Two isostructural highly porous metal−organic frameworks, the wellknown {Cu 3 (BTC) 2 } n (BTC = 1,3,5-benzenetricarboxylate), often appointed with the name HKUST-1, and {Zn 3 (BTC) 2 } n , have been investigated as models for the buildup of dielectric properties, differentiating the role of chemi-and physisorbed guest molecules and that of specific intraframework and framework-guest linkages. For this purpose, electron charge density analysis, impedance spectroscopy, density functional theory simulations, and atomic partitioning of the polarizabilities have been exploited. These analyses at different degrees of pores filling enabled one to observe structural and electronic changes induced by guest molecules, especially when chemisorbed. The electrostatic potential inside the pores allows one to describe the absorption mechanism and to estimate the polarization of guests induced by the framework. The dielectric constant shows very diverse frequency dependence and magnitude of real and imaginary components as a consequence of (I) capture of guest molecules in the pores during synthesis, (II) MOF activation, and (III) water absorption from the atmosphere after activation. Comparison with calculated static-dielectric constant and atomic polarizabilities of the material has allowed for evaluating building blocks' contribution to the overall property, paving the way for reverse crystal engineering of these species.
. (2017) Combining microscopic and macroscopic probes to untangle the single-ion anisotropy and exchange energies in an S=1 quantum antiferromagnet. Physical Review B (Condensed Matter and Materials Physics), 95 (13). 134435. Permanent WRAP URL:http://wrap.warwick.ac.uk/87422 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. A note on versions:The version presented in WRAP is the published version or, version of record, and may be cited as it appears here.For more information, please contact the WRAP Team at: wrap@warwick.ac.ukCombining micro-and macroscopic probes to untangle single-ion anisotropy and exchange energies in a S = 1 quantum antiferromagnet The magnetic ground state of the quasi-one-dimensional spin-1 antiferromagnetic chain is sensitive to the relative sizes of the single-ion anisotropy (D) and the intrachain (J) and interchain (J ) exchange interactions. The ratios D/J and J /J dictate the material's placement in one of three competing phases: a Haldane gapped phase, a quantum paramagnet and an XY -ordered state, with a quantum critical point at their junction. We have identified [Ni(HF)2(pyz)2]SbF6, where pyz = pyrazine, as a rare candidate in which this behavior can be explored in detail. Combining neutron scattering (elastic and inelastic) in applied magnetic fields of up to 10 tesla and magnetization measurements in fields of up to 60 tesla with numerical modeling of experimental observables, we are able to obtain accurate values of all of the parameters of the Hamiltonian [D = 13.3(1) K, J = 10.4(3) K and J = 1.4(2) K], despite the polycrystalline nature of the sample. Densityfunctional theory calculations result in similar couplings (J = 9.2 K, J = 1.8 K) and predict that the majority of the total spin population resides on the Ni(II) ion, while the remaining spin density is delocalized over both ligand types. The general procedures outlined in this paper permit phase boundaries and quantum-critical points to be explored in anisotropic systems for which single crystals are as yet unavailable.
Two Cu coordination polymers [CuCl(pyz)](BF) 1 and [CuBr(pyz)](BF) 2 (pyz = pyrazine) were synthesized in the family of quasi two-dimensional (2D) [Cu(pyz)] magnetic networks. The layer connectivity by monatomic halide ligands results in significantly shorter interlayer distances. Structures were determined by single-crystal X-ray diffraction. Temperature-dependent X-ray diffraction of 1 revealed rigid [Cu(pyz)] layers that do not expand between 5 K and room temperature, whereas the expansion along the c-axis amounts to 2%. The magnetic susceptibility of 1 and 2 shows a broad maximum at ∼8 K, indicating antiferromagnetic interactions within the [Cu(pyz)] layers. 2D Heisenberg model fits result in J = 9.4(1) K for 1 and 8.9(1) K for 2. The interlayer coupling is much weaker with | J| = 0.31(6) K for 1 and 0.52(9) K for 2. The electron density, experimentally determined and calculated by density functional theory, confirms the location of the singly occupied orbital (the magnetic orbital) in the tetragonal plane. The analysis of the spin density reveals a mainly σ-type exchange through pyrazine. Kinks in the magnetic susceptibility indicate the onset of long-range three-dimensional magnetic order below 4 K. The magnetic structures were determined by neutron diffraction. Magnetic Bragg peaks occur below T = 3.9(1) K for 1 and 3.8(1) K for 2. The magnetic unit cell is doubled along the c-axis ( k = 0, 0, 0.5). The ordered magnetic moments are located in the tetragonal plane and amount to 0.76(8) μ/Cu for 1 and 0.6(1) μ/Cu for 2 at 1.5 K. The moments are coupled antiferromagnetically both in the ab plane and along the c-axis. The Cu g-tensor was determined from electron spin resonance spectra as g = 2.060(1), g = 2.275(1) for 1 and g = 2.057(1), g = 2.272(1) for 2 at room temperature.
We have investigated the magnetic and electronic structures of crystalline dimethylammonium copper formate [(CH3)2NH2]Cu(HCOO)3; a model compound that belongs to a wide class of hybrid organic-inorganic perovskites. We present the...
The reaction of copper(II) chloroacetate (1d) with pyrazole (Hpz) mainly yielded the mononuclear compound [Cu(mu-ClCH2COO)(2)(Hpz)(2)] (2m), which self-assembled generating a one-dimensional coordination polymer. Moreover, the concomitant isolation of the tetranuclear [{Cu-2(mu-pz)(mu-OCH2COO)(Hpz)(MeOH)}(2)(mu-ClCH2COO)(2)] (3t) and hexanudear [{Cu-3(mu-OH)(mu-pz)(3)(Hpz)(2)}(2)(mu-ClCH2COO)(2)](Cl)(2) (4h) species evidenced the occurrence of a peculiar, previously unreported, dehydrochlorination reaction and the formation of the trinuclear triangular moiety [Cu-3(mu(3)-OH)(mu-pz)(3)]. Theoretical calculations based on density functional theory including solvation effects indicate a possible pathway for the formation of 3t. Interestingly, besides the energy minimum corresponding to 3t, a further relative energy minimum is found for a species which can be considered a possible reaction intermediate
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