Structural characterization, hydrolytic stability and dynamics of cis-MoVIO22+ hydroquinonate/phenolate complexes. (15th September 2018)

• Record Type: Journal Article
• Authors: Drouza, Chryssoula; Hadjithoma, Sofia; Nicolaou, Maria; Keramidas, Anastasios D.
• Is Part Of: Polyhedron. Volume 152(2018)
• Page Start: 22
• Page End: 30
• Publication Date: 2018-09-15
• Subjects: Molybdenum -- Hydroquinones -- Non-innocent ligands -- Kinetics -- Hydrolytic stability; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2018.06.008
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: New mononuclear phenolate/hydroquinonate and dinuclear bridged-hydroquinonate cis -Mo VI O2 2+ complexes were synthesized and characterized in solid state and solution. The complexes retain their structure at the pD range 2–4, whereas hydrolyzes at the Mo VI -Ophenolate bond to form Mo VI O3 species. The very short Mo VI -Ophenolate bond is more labile than the Mo VI -Ocarboxylate . Abstract: Although, the investigation of the interactions of Mo VI ion with the "non-innocent" phenols/hydroquinones is essential for the understanding of the role of molybdenum in the biological systems, the Mo VI complexes of phenolate/hydroquinonate and their functionalized variants remain mainly unexplored. Reaction of Na2 Mo VI O4 with tripod iminodiacetate phenol/hydroquinone ligands in aqueous solutions resulted in the synthesis of mononuclear phenolate/hydroquinonate and dinuclear bridged-hydroquinonate cis -Mo VI O2 2+ complexes. The new complexes were isolated and characterized in solid state by X-ray crystallography. The 1 H, 13 C and 95 Mo NMR spectra of the aqueous solutions of the complexes show that they retain their structure at the pD range 2–4, with the dinuclear bridged-hydroquinonate cis -Mo VI O2 2+ to form two isomers which are in dynamic equilibrium. At pDs 4–7 the Mo VI -Ophenolate bond of the cis -Mo VI O2 2+ compounds hydrolyzes to form Mo VI O3 -iminodiacetate species. Variable temperature (VT) and 2D { 1 H} EXSY NMR spectroscopies where employed for the determination of the thermodynamic and activation parameters of the isomerization reaction between the dinuclear bridged-hydroquinonate cis -Mo VI O2 2+ isomers. The exchange mechanism between cis -Mo VI O2 2+ and the Mo VI O3 species were also investigated by 2D { 1 H} EXSY NMR spectroscopy. Despite of the higher strength of the Mo VI -Ophenolate bond, it is more labile than the Mo VI -Ocarboxylate bond. The rate determining step of the above exchange reactions was found to be the dissociation of the phenolate/hydroquinonate oxygen atom from Mo VI ion.