Metal Ion Directed Tautomeric Polymorphism in a Hydrazonamide/Hydrozonate System. Issue 1 (11th January 2017)

• Record Type: Journal Article
• Authors: Mandal, Arkalekha; Patel, Bhisma K.
• Is Part Of: ChemistrySelect. Volume 2:Issue 1(2017)
• Page Start: 494
• Page End: 503
• Publication Date: 2017-01-11
• Subjects: bite angle -- conformation -- hydrazonamide -- hydrogen bond -- tautomeric polymorphism.; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/slct.201601432
• Languages: English
• ISSNs: 2365-6549

Abstract

Abstract: Ortho and para ‐aminophenyl substituted hydrazonamide ligands viz . 2‐amino‐benzoic acid (amino‐pyridin‐2‐yl‐methylene)‐hydrazide and 4‐amino‐benzoic acid (amino‐pyridin‐2‐yl‐methylene)‐hydrazide) can exist in two tautomeric forms. The hydrazonamide (keto) form of the former ligand is only observed in free ligand, while its enolate form exists in some of its metal complexes. Both hydrazonamide and hydrazonate tautomers possess a six membered intramolecular hydrogen bond between the o ‐amino group and amide oxygen or imino nitrogen respectively. As a result, hydrazonamide and hydrazonate tautomeric forms exist in different molecular conformation and thus 'tautomeric polymorphism' is observed in this system. The evidence of tautomerism and consequent conformational change in metal complexes of 2‐amino‐benzoic acid (amino‐pyridin‐2‐yl‐methylene)‐hydrazide is well supported by both DFT and NBO studies. Abstract : Metal ion induced tautomeric polymorphism in a hydrazonamide/ hydrazonate tautomeric system is described herein. The ligands exist in hydrazonamide form in their Ni(II), Zn(II) and Cd(II) complexes whereas they are in hydrazonate tautomeric form in the Co(III) and Cu(II) complexes. This has been explored by crystallographic as well as computational and fluorescence studies.