The ll9Sn Mossbauer data and electronic reflectance spectra of the cubic caesium tin(l1) halides CsSn Br,-ZCI, ( x = 0-3) and their behaviour on heating suggest that the non-bonding tin(ll> electrons may be involved in a band structure rather than being located in non-bonding molecular orbitals in these materials.

The llsSn Mossbauer parameters for the solid phases isolated from the aqueous and molten MX-SnX, systems are reported ( M = Na, K, Rb, Cs, NH,: X = CI, Br). Data for complexes of types MSnX,, MX,MSnX,, and MSn,X, are discussed in terms of the likely environments for tin(ii) and of the use of tin bonding orbitals in complex formation. THE 119SnMossbauer parameters for the Et4Nf, Bun4N+, and Ph,As+ derivatives of the trihalogenostannate(I1) ions SnX,-, SnX,Y-, and SnXYZ-(X, Y, 2 = C1, Br, or I) have been r e p ~r t e d . ~? ~The data for a number of trifluoro-and pentafluorodi-stannates(11) have also been but there has been no systematic study of the alkali-metal and ammonium derivatives of the complex tin(I1) chloride and bromide species.Studies '-lo on tin(I1) halide solutions have shown that the stable and predominant species present is the trihalogenostannate(11) ion, SnX,-. In concentrated solutions of tin(I1) fluoride with insufficient fluoride to complex all of the tin as SnF,-, the polynuclear ion stannate(I1) ion, SnX,,-, appear to be erroneous. Detailed studies on the derivatives of the tin@) fluoride species have been reported 4-6511 and some alkali-metal and ammonium trichloro-l1 and tribromo-stannates@) 1 2 9 1 3 have been described. We have described 1 the preparation and properties of a series of caesium tin@) trihalide compounds which have cubic unit cells and we now report a Mossbauer study of the other phases isolated from aqueous MX-SnX, systems (M = Na, K, Rb, Cs, NH,; X = C1, Br) and the molten MBr-SnBr, systems (M = Na, K, Rb, NH,).SnX,-MX-H,O Systems.-The phases isolated from solutions containing various mole ratios SnX, : MX Compound KnSnCl

The products of the insertion reactions of a number of tin(ll) compounds SnXa (X = Cl. Br, 1, NCS, HCOa, and AcO) with [(w-C,H,)Fe(CO),],and (w-C,H,) Fe(CO.J,CI are compared with those from replacement of CI from [(n-C5H6) Fe(CO),],*SnCI, and (n-C,H,) Fe(CO),SnCI,.The llaSn Mossbauer parameters of both series of compounds [(n-C6HB)Fe(C0)2]2*SnX2 and (w-C6H5)Fe(CO),*SnX3 (X = CI, Br, I, NCS, HCO,, and AcO) show that the use of tin bonding electrons is dominated by the Sn-Fe bond. The trends in chemical isomer shift and quadrupole splitting can be explained with reference to the very short Sn-Fe bond lengths in these materials.The positive sign for e29Q can also be explained in terms of a high p-electron density on the tin atom in the direction of the Sn-Fe bond. The i.r. for the products of the insertion reactions are also presented. SEVERAL x-cyclopentadienyl iron carbonyl complexes containing the tin-iron bond have been prepared and compounds of the type (X-C~H~)F~(CO),*S~R, (R = Cl,,+ Br,3s5 I,q5 Me? Et,, and Ph2*) and [(x-C5Hs)-Fe(CO)d,*SnR1, (R1 = C1,3j6 Br? I,8 Me: Et,&' Ph,7 NCS,7,8 AcO,' SEt,' C5H5,7 OH,'have been reported. Some of these complexes can be prepared from either tin@) 3,5s6 or tin(1v) 2,3,7 starting materials and there is apparently no difference in the nature of the products from the two types of re: action.The crystal structures of the following compounds are known: (x-CsHs)Fe(CO),*SnR, (R = Cl,9 Br,s or Ph lo) and [(x-CsHs)Fe(CO)J3*SnR', (R' = Cl, ' C5H,,12 and NO, 14). In each case the tin atom is in a distorted tetrahedral environment in which the bonds to the iron atoms are very short (2-46-2-60 A) while those to the ligands are longer than the sums of the appropriate covalent radii. The bond angles in the tin environment are severely distorted from the ideal tetrahedral angles. These features can be explainedll in terms of an increase in the s-character of the tin orbitals used in the tin-iron bond formation with a corresponding increase in the p-character of the orbitals forming the other bonds with tin. Bryan and his co-workers have pointed out that in the (x-C,H,)Fe(CO),*SnX, complexes, the two halide moieties (-SnC1, and -SnBr,), differ in their conformations about the Sn-Fe bond axis and also differ in this respect from both of the conformationally independent molecules in the unit cell of (x-C,H,)Fe-(CO),*SnPh,. They interpret these differences as being a strong indication of free rotation about the metalmetal bond. This and the values of the Sn-Fe distances

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