With 252 Fo(hkl), least-squares solutions for the structure of Sc2Si20 ~ have been found in each of the space groups Cm, C2 and C2/m. After discussion, the correct space group is concluded to be C2/m and the Si-O-Si angle is therefore 180 ° [/n agreement with Zachariasen (1930)]. The Si-O distances are all close to 1.62/~; the Sc-O distances average 2.13/~. CRYSTAL STI~UCTURE OF TI-IORTVEITITE Sc~Si207been suggested. HemimorpMte, Zna(OH)~Si~.O7.H~.O, definitely if very high-precision data had been availwas one of these and in new work Barclay & Cox able. The data, which we actually collected, were (1960), with data for the h/c0 and 0]cl projections, sufficiently extensive (252 F(hkl) for a small facefound the Si-0-Si angle to be 133 °, in contrast to the centred cell) and sufficiently accurate (final discrep-180 ° reported by ]:to & West (1932). A reinvestigation ancy factors for each space group of about 13%) to of thortveitite was therefore imperative and this is have solved all the problems expected at the start of described in the present paper, the work; it was not quite accurate enough to have The problem has proved much more subtle than we absolutely settled the problem finally encountered. expected. We have found formal solutions, that is to Unfortunately as the two authors (G. A. B. and H. L.) say minima for the least-squares function, in each of concerned with the experimental work had left Leeds the three space groups Cm, C2 and C2/m allowed by by the time the third author (D. W. J. C.) had found the diffraction symmetry. In C2/m the Si-O-Si angle putative structures in all three space groups, it was

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Iodobis-(2,2'-bipyridyl)copper(11) iodide, Cu(C,,H,N,),I,, crystallises in the triclinic system with two molecules in the unit cell of dimensions a = 10.66 f 0.05, a = 93.3 & 0.5", p = 101-1The atoms were located from threedimensional Patterson and Fourier syntheses; refinement was by the method of least squares. The crystal is built of positively charged iodobis-(2,2'-bipyridy1)copper (11) ions and negatively charged iodide ions. The copper atom is surrounded by four nitrogen atoms and an iodine atom a t the corners of a slightly distorted trigonsl bipyramid. The iodine atom and two nitrogen atoms (from two different bipyridyl molecules) are in a plane containing the copper atom. The other two nitrogen atoms lie on a line (passing through the copper atom) which makes an angle of 9" with the normal to this plane. All five atoms are at normal covalent distances from the copper atom. b = 14.37 & 0.05, 0.5", y = 107-6 f 0.5". c = 7-44 f 0.05 A, THE compounds Cu(bipy),(ClO,), and Cu(phen),(ClO,),, which are formed between 2,2'bipyridyl and 1 ,lo-phenanthroline, respectively, and copper(1r) perchlorate, react with halide ions in nitrobenzene or nitromethane solutions to form monohalogenobis(che1ate)-copper@) ions. Crystalline compounds of the types [Cu(phen),X]ClO, (X = C1, Br, I, SCN, NO,, HCO,, OAc, and OBz) and [Cu(bipy),X]ClO, (X = C1, Br, I, and SCN-) have been isolated from aqueous-acetone solutions. These compounds behave as uni-univalent electrolytes in nitrobenzene and nitromethane solutions. The complexes Cu(phen),X,,nH,O ( X = = C1, n = 3 . 5 ; X = B r and I, n = 1; X = S C N , n = O ; X=H*CO, and OAc, n = 6) and Cu(bipy),X,,nH,O (X = C1, n = 6; X = Br, n'= 2; X = I and SCN, n = 0) are also uni-univalent electrolytes in nitromethane so1ution.l In the complex ions [Cu(phen),X]+ and [Cu(bipy),Xj+. the copper atom appears to have a co-ordination number of five in non-aqueous solvents unless a solvent molecule occupies the sixth position in an octahedral structure. In the solid state these ions could be octahedral by polymerisation. Nyholm 2 suggested that these ions have a trigonal bipyramidal stereochemistry because of a supposed large orbital contribution to their magnetic moments. Although this structure is correct, it was based on erroneous magnetic-susceptibility measurements; it has since been shown that their moments are normal for copper(r1) compounds (1.8-2.0 B.M.).lThe crystal-structure determination of iodobis-(2,2'-bipyridyl) copper(11) iodide was

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