Radius Of Metal Ion Research Articles

Synthesis and spectral properties of lanthanide double-decker complexes with tetrabenzoporphyrin and phthalocyanine

Mixed-ligand double-decker complexes containing tetrabenzoporphyrin and phthalocyanine fragments were synthesized by reaction of phthalocyanine dilithium salt with tetrabenzoporphyrin complexes of lutetium, dysprosium, gadolinium, neodymium, and lanthanum. A relation was found between spectral parameters of the obtained sandwich complexes and radii of the central metal ions.

Zinc‐Diluted Magnetic Metal Formate Perovskites: Synthesis, Structures, and Magnetism of [CH3NH3][MnxZn1−x(HCOO)3] (x=0–1)

The preparation, structures, and magnetic properties of a series of metal formate perovskites [CH(3)NH(3)][Mn(x)Zn(1-x)(HCOO)(3)] were investigated. The isostructural solid solution can be prepared in the complete range of x=0-1. The metal-organic perovskite structures consist of an anionic NaCl type [Mn(x)Zn(1-x)(HCOO)(3)(-)] framework with CH(3)NH(3)(+) templates located in the nearly cubic cavities and forming hydrogen bonds to the framework. When the proportion of Mn increased (i.e., x changed from 0 to 1), the lattice dimensions and metal-oxygen and metal-metal distances show a slight, nonlinear increase because of the increased averaged metal ionic radius and the local structure distortion. Through the series, the magnetism changes from the long-range ordering of spin-canted antiferromagnetism for x≥0.40 to paramagnetism when x≤0.30, and the percolation limit was estimated to be x(P)=0.31(2) for this simple cubic lattice. In the low-temperature region, enhancement of magnetization and the gradual decrease and final disappearance of coercive field, remnant magnetization, and spin-flop field upon dilution were observed through this isotropic Heisenberg magnetic series. IR spectroscopic and thermal properties were also investigated.

Adsorption Disciplinarian of Metal Ions on Collagen Fiber Immobilized Bayberry Tannin

Adsorption behavior disciplinarian of the immobilized tannins to metal ions was studied. Experiments showed that adsorption capacities of metal ions lied in ns grouse in the periodic table of elements were relatively low. For the metal ions lied in np grouse in the periodic table of elements, their adsorption capacity increased with the increasing in the radius of metal ions. Adsorption capacities of metal ions having low values in the first transition series in the periodic table of elements, such as Mn(II), Fe(II), Fe(III), Co(II) and Ni(II), were more lower than that of the metal ions having high values, such as Cr(VI), Mn(VII) and V(V). For the metal ions in the second, the third transition series and the actinide series, adsorption capacities were relatively higher than that of metal ions in lanthanide series.

ChemInform Abstract: Hydrated Metal Ions in Aqueous Solution: How Regular Are Their Structures?

AbstractReview: 106 refs.

Synthesis, structural and electrochemical features of alicyclic and aromatic α, α′- N2- and- S2-dioximate macrobicyclic cobalt(II,III) and ruthenium(II) tris-complexes

The triribbed-functionalized cobalt(II,III) and ruthenium(II) clathrochelate derivatives of the vic-dioximes with two nitrogen or sulfur atoms in α-positions to π-conjugated diazomethine chelate fragments of a macrobicyclic framework were obtained in moderate yields under mild and high dilution conditions by nucleophilic substitution of six reactive chlorine atoms of the boron-capped macrobicyclic cobalt and ruthenium(II) precursors with N 2- and S 2-dinucleophiles (ethylenediamine and the corresponding α-dithiols in the presence of triethylamine, respectively). The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–Vis, 1H and 13C{ 1H} NMR and EPR spectroscopies, magnetochemistry and X-ray crystallography. The MN 6-coordination polyhedra of all the X-ray studied clathrochelates possess a slightly distorted trigonal prismatic geometry. The encapsulated cobalt(II) ions are shifted from the centers of the cavities formed by the macrobicyclic ligand due to the Jahn–Teller distortion, while the ruthenium and iron(II) ions in their clathrochelate analogs do occupy these centers. The main geometrical parameters of the macrobicyclic frameworks vary with Shannon radius of an encapsulated metal ion. In the case of the tris-ethylenediamine cobalt(III) clathrochelate, the field strength of the macrobicyclic amine ligand is essentially lower than those for their aromatic and aliphatic analogs because of the negative σ para -effect of the ribbed alkylamine substituents. The magnetometry and EPR data confirmed the low-spin character of the cobalt(II) complexes synthesized. The electrochemically generated oxidized cobalt clathrochelates are stable in the CVA time scale, whereas their ruthenium- and iron-containing analogs as well as the reduced forms of all the cobalt, ruthenium and iron complexes obtained are unstable.

Influence of alkaline metal on performance of supported silicotungstic acid catalysts in glycerol dehydration towards acrolein

A series of supported silicotungstic acid (H 4SiW 12O 40· xH 2O) catalysts was prepared from selected silica and alumosilicate carriers. Alkaline metals lithium, potassium and caesium were added to modify catalyst Brønsted acidity. Physico-chemical characterisation of the catalysts was carried out with nitrogen adsorption (BET), X-ray diffraction (XRD), and infrared (IR) and Raman spectroscopy and revealed that the nature of the alkaline metal is significant for (i) specific surface area which rises with metal ion radii and (ii) dispersion of active compound formed from alkaline metal and silicotungstic acid on the support surface. Interestingly, acidic properties rather do not depend on nature of alkaline metal. The catalysts were catalytically evaluated at standardised reaction conditions in a continuous flow lab scale set-up (10 wt.% of glycerol in water, 225–300 °C, modified contact time 0.15 kg h mol −1). Among the tested supported catalysts, lithium exchanged H 4SiW 12O 40· xH 2O showed highest activity and maximum selectivity of 70% for acrolein at complete conversion. Main effect of alkaline metal addition can be seen in improved selectivity and activity, in particular with silica supported catalysts.

Hydrated metal ions in aqueous solution: How regular are their structures?

The hydration reaction is defined as the transfer of an ion or neutral chemical species from the gaseous phase into water, Mn+(g) → Mn+(aq). In this process, water molecules bind to metal ions through ion-dipole bonds of mainly electrostatic character. The hydration reaction is always strongly exothermic with increasing heat of hydration with increasing charge density of the ion. The structures of the hydrated metal ions in aqueous solution display a variety of configurations depending on the size and electronic properties of the metal ion. The basic configurations of hydrated metal ions in aqueous solution are tetrahedral, octahedral, square antiprismatic, and tricapped trigonal prismatic. This paper gives an overview of the structures of hydrated metal ions in aqueous solution with special emphasis on those with a non-regular coordination figure. Metal ions without d-electrons in the valance shell form regular aqua complexes with a coordination figure, allowing a maximum number of water molecules to be clustered around the metal ion. This number is dependent on the ratio of the metal ion radius to the atomic radius of oxygen in a coordinated water molecule (1.34 Å). The lighter lanthanoid(III) ions have a regular tricapped trigonal prismatic configuration with the M–O distance to the capping water molecules somewhat longer than to the prismatic ones. However, with increasing atomic number of the lanthanoid(III) ions, an increasing distortion of the capping water molecules is observed, resulting in a partial loss of water molecules in the capping positions for the heaviest lanthanoids. Metal ions with d4 and d9 valance shell electron configuration, as chromium(II) and copper(II), respectively, have Jahn–Teller distorted aqua complexes. Metal ions with low charge and ability to form strong covalent bonds, as silver(I), mercury(II), palladium(II), and platinum(II), often display distorted coordination figures due to the second-order Jahn–Teller effect. Metal ions with d10s2 valence shell electron configuration may have a stereochemically active lone electron pair (hemi-directed complexes) or an inactive one (holo-directed). The hydrated tin(II), lead(II), and thallium(I) ions are hemi-directed in aqueous solution, while the hydrated bismuth(III) ion is holo-directed. The structures of the hydrated cationic oxo-metal ions are reported as well.

Pyrazolate-bridged group 11 metal(I) complexes: Substituent effects on the supramolecular structures and physicochemical properties

Polynuclear homoleptic pyrazolate-bridged group 11 metal(I) complexes with three different alkyl substituted pyrazolate anions, 3,5-diisopropylpyrazolate (3,5- iPr 2pz − = L1 −), 3- tert-butyl-5-isopropylpyrazolate (3- tBu-5- iPrpz − = L3 −), and 3,5-di- tert-butylpyrazolate (3,5- tBu 2pz − = L4 −), i.e. [Cu( μ-3,5- iPr 2pz)] 3 ( CuL1), [Ag( μ-3,5- iPr 2pz)] 3 ( AgL1), [Au( μ-3,5- iPr 2pz)] 3 ( AuL1), [Cu( μ-3- tBu-5- iPrpz)] 4 ( CuL3), [Ag( μ-3- tBu-5- iPrpz)] 3 ( AgL3), [Au( μ-3- tBu-5- iPrpz)] 4 ( AuL3), [Cu( μ-3,5- tBu 2pz)] 4 ( CuL4), [Ag( μ-3,5- tBu 2pz)] 4 ( AgL4), and [Cu( μ-3,5- tBu 2pz)] 4 ( AuL4), were systematically synthesized in order to investigate the influence of pyrazole bulkiness on their structures and physicochemical properties. The structural characterization indicates that the geometries are greatly influenced by the steric hindrance exerted by the substituent groups of the pyrazolyl rings and the differences of the central metal (I) ionic radius (Cu + < Au + < Ag +). These complexes were also characterized by spectroscopic techniques, namely, UV–Vis, IR/far-IR, Raman, and luminescence spectroscopy.

Efficient Intramolecular Hydroalkoxylation of Unactivated Alkenols Mediated by Recyclable Lanthanide Triflate Ionic Liquids: Scope and Mechanism

Lanthanide triflate complexes of the type [Ln(OTf)(3)] (Ln=La, Sm, Nd, Yb, Lu) serve as effective, recyclable catalysts for the rapid intramolecular hydroalkoxylation (HO)/cyclization of primary/secondary and aliphatic/aromatic hydroxyalkenes in imidazolium-based room-temperature ionic liquids (RTILs) to yield the corresponding furan, pyran, spirobicyclic furan, spirobicyclic furan/pyran, benzofuran, and isochroman derivatives. Products are straightforwardly isolated from the catalytic solution, conversions exhibit Markovnikov regioselectivity, and turnover frequencies are as high as 47 h(-1) at 120 degrees C. The ring-size rate dependence of the primary alkenol cyclizations is 5>6, consistent with a sterically controlled transition state. The hydroalkoxylation/cyclization rates of terminal alkenols are slightly more rapid than those of internal alkenols, which suggests modest steric demands in the cyclic transition state. Cyclization rates of aryl-functionalized hydroxyalkenes are more rapid than those of the linear alkenols, whereas five- and five/six-membered spirobicyclic skeletons are also regioselectively closed. In cyclization of primary, sterically encumbered alkenols, turnover-frequency dependence on metal-ionic radius decreases by approximately 80-fold on going from La(3+) (1.160 A) to Lu(3+) (0.977 A), presumably reflecting steric impediments along the reaction coordinate. The overall rate law for alkenol hydroalkoxylation/cyclization is v approximately k[catalyst](1)[alkenol](1). An observed ROH/ROD kinetic isotope effect of 2.48 (9) is suggestive of a catalytic pathway that involves kinetically significant intramolecular proton transfer. The present activation parameters--enthalpy (DeltaH(++))=18.2 (9) kcal mol(-1), entropy (DeltaS(++))=-17.0 (1.4) eu, and energy (E(a))=18.2 (8) kcal mol(-1)--suggest a highly organized transition state. Proton scavenging and coordinative probing results suggest that the lanthanide triflates are not simply precursors of free triflic acid. Based on the kinetic and mechanistic evidence, the proposed catalytic pathway invokes hydroxyl and olefin activation by the electron-deficient Ln(3+) center, and intramolecular H(+) transfer, followed by alkoxide nucleophilic attack with ring closure.

Novel double-chained or double-layered metal diphosphonates: synergic coordination effect of two closely linked phosphonate moieties promoted by large metal ionic radius

Hydrothermal reactions of PbII or BaII ion with N,N-dimethylaminomethane-1,1-diphosphonic acid (H4L) afforded a double-chained lead(II) diphosphonate and a double-layered barium(II) diphosphonate, namely, [Pb(H2L)] (1) and [Ba2(H2L)2] (2). The two closely linked phosphonate moieties in the diphosphonate ligand exhibit a highly synergic coordination effect, which is mainly promoted by the large ionic radius of the PbII or BaII ion. More interestingly, the unusual double-layer structure in 2 contains cubane-like Ba8 cages and each cage is face-shared with four adjacent ones.

Molecular mobility in protein solutions containing metal ions with various ionic radii

Using methods of photon-correlation spectroscopy and polarized fluorescence pH, the dependencies of the translation and rotary diffusion coefficients of collagen and bovine serum albumen in solutions on NaCl and KCl salts at various ion forces have been obtained. It is shown that the size of the metal ionic radius affects intermolecular interactions and the mobility of albumen molecules in solution. The effect of the potassium ion, with its large ionic radius, compared with Na ions, is analogous to the effect of heavy metals ions, since it results in albumen molecule aggregation near the isoelectric point.

Metal hydrides-structure and band structure

Previous calculations for Group IIIB transition metal and rare earth compounds with hydrogen showed that for the dihydrides a new band is added below the Fermi energy. This bond corresponds to the antibonding combination of the two hydrogen 1s-orbitals in the unit cell. The original transition metal s-band hybridizes with the bonding combination of the two hydrogens, the implications being that for compounds with only one hydrogen per unit cell no new band is formed and the additional electron goes into host metal states. This result has now been verified by calculations for YH and PdH. Previous conclusions about the relative stability of the trivalent trihydrides have been extended to Groups IVB, VB, and VIB dihydrides. The relative position of the added hydrogen bands below the Fermi energy determines the relative stability of a structure. This position depends primarily on interatomic distance. Thus the trihydride forms only for yttrium and the rare earths and not for scandium. The dihydride only forms for transition metals and rare earths for which the metal ion radius (which determines the metal spacing but not the structure) is greater than 1.25 Å. The monohydride forms only when the dihydride is relatively unstable and the density of states in the d-band is high, e.g. VH, NbH, TaH, NiH, and PdH. Quantitative substantiation of these ideas from band structure calculations will be presented.

Factors Governing Metal−Ligand Distances and Coordination Geometries of Metal Complexes

The metal-ligand (M-L) distances play a central role in determining the structure and reactivity of the metal complex and in metal discrimination in proteins. They reflect properties of the metal ion and the ligand during their coordination as well as the environment. However, the variation of the M-L distances as a function of the properties of the metal cation and its donor atoms had not been systematically analyzed, and no public website listing the M-L distances from metal complexes was available. Herein, the distances around 63 different types of metal ions in approximately 200,000 high-resolution crystal structures in the Cambridge Structural Database as well as their preferred coordination geometries have been determined. The dependence of these distances on (i) the donor atom's charge and charge-donating ability, (ii) the donor atom's size, (iii) the metal ion's oxidation state and charge-accepting ability, and (iv) the metal ion's size has also been determined. The concept of ligand coordination number (CN) was introduced to take into account the effect of the number of constituent ligand atoms on the M-L distances in addition to the number of metal-bound ligands. We propose grouping the M-L distances according to both the metal CN and the ligand CN. The mean M-L distance corresponding to a given metal CN and ligand CN was found to be linearly correlated with the metal's ionic radius in going down a main group or in going across the first three rows of the periodic table. The M-L distances as a function of the metal and ligand coordination numbers are available via http://bioit.ibms.sinica.edu.tw/CSD.htm

Synthesis, characterization, and kinetic study of Mn(DPM)3 used as precursor for MOCVD

Highly pure Mn(DPM)3 (DPM-2,2,6,6-tetramethyl-3, 5-heptanedionato) complex, usually used as precursor for metal-organic chemical vapor deposition, was synthesized and characterized by elemental analyses, 1H-NMR spectroscopy, mass spectroscopic analysis, thermogravimetry, and differential scanning calorimetry. The thermal decomposition behavior of the complex is sensitive to the ambient gases, and the oxygen atmosphere will accelerate the decomposition and oxidation of the complex. According to mass spectroscopic analysis at elevated temperature, one of the three DPM groups in Mn(DPM)3 will dissociate primarily, following with dissociation of +C(CH3)3 and +OCCH2COC(CH3)3 groups in sequence. It can be interpreted by the difference of metal ion radius. The kinetic parameters of activation energy and frequency factor were computed using different models and thereinto D2 model best adjusted the experimental isothermal thermogravimetric data.

Thermodynamic Properties of Lanthanides and Actinides for Reductive Extraction of Minor Actinides

The excess thermodynamic quantities of lanthanides and actinides in molten salts and liquid metals were studied for reductive extraction of minor actinides. The excess enthalpies and entropies of those elements in the molten chloride phase were found to be correlated with the ionic radii of metal ions possibly due to complex formation. In the liquid metal phase, on the other hand, the excess enthalpies were explained with Miedema's atomistic model and the excess entropies were explained with the vibrational entropy due to alloy formation. Using these correlations and models, some missing values of the excess thermodynamic quantities were evaluated and the separation factors of minor actinides from lanthanides were calculated in different reductive extraction systems. The higher separation factors were obtained in the system using aluminum or gallium than in the system using bismuth or cadmium as the liquid metal phase.

Enhanced H2 Adsorption in Isostructural Metal−Organic Frameworks with Open Metal Sites: Strong Dependence of the Binding Strength on Metal Ions

Metal-organic frameworks (MOFs) with open metal sites exhibit a much stronger H2 binding strength than classical MOFs, due to the direct interaction between H2 and the coordinately unsaturated metal ions. Here we report a systematic study of the H2 adsorption on a series of isostructural MOFs, M2(dhtp) (M = Mg, Mn, Co, Ni, Zn). The experimental, initial isosteric heats of adsorption for H2 (Qst) of these MOFs range from 8.5 to 12.9 kJ/mol, with increasing Qst in the following order: Zn, Mn, Mg, Co, and Ni. The H2 binding energies derived from first-principles calculation follow the same trend as the experimental observation on Qst, confirming the electrostatic Coulomb attraction between the H2 and the open metals being the major interaction. We also found a strong correlation between the metal ion radius, the M-H2 distance, and the H2 binding strength, which provides a viable, empirical method to predict the relative H2 binding strength of different open metals.

The Coordination Chemistry of Benzimidazole-5,6-dicarboxylic Acid with Mn(II), Ni(II), and Ln(III) Complexes (Ln = Tb, Ho, Er, Lu)

The first coordination chemistry of a multidentate ligand benzimidazole-5,6-dicarboxylic acid (H2L) was investigated, and six novel two-dimensional (2D) coordination polymers based on this ligand, namely, [MnL]n (1), {[Ni2L2(H2O)4]·3H2O}n (2), {[Tb(L)(HL)(H2O)]·H2O}n (3) and {[Ln2L2(HL)2(H2O)2]}n (Ln = Ho (4), Er (5), Lu (6)), were synthesized under hydrothermal conditions. Compund 1 shows a novel coordination network with 4462 topology and contains unusual five-coordinated one-dimensional {Mn−O}n chains along the b-axis. Compound 2 is a 2D layer structure of 4.82 topology in the ab plane and displays a three-dimensional (3D) supramolecular network via multiple intermolecular hydrogen bonds. Compound 3 also shows a 4462 topology, but its coordination network is completely different from compound 1. Compounds 4−6 were isostructural, and each Ln (Ln = Ho (4), Er (5), Lu (6)) center in the framework acts as a five-connected node to give rise to a unique network with a (3.4.6)(32.4.5.62.74) topology in the ab plane. Six complexes exhibit six types of bridging modes of the ligand. The numbers of L ligands around the metal centers increase from 3 (Ni) to 4 (Mn) and finally to 5 (Ln) as a result of an increase in metal ionic radii. The temperature-dependent magnetic susceptibility data have been explained with the Fisher model, with parameters g = 2.05, J = −3.06 cm−1 for 1, and g = 2.09, J = −0.35 cm−1 for 2, indicating antiferromagnetic coupling. The luminescent properties of 3 were studied.

Lanthanide Triflate-Catalyzed Arene Acylation. Relation to Classical Friedel–Crafts Acylation

Lanthanide trifluoromethanesulfonates, Ln(OTf) 3 (OTf (-) = trifluoromethanesulfonate), serve as effective precatalysts for the rapid, regioselective, intermolecular acylation of activated arenes. This contribution probes mechanism and metal ionic radius effects in the catalytic lanthanide triflate-mediated acylation of anisole with acetic anhydride. Kinetic studies of Ln(OTf) 3 (Ln = La, Eu, Yb, Lu)-mediated anisole acylation with acetic anhydride in nitromethane reveal the rate law nu approximately k 3 [Ln (3+)] (1)[acetic anhydride] (1)[anisole] (1). Eyring and Arrhenius analyses yield Delta H++ = 12.9 (4) kcal.mol (-1), Delta S++ = -44.8 (1.3) e.u., and E a = 13.1 (4) kcal.mol (-1) for Ln = Yb, with the negative Delta S++ implying a highly organized transition state. The observed primary kinetic isotope effect of k H/ k D = 2.6 +/- 0.15 is consistent with arene C-H bond scission in the turnover-limiting step. The proposed catalytic pathway involves precatalyst formation via interaction of Ln(OTf) 3 with acetic anhydride, followed by Ln (3+)-anisole pi-complexation, substrate-electrophile sigma-complex formation, and turnover-limiting C-H bond scission. Lanthanide size effects on turnover frequencies are consistent with a transition state lacking significant ionic radius-dependent steric constraints. Substrate-Ln (3+) interactions using paramagnetic Gd (3+) and Yb (3+) NMR probes and factors affecting reaction rates such as arene substituent and added LiClO 4 cocatalyst are also explored.

Synthesis, characterization, potentiometric and thermodynamic studies of transition metal complexes with 1-benzotriazol-1-yl-1-[( p -methoxyphenyl) hydrazono]propan-2-one†

A new series of Mn2+ and Co2+ complexes with 1-benzotriazol-2-yl-1-[(p-methoxyphenyl)-hydrazono]propan-2-one (BMHP) were synthesized and characterized by the elemental analysis, magnetic and different spectral techniques. Proton dissociation constant of the free ligand and the stepwise stability constants of its metal complexes were determined potentiometrically in 0.1 M KC1 and 40% (v/v) ethanol–water. The dissociation constants of the free ligand and its metal complexes were determined at different temperatures and the corresponding thermodynamic parameters were calculated and discussed. The dissociation process was found to be non-spontaneous, endothermic and entropically unfavorable. The changes in the standard ΔG 0 and ΔH 0 accompanying complexation were decreased with increasing metal ionic radius but increased with increasing electronegativity, ionization enthalpy, and hydration enthalpy of the metal ion. The values of (−ΔG 0) and (−ΔH 0) were in the order: Mn2+ < Co2+ < Ni2+ < Cu2+, in accord with the Irving-Williams order. The complexes were found to be stabilized by both enthalpy and entropy changes and the results suggest that complexation is an enthalpy-driven process. The distribution diagrams of the complexes in solution were evaluated. †Presented at the 37th International Conference of Coordination Chemistry (37th ICCC), Cape Town, 13–18 August, 2006.

Controlled Aggregation of Gold Nanoparticle Networks Induced by Alkali Metal Ions

Gold nanoparticle networks were obtained by linking them with cysteine modified triethyleneglycols. The oligo-ether linker molecule initially having a linear structure probably adopts a crown ether type structure upon complexation with alkali metal ions that leads to a controlled aggregation of the network. The extent of aggregation depends on the degree of conformational change in the molecule upon complexation with the metal ion, which in turn is governed by the metal ion radius leading to a dependence of red shift of the surface plasmon resonance on the metal ion radius. Since this network is present in the organic solvent they also act as phase transferring agent for the alkali metal ions from aqueous to organic media.