Formation of a “less stable” polyanion directed and protected by electrophilic internal surface functionalities of a capsule in growth: [{Mo 6 O 19 } 2− ⊂{Mo vi 72 Fe iii 30 O 252 (ac) 20 (H 2 O) 92 }] 4−

The spherical capsule skeleton of the host-guest system [{Mo6O19}2- subset {Mo(VI)72Fe(III)30O252(CH3COO)20(H2O)92}]4- 1a--built up by 12 {(Mo(VI))Mo(VI)5} type pentagonal units linked by 30 Fe(III) centers which span the unique icosahedral Archimedean solid, the icosidodecahedron--can now be constructed deliberately and with a simpler composition than before from an acidified aqueous molybdate solution containing the mentioned (virtual) pentagonal units; the encapsulated hexamolybdate--normally not formed in water--is built up in an unprecedented way concomitant with capsule growth, while being directed by the corresponding internal electrophilic surface functionalities.