What is the structure of hydrated beryllium chloride [closed]








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Is there water of crystallization or does water act as ligand? Also Be2+ is smaller than Li 2+ then why Li2+ has only 2 water molecules as ligands




As others have already mentioned it's more of a $\ce{[Be(H2O)4]Cl2}$ if you want to write it like this. It becomes much more visible if we move to the solid state structure. I'm adding a picture of the unit cell of $\ce{BeCl2 x 2 H2O}$ here as well. From this you can see that each beryllium cation is tetrahedrally surrounded by four water molecules. And that's pretty much it. This 'unit' has some chloride around it but there is no direct contact between the beryllium and the chloride.


Calcium is another famous candidate for this behaviour. For $\ce{CaCl2}$ hydrates we have, if I remember correctly trigonal prisms of calcium that are surrounded by water. Those prisms stack along their triangular faces. The chloride anions are always only in the second coordination sphere.


Now imagine you add a little heat to this. You already have your oxides close to cations that from really stable bonds with oxygen. Instead of water leaving it will destabilize the $\ce{O-H}$ bond in $\ce{H2O}$ and release $\ce{HCl}$ rather than $\ce{H2O}$. That's how those basic chlorides and related compounds form and the reason why you cannot make their anhydrous form from heat directly.


For your comparison with $\ce{LiCl}$ (hydrated). Lithium is $\ce{Li^+}$ while beryllium is $\ce{Be^2+}$. This by HSAB theory there will be a much stronger and shorter bond between beryllium and oxygen than for beryllium and chloride while for lithium this is much weaker. At this point we have to take the covalency into consideration as well but for pure comparison I rather keep it ionic.


If we compare the distances for both compounds we get *d*( $\ce{Li-Cl}$) = 264 pm and *d*( $\ce{Li-O}$) = 204 pm which means we can consider a $\ce{Li-Cl}$ bond here (that gives us an octahedron of the composition $\ce{[Li(H2O)2Cl4]^3-}$). For the beryllium compound we get *d*( $\ce{Be-O}$) = 160 pm and *d*( $\ce{Be...O}$) = 378 pm.


[![Unit cell of  <span class=](https://i.stack.imgur.com/XSxsv.png)$\ce{BeCl2 x 2 H2O}$" />](https://i.stack.imgur.com/XSxsv.png)


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