Direct observation of molecular-level template action leading to self-assembly of a porous framework

Abstract

(Figure presented) The molecular steps involved in the self-assembly of Cu3(BTC)2 (BTC=1,3,5-benzenetricarboxylic acid) metal-organic frameworks that enclose Keggin-type H3PW 12O40 heteropolyacid molecules were unraveled by using solution 17O, 31P, and 183WNMR spectroscopy, small-angle X-ray scattering, near-IR spectroscopy, and dynamic light scattering. In aqueous solution, complexation of Cu2+ ions with Keggin-type heteropolyacids was observed. Cu2+ ions are arranged around the Keggin structure so that linking through benzenetricarboxylate groups results in the formation of the Cu3(BTC)2 MOF structure HKUST-1. This is a unique instance in which a templating mechanism that relies on specific molecular-level matching and leads to explicit nanoscale building units can be observed in situ during formation of the synthetic nanoporous material. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.