T. N. Polynova

Crystal and molecular structure of ethylaminodimethylenephosphonic acid

An x-ray diffraction structural analysis was carried out on the complexing agent ethylaminodimethy!enephosphonic acid C2HsN(CH2PO3H2)2 using a Syntex P1 automatic diffractometer and %MoK~ radiation. The unit cell parameters were a = 8.711(2), b = 12.312(5), c = 8.763(8) ~, Z = 4, space group P212~21. The structure was solved by the direct method and refined by the method of least squares to R = 0.03. This complexing agent has zwitter-ionic structure. The phosphorus-oxygen distance in the phosphonic acid groups range from 1.491 to 1.557 ~ and the distance corresponding to the P----O distance (1.504 ~) hardly differs from those found for P-OH single bonds. The C--N--C bond angles are in the range from 112 ~ to 113 ~ , while the O--P--O bond angles range from 109 ~ to 116 ~ Intermolecular hydrogen bonds connect the acid molecules in strips along the z-axis. There are no intramolecular hydrogen bonds and, in contrast to carboxylic acid analogs, do not form internal H-rings.