I came across a question in which the following reaction was taking place:
$$ \ce{Mg4C3 + H2O -> CH3CH \bond{#} CH} $$
Each $\ce{Mg}$ atom must be present in a +2 oxidation state, thus the total charge of the cation is +8. We thus have a $\ce{C3^{8-}}$ anion. The only structure of this $\ce{C3^{8-}}$ anion I could come up with was three carbons attached to each other in a linear fashion, with the terminal carbons each bearing a -3 charge and the central carbon bearing a -2 charge.
From this anion I would have assumed that the product formed upon hydrolysis is propane, but the product formed in the above reaction is propyne, just like when $\ce{Mg2C3}$ undergoes hydrolysis.
I'm guessing that the explanation for propyne being formed is the actual lattice structure of $\ce{Mg4C3}$, but I couldn't find any literature referencing this reaction or the structure of $\ce{Mg4C3}$.
The question is taken from:
- V.K. Jaiswal, s-block elements, Problems in Inorganic Chemistry, Thirteenth Edition, Page 331, question 36