Systematic study of the interaction between V-IV centres and lanthanide ions M-III in well defined {(V2MIII)-M-IV}{(AsW9O33)-W-III}(2) sandwich type clusters: Part 1

A new type of heteropolytungstate is reported that contains in a triangular arrangement one lanthanide f element and two d transition metals in form of heteroatoms. The first example in this series is the monoclinic Na3K5[((VO)(2)Dy(H2O)(4)K-2(H2O)(2)Na(H2O)(2))(alpha-B-AsW9O33)(2)] center dot a23H(2)O (1) which was prepared from an acidified aqueous solution of Na2WO4 center dot 2H(2)O, As2O3 and VOSO4 center dot 5H(2)O to which Dy3+ ions were added. The single crystal X-ray structure analysis shows that the anion 1a consists of two [alpha-B-(AsW9O33)-W-III](9-) trilacunary Keggin type units linked by two VO2+, one Dy3+ as well as two K+ stop and one Na+ ion, resulting in a sandwich-type structure with idealized C-2v symmetry. The complete magnetochemical analysis shows very interesting magnetic properties, which will be considered in the full series together with the properties of the homologous compounds in due course.