Trans-bent geometry

What is the nature of the multiple metal-metal bonds Let us consider the specific example of HW WH, whose NBO Lewis structure exhibits five metal-metal bonds. Figure 4.24 displays the strongly trans-bent geometry of HW=WH and contour diagrams of the five metal-metal bond NBOs, each drawn in a chosen contour plane (specified in the lower-left-hand corner of the panel) to emphasize its distinguishing characteristics. 

Reduction of the distannynes with sodium or potassium gives the radical anions. [Ar Sn=SnAr ] has the trans-bent geometry given in Table 11, and shows an ESR spectrum with g= 2.0691, (ll7Sn) 0.83 mT and (117Sn) = 0.85 mT, indicating a very low unpaired spin density on tin. The main line is about 0.6mT wide, and no proton coupling is resolved. 

Another way to rationalize the trans-bent geometries is through an-a mixing model (28,95,145), using the second-order Jahn-Teller effect as... 

C. R. Landis, andF. Weinhold, Origin of Trans-Bent Geometries in Maximally Bonded Transition Metal and Main Group Molecules, J. Am. Chem. Soc. 128, 7335-7345 (2006). 

The first stable compound containing an Sb=Sb donble bond was only reported in 1998 with (Tbt)Sb=Sb(Tbt) (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl) (9). The molecule was prepared in high yield as deep green crystals. The molecule has a trans-bent geometry. 

Figure 22 Geometry of alkene and alkene analogs (a) planar geometry, angle between CH2 plane and C-C bond =0° (b) trans-bent geometry, angle between ER2 plane and E-E bond > 0°...

Figure 26 Resonance forms for E-E bonds in [REER] " (E = group 13, n = 2 E = group 14, n = 0) (a) bond order 3 one a bond, two tt bonds linear geometry (b) bond order 2 one a, one 7T bond, one lone pair trans-bent geometry (c) bond order 1 one a bond, two lone pairs strongly trans-bent geometry...

The most informative data should be its Si NMR data for the central triply bonded Si atoms. The resonance of sp-hybridyzed Si atom in RsiSi SiRsi is observed at 89.9 ppm and is shifted upheld compared with those of the silyl-substituted disilenes (ca. 142-155 ppm).Similar up-field shift is observed in the NMR chemical shifts of the silyl-substituted alkenes (ca. 188-197 ppm) and alkynes (112-114ppm). The molecular stracture of the RsiSi=SiRsi was revealed by X-ray crystallographic analysis (Figure 18). ft has a trans-bent geometry [Si-Si-Si(Rsi)... 

At the MP4(SDTQ)/6-311 G //MP2/6-31 G + ZPE level of theory, HeBCH Is predicted to be unstable toward helium dissociation by -6.0 kcal/mol [4], Calculated at the MP2/6-31G(d,p) level, HeBCH He + HCB ( A, 2tc) is -5.7 kcal/mol [11]. HeBCH is clearly a minimum on the 6-31G and MP2/6-31G potential energy surfaces however, while the predicted structure of HeBCH at the SCF level is linear, inclusion of correlation energy at MP2 predicts a trans bent geometry [4]. 

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