Unprecedented structural evidence for pyrrole-imine to azafulvene-amine tautomerization in iminopyrrolyl Schiff's base ligand: Coexistence of both tautomer's in a single crystal

a b s t r a c t
The treatment of bulky iminopyrrole Schiff base of composition [2-(Ph3CN=CH)C4H3NH] (1) with an�hydrous NiBr2 yielded corresponding bromide salt of chemical composition [{2-(Ph3CN=CH)-C4H3NH}-Br-{2-(Ph3CN(H)-CH)=C4H3NH}] (2) in good yield. The solid-state structure of compound (2) was estab�lished by using single crystal X-ray diffraction analysis. The X-ray crystallographic studies revealed that the bulky iminopyrrolyl ligand undergoes pyrrole-imine to azafulvene-amine tautomerization in the pres�ence of external stimuli such as NiBr2 and forms air-stable bromide salt of iminopyrrolyl Schiff base without having any significant covalent interactions between them. The existence of intra-molecular H�Br interactions along with inter-molecular hydrogen bonding in compound (2) made this bromide salt unique unprecedented structural evidence for the co-existence of both tautomeric forms in a single crys�tal. Moreover, the insight of compound (2) was investigated by DFT computational studies and Hirshfeld
surface analysis