The compounds Cs12[VIV 18O42(H2O)]·14H2O (1a), K12[VIV 18O42(H2O)]·16H2O (1b), Rb12[VIV 18O42(H2O)]·19H2O (1c), K9[H3VIV 18O42(H2O)]·14H2O·4N2H4 (1d), K11[H2VIV 18O42(Cl)]·13H2O·2N2H4 (2a), K9[H4VIV 18O42(Br)]·14H2O·4N2H4 (2b), K9[H4VIV 18O42(I)]·14H2O·4N2H4 (2c), K10[H3VIV 18O42(Br)]·13H2O·0.5N2H4 (2d), K9[H4VIV 18O42(NO2)]·14 H2O·4N2H4 (3), Cs11[H2VIV 18O42(SH)]·12H2O (4), K10[HVIV 16VV 2O42(Cl)]·16H2O (5a), Cs9[H2VIV 16VV 2O42(Br)]·12H2O (5b), K10[HVIV 16VV 2O42(Br)]·16H2O (5c), Cs9[H2VIV 16VV 2O42(I)]·12H2O (5d), K10[HVIV 16VV 2O42(I)]·16H2O (5e), K10[HVIV 16VV 2O42(HCOO)]·15H2O (6), (NEt4)5[VIV 10VV 8O42(I)] (7), and Na6[H7VIV 16VV 2O42(VO4)]·21H2O (8) have been characterized by elemental analyses, redox titrations, IR and EPR spectroscopy, and magnetic susceptibility measurements, as well as by single crystal X-ray structure analyses. The anions containas a common structural featurean approximately spherical {V18O42} shell, which can act as a unique host system for neutral and anionic guests. Remarkably, the electron population of these clusters candepending on the specific reaction conditionsbe varied in a wide range between 10 and 18 3d electrons without changing the overall structure. The related magnetic properties in connection with the phenomenon of electron-dependent spin organization on a spherical cluster shell have been discussed in detail.

The novel title compound {NiII 4MoV 12} demonstrates the concept of generating targeted spin topologies using reduced polyoxometalates:  The four electrophilic nickel centersforming a tetrahedronare fixed by a nucleophilic highly reduced diamagnetic ε-Keggin cluster of T d symmetry generated in solution. This cluster not only has a structural role but actually participates in the transmission of the exchange interaction.

A new type of giant-wheel-shaped anion (see title) is obtained during the formation of the “classical” tetradecameric molybdenum-blue-type species [{Mo2}{Mo8}{Mo1}]14 in the presence of Pr3+. The Pr3+ cations substitute {Mo2} units and thereby increase the curvature of each ring, which leads to destruction and smaller ring sizes.