Bis(adamantan-1-aminium) hydrogen phosphate fumaric acid sesquisolvate.

The asymmetric unit of the title compound, 2C(10)H(18)N(+)·HPO(4) (2-)·1.5C(4)H(4)O(4), contains two adamantan-1-aminium cations, one hydrogen phosphate anion, and one and a half mol-ecules of fumaric acid, one of which exhibits crystallographic inversion symmetry. Each HPO(4) (2-) anion is hydrogen bonded, via all of its O atoms, to four NH(3) (+) groups of the adamantan-1-aminium cations, forming chains along [100]. These chains are, in turn, inter-connected via a set of O-H⋯O hydrogen bonds involving the fumaric acid solvent mol-ecules, forming layers parallel to (001). Weak C-H⋯O inter-actions lead to a consolidation of the three-dimensional set-up.