Oxomolybdenum(VI) and (IV) complexes of pyrazole derived ONO donor ligands – synthesis, crystal structure studies and spectroelectrochemical correlation

Four cis-dioxomolybdenum complexes of general formula [MoO2(Ln)EtOH] (n = 1–4) and one oxomolybdenum(IV) complex [MoO(L4)EtOH], with potentially tridentate Schiff bases derived from 5-methyl pyrazole-3-carbohydrazide and salicylaldehyde/substituted salicylaldehyde/o-hydroxy acetophenone have been prepared. The Mo(IV) complex is derived from the Mo(VI) dioxo complex by oxotransfer reaction with PPh3. The complexes are characterized by elemental analysis, electronic spectra, IR, 1H NMR, and by cyclic voltammetry. All the Mo(VI) species are crystallographically characterized. The complexes have a distorted octahedral structure in which the ligand behaves as a binegative donor one, leaving the pyrazole –N uncoordinated towards the metal center. It is also revealed from the crystal structure that the Mo(VI) center enjoys an NO5 donor environment.

A few cis-dioxomolybdenum(VI) complexes have been prepared with pyrazole derived Schiff base ligands. One of these complexes has been subjected to oxo-transfer reaction with PPh3 to produce the corresponding oxomolybdenum(IV) complex. A comparative account of the Mo(VI) complexes regarding the redox stability and spectral behavior has been correlated with the variation of electron donating properties of the ligands.Figure optionsDownload as PowerPoint slide