# Are high spin complexes and spin free complexes the same thing?

While solving some Coordination Compounds problems, I came across a problem that asked

Select which complex is high spin or spin free octahedral complex.

The term 'spin free' sounds like a complex with no unpaired electrons and I know high spin complexes are those which have unpaired electrons. But the question was was single correct and this got me confused.

Do the terms high spin and spin free bear the same meaning?

• The answers seem to show that, at least in the context of inorganic coordination chemistry, these terms are used synonymously. However, as you noted, in most other contexts, "spin-free" is generally taken to mean "free of spin" or "no spin dependence": see pubs.acs.org/doi/10.1021/j100842a004 and aip.scitation.org/doi/abs/10.1063/1.466508 Oct 27, 2021 at 17:46

Spin Free Complex means that the electrons are free to spin! High spin complexes are the ones with Weak Field Ligands which aren't able to pair up electrons of the central ion.

Hence the 2 terms are usually used synonymously. On the same lines Low Spin Complexes and Spin Paired Complexes are used synonymously!

• Is this a regional dialect? I do find sources where "spin-free" is used in this way, but at least in US-English, "X-free" would mean something that lacks, or is free of, "X", see guilt-free, fat-free, worry-free. Oct 27, 2021 at 15:16
• I am not really sure if it's taken from a dialect but that's what it's used for in chemistry. I 100% agree that is confusing, high spin complex is a much better word to use. Oct 27, 2021 at 17:35
• @Tyberius Asbestos free cereals Apr 15 at 13:44
• i dont think Spin Free Complex means that the electrons are free to spin, i think it means there are orbitals with spin momentum (since electrons cant technically spin) Apr 15 at 13:47

In a paper by the renowned chemist, F. Albert Cotton,

"Magnetic Investigations of Spin-free Cobaltous Complexes. III. On the Existence of Planar Complexes"

they investigate "spin-free" complexes which the authors defines as complexes with three unpaired electrons. Following this definition of spin-free complexes does not necessary imply high-spin, as in the case of some octahedral Cr(III) complexes, which have three unpaired electrons that can occupy the $$t_{2g}$$ energy level, making it low spin.

Side Note:

This definition of spin-free may be how Al. Cotton defined it for his paper; this is not a claim that it is representative of the entire group. Additionally, this paper is from the 1960s so contemporary definitions may differ.