Adduct Formation Between Diphenyltin Dichloride and 2-phenyl-1 , 3-dithiane trans-1-trans-3-dioxide . Preparation , Spectroscopy , Crystal and Molecular Structure of [ Ph 2 SnCl 2 . CH 2 ( CH 2 ) 2 SOCH ( Ph ) SO ]

Um novo aduto pentacoordenado de Sn (IV) foi preparado a partir de dicloreto de difenilestanho (IV) e do dissulfóxido 2-fenil-1,3-ditiano trans-1,trans-3-dióxido. O estudo espectroscópico e por difração de raios-X mostrou ser o novo composto um exemplo raro de aduto pentacoordenado 1:1 entre uma espécie organometálica de Sn (IV) e um ligante neutro. Apesar de ser difuncional, o ligante apresenta-se monodentado, em virtude de sua geometria peculiar. Ademais, o aduto não mostra evidência de interação intermolecular forte, formando moléculas discretas.


Introduction
Most 1:1 adducts of diorganotin (IV) dihalides with Lewis donor ligands are actually six-coordinate dimeric species, in particular when the organic group is methyl 1 .Only a few adducts of this type are truly pentacoordinate 2 , such as that formed between diphenyltin (IV) dichloride with benzothiazole 2 , and those between both diphenyltin (IV) dichloride and trimethyltin (IV) chloride with 2,6-dimethylpyridine 3 , as well as that which occurs between dimethyltin (IV) dichloride and dibenzylsulphoxide 4 .A curious example is given by the pyrazine adducts with dimethyltin (IV) dichloride and diphenyltin (IV) dichloride.Both cases produce polymeric chains in which the ligand and the organotin moiety alternate.The first of these adducts has a structure made up exclusively of six-coordinate tin atoms in the chains.The second, however, forms alternating chains containing five-and six-coordinate tin centres, respectively 5 .
We report here the preparation and the spectroscopic and structural study of a true pentacoordinate adduct in-volving diphenyltin (IV) dichloride and the disulphoxide 2 Of the two SO functional groups only one formed a bond with the Sn atom, and no appreciable intermolecular interaction was observed between individual adduct molecules.

Experimental
The ligand was kindly provided by Prof. C. Celso, who had previously synthesised it.
Equal amounts (1.45 m mole) of both Ph2SnCl2 and the ligand were dissolved in 10 mL of dry EtOH.After refluxing for 2 h, the mixture was filtered, and a clear solution obtained.Slow cooling and evaporation of this solution yielded an abundant crop of needle-like colourless crystals.These were filtered off and washed with ether.The yield of pure product was 0.60 g (72%), and the adduct decomposed at 177 °C.An attempt to prepare a 2:1 adduct using a large excess of ligand was unsuccessful.C, H analysis of the product gave C, 46.02; H, 3.82%; calculated for C22H22O2S2Cl2Sn gives C, 46.18; H, 3.85%.I. R. spectra were recorded from a 283 B Perkin-Elmer instrument using CsI pellets.Mössbauer spectra were obtained from a constant acceleration spectrometer moving a CaSnO3 source at room temperature.Samples were analysed at 85 K with respect to that source. 119Sn NMR spectra were run in CDCl3 in a 250 MHz Bruker instrument, using Me4Sn as a reference.The molecular structure of the adduct was established by a single crystal diffraction study using an Enraf-Nonius CAD-4 diffractometer.

Results and Discussion
Table 1 presents spectroscopic data for our adduct as well as for its precursors.The I.R. spectrum of the ligand shows only one SO band at 1044 cm -1 , which in the adduct appears at 1044 and 950 cm -1 , indicating two different SO groups.This is consistent with the fact that one SO function is bonded to the metal, causing the shift to lower frequency (950 cm -1 ), whereas the other SO group remains uncomplexed, which accounts for its practically unchanged frequency.The I.R. spectrum also shows a band at 420 cm -1 , which we assigned to the SnO vibration 6 .The SnCl bands were shifted to lower frequencies compared to the precursor Ph2SnCl2, which is characteristic of adducts of organotin halides 6 .
The 119 Sn NMR spectrum in CDCl3 showed a single absorption at δ -62, upfield from Ph2SnCl2, due to enhanced shielding of the Sn nucleus in the adduct 7 , compared to the precursor (δ -33).
The 119 Sn Mössbauer spectrum of the adduct showed an increase in the quadrupole splitting and no variation in the isomer shift, compared to Ph2SnCl2.The increase in the quadrupole splitting may be accounted for by a greater asymmetry in the electronic density distribution around the Sn nucleus, whereas the invariance in δ is surprising.An expansion in the coordination number of tin upon adduct formation usually tends to produce lower δ values as a consequence of rehybridisation and less s orbital participation in the overall hybrid orbitals 8 .Of course δ values do not depend only on the hybridisation of tin, but also on the total charge distribution, i.e., on the polarisation of the bonds.The two effects may have acted here to balance each other out, leading to the same value of δ in both the precursor and the adduct.
Figure 1 shows the molecular structure of the adduct and Fig. 2 the corresponding unit cell.Table 2 presents the most important bond distances and angles, as well as some of the dihedral angles of the adduct.
Figure 1 shows the adduct as a pentacoordinate trigonal bipyramidal species, and Fig. 2 shows the arrangement of the individual molecules in their unit cell.The monomeric character of the adduct is shown by the fact that the Sn-Cl'(1) distance, between the Sn atom of a given molecule and the axial Cl' atom of its nearest neighbour was found to be 4.29 Å, greater than the sum of the van der Waals radii of Sn (2.20 Å) and Cl (1.70-1.90Å) 10 .Figure 2 clearly shows that the self-association so common in organotin compounds is not present in this case, and the complex is indeed pentacoordinate.Additional crystallographic data can be obtained from the authors on request.