Vanadium( IV ) and mixed-valence vanadium( IV / V ) oxygen clusters with novel electronic properties, including the examples [V 12 As 8 O 40 (HCO 2 )] n– (n= 3 or 5)

The mixed valence compounds [NHEt3]2[NH2Me2][V12As8O40(HCO2)]·2H2O 1 and Na5[V12As8O40(HCO2)]·18H2O 2 containing isostructural V–O clusters with encapsulated formate ions and different electron populations, and their characterization are reported; in structurally related V–O clusters spin–spin coupling increases with increasing numbers of VIV centres in a nearly continuous way.