Unusual Bonds and Coordination Geometries

Monica Moya-Cabrera, Vojtech Jancik and Raymundo Cea-Olivares Instituto de Qmmica, Universidad Nacional Autonoma de Mexico 

This chapter deals with structurally characterized tin(II) and tin(IV) compounds containing either unusual bonds to tin atoms or unique geometric arrangements around the tin center. While we emphasize molecular compounds, selected examples of supramolecular assemblies featuring unusual structural traits are also discussed. Strictly inorganic compounds will not be considered, as they are amply described elsewhere.  

Treatment of [SnCl HC(CMeNAr)2 ] with AlH3-NMc3 yielded the first monomeric and terminal tin (II) hydride [SnH HC(CMeNAr)2 ] (3). DFT calculations show that the electron density of the lone pair of electrons contributes to the Sn—H bond and further analyses exhibit a 70% participation of the 

Other examples of structures bearing Li—Sn bonds include the dimeric structures [LiSn(Si Bu2Me)3]2 (11) and [Li(thf)Sn(SiMe3)3]2 (12), as well as the tripodal triamido stannates Li(thf)3Sn HC[Me2SiN(p-tolyl)]3 (13) 2 nd Li(thf)3Sn HC[Me2SiN[(S )-l-(l-naphthyl)ethyl)]3 (14).13 

There is just one example of the Zintl anion [Sng] with a Cs—Sn interaction, K([2.2.2]crypt)]Cs7[Sn9]2-(en)3 (30). The crystal structure of 30 reveals an arrangement build from layers with composition (Cs7[Sn9]2) , which are separated by [K-([2.2.2]crypt]+ units. The Cs—Sn contacts are in the range of 3.84 to 4.18 A, which are comparable with those observed in the cesium benzyldihypersilylstannanide 31, 4.04 and 4.28 A.  

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Structural Characterization. The tridentate coordination geometry of di-terf-butyl tin pz, 62a, is evident in the crystal structure (Fig. 10). The Sn-N and S-S bond lengths are larger due to this unusual coordination... 

Numerous triosmium-platinum clusters have been prepared, many of them derived from Os3Pt(/i-H)2(CO)10(PR3) (1) (40,40a). Although, as discussed in Section III, the participation in cluster bonding of the tangential orbitals of nonconical PtL units may be difficult to predict a priori, the observed tetrahedral skeleton of 1 (40,40a) and nonplanar coordination geometry at the Pt atom suggest that the Pt atom should behave as an 18-electron center. The 58-CVE count therefore implies that the cluster is unsaturated, and this is consistent with EHMO studies (88,98) and the high chemical reactivity of 1. The crystal structures of la (40,40a) and the 58-CVE derivatives 21 (108) and 22 (118) all show unusually short Os(/ -H)Os distances [2.789(1),... 

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