My textbook writes hydronium ion as [H(H2O)]+, is this correct? [closed]

Question

[...] Thus, it bonds to the oxygen atom of a solvent water molecule to give trigonal pyramidal hydronium ion, $\ce{H3O^+}$ $\ce{\{[H (H2O)]^+\}}$ (see box). In this chapter we shall use $\ce{H^+(aq)}$ and $\ce{H3O+(aq)}$ interchangeably to mean the same i.e., a hydrated proton.

Isn’t this the way to write coordinate compounds? This may sound dumb but is the hydronium ion a complex compound?

The box that this passage refers to:

Hydronium and Hydroxyl Ions
Hydrogen ion by itself is a bare proton with very small size (~$\pu{{e-15} m}$ radius) and intense electric field, binds itself with the water molecule at one of the two available lone pairs on it giving $\ce{H3O+}$, This species has been detected in many compounds (e.g., $\ce{H3O+Cl-}$) in the solid state. In aqueous solution the hydronium ion is further hydrated to give species like $\ce{H5O2+}$, $\ce{H7O3+}$, $\ce{H9O4+}$. Similarly the hydroxyl ion is hydrated to give several ionic species like $\ce{H3O2-}$, $\ce{H5O3-}$, $\ce{H7O4-}$, etc.

Source Chemistry Part 1, Textbook for Class XI National Council of Educational Research and Training (https://ncert.nic.in), NCERT Publications (version: October 2019 Ashwina 1941) https://ncert.nic.in/textbook/pdf/kech107.pdf

Answer 1

In water solution context, it is recommended and preferred to use $\ce{H+(aq)}$, as products of proton interaction with water are complex and still subject of research. $\ce{[H(H2O)]+}$ would be better to write as $\ce{[H(H2O)_n]+}$, what is nothing else than $\ce{H+(aq)}$.

An isolated, solvated hydronium is also possible in other protic solvents, where water is a minor/trace component. Hydronium is also abundant molecular ion in an interstellar space.

Solid structures with hydronium are known, like hydronium perchlorate [$\ce{H3O+}$][$\ce{ClO4-}$]. The corresponding bisulfate compound, $[\ce{H3O^+}][\ce{HSO4^-}]$, requires chilling to solidify, but even when melted the saltlike association of $\ce{H3O^+}$ and $\ce{HSO4^-}$ ions increases the viscosity and decreases the ionic conductivity of equimolar sulfuric acid-water solutions.

See hydronium and oxonium for more.

Answer 2

$\ce{H3O+}$ does not exist in aqueous solution outside text books

Due to the strong hydrogen bonds the species is better described as a mixture of $\ce{H5O2+}$, $\ce{H19O9+}$ or maybe $\ce{H37O18+}$ (though I just made those up). The point is that there exists a network of regular water around this lone proton that arranges itself according to the electrostatic potential of this proton. This solvation effect has very concrete implications.

To me the $\ce{[H(H2O)]+}$ notation more strongly conveys this message. There is a free proton in there, transiently coordinated by the solvent, water. The same thing happens in other hydrated chalcogenids and halogens. $\ce{HF}$ is similarily coordinated in aqueous solutions - and this shielding contributes to the weak apparent acidity of $\ce{HF}$.