Polyoxotungstenphosphate complexes with hexamethylenetetramine and copper ions

Previously undescribed in the literature complexes of tungsten phosphate metallates with copper ions Cu²⁺ and hexamethylenetetramine of the composition Rb₅[PW₁₁O₃₉Cu(H₂O)] ‧ 9H₂O (I), Rb₅[PW₁₁O₃₉Cu(C₆H₁₂N₄)] ‧ ‧ 10H₂O (II), Rb₅[PW₁₁O₃₉Zn_0.95Cu_0.05(H₂O)] ‧ 9H₂O (III) and Rb₅[PW₁₁O₃₉Zn_0.95Cu_0.05(C₆H₁₂N₄)] ‧ 10H₂O (IV) were synthesized and studied by electron and IR spectroscopy, X-ray phase analysis and electron paramagnetic resonance. The shift of the absorption maximum of copper ions to the long-wavelength region of the spectrum upon transition from [Cu(H₂O)₆]²⁺ to [PW₁₁O₃₉Cu(H₂O)]^5–, [PW₁₁O₃₉Zn_0.95Cu_0.05(H₂O)]^5–, [PW₁₁O₃₉Cu(C₆H₁₂N₄)]^5– and [PW₁₁O₃₉Zn_0.95Cu_0.05(C₆H₁₂N₄)]^5–is the result of a change in the magnitude of the ligand field strength in the inner sphere of the complexes. The electron paramagnetic resonance method has established that the magnitude of the ligand field around the octahedrally coordinated Cu²⁺ ions of complexes (III) and (IV) is significantly different: the height of the potential barrier of the crystal field at the location of the Cu²⁺ ion differs more than twofold, which is due to the replacement of a water molecule by a hexamethylenetetramine molecule C₆H₁₂N₄. The results of the studies can be useful in the synthesis and establishment of the structure of other polyoxotungstenmetallates with paramagnetic ions in the inner sphere of the complexes.