Sn cation

The sulfur-nitrogen bond length in thiazyl salts is about 1.42 A and the vibrational frequency [v(SN] occurs at 1437 cm in [SNJiAsFg]. The [SN]" cation exhibits an " N NMR resonance at ca. 200 ppm and this technique is useful for monitoring reactions of [SN]". ... 

The first [SsNs]" salt was reported in 1969. These salts are moisture sensitive, but they dissolve without decomposition in SOCI2 or formic acid. The [SsNs]" cation is formed by the reaction of S4N4 with the [SN]" cation (Scheme 5.3). " ... 

SiDi.5Fe4Sni2S32. The presence of these three neighbors decreases the symmetry around the Sn cations leading to an increase in the linewidth of the peak. 

Fig. 15. Structure of the (Me5C5) Sn+ cation in (Me5C5) Sn+ BF (79a). Reprinted with permission from Chem. Ber. 113, 761 (1980). Copyright by Verlag Chemie...

The [S2N]+ cation is an important reagent in S-N chemistry,63 especially in thermally allowed cycloaddition reactions with organic nitriles and alkynes, which give quantitative yields of heterocyclic cations (Scheme 3). It is conveniently prepared by reaction of S3N2C12 with AsF5 and S8 in liquid S02.63b The [SNS]+ cation is linear with S-N bond distances in the range indicating a bond order of two, i.e., S=N+=S. 

The 14 re-electron [S Ns]"1" cation is formed by the reaction of S4N4 with the [SN]+ cation.42 The planar, 10-membered ring usually has an azulene shape (19), with alternating sulfur and nitrogen atoms. Electrochemical reduction of S5N5+ salts in acetonitrile produces the polymer (SN)X. 

A systematic route into non-fused derivatives appears to be from the reactivity of [S4][AsF6]2 and [Sg][AsF6]2 with alkynes.87 The equi-molar mixture of S42+ and Sg2+ appears to act as if it were S3+ although there is little evidence of this species in solution itself. The reactivity of this hypothetical S3+ radical appears to mimic that of the closed-shell SNS+ cation but with an additional electron in a ji orbital. Using this method Passmore has isolated 7 (R=CF3, R=C02Me). 

Figure 4 shows a sequence of cyclic voltammograms recorded in a CO saturated solution of 0.5 M H.SO, which contained 10-5 M SnCl,. These voltammograms were recorded by increasing the upper limit of the potential during successive cycles. The major feature is the CO oxidation peak at 0.6 V(SCE) that is observed in the later scans. For cycles with an upper limit below this potential, there is a second, smaller oxidation feature at about 0.4 V. Control experiments using an SnCl /H.SO solution without CO show that this feature can be assigned to the oxidation of adsorbed Sn atoms. We note that the Sn oxidation step does not produce a well-resolved current maximum in the curves in Figure 4. We interpret this to indicate that adsorbed CO molecules are rapidly oxidized by newly generated Sn cations, thus regenerating the Sn adatoms and allowing further oxidation current to flow.

It was shown that modification of the electrode surface by Ni +, Co +, Cd +, Ge +, and Sn + cations (adatoms) enhances the catalytic activity and there are changes in the selectivity with respect to ammonium ions and hydroxylamine. 

The optimized sodium cation positions in a six-ring of FAU zeolite structure containing two A1 atoms in para-position (denoted as Na-Al-2p) ° is shown in Figure 1. This position of the cation is representative for Sn cation position in Y and X zeolites," as well as the position of Na in Na-EMT zeolite. As expected, for this and the other zeolite model structures, Na" prefers positions near to oxygen centers bonded to A1 atoms rather than those of Si-O-Si bridges. Also, tbe cation is far from oxygen centers which are connected to compensating cations, an additional proton in this case. 

The SNS+ cation is a linear species isoelectronic with CS2. The S-N bond distances are 146-147pm. The NS2+ cation exhibits a very narrow " N NMR resonance at —91 ppm (y /2= 8Hz) in SO2 and this technique is useful for monitoring reactions of the cation. ... 

Finally, we mention studies of the rutile SnO2(110) surface [145,164-166]. Despite the absence of partially filled d orbitals on Sn cations, the surface characteristics of Sn02 are qualitatively similar to those of Ti02- The same is true for the non-stoichiometric (1 x 1) and (1 X 2) surfaces, which present a distribution of defect states in the gap [166]. The authors, however, argue that some quantitative differences with respect to Ti02 take place, which are due to the much larger polarisability of the Tin atoms, compared to the Titaniums. 

Fig. 7. Ball model illustrations of (a) the ideal, stoichiometric surface of Sn02 (110), (b) the surface missing all bridging oxygen anions and (c) the surface with in-plane oxygen vacancies. The small solid circles represent Sn cations while the large open circles represent O anions. V.A. Gercher, D.F. Cox, and J.-M. Themlin, Surface Science, v. 306 (1994). Reproduced by permission of Elsevier Publications.

Fig. 8. Surface structures for SnO2(110). Large open circles are O small filled circles are Sn. (a) Stoichiometric 1x1 reconstruction with rows of bridging oxygen ions. All the surface Sn cations are in the +4 oxidation state, (b) Bare 1x1 reconstruction in which all the bridging oxygen ions are removed to leave both 4- and 5-coordmate surface Sn cations. To maintain electrostatic neutrality half the surface Sn cations are reduced to the +2 state, (c) One possible model for a (1x2) reconstruction with alternately missing rows of bridging oxygen.

Quantitative indications on the strength of Sn cations were obtained by Pickert et al., who calculated the electrostatic field along the three-fold cubic axis in the zeolite cavity near a surface cation at Sn for a particular fully ionic model at a Y zeolite with Si/Al = 2. Further calculations were later made by E. Dempsey ... 

Capobianco C. J., Dr e M. J., and DeAro J. A. (1999) Siderophile geochemistry of Ga, Ge and Sn cationic oxidation states in silicate melts and the effect of composition in iron-nickel alloys. Geochim. Cosmochim. Acta 63, 2667-2677. 

A fascinating recent development in imidotin-cluster chemistry involves the isolation of a series of double cubanes, which contain an Sn7(tt3-NR)8 core. Wright and coworkers have demonstrated that when pyridinyl or pyrimidinyl groups are present on the imido nitrogen centers, the unusual double-cubane clusters 55-60 are obtained (Scheme 2.2.11), rather than the [Sn()a3-NR)]4 cubanes. These clusters are comprised of two interlocked [Sn( a3-NR)]4 cubanes, which share one tin vertex. The central tin center is formally in the +4 oxidation state, so that these double cubanes may be viewed as involving the coordination of two [Sn3()a3-NR)4] anions, such as those present in the clusters 53 and 54, to a central Sn+" cation. The presence of both Sn(II) and Sn(IV) centers was verified by Sn NMR spectroscopy. The deposition of tin metal was observed during the syntheses of 55-60, suggesting that... 

When metals are incorporated on chlorided AI2O3-G catalyst both acid and metal sites are available for the reaction. Thus, in addition to dehydration, dehydrogenation product acetone was also formed with Pt/A Os-H catalyst. Sn/AbOa-I has also been found active for dehydration of 2-propanol to propylene which could be due to the presence of Sn cations acting as Lewis acid sites as tin is practically unreduced when added to alumina in... 

The detection of transferred hyperfine interaction at diamagnetic Sn cations in oxides of the garnet type (see Chapter 14) prompted a study of isoelectronic Sb + in magnetic oxides of the phase Nii+jxFei 3 Sb,04 [28]. These are spinel oxides with antimony at the octahedral B sites and Fe and Ni distributed on both the tetrahedral A sites and the B sites. The preliminary data show considerable magnetic interactions at the Sb sites, but... 

It is clear that some of the Sn cations in the B-site Sn04 groups are reduced but no one has determined the extent of such reduction. It is apparent that only a small fraction of such groups are affected. Otherwise the lattice structure would not be maintained. Note that a significant difference in ionic radius occurs when stannic tin is reduced to stannous tin. X-ray analj is shows no difference between the air-fired and the reduced phosphors. K. Th. Wilke studied this phenomenon in 1957 and proposed the following mechanism, given as 3.1.90. on the next page. 

However, the re-fired phosphor presents another problem. When the reduction step takes place, we have the formation of the divalent cation, Sn, which prefers a tetrahedral environment in the lattice. But, the Sn cation resides on an octahedral site. Furthermore, it is likely that oxygen vacancies are created via ... 

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