Strukturen ladungsgestörter Moleküle, 47 [1 , 2 ] Dinatrium- und Dikalium-Nitranilate: Die Cyanin-Verzerrung der Kohlenstoff-Sechsringe / Structures of Charge-Perturbed Molecules 47 [1,2] Disodium and Dipotassium Nitranilates: The Cyanine Distortion of the Six-Membered Carbon Ring

Crystals of lemon yellow dipotassium nitranilate and of yellow disodium nitranilate di­hydrate have been grown and their structures determined at 290 and 200 K. The six-member- ed, O₂N-disubstituted rings show a pronounced cyanine distortion with all four CO bonds identical and the two (OCC(NO₂)CO)^⊖ chains connected by single CC bonds of each 156 pm length. In the anhydrous K^⊕ salt, the ring is planar, but in the Na^⊕ hydrate salt it exhibits a twist conformation. Quantum chemical calculations allow to reproduce the structure in every detail, demonstrate strong charge alternation along the cyanine chains with considerable delocalization into the O₂N acceptor substituents, and suggest that the rather long connecting CC bonds contain positively charged carbon centers on both ends. In addition, metal ion coordination effects as well as the rather high pK_a value of nitranilic acid are rationalized.