# Why are d orbitals used in the hybridisation of PCl5 and similar compounds? [duplicate]

Phosphorus uses its $\ce{3s}$, three $\ce{3p}$ and one $\ce{3d}$ orbitals for its hybridization in $\ce{PCl5}$ and similar compounds.

However, shouldn't it use its $\ce{4s}$ rather than $\ce{3d}$ orbitals as the former is of lower energy?

I initially thought that this was not the case because hybridization cannot take place between orbitals of different principal quantum numbers, but then learnt that this indeed was possible, for example in coordination compounds with $\ce{dsp^2}$ hybridization such as $\ce{[Pt(NH3)2Cl2]}$.

• The use of d-orbitals in hybridisation schemes has often be disproved, they do not play a significant role. The bonding is better described by multi-centre bonds. Unfortunately it is very often still taught, even though it is wrong. Sep 18 '17 at 8:08
• Regarding hybridisation in coordination compounds: chemistry.stackexchange.com/q/76726/16683 Sep 18 '17 at 10:37
• Regarding main group compounds, see e.g. J. Am. Chem. Soc. 1990, 112 (4), 1434–1445 Sep 18 '17 at 10:39
• chemistry.stackexchange.com/questions/18427/… Sep 18 '17 at 14:07
• I linked that one as a duplicate because it shows the currently accepted theory.
– Jan
Sep 18 '17 at 16:04