Bridging Carboxylate Research Articles

Crystal structure and spectral properties of the heterometallic 3d-4f complex of gadolinium (III) – cobalt (II) with ethylenediamine-N,N,N′,N′-tetraacetic acid

The 4f-3d heteronuclear complex Co3Gd2(EDTA)11∙9·5H2O was synthesized by the "block" synthesis method using protonated ethylenediaminetetraacetate Co(II) and Gd(III) nitrate. The complex was fully characterized by means of elemental, thermal and X-ray structural analyses, as well as by the methods of diffuse reflection spectroscopy and IR spectroscopy. The complex crystallizes in monoclinic system (space group C2) with lattice parameters a = 15.8142(3) Å, b = 14.5875(3) Å, c = 14.6808(3) Å, α = γ = 90°, β = 116.5009(10)°.The complex is a 2D coordination polymer in which each Gd(III) ion is connected to with three atoms Co(II) atoms through tridentate bridging carboxylate groups of EDTA, and each Co atom has two neighboring Gd(III) atoms. The polymer layers are packed in parallel, outer-sphere water molecules are located between the layers, forming a branched system of hydrogen bonds.

Adsorption and Photo-Degradation of Organophosphates on Sulfate-Terminated Anatase TiO2 Nanoparticles

The adsorption and photocatalytic degradation of trimethyl phosphate (TMP) and triethyl phosphate (TEP), two environmentally relevant model pollutants, have been studied on commercial anatase TiO2 and sulfate-terminated anatase TiO2 nanoparticles by means of operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and 2D correlation spectroscopy (2D COS). It is concluded that both TMP and TEP adsorb dissociatively on anatase TiO2, while on the sulfate-terminated anatase TiO2, TMP and TEP adsorb associatively. Upon UV illumination, TMP and TEP are completely oxidized on sulfate-terminated anatase TiO2, as evidenced by the evolution of the IR bands characteristic for water and carbon dioxide. In contrast, on anatase TiO2, UV illumination leads to the formation of stable surface-coordinated carboxylate products, which impedes complete oxidation. 2D COS analysis suggests that parallel reaction pathways occur during oxidation under UV illumination, viz. methoxide/ethoxide (ads) → carboxylates (ads) and methoxide/ethoxide (ads) → aldehydes (ads) → carboxylates (ads). A parallel reaction occurs on sulfated TiO2 that yields CO2 and H2O by direct radical reactions with the methoxide groups with little, or no, formation of surface-coordinated intermediates. Sulfated TiO2 favor the formation of aldehyde intermediates, with reaction rates 10 times and 30 times faster for TMP and TEM, respectively, compared with commercial anatase TiO2. About 37% (33%) and 32% (24%) of TMP (TEP) were degraded on sulfated-terminated TiO2 and pure TiO2, respectively, after the first 9 min of UV illumination. We show that the sulfate-functionalization of TiO2 has two main functions. First, it prevents the formation of strongly bonded bridging carboxylates, thereby alleviating deactivation. Second, it promotes full oxidation of the organic side-chains into carbon dioxide and water. Improved electron-hole separation by the electrophilic S(VI) in combination with the blocking of bridging reaction intermediates is proposed to contribute to the improved activity. The presented results give insights into how acidic surface modifications change adsorbate surface chemistries, which can be used to increase the sustained activity of low-temperature photocatalysts.

Quantification of carboxylate-bridged di-zinc site stability in protein due ferri by single-molecule force spectroscopy.

Carboxylate-bridged diiron proteins belong to a protein family involved in different physiological processes. These proteins share the conservative EXXH motif, which provides the carboxylate bridge and is critical for metal binding. Here, we choose de novo-designed single-chain due ferri protein (DFsc), a four-helical protein with two EXXH motifs as a model protein, to study the stability of the carboxylate-bridged di-metal binding site. The mechanical and kinetic properties of the di-Zn site in DFsc were obtained by atomic force microscopy-based single-molecule force spectroscopy. Zn-DFsc showed a considerable rupture force of ~200 pN, while the apo-protein is mechanically labile. In addition, multiple rupture pathways were observed with different probabilities, indicating the importance of the EXXH-based carboxylate-bridged metal site. These results demonstrate carboxylate-bridged di-metal site is mechanically stable and improve our understanding of this important type of metalloprotein.

A 3D Coordination Polymer Based on Syn-Anti Bridged [Mn(RCOO)2]n Chains Showing Spin-Canting with High Coercivity and an Ordering Temperature of 14 K

A new 3D manganese(II) coordination polymer, formulated as [Mn3(HL)6] (1) (where H2L = 6-hydroxypicolinic acid), has been hydrothermally synthesized and characterized by single-crystal X-ray crystallographic analysis along with other spectroscopic and magnetic techniques. Structural analysis shows that the compound crystallizes in the monoclinic C2/c space group and is a non-porous 3D coordination polymer formed by three different Mn(II) centres connected by 6-hydroxypicolinic acid ligands in their keto form. Each Mn(II) centre shows a distorted octahedral coordination environment. Neighbouring Mn(II) centres are connected by two different syn-anti bridging carboxylate groups to form regular coordination chains. There are two different [Mn2(RCOO)2] units along the chain, formed by two crystallographically independent Mn centres (Mn1 and Mn2). These chains are further connected by HL− ligands to form a 3D coordination network. Interestingly, both the hydroxy and the carboxylate groups of the ligands are deprotonated and coordinated to the metal centres, whereas the pyridyl group is protonated and uncoordinated, although it participates in strong hydrogen bonding interactions with oxygen atoms of the HL− ligand, as shown by the Hirshfeld surface analysis. Both the absorption and emission spectra of the compound have also been measured. Variable temperature magnetic studies reveal the presence of a spin-canted antiferromagnetic behaviour with a high coercivity of 40 mT at 2 K and an ordering temperature of 14 K.

Trinuclear heterometallic CuII–MII (M = Mn and Co) complexes of N,O donor ligands with o-nitro benzoate anion: Structures, magnetic properties and catalytic oxidase activities

Three new heterometallic complexes [(CuL1)2Mn(o-(NO2)C6H4CO2)2] (1), and{[(CuL2)2Mn(o-(NO2)C6H4CO2)2]·2CH3CN} (2) and {[(CuL2)2Co(o-(NO2)C6H4CO2)2]·2H2O} (3) have been synthesized using [CuL1]/[CuL2] as metalloligands (where H2L1 = N,N′-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine, H2L2 = N,Ń-bis(methyl2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Structural characterization of complexes (1–3) show that contains linear trinuclear architecture, where the terminal [CuL1]/[CuL2] units are coordinated to the central MnII (for 1 and 2)/CoII (for 3) through double phenoxido bridge along with a syn-syn bridging carboxylate anion. Complexes 1 and 2 exhibit biomimetic catecholase-like activity with the turn over numbers (kcat) of 164 and 140 h−1, respectively. The mass spectral study suggest the most probable mechanism of this biomimetic oxidase reaction whereas, cyclic voltammetry measurements indicate that CuII is reducible to CuI during catalysis. Variable temperature (2–300 K) magnetic susceptibility measurements reveal that all complexes (1–3) possess an overall antiferromagnetic coupling between CuII and the hetero metal ions with J values of –7.027(2), –7.076(1) and –2.2(1) cm−1, respectively.

Synthesis, Structural, Magnetic and Computational Studies of a One-Dimensional Ferromagnetic Cu(II) Chain Assembled from a New Schiff Base Ligand

A new asymmetrically substituted ONOO Schiff base ligand N-(2′-hydroxy-1′-naphthylidene)-3-amino-2-naphthoic acid (nancH2) was prepared from the condensation of 2–hydroxy–1–naphthaldehyde and 3–amino–2–naphthoic acid. nancH2 reacts with Cu2(O2CMe)4·2H2O in the presence of Gd(O2CMe)3·6H2O to afford a uniform one-dimensional homometallic chain, [CuII(nanc)]n (1). The structure of 1 was elucidated via single crystal X-ray diffraction studies, which revealed that the Cu(II) ions adopt distorted square planar geometries and are coordinated in a tridentate manner by an [ONO] donor set from one nanc2− ligand and an O− of a bridging carboxylate group from a second ligand. The bridging carboxylato group of the nanc2− ligand adopts a syn, anti-η1:η1:μ conformation linking neighboring Cu(II) ions, forming a 1D chain. The magnetic susceptibility of 1 follows Curie–Weiss law in the range 45–300 K (C = 0.474(1) emu K mol-1, θ = +7.9(3) K), consistent with ferromagnetic interactions between S = ½ Cu(II) ions with g = 2.248. Subsequently, the data fit well to the 1D quantum Heisenberg ferromagnetic (QHFM) chain model with g = 2.271, and J = +12.3 K. DFT calculations, implementing the broken symmetry approach, were also carried out on a model dimeric unit extracted from the polymeric chain structure. The calculated exchange coupling via the carboxylate bridge (J = +13.8 K) is consistent with the observed ferromagnetic exchange between neighbouring Cu(II) centres.

A tetracobalt(II) cluster with a two vertex truncated dicubane topology endogenously supported by carboxylate-based (2-pyridyl)methylamine ligands: magneto-structural and DFT studies.

A reaction between CoCl2 and L3-(CO2-)2 (2 : 1 stoichiometry) in CH3OH affords a discrete complex [CoII4-{L3-(CO2-)2}2(μ3-OCH3)2(CH3OH)2(H2O)2Cl2] (1) [L3-(CO2-)2 = 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)]. The structure of 1 reveals two terminal mononuclear CoII{L3-(CO2-)2}Cl units connected by a dimeric CoII2(μ3-OCH3)2(CH3OH)2(H2O) unit present in the centre through two methoxo (μ3-OCH3)- and two carboxylate (μ-1,1-OCO-) bridges affording a tetranuclear coordination cluster of Co(II) with a defective dicubane topology. In 1, Co1 (terminal) has distorted octahedral CoIIN2O3Cl and the central Co2 has CoIIO6 coordination. Such coordination arrangements afford the observed topology. Variable-temperature magnetic studies reveal anti-ferromagnetic coupling in 1. Three magnetic exchange interactions (one anti-ferromagnetic and two ferromagnetic: J1 = +3.3 cm-1 (Co⋯Co 3.176 Å; μ-1,1-OCO- and μ3-OCH3 bridges), J2 = -2.5 cm-1 (Co⋯Co 3.228 Å; μ-1-OCO- and μ3-OCH3 bridges) and J3 = +10.6 cm-1 (Co⋯Co 3.084 Å; two μ3-OCH3 bridges)) have been identified, with the inclusion of the orbital reduction parameter (α = Aκ = 1.38), spin-orbit coupling (λ = -158 cm-1) and axial distortion (energy gap Δ = -975 cm-1 between singlet and doublet levels), rationalized by density functional theory (DFT) calculations.

New insights into pertinent Fe-complexes for the synthesis of iron via the instant polyol process.

Chemically synthesized iron is in demand for biomedical applications due to its large saturation magnetization compared to iron oxides. The polyol process, suitable for obtaining Co and Ni particles and their alloys, is laborious in synthesizing Fe. The reaction yields iron oxides, and the reaction pathway remains unexplored. This study shows that a vicinal polyol, such as 1,2-propanediol, is suitable for obtaining Fe rather than 1,3-propanediol owing to the formation of a reducible Fe intermediate complex. X-ray absorption spectroscopy analysis reveals the ferric octahedral geometry and tetrahedral geometry in the ferrous state of the reaction intermediates in 1,2-propanediol and 1,3-propanediol, respectively. The final product obtained using a vicinal polyol is Fe with a γ-Fe2O3 shell, while the terminal polyol is favourable for Fe3O4. The distinct Fe-Fe and Fe-O bond lengths suggest the presence of a carboxylate group and a terminal alkoxide ligand in the intermediate of 1,2-propanediol. A large Fe-Fe bond distance suggests diiron complexes with bidentate carboxylate bridges. Prominent high-spin and low-spin states indicate the possibility of transition, which favors the reduction of iron ions in the reaction using 1,2-propanediol.

Exploiting Strong {CrIII–DyIII} Ferromagnetic Exchange Coupling to Quench Quantum Tunneling of Magnetization in a Novel {CrIII2DyIII3} Single-Molecule Magnet

The {3d–4f} pentanuclear complexes with the formula [CrIII2LnIII3(PhCO2)7(OH)6 (iPrO)(NO3)(H2O)3] (iPrO = isopropoxide) (where Ln = Dy (1), Gd (2)) have been synthesized and characterized using magnetic and theoretical studies. The metal core of complexes 1 and 2 has a trigonal bipyramidal arrangement with three LnIII ions in the triangular plane and two CrIII ions occupying the axial positions. These ions are held together by six μ3-OH bridges and seven carboxylate bridges. The dc magnetic susceptibility data reveal ferromagnetic interactions presiding between CrIII and LnIII ions in 1 and 2. The fitting of the susceptibility curve employing the DFT calculated J (vide infra), yield JGdIII–GdIII = +0.008 cm–1, JCrIII–GdIII = +0.27 cm–1, and JCrIII–CrIII = −0.007 cm–1 for 2. The dynamic (ac) magnetic susceptibility studies on 1 indicate slow relaxation of magnetization with a Ueff value of 30.9 K (21.4 cm–1) and τ0 = 4.09 × 10–10 s. These extracted parameters are among the highest for any reported {CrIIIDyIII} complexes. DFT and ab initio CASSCF/RASSI–SO/SINGLE_ANISO/POLY_ANISO calculations were carried out to estimate the exchange interactions and their role in quenching the quantum tunneling of magnetization (QTM) behavior. Ab initio calculations on the DyIII ions reveal three asymmetric DyIII centers with the estimated single ion barrier in the range of 78–184 cm–1, however, with a large QTM probability. Despite a triangular {Dy3} motif, the gzz axes do not align in the triangular plane as observed in the {CrIIIDyIII6} single-molecule toroids (SMT) reported earlier by us. This is essentially due to the presence/absence of the iPrO–/carboxylate group that alters the charge distribution around the DyIII ion and hence the orientation of the corresponding gzz axis. The combination of DFT and ab initio CASSCF calculations yield JDyIII–DyIII = +0.012 cm–1, JCrIII–DyIII = +1.20 cm–1, and JCrIII–CrIII = −0.95 cm–1 for 1. The mechanism of magnetization relaxation developed for the {CrIII2DyIII3} cluster reveals that the relatively strong ferromagnetic CrIII–DyIII exchange interaction reduces the ground state QTM significantly yielding a Ueff of 38.6 cm–1, which agrees with the experimental value. Thus, our study iterates the importance of CrIII ion to enhance the exchange coupling in the {3d–4f} family of clusters.

Anion-directed structural diversification in four new Cd(II) compounds of a flexible polyether-based dicarboxylic acid

• With a less explored linker 3,6,9-trioxaundecanedioic acid (H 2 toua) a series of complexes with Cd(II) salts containing different counter anions (Cl - , ClO 4 - , OAc - , and NO 3 - ) were synthesized. • A discrete neutral compound [Cd(H 2 toua)Cl 2 ] . H 2 O ( 1 ) is obtained with Cl - whereas a 1D polymeric chain {[Cd(Htoua)(H 2 O)](ClO 4 )} n ( 2 ) is obtained with ClO 4 - counter anion. • Different morphologies are observed with different counter anion analyzed by SEM technique. • Their thermal behavior, Hirshfeld Surface analysis and luminescent properties were also investigated. In this work, we report the chemistry of an unexplored flexible polyether based dicarboxylic acid (3,6,9-trioxaundecanedioic acid, H 2 toua) with four different cadmium salts. With CdCl 2 . H 2 O or Cd(ClO 4 ) 2 . H 2 O in a 1:1 ratio, it remarkably forms a discrete compound [Cd(H 2 toua)Cl 2 ] . H 2 O ( 1 ) and a polymeric ionic compound, {[Cd(Htoua)(H 2 O)](ClO 4 )} n ( 2 ), respectively, as determined by the single crystal X-ray diffraction. In both cases, for the heptacoordinated Cd(II) all basal donor atoms are from the ligand (three ether oxygen and two oxygen atoms from the fully intact or mono-deprotonated carboxylic acid groups, respectively) but with a major difference in axial (trans to each other) coordinated atom types - two chlorines in 1 while one water molecule and a bridging carboxylate oxygen in 2 . Unlike 1 , the carboxylate group of Htoua bridges between the Cd(II) centers for the formation of a 1D polymeric chain in 2 . Furthermore, Hirshfeld surface analysis of the various intermolecular interactions enables quantifiable contributions to crystal packing, revealing the key differences in the interactions encountered by 1 and 2 . Using Cd(OAc) 2 . 6H 2 O as the metal salt, it is possible to make [Cd(toua)] . H 2 O ( 3 ), due to the formation of easily removable volatile acetic acid by-product. On the other hand, a nitrate analogue of 2 , i.e., {[Cd(Htoua)(H 2 O)](NO 3 )} n ( 4 ) is isolated if Cd(NO 3 ) 2 . 4H 2 O is used. All these compounds were characterized by a number of spectroscopic and microscopic methods. Their thermal behaviour and luminescence properties were also determined.

Syntheses and structural characterizations of the first coordination polymers assembled from the Ni(cyclam)2+ cation and the benzene-1,3,5-tri-carboxyl-ate linker.

The asymmetric unit of catena-poly[[[(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)nickel(II)]-μ2-5-carb-oxy-benzene-1,3-di-carboxyl-ato-κ2 O 1:O 3] octa-hydrate], {[Ni(C9H4O6)(C10H24N4)]·8H2O} n (I), consists of a macrocyclic Ni2+ cation, a carboxyl-ate dianion and eight highly disordered water mol-ecules of crystallization. The components of the compound catena-poly[[[(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)nickel(II)]-μ2-5-carb-oxy-benzene-1,3-di-carboxyl-ato-κ2 O 1:O 3] monohydrate], {[Ni(C9H4O6)(C10H24N4)]·H2O} n (II), are two crystallographically unique centrosymmetric macrocyclic dications, a carboxyl-ate dianion and one water mol-ecule of crystallization. In each compound, the metal ion is coordinated in the equatorial plane by the four secondary N atoms of the macrocyclic ligand, which adopts the most energetically stable trans-III conformation, and two mutually trans O atoms of the carboxyl-ate anions in a slightly tetra-gonally distorted trans-NiN4O2 octa-hedral geometry. The crystals of both compounds are composed of parallel coordination polymeric chains running along the [010] direction in I and the [110] and [10] directions in II. The bridging carboxyl-ate anions display different modes of coordination connected with the relative orientation of coordinated O atoms, i.e., remote in I and inter-mediate in II, thus resulting in essentially different distances between the Ni atoms in the chains [11.0657 (4) and 8.9089 (2) Å in I and II, respectively]. As a result of hydrogen-bonding inter-actions, the chains are joined together in sheets oriented parallel to the (10) and (001) planes in I and II, respectively.

Structural Variety of Niobium(V) Polyoxo Clusters Obtained from the Reaction with Aromatic Monocarboxylic Acids: Isolation of {Nb2 O}, {Nb4 O4 } and {Nb8 O12 } Cores.

The reactivity of aryl monocarboxylic acids (benzoic, 1- or 2-naphtoic, 4'-methylbiphenyl-4-carboxylic, and anthracene-9-carboxylic acids) as complexing agents for the ethoxide niobium(V) (Nb(OEt)5 precursor has been investigated. A total of eight coordination complexes were isolated with distinct niobium(V) nuclearities as well as carboxylate complexation states. The use of benzoic acid gives a tetranuclear core Nb4 (μ2 -O)4 (L)4 (OEt)8 ] (L=benzoate (1)) with four Nb-(μ2 -O)-Nb linkages in a square plane configuration. A similar tetramer, 7, was obtained with 2-naphtoic acid by using a 55 % humid atmosphere synthetic route. Two types of dinuclear brick were identified with one central Nb-(μ2 -O)-Nb linkage; they differ in their complexation state, with one bridging carboxylate ([Nb2 (μ2 -O)(μ2 -OEt)(L)(OEt)6 ], with L=1-naphtoate (3) or anthracene-9-carboxylate (5)) or two bridging carboxylate groups ([Nb2 (μ2 -O)(L)2 (OEt)6 ], with L=4'-methylbiphenyl-4-carboxylic (4) or anthracene-9-carboxylate (6)). An octanuclear moiety [Nb8 (μ2 -O)12 (L)8 (η1 -L)4-x (OEt)4+x ] (with L=2-naphtoate, x=0 or 2; 8) was obtained by using a solvothermal route in acetonitrile; it has a cubic configuration with niobium centers at each node, linked by 12 μ2 -O groups. The formation of the niobium oxo clusters was characterized by infrared and liquid 1 H NMR spectroscopy in order to analyze the esterification reaction, which induces the release of water molecules that further react through oxolation with niobium atoms, in different {Nb2 O}, {Nb4 O4 } and {Nb8 O12 } nuclearities.

Side-Group Effect on the Slow Relaxations of {Dy2} Single-Molecule Magnets with Confined N2O6 Donors.

Deep insights into and substantial enhancement of the effective anisotropy energy barrier for magnetization reversal (Ueff) are vitally important for the technological applications of dysprosium(III)-based single-molecule magnets (Dy-SMMs). To fully refine the ligand-field effect on spin relaxation, four centrosymmetric {Dy2} entities with formula [Dy2(CH3OH)2L2(RCOO)2] (H2L = 2-hydroxy-N'-((pyridin-2-yl)methylene)benzohydrazide) have been solvothermally prepared by varying the side groups of carboxylate coligands (RCOO-, R = CF3 for 1, H for 2, CH3 for 3, and Cp2Fe for 4). Structural analyses reveal that all of the DyIII carriers in 1-4 have the same N2O6 donor environments, and the non-coordinative R groups attached to the equatorial carboxylate bridges have not substantially changed the binding ability of the shortest Dy-Ophenolate bonds located at the axial position of the ligand field. Interestingly, the side groups have monotonically decreased the zero-field Ueff barriers of these weak antiferromagnetically coupled {Dy2} analogues from 721 K down to 379 K. Further electronic structure calculations demonstrate that the main magnetic axes of 1-4 are highly dominated by these comparable Dy-Ophenolate short bonds, and the g tensors have produced gradually increased transverse components responsible significantly for the decreased Ueff barriers. Additionally, thermally assisted relaxations occur preferably through the second (for 1) and the first (for 2-4) Kramer doublets. These interesting findings afford a new side-group effect to comprehensively understand the magnetostructural relationships and advance the rational design of high-performance Dy-SMMs.

Alkaline-Earth Chalcogenide Nanocrystals: Solution-Phase Synthesis, Surface Chemistry, and Stability.

Increasing demand for effective energy conversion materials and devices has renewed interest in semiconductors comprised of earth-abundant and biocompatible elements. Alkaline-earth sulfides doped with rare earth ions are versatile optical materials. However, relatively little is known about controlling the dimensionality, surface chemistry, and inherent optical properties of the undoped versions of alkaline-earth mono- and polychalcogenides. We describe the colloidal synthesis of alkaline-earth chalcogenide nanocrystals through the reaction of metal carboxylates with carbon disulfide or selenourea. Systematic exploration of the synthetic phase space allows us to tune particle sizes over a wide range using a mixture of commercially available carboxylate precursors. Solid-state NMR spectroscopy confirms the phase purity of the selenide compositions. Surface characterization reveals that bridging carboxylates and amines preferentially terminate the surface of the nanocrystals. While these materials are colloidally stable in the mother solution, the selenides are susceptible to oxidation over time, eventually degrading to selenium metal through polyselenide intermediates. As part of these investigations, we have developed the colloidal syntheses of barium di- and triselenides, two among few reported nanocrystalline alkaline-earth polychalcogenides. Electronic structure calculations reveal that both materials are indirect band gap semiconductors. The colloidal chemistry presented here may enable the synthesis of more complex, multinary chalcogenide materials containing alkaline-earth elements.

Improvement of the Proton Conduction of Copper(II)-Mesoxalate Metal-Organic Frameworks by Strategic Selection of the Counterions.

Three copper(II)/mesoxalate-based MOFs with formulas (H3O)[Cu9(Hmesox)6(H2O)6Cl]·8H2O (1), (NH2Me2)0.4(H3O)0.6[Cu9(Hmesox)6(H2O)6Cl]·8H2O (2), and (enH2)0.25(enH)1.5[Cu6(Hmesox)3(mesox)(H2O)6Cl0.5]Cl0.5·5.25H2O (3) were synthesized (H4mesox = mesoxalic acid = 2,2-dihydroxypropanedioic acid, en = ethylenediamine). Essentially, all of the compounds display the same anionic network with a different arrangement of the cations, which have a remarkable effect on the proton conduction of the materials, ranging from 1.16 × 10–4 S cm–1 for 1 to 1.87 × 10–3 S cm–1 for 3 (at 80 °C and 95% RH). These compounds also display antiferromagnetic coupling among the copper(II) ions through both the carboxylate and alkoxido bridges. The values of the principal magnetic coupling constants were calculated by density functional theory (DFT), leading to congruent values that confirm the predominant antiferromagnetic nature of the interactions.

Bifunctional metal–organic frameworks afforded by postsynthetic modification for efficient cycloaddition of CO2 and epoxides

AbstractBifunctional ionic metal–organic frameworks (MOFs) containing Lewis acid sites (unsaturated metal sites) and halide ions (Cl−, Br−, and I−) have attracted increasing attention due to their extra high activity for the cycloaddition of CO2 with epoxides. Herein, a novel microporous MOF (1‐Eu), namely, [Eu3(L)2(HCOO)(H2O)5]·14H2O (H4L = 2,6‐di(2,4‐dicarboxyphenyl)‐4‐(pyridine‐4‐yl)pyridine), has been synthesized by using a new bipyridyl‐based tetracarboxylate ligands (H4L). Structural analyses show that 1‐Eu is a 3D framework in which 1D chains with alternating triple and single carboxylate bridges are interlinked by the L ligands and contains microporous channels with uncoordinated pyridyl N atoms, which are easy to be modified by N‐methylation. Therefore, three bifunctional N‐methylation 1‐Eu MOFs, 1‐Eu‐MeX (X = Cl−, Br−, and I−), were successfully prepared from the 1‐Eu MOF by a postsynthetic modification (PSM) method. 1‐Eu‐MeX can efficiently catalyze the cycloaddition reaction without any cocatalyst and solvent. Among them, the 1‐Eu‐MeI catalyst displays the highest catalytic performance. Our work thus represents a rare demonstration of ionic MOFs as heterogeneous catalysts for efficient CO2 fixation with epoxides. More significantly, 1‐Eu‐MeX are the first reported Eu‐based ionic MOFs with the bipyridyl‐based tetracarboxylate ligand.

Effect of iron substitution in cryptomelane on the heterogeneous reaction with isoprene

Biogenic isoprene is an important pollutant for regional air quality. Being ubiquitously distributed on the earth surface, manganese (hydr)oxides should play a vital role in the transformation of isoprene. Cryptomelane is a typical manganese oxide with isomorphous substitution of Fe for Mn, but less attention has been paid to its heterogeneous reaction with isoprene. When Fe3+ replaces Mn3+, K+ is depleted and Mn3+ is oxidized to Mn4+. In contrast, oxygen vacancies are formed when Fe3+ substitutes Mn4+. Fe substitution creates weak crystallites and abundant mesopores, resulting in the increase of isoprene adsorption. As found by theoretical calculations, the Mn4+–O2- bonds at the cross sections of the tunnels is more active than that on the outer wall of the tunnels. After the adsorption of isoprene, bridging carboxylate species and hydrogen-bonding water are produced and the surface octahedra are distorted, i.e., Mn4+O6 → Mn3+O6-δ. As the heat facilitates the breakage of Mn4+–O2-, the increase of environmental temperature enhances the oxidation of isoprene. The above findings shed light on the effect of Fe substitution in cryptomelane to enhance the oxidation of isoprene, and illustrates that heterogeneous reaction with isoprene impairs the transformation of other environmental substances on cryptomelane.

Hydrophilic CO-Releasing Material of PEGlyated Ruthenium Carbonyl Complex.

The poor water-solubility and instability of Ru(II) carbonyl complex hamper the therapeutic application as CO releasing materials (CO-RMs). To enhance the hydrophilicity and bio-utility of CO, a robust Ru(I) carbonyl sawhorse skeleton was grafted with water-soluble PEGylated sidearm. In this case, 12 PEGylated sawhorse Ru2(CO)4 complexes were prepared with satisfactory yields and characterized by IR and 1H- and 13C- NMR. X-ray diffraction analysis of CO-RM 8, 13 and 14 revealed the featured diruthenium sawhorse skeleton and PEGylated axial ligands. The flask-shaking method measures the water-solubility of CO-RMs, indicating that both bridging carboxylate ligands and PEGlyated axial ligands regulate the hydrophilicity of these CO-RMs. Under photolysis conditions, CO-RM 4–13 sustainable released therapeutic amounts of CO in the myoglobin assay. The correlation of the CO release kinetics and hydrophilicity of CO-RMs demonstrated that the more hydrophilic CO-RM released CO faster. The biological test found that the low cytotoxic CO-RM 4 showed a specific anticancer activity toward HT-29 tumour cells.

Structural characterization and antimicrobial evaluation of chromium(III) and cobalt(III) complexes with 2,2-diMe-1,3-pdta: Tuning dimensionality of coordination polymer and the water content by alkyl substitution

Hexadentate 2,2-dimethyl-1,3-propanediamine-N,N,N’,N’-tetraacetate (2,2-diMe-1,3-pdta) ligand, containing two methyl substituents at the central carbon atom of a 1,3-propanediamine, has been prepared and used for the synthesis of Na[Cr(2,2-diMe-1,3-pdta)]·3.75H2O (1) and Na[Co(2,2-diMe-1,3-pdta)]·3.88H2O (2) complexes. These complexes were characterized by IR and electronic absorption spectroscopy, and single-crystal X-ray diffraction analysis. NMR (1H and 13C) spectroscopy was additionally applied for the characterization of complex 2. Crystallographic data indicate that the two investigated crystals are isostructural and contain 2,2-diMe-1,3-pdta ligand coordinated to metal ion through 2N and 4O atoms forming an octahedral complex in which the six-membered 1,3-propanediamine chelate ring adopts a twist-boat conformation. There are four such complex anions in the symmetry independent part of the unit cell. Each complex anion is further connected to the sodium counterion(s) via the bridging carboxylate group(s). Structural changes in 2,2-diMe-1,3-pdta-Cr(III) complex stimulated solely by the presence of alkyl side groups are discussed. The present study shows that in 1,3-pdta-type complexes of Cr(III) and Co(III), the environment at coordination centre can be modified by introducing substitution in one of the carbon atoms of the diamine and the resulting difference in the subunit structure can bring about noticeable change in molecular and crystal structure. The examples illustrate the importance of the steric effect for the fine tuning of the dimensionality of the resulting coordination polymer and the water content. The antimicrobial activity of complexes 1 and 2 was evaluated against different bacterial and Candida spp., while their cytotoxic effects were tested on the normal human lung fibroblast cell line (MRC-5).

Tuning three coordination polymers with dinuclear metal units via pH control: syntheses, structures, and magnetic properties

The self-assembly of three coordination polymers with dinuclear metal units, namely {[Co2(bpta)(phen)2]·2H2O}n (1), {[Co2(bpta)(phen)(H2O)]·4H2O·CH3CN}n (2), and {[Ni2(bpta)(phen)(H2O)]·2H2O·0.5CH3CN}n (3), has been tuned via the control of pH under solvothermal conditions. The structures are characterized by FTIR spectroscopy, elemental analysis, single-crystal X-ray diffraction and powder X-ray diffraction analysis. The H4bpta ligands exhibit μ6-κ2:κ1:κ2:κ1 and μ7-κ2:κ2:κ1:κ2 coordination modes in the complexes 1–3. The octahedral metal ions are connected by carboxylate and μ2-O bridges to form [Co2(μ-OCO)2] and [M2(μ-OCO)2(μ2-O)] SBUs, respectively. Complex 1 shows a 2D framework with {44.62} sql-net topology. Complexes 2 and 3 display 3D networks with {42.84} pts-net topology. Magnetic studies reveal that 1 and 2 exhibit weak antiferromagnetic interactions in the double- and triple-bridged dimeric cobalt(II) units (J ​= ​−0.53(6) cm−1 for 1, and −E2/k ​= ​−0.77 ​K for 2, respectively). Complex 3 shows a ferromagnetic interaction (J ​= ​2.44(1) cm−1) between two dimeric Ni(II) ions.