Microporous metal-organic frameworks built on a Ln3 cluster as a six-connecting node

Two novel microporous metal-organic frameworks, {[Pr-3(ATPT)(2)(HATPT)(4)]center dot(NO3)center dot 8H(2)O}(n) (1) and {[Nd-3(ATPT)(3)(HATPT)(3)]center dot 9H(2)O}(n) (2) (H(2)ATPT = 2-aminoterephthalic acid), were synthesized by slow diffusion of aqueous solution of H2ATPT and Pr(NO3)(3)center dot 6H(2)O or Nd(NO3)(3)center dot 6H(2)O 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 eta(1):eta(1):eta(1):eta(2) 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 Ln(3) 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 Pr-3 unit and six methanol molecules per Nd-3 unit, respectively, can be absorbed into the dehydrated microporous frameworks.