Tin II Clusters

Department of Chemistry, University of Calgary, Alberta, Canada 2.2.1 Introduction 

The purpose of this chapter is to provide the reader with an overview of the significant findings in tin(II) cluster chemistry up to mid-2007. Although the majority of investigations have involved imidotin clusters, there have been important developments in the last 10 years in our knowledge of related phosphidotin clusters (see Section 2.2.6). 

Transition-metal complexes of [Sn( a3-NR)]4 cubanes have also been reported. The reaction of Fe2(CO)9 with [Sn( a3-NSiEt3)]4,8, produces the complex [Sn()a3-NSiEt3)]4-2Fe(CO)4,36, in 82% yield, even when an excess of Fe2(CO)9 is used. The presence of only two broad signals for the ethyl substituents in the NMR spectrum suggests that the iron centers scramble in solution, cf. 35. A series of related transition-metal complexes of 4 have been mentioned in reviews, however no details have been reported for the complexes 37a-d.  

The reaction of the cubane 4 with an excess of SO2 results in the rapid formation of the dimeric compound 38, in which two imidotin cubanes are bridged by two sulfito ligands. The retention of the cubane structure is unexpected, since SO2 is known to insert readily into Sn-NR2 bonds. The dimer 38 is the only known complex in which two [Sn()a3-NR)]4 cubane clusters are strongly linked. 

in an unspecified low yield. When the same reaction was carried out in the presence of 30a, the yield of 40 was increased to 14%. The solid-state structure of 40 revealed a distorted six-coordinate geometry at the phosphorus center. The phosphorus atom is strongly bound to five of the tin atoms, with Sn-P distances in the range 2.580(4)-2.725(3) A, while the contact to the unique tin center is considerably longer, at 3.298(3) 

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DR. HAIGHT We are now about to tackle the problem of distinguishing between the reactivities of mononuclear and polynuclear molybdenum species. We added mononuclear molybdenum- tin(II) complexes to water and to perchlorate and our evidence right now is that it becomes a cluster very fast when you do this. 

In the case of giant wheel (molybdenum blue) compounds, the general synthetic strategy involves the acidification (pH 1) and reduction of an aqueous molybdate(VI) solution [possible reducing agents iron powder, tin(II) chloride, molybdenum(V) chloride, ascorbic acid, cysteine, hydroxylamine, hypophos-phorous acid, sodium dithionite, or hydrazine sulfate].On the other hand, an icosahedral ball-shaped cluster can be formed in an aqueous Mo(VI)... 

Westerhausen, ef a/., have converted Sn[N(SiMe3)2]2 into a number of crystalline tin(II)-containing cluster compounds, as summarised in Scheme 9.18 i3 -i40a,i40b... 

In the structure of a closely related compound to that just described, i.e. tetrakis[( o.3-2,5-dimethoxyphenylimido)tin(II)] (5), characterized as a hemi-toluene solvate, dimeric pairs of Su4N4 clusters associate via Sn7... tt interactions as well as a series of C-H... O contacts. By contrast to that observed for 4.1.5(C7H7), no further aggregation occurs between molecules via Sn... tt interactions. 

The tetranuclear structure of tetrakis[( i3-2,4-dimethoxyphenylimido)tin(II)] (19), is related to the Su4N4 cubes described above as (4) and (5), each of which was characterized as a solvate. Although this structure came out as a hit in the described search of the CSD, disorder in the aromatic rings preclude a detailed analysis of the crystal packing. However, it is apparent that a linear chain is found, mediated by the formation of a pair of Sn... tt interactions on either side of the cluster, as described for (5). 

Advances in techniques include sophisticated NMR methods, both in solution and the solid-state, and computational methods, and these, coupled with X-ray diffraction and other established methods, have been applied to the study of a wide variety of structures. Topics covered in the book include Sn(II) clusters, tin Zintl ions, Sn(II) heterobimetallic compounds, RsSn+ cations, stannylenes (R2Sn ), stannenes (R2Sn=SnR2 and R2Sn=CR2), stannynes (RSn=SnR), organotin oxide, carboxylate and sulfonate clusters, dendrimers and macrocycles, organotin polymers, Sh-tt interactions, unusual bondings and structures, and compounds with non-linear optical properties. 

Zoller, T., lovkova-Berends, L, Dietz, C, Berends, T., and Jurkschat, K. (2011) On the reaction of elemental tin with alcohols a straightforward approach to tin(II) and tin(IV) alkoxides and related tinoxo clusters. Chem, Eur. 17, 2361-2364. 

Transition metal compounds in various form such as metal carbonyls 0), carbonyl clusters (2), Pt(II) chloride/tin chloride (3) PtLn (L=PR3) (4), etc. have been proposed as homogeneous catalysts for the water gas shift (wgs) reaction (eq. 1). Some of them are reportedly active at relatively low temperature (<150°)... 

Inorganic chemists generally are unhappy with formulations of tin in oxidation state III. The formulation here ought not to be taken too seriously. Disproportionation into Sn(IV) and Sn(II) conceivably may occur. Alternatively, SnlllO(OH) may well correspond to trapping of an electron by a cluster of tin ions. 

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