Crystal structure of histamine diphosphate monohydrate

Abstract

The crystal structure of histamine diphosphate monohydrate has been established by two independent investigations, one with Mo-K_α and the other with Cu-K_α scintillation counter data. The unit cell is monoclinic, space group P2₁/c, Z= 4, with dimensions (mean of the two), a= 7·98, b= 13·18, c= 13·17 Å, and β= 111·1°. In each case the structure was solved from Patterson and electron-density maps, and refined by least-squares methods to R 0·072 (for 1554 reflexions; Mo radiation) and 0·044 (for 2104 reflexions; Cu radiation). There are no significant differences between the results of the two investigations. The atoms of the histamine cation lie in two almost perpendicular planes, the plane of the imidazole ring and that of the side chain. The bond lengths and angles are similar to the corresponding values in histidine hydrochloride monohydrate. The dimensions of the two PO₂(OH)₂^– ions are P–O 1·51 Å, P–OH 1·57 Å, O–P–O 115·5°, HO–P–OH 107·0°. The most important feature of the packing is a complex system of O–H ⋯ O and N–H⋯O hydrogen bonds.