engleski

Multiple crystalline forms of 1,5- bis(salicylidebne)carbohydrazide

Carbohydrazide, as a higher urea homologue, offers a versatile platform for tailoring Schiff bases, either mono- or bis-substituted ones. Over the years, such systems have been recognized as supreme multitopic ligands for the construction of extended metal-organic architectures, but also as functional molecules for e.g. selective anion binding. Reactions of salicylaldehyde and carbohydrazide afforded, depending on the synthetic procedure and crystallization conditions, mono(salicylidene)carbohydrazide and a diver¬sity of crystalline forms of 1, 5- bis(salicylidene)carbohydrazide: three polymorphs and two solvates. All crystalline forms of 1, 5-bis(salicylidene)carbohydrazide comprise the same tautomer of the title compound. As established via X-ray crystallography, IR spectroscopy, and CP MAS NMR its salicylidene residues adopt the enol- imino form while the carbamide fragment is in all cases found in the keto form. Conformations of 1, 5-bis(salicylidene)carbohydrazide molecules and their hydrogen-bonding patterns are similar for two polymorphs while the third one in this context significantly differs. All solid phases of 1, 5- bis(salicylidene)carbohydrazide undergo complicated degradation upon heating, yielding salicylideneazine, CO2, and N2 either directly or via intermediates as established by thermal analyses. In addition, relative phase stability was inspected mechanochemically and by solvent- mediated experiments.

Carbohydrazide ; Schiff base ; polymorphism ; thermal reactivity

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