Microporous Metal−Organic Frameworks Built on a Ln₃ Cluster as a Six-Connecting Node

Abstract

Two novel microporous metal−organic frameworks, {[Pr3(ATPT)2(HATPT)4]·(NO3)·8H2O}n (1) and {[Nd3(ATPT)3(HATPT)3]·9H2O}n (2) (H2ATPT = 2-aminoterephthalic acid), were synthesized by slow diffusion of aqueous solution of H2ATPT and Pr(NO3)3·6H2O or Nd(NO3)3·6H2O in 2-propanol. X-ray diffraction analyses reveal that their three-dimensional structures are composed of ATPT spacers and trinulcear lanthanide nodes, in which there are two crystallographically independent lanthanide atoms, nine- and twelve-coordinated. Twelve ATPT anions, adopting an unprecedented pentadentate η1:η1:η1:η2 bridging coordination mode, ligate the trinuclear node. Each pair of ATPT anions acts as a double bridge and is considered as one connection. Thus each trinuclear core is connected to the six nearest Ln3 neighbors forming a NaCl-type crystal lattice with a three-dimensional intersecting channel system of ca. 1.3-nm spacing between the centers of the adjacent clusters. The guest water molecules located in the large cavities can be removed without ruining the microporous framework. Thermal gravimetric and powder X-ray diffraction analyses confirm that small molecules, four methanol molecules per Pr3 unit and six methanol molecules per Nd3 unit, respectively, can be absorbed into the dehydrated microporous frameworks.