Study of the structure of (carbamimidoylsulfanyl)acetic (“pseudothiohydantoic”) acid by XRD and PM6 methods

It was shown by the method of powder X-ray diffraction analysis that in the crystalline state the product of the reaction of thiourea with chloroacetic acid in water, (carbamimidoylsulfanyl)acetic acid, existed in the zwitter-ion tautomeric form. The structure consists of virtually planar infi nite layers normal to the c axis of the unit cell which are bound by van der Waals interactions. The layers are formed by infi nite rows elongated along the b axis of the unit cell consisting of materially planar zwitter-ionic molecules linked by strong bifurcated hydrogen bonds. The results of quantum-chemical calculations by PM6 method are in agreement with the XRD results: whereas an isolated molecule exists in nonzwitter-ionic tautomeric form, in the crystal only the zwitterionic tautomer is present.