inorganic chemistry - Structure of Borax

The structure of Borax has really baffled me. Its formula is $\ce{Na2B4O7.10H2O}$ and it is formulated as $\ce{Na2[B4O5(OH)4].8H2O}$.
2 structures of Borax given on the internet are

Can anybody explain that why the formulas mentioned on different websites are different.Something is strange about this compound because even Wikipedia does not give the structure.

It only says

there are two four-coordinate boron atoms (two $\ce{BO4}$ tetrahedra) and two three-coordinate boron atoms (two $\ce{BO3}$ triangles).

Answer

Greenwood and Earnshaw's Chemistry of the Elements, 2nd ed. (p 206) writes that the structures of the borates are rather complicated:

It is clear [...] that, without structural data, the stoichiometry of these borate minerals gives little indication of their constitution.

As such, for example, $\ce{KB5O8.4H2O}$ is more properly formulated as $\ce{K[B5O6(OH)4].2H2O}$. You've also noticed that borax, $\ce{Na2B4O7.10H2O}$ is more properly formulated as $\ce{Na2[B4O5(OH)4].8H2O}$. This means that the structure of borax does not simply consist of $\ce{Na+}$ ions and $\ce{B4O7^2-}$ anions with waters of crystallisation.

Therefore I would guess that both structures are, more likely than not, incomplete.

A further illustration is afforded by borax which is normally formulated $\ce{Na2B4O7.10H2O}$, but which contains tetranuclear units $\ce{B4O5(OH)4]^2-}$ formed by fusing 2 $\ce{B3O3}$ rings which each contain 2 $\ce{BO4}$ (shared) and 1 $\ce{BO3}$ unit; borax should therefore be written as $\ce{Na2[B4O5(OH)4] .8H2O}$.

(grey - boron; white - oxygen; black - hydrogen).