Solvent Water Molecules Research Articles

Syntheses and crystal structures of 2-(p-tol-yl)-1H-perimidine hemihydrate and 1-methyl-2-(p-tol-yl)-1H-perimidine.

The title compounds, 2-(4-methylphenyl)-1H-perimidine hemihydrate (1, C18H14N2·0.5H2O) and 1-methyl-2-(4-methylphenyl)-1H-perimidine (2, C19H16N2), were prepared and characterized by 1H NMR and single-crystal X-ray diffraction. The organic mol-ecule of the hemihydrate lies on a twofold rotation axis while the water mol-ecule lies on the inter-section of three twofold rotation axes (point group symmetry 222). As a consequence, the hydrogen atoms that are part of the N-H group and the water mol-ecule as well as the CH3 group of the p-tolyl ring are disordered over two positions. In compound 1, the perimidine and the 2-aryl rings are slightly twisted while its N-methyl-ated derivative 2 has a more distorted conformation because of the steric repulsion between the N-methyl group and the 2-aryl ring. In the crystal structures, mol-ecules of perimidine 2 are held together only by C-H⋯π contacts while the parent perimidine 1 does not exhibit this type of inter-action. Its crystal packing is established by inter-molecular N-H⋯O hydrogen bonds with the solvent water mol-ecules and additionally stabilized by π-π stacking.

Schiff base (Z)-4-((furan-2-ylmethylene)amino) benzenesulfonamide: Synthesis, solvent interactions through hydrogen bond, structural and spectral properties, quantum chemical modeling and biological studies

A new Schiff base (Z)-4-((furan-2-ylmethylene)amino)benzenesulfonamide (FURNI) was synthesized by the reaction reaction between furfural and sulfanilamide followed by characterization using IR, UV–Visible, 1HNMR, and 13CNMR spectral techniques. This was followed by electronic structure studies using DFT and TD-DFT. We simulated the IR spectrum using B3LYP/aug-ccPVDZ level of theory, followed by a comparison with experimental spectra and detailed potential energy distribution and vibrational assignment analysis. The comparison of experimental UV and simulated UV spectrum using TD-DFT CAM-B3LYP/ aug-ccPVDZ in DMSO solvent atmosphere gave good agreement. The compound is found to interact with the solvent water molecule. Energy decomposition analysis showed that there exists a strong hydrogen bond between the compound and the solvent water. As Schiff bases are biologically active, we checked for the potential activity of the synthesized compound with the help of ADMET prediction and found it to be active. Wavefunctions related properties like ELF, ALIE, LOL, and ELF are also reported. Prediction of biological activity spectrum study indicated possible antimicrobial activity against bacteria and fungus, which is supported by molecular docking against human mitochondrial (2WYA) protein with a docking score of −7.2 kcal/mol. Experimental antibacterial and antifungal studies using the compound and standard drugs confirmed this prediction.

Solvent effects on the NMR shieldings of stacked DNA base pairs.

Stacking effects are among the most important effects in DNA. We have recently studied their influence in fragments of DNA through the analysis of NMR magnetic shieldings, firstly in vacuo. As a continuation of this line of research we show here the influence of solvent effects on the shieldings through the application of both explicit and implicit models. We found that the explicit solvent model is more appropriate for consideration due to the results matching better in general with experiments, as well as providing clear knowledge of the electronic origin of the value of the shieldings. Our study is grounded on a recently developed theoretical model of our own, by which we are able to learn about the magnetic effects of given fragments of DNA molecules on selected base pairs. We use the shieldings of the atoms of a central base pair (guanine-cytosine) of a selected fragment of DNA molecules as descriptors of physical effects, like π-stacking and solvent effects. They can be taken separately and altogether. The effect of π-stacking is introduced through the addition of some pairs above and below of the central base pair, and now, the solvent effect is considered including a network of water molecules that consist of two solvation layers, which were fixed in the calculations performed in all fragments. We show that the solvent effects enhance the stacking effects on the magnetic shieldings of atoms that belong to the external N-H bonds. The net effect is of deshielding on both atoms. There is also a deshielding effect on the carbon atoms that belong to CO bonds, for which the oxygen atom has an explicit hydrogen bond (HB) with a solvent water molecule. Solvent effects are found to be no higher than a few percent of the total value of the shieldings (between 1% and 5%) for most atoms, although there are few for which such an effect can be higher. There is one nitrogen atom, the acceptor of the HB between guanine and cytosine, that is more highly shielded (around 15 ppm or 10%) when the explicit solvent is considered. In a similar manner, the most external nitrogen atom of cytosine and the hydrogen atom that is bonded to it are highly deshielded (around 10 ppm for nitrogen and around 3 ppm for hydrogen).

Triangulo-{ErIII 3} complex showing field supported slow magnetic relaxation.

The triangulo-{Er3} complex [Er3Cl(o-van)3(OH)2(H2O)5]Cl3·nH2O (n = 9.4; H(o-van) = o-vanillin) (1) was generated by an in situ method. The isolated Er(iii) complex 1 was characterized by elemental analysis and molecular spectroscopy. The results of single crystal X-ray diffraction studies have shown that 1 is built up of trinuclear [Er3Cl(o-van)3(OH)2(H2O)5]3+ complex cations, chloride anions and water solvate molecules. Within the complex cation the three Er(iii) central atoms are placed at the apexes of a triangle which are bridged by three (o-van)− ligands with additional chelating functions and two μ3-OH− ligands. Additionally five aqua and one chlorido ligands complete the octa-coordination of the three Er(iii) atoms. AC susceptibility measurements reveal that the compound exhibits slow magnetic relaxation with two relaxation modes.

Halogen bonding in cadmium(II) MOFs: its influence on the structure and on the nitroaldol reaction in aqueous medium.

A solvothermal reaction of Cd(II) with the dicarboxyl-functionalized arylhydrazone pro-ligands, 5-(2-(2,4,6-trioxotetrahydro-pyrimidin-5(2H)-ylidene)hydrazineyl)isophthalic acid (H5L1) and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl)isophthalic acid (H3L2), or their halogen bond donor centre(s) decorated analogs 2,4,6-triiodo-5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)hydrazineyl)isophthalic acid (H5L3) and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl)-2,4,6-triiodoisophthalic acid (H3L4), leads to the formation of known [Cd(H3L1)(H2O)2]n (1) and new {[Cd(HL2)(H2O)2(DMF)]·H2O}n (2), [Cd(H3L3)]n (3) and {[Cd2(μ-H2O)2(μ-H2L4)2(H2L4)2]·2H2O}n (4) coordination compounds, respectively. The aggregation of mononuclear units via Cd-OC and Cd-OH2 coordination and CAr-I⋯I types of intramolecular halogen bonds lead to a dinuclear tecton 4. Both CAr-I⋯O and CAr-I⋯I types of intermolecular halogen bonds play a fundamental role in the supramolecular architectures of the obtained metal-organic frameworks 3 and 4. Theoretical (DFT) calculations confirmed the presence of the CAr-I⋯O and CAr-I⋯I halogen bonds in 3 and 4 and allowed their characterisation. The formation of intermolecular noncovalent interactions between the attached iodine substituents to the hydrazone ligands and polar solvent (water or methanol) molecules promoted, at least in part, the solubility of the corresponding complexes (3 and 4), which act as homogeneous catalyst precursors in the Henry reaction between aldehydes and nitroethane. The corresponding β-nitroalkanol products were obtained in good yields (66-79%) and with good diastereoselectivity (threo/erythro ca. 72 : 28) in water at room temperature.

Site dependent catalytic water dissociation on an anisotropic buckled black phosphorus surface.

Black phosphorus (BP) is unique among 2D materials due to its anisotropic puckered structure. It has been used as a multifunctional catalyst for various purposes. In this study, we performed first principles molecular dynamics simulations to understand the water-splitting reaction on a bi-layer BP surface. We focused on the site-specific aqueous reactivity of the buckled surface. A difference in the axis-dependent reactivity is observed owing to edge defects and exposed sites. Thus, we believe that BP edges, which significantly affect the interfacial water or organic solvent molecules, must exhibit very different edge-dependent reactivity. Experiments suggested the increasing catalytic efficiency of undisturbed BP in the order bulk, few-layered BP, and BP quantum dots. We choose three active sites to investigate the mechanistic details of the OER: the zigzag (ZZ), armchair (AC), and bulk sites. This study will provide insight into the enhanced catalytic activity when more edges are exposed as the active surface. We hope to clarify the reactive pathway in an aqueous solution supported by bi-layer BP by exploring the two different mechanisms for forming the OOH* complex. We explore and report two mechanisms: a simple push-pull reaction for oxygen-oxygen bond formation, the nucleophilic attack by formed OH- and an attack by a water molecule. The free energy barriers procured for mechanism 1 taking place at the zigzag, armchair, and bulk sites are 7.59 ± 0.33, 9.04 ± 0.01, and 12.80 ± 0.09 kcal mol-1, respectively. For mechanism 2 the free energy barriers are 7.62 ± 0.11, 9.15 ± 0.16, and 11.63 ± 0.11 kcal mol-1 for the ZZ, AC, and bulk sites. The interlink between both the mechanisms is established concerning the reported free energy barriers for OOH* formation. The ZZ site is found to lower the activation barrier for the rate-determining step, followed by the AC and bulk.

Effect of electrolyte anions on the cycle life of a polymer electrode in aqueous batteries

Redox polymers are a class of high-capacity, low-cost electrode materials for electrochemical energy storage, but the mechanisms governing their cycling stability are not well understood. Here we investigate the effect of anions on the longevity of a p-dopable polymer through comparing two aqueous zinc-based electrolytes. Galvanostatic cycling studies reveal the polymer has better capacity retention in the presence of triflate anions than that with sulfate anions. Based on electrode microstructural analysis and evolution profiles of the cell stacking pressure, the origin of capacity decay is ascribed to mechanical fractures induced by volume change of the polymer active materials during repeated cycling. The volume change of the polymer with the triflate anion is 61% less than that with the sulfate anion, resulting in fewer cracks in the electrodes. The difference is related to the different anion solvation structures—the triflate anion has fewer solvated water molecules compared with the sulfate anion, leading to smaller volume expansion. This work highlights that anions with low solvation degree are preferable for long-term cycling.

Protonation induced self-complementarity of rod-like Cu(NTA)(bpeH) units and their layered supramolecular self-assembly entrapping heptamer like water clusters

Molecular self-assembly is the most important methodology for synthesizing novel materials including nano-materials. The ultimate challenge for scientists is to predict the self-assembled pattern of a set of molecular components. The labile nature of self-assembly arises from weak intermolecular forces which makes the outcome diverse, as small changes in physicochemical condition changes the course of self-assembly strongly. A one-pot reaction of 1,2-bis(4-pyridyl)ethylene (bpe), potassium salt of nitrilo-tri-acetic acid (K3NTA) and basic CuCO3 in an acidic medium (around pH = 4) give rise to a metal–organic complex with molecular formula C18H17CuN3O6.6(H2O) (henceforth it will be referred to as Cu-NTA-bpeH, where bpeH is singly protonated 1,2-bis(4-pyridyl)ethylene) whose self-assembly in the solid state shows that even a simple protonation event can drastically influence the course of the self-assembly. Further complication may arise from the participation of solvent water molecules in an unpredictable manner like the appearance of a new water-carboxylate heptamer cluster in the present crystal structure. The study of this simple system shows that pH-controlled protonation can lead to self-complementary metal organic units with interesting supramolecular architecture. The self-assembled system has been characterized by X-ray structural studies, Hirshfeld fingerprint and surface analysis, DFT computational studies as well as TG-DTA studies. The present crystal, which is analogous to clathrate hydrate, can possibly act as gas absorption and storage medium for future use.

Photocytotoxicity and photoinduced phosphine ligand exchange in a Ru(ii) polypyridyl complex.

Two new tris-heteroleptic Ru(ii) complexes with triphenylphosphine (PPh3) coordination, cis-[Ru(phen)2(PPh3)(CH3CN)]2+ (1a, phen = 1,10-phenanthroline) and cis-[Ru(biq)(phen)(PPh3)(CH3CN)]2+ (2a, biq = 2,2′-biquinoline), were synthesized and characterized for photochemotherapeutic applications. Upon absorption of visible light, 1a exchanges a CH3CN ligand for a solvent water molecule. Surprisingly, the steady-state irradiation of 2a followed by electronic absorption and NMR spectroscopies reveals the photosubstitution of the PPh3 ligand. Phosphine photoinduced ligand exchange with visible light from a Ru(ii) polypyridyl complex has not previously been reported, and calculations reveal that it results from a trans-type influence in the excited state. Complexes 1a and 2a are not toxic against the triple negative breast cancer cell line MDA-MB-231 in the dark, but upon irradiation with blue light, the activity of both complexes increases by factors of >4.2 and 5.8, respectively. Experiments with PPh3 alone show that the phototoxicity observed for 2a does not arise from the released phosphine ligand, indicating the role of the photochemically generated ruthenium aqua complex on the biological activity. These complexes represent a new design motif for the selective release of PPh3 and CH3CN for use in photochemotherapy.

(μ-2,2',2'',2'''-{[Pyrazine-2,3,5,6-tetra-yltetra-kis(methyl-ene)]tetra-kis(sulfanedi-yl)}tetra-acetato)bis-[aqua-nickel(II)] hepta-hydrate.

Reaction of the ligand 2,2',2'',2'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene)]tetra-kis-(sulfanedi-yl)}tetra-acetic acid (H4L1), with NiCl2 leads to the formation of a binuclear complex, (μ-2,2',2'',2'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene)]tetra-kis-(sulfanedi-yl)}tetra-acetato-κ5 O,S,N 1,S',O':κ5 O'',S'',N 4,S''',O''')bis[aqua-nickel(II)] hepta-hydrate, {[Ni2(C16H16N2O8S4)(H2O)2]·7H2O} (I). It crystallizes with two half mol-ecules in the asymmetric unit. The complete mol-ecules are generated by inversion symmetry, with the center of the pyrazine rings being located at crystallographic centres of inversion. The ligand coordinates two NiII ions in a bis-penta-dentate manner and the sixfold coordination sphere of each nickel(II) atom (NiS2O3N) is completed by a water mol-ecule. The complex crystallized as a hepta-hydrate. The binuclear complexes are linked by Owater-H⋯Ocarbon-yl hydrogen bonds, forming layers parallel to the (101) plane. This layered structure is additionally stabilized by weak C-H⋯O hydrogen bonds. Further O-H⋯O hydrogen bonds involving binuclear complexes and solvent water mol-ecules, together with weak C-H⋯S hydrogen bonds, link the layers to form a supra-molecular framework.

Hydration and Hydrogen Bond Order of Octadecanoic Acid and Octadecanol Films on Water at 21 and 1 °C.

The temperature-dependent hydration structure of long-chain fatty acids and alcohols at air-water interfaces has great significance in the fundamental interactions underlying ice nucleation in the atmosphere. We present an integrated theoretical and experimental study of the temperature-dependent vibrational structure and electric field character of the immediate hydration shells of fatty alcohol and acid headgroups. We use a combination of surface-sensitive infrared reflection-absorption spectroscopy (IRRAS), surface potentiometry, and ab initio molecular dynamics simulations to elucidate detailed molecular structures of the octadecanoic acid and octadecanol (stearic acid and stearyl alcohol) headgroup hydration shells at room temperature and near freezing. In experiments, the alcohol at high surface concentration exhibits the largest surface potential; yet we observe a strengthening of the hydrogen-bonding for the solvating water molecules near freezing for both the alcohol and the fatty acid IRRAS experiments. Results reveal that the hydration shells for both compounds screen their polar headgroup dipole moments reducing the surface potential at low surface coverages; at higher surface coverage, the polar headgroups become dehydrated, which reduces the screening, correlating to higher observed surface potential values. Lowering the temperature promotes tighter chain packing and an increase in surface potential. IRRAS reveals that the intra- and intermolecular vibrational coupling mechanisms are highly sensitive to changes in temperature. We find that intramolecular coupling dominates the vibrational relaxation pathways for interfacial water determined by comparing the H2O and the HOD spectra. Using ab initio molecular dynamics (AIMD) calculations on cluster systems of propanol + 6H2O and propionic acid + 10H2O, a spectral decomposition scheme was used to correlate the OH stretching motion with the IRRAS spectral features, revealing the effects of intra- and intermolecular coupling on the spectra. Spectra calculated with AIMD reproduce the red shift and increase in intensity observed in experimental spectra corresponding to the OH stretching region of the first solvation shell. These findings suggest that intra- and intermolecular vibrational couplings strongly impact the OH stretching region at fatty acid and fatty alcohol water interfaces. Overall, results are consistent with ice templating behavior for both the fatty acid and the alcohol, yet the surface potential signature is strongest for the fatty alcohol. These findings develop a better understanding of the complex surface potential and spectral signatures involved in ice templating.

Bridging Structure, Dynamics, and Thermodynamics: An Example Study on Aqueous Potassium Halides.

Aqueous salt systems are ubiquitous in all areas of life. The ions in these solutions impose important structural and dynamic perturbations to water. In this study, we employ a combined neutron scattering, nuclear magnetic resonance, and computational modeling approach to deconstruct ion-specific perturbations to water structure and dynamics and shed light on the molecular origins of bulk thermodynamic properties of the solutions. Our approach uses the atomistic scale resolution offered to us by neutron scattering and computational modeling to investigate how the properties of particular short-ranged microenvironments within aqueous systems can be related to bulk properties of the system. We find that by considering only the water molecules in the first hydration shell of the ions that the enthalpy of hydration can be determined. We also quantify the range over which ions perturb water structure by calculating the average enthalpic interaction between a central halide anion and the surrounding water molecules as a function of distance and find that the favorable anion-water enthalpic interactions only extend to ∼4 Å. We further validate this by showing that ions induce structure in their solvating water molecules by examining the distribution of dipole angles in the first hydration shell of the ions but that this perturbation does not extend into the bulk water. We then use these structural findings to justify mathematical models that allow us to examine perturbations to rotational and diffusive dynamics in the first hydration shell around the potassium halide ions from NMR measurements. This shows that as one moves down the halide series from fluorine to iodine, and ionic charge density is therefore reduced, that the enthalpy of hydration becomes less negative. The first hydration shell also becomes less well structured, and rotational and diffusive motions of the hydrating water molecules are increased. This reduction in structure and increase in dynamics are likely the origin of the previously observed increased entropy of hydration as one moves down the halide series. These results also suggest that simple monovalent potassium halide ions induce mostly local perturbations to water structure and dynamics.

Synthesis, crystal structure and characterization of two new metal-organic frameworks with 1,3,5-tris[(1H-imidazol-1-yl)methyl]benzene and cyclohexane-1,3,5-tricarboxylate ligands

Two new metal-organic frameworks (MOFs) {[Cu3(timb)2(chtc)2]·14H2O}n, (I) and {[Co3(timb)2(chtc)2]·6H2O}n, (II) were hydrothermally synthesized by corresponding metal salt with mixed organic ligands of 1,3,5-tris[(1H-imidazol-1-yl)methyl]benzene (timb) and cyclohexane-1,3,5-tricarboxylic acid (H3chtc). Crystal structural analysis reveals that they exhibit varied structures. In the MOFs (I), CuII adopts an four coordination geometry, timb and cyclohexane-1,3,5-tricarboxylate ligands bridge neighboring CuII centers to result in two different one-dimensional knotted chains along the [0 − 1 2] and [1 0 − 1] directions, respectively. The two kinds of chains intersect each other vis CuII centers, resulting in a two-dimensional layered structure running parallel to the (1 2 1) plane. Adjacent layers are further linked by water moleculars via classical O–H…O hydrogen-bonding interactions, giving rise to a three-dimensional supramolecular network structure in the solid state. While in MOFs (II), the cyclohexane-1,3,5-tricarboxylate anions link the CoII cations to generate a two-dimensional sheeted metal-organic structure running parallel to the bc plane. Adjacent sheets are further bridged by timb ligands, forming a porous three-dimensional metal-organic framework with a rare (3, 4)-connected (6.82)2(62.84)3(62.8)2 topology. The solvent water molecules guest in the micropores of porous framework via water-carboxylate O–H…O hydrogen bonds. In addition, their thermal stabilities have also been investigated.

Real-time in-situ quantification of protein secondary structures in aqueous solution based on ATR-FTIR subtraction spectrum

Changes occur in protein secondary structures during food processing, pharmaceutical research, and enzymatic reactions, etc. To date, most studies to quantify the protein secondary structures in aqueous solution have just involved semi-quantitative analysis and cannot achieve real-time measurements. In this study, attenuated total internal reflectance Fourier transform infrared spectroscopy was used to analyze the protein secondary structures, and buffer solution subtraction was used to minimize the interference of water and other solvent molecules. A novel calculation and correction method including acquisition parameters, subtraction spectrum criteria, second derivative spectra, Fourier self-deconvolution (FSD), peak fitting and peak assignment, was developed and applied to the amide I band of buffer-subtraction spectrum for optimization. It is found that the calculation and correction method achieved good reproducibility and high accuracy with the protein’s secondary structure results of 10 replicates, with the maximum coefficient of variation of less than 0.2 and the maximum difference within the group of less than 0.03. Moreover, the quantitative results from this method were consistent with the results of circular dichroism experiments and molecular simulation. Thus, the proposed method is suitable for directly analyzing protein secondary structures in aqueous solutions with a wide range of concentrations and in different buffer systems.

Tetra-ammonium μ-ethyl-enedi-amine-tetra-acetato-1κ3 O,N,O':2κ3 O'',N',O'''-bis-[trioxidotungstate(VI)] tetra-hydrate.

The title compound, (NH4)4[W2(C10H12N2O8)O6]·4H2O, was obtained from a mixture of tungstic acid, ammonia and ethyl-enedi-amine-tetra-acetic acid (H4edta) in a 2:4:1 ratio. The anion of the complex contains two WO3 units and one bridging edta4- ligand. Each central metal atom is tridentately coordinated by nitro-gen and two carboxyl-ate groups of the edta4- ligand, together with the three oxido ligands, producing a distorted octa-hedral coordination environment around each tungsten atom. The center of the carbon-carbon bond of the ethyl-ene bridge represents a crystallographic inversion center. The crystal structure consists of a three-dimensional supra-molecular framework built up by the dinuclear cations, the ammonium counter-ions and the solvent water mol-ecules via hydrogen bonds of the N-H⋯O and O-H⋯O type.

Chemistrees: Data-Driven Identification of Reaction Pathways via Machine Learning.

We propose to analyze molecular dynamics (MD) output via a supervised machine learning (ML) algorithm, the decision tree. The approach aims to identify the predominant geometric features which correlate with trajectories that transition between two arbitrarily defined states. The data-driven algorithm aims to identify these features without the bias of human “chemical intuition”. We demonstrate the method by analyzing the proton exchange reactions in formic acid solvated in small water clusters. The simulations were performed with ab initio MD combined with a method to efficiently sample the rare event, path sampling. Our ML analysis identified relevant geometric variables involved in the proton transfer reaction and how they may change as the number of solvating water molecules changes.

Isolation and Identification of Pseudo Seven-Coordinate Ru(III) Intermediate Completing the Catalytic Cycle of Ru-bda Type of Water Oxidation Catalysts

Isolation and Identification of Pseudo Seven-Coordinate Ru(III) Intermediate Completing the Catalytic Cycle of Ru-bda Type of Water Oxidation Catalysts

Heteroleptic complexes of Ni(II) with 2,2′-bipyridine and benzoato ligands. Magnetic properties of [Ni(bpy)(Bz)2

Under various experimental conditions seven complexes have been crystallized from the systems Ni(II) – HBz – bpy (HBz = benzoic acid, bpy = 2,2′-bipyridine). The use of freshly prepared Ni(OH)2 as starting reagent leads to isolation of [Ni(bpy)(Bz)2] (1) and [Ni(bpy)3](Bz)2·5H2O (2). On the other hand, the use of nickel(II) nitrate as starting salt yielded 1 and also resulted in the formation of additional complexes in which the nitrate group entered into the final compositions, namely [Ni(bpy)2(Bz)](NO3)·2HBz (3), [Ni(bpy)2(Bz)](NO3)·1.25H2O (4), [Ni(bpy)2(H2O)(NO3)](NO3)·0.5HBz (5), [Ni(bpy)2(NO3)](NO3) (6) and [Ni(bpy)3](NO3)2·nH2O (n = 4.25) (7). The newly prepared complexes were characterized chemically and spectroscopically. The results of X-ray structure analyses of 1, 3–6 have shown that in all complexes, the Ni(II) atoms are hexacoordinated. Complex 1 exhibits a mononuclear molecular structure, while the ionic structures of 3–6 are built up of mononuclear complex cations with a heteroleptic coordination sphere around the Ni(II) atoms and by nitrate anions. In addition, the structures of 3–5 contain HBz solvate molecules or water molecules. The magnetic properties of 1 were studied in the temperature range 1.8–300 K showing that 1 is characterized by the presence of single-ion anisotropy of the easy-axis type with a value of D/kB = −6.32 K and a strong rhombic term with E/D = 0.327. Theoretical calculations using the ORCA package also confirm a significant influence of rhombic anisotropy.

Synthesis, crystal structure and magnetic properties of poly[[diaqua{μ6-2-[bis-(carboxyl-atometh-yl)amino]-terephthalato}-dicobalt(II)] 1.6-hydrate

The asymmetric unit of the polymeric title compound {[Co2(C12H7NO8)(H2O)2]·1.6H2O} n comprises two CoII ions, which are coordinated by fully deprotonated 2-aminodi-acetic terephthalic acid (adtp4-) and terminal water mol-ecules in distorted octa-hedral N1O5 and O6 coordination environments. The title compound features tetra-nuclear CoII units bridged by κ 3 O:O:O'- and κ 3 O:O,O'-carboxyl-ate groups, which are joined into ribbons via syn-anti carboxyl-ate bridges. The parallel adtp4- ligands with an alternately reversed arrangement further link adjacent CoII ribbons into (010) layers, which are assembled into a three-dimensional supra-molecular network via inter-molecular hydrogen bonds. The disordered water solvent mol-ecules are situated in channels parallel to [100]. Magnetic measurements and analyses reveal that the title compound displays anti-ferromagnetic behaviour. The purity of the title compound was characterized by X-ray powder diffraction.

Elucidating the Role of Aqueous Solvent in an Iron‐Based Water Oxidation System by DFT‐based Molecular Simulation

AbstractWater solvent plays an important role in catalytic water oxidation to dioxygen, in particular in the O−O bond formation process. In this work, we revisit the mechanism of O−O bond formation catalyzed by a mononuclear iron catalyst [Cl−FeIII(dpa)−Cl]+, in a DFT‐based molecular dynamics (DFT‐MD) study that incorporates explicit solvent and thermal fluctuations. Two possible mechanisms for the crucial O−O bond formation, namely water nucleophilic attack (WNA) and nitrate nucleophilic attack (NNA) on the high‐valent FeV‐oxo moiety, were considered and found to have similar barriers (15 kcal/mol vs 16 kcal/mol). Comparison with static DFT calculations demonstrated the important role of water solvent molecules, especially for the NNA pathway. For this mechanism, the interaction of the negatively‐charged nitrate with solvent molecules is substantial, giving rise to a free energy barrier increase of 7.7 kcal/mol compared with static DFT calculations. The study suggests that for molecular water‐oxidation catalysts, the local aqueous solvation structure and its thermal fluctuations plays a significant role in the crucial O−O bond formation step. The study also elucidates the role of the nitrate ion as a co‐catalyst, a notion that may serve as a potential design rule for developing improved water oxidation catalysts.