I will keep it brief; if I generalize what an assignment is telling me, then a metal complex with 2 (iso)thiocyanate ligands would be named "bis(isothiocyanate)...metal(oxidation state) or bis(thiocyanate)...metal(oxidation state). From what I can tell (1) (2), (iso)thiocyanate ligands are exclusively monodentate... so why do they get the bis-tris-tetrakis-etc. prefix? I thought that those were reserved for polydentate ligands (3) or ligands already containing one or more di-tri-tetra-etc. prefixes. Thanks!


1 Answer 1


The answer to your title question is: Yes, they are monodentate.

But I think you have a misconception about when to use which type of counting: It does not depend on whether the ligand is polydentate or not.

The IUPAC guide states that you use the bis-tris-tetrakis-etc. prefix when you want to avoid confusion:

The prefixes are ‘di’, ‘tri’, ‘tetra’,etc., for use withnames for simple entities, or ‘bis( )’, ‘tris( )’, ‘tetrakis( )’,etc., for names for most entities which themselves contain multiplicative prefixes or locants. Care must also be taken in situations when use of a simple multiplicative prefix may be misinterpreted, e.g., tris(iodide) must be used for $\ce{3I−}$ rather than triiodide (which is used for $\ce{I3^−}$), and bis(phosphate) rather than diphosphate (which is used for $\ce{P2O7^{4−}}$).

Source: https://iupac.org/cms/wp-content/uploads/2018/05/Inorganic-Brief-Guide-V1-3.pdf

So while in the case of thiocyanates and isothiocyanates I don't see that there is any confusion avoided by using bis( ), it is certainly not wrong.


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