Fe Ligand Research Articles

Lattice oxygen-mediated Co–O–Fe formation in Co-MOF via Fe doping and ligand design for efficient oxygen evolution

The rational design of metal-organic frameworks (MOFs) provides potential opportunities for improving energy conversion efficiency. However, developing efficient MOF-based electrocatalysts remains highly challenging. Herein, a strategy involving strain engineering is developed to promote the electrocatalytic performance of MOFs by optimizing electronic configuration and improving the active site. As expected, the optimized CoFe–BDCNO2 exhibits a low overpotential of 292 mV at 10 mA cm–2 and a small Tafel slope of 31.6 mV dec–1 as oxygen evolution reaction (OER) electrocatalyst. Notably, when CoFe–BDCNO2 is prepared on Nickel foam (NF), the overpotential is only 345 mV at 1 A cm–2, which ensures efficient water oxidation properties. Integrating CoFe–BDCNO2/NF anode in membrane electrode assembly (MEA) for overall water splitting and CO2 reduction reaction (CO2RR) tests, the results show that the cell voltages of CoFe–BDCNO2/NF are 3.14 and 3.09 V at 300 mA cm–2 (25 °C), respectively, indicating that MOFs have various practical application prospects. The research of the structure-performance relationship reveals the lattice oxygen oxidation mechanism (LOM) where the Co-O-Fe bond is formed during the OER process by changing the electronic environment and coordination structure of CoFe–BDCNO2, and with high valence Co as active center, which provides a deep understanding of the structure design of MOFs and their structural transformation during OER.

Discovery, isolation, and characterization of diazeniumdiolate siderophores.

The C-diazeniumdiolate (N-nitrosohydroxylamine) group in the amino acid graminine (Gra) is a newly discovered Fe(III) ligand in microbial siderophores. Graminine was first identified in the siderophore gramibactin, and since this discovery, other Gra-containing siderophores have been identified, including megapolibactins, plantaribactin, gladiobactin, trinickiabactin (gramibactin B), and tistrellabactins. The C-diazeniumdiolate is photoreactive in UV light which provides a convenient characterization tool for this type of siderophore. This report details the process of genomics-driven identification of bacteria producing Gra-containing siderophores based on selected biosynthetic enzymes, as well as bacterial culturing, isolation and characterization of the C-diazeniumdiolate siderophores containing Gra.

Synthesis, Characterization and Breast Anti-cancer Activity of Iron(II), Cobalt(II), Nickel(II) and Copper(II) Complexes with a Hexadentate Schiff Base Ligand Derived from 2,5-Dihydroxy-1,4-benzoquinone with 5-Amino-2-methylphenol

The complexes of Fe(II), Co(II), Ni(II), and Cu(II) Schiff base ligand derived from 2,5-dihydroxy-1,4-benzoquinone and 5-amino-2-methylphenol were synthesized. The ligand was synthesized by the reaction between the mentioned ketone and amine in 1:2 molar ratio, respectively. The four metal complexes were synthesized by refluxing the ligand with the related metal(II) chloride salts. The synthesized compounds were characterized using FTIR spectroscopy, UV-visible, 1H-NMR, conductivity, atomic absorption, magnetic susceptibility, and thermogravimetric analysis. According to the results, the chelation between metals and ligand occurs with the imine groups and the deprotonated hydroxyl groups of 2,5-dihydroxy-1,4-benzoquinone and 5-amino-2-methylphenol in the ligand. The conductivity test of the four complexes shows the non-electrolytic nature of them. The magnetic susceptibility values of Fe(II), Co(II), Ni(II), and Cu(II) complexes are 4.20, 4.11, 2.97, and 2.34 B.M, respectively. The thermogravimetric and atomic absorption analyses suggest the general chemical formula for the complexes is [M2(L)(H2O)6]. In addition, the ligand and one of its metal complexes (Co(II) complex) were examined against breast cancer cells, and they gave the IC50 of 101.24 and 129.2 µg/mL, respectively. This result suggests that Co(II) complex is a better anti-cancer agent in comparison with the ligand.

Ferrate(VI)/Periodate System: Synergistic and Rapid Oxidation of Micropollutants via Periodate/Iodate-Modulated Fe(IV)/Fe(V) Intermediates.

The presence of organic micropollutants in water sources worldwide has created a need for the development of effective and selective oxidation methods in complex water matrices. This study is the first report of the combination of ferrate(VI) (Fe(VI)) and periodate (PI) for synergistic, rapid, and selective elimination of multiple micropollutants. This combined system was found to outperform other Fe(VI)/oxidant systems (e.g., H2O2, peroxydisulfate, and peroxymonosulfate) in rapid water decontamination. Scavenging, probing, and electron spin resonance experiments showed that high-valent Fe(IV)/Fe(V) intermediates, rather than hydroxyl radicals, superoxide radicals, singlet oxygen, and iodyl radicals, played a dominant role in the process. Further, the generation of Fe(IV)/Fe(V) was evidenced directly by the 57Fe Mössbauer spectroscopic test. Surprisingly, the reactivity of PI toward Fe(VI) is rather low (0.8223 M-1 s-1) at pH 8.0, implying that PI was not acting as an activator. Besides, as the only iodine sink of PI, iodate also played an enhanced role in micropollutant abatement by Fe(VI) oxidation. Further experiments proved that PI and/or iodate might function as the Fe(IV)/Fe(V) ligands, causing the utilization efficiency of Fe(IV)/Fe(V) intermediates for pollutant oxidation to outcompete their auto-decomposition. Finally, the oxidized products and plausible transformation pathways of three different micropollutants by single Fe(VI) and Fe(VI)/PI oxidation were characterized and elucidated. Overall, this study proposed a novel selective oxidation strategy (i.e., Fe(VI)/PI system) that could efficiently eliminate water micropollutants and clarified the unexpected interactions between PI/iodate and Fe(VI) for accelerated oxidation.

Effect of calcium and trace metals (Cd, Cu, Mn, Ni, Zn) on root iron uptake in relation to chemical properties of the root-excreted ligands.

Interferences of major cations (Ca2+, Mg2+) and trace metals (TM, i.e. Cd2+, Cu2+, Mn2+, Ni2+ and Zn2+) in root Fe uptakewere evaluated. Root Fe uptake was modelled including the reactions of the root exuded ligand with the soil major and trace cations. Fe uptake was simulated with different ligands representing various affinities for the cations, the latter varying in concentration. The stability constant of Fe complexes (KFeL) does not influence Fe uptake, contrarily to the ligand parameters for Fe-hydroxide dissolution. Fe uptake decreases when KCaL or Ca2+ in solution increases. Presence of TM has nearly no influence on Fe uptake when the TM complexes have low stability constants (KML), as in the case of oxalate and citrate complexes. When ligands have high KML, like EDTA, DFO-B or mugineic acid (MA), TM reduces Fe uptake by 51-55%, and much more in the case of TM contamination. Exudation of Fe ligands with low KML has no negative effect on TM uptake, which can increase if the dissociation rate is high, as for Cu complexes. Ligands with high KML (EDTA, DFO-B, MA) greatly reduce TM uptake, only if their hydrated cations can be absorbed. Calcium does not significantly reduce Fe uptake when Ca-complexes have KCaL < 104. Consequently, ligands like oxalate or MA should be efficient in most soils. TM should perturbate Fe uptake mediated by ligands with high KML such as MA, but not oxalate. Plants exuding phytosiderophores should also absorb TM complexes to avoid micronutrient deficiencies.

The influence of light on the availability of photoreactive and photostable iron(III)–ligand complexes to diatoms

AbstractUptake of iron (Fe) by eukaryotic phytoplankton is suggested to proceed by a reductive pathway in which Fe(III) bound to inorganic and organic ligands is reduced prior to Fe internalization. Photochemical reduction of the Fe–ligand complexes can increase Fe bioavailability, but the role of light in regulating physiological processes related to Fe acquisition is not well known. Here, we report how model Fe–ligand complexes differing in photolability affected growth, cellular Fe reduction, and Fe uptake rates of two marine diatoms as a function of irradiance. Growth rates of Thalassiosira oceanica and Phaeodactylum tricornutum in media amended with Fe complexed with ethylenediaminetetraacetic acid (Fe‐EDTA) and desferrioxamine B (FeDFB) increased linearly with light between 50 and 400 μmol photons m−2 s−1 under Fe‐limiting conditions. Steady‐state Fe uptake rates (ρSS) were also light dependent, increasing proportionally with growth irradiance for both Fe–ligand complexes. Photolysis of the Fe‐EDTA complex could explain the increase in ρSS in Fe‐EDTA‐amended medium because it increased [Fe(III)’], but it could not account for the faster rate of Fe uptake from FeDFB at high light because FeDFB is photostable. Short‐term Fe uptake rates measured in the absence of photochemically mediated Fe(III) reduction showed that cells preconditioned to high growth irradiance took up Fe faster than cells grown at low light. Thus, growth at high light induced a physiological response that increased Fe uptake. High growth irradiance also increased the rate of cellular Fe(III)’ reduction in the dark, similar to its stimulatory effect on short‐term Fe uptake. These results identify a previously unrecognized Fe–light interaction that could be important in enhancing Fe availability to diatoms. We suggest that the light effect could be the result of a light‐dependent regulation of cellular Fe(III) reduction.

Nonlinear optical limiting effect and charge transfer dynamics in a Fe-porphyrin metal-organic framework

The nonlinear absorption effect in a Fe-porphyrin metal-organic framework (Co-TCPP(Fe) MOF) was studied using the nanosecond Z-scan technique, which showed an enhanced reverse saturation absorption (RSA) compared with TCPP(Fe) ligand. By femtosecond transient absorption (fs-TA) measurements, the charge transfer dynamics of MOF are unveiled. Compared with TCPP(Fe) ligand, the ultrafast formation of charge separation states (CSSs) with extra-long lifetime (&gt; 3.5 ns) detracts the recombination of electron-hole pairs, resulting in an enhanced excited state absorption (ESA). Based on the strong ESA caused by CSSs absorption, the MOF nanosheets showed an excellent optical limiting (OL) effect with the OL threshold of 0.89 J/cm2.

Bipolar Membranes Containing Iron-Based Catalysts for Efficient Water-Splitting Electrodialysis.

Water-splitting electrodialysis (WSED) process using bipolar membranes (BPMs) is attracting attention as an eco-friendly and efficient electro-membrane process that can produce acids and bases from salt solutions. BPMs are a key component of the WSED process and should satisfy the requirements of high water-splitting capability, physicochemical stability, low membrane cost, etc. The water-splitting performance of BPMs can be determined by the catalytic materials introduced at the bipolar junction. Therefore, in this study, several kinds of iron metal compounds (i.e., Fe(OH)3, Fe(OH)3@Fe3O4, Fe(OH)2EDTA, and Fe3O4@ZIF-8) were prepared and the catalytic activities for water-splitting reactions in BPMs were systematically analyzed. In addition, the pore-filling method was applied to fabricate low-cost/high-performance BPMs, and the 50 μm-thick BPMs prepared on the basis of PE porous support showed several times superior toughness compared to Fumatech FBM membrane. Through various electrochemical analyses, it was proven that Fe(OH)2EDTA has the highest catalytic activity for water-splitting reactions and the best physical and electrochemical stabilities among the considered metal compounds. This is the result of stable complex formation between Fe and EDTA ligand, increase in hydrophilicity, and catalytic water-splitting reactions by weak acid and base groups included in EDTA as well as iron hydroxide. It was also confirmed that the hydrophilicity of the catalyst materials introduced to the bipolar junction plays a critical role in the water-splitting reactions of BPM.

Tuning the Coordination Microenvironment of Central Fe Active Site to Boost Water Electrolysis and Oxygen Reduction Activity.

In heterogeneous catalysis, single-atom catalysts are the frontier and important prototypes for many reactions, and revealing the intrinsic structure-activity relationship is presently a critical task, but remains challenging. In this work, water electrolysis and oxygen reduction performances of FeXYi N3 -i (X, Y = B, C, O, P and S; i= 0, 1) moiety in Fe-porphyrin are studied by the first-principles calculations, aiming at unraveling how and why tuning the coordination microenvironment of the active metal atom can improve the activity. It can be concluded that breaking the coordination shell symmetry breaks the well-accepted standard scaling relationship, adjusts *O adsorption behavior and thus optimizes the oxygen evolution reaction (OER) activity, for example, to an extremely low overpotential of 0.17V. In combination with the Fe atom spin configuration and ligand field theory, the dramatically improved OER activity can be well explained. In the present work, the significance of the coordination microenvironment of central metal atom in studies of electrocatalysis is highlighted.

(Digital Presentation) Engineering of Ni-Based Electrocatalysts for Direct Urea Oxidation

In the water-energy nexus framework, the alternate renewable energy sources can be stored into molecular hydrogen or electricity with simultaneous water purification through wastewater electrolysis cell or wastewater fuel cell. Urea oxidation reaction (UOR) has been interrogated to enhance the energy efficiency and to recover energy from urea-rich wastewater. Nickel-based catalysts are up-to-date the most widely investigated materials as the UOR electrocatalyst. This presentation introduces our recent approaches for preparation of the UOR electrocatalysts by i) galvanostatic electro-deposition of mixed metal (oxy)hydroxide (NiFeOx or NiCoOx) with variable mixing ratios, ii) potentiostatic dealloying of commercial alloys (e.g. Ni-Fe, Fe-Ni, and Ni-Cr-Co) under variable pH, and iii) one-pot thermochemical treatment of NiFe alloy foam (NFF), both as substrate and catalyst source to create a self-supporting UOR electrocatalyst. The secondary elements (Fe and Co) were found to accelerate the formation of NiOOH (the active site for UOR), by partial charge transfer among the mixed metals. On the other hand, oxalic acid treatment of NFF generated prismatic NiFe-oxalate (O-NFF) which marked surprisingly small overpotential and Tafel slope for UOR. The coexistence of Fe and oxalate ligand simultaneously shift the surface electronic structure which in-turn affected the adsorption of reactants and desorption of products. The UOR on the engineed electrocatalysts could be further utilized for urea electrolysis (for molecular hydrogen production) or urea fuel cell.

Primary and secondary antioxidant properties of scutellarin and scutellarein in water and lipid-like environments: A theoretical investigation

The scavenging capability of scutellarin flavonoid against the OOH radical has been studied, at Density Functional level of theory, by considering different reaction mechanisms in both lipid-like and water media. In water phase, the neutral and charged species present in solution, identified from the computed pKa equilibria, have been determined. Furthermore, the complexation ability of Scutellarin and its metabolite scutellarein with respect to the Cu2+ and Fe3+ ions has been determined at the same level of theory. From the obtained rate constants results that scutellarin is a better Fe(III) ligand while scutellarein show a revers behavior. The glucuronidation process affect both the primary and secondary antioxidant properties of the systems.

Resolving Femtosecond Solvent Reorganization Dynamics in an Iron Complex by Nonadiabatic Dynamics Simulations.

The ultrafast dynamical response of solute–solvent interactions plays a key role in transition metal complexes, where charge transfer states are ubiquitous. Nonetheless, there exist very few excited-state simulations of transition metal complexes in solution. Here, we carry out a nonadiabatic dynamics study of the iron complex [Fe(CN)4(bpy)]2– (bpy = 2,2′-bipyridine) in explicit aqueous solution. Implicit solvation models were found inadequate for reproducing the strong solvatochromism in the absorption spectra. Instead, direct solute–solvent interactions, in the form of hydrogen bonds, are responsible for the large observed solvatochromic shift and the general dynamical behavior of the complex in water. The simulations reveal an overall intersystem crossing time scale of 0.21 ± 0.01 ps and a strong reliance of this process on nuclear motion. A charge transfer character analysis shows a branched decay mechanism from the initially excited singlet metal-to-ligand charge transfer (1MLCT) states to triplet states of 3MLCT and metal-centered (3MC) character. We also find that solvent reorganization after excitation is ultrafast, on the order of 50 fs around the cyanides and slower around the bpy ligand. In contrast, the nuclear vibrational dynamics, in the form of Fe–ligand bond changes, takes place on slightly longer time scales. We demonstrate that the surprisingly fast solvent reorganizing should be observable in time-resolved X-ray solution scattering experiments, as simulated signals show strong contributions from the solute–solvent scattering cross term. Altogether, the simulations paint a comprehensive picture of the coupled and concurrent electronic, nuclear, and solvent dynamics and interactions in the first hundreds of femtoseconds after excitation.

Atmospheric Iron and Aluminium Deposition and Sea-Surface Dissolved Iron and Aluminium Concentrations in the South China Sea off Malaysia Borneo (Sarawak Waters)

South China Sea (SCS) is an oligotrophic sea which usually receives low nutrients supply. However, massive atmospheric dust input was occurred during the haze event in Southeast Asia for almost every year. The input of dissolved iron (DFe) and dissolved aluminium (DAl) from dust and nearby land into SCS off Sarawak Borneo region during the worst haze event in 2015 of the Southeast Asia were investigated. The estimation dust deposition during this study was 0.162 mg/m2/yr. The atmospheric fluxes of total Fe and total Al at the offshore Sarawak waters were 0.611 µmol/m2/yr and 2.03 µmol/m2/yr, respectively, where the readily available dissolved Fe and Al from the dust were 0.11 µmol/m2/yr (DFe) and 0.31 µmol/m2/yr (DAl). Fe has higher solubility (17.78%) than Al (15.21%). The lateral fluxes (e.g. from the nearby land) were 37.08 nmol/m2/yr (DFe) and 125 nmol/m2/yr (DAl), with strong Fe organic ligand class L1 (log K:22.43 – 24.33). High concentrations of DFe and DAl at the surface water of the offshore region, coincided with high concentration of macronutrients due to the prevailing south-westerly winds originated from the west Kalimantan. Low residence times, ~0.92 (DFe) and ~1.31 (DAl) years, corresponded well with DAlexcess in surface seawater due to biological utilization of DFe. Future works emphasize on natural organic Fe(III) ligands and phytoplankton study are needed for better understanding on biogeochemistry of Fe and Al at SCS off Malaysia Borneo.

Mechanochemically Synthesised Flexible Electrodes Based on Bimetallic Metal-Organic Framework Glasses for the Oxygen Evolution Reaction.

The melting behaviour of metal-organic frameworks (MOFs) has aroused significant research interest in the areas of materials science, condensed matter physics and chemical engineering. This work first introduces a novel method to fabricate a bimetallic MOF glass, through melt-quenching of the cobalt-based zeolitic imidazolate framework (ZIF) [ZIF-62(Co)] with an adsorbed ferric coordination complex. The high-temperature chemically reactive ZIF-62(Co) liquid facilitates the formation of coordinative bonds between Fe and imidazolate ligands, incorporating Fe nodes into the framework after quenching. The resultant Co-Fe bimetallic MOF glass therefore shows a significantly enhanced oxygen evolution reaction performance. The novel bimetallic MOF glass, when combined with the facile and scalable mechanochemical synthesis technique for both discrete powders and surface coatings on flexible substrates, enables significant opportunities for catalytic device assembly.

Mechanochemically Synthesised Flexible Electrodes Based on Bimetallic Metal–Organic Framework Glasses for the Oxygen Evolution Reaction

AbstractThe melting behaviour of metal–organic frameworks (MOFs) has aroused significant research interest in the areas of materials science, condensed matter physics and chemical engineering. This work first introduces a novel method to fabricate a bimetallic MOF glass, through melt‐quenching of the cobalt‐based zeolitic imidazolate framework (ZIF) [ZIF‐62(Co)] with an adsorbed ferric coordination complex. The high‐temperature chemically reactive ZIF‐62(Co) liquid facilitates the formation of coordinative bonds between Fe and imidazolate ligands, incorporating Fe nodes into the framework after quenching. The resultant Co–Fe bimetallic MOF glass therefore shows a significantly enhanced oxygen evolution reaction performance. The novel bimetallic MOF glass, when combined with the facile and scalable mechanochemical synthesis technique for both discrete powders and surface coatings on flexible substrates, enables significant opportunities for catalytic device assembly.

Structural evaluation of cytochrome c by Raman spectroscopy and its relationship with apoptosis and protein degradation in postmortem bovine muscle

Structural changes of cytochrome c and its relationship with apoptosis and protein degradation of bovine muscle during postmortem aging were investigated. Results from amide I and amide II ~ VI showed that the π* orbital d electron decreased, the π electron density increased, and the frequency of the C–N stretching vibration increased. The distance between heme Fe and N atoms of the porphyrin decreased, the bond length decreased, and the heme core size decreased. Besides, Fe ligand vibration related Raman bands of cytochrome c had red (right) shift gradually with the extension of aging. The apoptotic rate and the degradation products of desmin and troponin-T were increased (P < 0.05). Correlation analysis results suggested that Fe ligand vibration, not amide I ~ VI related Raman bands were correlated with cytochrome c mediated apoptosis and degradation of myofibrillar protein of bovine muscle during aging.

Insight into the Electronic Structure of Biomimetic Dinitrosyliron Complexes (DNICs): Toward the Syntheses of Amido-Bridging Dinuclear DNICs.

The ubiquitous function of nitric oxide (NO) guided the biological discovery of the natural dinitrosyliron unit (DNIU) [Fe(NO)2] as an intermediate/end product after Fe nitrosylation of nonheme cofactors. Because of the natural utilization of this cofactor for the biological storage and delivery of NO, a bioinorganic study of synthetic dinitrosyliron complexes (DNICs) has been extensively explored in the last 2 decades. The bioinorganic study of DNICs involved the development of synthetic methodology, spectroscopic discrimination, biological application of NO-delivery reactivity, and translational application to the (catalytic) transformation of small molecules. In this Forum Article, we aim to provide a systematic review of spectroscopic and computational insights into the bonding nature within the DNIU [Fe(NO)2] and the electronic structure of different types of DNICs, which highlights the synchronized advance in synthetic methodology and spectroscopic tools. With regard to the noninnocent nature of a NO ligand, spectroscopic and computational tools were utilized to provide qualitative/quantitative assignment of oxidation states of Fe and NO in DNICs with different redox levels and ligation modes as well as to probe the Fe-NO bonding interaction modulated by supporting ligands. Besides the strong antiferromagnetic coupling between high-spin Fe and paramagnetic NO ligands within the covalent DNIU [Fe(NO)2], in polynuclear DNICs, the effects of the Fe···Fe distance, nature of the bridging ligands, and type of bridging modes on the regulation of the magnetic coupling among paramagnetic DNIU [Fe(NO)2] are further reviewed. In the last part of this Forum Article, the sequential reaction of {Fe(NO)2}10 DNIC [(NO)2Fe(AMP)] (1-red) with NO(g), HBF4, and KC8 establishes a synthetic cycle, {Fe(NO)2}9-{Fe(NO)2}9 DNIC [(NO)2Fe(μ-dAMP)2Fe(NO)2] (1) → {Fe(NO)2}9 DNIC [(NO2)Fe(AMP)][BF4] (1-H) → {Fe(NO)2}10 DNIC 1-red → DNIC 1, for the transformation of NO into HNO/N2O. Of importance, the NO-induced transformation of {Fe(NO)2}10 DNIC 1-red and [(NO)2Fe(DTA)] (2-red; DTA = diethylenetriamine) unravels a synthetic strategy for preparation of the {Fe(NO)2}9-{Fe(NO)2}9 DNICs [(NO)2Fe(μ-NHR)2Fe(NO)2] containing amido-bridging ligands, which hold the potential to feature distinctive physical properties, chemical reactivities, and biological applications.

Fabrication of hydrophobic Fe-based metal-organic framework through post-synthetic modification: Improvement of aqueous stability

Synthesis of aqueous steady metal-organic frameworks is a critical issue to expand their photocatalyst applications in water treatment. In the current study, MIL-101(Fe)-NH2 was selected as the template, and grafting of 4-(trifluoromethyl)phenyl isocyanate was achieved by a postsynthetic modification method. As a result, a novel MIL-101(Fe)-1-(4-(trifluoromethyl)phenyl)urea (named MIL-101(Fe)-TfmPU) was fabricated. X-ray photoelectron spectroscopy confirmed the grafting of amino groups to form urea groups. Water contact angle of MIL-101(Fe)-TfmPU reached 151°, implying a superhydrophobicity. Introduction of carbamido-benzene-trifluoromethyl arm reduced the surface energy, and it may act as a shield for the coordination bonds between Fe core and ligands due to its steric hindrance. This raising hydrophobicity resulted in a significant improvement on water stability. After 7 d water exposure, MIL-101(Fe)-TfmPU possessed better stability with less Fe ion release and highly intact structure compared to its parent MIL-101(Fe)-NH2. In the photocatalysis reaction with visible light and oxidant donor (H2O2), MIL-101(Fe)-TfmPU demonstrated a high degradation efficiency of ciprofloxacin with a reaction rate at 0.0636 min−1. The dominant reaction mechanism was OH· oxidation. Acid condition was benefitcial for this photocatalysis reaction and its stability, while room temperature variation (278−318 K) had a negligible effect. In different actual water mediums, photocatalysis efficiency, crystal structure and chemical bonds of MIL-101(Fe)-TfmPU were all retained. Generally, the water stability of MIL-101(Fe)-TfmPU was successfully enhanced to ensure its photocatalysis applications in the aqueous mediums.

Theoretical inspection of the spin-crossover [Fe(tzpy)2(NCS)2] complex on Au(100) surface.

We explore the deposition of the spin-crossover [Fe(tzpy)2(NCS)2] complex on the Au(100) surface by means of density functional theory (DFT) based calculations. Two different routes have been employed: low-cost finite cluster-based calculations, where both the Fe complex and the surface are maintained fixed while the molecule approaches the surface; and periodic DFT plane-wave calculations, where the surface is represented by a four-layer slab and both the molecule and surface are relaxed. Our results show that the bridge adsorption site is preferred over the on-top and fourfold hollow ones for both spin states, although they are energetically close. The LS molecule is stabilized by the surface, and the HS-LS energy difference is enhanced by about 15%-25% once deposited. The different Fe ligand field for LS and HS molecules manifests on the composition and energy of the low-lying bands. Our simulated STM images indicate that it is possible to distinguish the spin state of the deposited molecules by tuning the bias voltage of the STM tip. Finally, it should be noted that the use of a reduced size cluster to simulate the Au(100) surface proves to be a low-cost and reliable strategy, providing results in good agreement with those resulting from state-of-the-art periodic calculations for this system.

Deposition of the Spin Crossover FeII -Pyrazolylborate Complex on Au(111) Surface at the Molecular Level.

The interaction at the molecular level of the spin-crossover (SCO) FeII ((3,5-(CH3 )2 Pz)3 BH)2 complex with the Au(111) surface is analyzed by means of rPBE periodic calculations. Our results show that the adsorption on the metallic surface enhances the transition energy, increasing the relative stability of the low spin (LS) state. The interaction indeed is spin-dependent, stronger for the low spin than the high spin (HS) state. The different strength of the Fe ligand field at low and high temperature manifests on the nature, spatial extension and relative energy of the states close to the Fermi level, with a larger metal-ligand hybridization in the LS state. This feature is of relevance for the differential adsorption of the LS and HS molecules, the spin-dependent conductance, and for the differences found in the corresponding STM images, correctly reproduced from the density of states provided by the rPBE calculations. It is expected that this spin dependence will be a general feature of the SCO molecule-substrate interaction, since it is rooted in the different ligand field of Fe site at low and high temperatures, a common hallmark of the FeII SCO complexes. Finally, the states involved in the LIESST phenomenon has been identified through NEVPT2 calculations on a model reaction path. A tentative pathway for the photoinduced LS→HS transition is proposed, that does not involve the intermediate triplet states, and nicely reproduces both the blue laser wavelength required for the activation, and the wavelength of the reverse HS → LS transition.