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    STUDIA PHYSICA - Issue no. 2 / 2006  
         
  Article:   SPECTROSCOPIC AND MAGNETIC INVESTIGATION OF TETRANUCLEAR MN(II) CLUSTER ENCAPSULATED IN SANDWICH-TYPE HETEROPOLYANION.

Authors:  M. HOSSU, D. RUSU, M. RUSU, L. DAVID, A. MARCU. 		 
       
         
  Abstract:  The sandwich-type Na10[Mn4(H2O)2(AsW9O34)2]∙27H2O complex was prepared and investigated through spectroscopic (FT-IR, UV-VIS, ESR) methods and magnetic susceptibility measurements. The analysis of the co-ordination mode of transition metal ions was made by means comparison between the FT-IR spectra of the sandwich-type complex with those of Na9[AsW9O34]∙11H2O ligand. The relatively small shift (9 cm-1) of the υasym(W=Ot) vibration band is due to the fact the terminal Ot atoms are not involved in the co-ordination. The opposite shift of υasym(W-Oe-W) and υasym(W-Oc-W) frequencies for the bandings from the belt region shows the co-ordination of each metallic ion at these oxygen atoms. The more intense band in the UV spectra corresponding to the pπ(Ot) → dπ*(W) transitions is centred at 49100 cm-1 and 49300 cm-1 for ligand and complex respectively. This is in agreement with the co-ordination of the Mn (II) ions in the lacunary region of the ligand and not to the terminal oxygen atoms. The broader band centred at 39732 cm-1 in the ligand spectrum belongs to the pπ(Oc,e) → dπ*(W) change transfer transition in the tricentric bonds. This band is shifted towards lower energies in the case of the complex (at 39467 cm-1). The Gaussian deconvolution of the visible spectrum shows the presence of a band centered at 29340 cm1 assigned to the 6A1g(S) 4Eg(D) transition of the MnII ions in Oh distorted symmetry. The value of the effective magnetic moment μeff = 11.81μB corresponds to an S = 5 spin state. The EPR spectrum of the complex obtained at room temperature indicate the presence of antiferromagnetic coupling between the Mn(II) ions.  
         
     
         
         
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