Synthesis and Physical-Chemical Study of Two Sandwich-Type Heteropolyoxometalates With Dinuclear Vanadium Clusters
Nicoleta Jooa, Mihaela Hossub, Dan Rusuc,
Anca Marcub, Mariana Rusua, Cristina Pascad and
a Deptment of Chemistry, “Babes-Bolyai” University, 11 Arany Janos Str., 400028, Cluj-Napoca, Romania
b Deptment of Physics, “Babes-Bolyai” University, 1 Kogalniceanu Str., 400084, Cluj-Napoca, Romania
c Deptment of Chemistry – Physics, “Iuliu Hatieganu” Medical and Pharmaceutical University, 6 Pasteur Str.,
400349, Cluj-Napoca, Romania
d Departmant of Biology, “Babes-Bolyai” University, 5–7 Clinicilor Str., 400006, Cluj-Napoca, Romania
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The sandwich-type K12[(VO)2Sb2W20O70] · 31H2O (1) and K11[(VO)2Bi2W20O70] · 21H2O (2) heteropolyoxotungstates were investigated by means of elemental analyses, thermogravimetric and spectroscopic (FT-IR, UV–VIS and EPR) methods.
The analysis of vanadium ions coordination mode was made comparing the FT-IR spectra of the complexes 1 and 2 with the K12[Sb2W22O74(OH)2] · 38H2O (L1) and K12[Bi2W22O74(OH)2] · 40H2O (L2) ligands. FT-IR spectra of the complexes show the presence of the V=O bonds characterized by νas(V=O) vibrations. In both complexes, the coordination of the vanadium shifts the νs(W–Oc,e–W) vibration bands. In UV spectra, the charge transfer pπ(Oc,e) → dπ*(W) band is shifted in complexes compared to the ligands spectra with ≈ 245 nm for 1 towards higher wavelength and with ≈ 250 nm for 2 towards lower wave numbers.
Visible spectra contain 2B2(dxy) → 2E(dxz,yz) and 2B2(dxy) → 2B1(dx2 –y2) transition bands for vanadyl ions in C4v local symmetry, at 12020 cm–1 respectively 14710 cm–1 for the complex 1, and at 12405 cm–1 and 15905 cm–1 for the complex 2. The powder EPR spectra at room temperature exhibit eight components both in the perpendicular and in the parallel bands and are typical for mononuclear oxovanadium species in axial environment.
Keywords: Heteropolyoxotungstates, VO complexes, FT-IR spectroscopy, UV-VIS spectroscopy, EPR spectroscopy