Coordinating and supramolecular prospects of unsymmetrically substituted carbohydrazides

Abstract

Unsymmetrically substituted carbohydrazides, containing chelating o-hydroxyaryl and non-chelating pyridyl subunits were synthesized via two-step functionalization of carbohydrazide. Anion binding and coordinative propensities of the compounds were tested in reactions with appropriate Mo(VI) species. Such procedures yielded four types of products: monomeric dioxomolybdenum(VI) complexes, dimeric and oligomeric/polymeric dioxomolybdenum(VI)-containing ensembles, hybrid hexamolybdate systems where the protonated ligand acts as cation and the hybrid hexamolybdate salts where the cation is the protonated form of the monomeric dioxomolybdenum(VI) complex. The solid-state structures of the compounds were elucidated by X-ray diffraction and infrared spectroscopy, while their thermal stability was inspected via thermogravimetric analysis and differential scanning calorimetry experiments. The behaviour of the ligands, monomeric, dimeric, and oligomeric/polymeric ensembles in DMSO solution was investigated by nuclear magnetic resonance. In the isolated materials, carbohydrazide ligands adopt altogether four distinctive protonation forms: neutral, monoprotonated in the corresponding hexamolybdate salt, doubly deprotonated while forming {MoO₂}²⁺ complexes, and neutral zwitterionic when shaping the hybrid salt. In all these structures the unsymmetrical carbohydrazide framework retains robust conformation and geometry.