Mnemonics help to by-heart things which are difficult to do so and which are important. I found mnemonics for studying the periodic table, electromagnetic series etc which were of great help. So, is there a mnemonic to study the spectrochemical series since knowing it will be of great help to find the geometry of a given co-ordination compound?

The spectrochemical series is a list of common ligands for transition metals in order of increasing ligand-field splitting parameter $\Delta$, which is the energy difference between the sets of $\ce{d}$ orbitals:

$$\ce{I-} < \ce{Br-} < \ce{S^2-} < \ce{SCN-} < \ce{Cl-} < \ce{NO3-} < \ce{N3-} < \ce{F-} < \ce{OH-} < \ce{H2O} \approx \ce{C2O4^2-} \text{ (oxalate)} < \ce{NCS-} < \ce{CH3CN} < \ce{py}\text{ (pyridine)} < \ce{NH3} < \ce{en}\text{ (ethylenediamine)} < \ce{bpy}\text{ (2,2'-bipydiridyl)} < \ce{phen}\text{ (1,10-phenanthroline)} < \ce{NO2-} < \ce{PPh3} < \ce{CN-} \approx \ce{CO}$$

Is there a mnemonic device for remembering this series?

  • 1
    $\begingroup$ I editing this question to make it clearer what the you were asking about. The spectrochemical series may not be familiar to everyone. $\endgroup$
    – Ben Norris
    Oct 5, 2013 at 14:33
  • $\begingroup$ I don't think you're required to memorize this series, and I don't think there's an easy mnemonic… $\endgroup$
    – F'x
    Oct 8, 2013 at 14:24

3 Answers 3


I would not recommend a mnemonic for the spectrochemical series for a number of reasons:

  1. Often, it depends on both metal and ligand and coordination geometry how big a certain splitting is.

  2. The splitting of some ligands ($\ce{NH3, H2O}$) is even dependent on the pH — even though that could sort-of be overcome by including their corresponding anions in the list.

  3. Any mnemonic is bound to be incomplete. N-heterocyclic carbenes (NHCs) are very important ligands especially in organometallic chemistry, but they aren’t on your list.

  4. Some ligands (e.g. $\ce{NO}$) can display very complex redox chemistry that defies them being ordered in a simple list.

  5. Rather than learning some list off by heart and rote memorising it later, it is much better to know why a ligand is strong- or weak-field and to deduce that property from the ligand’s structure.

The last point is most important. Rather than learning or attempting to remember that chloride is a weak-field ligand, ask yourself why. It is a π donor ligand that will split the $\mathrm{t_{2g}}$ orbitals of the central metal in a bonding–antibonding way, lifting the metal’s $\mathrm{t_{2g}}$ orbitals and lowering the energy difference. That way, I immediately know what to expect of (say) selenide $\ce{Se^2-}$ even if it is not present in the list. The strength of a certain ligand in this discussion is equivalent to the usual trends in the periodic table. Quickly memorised, no long mnemonic and applicable even to new ligands.


The following mnemonic could be used to remember the spectrochemical series:

I brought some colourful sweets from office containing water. Nisha ate nine in canteen corridor

$\ce{I- < Br- < SCN- < Cl- < S^{2-} < F- < OH- < C2O4^{2-} < H2O < NCS- < edta^{4-} < NH3 < en < CN- < CO}$

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    $\begingroup$ While this mnemonic is slightly better than the other answer it still is not a full English sentence that would make sense to me. $\endgroup$
    – Jan
    May 3, 2019 at 6:18

I use the following to remember the spectrochemical series;

I brought some cloth, nylon net from office, collect water near cyanomethane place, among each big pants, place no proper concentration or concern.

($\ce{I, Br, S, Cl, NO_3, N_2, F, OH, CrO_2, H_2O, CH_3CN, py, NH_3, en, bpy, phen, NO_2, PPh3, CN, CO}$ respectively.)

  • $\begingroup$ Wait wait wait. How do you distinguish between CN and CO? $\endgroup$
    – EJC
    Feb 8, 2016 at 10:43
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    $\begingroup$ This mnemonic doesn’t make sence to me because most of the word lists aren’t English sentences … $\endgroup$
    – Jan
    Feb 9, 2016 at 10:33
  • 4
    $\begingroup$ This mnemonic is actually just a collection of words that make next to no sense when put together. It doesn't help much either. How is it possible to say that Collect corresponds to CrO2? $\endgroup$
    – ShankRam
    Feb 9, 2016 at 14:01
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    $\begingroup$ Is there any mnemonic to remember this mnemonic? $\endgroup$
    – user5764
    Feb 28, 2016 at 11:57

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