Geometrically restricted intermediates in the self-assembly of an M12L24 cuboctahedral complex.

The self-assembly of a cuboctahedral M12 L24 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 M8 L16 (D4d ) and relatively long-lived M9 L18 (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 M9 L18 has the framework topology predicted by geometric discussion.