Metal-organic frameworks form a unique class of multifunctional hybrid materials and have myriad applications, including gas storage and catalysis. Their structure is usually achieved through the infinite coordination of metal ions and multidentate organic ligands by means of strong covalent bonds. Threaded molecules such as catenanes and rotaxanes have largely been restricted to comprising components of two-dimensional interlocking rings or polygons. There are very few examples of the catenation of polyhedral cages. Although it has been postulated that the infinite extended architecture can be obtained from the polycatenation of a discrete cage based on such threading, this has not been documented to date. Here we describe an infinite three-dimensional metal-organic framework composed of catenated polyhedral cages, in which the framework is achieved by mechanical interlocking of all of the vertices of the cages. The three-dimensional polycatenated framework shows twofold self-interpenetration in its crystal packing. The penetration of polycatenanes creates nanosized voids into which the Keggin polyoxometalate anions are perfectly accommodated as counteranions.
The three-dimensional framework of [Gd(H(2)O)(3)](3)[GdMo(12)O(42)]vdt.3H(2)O, which was synthesized from hydrothermal reaction, is built up from Silverton-type anions linked by nine coordinated gadolinium(III) cations. It is the first time that the paramagnetic lanthanide(III) cation is introduced into the Silverton-type anionic center in the heteropolymolybdate chemistry, and it acts as 18 dentate ligands coordinating to six Gd(III) atoms and linking up six other neighboring [Mo(12)GdO(42)](9-) units in a staggered manner to generate a remarkable three-dimensional framework. The magnetic susceptibility measurement suggests that the weak antiferromagnetic behavior results from the transformation of O-Mo-O units, which has been confirmed by EPR spectra.
We tested the performance of DNA barcoding in Acridoidea and attempted to solve species boundary delimitation problems in selected groups using COI barcodes. Three analysis methods were applied to reconstruct the phylogeny. K2P distances were used to assess the overlap range between intraspecific variation and interspecific divergence. “Best match (BM)”, “best close match (BCM)”, “all species barcodes (ASB)” and “back-propagation neural networks (BP-based method)” were utilized to test the success rate of species identification. Phylogenetic species concept and network analysis were employed to delimitate the species boundary in eight selected species groups. The results demonstrated that the COI barcode region performed better in phylogenetic reconstruction at genus and species levels than at higher-levels, but showed a little improvement in resolving the higher-level relationships when the third base data or both first and third base data were excluded. Most overlaps and incorrect identifications may be due to imperfect taxonomy, indicating the critical role of taxonomic revision in DNA barcoding study. Species boundary delimitation confirmed the presence of oversplitting in six species groups and suggested that each group should be treated as a single species.
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