Conducting Molecular Nanomagnet of DyIII with Partially Charged TCNQ Radicals

artículo científicoBifunctional electrically conducting single-molecule magnets are highly promising platforms for non-volatile memory devices and quantum computing applications. The development of these molecular materials, however, has largely been hindered by the lack of straightforward synthetic methods. Herein we demonstrate a facile and modular approach for the realization of bifunctional materials that does not require electrochemical or chemical oxidation to obtain partially charged organic radicals. Magnetic and electrical conductivity studies reveal that the Dy(III) compound exhibits slow relaxation of the magnetization between 5.0-8.0 K and semiconducting behavior over the range 180-350 K. DC magnetic fields suppress the quantum tunneling of the magnetization and affect the spin-canted antiferromagnetic interactions.U.S. Department of Energy

Facile synthesis of Cd-substituted zeolitic-imidazolate framework Cd-ZIF-8 and mixed-metal CdZn-ZIF-8

scientific paperZeolitic-imidazole framework ZIF-8 has attracted tremendous interests for the highresolution kinetic separation of propylene/propane mixture due to its effective aperture size in between the sizes of propylene and propane molecules. It is of great interest to fine-tune the effective aperture size of ZIF-8 either to improve its propylene/propane separation performances or to extend its use to the separation of other gas mixtures. It has been shown that substituting Zn with other metal nodes (e.g. Co) is a potential means to fine-tune the effective aperture size of ZIF-8. Here, we attempt to introduce another metal center, Cd, into ZIF-8 in a facile and scalable manner. Phase-pure Cd-ZIF-8 was successfully synthesized in methanol using a conventional solvothermal method, although it showed a narrow synthesis window. The presence of an organic base (triethylamine, TEA) was found critical not only for the facile synthesis of phase-pure Cd- ZIF-8 but also for the suppression of its phase transformation. A battery of characterizations including single-crystal X-ray structure solutions confirmed that the effective aperture size of Cd-ZIF-8 is the largest among its iso-structures (Zn-ZIF-8 and Co-ZIF-8). Finally, for the first time, mixed-metal CdZn-ZIF-8 crystals with various Cd/Zn ratios were solvothermally synthesized, demonstrating a further opportunity for varying the effective aperture sizes of ZIF-8 and its iso-structures.National Science Foundation Qatar National Research Fund Texas A&M Engineering Experimental Station

Relaxation Dynamics of Identical Trigonal Bipyramidal Cobalt Molecules with Different Local Symmetries and Packing Arrangements: Magnetostructural Correlations and ab inito Calculations

A family of isostructural, mononuclear CoII complexes with distorted trigonal bipyramidal coordination environments is reported. The degree of distortion as well as the overall symmetry of the molecules varies among the members of the series. Different experimental procedures resulted in the isolation of solvomorphs (pseudopolymorphs with different solvent content) for some of the family members. Importantly, their disparate packing arrangements lead to very different dynamic magnetic behavior. The results of magnetostructural correlations and ab initio calculations reveal that the deciding factor for SMM behavior is not the degree of distortion which, a priori, would be expected to be the case, but rather the interactions between neighboring molecules in the solid state.Department of Energy, Basic Energy Sciences, Materials Sciences Division Robert A. Welch Foundation for financial support Ciencia y Tecnología del Distrito Federal (ICyTDF) Spanish Ministerio de Economía y Competitivida

Magnetic ordering in self-assembled materials consisting of cerium(III) ions and the radical forms of 2,5-TCNQX 2 (X=Cl, Br)

Ribbon-like coordination polymers composed of CeIII ions and TCNQX2 (TCNQ=tetracyanoquinodimethane; X=Cl, Br), but not TCNQ radicals, show unexpected magnetic ordering (see picture; Ce green). This behavior reveals remarkable subtlety for magnetic properties of lanthanide–organic materials

Strong Ferromagnetic Exchange Coupling Mediated by a Bridging Tetrazine Radical in a Dinuclear Nickel Complex.

The radical bridged compound [(Ni- (TPMA))2-μ-bmtz•−](BF4)3·3CH3CN (bmtz = 3,6-bis- (2′-pyrimidyl)-1,2,4,5-tetrazine, TPMA = tris(2- pyridylmethyl)amine) exhibits strong ferromagnetic exchange between the S = 1 NiII centers and the bridging S = 1/2 bmtz radical with J = 96 ± 5 cm−1 (−2JNi‑radSNiSrad). DFT calculations support the existence of strong ferromagnetic exchange.Department of Energy Office of Science Graduate Fellowship, Instituto de Ciencia y Tecnología del Distrito Federal (ICyTDF) National Science Foundation (CHE-1310574) and the Robert A. Welch Foundation (A-1449)

Magnetic ordering in TCNQ-based metal-organic frameworks with host-guest interactions

Host–guest interactions between the aromatic molecules benzene, toluene, aniline and nitrobenzene and the redox-active TCNQ-based metal–organic framework (MOF), Fe(TCNQ)(4,4′-bpy) (1) (TCNQ = 7,7,8,8-tetracyanoquinodimethane), have been found to modulate spontaneous magnetization behaviours at low temperatures. An analogous MOF, Mn(TCNQ)(4,4′-bpy) (2) with isotropic Mn(II) ions as well as the two-dimensional compound Fe(TCNQ)(DMF)2·2DMF (3·2DMF), were also prepared as models for studying the effects of single-ion magnetic anisotropy and structural distortion on spin canting. The results indicate guest-dependent long range magnetic ordering occurs at low temperatures, which correlates with the electrostatic and steric effects of the incorporated aromatic guests.U.S. Department of Energ

Structural distortions of the spin-crossover material [Co(pyterpy)2](TCNQ)2 mediated by supramolecular interactions.

The incorporation of TCNQ˙− (7,7,8,8-tetracyanoquinodimethane) radicals as counterions for the spin-crossover material [Co(pyterpy)2](TCNQ)2·solvent (pyterpy = 4′-(4′′′-pyridyl)-2,2′:6′,2′′-terpyridine) leads to structural distortions of the [Co(pyterpy)2]2+ spin-crossover cation as compared to [Co(pyterpy)2](PF6)2. Variable temperature structural and magnetic studies indicate that the supramolecular π-stacking interactions between the terminal pyridyl groups and TCNQ radicals play a crucial role in the spin-crossover properties

Structural distortions of the spin-crossover material [Co(pyterpy)2](TCNQ)2 mediated by supramolecular interactions.

The incorporation of TCNQ˙− (7,7,8,8-tetracyanoquinodimethane) radicals as counterions for the spin-crossover material [Co(pyterpy)2](TCNQ)2·solvent (pyterpy = 4′-(4′′′-pyridyl)-2,2′:6′,2′′-terpyridine) leads to structural distortions of the [Co(pyterpy)2]2+ spin-crossover cation as compared to [Co(pyterpy)2](PF6)2. Variable temperature structural and magnetic studies indicate that the supramolecular π-stacking interactions between the terminal pyridyl groups and TCNQ radicals play a crucial role in the spin-crossover properties

Magnetic ordering in self-assembled materials consisting of cerium(III) ions and the radical forms of 2,5-TCNQX 2 (X=Cl, Br)

Ribbon-like coordination polymers composed of CeIII ions and TCNQX2 (TCNQ=tetracyanoquinodimethane; X=Cl, Br), but not TCNQ radicals, show unexpected magnetic ordering (see picture; Ce green). This behavior reveals remarkable subtlety for magnetic properties of lanthanide–organic materials

Strong Direct Magnetic Coupling in a Dinuclear CoII Tetrazine Radical Single-Molecule Magnet.

artículo científicoThe ligand-centered radical complex [(CoTPMA)2-μ-bmtz.−](O3SCF3)3⋅CH3CN (bmtz=3,6-bis(2′-pyrimidyl)-1,2,4,5-tetrazine, TPMA=tris-(2-pyridylmethyl)amine) has been synthesized from the neutral bmtz precursor. Single-crystal X-ray diffraction studies have confirmed the presence of the ligand-centered radical. The CoII complex exhibits slow paramagnetic relaxation in an applied DC field with a barrier to spin reversal of 39 K. This behavior is a result of strong antiferromagnetic metal–radical coupling combined with positive axial and strong rhombic anisotropic contributions from the CoII ions.National Science Foundation Ciencia y Tecnolog a del Distrito Federal (ICyTDF) STC