Distannenes structure

Similar to the Ge2H4, in Sn2H4 the four main structures are true minima while planar distannene is a saddle point. 

FIGURE 15. Molecular structure of the dipotassium salt of dianionic distannene 72b... 

The other four known distannenes all adopt a novel zwitterionic structure with a single dative bond, i.e. one stannylene fragment serves as electron-pair donor (Lewis base), the other as acceptor (Lewis acid) R2Sn —> SnR, hence they are not distannenes within a stricter definition. 

FIGURE 18. Molecular structure of zwitterionic distannene 81. Intramolecular N - Sn interactions are depicted as open lines (=)... 

The structure of 20 was determined by X-ray analysis, which showed an almost planar environment around the Sn=Sn double bond. All the previously reported distannenes have a trans-bent configuration around the Sn=Sn double bond34-38. The Sn=Sn double bond... 

The crystal structure of 21 was finally confirmed by X-ray analysis, which showed an unexpectedly short Sn=Sn double bond length of 2.68 A (Figure 6). This bond length is the shortest among all distannenes reported thus far (2.77-2.91 A)34-38, although it is longer than that in 20 (2.59 A). Another important feature of the allene 21 is a bent, rather... 

FIGURE 16. Molecular structure of distannene 73 in the crystal. Projection along the Sn=Sn bond illustrating the large twist angle r = 62.7°... 

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