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1.
Inorg Chem ; 2020 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-32338886

RESUMO

The thermal hysteresis in the cooperative spin crossover (SCO) polymer [Fe(trz)(Htrz)2]n[BF4]n (1) has been tuned by a simple ball milling grinding process. Mechanical treatment affects the size and morphology of the crystallite domains, as confirmed by multiple complementary techniques, including ESEM, DLS, and PXRD data. Upon milling, the regular cubic shape particles recrystallize with slightly different unit cell parameters and preferential orientation. This macroscopic change significantly modifies the thermally induced SCO behavior, studied by temperature-dependent magnetic susceptibility, X-ray diffraction, and DSC analysis. Transition temperatures downshift, closer to room temperature, while hysteresis widens, when particle sizes are actually decreasing. We relate this counterintuitive observation to subtle modifications in the unit cell, offering new alternatives to tune and enhance SCO properties in this class of 1D-cooperative polymers.

2.
J Phys Chem Lett ; 10(21): 6672-6678, 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31608645

RESUMO

Bismuth vanadate (BiVO4) has emerged as one of the most promising photoanode materials for solar fuel production. Oxygen vacancies play a pivotal role in the photoelectrochemical efficiency, yet their electronic nature and contribution to  n-type conductivity are still under debate. Using first-principles calculations, we show that oxygen vacancies in BiVO4 have two distinguishable geometric configurations characterized by either undercoordinated, reduced VIVO3 and BiIIO7 subunits or a VIV-O-VIV/V bridge (split vacancy), quenching the oxygen vacancy site. While both configurations have similar energies in the bulk, the (001) subsurface acts like an energetic sink that stabilizes the split oxygen vacancy by ∼1 eV. The barrierless creation of a bridging V2O7 unit allows for partial electron delocalization throughout the near-surface region, consistent with recent experimental observations indicating that BiVO4(001) is an electron-rich surface.

3.
J Am Chem Soc ; 141(36): 14306-14316, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31426632

RESUMO

Selective separation of enantiomers is a substantial challenge for the pharmaceutical industry. Chromatography on chiral stationary phases is the standard method, but at a very high cost for industrial-scale purification due to the high cost of the chiral stationary phases. Typically, these materials are poorly robust, expensive to manufacture, and often too specific for a single desired substrate, lacking desirable versatility across different chiral analytes. Here, we disclose a porous, robust homochiral metal-organic framework (MOF), TAMOF-1, built from copper(II) and an affordable linker prepared from natural l-histidine. TAMOF-1 has shown to be able to separate a variety of model racemic mixtures, including drugs, in a wide range of solvents of different polarity, outperforming several commercial chiral columns for HPLC separations. Although not exploited in the present article, it is worthy to mention that the preparation of this new material is scalable to the multikilogram scale, opening unprecedented possibilities for low-energy chiral separation at the industrial scale.

4.
Inorg Chem ; 58(17): 11308-11316, 2019 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-31411866

RESUMO

The 9-cobalt(II)-containing trimeric, cyclic polyanion [Co9(OH)3(H2O)6(PO4)2(B-α-GeW9O34)3]21- (1) was synthesized in an aqueous phosphate solution at pH 8 and isolated as a hydrated mixed sodium-cesium salt. Polyanion 1 was structurally and compositionally characterized in the solid state by single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, as well as thermogravimetric and elemental analyses. The magnetic and electrochemical properties of 1 were also studied and compared with those of its phosphorus analogue, [Co9(OH)3(H2O)6(HPO4)2(B-α-PW9O34)3]16- (Co9-P). The electrochemical water oxidation activity of the cesium salt of 1 under heterogeneous conditions was also studied and shown to be superior to that of Co9-P. The experimental results were supported by computational studies.

5.
Acta Crystallogr C Struct Chem ; 74(Pt 11): 1180-1181, 2018 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-30398170
6.
Front Chem ; 6: 537, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30467538

RESUMO

Chiral bipyrimidine-bridged dinuclear LnIII complexes of general formula [(µ-bipym){((+)-tfacam)3Ln}2] and [(µ-bipym){((-)-tfacam)3Ln}2], have been prepared from the assembly of Ln(AcO)3·nH2O (LnIII = Dy, Gd), (+)/(-)-3-(trifluoroacetyl)camphor enantiopure ligands ((+)/(-)-Htfacam) and bipyrimidine (bipym). The structure and chirality of these complexes have been supported by single-crystal X-Ray diffraction and circular dichroism. The study of the magnetic properties of the GdIII complexes revealed a very weak antiferromagnetic interaction between the GdIII ions through the bipyrimidine bridging ligand. Ab initio CASSCF calculations indicated that the ground Kramers doublet (KD) of both DyIII centers is almost purely axial with the anisotropy axis located close to the two tfacam-ligands at opposite sides of each DyIIIatom, which create an axial crystal field. In keeping with this, ac dynamic measurements indicated slow relaxation of the magnetization at zero field with U eff = 55.1 K, a pre-exponential factor of τo = 2.17·10-6 s and τQTM = 8 µs. When an optimal dc field of 0.1 T is applied, QTM is quenched and U eff increases to 75.9 K with τo = 6.16 × 10-7 s. The DyN2O8 coordination spheres and SMM properties of [(µ-bipym){((+)-tfacam)3Ln}2] and their achiral [(Dy(ß-diketonate)3)2(µ-bpym)]analogous have been compared and a magneto-structural correlation has been established, which has been supported by theoretical calculations. In contrast to the GdIII compounds, the magnetic exchange interaction between the DyIII ions has been calculated to be very weak and, generally, ferromagnetic in nature. Relaxation mechanisms for [(µ-bipym){((+)-tfacam)3Ln}2] and previously reported analogous have been proposed from ab initio calculations. As the magnetic exchange interaction found to be very weak, the observed magnetization blockade in these systems are primarily dictated by the single ion anisotropy of DyIII ions.

7.
J Am Chem Soc ; 140(38): 12040-12055, 2018 09 26.
Artigo em Inglês | MEDLINE | ID: mdl-30204436

RESUMO

A series of six exemplary cobalt-polyoxometalate (Co-POM) precatalysts have been examined to determine if they are molecular water-oxidation catalysts (WOCatalysts) or if, instead, they actually form heterogeneous, electrode-bound CoO x as the true WOCatalyst under electrochemically driven water-oxidation catalysis (WOCatalysis) conditions. Specifically, WOCatalysis derived from the following six Co-POMs has been examined at pH 5.8, 8.0, and 9.0: [Co4(H2O)2(PW9O34)2]10- (Co4P2W18), [Co9(H2O)6(OH)3(HPO4)2(PW9O34)3]16- (Co9P5W27), [ ßß-Co4(H2O)2(P2W15O56)2]16- (Co4P4W30), [Co(H2O)PW11O39]5- (CoPW11), [α1-Co(H2O)P2W17O61]8- (α1-CoP2W17), and [α2-Co(H2O)P2W17O61]8- (α2-CoP2W17). The amount of Co(II)aq in 500 µM solutions of each Co-POM was measured after 3 h of aging as well as from t = 0 for pH = 5.8 and 8.0 by µM sensitive Co(II)aq-induced 31P NMR line broadening and at pH = 9.0 by cathodic stripping. The amount of detectable Co(II)aq after 3 h for the six Co-POMs ranges from ∼0.25 to ∼90% of the total cobalt initially present in the Co-POM. For 12 out of 18 total Co-POM and different pH cases, the amount Co(II)aq detected after 3 h forms heterogeneous CoO x able to account for ≥100% of the observed WOCatalysis activity. However, under 0.1 M NaPi, pH 5.8 conditions for CoPW11 and α1-CoP2W17 where ∼1.5% and 0.25% Co(II)aq is detectable, the measured Co(II)aq cannot account for the observed WOCatalysis. The implication is that these two Co-POMs are primarily molecular, Co-POM-based, WOCatalysts under electrochemically driven, pH 5.8, phosphate-buffer conditions. Even for the single most stable Co-POM, α1-CoP2W17, CoO x is still an estimated ∼76× faster WOCatalyst at pH = 5.8 and an estimated ∼740× faster WOCatalyst at pH = 8.

8.
J Am Chem Soc ; 140(39): 12611-12621, 2018 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-30198265

RESUMO

The mixed-valence FeIIFeIII 2D coordination polymer formulated as [TAG][FeIIFeIII(ClCNAn)3]·(solvate) 1 (TAG = tris(amino)-guanidinium, ClCNAn2- = chlorocyanoanilate dianionic ligand) crystallized in the polar trigonal space group P3. In the solid-state structure, determined both at 150 and at 10 K, anionic 2D honeycomb layers [FeIIFeIII(ClCNAn)3]- establish in the ab plane, with an intralayer metal-metal distance of 7.860 Å, alternating with cationic layers of TAG. The similar Fe-O distances suggest electron delocalization and an average oxidation state of +2.5 for each Fe center. The cation imposes its C3 symmetry to the structure and engages in intermolecular N-H···Cl hydrogen bonding with the ligand. Magnetic susceptibility characterization indicates magnetic ordering below 4 K and the presence of a hysteresis loop at 2 K with a coercive field of 60 Oe. Mössbauer measurements are in agreement with the existence of Fe(+2.5) ions at RT and statistic charge localization at 10 K. The compound shows semiconducting behavior with the in-plane conductivity of 2 × 10-3 S/cm, 3 orders of magnitude higher than the perpendicular one. A small-polaron hopping model has been applied to a series of oxalate-type FeIIFeIII 2D coordination polymers, providing a clear explanation on the much higher conductivity of the anilate-based systems than the oxalate ones.

9.
Nat Catal ; 1(3): 208-213, 2018 Mar 08.
Artigo em Inglês | MEDLINE | ID: mdl-30079397

RESUMO

Water oxidation is a key reaction for the conversion of solar energy into chemical fuels, but effective water-oxidation catalysts are often based on rare and costly precious metals such as Pt, Ir or Ru. Developing strategies based on earth-abundant metals is important to explore critical aspects of this reaction, and to see whether different and more efficient applications are possible for energy systems. Herein, we present an approach to tuning a redox-active electrocatalyst based on the doping of molybdenum into the tungsten framework of [Co4(H2O)2(PW9O34)2]10-, known as the Weakley sandwich. The Mo-doped framework was confirmed by X-ray crystallography, electrospray ionization mass spectrometry and inductively coupled plasma optical emission spectrometry studies. The doping of molybdenum into the robust Weakley sandwich framework leads to the oxidation of water at a low onset potential, and with no catalyst degradation, whereby the overpotential of the oxygen evolution reaction is lowered by 188 mV compared with the pure tungsten framework.

10.
Dalton Trans ; 47(34): 11960-11967, 2018 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-30074599

RESUMO

Prussian blue analogs (PBAs) are versatile materials with a wide range of applications. Due to their tunability, intrinsic biocompatibility, as well as low toxicity, these nanoscale coordination polymers have been successfully studied as multimodal contrast agents for multiple imaging techniques. Herein, we report the expanded biomedical application of PBAs to X-ray computed tomography (CT). In our systematic study of the series A{MnII[FeIII(CN)6]} (A = K+, Rb+, Cs+), we showed that derivatives incorporating Rb+ and Cs+ ions in the tetrahedral sites of the parent face-centered cubic cyano-bridged networks exhibited substantially increased X-ray attenuation coefficients, thus yielding significant contrast compared to the clinically approved X-ray contrast agent iohexol at the same concentrations. Additionally, our µ-CT studies revealed that these PBAs could be useful as dual-energy CT contrast agents for different biological specimens by using the lower varying scanning X-ray tube voltages. Finally, in vitro studies using U87-Luc cells treated with PBAs, including cellular CT imaging and bioluminescence cell viability assays, revealed that PBAs were taken up by the glioblastoma cells, with moderate biocompatibility at concentrations below the mM range.

11.
Inorg Chem ; 57(12): 7077-7089, 2018 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-29877697

RESUMO

The magnetic behavior and electric properties of the hybrid radical salt [BEDT-TTF]2[CuCl4] have been revisited through extended experimental analyses and DDCI and periodic DFT plane waves calculations. Single crystal X-ray diffraction data have been collected at different temperatures, discovering a phase transition occurring in the 250-300 K range. The calculations indicate the presence of intradimer, interdimer, and organic-inorganic π-d interactions in the crystal, a magnetic pattern much more complex than the Bleaney-Bowers model initially assigned to this material. Although this simple model was good enough to reproduce the magnetic susceptibility data, our calculations demonstrate that the actual magnetic structure is significantly more intricate, with alternating antiferromagnetic 1D chains of the organic BEDT-TTF+ radical, connected through weak antiferromagnetic interactions with the CuCl42- ions. Combination of experiment and theory allowed us to unambiguously determine and quantify the leading magnetic interactions in the system. The density-of-states curves confirm the semiconductor nature of the system and the dominant organic contribution of the valence and conduction band edges. This general and combined approach appears to be fundamental in order to properly understand the magnetic structure of these complex materials, where experimental data can actually be fitted from a variety of models and parameters.

12.
Dalton Trans ; 47(34): 11895-11902, 2018 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-29923570

RESUMO

The magnetic behavior of the polyanion [Fe3(µ-L)6(H2O)6]6- (L2- = (1,2,4-triazol-4-yl)ethanedisulfonate) as the corresponding dimethylammonium salt shows memory effect above room temperature, with a dynamic thermal hysteresis cycle over 90 K and temperature-induced excited spin state trapping (TIESST) phenomena at the highest temperatures reported. Taking advantage of the polyanionic nature of this trimetallic complex, we were able to substitute the dimethylammonium cations by the monovalent heavy alkali metal cesium. This methathesis yielded the salt Cs6[Fe3(µ-L)6(H2O)6], with different molecular packing that increases the number and strength of cation-anion interactions, including a more robust H-bonded network. In this phase, the spin transition still occurs above room temperature, but it is more abrupt and narrow (≈50 K wide hysteresis). Despite these differences, TIESST is observed with almost identical characteristic temperature (TTIESST = 240 K) than in the parent compound, which is an additional experimental evidence supporting the molecular origin of the TIESST behavior in these materials.

13.
ChemSusChem ; 10(22): 4552-4560, 2017 11 23.
Artigo em Inglês | MEDLINE | ID: mdl-28967707

RESUMO

The realization of artificial photosynthesis may depend on the efficient integration of photoactive semiconductors and catalysts to promote photoelectrochemical water splitting. Many efforts are currently devoted to the processing of multicomponent anodes and cathodes in the search for appropriate synergy between light absorbers and active catalysts. No single material appears to combine both features. Many experimental parameters are key to achieve the needed synergy between both systems, without clear protocols for success. Herein, we show how computational chemistry can shed some light on this cumbersome problem. DFT calculations are useful to predict adequate energy-level alignment for thermodynamically favored hole transfer. As proof of concept, we experimentally confirmed the limited performance enhancement in hematite photoanodes decorated with cobalt hexacyanoferrate as a competent water-oxidation catalyst. Computational methods describe the misalignment of their energy levels, which is the origin of this mismatch. Photoelectrochemical studies indicate that the catalyst exclusively shifts the hematite surface state to lower potentials, which therefore reduces the onset for water oxidation. Although kinetics will still depend on interface architecture, our simple theoretical approach may identify and predict plausible semiconductor/catalyst combinations, which will speed up experimental work towards promising photoelectrocatalytic systems.


Assuntos
Processos Fotoquímicos , Fotólise , Semicondutores , Água/química , Catálise , Eletroquímica/métodos , Eletrodos , Compostos Férricos/química , Ferrocianetos/química , Oxirredução , Termodinâmica
14.
ACS Appl Mater Interfaces ; 9(43): 37671-37681, 2017 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-28975785

RESUMO

The efficient integration of photoactive and catalytic materials is key to promoting photoelectrochemical water splitting as a sustainable energy technology built on solar power. Here, we report highly stable water splitting photoanodes from BiVO4 photoactive cores decorated with CoFe Prussian blue-type electrocatalysts (CoFe-PB). This combination decreases the onset potential of BiVO4 by ∼0.8 V (down to 0.3 V vs reversible hydrogen electrode (RHE)) and increases the photovoltage by 0.45 V. The presence of the catalyst also leads to a remarkable 6-fold enhancement of the photocurrent at 1.23 V versus RHE, while keeping the light-harvesting ability of BiVO4. Structural and mechanistic studies indicate that CoFe-PB effectively acts as a true catalyst on BiVO4. This mechanism, stemming from the adequate alignment of the energy levels, as showed by density functional theory calculations, allows CoFe-PB to outperform all previous catalyst/BiVO4 junctions and, in addition, leads to noteworthy long-term stability. A bare 10-15% decrease in photocurrent was observed after more than 50 h of operation under light irradiation.

15.
J Am Chem Soc ; 138(49): 16037-16045, 2016 12 14.
Artigo em Inglês | MEDLINE | ID: mdl-27960335

RESUMO

The development of upscalable oxygen evolving electrocatalysts from earth-abundant metals able to operate in neutral or acidic environments and low overpotentials remains a fundamental challenge for the realization of artificial photosynthesis. In this study, we report a highly active phase of heterobimetallic cyanide-bridged electrocatalysts able to promote water oxidation under neutral, basic (pH < 13), and acidic conditions (pH > 1). Cobalt-iron Prussian blue-type thin films, formed by chemical etching of Co(OH)1.0(CO3)0.5·nH2O nanocrystals, yield a dramatic enhancement of the catalytic performance toward oxygen production, when compared with previous reports for analogous materials. Electrochemical, spectroscopic, and structural studies confirm the excellent performance, stability, and corrosion resistance, even when compared with state-of-the-art metal oxide catalysts under moderate overpotentials and in a remarkably large pH range, including acid media where most cost-effective water oxidation catalysts are not useful. The origin of the superior electrocatalytic activity toward water oxidation appears to be in the optimized interfacial matching between catalyst and electrode surface obtained through this fabrication method.

16.
Inorg Chem ; 55(24): 12851-12862, 2016 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-27989203

RESUMO

Prussian blue and its related compounds are formed by cheap and abundant metals and have shown their importance in the generation of new fuels by renewable sources. To optimize these compounds it is important to understand their electronic structure and thus establish robust structure-activity relationships. To this end, we employed theoretical simulations based on density functional theory, employing functionals of different degree of complexity, including pure generalized gradient approximation (GGA) and GGA+U functionals, which introduce self-interaction correction terms through the Hubbard parameter, and compared those to the hybrid functionals HSE03 and HSE06. With this robust setup, we can identify an appropriate computational scheme that provides the best compromise between computational demand and accuracy. A complete database considering Berlin green and Prussian blue and white for all alkaline cations is presented.

17.
Chemistry ; 21(50): 18168-76, 2015 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-26541771

RESUMO

A new class of hexameric Ln12 -containing 60-tungstogermanates, [Na(H2 O)6 ⊂Eu12 (OH)12 (H2 O)18 Ge2 (GeW10 O38 )6 ](39-) (Eu12 ), [Na(H2 O)6 ⊂Gd12 (OH)6 (H2 O)24 Ge(GeW10 O38 )6 ](37-) (Gd12 ), and [(H2 O)6 ⊂Dy12 (H2 O)24 (GeW10 O38 )6 ](36-) (Dy12 ), comprising six di-Ln-embedded {ß(4,11)-GeW10 } subunits was prepared by reaction of [α-GeW9 O34 ](10-) with Ln(III) ions in weakly acidic (pH 5) aqueous medium. Depending on the size of the Ln(III) ion, the assemblies feature selective capture of two (for Eu12 ), one (for Gd12 ), or zero (for Dy12 ) extra Ge(IV) ions. The selective encapsulation of a cationic sodium hexaaqua complex [Na(H2 O)6 ](+) was observed for Eu12 and Gd12 , whereas Dy12 incorporates a neutral, distorted-octahedral (H2 O)6 cluster. The three compounds were characterized by single-crystal XRD, ESI-MS, photoluminescence, and magnetic studies. Dy12 was shown to be a single-molecule magnet.

18.
J Am Chem Soc ; 137(37): 11924-7, 2015 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-26340106

RESUMO

Reaction of the polysulfonated triazole ligand L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate) with iron(II) salts in water yields the trimeric species [Fe3(µ-L)6(H2O)6](6-). This polyanion, as the dimethylammonium salt, shows a thermally induced spin transition above room temperature for the central Fe position in the trimer with a large hysteresis cycle (>85 K) and remarkably slow dynamics. This allows easy quenching of the metastable high-spin (HS) state via gradual cooling (5 K min(-1)). Once it is trapped, the HS state remains metastable. Thermal energy is not able to promote relaxation into the low-spin ground state below 215 K, with a characteristic TTIESST = 250 K, the highest temperature ever observed for thermal trapping of an excited spin state in a switchable molecular material.

19.
Inorg Chem ; 54(10): 4678-87, 2015 May 18.
Artigo em Inglês | MEDLINE | ID: mdl-25950646

RESUMO

The reaction of 1,2,4-triazole and NaF with M(ox) (M = transition-metal dication; ox = oxalate dianion) under hydrothermal conditions has led to the isolation of a variety of hybrid organic-inorganic coordination polymers. Four structurally different 3D networks were obtained, depending on the transition metal, with stoichiometry [M2(H2O)(µ2-ox)][M2(µ3-trz)6] [M = Fe (1), Co (2), Ni (3)], [Zn2(H2O)(µ3-trz)2(µ2-ox)] (4), [Mn3(µ3-trz)2(µ6-ox)(µ3-F)2] (5), and [Fe3(µ3-trz)2(µ6-ox)(µ2-F)2] (6). In all cases, the magnetic behavior is dominated by antiferromagnetic exchange interactions between paramagnetic centers. Remarkably, 5 and 6 present a novel magnetic connectivity around the oxalate anion: a µ6-bridging mode. This magnetic geometry promotes multiple triangular arrangements among antiferromagnetically coupled spin carriers, resulting in a complex magnetic network because of the presence of competing interactions. These materials exhibit spontaneous magnetization below 9 and 66 K, respectively.

20.
Inorg Chem ; 53(21): 11675-81, 2014 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-25338262

RESUMO

Co(II) complexes of aminotrisphenolate ((ArO)3N(3-)) ligands can be prepared straightforwardly in high yield. X-ray analysis reveals these complexes to comprise of two different hemispheres, one containing an anionic Co((ArO)3N)(-) and the other a cationic (ArO)3NH(+) unit, which are associated through hydrogen bonding. These Co(II) complexes can be easily converted into their Co(III) analogues in air in the presence of suitable bases such as dimethylaminopyridine and 2,2'-bipyridine, and the structural features and magnetic properties of these latter compounds are also reported.

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