PDF《sorption behaviours》

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oxidation of organic molecules by air or dioxygen (O2) is fundamental in the biosystem and has long been pursued in industry and chemical sciences27C29. Because the energy barrier for electron transfer from singlet organic substrates to the triplet O2 is generally very high30, harsh reaction conditions and/or ef?cient catalysts are usually necessary to activate the O2 molecule for aerobic oxidization, so that the earth atmosphere can maintain a high O2 concentration. Natural enzymes are well known as highly selective and ef?cient catalysts under mild conditions. For instance, the highly ef?cient O2 activation centres in various copper proteins, such as galactose oxidase, tyrosinase and dopamine b-monooxygenase, have been extensively studied or used as structural models for synthetic catalysts. Considering that PCPs generally lack suf?cient robustness, reactivity and/or O2-activation ability to allow aerobic oxidation of themselves, we designed and synthesized a porous metal azolate framework (MAF)4 on the basis of Cu(I) and a methylene-bridged bis-triazolate ligand (Fig. 1). Although Cu(I)-based PCPs are very scarce because Cu(I) can be easily oxidized as Cu(II) by air to destroy the original metalCligand connectivity31, azolate derivatives have been demonstrated as suitable ligands for highly stable PCPs even with Cu(I) (ref. 4), and the coordination between Cu(I) and triazolate can be expected to give low-coordinated metal centres similar to those in the O2-activating copper proteins. Furthermore, the methylene bridge in a diarylmethane-type ligand is obviously ?exible and oxidizable (activated by two aromatic rings)32, which could be oxidized in suitable catalytic conditions to form a more rigid and polar ketone group. Results Preparation and characterization of the porous crystal. Col- ourless crystals of the titled compound, MAF-42, were synthesized in its large-pore (lp) form as [Cu4(btm)2] ? C6H6 (denoted as C6H6@MAF-42-lp, H2btm ? bis(5-methyl-1,2,4- triazolate-3-yl)methane) by solvothermal reaction of H2btm and [Cu(NH3)2]OH in a mixed aqueous ammonia/methanol/ benzene solvent. Single-crystal X-ray diffraction analysis (Supplementary Table 1) showed that MAF-42-lp is a three- dimensional (3D) porous coordination framework composed of ?ve independent (two of them locate at twofold axes with occu- pancies of 1/2) Cu(I) ions and two independent, fully deproto- nated btm2 ? ligands in a 2:1 molar ratio. As expected, all btm2 ? ligands are six-coordinated and the average coordination number of Cu(I) ions is three4. Nevertheless, each Cu(I) ion either adopts the linear, distorted T-shaped or tetrahedral coordination geometry (Supplementary Fig. 1). The two independent ligands have different surrounding environments. The methylene group (C4) of one ligand is adjacent to a two- and two three- coordinated Cu(I) ions, while that (C11) of another ligand is only adjacent to two three- and a four-coordinated Cu(I) ions (Supplementary Table 2). The two triazolate rings of btm2 ? are not coplanar because they are linked by a sp3 hybridized methylene C atom. The 3D coordination framework can be regarded as a cross-packing structure of ribbon-like fragments (Supplementary Fig. 2), which retains large 1D rhombic channels (void 37.8%, cross-section size 4.8 ? 7.1C6.0 ? 10.8 ?2) with disordered benzene molecules ?lled inside. It should be noted that the Cu(I) ions and methylene groups are fully exposed on the pore surface (Fig. 2a). Thermogravimetry (TG) and powder X-ray diffraction (PXRD) measurements of C6H6@MAF-42-lp showed that the benzene molecules can be completely removed below