2pyridine19) isomers of the type SnC1,,2L are known. Attention has recently been drawn to the erroneous conclusions of vibrational spectroscopy in stereochemical deductions of this kind.20 We felt it worthwhile to examine SnC1,,2MeCN by single-crystal X-ray diffraction methods to establish the structure and to assign in some detail the vibrational spectrum.A. X-Ray Stmcture Determination Suitable crystals of SnC1,,2MeCN were mounted in sealed Pyrex capillaries and cell data were obtained from preliminary measurements using oscillation, Weissenberg and precession photographs. Crystal Data.-C,H,Cl,N,Sn, M = 343.6, Monoclinic, a = 6.12 & 0.02, b = 13.72 & 0.02, c = 13.38 & 0.02 A, p = 100.4 & 0-3", D, = 2.02 0.02 (by flotation), 2 = 4, D, = 2.06. Space group P2Jc from systematic absence h0Z for Z = 2n + 1 and OR0 for Fc = 292 + 1. Cu-K, radiation A = 1.5418 A, r/.(Cu-K,) = 275.7 cm.-l; Mo-K, radiation A = 0.7107 A, r/.(Mo-K,) = 35-3 cm.-l.The needle axis is the a axis and a crystal 0.8 x 0.3 x 0.3 mm. was used for data collection. Data were recorded by the multiple-film equi-inclination Weissenberg technique for the layers 0-5kZ with zirconiumfiltered Mo-K, radiation ; intensities were estimated visually by means of a graduated wedge. 1699 intensities were measured, of which 557 were considered unobserved, and were scaled approximately by means of precession photographs. The ' unobserved ' reflections were given an intensity equal to one half the minimum

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