AB-INITIO MODELING OF THE ENDOHEDRAL REACTIVITY OF POLYOXOMETALATES -2 - ELECTROSTATIC POTENTIAL DISTRIBUTIONS IN ELECTRONICALLY INVERSE HOSTS

Ab initio Hartree-Fock calculations have been carried out on the octad ecavanadate ion (V18O42)(12-) 1, on its protonated derivative (H4V18O4 2)(8-) 2, and on the vanadophosphate cluster [V7O12(O3PH)(6)](-) 3, ta ken as a model for [V7O12(O3PPh)(6)](-) 3'. The spheroidal clusters 2 and 3' have recently been characterized as 'electronically inverse hos ts' in the encapsulation complexes Cs-9[X@H4V18O42]. 12H(2)O (X = Br, I) and (Ph4P)(2)[Cl@V7O12(O3PPh)(6)]. An estimate of the electrostatic potential distribution including the contribution of the lattice pote ntial yields highly positive values of the potential inside the host c avities For 2 and 3. Those values are larger than the electrostatic po tential computed at a vacant chloride site of the CsCl crystal, thus e xplaining the thermodynamic stability of the encapsulated anions. (C) Academie des Sciences/Elsevier, Paris.