UNUSUAL STEPWISE ASSEMBLY AND MOLECULAR GROWTH - [H14MO37O112](14-) AND [H3MO57V6(NO)(6)O-189(H2O)(12)(MOO)(6)](21-)

The understanding of the formation of complex molecular systems from s imple building blocks by conservative self-assembly processes is still a challenge. We report the synthesis and structural characterization of the large reduced polyoxometallate compounds (NH4)(14)[H14Mo37O112] . 35 H2O (1), (NH4)(21)[H3Mo57V6(NO)(6)O-183(H2O)(18)]. 55H(2)O (2) (b y an improved synthesis) and Na-3(NH4)(18)[H3Mo63V6(NO)(6)O-195(H2O)(1 2)]. 41H(2)O (3). The cluster systems are formed by a stepwise growth process. This implies the appearance, during the cluster formation, of ephemeral polyoxometallate intermediates (some of which we were able to isolate). The negative charge and therefore the nucleophilicity of the intermediate cluster fragments increase when they are reduced, res ulting in further attraction of electrophiles and thus in growth of mo lecular systems. IN the case of the cluster anion of 3 we observed, co rrespondingly, the loss of an [MoO](4+) oxometallate fragment by air o xidation; this implies that aits uptake and release are controlled by th degree of reduction of the cluster. correspondingly, intermediates between the anions of 2 and 3 of the {Mo57+xV6} type could be isolated . The unusual anion of 1 is formed by symmetry breaking processed.