InterviewSolution
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InterviewSolution
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Suggest reasons why the B–F bond lengths in BF3 (130 pm) and BF4– − (143 pm) differ. |
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Answer» The B–F bond length in BF3 is shorter than the B–F bond length in BF4– . BF3 is an electron deficient species. With a vacant p-orbital on boron, the fluorine and boron atoms undergo pn–pn back-bonding to remove this deficiency. This imparts a double bond character to the B–F bond. This double-bond character causes the bond length to shorten in BF3 (130 pm). However, when BF3 coordinates with the fluoride ion, a change in hybridization from sp2 (in BF3) to sp3 (in BF4–) occurs. Boron now forms 4σ bonds and the double-bond character is lost. This accounts for a B–F bond length of 143 pm in BF4– ion. |
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