# Do metal ions of 4d and 5d series always form low spin complex?

I've recently come across a source where it stated that all 4d and 5d metals form low spin complexes irrespective of the strength of ligand.

I'm not sure of the authenticity of the source and couldn't figure out the reason for this phenomenon, thereby enquiring about it.

I feel that the splitting energy is higher than pairing energy in this case, but I am not able to justify it properly.

• Please add the source – Avnish Kabaj Apr 21 '18 at 13:26
• I'm not able to recall the exact source, but I do remember reading the exact statement. – Ritwik Das Apr 21 '18 at 13:29
• I've been taught the same fact, and am interested in an answer to this question. Sadly, I wasn't able to verify the fact from both JD Lee and VK Jaiswaal inorganic :( – Gaurang Tandon Apr 21 '18 at 13:41
• @GaurangTandon Even I searched all my books and was unable to find anything regarding this concept. – Ritwik Das Apr 21 '18 at 13:45
• Related: Why is [PdCl4]2- square planar whereas [NiCl4]2- is tetrahedral? (read the answer) – orthocresol Apr 21 '18 at 14:23

While the vast majority of the compounds and complexes of the heavier transition metals are low spin (where that concept has any meaning) $$\ce{PdF2}$$ is one exception, which is unusual not only this way but also having $$\ce{Pd^2+}$$ in an octahedral environment (see e.g. Wikipedia). Thus your source is not quite correct.