Hydrogen bonding and thermal vibrations in crystalline phosphate salts of histidine and imidazole

Salts of composition Im.H3PO4 and L-His.2H3PO4 were prepared and analyzed by X-ray crystallography. The Im salt forms a rather complicated crystal structure with two chemical formula units in the crystal chemical unit and the crystals of the His salt contain unionized molecular H3PO4. There are networks of short strong hydrogen bonds in both crystals, and the hydrogen bonding noticeably affects the O-atom thermal vibrations. The hydrogenbonding geometries indicate that N-H...O-P and P-O-H...O-P bonds are generally the strongest N-H...O and O-H...O bonds that can form in biochemical systems, and the strong hydrogen bonding significantly affects the P-O bond strengths. Crystal data: L-histidinium dihydrogen orthophosphate 10N302 .H2PO4 .Ha PO4,