Modulating the Magnetic Dynamics of Five‐Coordinate DyIII Single‐Molecule Magnets by the Substitution Effect on the Axial Ligand

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Two five-coordinate mononuclear DyIII single-molecule magnets [(TrapenTMS)Dy(L)] (Trapen = tris(2-aminobenzyl) amine; TMS = SiMe3; L = OPMe31, OPEt32) have been synthesized by the reaction of [(TrapenTMS)Dy(THF)] and OPMe3, OPEt3, respectively. The molecular structures of 1 and 2 were fully established by single crystal X-ray diffraction. The centre DyIII ions of both complexes exhibit distorted triangular bipyramid geometries, varying with different neutral ligands L on the apex. The TrapenTMS ligand forms the pyramid base of the trigonal bipyramid. Subtle structural modifications of the axial O-ligand terminal substituent result in different dynamic magnetic behaviors.Magnetic data analysis reveals that 1 and 2 exhibit the characteristic behavior of SMM without a dc field, accompanying an unambiguous quantum tunneling of the magnetization. Field-induced slow magnetic relaxation was observed for 1 and 2 under an applied bias dc field of 1000 Oe, the relaxation energy barriers are 107 K and 88 K for 1 and 2, respectively. We have investigated the differences in magnetism and magnetic anisotropy between the two complexes by ab initio calculations.

Construction of Azo‐linked Covalent Organic Frameworks via Monomer Exchange for Enhanced Photocatalytic Performance

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The structural uniqueness of covalent organic frameworks (COFs) has brought great potential for their applications in photocatalysis. However, existing linkages of COF always lead to poor electron delocalization and inadequate stability. Therefore, two novel azo-linked COFs AZO-B-COF and AZO-T-COF were successfully constructed by the monomer exchange method. Significantly, two as-synthesized azo COFs presented a much higher photodegradation rate of 96% and 51% for AZO-T-COF and AZO-B-COF, respectively, which was in sharp contrast to the almost 0 degradation rate of imine COFs. And as expected, AZO-T-COF could be cycled at least 5 runs without a significant decrease in catalytic efficiency. Systematical experiments and theoretical calculations showed that comparing with imine COFs, conjugated structure of azo COFs broadened the visible-light absorption range and improved the transfer efficiency of the photocarriers. The N-rich azo bonds acted as an electron acceptor and made the materials better planarity. This work not only enriches COFs family but also demonstrated the superiority of azo-linked COFs.

Mechanistic Insights into the [3+1] Cycloadditions of Me3SiN3 on Bis‐silylene and the Formation of Pseudo‐Silaazatriene

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The reaction mechanism for the formation of the pseudo-silaazatriene 1 by the reaction of 1 equivalent of bis-silylene with 3 equivalents of azide Me3SiN3 has been explored at M06/def2-TZVPP//BP86-D3(BJ)/def2-TZVPP level of theory. The reaction mechanism is guided by the high Lewis basicity of the silicon lone pair and the high Lewis acidic character of Si-N bonds, as well as by the high tendency to eliminate N2 from Me3SiN3. The first step of the reaction is the formation of [3+1] cycloaddition product (I1) by the synergetic interactions of the lone pair on the silylene silicon with the π* molecular orbital of Me3SiN3 which is majorly localized on the terminal nitrogen atom, and the donation of the σ-type lone pair on the nitrogen atom connected to the SiMe3 group with the Si-N σ* orbital on silylene. The elimination of N2 from I1 results in the formation of pseudo-silaimine intermediate I2 having a dicoordinated, monovalent nitrogen atom. The Si-Si bond cleavage of I2 results in intermediate I3, which is susceptible to [3+1] cycloaddition reaction with two molecules of Me3SiN3 in a stepwise manner results in I7 having two silaimine and one silaamine moieties. Further 1,3-silyl migration results in pseudo-silaazatriene 1.