Structures of photochemically prepared mixed-valence polyoxovanadate clusters: oblong [V18O44(N3)]14− , superkeggin [V18O42(PO4)]11− and doughnut-shaped [V12B32O84Na4]15 − anions

Three mixed-valence polyoxovanadates, Na 12 H 2 [V 18 O 44 (N 3 )]·30H 2 O 1, K 8.5 H 2.5 [V 18 O 42 (PO 4 )]·19H 2 O 2 and H 15 [V 12 B 32 O 84 Na 4 ]·13H 2 O 3 have been photochemically synthesized and characterized by X-ray single-crystal analysis and magnetic susceptibility measurements. The [V 18 O 44 (N 3 )] 14- anion has an oblong structure encapsulating a linear N 3 - anion with approximate D 2h symmetry. The extent of reduction is different from that in [V 18 O 44 (N 3 )] 7- prepared by thermal decomposition of [V 19 O 50 ] 17- in the presence of N 3 - at 75 °C. The [V 18 O 42 (PO 4 )] 11- anion has a superkeggin structure with a PV 12 O 40 Keggin unit capped by six VO moieties which lie above six rectangle faces of the T d -distorted cuboctahedron defined by the V atoms in the Keggin unit. The [V 12 B 32 O 84 Na 4 ] 15 - anion contains an edge-sharing dodecagonal array of OVO 4 square pyramids, sandwiched by two hexadecaborates to produce a cyclic doughnut-shaped framework. The crystallographic analysis indicates that the cavity produced by the cyclic [V 12 B 32 O 84 ] 19- anion is occupied by a tetragonal Na 4 4+ moiety. The paramagnetic complexes 1–3 show the antiferromagnetic exchange interaction which is discussed in terms of the nearest V · · · V distances in the anion.