This is the iron complex in question:


I'm pretty sure according to the nomenclature it should be: pentaaquahexachloroiron(III) but I wanted to check somewhere to be sure.


In coordination chemistry square brackets denote inner coordination sphere; $\ce{[H2O]5}$ makes little sense in this context. It looks like the correct molecular formula for this compound appears to be $\ce{[FeCl2(H2O)4]+[FeCl4]- * H2O}$ according to the crystal structure determined by Szymański [1].

The IUPAC-compliant name proposed by the author is tetraaqua-cis-dichloroiron(III) tetrachloroferrate(III) monohydrate.

Crystal structure of FeCl2(H2O)4]⁺[FeCl4]⁻·H2O

Figure 1. Asymmetric unit $\ce{[FeCl2(H2O)4]+[FeCl4]- * H2O}$ (ICSD-8198) with added hydrogen atoms. Color code: $\color{#EEEEEE}{\Large\bullet}~\ce{H}$; $\color{#FF0D0D}{\Large\bullet}~\ce{O}$; $\color{#1FF01F}{\Large\bullet}~\ce{Cl}$; $\color{#E06633}{\Large\bullet}~\ce{Fe}$.


  1. Szymański, J. T. The Crystal Structure of Tetraaqua-cis-Dichloroiron(III) Tetrachloroferrate(III) Monohydrate (Ferric Chloride $2\frac 1 2$-Hydrate). Acta Cryst. B 1979, B35 (9), 1958–1963. https://doi.org/10.1107/S0567740879008244.
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