Consider Table 11.12 above from Huheey, 4th Ed. Compare the Cr-P bond lengths in
ID: 495341 • Letter: C
Question
Consider Table 11.12 above from Huheey, 4th Ed. Compare the Cr-P bond lengths in the phosphine and the phosphine complexes. Compare the Cr-C (trans to P) bond lengths in the phosphine and the phosphine complexes. Compare the C-O (trans to P) in the phosphine and the phosphine complexes. Use and follow the handout "Compare, " to decide whether bonds are statistically significantly different or not. Rank the two phosphorous containing ligands in their ability to pi bond using your results. Explain the differences using pi-backbonding arguments. Why do we compare trans ligands?Explanation / Answer
As electron-withdrawing (electronegative) groups are placed on the phosphorous atom, the sigma-donating capacity of the phosphine ligand tends to decrease. At the same time, the energy of the pi-acceptor (sigma-*) on phosphorous is lowered in energy, providing an increase in backbonding ability. Thus phopholite are a better pi acceptor than phosphins. Now, greater the backbonding from metal to ligand, greater will be the bond order between Metal and ligand. Hence with phopspholite ligand, Cr-P bond is shorter.
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If the Cr-P bond order increases, Cr-C bond order will decrease which will lead to a increase in bond length
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If the Cr----> P back bonding increases, Cr----> CO backbonding will decrease. This will lead to increase in bond order in CO . As a result , CO bond length will increase.
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