Geometrically Restricted Intermediates in the Self-Assembly of an M12L24 Cuboctahedral Complex

The self‐assembly of a cuboctahedral M12L24 complex is traced by time‐dependent NMR spectroscopy and mass spectrometry. The metastable intermediate structures that exist during the self‐assembly process are not a chaotic mixture of numerous species, but instead are geometrically restricted. Short‐lived M8L16 (D4d) and relatively long‐lived M9L18 (D3h) are fully characterized as major intermediates. Employing a ligand with a smaller bend angle (112°) allows these two species to be kinetically trapped and more clearly observed by NMR spectroscopy. X‐ray crystallography shows that M9L18 has the framework topology predicted by geometric discussion. Geometrically dictated: Due to the geometrically restricted number of possible structures, the intermediates of self‐assembly are rather relatively ordered than a chaotic mixture of numerous species. Two prominent metastable intermediates, M8L16 and M9L18, are well characterized during the self‐assembly of an M12L24 cuboctahedral complex.