Variation Of Coordination Number Research Articles

Metal–organophosphine and metal–organophosphonium frameworks with layered honeycomb-like structures

Phosphanotriylbenzenecarboxylic acid (ptbcH(3); P(C(6)H(4)-p-CO(2)H)(3)) and its methyl phosphonium iodide derivative (mptbcH(3)I; {H(3)CP(C(6)H(4)-p-CO(2)H)(3)}I) have been used as organic building blocks in reaction with Zn(ii) salts to obtain a series of related two-dimensional coordination polymers with honeycomb-like networks. The variable coordination number and oxidation states available to phosphorus have been exploited to produce a family of related phosphine coordination materials (PCMs) using a single ligand precursor. The phosphine carboxylate trianion, ptbc(3-), reacted with Zn(ii) to form 3,3-connected undulating hexagonal sheets based on tetrahedral P and Zn nodes, where Zn-ptbc = 1 : 1. When hydroxide was used as an additional framework ligand, Zn(4)(OH)(2) clusters were obtained. The clusters support 6,3-connected bilayers that consist of pairs of fused hexagonal sheets (Zn-ptbc = 2 : 1) with intra-layer pore spaces. The Zn(4)(OH)(2) clusters are also coordinated by solvent, which was preferentially displaced when the bilayer material was synthesized in the presence of ethylene diamine. Treatment of ptbc(3-) with MeI resulted in methylation of the phosphine to give the P(v) phosphonium iodide salt derivative. The formally dianionic methylphosphonium tricarboxylate building block, mptbc(2-), has the same trigonal-pyramidal bridging geometry as the parent phosphine. However, mptbc(2-) reacted with Zn(ii) on a 1 : 1 stoichiometric ratio to give an unusual trilayer sheet polymer that is based exclusively on 3-connected nodes. Solid-state (31)P NMR studies confirmed that the phosphine ligands were resistant to oxidation upon solvothermal reaction under aerobic conditions.

Tripodal Tetraamine Ligands Containing Three Pyridine Units: The other Polypyridyl Ligands

AbstractThe chemistry of tripodal ligands containing three (2‐pyridyl)‐alkyl arms attached to an aliphatic N atom (tripyridyl tripodal ligands) is reviewed. An outline of the variety of such ligands is given and methods for their synthesis are detailed. The structures of metal complexes containing tripyridyl tripodal ligands are briefly discussed, with particular emphasis on the structures adopted by complexes containing metal ions of varying coordination number. A brief overview of the complexes of tpa, the most widely used tripyridyl tripodal ligand, and its derivatives, is given. The electronic properties of tripyridyl tripodal ligands are detailed, as determined from spectroscopic, NMR, magnetochemical, electrochemical and pKa measurements on their metal complexes. Some examples of the reactivity of complexes containing tripyidyl tripodal ligands are given which outline the importance of both steric and electronic effects of the ligands in determining the reactivity of the metal complexes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Interstitial oxide ion conductivity in the layered tetrahedral network melilite structure

High-conductivity oxide ion electrolytes are needed to reduce the operating temperature of solid-oxide fuel cells. Oxide mobility in solids is associated with defects. Although anion vacancies are the charge carriers in most cases, excess (interstitial) oxide anions give high conductivities in isolated polyhedral anion structures such as the apatites. The development of new families of interstitial oxide conductors with less restrictive structural constraints requires an understanding of the mechanisms enabling both incorporation and mobility of the excess oxide. Here, we show how the two-dimensionally connected tetrahedral gallium oxide network in the melilite structure La(1.54)Sr(0.46)Ga(3)O(7.27) stabilizes oxygen interstitials by local relaxation around them, affording an oxide ion conductivity of 0.02-0.1 S cm(-1) over the 600-900 degrees C temperature range. Polyhedral frameworks with central elements exhibiting variable coordination number can have the flexibility needed to accommodate mobile interstitial oxide ions if non-bridging oxides are present to favour cooperative network distortions.

Porous lanthanide–copper coordination frameworks exhibiting reversible single-crystal-to-single-crystal transformation based on variable coordination number and geometry

Two serial heterometallic Ln–Cu coordination polymers [Ln2Cu(NIPH)4(H2O)4]·6H2O (Ln = Gd (1a), Nd (2a), Sm (3a), Eu (4a), Tb (5a), Dy (6a), Ho (7a) and Er (8a)) and [Ln2Cu(NIPH)4(H2O)2] (Ln = Gd (1b), Nd (2b), Sm (3b), Eu (4b), Tb(5b), Dy (6b), Ho (7b) and Er (8b) (NIPH = 5-nitroisophthalate) have been successfully synthesized and exhibit reversible single-crystal-to-single-crystal transformation behavior based on a dehydration and rehydration process involving coordinated and uncoordinated water molecules. The coordination polymers 1a–8a and 1b–8b belong to two sets of isomorphous coordination frameworks respectively; their 3D frameworks are constructed by different heterometallic polynuclear chains. For the serial crystals 1a–8a, the Ln3+ and Cu2+ ions are 8-coordinate and 4-coordinate respectively. While for the other serial crystals, 1b–8b, the Ln3+ and Cu2+ ions are 9-coordinate and 6-coordinate respectively. La3+, Ce3+ and Pr3+ were also employed to construct Ln–Cu coordination frameworks [LaCu(NIPH)2(HNIPH)(H2O)2]·2H2O (La-1), [La2Cu(NIPH)4(H2O)2] (La-2), [Ce2Cu(NIPH)4(H2O)6] (Ce-1) and [Pr2Cu(NIPH)4(H2O)4]·6H2O (Pr-a), which do not display the crystal-to-crystal transformation characteristic.

Influence of pore structure on drying kinetics: A pore network study

AbstractA pore network model for convective drying is applied to investigate the influence of structure on drying behavior. The isothermal drying model is based on the work of Prat, and uses invasion percolation concepts, neglecting any viscous or gravitational effects. Pore structures of different pore‐size distribution and coordination number are studied in two‐ and three‐dimensions. Results are given as phase distributions or moisture profiles during drying, as well as drying rate curves. Significant differences in drying kinetics are reported for a variation in coordination number of monomodal networks. Bimodal pore structures can produce dramatically higher drying rates, but only for certain spatial correlations of small and large pores. Finally, influence of product thickness and importance of boundary layer modeling are addressed. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Na[H2TETA]0.5 [ZnPO4]2×0.5H2O or TJPU‐1: A New Zincophosphate Open‐Structure Co‐Templated by Sodium and Organoamine.

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Quantum mechanical charge field molecular dynamics simulation of the TiO2+ ion in aqueous solution

Structural and dynamical properties of the TiO(2+) ion in aqueous solution have been investigated by using the new ab initio quantum mechanical charge field (QMCF) molecular dynamics (MD) formalism, which does not require any other potential functions except those for solvent-solvent interactions. Both first and second hydration shell have been treated at Hartree-Fock (HF) quantum mechanical level. A Ti-O bond distance of 1.5 A was observed for the [Ti=O](2+) ion. The first hydration shell of the ion shows a varying coordination number ranging from 5 to 7, five being the dominant one and representing one axial and four equatorial water molecules directly coordinated to Ti, which are located at 2.3 A and 2.1 A, respectively. The flexibility in the coordination number reflects the fast exchange processes, which occur only at the oxo atom, where water ligands are weakly bound through hydrogen bonds. Considering the first shell hydration, the composition of the TiO(2+) hydrate can be characterized as [(H(2)O)(0.7)(H(2)O)(4) (eq)(H(2)O)(ax)](2+). The second shell consists in average of 12 water molecules located at a mean distance of 4.4 A. Several other structural parameters such as radial and angular distribution functions and coordination number distributions were analyzed to fully characterize the hydration structure of the TiO(2+) ion in aqueous solution. For the dynamics of the TiO(2+) ion, different sets of dynamical parameters such as Ti=O, Ti-O(eq), and Ti-O(ax) stretching frequencies and ligands' mean residence times were evaluated. During the simulation time of 15 ps, 3 water exchange processes in the first shell were observed at the oxo atom, corresponding to a mean residence time of 3.6 ps. The ligands' mean residence time for the second shell was determined as 3.5 ps.

Na[H2TETA]0.5[ZnPO4]2·0.5H2O or TJPU-1: A New Zincophosphate Open-structure Co-templated by Sodium and Organoamine

Synthetic open-structured materials attract increasing attention for wide applications in catalysis, ion-exchange or intercalation. Metal phosphates are possibly the fastest expanding group of open-framework inorganic materials in the past decade. The structural diversity that stemmed from the variable coordination number and oxidation states has directed to the extensive expansion of open-framework metal phosphates. Since the bivalent metal phosphates (+2, +5) are associated with the same total charge as aluminosilicate zeolites (+3, +4), phosphate-based framework structures containing bivalent metals are considerably pursued. After the discovery of the first open-framework zincophosphate with zeolite topologies reported by G. D. Stucky, a great deal of effort has been devoted to isolating novel open-structures within this system. And this compound group has experienced extraordinary expansion in terms of the diversity of their structures and compositions. Zincophosphates with zero-, one-, two-, and three-dimensional architectures have been isolated, in which an eye-catching result is the gigantic pore structure with 24-membered rings in ND-1. This variety was achieved by varying a number of factors that can influence the structure, including template, pH, solvent, reaction temperature, additives, zinc source and others. On the other hand, the pursuit of chiral molecular sieves is of great interest with respect to the applications in enantioselective separation and syntheses. However, only a few inorganic chiral frameworks were known up to now. For the syntheses of open-structured crystals, both alkali cations and organoamine are used as structure directing reagent separately in the literatures. Although there are some compound containing both of them, systematically investigation of the co-template effect of alkali cations and organoamines is seldom. Our group has focused on metal phosphate open-structures for many years. Recently, we are interest in exploring new open-framework metal phosphates co-templated by alkali cation and organoamine. This approach has successfully yielded a new zincophosphate openstructure, Na[H2TETA]0.5[ZnPO4]2·0.5H2O (TETA = triethylenetetraamine) or TJPU-1 (TJPU = Tianjin Polytechnic University), with the zeolite CZP topology. This compound contains left-handed chiral channels along its c axis. Here we report its synthesis and crystal structure. Experimental Section

The Role of Ca and Na Ions in the Effect of F Ion on Silicate Polymerization in Molten Silicate System

For CaO–CaF2–SiO2 and CaO–CaF2–Na2O–SiO2 systems, the effect of Na and Ca cation ions on the polymerization of silicate slags containing F ions and their structures are investigated by using molecular dynamics simulation. The substitution of F for O in the CaO–SiO2 melts enhances the polymerization of the melt due to the formation of loosely bonded Ca–2F complexes. The substitution of Na ions for Ca ions without changing the total number of F, O and Si ions in the CaO–CaF2–Na2O–SiO2 melts has a negligible effect on the distribution of silicate complex anions. For the CaO–CaF2–Na2O–SiO2 system, the existence of the loosely bonded Ca–2F and Na–F complex are confirmed from the running coordination number variation. The relative amounts of the loosely bonded Ca–2F and Na–F complex in the CaO–CaF2–Na2O–SiO2 system are depended on Na/Ca ratio. It is found that the loosely bonded Ca–2F and Na–F complexes in the CaO–CaF2–Na2O–SiO2 melts are not randomly distributed but are clustered.

Simulation study of effect of cooling rate on evolution of microstructures during solidification of liquid metal Cu

A molecular dynamics simulation has been performed on the solidification process of liquid metal Cu by adopting the quantum Sutton-Chen many-body potentials at four different cooling rates. Through the pair distribution function，bond-type indices, coordination number, MSD, and visualized analysis, it is found that the cooling rate plays a critical role in the evolution of microstructures of liquid metal Cu. At the cooling rate of 1.0×014K/s, the amorphous structures will be formed in the system; at the cooling rate of 1.0×1013K/s, 1.0×1012K/s and 1.3×1011K/s, the mixed crystal structures of fcc and hcp formed mainly with 1421 bond-type will coexist in the system, and their corresponding crystallization temperatures are 373K, 773K, 873K, respectively. Namely, slower the cooling rate, higher the crystallization temperature, and higher the degree of crystallization; and slower the cooling rate, greater the number of 1421 bond-type, greater the proportion occupied by fcc in the mixed crystal. At the same time, it is found that the variation of the mean coordination number of atoms is closely related to that of 1551, 1441, 1661 bond-types, which reflects that the varying rule of the symmetric configurations in the system is related to the variation of the coordination number. In visualized analysis, the amorphous and crystal structures in 2D cross sections and the concrete structures of both the basic clusters of fcc and hcp in 3D were displayed by means of center-atom method.

Silver Coordination Polymers — From Simple Complexes to Functional Networks

The features of silver coordination polymers in terms of coordination numbers and geometries, combination of metal-ligand and other supramolecular interactions, silver-silver interactions and photophysical, electronic and biomedical applications, are discussed. The interplay of all these interactions is seen, where the observed solid-state structure has numerous subtle interactions dictating the network that is formed. The use of metal centers with variable coordination geometries and coordination numbers contrasts with the usual approaches to metallosupramolecular chemistry.

Thermotropic lanthanidomesogens

Due to their high and variable coordination numbers leading to poorly predictable three-dimensional coordination spheres, the trivalent lanthanide metal ions are challenging molecular objects for introduction into thermotropic liquid crystals. Conversely, their predictive electronic, optical and magnetic metal-centred properties make them particularly attractive for being incorporated into switchable macroscopic materials responding to external electric and magnetic stimuli. We briefly describe here some of the important concepts and strategies leading to the recent successful preparation of luminescent thermotropic lanthanide-containing mesophases, for which the generic term lanthanidomesogens is proposed.

The Crystal Structure of α‐La2Mo2O9 and the Structural Origin of the Oxide Ion Migration Pathway.

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The Crystal Structure of α-La2Mo2O9 and the Structural Origin of the Oxide Ion Migration Pathway

We describe for the first time the full 3D atomic structure of room-temperature α-La2Mo2O9. The material, despite its simple chemical formula, has a remarkable 312 crystallographically unique atoms and is thus one of the most complex oxide structures reported to date. Despite this complexity, the structural results offer significant insight into the O2- migration pathway in the anion conducting high-temperature form, β-La2Mo2O9. The material contains a mixture of 4, 5, and 6 coordinated Mo sites, suggesting that variable Mo coordination number is a key factor in providing a low-energy O2- conduction pathway. We provide quantitative analysis showing that the positions in the ordered array of 216 oxygen sites of α-La2Mo2O9 are directly related to the average sites occupied in β-La2Mo2O9, providing compelling evidence that the high-temperature conducting form of the material has a time-averaged version of the low-temperature structure.

Lattice gas simulations of two-dimensional liquid foams

Liquid foam is a dense random packing of gas bubbles in a small amount of immiscible liquid containing surfactants. The liquid within the Plateau borders, although small in volume, causes considerable difficulties to investigations of the physical properties of foams, and the situation becomes even more complicated if the flow of the liquid through the foam is considered too. Here we propose a fresh approach to tackling these issues by introducing a discrete two-dimensional hybrid lattice gas model of liquid foams. While lattice gas models have been used to model two-phase liquids in the past, their application to the study of liquid foams is novel and proves promising. We represent bubble surfaces by a finite number of nodes, and model the surrounding liquid as a lattice gas (with a finite number of liquid particles). The gas in the bubbles is treated as an ideal gas at constant temperature. The model is tested by choosing an arbitrarily shaped bubble that evolves into a circular shape in agreement with Laplace’s law. The model is then employed to simulate periodic ordered and disordered dry and wet foams. Since our model is specifically designed to handle wet foams up to a critical liquid fraction of 0.16 (void fraction of random packing of disks), we are able to compute the variation in coordination number (average number of neighbours of a bubble) over the whole range of liquid fractions, and we find it to be a linear function of the shear modulus.

A comparison of the gas, solution, and solid state coordination environments for the copper(II) complexes of a series of aminopyridine ligands of varying coordination number

The synthesis and characterization of the copper(II) complexes of a series of aminopyridine ligands that range from tri- to heptadentate is described. The ligands include the tripod ligand tris(2-((2-pyridylmethyl)amino)ethyl)amine, TREN-pyr, and the following linear ligands: (2-pyridylmethyl)(2-(2-(2-((2-pyridylmethyl)amino)ethyl)amino)ethyl)amine, TRIEN-pyr; bis(2-((2-pyridylmethyl)amino)ethyl)amine, DIEN-pyr; (2-pyridylmethyl)(2-((2-pyridylmethyl)amino)ethyl)amine, EN-pyr; bis(2-pyridylmethyl)amine, AM-pyr; and methyl(2-((-pyridylmethyl)amino)ethyl)amine, MeEN-pyr. The following methods were used to determine the binding geometries of the Cu(II) complexes in the solid, solution, and gas phases: magnetic susceptibility measurements, absorption spectroscopy, EPR spectroscopy, electrochemistry, and analyzing the gas phase ion-molecule reactions in a mass spectrometer. The solid state structures for the TRIEN-pyr and DIEN-pyr complexes were determined by X-ray crystallography. [Cu(TRIEN-pyr)](BF 4) 2 crystallized in the octahedral system, space group Pbca, with a=9.4107(7), b=17.536(13), c=30.132(6) Å, and Z=8 ( R=0.064, R w=0.060). [Cu(DIEN-pyr)](BF 4) 2 crystallized in the octahedral system, space group Pbca, with a=29.137(5), b=14.829(3), c=9.850(1) Å, and Z=8 ( R=0.071, R w=0.066). The coordination numbers of the Cu(II) complexes in this study are dependent on the denticity of the ligand. The complexes with AM-pyr, MeEN-pyr and TRIEN-pyr appear to be six-coordinate, DIEN-pyr to be five-coordinate and the EN-pyr to be four-coordinate in the solid state. The TREN-pyr complex was isolated as a dimer in the solid state but appears to be a tetragonally distorted monomeric complex in the solution and gas phases. For all of the complexes except DIEN-pyr, the coordination sphere appears to be independent of the phase of the complex. The Cu(II) DIEN-pyr complex appears to be five-coordinate in the solid phase, a mixture of four- and five-coordinate in the solution phase, and predominately four-coordinate in the gas phase.

Interplay between the structure and properties of new metastable carbon phases obtained under high pressures from fullerite C60 and carbyne

A brief review of structural, electrotransport, optical, elastic, and mechanical properties of carbon phases synthesized under pressure by heating fullerite C60 and carbynoid materials is given. A large variety of carbon modifications with a variable bonding type, a variable mean coordination number, a variable molecular or atomic structural type, a variable characteristic dimensionality (from zero-to three-dimensional structures), a variable degree of covalence, etc., were prepared. Emphasis in the review is given to the elucidation of the interplay between the structural and topological characteristics of carbon phases and their key electronic and mechanical properties. A version of the kinetic phase diagram of fullerite C60 transformations on heating under pressure is also suggested. This version is modified with respect to the interpretations known in the literature.

Density-functional investigation on the mechanism of H-atom abstraction by lipoxygenase.

Using experimentally calibrated density functional calculations on models of the active site of soybean lipoxygenase 1 (SLO-1), insight has been obtained into the coordination flexibility of the iron active site and its molecular mechanism of catalysis. The ferrous form of SLO-1 shows a variation in coordination number in solution that is related to a weakly coordinating Asn694 ligand. From the calculations it is determined that the weak Fe-O(694) bond associated with this coordination flexibility is due to a sideways tilted geometry of Asn694 that is imposed on the site by the protein. Release of this constraint (by altering the hydrogen bonding network) leads to a pure six-coordinate site. In contrast, the ferric form of the enzyme stays five-coordinate. In this case, deprotonation of a coordinated water gives a strong hydroxo donor in the cis position to Asn694, weakening the Fe-O(694) bond. Hence, Asn694 is a stronger ligand to the reduced relative to the oxidized site. Using these experimentally calibrated models, the reaction energy for H-atom transfer in SLO-1 has been calculated to be about -18 kcal/mol. The observed change in coordination number going from five-coordinate in ferric to six-coordinate in ferrous SLO-1 increases the reduction potential of the iron active site. Hence, the protein adjusts the active site for optimal reactivity. Analysis of the electronic structure along the reaction coordinate shows that the H-atom transfer in SLO-1 actually corresponds to a proton-coupled electron transfer (PCET). The transferred electron does not localize on the proton, but tunnels directly from the substrate to the ferric active site in a concerted proton tunneling-electron tunneling (PTET) process. The covalently linked Fe-O-H-C bridge in the transition state lowers the energy barrier and provides an efficient superexchange pathway for this tunneling. The thermal barrier for the PTET process is estimated from the calculations to be about +15 kcal/mol including zero-point energy corrections. This corresponds to a thermal reaction rate of k(therm) approximately 1 s(-1). In comparison, the rate of proton tunneling can be as high as 2 x 10(9) s(-1) under these conditions.

Vanadium(IV)-citrate complex interconversions in aqueous solutions. A pH-dependent synthetic, structural, spectroscopic, and magnetic study.

Citrate is abundantly encountered in biological fluids as a natural metal ion chelator. Vanadium participates in biological processes as a catalyst in the active sites of metalloenzymes, as a metabolic regulator, as a mitogenic activator, and as an insulin-mimicking agent. Thus, vanadium chemistry with natural chelators, such as citrate, may have immediate implications on its role in a cellular milieu, and its action as a biological agent. In an effort to comprehend the aqueous chemistry of one of vanadium's oxidation states, namely, V(IV), implicated in its biological activity, reactions of VCl(3) and citric acid were pursued in water and led to V(IV)-citrate complexes, the nature and properties of which depend strongly on the solution pH. Analytical, FT-IR, UV/vis, EPR, and magnetic susceptibility data supported the formulation of X(4)[[VO(H(-1)Cit)](2)] x nH(2)O (H(-1)Cit = C(6)H(4)O(7)(4-); X = K(+), n = 6 (1); X = Na(+), n = 12 (2); X = NH(4)(+), n = 2 (3)) (pH approximately 8) and X(3)[[V(2)O(2)(H(-1)Cit)(Cit)]] x nH(2)O (X = K(+), n = 7 (4)) (pH approximately 5). Complex 2 crystallizes in space group P2(1)/c, a = 11.3335(9) A, b = 15.788(1) A, c = 8.6960(6) A, beta = 104.874(3) degrees, V = 1503.8(2), Z = 2. Complex 3 crystallizes in space group P one macro, a = 9.405(1) A, b = 10.007(1) A, c = 13.983(2) A, alpha = 76.358(4) degrees, beta = 84.056(4) degrees, gamma = 66.102(4) degrees, V = 1169.2(3), Z = 2. Complex 4 crystallizes in space group P2(1)nb, a = 9.679(4) A, b = 19.618(8) A, c = 28.30(1) A, V = 5374.0(4), Z = 8. The X-ray structures of 1-4 are V(2)O(2) dimers, with the citrate displaying varying coordination numbers and modes. 1 exhibits a small ferromagnetic interaction, whereas 4 exhibits an antiferromagnetic interaction between the V(IV) ions. 1 and 4 interconvert with pH, thus rendering the pH a determining factor promoting variable structural, electronic, and magnetic properties in V(IV)-citrate species. The observed aqueous behavior of 1-4 is consistent with past solution speciation studies, and contributes to the understanding of significant aspects of the biologically relevant vanadium(IV)-citrate chemistry.

Random walks and reactions on dendrimer structures

We perform model calculations of individual particle random walks on dendrimer structures, due to the emerging interest and wealth of recent experimental data. We use varying coordination numbers and generation orders. We find that it is practically impossible to verify numerically the customary walk properties with the existing asymptotic formalism, because of finite-size effects, even at short times and large system sizes. Several different sets of boundary conditions are employed, producing large differences in the observed behavior for the number of sites visited at least once, as a function of time, S N . We also investigate the case of reacting (annihilating) particles, using the well-known A+A and A+B models, in which case we find an anomalous scaling for the decay of the particle density, with the scaling exponents being f=0.80±0.03 and 0.50±0.03, respectively. We discuss how diffusion in dendrimers is analogous to biased random walks in one dimension, which demonstrates a breakdown of the usual scaling between the reaction progress (or reactant survival) and S N . An appendix gives results for biased walks in one dimension.