Water Ligands Research Articles

Heterocyclic nitrogen donor complexes of aluminium, gallium and indium with weakly coordinating triflate anions

The reactions of M(OTf)3 (M = Al, Ga, In; OTf = CF3SO3–) with 2,2′:6′,2′’- terpyridyl (terpy) in CH2Cl2 gave mer-[M(OTf)3(terpy)], whilst with 2,2′-bipyridyl (bipy) and 1,10-phenanthroline (phen) the products isolated were cis-[M”(OTf)2(bipy)2]OTf (M” = Al, Ga), cis-[In(OTf)(H2O)(bipy)2][OTf]2, cis-[Al(OTf)2(phen)2][OTf] and [In(H2O)2(phen)2][OTf]3. The X-ray structures of mer-[In(OTf)3(terpy)], cis-[Ga(OTf)2(bipy)2][OTf] and cis-[In(OTf)(H2O)(bipy)2][OTf]2, along with those of the minor by-products, cis-[Ga(H2O)2(phen)2][OTf]3 and the hydroxide-bridged dimer [{In(terpy)(OTf)}2(µ-OH)2][OTf]2 were also obtained, all of which show six-coordination at the metal ion. While the anhydrous complexes show κ1-coordination of the triflate to the metal ion, those species with coordinated water (or hydroxide) ligands show significant H-bonding interactions between the water H atoms and the O-atoms from triflate anions. The complexes were characterised by IR, 1H, 13C{1H}, 19F{1H} and 27Al NMR spectroscopy, together with microanalysis. The 19F{1H} NMR spectra suggest that in MeCN solution the coordinated triflates are displaced by the solvent, but the original complexes appear to reform on removal of the MeCN in vacuo.

Bioinspired cobalt molecular electrocatalyst for water oxidation coupled with carbon dioxide reduction

AbstractTo mimic photosynthesis in green plants, it is a crucial challenge to drive water oxidation and CO2 reduction in one single system. In this study, we present a bioinspired trinuclear pyridinedicarboxylate cobalt complex (Et3NH)2[CoIII2CoII(OH2)(pda)5]·H2O (1) that is capable of homogeneously electrocatalytic water oxidation and CO2 reduction simultaneously. The designed mix‐valent cobalt complex is in a V‐configuration composed of two terminal CoIII ions and one central CoII ion coordinated with one water ligand, which is resemble to aqua ligation of the natural catalytic complex in oxygen‐evolving complex (OEC). The electrochemical results show that this trinuclear cobalt complex could electrocatalyze water oxidation under neutral condition at the potentials of 1.15 V and 2.00 V versus NHE, with the Faraday efficiency as high as about 96% and 82%, and the TOF of 2.22 and 10.20 s−1, respectively. Meanwhile, it also displays electrocatalytic activity for the reduction of CO2 to CO with the TOF of 0.93 s−1. The cobalt complex has good catalytic performance for the conversion of H2O and CO2 into O2 and CO, respectively, which may be mainly due to the key role of the flexible water ligand on the central CoII ion in the catalytic process. This work represents the first multinuclear cobalt complex for mimicking bio‐system to drive water oxidation coupled with carbon dioxide reduction simultaneously.

Hybrid QM/MM Simulations Confirm Zn(II) Coordination Sphere That Includes Four Cysteines from the P2 × 4R Head Domain.

To ascertain the role of Zn(II) as an allosteric modulator on P2X4R, QM/MM molecular dynamic simulations were performed on the WT and two P2X4R mutants suggested by previous electrophysiological data to affect Zn(II) binding. The Gibbs free energy for the reduction of the putative P2X4R Zn(II) binding site by glutathione was estimated at −22 kcal/mol. Simulations of the WT P2X4R head domain revealed a flexible coordination sphere dominated by an octahedral geometry encompassing C126, N127, C132, C149, C159 and a water molecule. The C132A mutation disrupted the metal binding site, leading to a coordination sphere with a majority of water ligands, and a displacement of the metal ion towards the solvent. The C132A/C159A mutant exhibited a tendency towards WT-like stability by incorporating the R148 backbone to the coordination sphere. Thus, the computational findings agree with previous experimental data showing Zn(II) modulation for the WT and C132A/C159A variants, but not for the C132A mutant. The results provide molecular insights into the nature of the Zn(II) modulation in P2X4R, and the effect of the C132A and C132A/C159A mutations, accounting for an elusive modulation mechanism possibly occurring in other extracellular or membrane protein.

Calcium Chelidonate: Semi-Synthesis, Crystallography, and Osteoinductive Activity In Vitro and In Vivo.

Calcium chelidonate [Ca(ChA)(H2O)3]n was obtained by semi-synthesis using natural chelidonic acid. The structure of the molecular complex was determined by X-ray diffraction analysis. The asymmetric unit of [Ca(ChA)(H2O)3]n includes chelidonic acid coordinated through three oxygen atoms, and three water ligands. The oxygen atoms of acid and oxygen atoms of water from each asymmetric unit are also coordinated to the calcium of another one, forming an infinite linear complex. Calcium geometry is close to the trigonal dodecahedron (D2d). The intra-complex hydrogen bonds additionally stabilize the linear species, which are parallel to the axis. In turn the linear species are packed into the 3D structure through mutual intercomplex hydrogen bonds. The osteogenic activity of the semi-synthetic CaChA was studied in vitro on 21-day hAMMSC culture and in vivo in mice using ectopic (subcutaneous) implantation of CaP-coated Ti plates saturated in vitro with syngeneic bone marrow. The enhanced extracellular matrix ECM mineralization in vitro and ectopic bone tissue formation in situ occurred while a water solution of calcium chelidonate at a dose of 10 mg/kg was used. The test substance promotes human adipose-derived multipotent mesenchymal stromal/stem cells (hAMMSCs), as well as mouse MSCs to differentiate into osteoblasts in vitro and in vivo, respectively. Calcium chelidonate is non-toxic and can stimulate osteoinductive processes.

Dinuclear Fe(III) Hydroxypropyl-Appended Macrocyclic Complexes as MRI Probes.

Four high-spin Fe(III) macrocyclic complexes, including three dinuclear and one mononuclear complex, were prepared toward the development of more effective iron-based magnetic resonance imaging (MRI) contrast agents. All four complexes contain a 1,4,7-triazacyclononane macrocyclic backbone with two hydroxypropyl pendant groups, an ancillary aryl or biphenyl group, and a coordination site for a water ligand. The pH potentiometric titrations support one or two deprotonations of the complexes, most likely deprotonation of hydroxypropyl groups at near-neutral pH. Variable-temperature 17O NMR studies suggest that the inner-sphere water ligand is slow to exchange with bulk water on the NMR time scale. Water proton T1 relaxation times measured for solutions of the Fe(III) complexes at pH 7.2 showed that the dinuclear complexes have a 2- to 3-fold increase in r1 relaxivity in comparison to the mononuclear complex per molecule at field strengths ranging from 1.4 T to 9.4 T. The most effective agent, a dinuclear complex with macrocycles linked through para-substitution of an aryl group (Fe2(PARA)), has an r1 of 6.7 mM-1 s-1 at 37 °C and 4.7 T or 3.3 mM-1 s-1 per iron center in the presence of serum albumin and shows enhanced blood pool and kidney contrast in mice MRI studies.

Probing Metal-Dependent Phosphate Binding for the Catalysis of the 17E DNAzyme.

The RNA-cleaving 17E DNAzyme exhibits different levels of cleavage activity in the presence of various divalent metal ions, with Pb2+ giving the fastest cleavage. In this study, the metal-phosphate interaction is probed to understand the trend of activity with different metal ions. For the first-row transition metals, the lowest activity shown by Ni2+ correlates with the inhibition by the inorganic phosphate and its water ligand exchange rate, suggesting inner-sphere metal coordination. Cleavage activity with the two stereoisomers of the phosphorothioate-modified substrates, Rp and Sp, indicated that Mg2+, Mn2+, Fe2+, and Co2+ had the highest Sp:Rp activity ratio of >900. Comparatively, the activity was much less affected using the thiophilic metals, including Pb2+, suggesting inner-sphere coordination. The pH-rate profiles showed that Pb2+ was different than the rest of the metal ions in having a smaller slope and a similar fitted apparent pKa and the pKa of metal-bound water. Combining previous reports and our current results, we propose that Pb2+ most likely plays the role of a general acid while the other metal ions are Lewis acid catalysts interacting with the scissile phosphate.

Thermochemical studies of hydrated manganese dications, Mn2+(H2O)x (x = 4–9), using guided ion beam tandem mass spectrometry

The experimental hydration energies of Mn2+(H2O)x complexes, where x = 4–9, are determined by threshold collision-induced dissociation (TCID) with Xe using a guided ion beam tandem mass spectrometer, coupled with an electrospray ionization (ESI) source. The ESI source naturally produces intense beams of the x = 7–9 complexes, but smaller complexes, x = 4–6, can be formed using an in-source fragmentation technique. For all systems, the dominant fragmentation processes observed are sequential loss of water ligands, but at x = 4 and 5, charge separation (CS) reactions are observed where formation of singularly charged species becomes competitive. Kinetic energy-dependent cross sections are obtained and analyzed to yield 0 K bond dissociation energies (BDEs) for the losses of one and two water ligands, which are then converted to 298 K binding enthalpies and Gibbs energies. Barrier heights for three different CS reactions are also determined. These thermodynamic results are compared with values obtained theoretically, with reasonable agreement being achieved. Theoretical geometry and single-point energy calculations are performed at B3LYP, B3P86, M06, and MP2(full) levels of theory.

Water-oriented magnetic anisotropy transition

Water reorientation is essential in a wide range of chemical and biological processes. However, the effects of such reorientation through rotation around the metal–oxygen bond on the chemical and physical properties of the resulting complex are usually ignored. Most studies focus on the donor property of water as a recognized σ donor-type ligand rather than a participant in the π interaction. Although a theoretical approach to study water-rotation effects on the functionality of a complex has recently been conducted, it has not been experimentally demonstrated. In this study, we determine that the magnetic anisotropy of a Co(II) complex can be effectively controlled by the slight rotation of coordinating water ligands, which is achieved by a two-step structural phase transition. When the water molecule is rotated by 21.2 ± 0.2° around the Co–O bond, the directional magnetic susceptibility of the single crystal changes by approximately 30% along the a-axis due to the rotation of the magnetic anisotropy axis through the modification of the π interaction between cobalt(II) and the water ligand. The theoretical calculations further support the hypothesis that the reorientation of water molecules is a key factor contributing to the magnetic anisotropy transition of this complex.

Adrenodoxin and Substrate Binding Modulate the Vitamin‐D Metabolizing Human Cytochrome P450 24A1

Vitamin-D3 insufficiency is associated with rickets, cardiovascular disease, and chronic kidney disease, and therefore impacts nearly 50% of the U.S. population. In humans, vitamin-D3 is metabolized by a series of cytochrome P450 enzymes, including inactivation by the mitochondrial cytochrome P450 enzyme CYP24A1. CYP24A1 in humans first hydroxylates either the carbon-23 or carbon-24 position of 1,25-(OH)2D3. The human isoform of CYP24A1 is not easily expressed and purified recombinantly. Therefore, most current structural studies are based on the rat isoform, which does not display carbon-23 regioselective hydroxylation. As a way to study the human isoform, we have initiated use of a cleavable fusion construct of human CYP24A1 with its reduction-oxidation protein partner adrenodoxin. Cleaved and isolated human CYP24A1 provides a platform for interrogating the structural effects of an Adx-CYP24A1 complex on substrate, analog, and inhibitor binding. Notably, we observed that the presence Adx weakens the interaction between human CYP24A1 1.5-fold, while also increasing the population of the high spin shift that results from displacement of a water ligand. This effect is not seen with 1-(OH)D3, a vitamin-D3 analog, suggesting that specific substrate binding relates allosterically to Adx recognition. The path of this allostery is investigated by specific point mutations. These findings provide mechanistic insight into the interrelated nature of step I (substrate binding) and step II (redox partner binding) of a multi-functional mitochondrial cytochrome P450 enzyme.

Truly Monodisperse Molecular Nanoparticles of Cerium Dioxide of 2.4 nm dimensions: A {Ce100 O167 } Cluster.

Ultra-small nanoparticles of CeO2 obtained in molecular form, so-called molecular nanoparticles, have been limited to date to a family whose largest member is of nuclearity Ce40 with a {Ce40 O58 } core atom count. Herein we report that a synthetic procedure has been developed to the cation [Ce100 O149 (OH)18 (O2 CPh)60 (PhCO2 H)12 (H2 O)20 ]16+ , a member with a much higher Ce100 nuclearity and a {Ce100 O167 } core that is more akin to the smallest ceria nanoparticles. Its crystal structure reveals it to possess a 2.4 nm size and high D2d symmetry, and it has also allowed identification of core surface features including facet composition, the presence and location of Ce3+ and H+ (i.e. HO- ) ions, and the binding modes of the ligand monolayer of benzoate, benzoic acid, and water ligands.

Truly Monodisperse Molecular Nanoparticles of Cerium Dioxide of 2.4 nm dimensions: A {Ce100O167} Cluster

AbstractUltra‐small nanoparticles of CeO2 obtained in molecular form, so‐called molecular nanoparticles, have been limited to date to a family whose largest member is of nuclearity Ce40 with a {Ce40O58} core atom count. Herein we report that a synthetic procedure has been developed to the cation [Ce100O149(OH)18(O2CPh)60(PhCO2H)12(H2O)20]16+, a member with a much higher Ce100 nuclearity and a {Ce100O167} core that is more akin to the smallest ceria nanoparticles. Its crystal structure reveals it to possess a 2.4 nm size and high D2d symmetry, and it has also allowed identification of core surface features including facet composition, the presence and location of Ce3+and H+ (i.e. HO−) ions, and the binding modes of the ligand monolayer of benzoate, benzoic acid, and water ligands.

Plasma-Initiated Graft Polymerization of Acrylic Acid onto Fluorine-Doped Tin Oxide as a Platform for Immobilization of Water-Oxidation Catalysts.

The discovery of new and versatile strategies for the immobilization of molecular water-oxidation catalysts (WOCs) is crucial for developing clean energy conversion devices [e.g., (photo)electrocatalytic cells for water splitting]. The traditional approach for surface attachment to transparent conductive oxides [e.g., fluorine doped tin oxide (FTO)] is via synthetic modification of the ligand architecture to incorporate functional groups such as carboxylic acids (-COOH) or phosphonates (-PO3H2) prior to immobilization. However, challenges arising from desorption and the cumbersome derivatizations steps have limited the scope and applications of surface-bound WOCs. Herein, we report the successful immobilization of underivatized Ru(II)-based WOCs (Ru-Cat1 = [Ru(tpy) (bpy) (H2O)]2+ (tpy = 2,2':6'2″-terpyridine and bpy = 2,2'-bipyridine) and Ru-Cat2 = [Ru(Mebimpy) (bpy) (H2O)]2+ (Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl) pyridine)) and the Ru(II) polypyridyl chromophore Ru-C3 = [Ru(bpy)3]2+ onto a FTO plasma-grafted poly(acrylic acid) surface (PAA|FTO). Various characterization techniques such as attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, and cyclic voltammetry measurements provide evidence for the plasma-induced grafted PAA|FTO film and immobilization. Surface stability and electrocatalytic properties of these new hybrid composite films upon cycling were investigated at different pH values. Immobilized Ru-Cat1 and Ru-Cat2 onto PAA|FTO displayed pH-dependent (RuIII/RuII) couples and onset potentials indicative of PCET (proton-coupled electron transfer) reactions. Based on cyclic voltammetry results and spectroscopic monitoring, the immobilized WOCs Ru-Cat1 and Ru-Cat2 exhibited a higher surface stability in neutral aqueous solutions relative to Ru-C3 upon electrochemical oxidation. We attribute the surface PCET and stability to the presence of a water ligand in the coordination sphere of immobilized Ru-Cat1 and Ru-Cat2 which can H-bond with negatively charged carboxylate groups of the cross-linked PAA brushes. Our findings demonstrate that the plasma-grafted polymeric network onto FTO offers a versatile platform to directly anchor unmodified homogeneous WOCs or chromophores for potential applications in solar-to-fuel energy conversion.

The guanidinium t-diaqua-bis(oxalato)chromate(III) dihydrate complex: synthesis, crystal structure, EPR spectroscopy and magnetic properties

Abstract A new salt (CH6N3)[t-Cr(C2O4)2(H2O)2]·2H2O (1) (CH6N3 + = guanidinium cation) has been synthesized and characterized by single-crystal X-ray diffraction, FT-IR and UV–Vis spectroscopies, elemental and thermogravimetric analyses. In the crystal structure of 1, the chromate(III) ion lies on an inversion center in the form of an elongated octahedron. The coordination sphere consists of four oxygen atoms of two chelating oxalato ligands in the equatorial plane and two axial oxygen atoms of water ligands. The structural feature of focal interest in the structure of 1 is the formation of pillars of [Cr(C2O4)2(H2O)2]− complex anions and CH6N3 + guanidinium cations, with the next-neighbor cations rotated by an angle of 60° relative to each other. O–H···O and N–H···O hydrogen bonds play an important role in the construction of the three-dimensional network. The electron paramagnetic resonance (EPR) and magnetic properties of 1 have also been investigated.

Mn(II) and Co(II) mixed-ligand coordination compounds with acesulfame and 3-aminopyridine: synthesis and structural properties

Two mixed ligand complexes containing acesulfame (acs) and 3-aminopyridine (3-ap) ligands of Mn(II) and Co(II) were synthesized. The obtained compounds were characterized by various analysis methods. The geometries of complexes, C18H28MnN6O12S2 (1) and C18H32CoN6O14S2 (2), are distorted octahedra. Coordination of metal cations is provided by two molecules of 3-ap and four water ligands. In both structures, the 2+ charge of the metal required two monoanionic acs molecules located outside the coordination sphere. Complex 1 contains no hydrate water, while 2 contains two molecules of hydrate water. The crystal system of 1 is monoclinic and space group P21/c, while the crystal system of 2 is triclinic and space group P-1. Data on the removal of hydrate and crystalline waters in structures from thermal analysis curves support the described molecular structures. The bending vibrations of the bonds obtained from the FT-IR spectra match the crystal structure described. As a result of thermal analysis of both complexes, it was determined that the relevant metal cations remained in the reaction vessel as oxide (MnO and CoO) residues.

Solid state structure of sodium β-1-thiophenyl glucuronate identifies 5-coordinate sodium with three independent glucoronates

Glucuronic acid is a key component of the glycosaminoglycans (GAGs) Chrondroitin Sulfate (CS), Heparin/Heparan sulfate (HS) and Hyaluronic Acid (HA), as well an important metabolite derivative. In biological systems the carboxylate of uronic acids in GAGs is involved in important H-binding interactions, and the role of metal coordination, such as sodiated systems, has indications associated with a number of biological effects, and physiological GAG-related processes. In synthetic approaches to GAG fragments, thioglycoside intermediates, or derivatives from these, are commonly employed. Of the reported examples of sodium coordination in carbohydrates, 6-coordinate systems are usually observed often with water ligands involved, Herein we report an unexpected 5-coordinate sodiated GlcA crystal structure of the parent GlcA, but as a thioglycoside derivative, whose crystal coordination differs from previous examples, with no involvement of water as a ligand and containing a distorted trigonal bypramidal sodium with each GlcA having five of 6 oxygens sodium-coordinated.

Lead(II) Tetracyanidoborates with Pb 2 O 2 Dimers Embedded in Network Structures

First lead(II) tetracyanidoborates were synthesized and the crystal structures of [Pb2(H2O)4{B(CN)4}4] (1) and [Pb2(O2CCH3)2{B(CN)4}2(C2H5OH)2] (2) were determined by X-ray diffraction. Both compounds contain dinuclear centrosymmetric Pb2O2 cores. The Pb(II) ions in both compounds have heteroleptic holodirected coordination environments constituted by three O and five N atoms (O3N5) in 1 different from that in 2, which is constituted by four O and four N atoms (O4N4). In 1 the bridging O atoms of the Pb2O2 unit belong to the water ligands, whereas in 2 one O atom of each of the two acetate ligands has the bridging functionality whereas the second one is terminally bonded, i. e. the acetate ligand coordinates in a μ2-η2:η1 fashion. In 2, all four N atoms of the tetracyanidoborate anion are coordinated to neighboring Pb2O2 units, whereas in 1 free cyanido groups exist. Nevertheless, in both structures the dinuclear Pb units are three-dimensionally interconnected, i. e. they are Pb(II) coordination networks. On heating compound 1 loses the aqua ligands and anhydrous Pb[B(CN)4]2 forms.

Dynamics and Multiconfiguration Potential Energy Surface for the Singlet O2 Reactions with Radical Cations of Guanine, 9-Methylguanine, 2'-Deoxyguanosine, and Guanosine.

Reactions of electronically excited singlet oxygen (1O2) with the radical cations of guanine (9HG•+), 9-methylguanine (9MG•+), 2'-deoxyguanosine (dGuo•+), and guanosine (Guo•+) were studied in the gas phase by a combination of guided-ion-beam mass spectrometric measurement of product ions and cross sections as a function of collision energy (Ecol) and electronic structure calculations of the reaction potential energy surface (PES) at various levels of theory. No product could be captured in the 1O2 reaction with bare 9HG•+ or 9MG•+, because energized products decayed rapidly to reactants before being detected. To overcome this unfavorable kinetics, monohydrated 9HG•+·H2O and 9MG•+·H2O were used as reactant ions, of which the peroxide product ions were stabilized by energy relaxation via elimination of the water ligand. Reaction cross sections for 9HG•+·H2O and 9MG•+·H2O decrease with increasing Ecol, becoming negligible above 0.6 eV. This indicates that the reactions are exothermic with no barriers above reactants and the heat of formation of the products is sufficiently large to overcome their water ligand elimination energy (0.7 eV). Peroxide product ions were also detected in the 1O2 reactions with unhydrated dGuo•+ and Guo•+, in which intramolecular vibrational redistribution was able to stabilize oxidation products. 9MG•+ was utilized as a model system to explore the reaction PES for the initial 1O2 addition to the guanine radical cation. Calculations were carried out using single-reference ωB97XD, RI-MP2, and DLPNO-CCSD(T) and multireference CASSCF and CASPT2. Although the same PES profile was obtained at different levels of theory, the energies of the mixed open- and closed-shell 1O2 reactant and the open-shell reaction intermediates, transition states, and products are sensitive to the theories. By taking into account both static and dynamic electron correlations, the CASPT2 PES has provided the best agreement with the experimentally measured reaction thermodynamics and predicted 8-peroxide as the most probable initial oxidation product of the guanine radical cation.

Computational Insights into As(V) Removal from Water by the UiO-66 Metal–Organic Framework

Metal–organic frameworks (MOFs) such as UiO-66 have shown great promise for the removal of toxic As(V) species from water, but the precise adsorption mechanism is not yet well understood. In this study, we use density functional theory calculations and cluster models to determine accurate energetics and geometries for the adsorption of As(V) species present under varying pH conditions, namely, arsenic acid and related oxyanions. As a result of this analysis, we identify a new adsorption mode in which two As(V) molecules adsorb in a monodentate fashion on two neighboring Zr open metal sites resulting from capping ligand displacement. This mode is preferred over other adsorption modes previously proposed in the literature at acidic and neutral pH. Multidentate adsorption modes involving adsorption of a single As(V) molecule onto both neighboring Zr sites become more competitive as the pH increases, consistent with the lower adsorption performance observed at basic pH. Additionally, we study the influence of the ligands capping the Zr sites on As(V) adsorption thermodynamics. We show that the hydroxide–water ligand pair is the capping ligand most easily displaced by adsorbing As(V) species, suggesting that defects present in the aqueous environment are the ideal site for As(V) species adsorption. Furthermore, we find that adsorption of phosphate oxyanions can thermodynamically compete with As(V) adsorption, thus potentially explaining the observed decreased As(V) adsorption performance in the presence of phosphates. The molecular-level insights gained in this study are used to draw general design principles for the development of new MOFs that can be employed to remove toxic oxyanions from water.

Crystallographic and Computational Electron Density of dx2-y2 Orbitals of Azo-Schiff Base Metal Complexes Using Conventional Programs.

The crystal structures of two azobenzene derivative Schiff base metal complexes (new C44H40CuN6O2 of P-1 and known C44H38MnN6O7 of P21/c abbreviated as Cu and Mn, respectively) were (re-)determined experimentally using conventional X-ray analysis to obtain electron density using a PLATON program. Cu affords a four-coordinated square planar geometry, while Mn affords a hexa-coordinated distorted octahedral geometry whose apical sites are occupied by an acetate ion and water ligands, which are associated with hydrogen bonds. The π-π or CH-π and hydrogen bonding intermolecular interactions were found in both crystals, which were also analyzed using a Hirshfeld surface analysis program. To compare these results with experimental results, a density functional theory (DFT) calculation was also carried out based on the crystal structures to obtain calculated electron density using a conventional Gaussian program. These results revealed that the axial Mn-O coordination bonds of Mn were relatively weaker than the in-plane M-N or M-O coordination bonds.

Manganese(II) complexes derived from acyclic ligands having flexible alcohol arms: structural chracterization and SOD and catalase mimetic studies.

In this work, a series of seven MnII complexes of noncyclic flexible ligands derived from 2,6-diformylpyridine and ethanolamine or alkyl-substituted ethanolamines were prepared and characterized, six structurally by single-crystal X-ray diffraction studies. The complexes are dichlorido{2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]diethanol}manganese(II), [MnCl2(C11H15N3O2)] or [MnCl2(L1)], (2), bis{μ-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]diethanol}bis[dithiocyanatomanganese(II)], [Mn2(NCS)4(C11H15N3O2)2] or [Mn2(NCS)4(L1)2], (3), chlorido{1,1'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-2-ol)}manganese(II) chloride monohydrate, [MnCl(C13H19N3O2)(H2O)]Cl·H2O or [MnCl(L2)(H2O)]Cl·H2O, (4), {1,1'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-2-ol)}dithiocyanatomanganese(II), [Mn(NCS)2(C13H19N3O2)] or [Mn(NCS)2(L2)], (5), aquadichlorido{2,2'-dimethyl-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-1-ol)}manganese(II) 0.3-hydrate, [MnCl2(C15H23N3O2)(H2O)]·0.3H2O or [MnCl2(L3)(H2O)]·0.3H2O, (6), (dimethylformamide){2,2'-dimethyl-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-1-ol)}dithiocyanatomanganese(II), [Mn(NCS)2(C15H23N3O2)(C3H7NO)] or [Mn(NCS)2(L3)(DMF)], (7), and (dimethylformamide){2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(butan-1-ol)}dithiocyanatomanganese(II) dimethylformamide monosolvate, [Mn(NCS)2(C15H23N3O2)(C3H7NO)]·C3H7NO or [Mn(NCS)2(L4)(DMF)]·DMF, (8). The crystal structure of ligand L1 is also reported, but that of (5) is not. All four ligands (L1-L4) have five potential donor atoms in an N3O2 donor set, i.e. three N (pyridine/diimine donors) and two alcohol O atoms, to coordinate the MnII centre. The N3O2 donor set coordinates to the metal centre in a pentagonal planar arrangement; seven-coordinated MnII complexes were obtained via coordination of two auxiliary ligands (anions or water molecules) at the axial positions. However, in some cases, the alcohol O-atom donors remain uncoordinated, resulting in five- or six-coordinated MnII complexes. The structurally characterized complexes were tested for their catalytic scavenging of superoxide and peroxide. The results indicated that the complexes with coordinated exogenous water or chloride ligands showed higher SOD activity than those with exogenous thiocyanate ligands.