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1.
J Phys Chem Lett ; 11(15): 5856-5862, 2020 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-32615766

RESUMO

Flexible metal-organic frameworks (MOFs) exhibit a variety of phenomena attractive for basic and applied science. DUT-49(Cu) is one of the remarkable representatives of such MOFs, where phase transitions are coupled to pressure amplification and "negative gas adsorption". In this work we report important insights into structural transitions of DUT-49(Cu) upon physi- and chemisorption of gases and volatile liquids obtained by in situ electron paramagnetic resonance (EPR) spectroscopy. In this method, phase transitions are detected via the zero-field splitting in dimeric copper(II) units. First, a new approach was validated upon physisorption of n-butane. Then, using diethyl ether, we for the first time demonstrated that chemisorption can also trigger phase transition in DUT-49(Cu). On the basis of the EPR results, the transition appears completely reversible. The developed EPR-based approach can also be extended to other flexible MOFs containing paramagnetic metal paddlewheels, where high sensitivity and spectral resolution allow in situ studies of stimuli-induced structural variability.

2.
Inorg Chem ; 59(15): 10746-10755, 2020 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-32672944

RESUMO

Herein, we combine for the first time SQUID magnetometry, cw-EPR, THz-EPR, and paramagnetic NMR spectroscopies to study the magnetic properties of a high-spin cobalt(II) heteroscorpionate complex. Complementary information provided by these methods allowed precise determination of the magnetic interaction parameters, thereby removing the ambiguity inherit to single-method studies. We systematically investigate the extent to which information about the magnetic interaction parameters can be deduced from reduced data sets. The detailed study revealed significant different magnetic properties in solid state and solution. To further exploit the information content of the solution NMR experimental results, we introduce the new concept of reduced paramagnetic shift. It allows for the determination of the magnetic axes and, subsequently, full NMR signal assignment. It is shown that even in complicated cases, in which common NMR analytics (integral intensities, relaxation factors, etc.) fail, it yields robust results.

3.
Dalton Trans ; 2020 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-32301949

RESUMO

Copper(ii) complexes with stable nitroxide radicals are capable of magnetostructural spin-crossover like anomalies induced by external stimuli. Photoswitching in such systems is particularly important; however, retrieving the properties of photoinduced states is challenging and requires development of novel approaches. In this work, we investigate the exchange interactions in metastable photoinduced states of two compounds containing copper(ii)-nitroxide dyads. Using Electron Paramagnetic Resonance (EPR) with photoexcitation we obtain temperature dependence of magnetic susceptibility in the photoinduced state and estimates for the corresponding values of exchange coupling in the studied complexes. The interplay between intra- and inter-cluster exchange couplings is considered and analyzed. The proposed methodology is applicable also to other photoswitchable exchange-coupled systems.

4.
Artigo em Inglês | MEDLINE | ID: mdl-32315516

RESUMO

The one-step synthesis and characterization of a new and robust titanium-based metal-organic framework, ACM-1, is reported. In this structure, which is based on infinite Ti-O chains and 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl) tetrabenzoic acid as a photosensitizer ligand, the combination of highly mobile photogenerated electrons and a strong hole localization at the organic linker results in large charge-separation lifetimes. The suitable energies for band gap and conduction band minimum (CBM) offer great potential for a wide range of photocatalytic reactions, from hydrogen evolution to the selective oxidation of organic substrates.

5.
Artigo em Inglês | MEDLINE | ID: mdl-32188247

RESUMO

Pressure-induced amorphization is one of the processes inhibiting functional properties of metal-organic frameworks (MOFs). Such amorphization often occurs when MOFs are being shaped for practical applications, as well as during certain exploitations. Typically, the porosity of MOFs, which is crucial for sorption, separation, and catalysis, suffers under external pressure. We report a new experimental approach for efficient monitoring of pressure-induced processes in MOFs that employs trace amounts of spin probes (stable nitroxide radicals) embedded in the pores of MOF and detection by electron paramagnetic resonance (EPR). EPR spectra of spin probes in MOF ZIF-8 demonstrate significant changes upon pressure-induced amorphization, whose extent can be quantitatively determined from the spectral shapes. Moreover, stabilization of ZIF-8 against amorphization via reversible adsorption of various guests was studied using this approach. Mitigation effect depends on diffusion parameters and localization of guest molecules in the cavity, and maintaining of the structure and permeability up to 80% was achieved even at 1.15 GPa applied. Therefore, the proposed methodology allows significant mitigation of MOF amorphization under external pressure and conveys further perspectives of the controlled adjustment of stabilizing agents for various MOFs and their applications.

6.
Inorg Chem ; 59(3): 2037-2050, 2020 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-31971794

RESUMO

Cu-modified zeolites have enormous potential as the catalysts facilitating the conversion of methane to methanol. It becomes important to investigate the active sites and the reaction mechanisms involved. In this paper, several spectroscopic methods such as UV-vis diffuse reflectance spectroscopy (UV-vis DRS), pulse electron paramagnetic resonance (EPR), diffuse reflectance Fourier transform infrared spectroscopy, and solid-state (13C MAS) NMR have been employed to characterize the state of the Cu sites and the intermediates formed during the catalyst activation and methane-to-methanol transformation on Cu/H-ZSM-5 zeolite with low (0.10 wt %) Cu content. UV-vis DRS and EPR data imply the presence of two types of Cu2+ cations bound to the zeolite framework Si-O--Al sites (Z). One of them is a species of the type Z[Cu(II)O] or Z[Cu(II)(OH)] with extra-framework O- or OH- ligands. The other one refers to Z2Cu(II) species without extra-framework O-containing ligands. CW EPR studies reveal that the Z2Cu(II) species are the major part of the Cu(II) sites present in the zeolite. 1H HYSCORE and DRIFTS data are supportive of the formation of a molecular complex of methane and Z2Cu(II) species, with a strongly polarized C-H bond and a 3.3 Å separation between the hydrogen atom of methane and Cu. 13C MAS NMR provides evidence for the formation of both the surface methoxy intermediate and physisorbed methanol. It is suggested that experimentally identified Z[Cu(II)O] or Z[Cu(II)(OH)] are those sites that provide a homolytic cleavage of the methane C-H bond to yield surface bound methoxy species and/or methanol molecule, the possibility that has been recently justified with density functional theory ( Kulkarni et al. Catal. Sci. Technol. 2018 , 8 , 114 ). The comparison of the amount of the surface methoxy intermediates formed and the number of different Cu(II) sites present in the zeolite allowed us to conclude the involvement of Z2Cu(II) sites in methane C-H bond activation. The mechanism of methane activation on Z2Cu(II) sites has been proposed. It includes two steps: (1) the formation of the molecular complex of methane with Z2Cu(II); (2) heterolytic dissociation of the polarized C-H bond affording surface copper(II) hydride and methoxy species, both bound to zeolite framework Si-O--Al sites.

7.
Chemistry ; 26(12): 2705-2712, 2020 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-31851392

RESUMO

Trityl radicals (TAMs) have recently appeared as an alternative source of spin labels for measuring long distances in biological systems. Finland trityl radical (FTAM) served as the basis for this new generation of spin labels, but FTAM is rather lipophilic and susceptible to self-aggregation, noncovalent binding with lipophilic sites of proteins, and noncovalent docking at the termini of duplex DNA. In this paper the very hydrophilic OX063 TAM with very low toxicity and little tendency for aggregation is used as the basis for a spin label. Human serum albumin (HSA) labeled with OX063 has an intense narrow line typical of TAM radicals in solution, whereas HSA labeled with FTAM shows broad lines and extensive aggregation. In pulse EPR measurements, the measured phase memory time TM for HSA labeled with OX063 is 6.3 µs at 50 K, the longest yet obtained with a TAM-based spin label. The lowered lipophilicity also decreases side products in the labeling reaction.


Assuntos
Indicadores e Reagentes/química , Mesilatos/química , Albumina Sérica Humana/química , Compostos de Sulfidrila/química , Espectroscopia de Ressonância de Spin Eletrônica , Interações Hidrofóbicas e Hidrofílicas , Estrutura Molecular , Marcadores de Spin , Relação Estrutura-Atividade , Temperatura
8.
Beilstein J Org Chem ; 15: 2664-2670, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31807201

RESUMO

The unexpected formation of a highly strained polycyclic amine was observed in a one-pot synthesis from cyclopentanone, dimethyl fumarate and ammonium acetate. This multistep reaction includes 1,3-dipolar cycloaddition of dimethyl fumarate to the cyclic azomethine ylide formed in situ from cyclopentanone and ammonia. The polycyclic amine product was easily converted into a sterically shielded polycyclic nitroxide. The EPR spectra and spin relaxation behavior of the nitroxide were studied in solution. The spin relaxation seems well suited for the use as a biological spin label and are comparable with those of cyclic nitroxides with two spirocyclic moieties adjacent to the N-O · group.

9.
Molecules ; 24(24)2019 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-31847326

RESUMO

Vanadium(IV) complexes are actively studied as potential candidates for molecular spin qubits operating at room temperatures. They have longer electron spin decoherence times than many other transition ions, being the key property for applications in quantum information processing. In most cases reported to date, the molecular complexes were optimized through the design for this purpose. In this work, we investigate the relaxation properties of vanadium(IV) ions incorporated in complexes with lanthanides using electron paramagnetic resonance (EPR). In all cases, the VO6 moieties with no nuclear spins in the first coordination sphere are addressed. We develop and implement the approaches for facile diagnostics of relaxation characteristics in individual VO6 moieties of such compounds. Remarkably, the estimated relaxation times are found to be close to those of other vanadium-based qubits obtained previously. In the future, a synergistic combination of qubit-friendly properties of vanadium ions with single-molecule magnetism and luminescence of lanthanides can be pursued to realize new functionalities of such materials.


Assuntos
Complexos de Coordenação/química , Espectroscopia de Ressonância de Spin Eletrônica , Elementos da Série dos Lantanídeos/química , Fenômenos Magnéticos , Vanádio/química , Algoritmos , Complexos de Coordenação/síntese química , Hidrogênio , Modelos Teóricos , Conformação Molecular , Transição de Fase
10.
Nucleic Acids Res ; 47(22): 11850-11860, 2019 12 16.
Artigo em Inglês | MEDLINE | ID: mdl-31724718

RESUMO

The features of previously unexplored labile complexes of human 40S ribosomal subunits with RNAs, whose formation is manifested in the cross-linking of aldehyde derivatives of RNAs to the ribosomal protein uS3 through its peptide 55-64 located outside the mRNA channel, were studied by EPR spectroscopy methods. Analysis of subatomic 40S subunit models showed that a likely site for labile RNA binding is a cluster of positively charged amino acid residues between the mRNA entry site and uS3 peptide 55-64. This is consistent with our finding that the 3'-terminal mRNA fragment hanging outside the 40S subunit prevents the cross-linking of an RNA derivative to this peptide. To detect labile complexes of 40S subunits with RNA by DEER/PELDOR spectroscopy, an undecaribonucleotide derivative with nitroxide spin labels at terminal nucleotides was utilized. We demonstrated that the 40S subunit channel occupancy with mRNA does not affect the RNA derivative binding and that uS3 peptide 55-64 is not involved in binding interactions. Replacing the RNA derivative with a DNA one revealed the importance of ribose 2'-OH groups for the complex formation. Using the single-label RNA derivatives, the distance between the mRNA entry site and the loosely bound RNA site on the 40S subunit was estimated.

11.
Materials (Basel) ; 12(23)2019 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-31771118

RESUMO

The d-group Kramers ions, having strong zero field splitting (ZFS) with axial symmetry and a negative D value for the ZFS Hamiltonian, are widely considered as candidates for use as single molecular magnets (SMMs). An important need is the means to switch the SMM between its states in a reasonably short and predictable period of time, which is generally not available. We propose an approach, Zeeman-far infrared (ZeFIR) double resonance, in which circularly polarized alternating magnetic fields in the far infrared (FIR) range induce selective magnetic dipole transitions between different Kramers doublets of the SMM and polarized microwave (mw) pulses transfer excitation inside the upper Kramers doublet. A combination of FIR and mw pulses allows unidirectional switching between +S and -S states of the ion. The proposed approach is considered for a model quartet system with total spin S = 3/2, which seems to be the most promising object for selective resonance manipulations of its states by circularly polarized radiation.

12.
J Phys Chem B ; 123(46): 9956-9962, 2019 11 21.
Artigo em Inglês | MEDLINE | ID: mdl-31651169

RESUMO

Ionic liquids (ILs) show a variety of unusual and intriguing properties on a molecular level. Recently, a new type of structural anomaly occurring in neat ILs near their glass transition temperatures (Tg) has been found. In particular, the coexistence of two types of IL environments was observed, one of which progressively suppresses the molecular mobility upon temperature increase within ∼(Tg-60 K) and Tg. To clarify the nature of these anomalies, their general characteristics, and potential for applications, in this work we investigated the molecular mobility in binary mixtures of IL [Bmim]BF4 with water using electron paramagnetic resonance spectroscopy and spin probes (stable nitroxides TEMPO-D18, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, and 14-carbamoyl-7-azadispiro[5.1.5.2]pentadeca-14-ene-7-oxyl). In a series of such mixtures with water content xH2O = 0.2-50 wt %, we detected similar anomalies to those found in neat IL (xH2O = 0). For xH2O < 2.5 wt %, the differences in manifestations of structural anomalies are negligible compared to those in neat ILs. In the range 2.5 ≤ xH2O < 5 wt %, an abrupt partial suppression of anomaly is observed, but further increase of the water content up to xH2O = 50 wt % has no impact on anomaly since, most plausibly, it leads only to the growth of the water-rich domains. Consequently, the observed structural anomalies are rather robust against the presence of water in ILs, which is beneficial for their potential applications.

13.
Materials (Basel) ; 12(19)2019 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-31547101

RESUMO

The Novosibirsk Free Electron Laser (NovoFEL) facility is able to produce high-power tunable terahertz (THz) laser radiation in quasi-continuous mode. The ability to control/shape this THz radiation is required in a number of user experiments. In this work we propose a modulation approach suitable for free electron lasers based on recuperation design. It allows for generating THz macropulses of a desirable length, down to several microseconds (limited by a quality factor of FEL optical resonator). Using this approach, macropulses in the time window from several microseconds to several hundred microseconds have been shown for three possible frequency ranges: mid-infrared (~1100 cm-1), far-infrared (~200 cm-1) and THz (~40 cm-1). In each case, the observed rise and decay of the macropulse have been measured and interpreted. The advantage of using short macropulses at the maximum peak power available has been demonstrated with the time-resolved Electron Paramagnetic Resonance (EPR) spectroscopy.

14.
Front Pharmacol ; 10: 953, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31555136

RESUMO

Voltage-gated sodium (NaV) channels are essential for the normal functioning of cardiovascular, muscular, and nervous systems. These channels have modular organization; the central pore domain allows current flow and provides ion selectivity, whereas four peripherally located voltage-sensing domains (VSDs-I/IV) are needed for voltage-dependent gating. Mutations in the S4 voltage-sensing segments of VSDs in the skeletal muscle channel NaV1.4 trigger leak (gating pore) currents and cause hypokalemic and normokalemic periodic paralyses. Previously, we have shown that the gating modifier toxin Hm-3 from the crab spider Heriaeus melloteei binds to the S3-S4 extracellular loop in VSD-I of NaV1.4 channel and inhibits gating pore currents through the channel with mutations in VSD-I. Here, we report that Hm-3 also inhibits gating pore currents through the same channel with the R675G mutation in VSD-II. To investigate the molecular basis of Hm-3 interaction with VSD-II, we produced the corresponding 554-696 fragment of NaV1.4 in a continuous exchange cell-free expression system based on the Escherichia coli S30 extract. We then performed a combined nuclear magnetic resonance (NMR) and electron paramagnetic resonance spectroscopy study of isolated VSD-II in zwitterionic dodecylphosphocholine/lauryldimethylamine-N-oxide or dodecylphosphocholine micelles. To speed up the assignment of backbone resonances, five selectively 13C,15N-labeled VSD-II samples were produced in accordance with specially calculated combinatorial scheme. This labeling approach provides assignment for ∼50% of the backbone. Obtained NMR and electron paramagnetic resonance data revealed correct secondary structure, quasi-native VSD-II fold, and enhanced ps-ns timescale dynamics in the micelle-solubilized domain. We modeled the structure of the VSD-II/Hm-3 complex by protein-protein docking involving binding surfaces mapped by NMR. Hm-3 binds to VSDs I and II using different modes. In VSD-II, the protruding ß-hairpin of Hm-3 interacts with the S1-S2 extracellular loop, and the complex is stabilized by ionic interactions between the positively charged toxin residue K24 and the negatively charged channel residues E604 or D607. We suggest that Hm-3 binding to these charged groups inhibits voltage sensor transition to the activated state and blocks the depolarization-activated gating pore currents. Our results indicate that spider toxins represent a useful hit for periodic paralyses therapy development and may have multiple structurally different binding sites within one NaV molecule.

15.
Nano Lett ; 19(9): 6506-6510, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31449756

RESUMO

Metal-organic frameworks (MOFs) are the promising nanomaterials for separation of molecules with close dimensions and structures, such as various types of isomers. The efficiency of separation can be greatly enhanced if the apertures of the nanosized windows, controlling the diffusion of a particular molecule inside the cavities, are fine-tuned by external stimuli. We report the new approach for precise measurement of window sizes in ZIF-8 MOF and employ it in efficient separation of xylenes, which is of high practical importance. For this sake, we synthesized ZIF-8 with embedded stable nitroxides in the pores and applied electron paramagnetic resonance spectroscopy for in situ kinetic measurement of the diffusion of various guest molecules through the material. Slight variation of temperature within 298-333 K allowed tuning of the windows and reaching optimum conditions for separation of p-, m-, and o-xylenes with the efficiency up to 92-95%. The developed methodology provides deeper understanding of steric and kinetic aspects of molecular diffusion in ZIF-8 and paves the way to rational optimization of other MOF-based separation applications.

16.
Nucleic Acids Res ; 47(15): 7767-7780, 2019 09 05.
Artigo em Inglês | MEDLINE | ID: mdl-31329919

RESUMO

A DNA molecule is under continuous influence of endogenous and exogenous damaging factors, which produce a variety of DNA lesions. Apurinic/apyrimidinic sites (abasic or AP sites) are among the most common DNA lesions. In this work, we applied pulse dipolar electron paramagnetic resonance (EPR) spectroscopy in combination with molecular dynamics (MD) simulations to investigate in-depth conformational changes in DNA containing an AP site and in a complex of this DNA with AP endonuclease 1 (APE1). For this purpose, triarylmethyl (TAM)-based spin labels were attached to the 5' ends of an oligonucleotide duplex, and nitroxide spin labels were introduced into APE1. In this way, we created a system that enabled monitoring the conformational changes of the main APE1 substrate by EPR. In addition, we were able to trace substrate-to-product transformation in this system. The use of different (orthogonal) spin labels in the enzyme and in the DNA substrate has a crucial advantage allowing for detailed investigation of local damage and conformational changes in AP-DNA alone and in its complex with APE1.


Assuntos
DNA Liase (Sítios Apurínicos ou Apirimidínicos)/química , DNA/química , Oligonucleotídeos/química , Marcadores de Spin/síntese química , Sequência de Bases , Sítios de Ligação , Clonagem Molecular , DNA/genética , DNA/metabolismo , Dano ao DNA , DNA Liase (Sítios Apurínicos ou Apirimidínicos)/genética , DNA Liase (Sítios Apurínicos ou Apirimidínicos)/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica , Escherichia coli/genética , Escherichia coli/metabolismo , Expressão Gênica , Vetores Genéticos/química , Vetores Genéticos/metabolismo , Humanos , Simulação de Dinâmica Molecular , Conformação de Ácido Nucleico , Oligonucleotídeos/metabolismo , Ligação Proteica , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre Proteínas , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Especificidade por Substrato
17.
Angew Chem Int Ed Engl ; 58(38): 13271-13275, 2019 09 16.
Artigo em Inglês | MEDLINE | ID: mdl-31322814

RESUMO

Precise nanoscale distance measurements by pulsed electron paramagnetic resonance (EPR) spectroscopy play a crucial role in structural studies of biomolecules. The properties of the spin labels used in this approach determine the sensitivity limits, attainable distances, and proximity to biological conditions. Herein, we propose and validate the use of photoexcited fullerenes as spin labels for pulsed dipolar (PD) EPR distance measurements. Hyperpolarization and the narrower spectrum of fullerenes compared to other triplets (e.g., porphyrins) boost the sensitivity, and superior relaxation properties allow PD EPR measurements up to a near-room temperature. This approach is demonstrated using fullerene-nitroxide and fullerene-triarylmethyl pairs, as well as a supramolecular complex of fullerene with nitroxide-labeled protein. Photoexcited triplet fullerenes can be considered as new spin labels with outstanding spectroscopic properties for future structural studies of biomolecules.

18.
Dalton Trans ; 48(28): 10723-10732, 2019 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-31246209

RESUMO

The new bis-o-iminobenzosemiquinonate nickel and cobalt complexes (imSQt-Bu)2M (M = Ni (1), Co (2)), where imSQ is a radical anion of 4,6-di-tert-butyl-N-(tert-butyl)-o-iminobenzoquinone, were synthesized and characterized in detail. The molecular structures of 1 and 2 have been established by single-crystal X-ray analysis. The metal atoms in 1 and 2 have a distorted tetrahedral environment, and the dihedral angles between the planes of two radical imSQ ligands are approximately 80° in both complexes. According to the structural and spectroscopy data along with magnetic susceptibility measurements the electronic structure of the complexes should be interpreted definitely as a high spin metal center NiII (d8, S = 1) in 1 and CoII (d7, S = 3/2) in 2 bonded with two o-iminobenzosemiquinonate radicals (Srad = 1/2). The strong antiferromagnetic metal-ligand spin interactions in both complexes lead to the observed St = 0 and St = 1/2 ground states in 1 and 2, respectively. The computational DFT UB3LYP/6-311++G(d,p) studies performed on 1 and 2 are in good agreement with experimental data. Complexes 1 and 2 have similar electrochemical properties. The electrochemical reduction of the complexes includes two quasi-reversible one-electron-transfer waves in the cathodic region corresponding to the formation of the anions [M(AP)2]2- and [(imSQ)M(AP)]1- (AP - dianion of 4,6-di-tert-butyl-N-(tert-butyl)-o-iminobenzoquinone), while in the anodic region only one quasi-reversible redox process was registered. All redox processes are shown to be ligand-based.

19.
Inorg Chem ; 58(13): 8471-8479, 2019 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-31184867

RESUMO

Nanosized structural defects in metal-organic frameworks (MOFs) attract growing attention and often remarkably enhance functional properties of these materials for various applications. In this work, a series of MOFs [Cu2(TPTA)1- x(BDPBTR) x] (H4TPTA, [1,1':3',1″-terphenyl]-3,3'',5,5''-tetracarboxylic acid; H4BDPBTR, 1,3-bis(3,5-dicarboxyphenyl)-1,2,4-benzotriazin-4-yl radical)) with a new stable radical linker doped into the structure has been synthesized and investigated using Electron Paramagnetic Resonance (EPR). Mixed linkers H4TPTA and H4BDPBTR were used to bridge copper(II) paddle-wheel units into a porous framework, where H4BDPBTR is the close structural analogue of H4TPTA. MOFs with various x = 0-0.4 were investigated. EPR studies indicated that the radical linker binds to the copper(II) units differently compared to diamagnetic linker, resulting in the formation of nanosized structural defects. Moreover, remarkable kinetic phenomena were observed upon cooling of this MOF, where slow structural rearrangements and concomitant changes of magnetic interactions were induced. Thus, our findings demonstrate that doping of structurally mimicking radical linkers into MOFs represents an efficient approach for designing target nanosized defects and introducing new magnetostructural functionalities for a variety of applications.

20.
Inorg Chem ; 58(10): 6811-6820, 2019 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-31067041

RESUMO

Two new isostructural microporous coordination frameworks [Mn3(Hpdc)2(pdc)2] (1) and [Mg3(Hpdc)2(pdc)2] (2) (pdc2- = pyridine-2,4-dicarboxylate) showing primitive cubic (pcu) topology have been prepared and characterized. The pore aperture of the channels is too narrow for the efficient adsorption of N2; however, both compounds demonstrate substantially higher uptake of CO2 (119.9 mL·g-1 for 1 and 102.5 mL·g-1 for 2 at 195 K, 1 bar). Despite of their structural similarities, 2 shows a typical reversible type I isotherm for adsorption/desorption of CO2, while 1 features a two-step adsorption process with a very broad hysteresis between the adsorption and desorption curves. This behavior can be explained by a combination of density functional theory calculations, sorption, and X-ray diffraction analysis and gives insights into the further development of new sorbents showing adsorption/desorption hysteresis.

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