In Concise Inorganic Chemistry by JD Lee (4th edition; adapted by Sudarshan Guha), page 76 under the topic "Back Bonding" it is given:

For $\ce{SCl2}$ the bond angle is 102° since the lone pair of $\ce{S}$ or $\ce{Cl}$ atoms need not be delocalised due to the availability of vacant d orbitals of their own.

Kindly note, the delocalisation the author is talking about is the delocalisation of electrons in back bonding.

I am unable to understand why back bonding doesn't take place even though the conditions are satisfied. Is it because of the availability of empty orbitals in both the atoms involved, the π-electrons are confused to which atom they must bond to, to form back bonding? Is it right to say that back bonding doesn't take place when the electron-donating atom itself has empty orbitals?

Kindly explain the above-mentioned statement and tell me whether my reasoning is correct or not.

  • 4
    $\begingroup$ The author is using an outdated concept of d orbital participation. It requires all sorts of somersaults like the one you just found. Forget it. Neither sulphur nor chlorine nor any main group element use their d orbitals in any noteworthy way, shape or form and that is why there can be no back bonding in $\ce{SCl2}$. $\endgroup$ – Jan Aug 24 '19 at 17:44
  • $\begingroup$ Maybe this could help. The extent of back-bonding follows the order, $\ce{2p\pi-2p\pi > 3p\pi-3p\pi > 4p\pi-4p\pi}$ due to large distance of higher orbitals from nucleus. $\endgroup$ – Rahul Verma Aug 25 '19 at 3:10
  • $\begingroup$ @Jan, I understand that. But we are supposed to learn this for an exam. Could you please give me some kind of temporary explanation for understanding this concept? $\endgroup$ – Guru Vishnu Sep 26 '19 at 6:46
  • $\begingroup$ @Intellex I can’t because I refuse to do these somersaults. $\endgroup$ – Jan Sep 30 '19 at 13:33
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    $\begingroup$ I already said that there is no back-bonding, I really cannot say much more. The d orbitals are not accessible, hence there are no empty orbitals to form a back-bonding interaction. Your book is wrong. I also know that it is a very common resource for many people, but unfortunately it contains some old, outdated, and disproved concepts. $\endgroup$ – Martin - マーチン Nov 2 '19 at 12:45

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