There are heteropoly-acids and isopoly-acids, two classes of polynuclear compounds with and without heteroatoms within its molecular structures, respectively. These are the names widely used in the literature for a long time[1].

Why two non-homogeneous prefixes ("iso-" vs "hetero-") are used? Wouldn't it make more sense to denote these names with consistent prefixes showing parity ("hetero-" vs "homo-"; "aniso-" vs "iso")? For instance, IUPAC Red Book utilized the terms "homopolyatomic" vs "heteropolyatomic" in chapter IR-5 Compositional Nomenclature, and Overview of Names of Ions and Radicals [2, p. 68].

Wouldn't heteropoly-acid and homopoly-acids pair be morphologically more accurate, since it's a heteroatom presence that allows that distinction, just like in case of homocyclic vs heterocyclic or homopolyatomic vs heteropolyatomic species?


  1. Middleton, A. R. J. Chem. Educ. 1933, 10 (12), 726 DOI: 10.1021/ed010p726.
  2. IUPAC “Red Book” Nomenclature of Inorganic Chemistry; Connelly, N. G., Royal Society of Chemistry (Great Britain), International Union of Pure and Applied Chemistry, Eds.; IUPAC Recommendations; Royal Society of Chemistry Publishing/IUPAC: Cambridge, UK, 2005.

1 Answer 1


Wouldn't heteropoly-acid and homopoly-acids pair be morphologically more accurate (than heteropoly-acid and isopoly-acids)?

I completely agree with andselisk of this suggestion because the former makes more sense than latter in this regards. For instance, as correctly pointed out in the question, the IUPAC Red Book has utilized the terms "homopolyatomic" vs "heteropolyatomic" in the chapter, IR-5: Compositional Nomenclature, and Overview of Names of Ions and Radicals (p. 68-82, Ref.1). A few examples given for the homopolyatomic cations in the section IR- are $\ce{O2^+}$, $\ce{S4^2+}$, $\ce{Hg2^2+}$, and $\ce{Bi5^4+}$ (p.71). Likewise, few examples of heteropolyatomic cations are also given in the following section IR-, which are $\ce{NH4^+}$, $\ce{H3O^+}$, $\ce{PH4^+}$, and $\ce{SbF4^+}$ (p.71). Thus, it make perfect sense of using the terms "homopolyatomic" and "heteropolyatomic" in the context, since it's the presence of heteroatom in the latter case ($\ce{N, O, P,}$ and $\ce{Sb}$, respectively) that allows the distinction.

Nonetheless, in another chapter in Ref.1 (IR-8: Inorganic Acids and Derivatives, p. 124-141) has utilized the terms "homopolyoxy acids" and "heteropolyoxy acids" to described polyoxy acids:

Examples 1, 3–6 and 14 above demonstrate that homo- and heteropolyoxoacids and their partially dehydronated forms […] (p.136, ref.1)

For instance, the example 1 and 4 mentioned in the excerpt are $\ce{H2PO7^2-}$ and $\ce{H4[SiW_{12}O_{40}]}$, respectively (Section: IR-8.4, p. 135, Ref.1). As we all know that $\ce{H4PO7}$ is an example of isopoly-acids and $\ce{H4[SiW_{12}O_{40}]}$ (Ref.2) is an example of heteropoly-acids. Thus, even if these unconventional names are frequently use in inorganic chemistry literature to date, I think IUPAC is already recognized the necessity to keep consistency in the naming.


  1. Nomenclature of Inorganic Chemistry: IUPAC recommendations 2005 (Issued by the Division of Chemical Nomenclature and Structure Representation in collaboration with the Division of Inorganic Chemistry); Prepared for publication by N. G. Connelly, et al.; RSC Publishing (for the International Union of Pure and Applied Chemistry): Cambridge, United Kingdom, 2005 (ISBN: 0-85404-438-8).
  2. Li Min Yang, Zhi Kui Yin, and Li Qiang Wu, "$\ce{H4[SiW_{12}O_{40}]}$: An efficient catalyst for the synthesis of new spiro-[dibenzo[a,i]xanthene-14,3′-indoline]-2′,8,13-triones," Chinese Chemical Letters 2012, 23(3), 265-268 (DOI: https://doi.org/10.1016/j.cclet.2012.01.002).

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