Aryl-substituted 1-arylhydrazo-naphthalen-2-ones and 1-arylazo-naphthalen-2-ols display ...HN-N=C-C=O... <-/-> ...N=N-C=C-OH... ketohydrazone-azoenol prototropic tautomerism in the solid state by forming a strong intramolecular resonance-assisted H-bond (RAHB) that can change from pure N-H...O to pure O-H...N through dynamically disordered N-H...O <-/-> O-H...N bonds according to the electronic properties of the substituents. The compounds of the series aryl = 4-F-phenyl, 4-CH3-phenyl, 4-Cl-phenyl, and 1-naphthalenyl and their cocrystals with TCNQ have been studied by X-ray crystallography at temperature variable from 100 to 295 K. The packing is extensively discussed in terms of charge-transfer (CT) or electron donor-acceptor (EDA) interactions, showing that the herringbone packing of pure azonaphthols and the columnar one of their TCNQ cocrystals are respectively determined by specific sigma*<-pi and pi*<-pi interactions. It is shown that cocrystallization with TCNQ induces two main effects: (i) in TCNQ itself, a significant change from quinoid to aromatic geometry, from which a CT of some 0.40 e can be estimated; (ii) in azonaphthols, a shift of the N-H...O <-/-> N...H-O equilibrium towards the pure N-H...O tautomer, accompanied by a decrease of pi-delocalization inside the conjugated ...HN-N=C-C=O... resonant fragment. These findings suggest that through-space effects caused by TCNQ cocrystallization on the RAHB equilibrium are formally equivalent to through-bond effects caused by the aryl substituents.
Solid-State N-H...O/O-H...N Tautomerism in Resonance-Assisted 1-(Arylazo)-2-Naphthols and its Trough-Space pi*<-pi Perturbation in TCNQ Cocrystals. A Variable-Temperature X-Ray Crystal Study
GILLI, Gastone;BERTOLASI, Valerio;GILLI, Paola
2013
Abstract
Aryl-substituted 1-arylhydrazo-naphthalen-2-ones and 1-arylazo-naphthalen-2-ols display ...HN-N=C-C=O... <-/-> ...N=N-C=C-OH... ketohydrazone-azoenol prototropic tautomerism in the solid state by forming a strong intramolecular resonance-assisted H-bond (RAHB) that can change from pure N-H...O to pure O-H...N through dynamically disordered N-H...O <-/-> O-H...N bonds according to the electronic properties of the substituents. The compounds of the series aryl = 4-F-phenyl, 4-CH3-phenyl, 4-Cl-phenyl, and 1-naphthalenyl and their cocrystals with TCNQ have been studied by X-ray crystallography at temperature variable from 100 to 295 K. The packing is extensively discussed in terms of charge-transfer (CT) or electron donor-acceptor (EDA) interactions, showing that the herringbone packing of pure azonaphthols and the columnar one of their TCNQ cocrystals are respectively determined by specific sigma*<-pi and pi*<-pi interactions. It is shown that cocrystallization with TCNQ induces two main effects: (i) in TCNQ itself, a significant change from quinoid to aromatic geometry, from which a CT of some 0.40 e can be estimated; (ii) in azonaphthols, a shift of the N-H...O <-/-> N...H-O equilibrium towards the pure N-H...O tautomer, accompanied by a decrease of pi-delocalization inside the conjugated ...HN-N=C-C=O... resonant fragment. These findings suggest that through-space effects caused by TCNQ cocrystallization on the RAHB equilibrium are formally equivalent to through-bond effects caused by the aryl substituents.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
