Back bond figure

Structures have been determined for a number of these compounds, showing that the Rh-P bonds are little affected by the m-ligands (Figure 2.22). The shorter Rh-C distance in the thiocarbonyl is probably a result of greater Rh=C back-bonding. Addition of S02 results in the formation of a 5-coordinate (sp) adduct with the expected lengthening in all bonds. 

Figure 6-13. Synergic back-bonding in a platinum alkene complex. In (a), the interaction of a (filled) platinum 5d orbital with the tf molecular orbital of the alkene is shown, whilst in (b), the interaction of a dsp hybrid orbital with the n molecular orbital of the alkene is shown. Note that the two interactions result in electron density moving in opposite directions.

Figure 2 Directionality parameters describing the E-XY interaction (a and b) for phosphine-chalcogenide donors in the case of a one a-bond, and three n back-bonds description of the P-E bond (c). For an alternative description of the P-E bond (see Chapter 5)...

Particularly interesting are the homoleptic complexes 46 to 49 (Figure 2.3-7) in which Ni or Pt atoms are tetrahedrally coordinated by four Ga-R or In-R ligands [71, 72]. These compounds are analogues of Ni(CO)4. They have relatively short M-Ga or M-In bond lengths, and quantum-chemical calculations verify an effective 71-back bonding of electron density from the transition metal atom into the empty p-orbitals of the E-R groups. 

FIGURE 5. View of the P=C bond as a o bond and a n bond formed by back-bonding into an antibonding orbital of e symmetry on the phosphine moiety... 

Figure 19 The back-bonding from a filled metal d orbital to an empty phosphorus 3d orbital in the PX3 ligand taking the internuclear axis as the z axis. An exactly similar overlap occurs in the yz plane using the dyl orbitals...

Fibroin, the fibrous protein found in silk, has a secondary structure called a beta- (/8-) pleated sheet, in which a polypeptide chain doubles back on itself after a hairpin bend. The two sections of the chain on either side of the bend line up in a parallel arrangement held together by hydrogen bonds (Figure 24.8). Although not as common as the a-helix, small pleated-sheet regions are often found in proteins. 

Figure 2-30. Competing polarisation and back-bonding effects control the acidity of a pyrazinium cation co-ordinated to ruthenium(ii)...

Figure 5-47. The condensation of diacetyl with methylamine in the presence of iron(n) yields the iron(n) complex of the conjugated diimine. In the absence of metal ion, little of the imine is obtained. A number of factors are of importance in this reaction, including the strong back-bonding between the 7t-acceptor diimine and the low-spin d6 metal centre.

---