Metal Countercations Research Articles

Gallium(III) complexes with 1,3-pdta-type of ligands: The influence of an alkyl substituent in 1,3-propanediamine chain and the metal counter cation on the structural properties of the complex

The hexadentate 1,3-propanediamine-N,N,N’,N’-tetraacetate (1,3-pdta4−) and (±)-1,3-pentanediamine-N,N,N’,N’-tetraacetate (1,3-pndta4−) ligands were used for the synthesis of two new gallium(III) complexes, Na[Ga(1,3-pdta)]·3H2O (1) and Ba[Ga(1,3-pndta)]2·3H2O (2). Complexes 1 and 2 were characterized by IR and NMR (1H and 13C) spectroscopy and single crystal X-ray diffraction analysis. The obtained results have shown that both hexadentate 1,3-pdta4− and 1,3-pndta4− ligands are coordinated to gallium(III) ion through the two nitrogen and four carboxylate oxygen atoms. Both complexes show significant octahedral distortion since the mean angular deviation is nearly four degrees per angle. However, the octahedral distortion of complex 2 is lower than of 1, as indicated by the ΣΔ(Oh) values (48° and 49° versus 53°, respectively). The binding interactions of the complexes 1 and 2 with calf thymus DNA (ct-DNA) and bovine serum albumin (BSA) were studied by fluorescence emission spectroscopy. Both complexes can bind to the serum albumin reversibly, while their affinity to ct-DNA is rather low.

Cobalt(III) complexes with (±)-1,3-pentanediamine-N,N,N’,N’-tetraacetate. The influence of nature of alkali and alkaline earth metal counter cations on the supramolecular association of the complex

The coordination of hexadentate (±)-1,3-pentanediamine-N,N,N’,N’-tetraacetate (1,3-pndta) ligand with Co(III) has been investigated. Four octahedral [Co(1,3-pndta)]− complexes containing different counter cations, Li[Co(1,3-pndta)]⋅4H2O (1a), Li[Co(1,3-pndta)]⋅2H2O (1b), K[Co(1,3-pndta)]⋅H2O (1c) and Ca[Co(1,3-pndta)]2⋅5H2O (1d), were synthesized and structurally characterized. Single-crystal X-ray diffraction analysis, IR, NMR (1H and 13C) and electronic absorption spectroscopy were used for characterization of 1a − d. The influence of the ethyl substituent of 1,3-propanediamine chain in 1,3-pndta and the nature of metal counter cation on the structural modalities of carboxylate bridging groups in 1a − d were established by comparing with the analogous [M(1,3-pdta)] n − (1,3-pdta = 1,3-propanediamine-N,N,N’,N’-tetraacetate) and [M(1,3-pndta)] n − complexes (M = Co(III), Cr(III) and Ni(II)). Our studies have shown that the supramolecular association of the complexes is primarily governed by the size of the alkali or alkaline earth metal counter cation and its templating ability, while ethyl substituents, in most cases, prevent the formation of 3D polymeric frameworks.

Secondary-Bond-Driven Construction of a Polar Material Exhibiting Strong Broad-Spectrum Second-Harmonic Generation and Large Birefringence.

Considerable effort has been invested in the development of non-centrosymmetric (NCS) inorganic solids for ferroelectricity-, piezoelectricity- and, particularly, optical nonlinearity-related applications. While great progress has been made, a persistent problem is the difficulty in constructing NCS materials, which probably stems from non-directionality and unsaturation of the ionic bonds between metal counter-cations and covalent anionic modules. We report herein a secondary-bond-driven approach that circumvents the cancellation of dipole moments between adjacent anionic modules that has plagued second-harmonic generation (SHG) material design, and which thereby affords a polar structure with strong SHG properties. The resultant first NCS counter-cation-free iodate, VO2 (H2 O)(IO3 ) (VIO), a new class of iodate, crystallizes in a polar lattice with VO2 (H2 O)(IO3 )] zigzag chains connected by weak hydrogen bonds and intermolecular forces. VIO exhibits very large SHG responses (18 × KH2 PO4 @ 1200 nm, 1.5 × KTiOPO4 @ 2100 nm) and sufficient birefringence (0.184 @ 546 nm). Calculations and crystal structure analysis attribute the large SHG responses to consistent polarization orientations of the VO2 (H2 O)(IO3 )] chains controlled by secondary bonds. This study highlights the advantages of manipulating the secondary bonds in inorganic solids to control NCS structure and optical nonlinearity, affording a new perspective in the development of high-performance NLO materials.

Synthesis and Reactivity of Alkali Metal Hydrido-Magnesiate Complexes which Exhibit Group 1 Metal Counter-Cation Specific Stability.

Reactions of the series of alkali metal amides M(HMDS) (M = Li-Cs; HMDS = [N(SiMe3)2]-) with the neutral magnesium(II) hydride compound [Mg(BDIDipp)(μ-H)]2 (BDIDipp = [CH{C(Me)NDipp}2], Dipp = 2,6-iPr2-C6H3) have been carried out. When M = Li or Na, the reactions yielded Mg(BDIDipp)(HMDS) and MH as the primary products. In the sodium amide reaction, [Na2(HMDS)][{Mg(BDIDipp)}2(H)3] was obtained as a low-yield by-product. When M = K-Cs, the reactions gave the group 1 metal hydrido-magnesiates, M2[Mg(BDIDipp)(HMDS)(H)]2·(benzene)n (n = 0 or 1), the thermal stability of which increases with the increasing molecular weight of the alkali metal involved. Reactions of Cs2[Mg(BDIDipp)(HMDS)(H)]2·(benzene) with 18-crown-6 and CO gave the first monomeric alkali metal hydrido-magnesiate [Cs(18-crown-6)][Mg(BDIDipp)(HMDS)(H)] and the ethenediolate complex Cs2[{Mg(BDIDipp)(HMDS)}2(μ-C2H2O2)], respectively. The new synthetic route to alkali metal hydrido-magnesiates described herein may facilitate further reactivity studies of this rare compound class.

Dynamic and Static Assembly of Sulfated Cellulose Nanocrystals with Alkali Metal Counter Cations.

Sulfate groups on cellulose particles such as cellulose nanocrystals (CNCs) provide colloidal stability credit to electrostatic repulsion between the like-charged particles. The introduction of sodium counter cations on the sulfate groups enables drying of the CNC suspensions without irreversible aggregation. Less is known about the effect of other counter cations than sodium on extending the properties of the CNC particles. Here, we introduce the alkali metal counter cations, Li+, Na+, K+, Rb+, and Cs+, on sulfated CNCs without an ion exchange resin, which, so far, has been a common practice. We demonstrate that the facile ion exchange is an efficient method to exchange to any alkali metal cation of sulfate half esters, with exchange rates between 76 and 89%. The ability to form liquid crystalline order in rest was observed by the presence of birefringence patterns and followed the Hofmeister series prediction of a decreasing ability to form anisotropy with an increasing element number. However, we observed the K-CNC rheology and birefringence as a stand-out case within the series of alkali metal modifications, with dynamic moduli and loss tangent indicating a network disruptive effect compared to the other counter cations, whereas observation of the development of birefringence patterns in flow showed the absence of self- or dynamically-assembled liquid crystalline order.

Palladium-Catalyzed Enantioselective β-C(sp3)-H Activation Reactions of Aliphatic Acids: A Retrosynthetic Surrogate for Enolate Alkylation and Conjugate Addition.

Enolate alkylation and conjugate addition into an α,β-unsaturated system have served as long-standing strategic disconnections for the installation of α- or β-substituents on carbonyl-containing compounds. At the onset of our efforts to develop C-H activation reactions for organic synthesis, we set our eye toward developing asymmetric β-C-H activation reactions of aliphatic acids with the perspective that this bond-forming event could serve as a more flexible retrosynthetic surrogate for both canonical carbonyl-related asymmetric transformations.In this Account, we describe our early efforts using strongly coordinating chiral oxazolines to probe reaction mechanism and the stereochemical nature of the C-H cleavage transition state. The characterization of key reactive intermediates through X-ray crystallography and computational studies suggested a transition state with C-H and Pd-OAc bonds being approximately coplanar for optimum interaction. We then moved forward to develop more practical, weakly coordinating monodentate amide directing groups, a necessary advance toward achieving the β-C-H activation of weakly coordinating native carboxylic acids. Throughout this journey, gradual deconvolution between a substrate's directing effect and its intimate interplay with ligand properties has culminated in the design of new ligand classes that ultimately allowed the competency of native carboxylic acids in β-C-H activation. These efforts established the importance of ligand acceleration in Pd-catalyzed C-H activation, where the substrate's weak coordination is responsible for positioning the catalyst for C-H cleavage, while the direct participation from the bifunctional ligand is responsible for enthalpically stabilizing the C-H cleavage transition state.Building upon these principles, we developed five classes of chiral ligands (MPAA, MPAQ, MPAO, MPAThio, MPAAM) to enable enantioselective β-C-H activation reactions, including carbon-carbon and carbon-heteroatom bond formation. The accumulated data from our developed enantioselective C-H activation reactions indicate that ligands possessing point chirality are most effective for imparting stereoinduction in the C-H activation step, the application of which enabled the desymmetrization and subsequent C-H functionalization of enantiotopic carbon and protons across a range of weakly coordinating arylamides and, more recently, free carboxylic acids. Progress in ligand design, in conjunction with the enabling nature of alkali metal countercations, led to the realization of a suite of β-methyl and now methylene C(sp3)-H activation reactions. These advancements also enabled the use of economical oxidants, such as peroxides and molecular oxygen, to facilitate catalyst turnover. In the future, continued progress in designing more efficient bifunctional chiral ligands is likely to provide a myriad of enantioselective β-C-H activation reactions of readily available native substrates.

Bulky countercation effects on the crystal packing of anionic dithiooxalato-containing Ni(ii), Pd(ii) and Pt(ii) complexes: spectroscopic–redox correlations

The metal ion, countercation and crystallization solvent control the packing of bis(dithiooxalato-k2S,S′)metallate(ii) complex anions in the solid state.

Counter Cations Affect Transport in Aqueous Hydroxide Solutions with Ion Specificity.

The anomalously high mobility of hydroxide and hydronium ions in aqueous solutions is related to proton transfer and structural diffusion. The role of counterions in these solutions, however, is often considered to be negligible. Herein, we explore the impact of alkali metal counter cations on hydroxide solvation and mobility. Impedance measurements demonstrate that hydroxide mobility is attenuated by lithium relative to sodium and potassium. These results are explained by ab initio molecular dynamics simulations and experimental vibrational hydration shell spectroscopy, which reveal substantially stronger ion pairing between OH- and Li+ than with other cations. Hydration shell spectra and theoretical vibrational frequency calculations together imply that lithium and sodium cations have different effects on the delocalization of water protons donating a hydrogen bond to hydroxide. Specifically, lithium leads to enhanced proton delocalization compared with sodium. However, proton delocalization and the overall diffusion process are not necessarily correlated.

Hexaniobate Cluster Anion Monolayers on Gold Nanoparticles: A New Structural Role for Alkali Metal Countercations.

Monolayer shells of polyoxotungstate cluster anions on gold nanoparticles in water were electrostatically stabilized by structurally integrated countercations, with formation constants, K, increasing in the order: Li+ < Na+ < K+ < TMA+ < Cs+ (TMA+ = tetramethylammonium). We now report that for hexaniobate cluster anions, K values increase in the same order, with the notable exception of TMA+, which is effectively unable to induce monolayer formation. These findings point to a new structural model in which hexaniobate anions form a spherical coordination polymer at the gold surface with alkali metal countercations serving as single-atom structural building units between hexaniobate linkers.

Anionic Bismuth-Oxido Carboxylate Clusters with Transition Metal Countercations.

Six new anionic bismuth-oxido clusters containing trifluoroacetate ligands were prepared. These include two new Bi6O8 clusters: [M(NCMe)2(H2O)4]3[Bi6(μ3-O)4(μ3-OH)4(CF3CO2)12] with an octahedral Bi6O4(OH)4 core (M = Ni, 1a; Co, 1b) and four Bi4O2 clusters, {[Co(NCMe)6][Bi4(μ3-O)2(CF3CO2)10]}n (2a), {[Co{HC(MeCO)2(MeCNH)}2][Bi4(μ3-O)2(CF3CO2)10]·2[CF3CO2]·2[CF3CO2H]·2[H2O]}n (2b), {[Cu(NCMe)4]2[Bi4(μ3-O)2(CF3CO2)10]·2[CF3CO2H]}n (2c), and {[Me4N]2[Bi4(μ3-O)2(CF3CO2)10]·2[CF3CO2H]}n (2d). These are among the first bismuth-oxido anionic clusters synthesized, and the first to have transition metal countercations. The Bi6O8 anion in 1a and 1b is a high-symmetry octahedron. Additionally, two of the new Bi4O2 clusters are arranged in 1D polymeric structures via bridging carboxylate ligands. The cation in compound 2c had not been previously characterized and was also observed in the synthesis of [Co{HC(MeCO)2(MeCNH)}2][Bi(NO3)6] (3). The new compounds were characterized using single crystal X-ray crystallography and elemental analysis.

An Alternative Method for Generating Arynes from ortho-Silylaryl Triflates: Activation by Cesium Carbonate in the Presence of a Crown Ether.

An alternative method for generating arynes from ortho-silylaryl triflates using cesium carbonate and 18-crown-6 is reported. The method was efficiently applied to a variety of reactions between several arynes and arynophiles. We also demonstrated that the efficiency of aryne generation is significantly affected by the alkali metal countercation of the carbonate.

Complex transition metal hydrides: linear correlation of countercation electronegativity versus T-D bond lengths.

For homoleptic 18-electron complex hydrides, an inverse linear correlation has been established between the T-deuterium bond length (T = Fe, Co, Ni) and the average electronegativity of the metal countercations. This relationship can be further employed towards aiding structural solutions and predicting physical properties of novel complex transition metal hydrides.

Chemical shifts of phenolic monomers in solution and implications for addition and self‐condensation

Alkali metal counter-cations alter the electron density of phenolates in solution by electrostatic interactions. This change in electron density affects their reactivity toward formaldehyde, hydroxymethylphenols, and isocyanates during polymerization. The electronic perturbation of phenolic model compounds in the presence of alkali metal hydroxides was investigated with (13)C and (1)H nuclear magnetic resonance in polar solvents relative to non-ionic controls, altering the chemical shifts of the model compounds, thus indicating changes in electron density using the chemical shift as a proxy. These shifts were attributed to Coulombic electrostatic interactions of the counter-cation with the phenolate anion that correlated to hydrated ionic radius and solvent dielectric constants. The predicted relative reaction rates for formaldehyde addition based on electron density ranking from (13)C nuclear magnetic resonance of the phenolic models was compared with the literature values. Predictions for condensation reactions of 2- and 4-hydroxymethylphenol from chemical shifts were consistent with published results. The results permit predictions for the reaction of phenolic compounds for the formation of thermosetting polymeric materials.

Vibrational Property Study of SrGa2H2 and BaGa2H2 by Inelastic Neutron Scattering and First Principles Calculations

Vibrational properties of the gallium hydrides SrGa2H2 and BaGa2H2 have been investigated by means of inelastic neutron scattering (INS) and first-principles calculations. The compounds contain Ga-H units being part of a two-dimensional polyanionic layer, [(GaH)(GaH)]2-. The INS spectra are composed of dispersed internal Ga-H bending and stretching modes at frequencies above 600 cm(-1) and external lattice modes at frequencies below 220 cm(-1). Frequencies of the internal modes are not susceptible to the metal countercation, indicating a strong integrity of the polyanionic layer as a building unit in the structures of SrGa2H2 and BaGa2H2. The Ga-H stretching modes have frequencies between 1200 and 1400 cm(-1), which is very low compared to molecular gallium hydrides. The weak Ga-H bond in SrGa2H2 and BaGa2H2 is balanced by Sr(Ba)-H interactions.

Thermal characterization of Flemion® membranes substituted by alkali metal cations

The thermal behavior of perfluorosulfonated membranes of three equivalent mass (EW=910, 1000 and 1100 g eq−1) has been studied for membranes in acid form and in the alkali metal countercations substituted samples. The water contents of the membranes decrease progressively with increasing EW and the countercations charge density. The monovalent cations substitutions increase the membranes thermal stability. DSC curves show a single endothermic peak around 120°C that give low peak temperature for low EW and high peak temperature for large cations size. The membrane mechanical properties changed for different EW and temperatures of membranes. Stress-strain analysis showed that K+ substituted membranes at both temperatures present a highest YM compared to the other alkali cation substitutions. The thermal properties of perfluorosulfonated membranes depend on the water contents, cation size, temperature and also on EW value.

Transition Metal-Catalyzed Organometallic Reactions that Have Revolutionized Organic Synthesis

Abstract The Pd- or Ni-catalyzed cross-coupling reactions of organometals containing Zn, Al, Zr, and B as well as related reactions of Mg and several other metals collectively represent the most widely applicable organic skeleton construction method discovered and developed over the past several decades, allowing the synthetic chemists to synthesize practically all types of organic compounds. Some of the seminal and critically important discoveries and early developments in the 1970s as well as their current scope (Tables 2 and 3) are briefly discussed. Some of the notable discoveries and developments include (1) identification of superior properties of Pd relative to Ni, (2) the broad scope of Pd- or Ni-catalyzed cross-coupling with respect to metal counter cations including Zn, Al, Zr, B, and Mg, (3) the hydrometallation–Pd-catalyzed cross-coupling tandem processes for selective syntheses of alkenes, dienes, oligoenes, and oligoenynes, (4) double metal catalysis involving Pd or Ni and added metal compounds containing Zn, In, Li, and others, and (5) realization of high turnover numbers (≥103–105) through the use of chelating phosphines, such as DPEphos and dppf. In these reactions, the metal counter cations in organometals and Pd or Ni are to work successively via transmetallation. The Zr-catalyzed alkyne carboalumination and the Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction) have provided efficient and selective routes to methyl-branched (E)-trisubstituted alkenylalanes and 2-substituted chiral alkylalanes, respectively. These reactions provide two additional examples of prototypical transition metal-catalyzed organometallic reactions. Significantly, they can be readily combined with the Pd- or Ni-catalyzed cross-coupling for the synthesis of trisubstituted alkenes embracing a wide variety of natural products, such as terpenoids, carotenoids, and others, as well as various chiral organics including deoxypolypropionates and saturated terpenoids. The Zr-catalyzed alkyne carboalumination has been applied to the synthesis of well over 100 complex natural products (Table 4), while the ZACA reaction has been transformed from a mere scientific novelty to a full-fledged asymmetric synthetic method that is catalytic in both transition metal (Zr) and chiral auxiliaries through a series of breakthroughs (Schemes 12–17).

Crystal Structure of New Selenosilicates Pb1.75M0.5SiSe4 (M: Cu and Ag).

AbstractFor Abstract see ChemInform Abstract in Full Text.

Crystal structure of new selenosilicates Pb 1.75M 0.5SiSe 4 (M = Cu and Ag)

The crystal structure of new selenosilicates Pb 1.75M 0.5SiSe 4 (M = Cu and Ag) was investigated using X-ray powder diffraction (space group I 4 ¯ 3 d , Pearson symbol cI116: a = 1.4345(1) nm for Pb 1.75Cu 0.5SiSe 4; a = 1.44995(2) nm for Pb 1.75Ag 0.5SiSe 4). The structure consists of isolated [SiSe 4] 4− tetrahedra and contains three different sites for metal counter-cations. The structure arrangement is similar to those of α-Pb 2GeS 4 and Tl 3VS 4.

Novel CuIII bis-1,2-dichalcogenene complexes with tunable 3D framework through alkaline cation coordination: a structural and theoretical study.

The deprotonated form of the ligands pyrazine-2,3-diselenol (pds) and pyrazine-2,3-dithiol (pdt) react with Cu(ClO(4))(2).6 H(2)O to form different Cu(III) complexes Na[Cu(III)(pds)(2)].2 H(2)O (1), Li[Cu(III)(pds)(2)].3 H(2)O (2), and Na[Cu(III)(pdt)(2)].2 H(2)O (4) depending on the countercation compound used as deprotonating agent (NaOH, LiOH). Two other Cu(III) complexes were obtained by replacement of the alkali metal cations with tetrabutylammonium (TBA(+)), namely, TBA[Cu(III)(pds)(2)] (3), and TBA[Cu(III)(pdt)(2)] (5). All complexes were characterized by (1)H and (13)C NMR and IR spectroscopy, electronic absorption, elemental analysis, cyclic voltammetry (CV), and X-ray crystallography. Electrical conductivity measurements on single crystals show that these salts exhibit insulating behavior. The crystal structure of these species revealed a lateral coordination capability of the N atoms of the pyrazine ring of both pds and pdt ligands towards the alkali metal ions, which leads to the build up of a net of coordinative bonds, hydrogen bonds, and contacts that result in the final 3D structure. Two parameters control the crystal engineering of the final 3D structures: the nature of the alkali metal countercation and the nature of the chalcogen atom (Se/S), which allow fine-tuning of complex 3D crystal lattice. Density functional calculations were performed on the [Cu(pds)(2)] and [Cu(pdt)(2)] systems to investigate the electronic structure of the complexes and understand their electronic and electrochemical behavior by studying the frontier molecular orbitals. This study also reveals whether the redox processes take place on the ligands or on the metal center, a question under continuous discussion in the literature.

Triplet dimers of silylbenzene anion radicals in low-temperature glass matrices

Anion radicals of o- and p-bis(trimethylsilyl)benzenes were found by ESR spectroscopy to form the corresponding triplet dimers in 2-methyltetrahydrofuran (MeTHF) glass matrices at low temperatures. The temperature dependence of the signal intensity of a triplet dimer has shown that the dimer has the triplet ground state. The spin–spin distances estimated with the D values increased with the increasing size of alkali metal countercations, indicating that the triplet dimer has a π −–M +–π − type sandwich structure. The stability of the triplet dimer depended remarkably on the coordination ability of the solvent; no triplet dimer was observed in tetrahydrofuran (THF).