STRUCTURES OF CHARGE-PERTURBED MOLECULES .47. DISODIUM AND DIPOTASSIUM NITRANILATES - THE CYANINE DISTORTION OF THE 6-MEMBERED CARBON RING

Crystals of lemon yellow dipotassium nitranilate and of yellow disodiu m nitranilate dihydrate have been grown and their structures determine d at 290 and 200 K. The six-membered, O2N-disubstituted rings show a p ronounced cyanine distortion with all four CO bonds identical and the two (OCC(NO2)CO)(circle minus) chains connected by single CC bonds of each 156 pm length. In the anhydrous K-circle plus salt, the ring is p lanar, but in the Na-circle plus hydrate salt it exhibits a twist conf ormation. Quantum chemical calculations allow to reproduce the structu re in every detail, demonstrate strong charge alternation along the cy anine chains with considerable delocalization into the O2N acceptor su bstituents, and suggest that the rather long connecting CC bonds conta in positively charged carbon centers on both ends. In addition, metal ion coordination effects as well as the rather high pK(a) value of nit ranilic acid are rationalized.