5-AMINO-3-IMINO-1,2,6,7-TETRACYANO-3H-PYRROLIZINE CHARACTERIZATION OFTHE SOLVENT-FREE SOLID-PHASE AND INTERACTION WITH AMMONIA AND WATER

The 5-amino-3-imino-1,2,6,7-tetracyano-3H-pyrrolizine (LH, C11H3N7), p reviously characterized as the 2:1 1-chloronaphthalene adduct, has bee n further investigated as a solvent-free solid phase. Strong intermole cular interactions take place in this phase, as revealed by the optica l spectra of evaporated LH thin films (lambda(max) = 615 and 570 nm) c ompared to the optical spectrum of LH in solution (lambda(max) = 580 n m). C-13 NMR spectra also support the occurrence of intermolecular att ractive CN group interactions in the solid state. X-Ray diffraction pa tterns indicate that the controlled sublimation process of LH (T-subl = 200 degrees C, 10(-6) mmHg) leads to films composed of highly orient ed crystallites, with two main sets of diffracting planes parallel to the film surface. The refractive index of LH as an evaporated thin fil m has also been determined in the 400-800 nm spectral range (n = 1-2). LH interacts with ammonia and/or water in the gas phase. In the first case the acid-base reaction (LH + NH3 reversible arrow L'. NH4+) occu rs. The resulting L' anion (L' = C11H2N7-) is the icyano-2H-pyrrol-2-y lidene)-1,1,2-tricyanoethanide (A, lambda(max) = 525 nm) or the isomer ,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinide (B, lambda(max) = 680 nm, depending on the relative amount of water to ammonia in the ga s phase. This reaction is driven by the hydrogen bonding of NH4+ to B and/or to water. In the second case a fast proton scrambling occurs.