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Spectroscopic investigation of tetranuclear clusters encapsulated in some polyoxometalate complexes

M. HOSSU1,* , D. RUSU2, M. RUSU3, O. COZAR1, C. PASCA4, L. DAVID1

Affiliation

  1. Iuliu Hatieganu” University, Faculty of Pharmacy, 400026 Cluj-Napoca, Romania
  2. “Babes-Bolyai” University, Faculty of Physics, 400084 Cluj-Napoca, Romania
  3. "Babes-Bolyai” University, Faculty of Chemistry, 400028, Cluj -Napoca, Romania
  4. “Babes-Bolyai” Univ., Dept. of Biol., Cluj-Napoca, Romania

Abstract

The sandwich-type Na6[Fe4(H2O)2(AsW9O34)2]·20H2O (1) and Na10[Co4(H2O)2(AsW9O34)2]·25H2O (2) complexes were prepared and investigated through spectroscopic (FT–IR, UV–VIS, ESR) methods and magnetic susceptibility measurements. The stretching vibration νas( W–Oc–W ) band is shifted in the IR spectra with 13 cm-1 and 12 cm-1 for (1) and (2) respectively, towards higher energies comparative to the Na9[AsW9O34]·11H2O ligand spectrum due to the involvement of the oxygen atoms at the coordination metallic ions. The opposite shift of νas(W–Oe–W) and νas(W–Oc–W) vibrations bands shows the coordination of each metallic ion at oxygen atoms from the belt region. The UV electronic spectra of the sandwich-type complex and of the ligand contain two bands characteristic for the ligand to metal change transfer in the heteropolyoxometalates frame. The more intense band corresponding to the pπ(Ot) → dπ*(W) transitions is centred at 49100 cm-1 (L), 49150 cm-1 (1) and 49300 cm-1 (2). This is in agreement with the coordination of the Co (II) and Fe (III) ions in the lacunary region of the ligand and not to the terminal oxygen atoms. The Gaussian deconvolution of the visible spectrum for complex (1) in aqueous solution shows the presence of a band centered at 29340 cm−1 assigned to the 6A1g(S) → 4Eg(D) transition for the Fe (III) ions in Oh distorted symmetry. Information about the local environment of Co (II) ions have been obtained by means of d–d transitions from the visible electronic spectrum performed in aqueous solution. Two bands of the Co complexes, at 16000 cm-1 and 19400 cm-1 are assigned to 4A2g(F)→ 4T1g(F) (υ2) and 4T1g(F)→ 4T1g(P) (υ3) transitions. The ESR spectrum of complex (1) shows the antiferromagnetic coupling of Fe (III) ions and the octahedral local symmetry around the metallic ions. The ESR spectrum of the Co complex obtained at T= 80 K contain a single very large signal centered at 3250 G..

Keywords

Heteropolyoxometalates, Clusters, Exchange and superexchange, Electron paramagnetic resonance.

Submitted at: Nov. 2, 2006
Accepted at: April 15, 2007

Citation

M. HOSSU, D. RUSU, M. RUSU, O. COZAR, C. PASCA, L. DAVID, Spectroscopic investigation of tetranuclear clusters encapsulated in some polyoxometalate complexes, Journal of Optoelectronics and Advanced Materials Vol. 9, Iss. 4, pp. 1000-1004 (2007)