L-phenylalaninium maleate

In the title compound, C9H12NO2+.C4H3O4-, the amino acid molecule exists in the cationic form and the maleic acid molecule in the mono-ionized state. In the semi-maleate anion, a nearly symmetric intramolecular O-H . . .O hydrogen bond is observed. The aggregation pattern observed in the title crystal has striking similarities with those observed in L-phenylalanine L-phenylalaninium formate and L-phenylalanine L-phenylalaninium perchlorate.