Autor: |
Ayingone Mezui CS; Equipe d'Electrochimie et de Photo-électrochimie, Laboratoire de Chimie Physique, Université Paris-Sud, UMR 8000 CNRS, Université Paris-Saclay , Orsay, F-91405, France., de Oliveira P; Equipe d'Electrochimie et de Photo-électrochimie, Laboratoire de Chimie Physique, Université Paris-Sud, UMR 8000 CNRS, Université Paris-Saclay , Orsay, F-91405, France., Teillout AL; Equipe d'Electrochimie et de Photo-électrochimie, Laboratoire de Chimie Physique, Université Paris-Sud, UMR 8000 CNRS, Université Paris-Saclay , Orsay, F-91405, France., Marrot J; Institut Lavoisier de Versailles, Université de Versailles St. Quentin, UMR 8180 CNRS, Université Paris-Saclay , Versailles, F-78035, France., Berthet P; Equipe Synthèse Propriétés et Modélisation des Matériaux, ICMMO, Université Paris-Sud, UMR 8182 CNRS, Université Paris-Saclay , Orsay, F-91405, France., Lebrini M; Institut Lavoisier de Versailles, Université de Versailles St. Quentin, UMR 8180 CNRS, Université Paris-Saclay , Versailles, F-78035, France., Mbomekallé IM; Equipe d'Electrochimie et de Photo-électrochimie, Laboratoire de Chimie Physique, Université Paris-Sud, UMR 8000 CNRS, Université Paris-Saclay , Orsay, F-91405, France. |
Abstrakt: |
The three polyoxotungstates [(NaOH 2 ) 2 Co II 2 (As 2 W 15 O 56 ) 2 ] 18- (1), [(NaOH 2 )(Co II OH 2 )Co II 2 (As 2 W 15 O 56 ) 2 ] 17- (2), and [(Co II OH 2 ) 2 Co II 2 (As 2 W 15 O 56 ) 2 ] 16- (3) have been prepared in aqueous solution upon mixing cobalt(II) salts with the ligand [As 2 W 15 O 56 ] 12- . The reaction of 1 or 2 with the Fe 3+ ion leads invariably to the same species [(Fe III OH 2 )(Co II OH 2 )Co II 2 (As 2 W 15 O 56 ) 2 ] 15- (4) possessing three cobalt atoms and a single iron atom. However, if the Fe-containing homologue of compound 1, that is, the polyoxotungstate [(NaOH 2 ) 2 Fe III 2 (As 2 W 15 O 56 ) 2 ] 16- (5), is employed instead to react with the Co 2+ ion, the species [(Co II OH 2 ) 2 Fe III 2 (As 2 W 15 O 56 ) 2 ] 14- (6) is obtained, having two cobalt atoms and two iron atoms. The compounds 1, 2, 3, 4, and 6 are described for the first time and have been characterized by several physicochemical methods such as FTIR, UV-visible, ATG, and elemental analysis. Structural analysis by single-crystal X-ray diffraction has been carried out with compounds 2 (monoclinic space group P2 1 /c, a = 17.0622(5) Å, b = 15.0828(4) Å, c = 32.0872(8) Å, β = 91.170(1)°, and Z = 2) and 3 (triclinic space group P1̅, a = 13.6137(7) Å, b = 13.8836(8) Å, c = 22.9276(6) Å, α = 89.906(3)°, β = 78.356(2)°, γ = 61.451(2)°, and Z = 1). Electrochemical studies undertaken with all the above-mentioned compounds and some of their homologues shed light on the influence of the chemical composition on their electrocatalytic properties toward substrates such as the nitrite ion and dioxygen. Magnetic measurements evidence anisotropic ferromagnetic interactions between Co 2+ ions and antiferromagnetic interactions between Fe 3+ ions. The nature and the strength of the Co 2+ -Fe 3+ interactions depend on the relative orientations of their 3d orbitals. The effective magnetic moment of the Co 2+ ions varies with the temperature and with the distortion of the octahedral sites in which they are located. |