Water Molecules In Coordination Sphere Research Articles

Solution and solid state structures of lanthanides(III) and uranyl(II) complexes of tripodal tris(2-pyridyl)-containing ligand on Ph3P(O) platform

Reaction of tris[2-(2′-pyridylmethoxy)phenyl]phosphine oxide (L) with f-element nitrates resulted in 1:1 complexes. The isolated complexes of ligand L with La(III), Eu(III), Tb(III), and U(VI) nitrates, and with La(III) chloride were studied in the solid state and solution by IR, Raman, and NMR spectroscopy, X-ray analysis, and also DFT calculations. Composition and structure of the complexes vary with lanthanide cation radius. According to the data of elemental analysis, vibrational spectroscopy, and X-ray diffraction, the ligand is coordinated in tridentate mode in crystalline La(III) and solid Eu(III) complexes: [Ln(OPO,N,Oeth-L)(H2O)(O,O-NO3)3], and in monodentate mode in crystalline complex [Tb(OPO-L)(H2O)2(O,O-NO3)3]. Nitrogen atoms of pyridine fragments of the ligand not involved in coordination produce intra- and intermolecular H-bonds with coordinated water molecules in the second coordination sphere of Ln(III). According to IR, NMR spectrometry, and DFT calculations, the structure of coordination polyhedron of the main species of Ln(III) complexes in acetonitrile solutions is retained including coordination of one of pyridine fragments in the second coordination sphere: [Ln{OPO,N,(N*),Oeth-L}(H2O)(O,O-NO3)3] and [Tb{OPO,(N*)-L}(H2O)2(O,O-NO3)3], where Ln = La, Eu, and N* is the nitrogen atom of pyridine fragment producing intramolecular H-bond with coordinated water molecule. According IR and Raman spectroscopy, ligand L is coordinated in bidentate mode in solid complex [UO2(OPO,N-L)(O,O-NO3)], and uncoordinated nitrogen atoms remain free. Solution structure of uranyl complex is labile and depends on solvent nature. Equilibria of complex species with variable coordination of nitrate ions, ligand L, and with probable involvement of water take place in CD3CN and CDCl3 solutions. Photophysical properties of the prepared Eu(III) and Tb(III) complexes were studied. The preliminary assessment of extraction properties of compound L was made. Stability of studied compounds in acetonitrile solutions was examined, and the structure of one of protolysis product of Eu(III) complex, [Eu(LH)(H2O)(NO3)4], was established by micro-IR and X-ray analysis.

Dimerization of Fe(III) Ion in an Aqueous Medium: Mechanistic Modelling and Effects of Ligands.

Aqueous iron solutions generally undergo spontaneous hydrolysis followed by aggregation resulting in the precipitation of nanocrystalline oxyhydroxide minerals. The mechanism of nucleation of such multinuclear oxyhydroxide clusters are unclear due to limited experimental evidence. Here, we investigate the mechanistic pathway of dimerization of Fe(III) ions using density functional theory (DFT) in aqueous medium considering effects of other ligands. Two hydrolyzed monomeric Fe(III) ions in aqueous medium may react to form two closely related binuclear products, the μ-oxo and the dihydroxo Fe2 dimer. Our studies indicate that the water molecules in the second coordination sphere and those co-ordinated to the Fe(III) ion, both participate in the dimerization process. The proposed mechanism effectively explains the formation of dihydroxo and μ-oxo Fe2 dimers with interconversion possibilities, for the first time. Results show, with only water molecules present in the second co-ordination sphere, dihydroxo Fe2 dimer is the thermodynamically and kinetically favored product with a low activation free energy. We calculated the step-wise reaction free energies of dimerization in the presence of nitrate ions in the first and second coordination sphere of Fe(III) ion separately, which shows that with nitrate ions in the second co-ordination sphere, the μ-oxo Fe2 dimer is the kinetically favored product.

Systematic Raman spectroscopic study of the complexation of uranyl with fluoride.

A simple aqueous complexing system of UO22+ with F- is selected to systematically illustrate the application of Raman spectroscopy in exploring uranyl(VI) chemistry. Five successive complexes, UO2F+, UO2F2(aq), UO2F3-, UO2F42-, and UO2F53-, are identified, as well as the formation constants except for the 1 : 5 species UO2F53-, which was experimentally observed here for the first time. The standard relative molar Raman scattering intensity for each species is obtained by deconvolution of the spectra collected during titrations. The results of relativistic quantum chemical first-principles and ab initio calculations are presented for the complete set of [UO2(H2O)mFn]2-n complexes (n = 0-5), both for the gas phase as well as for aqueous solution modelling bulk water using the conductor-like screening model. Electronic structure calculations at the Møller-Plesset second-order perturbation theory level provide accurate geometrical parameters and in particular reveal that k water molecules in the second coordination sphere coordinating to the F- ligands in the resulting [UO2(H2O)mFn]2-n(H2O)k complexes need to be treated explicitly in order to obtain vibrational frequencies in very good agreement with experimental data. The thermodynamics and structural information obtained in this work and the developed methodology could be instructive for the future experimental and computational research on the complexation of the uranyl ion.

Mixed-ligand complex [Cu4(bpy)4(PO4)2(CO3)(H2O)2]: synthesis, crystal structure and biological properties

The interaction in the system {Сu(OAc)2·H2O–phytic acid–2,2`-bipyridine (bpy)} in an aqueous-methanol solution led to the formation of a molecular mixed-ligand tetranuclear complex [(Cu4(bpy)4(PO4)2(CO3 )(H2O)2]13H2O (I), the structure of which was established based on the results of an X-ray diffraction experiment (CCDC 2262998). According to X-ray diffraction data, the molecule contains four nonequivalent Cu2+ cations, which coordinate two phosphate anions (PO43-, remaining as a result transformation of the phytate cycle), four neutral bpy, two water molecules and one carbonate anion fragment (CO32-). The presence of a large number of solvate water molecules in the outer coordination sphere created a hydrogen-bonded framework involved in the stabilization of the crystal packing. Study of antimycobacterial activity of I in against the non-pathogenic strain Mycolicibacterium smegmatis showed its high bioeffectiveness.

Ionic Liquid Assisted Exothermic Complexation of Trivalent Lanthanides with Fluorinated β Diketone: Multitechnique Approach with Theoretical Insight.

The complexation of the betadiketone,1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione (HFOD) was studied with trivalent lanthanide ions, viz. Nd3+, La3+, and Eu3+ in several methylimidazolium-based ionic liquids (Cnmim•NTf2, where, n = 4,6,8). In C6mim•NTf2, predominant formation of ML2+ and ML4- species was evidenced from the UV-vis absorption (Nd3+) as well as luminescence (Eu3+) spectral studies with log β2 ≈ 5.88 ± 0.04, log β4 ≈ 10.95 ± 0.06. The formation constants followed the trend C4mim•NTf2 > C6mim•NTf2 > C8mim•NTf2. The asymmetry factors for the ML2+ and ML4- species were found to be 1.2 and 1.59, respectively. The ML4- complex was found to have one primary coordination sphere water molecule with enhanced covalency between Eu3+ and O from HFOD (Judd Offelt constants Ω2 and Ω4 ≈ 17.2 and 2.35) compared to Eu3+aq, yet comparable to other β diketones. Complexation-induced temperature increase was confirmed by calorimetric measurements, indicating the exothermic complexation reaction (ΔHcomplexation ≈ -13.7 kJ mol-1), which is also spontaneous in nature (ΔG ≈ -68.1 kJ mol-1), with an enhancement in the entropy values. Due to complexation, the shifts in the peak positions (1686.66 cm-1, 1633.53 cm-1) associated with β diketone/ketone functional groups were evidenced. Density functional theory (DFT) calculation was performed to optimize the structural parameters including bond distance, bond angles, and energetics associated with the complexation.

Pyrrolidine-Derived Phenanthroline Diamides: An Influence of Fluorine Atoms on the Coordination of Lu(III) and Some Other f-Elements and Their Solvent Extraction.

Three pyrrolidine-derived phenanthroline diamides were studied as ligands for lutetium trinitrate. The structural features of the complexes have been studied using various spectral methods and X-ray. The presence of halogen atoms in the structure of phenanthroline ligands has a significant impact on both the coordination number of lutetium and the number of solvate water molecules in the internal coordination sphere. The stability constants of complexes with La(NO3)3, Nd(NO3)3, Eu(NO3)3, and Lu(NO3)3 were measured to demonstrate higher efficiency of fluorinated ligands. NMR titration was performed for this ligand, and it was found that complexation with lutetium leads to an approximately 13 ppm shift of the corresponding signal in the 19F NMR spectrum. The possibility of formation of a polymeric oxo-complex of this ligand with lutetium nitrate was demonstrated. Experiments on the liquid-liquid extraction of Am(III) and Ln(III) nitrates were carried out to demonstrate advantageous features of chlorinated and fluorinated pyrrolidine diamides.

Unassisted and Efficient Actinide/Lanthanide Separation with Pillar[5]arene-Based Picolinamide Ligands in Ionic Liquids

Actinide/lanthanide separation is crucial for the development of nuclear industries, while this is largely hindered by their similar chemical and physical properties. In this work, we report solvent extraction systems comprising different pillar[5]arene-based picolinamide ligands with various substituted groups and the ionic liquid, C4mimNTf2, for efficient actinide/lanthanide separation from acidic solutions. Changing the pyridine nitrogen basicity by substituting the chlorine group (−I effect) or methoxy group (+I effect) at the para-position changes the extraction performance of the ligands substantially. The chlorine group gave negative extraction performance while the methoxy group enhanced the metal ion extraction ability by three orders of magnitude. Extraction kinetics for Am3+ and Eu3+ was fast, and equilibrium distribution values were reached within 15 min with all three ligands. Slope analyses suggested that the stoichiometry of the extracted complexes of Am3+ and Eu3+ with the three ligands is M/L 2/1, and each metal ion is extracted following the cation exchange mechanism involving the transfer of three C4mim+ cations into the aqueous phase. Fluorescence spectroscopic investigation indicated that the extracted complexes were much distorted and ligands were directly coordinated to the metal ion with no sign of water molecules in the primary coordination sphere. The possible complexation structures of the ligands and the Eu3+ ion were optimized by density functional theory calculations, which confirmed that the differences in the extraction ability of the ligands originate from different bonding strength between pyridine nitrogens and metal ions.

The ab initio and experimental study of the spectroscopic and magnetic properties of Ho(III)-EDTA

In this paper the ab initio calculations of the electronic structure and the magnetic properties are discussed in the context of the experimental data for the Ho–EDTA complex. In the calculations different models of the cluster have been applied to examine the influence of various parts of the environment of the Ho(III)-EDTA complex on its properties. In particular, the calculations support the expectation that the presence of the water molecules in the first coordination sphere has considerable impact on the oscillator strengths of the electronic transitions and the magnetic susceptibility of the material under study. We have reconsidered the effect of the dynamical electron correlation on the magnetic susceptibility.

Yb to Tb Cooperative Upconversion in Supramolecularly Assembled Complexes in a Solution

The podand-type ligand L, based on a tertiary amine substituted by three pyridyl-6-phosphonic acid functions, forms hydrated complexes with Ln3+ cations. The luminescence properties of the YbL complex were studied in D2O as a function of the pD and temperature. In basic conditions, increases in the luminescence quantum yield and the excited state lifetime of the Yb centered emission associated with the 2F5/2 → 2F7/2 transition were observed and attributed to a change in the hydration number from two water molecules in the first coordination sphere of Yb at acidic pH to a single one in basic conditions. Upon the addition of TbCl3 salts to a solution containing the YbL complex in D2O, heteropolynuclear Yb/Tb species formed, and excitation of the Yb at 980 nm resulted in the observation of the typical visible emission of Tb as a result of a cooperative upconversion (UC) photosensitization process. The UC was further evidenced by the quadratic dependence of the UC emission as a function of the laser power density.

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

Developing A Novel Coumarone-Phenyl Amide Functionalized [Gd(III)-Pt(IV)] Complex as High T1, T2 Relaxive M-MRI Contrast Agent for Cancer Diagnosis

Pt(IV) cored Gd(III) metal complex as a multimodal MRI contrast agent for cancer diagnosis is reported. The hetero nuclear complex [Pr-(DO3-Ch-Ph-Am-Gd(III))2Pt(II)] is highly soluble in water and stable at room temperature. The complex shows high longitudinal (r1p = 24.43 mM-1 s-1) and transversal (r2p = 38.61 mM-1 s-1) relaxivity values in neat aqueous solution at pH =7 and at 27 oC. The relaxivity value of the complex is greater than the low molecular weight, FDA approved MRI contrast agents. The presence of two water molecules in the first coordination sphere and a replaceable hydrogen atom in the linker enhances the proton relaxation rate and gives a huge relaxivity value. The r2p/r1P ratio of 1.58 confirms that the complex is a T1-weighted contrast agent. The presence of high polar coumarone pendant arm and high rigid acridone moieties in the complex make the complex as better anticancer agent for ovarian cancer. The high polar nature of the coumarone, phenyl amide, acridone moiety will show better binding efficiency with ovarian cancer creating CA125 glycoprotein.

Combining the Best of Two Chelating Titans: A Hydroxypyridinone-Decorated Macrocyclic Ligand for Efficient and Concomitant Complexation and Sensitized Luminescence of f-Elements.

An ideal chelator for f-elements features rapid kinetics of complexation, high thermodynamic stability, and slow kinetics of dissociation. Here we present the facile synthesis of a macrocyclic ligand bearing four 1-hydroxy-2-pyridinone units linked to a cyclen scaffold that rapidly forms thermodynamically stable complexes with lanthanides (Sm3+ , Eu3+ , Tb3+ , Dy3+ ) and a representative late actinide (Cm3+ ) in aqueous media and concurrently sensitizes them. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed an increase in the Ln/An-O bond lengths following the trend Cm>Eu>Tb and EXAFS data were compatible with time-resolved luminescence studies, which indicated one to two water molecules in the inner metal coordination sphere of Eu(III) and two water molecules for the Cm(III) complex. Spectrofluorimetric ligand competition titrations against DTPA confirmed the high thermodynamic stability of DOTHOPO complexes, with pM values between 19.9(1) and 21.9(2).

How Phase Modifiers Disrupt Third-phase Formation in Solvent Extraction Solutions

ABSTRACT The structure of complex organic solutions based on N,N,N’,N’-tetraoctyldiglycolamide (TODGA) used in actinide separation processes were characterized after water and neodymium extraction. The organic phases were characterized using FTIR spectroscopy, ESI-MS spectrometry, Small and Wide Angle X-ray Scattering (SWAXS) and molecular dynamic simulations. The role of the “phase modifier” like 1-octanol (used in the innovative SANEX process) or the “co-extractant” like DMDOHEMA (used, for example, in the EURO-GANEX process) added to the organic phase to avoid third-phase formation was investigated at molecular and supramolecular scales. Without metallic cations in 0.2 mol/L TODGA solution in n-heptane, TODGA molecules are organized in monomers and small aggregates containing mainly two or three TODGA molecules. After Nd(NO3)3 extraction, complexes or aggregates are formed in which each neodymium cation is surrounded in average by 2 to 4 TODGA, 3 nitrate ions and 1 to 2 water molecules. Polymetallic species (aggregates) may also be formed. Adding 5%Vol 1-octanol or 0.5 mol/L DMDOHEMA to 0.2 mol/L TODGA solution in n-heptane leads to the formation of mixed aggregates containing TODGA and octanol molecules or TODGA and DMDOHEMA molecules. These molecules both interact directly with the extracted metallic cation in the organic phase, modifying the structure of the neodymium species, and improving their solubility in this organic phase. At least one TODGA molecule remains in the cation first coordination sphere in both cases and preserves its significant role in the complexation/selectivity of the cations. But it is clear that both 1-octanol and DMDOHEMA have a role in the speciation of the cations in the organic phase: 1-octanol replaces water molecules in the first coordination sphere of Nd, acting as a co-surfactant; DMDOHEMA drives the organization and DMDOHEMA molecules partially replace TODGA in the first coordination sphere of Nd.

Transition Metal Complexes with Flufenamic Acid for Pharmaceutical Applications-A Novel Three-Centered Coordination Polymer of Mn(II) Flufenamate.

Five complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with non-steroidal anti-inflammatory drug, flufenamic acid were synthesized: (1) [Mn3(fluf)6EtOH)(H2O)]·3EtOH; (2) [Co(fluf)2(EtOH)(H2O)]·H2O; (3) [Ni(fluf)2(EtOH)(H2O)]·H2O; (4) [Cu(fluf)2·H2O]; (5) [Zn(fluf)2·H2O]. All complexes were characterized by elemental analysis (EA), flame atomic absorption spectrometry (FAAS), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The crystal structure of 1 was determined by the single crystal X-ray diffraction technique. It crystallizes in the triclinic space group P with three independent Mn(II) cations, six coordinated flufenamato ligands augmented with water and ethanol molecules in the inner coordination sphere. In this crystal, manganese atoms are multiplied by symmetry and form infinite, polymeric chains which extend along the [001] dimension. The Hirshfeld Surface analysis revealed changes in interaction assemblies around all metal centers. The antioxidant and antimicrobial activities were established for all complexes and free ligand for comparison. All compounds exhibit good or moderate bioactivity against Gram-positive bacteria and yeasts.

Effect of the Heteroaromatic Antenna on the Binding of Chiral Eu(III) Complexes to Bovine Serum Albumin

The cationic enantiopure (R,R) and luminescent Eu(III) complex [Eu(bisoQcd)(H2O)2] OTf (with bisoQcd = N,N′-bis(2-isoquinolinmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate and OTf = triflate) was synthesized and characterized. At physiological pH, the 1:1 [Eu(bisoQcd)(H2O)2]+ species, possessing two water molecules in the inner coordination sphere, is largely dominant. The interaction with bovine serum albumin (BSA) was studied by means of several experimental techniques, such as luminescence spectroscopy, isothermal titration calorimetry (ITC), molecular docking (MD), and molecular dynamics simulations (MDS). In this direction, a ligand competition study was also performed by using three clinically established drugs (i.e., ibuprofen, warfarin, and digitoxin). The nature of this interaction is strongly affected by the type of the involved heteroaromatic antenna in the Eu(III) complexes. In fact, the presence of isoquinoline rings drives the corresponding complex toward the protein superficial area containing the tryptophan residue 134 (Trp134). As the main consequence, the metal center undergoes the loss of one water molecule upon interaction with the side chain of a glutamic acid residue. On the other hand, the similar complex containing pyridine rings ([Eu(bpcd)(H2O)2]Cl with bpcd = N,N′-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate) interacts more weakly with the protein in a different superficial cavity, without losing the coordinated water molecules.

Manganese Complex of a Rigidified 15-Membered Macrocycle: A Comprehensive Study.

Owing to the increasing importance of manganese(II) complexes in the field of magnetic resonance imaging (MRI), large efforts have been devoted to find an appropriate ligand for Mn(II) ion encapsulation by providing balance between the seemingly contradictory requirements (i.e., thermodynamic stability and kinetic inertness vs low ligand denticity enabling water molecule(s) to be coordinated in its metal center). Among these ligands, a large number of pyridine or pyridol based open-chain and macrocyclic chelators have been investigated so far. As a next step in the development of these chelators, 15-pyN3O2Ph and its transition metal complexes were synthesized and characterized using established methods. The 15-pyN3O2Ph ligand incorporates both pyridine and ortho-phenylene units to decrease ligand flexibility. The thermodynamic properties, protonation and stability constants, were determined using pH-potentiometry; the solid-state structures of two protonation states of the free ligand and its manganese complex were obtained by single crystal X-ray diffractometry. The results show a seven-coordinate metal center with two water molecules in the first coordination sphere. The longitudinal relaxivity of [Mn(15-pyN3O2Ph)]2+ was found to be 5.16 mM-1 s-1 at 0.49 T (298 K). Furthermore, the r2p value of 11.72 mM-1 s-1 (0.49 T), which is doubled at 1.41 T field, suggests that design of this Mn(II) complex does achieve some characteristics required for contrast imaging. In addition, 17O NMR measurements were performed in order to access the microscopic parameters governing this key feature (e.g., water exchange rate). Finally, manganese complexes of ligands with analogous polyaza macrocyclic scaffold have been investigated as low molecular weight Mn(CAT) mimics. Here, we report the H2O2 disproportionation study of [Mn(15-pyN3O2Ph)]2+ to demonstrate the versatility of this ligand scaffold as well.

Enhanced Near-IR Luminescence and Thermal-Resistant Properties of Yb(III) Complexes Under Solvent-Free Mechanochemical Conditions

Mechanochemical activation is of particular significance in the field of sustainable chemistry. This technique can transform mechanical energy into a chemical reaction under solvent-free conditions, while it has rarely been used in the preparation of near-infrared (NIR) luminescent materials. Here, an NIR luminescent complex with a homogeneous shuttlelike morphology was designed and synthesized through a facile mechanochemical process at room temperature. The successful coordination of Yb³⁺ with symmetrical terpyridine units and 2-thenoyltrifluoroacetonate synergistically allows the obtained Yb³⁺ ternary complex to reveal remarkable improvement in the NIR luminescent behavior and thermal-resistant performance compared with the mononuclear complex, Yb(tta)₃·3H₂O. This enhancement mainly benefits from the removal of water molecules in the first coordination sphere of Yb³⁺ through the introduction of terpyridines, thus preventing the diffusion of water molecules to Yb³⁺ complexes, and driving the formation of the Yb³⁺ complex with more effective coordination number and enhanced the NIR luminescence. This provided a promising environmentally friendly strategy to synthesize highly NIR luminescence materials for eliminating the influence of harmful organic solvents.

The Influence of Electrolyte Solutions on the Mechanical Properties of Bacterial Cellulose

The mechanical characteristics of bacterial cellulose (one of the most promising cellulose-based nanomaterials) fundamentally depend on its moisture content. It has been found that the effect of aqueous solutions of alkali metal chlorides on its strength and deformation properties is determined by the mobility of water molecules in the near coordination spheres of cation hydration shells.

Eu3+ luminescent ions detect water density anomaly

It is well known that water density varies anomalously with temperature. However, nowadays there is still a lack of agreement on the causes of this phenomenon. In this work, we use Eu3+ luminescent ion as a probe to investigate the changes in the arrangement of water molecules around the temperature of maximum density. The slight changes in the arrangement of water molecules in the first coordination sphere of Eu3+ ions due to the water density anomaly affect the variation with temperature of Eu3+ ions emission spectra and intensity decay time. This is the first time, to the best of our knowledge, that the effect of the anomaly in the density of water is detected by a luminescent material. From these experimental results we can infer that possibly the anomaly could be caused by variation in the length of hydrogen bonds between molecules with temperature for both water and heavy water.

Highly Efficient Extraction of Trivalent f‐Cations Using Several N‐Pivot Tripodal Diglycolamide Ligands in an Ionic Liquid: The Role of Ligand Structure on Metal Ion Complexation

Complexation of trivalent lanthanides and actinides was studied in a room temperature ionic liquid (RTIL) using five N‐pivot tripodal diglycolamide ligands (LI–LV) having different structural features, viz. spacer lengths and substituents. The nature of the metal/Ligand complex changed with the substitution of N atom near the tripodal platform from ML with LIII and LIV to ML2 with LI, LII and LV (where M = Eu3+/Nd3+/Am3+). With 0.2 mmol/L ligands, the distribution ratio of Am3+ at 1 m HNO3 followed the order: LI (210) > LII (42) > LIII (2.1) > LV (0.7) > LIV (0.2). The formation constants between Nd3+ and the ligands (log βML,ML2) followed an identical order, viz. LI > LII > LIII > LV > LIV. The extraction of Am3+ or Eu3+ with all the ligands followed a cation‐exchange extraction mechanism, which is in sharp contrast to the results obtained in a molecular solvent (n‐dodecane), where a solvation extraction mechanism prevalied. Luminescence studies on the Eu3+ extract in RTIL confimed the absence of water molecules in the inner coordination sphere of the complex. EXAFS studies indicated that all three DGA arms were binding to the Eu3+ cation.