Alkali Metal Complexes Research Articles

Alkali metal complexes having sterically bulky bis-iminopyrrolyl ligands – control of dimeric to monomeric complexes

Alkali metal salts of {(CHPh2)2-pyr} and {(CPh3)2-pyr} were prepared and in the molecular structures of these complexes a nuclearity shift from the dimer to monomer were observed due to the substitutions of CHPh2 to CPh3 groups in imine nitrogen of the ligand.

The interaction of NOTA as a bifunctional chelator with competitive alkali metal ions: a DFT study

This work investigates NOTA–alkali metal (Li+, Na+and K+and Rb+) complexation using density functional theory.

Charge Localisation in Heavy Alkali Metal Ion Complexes of 4,4'-Biphenyldicarboxylate

Crystal structure determinations on the isomorphous RbI and CsI complexes of 4,4′-biphenyldicarboxylate have shown the carboxylate entities to be coordinated in an unusual fashion where both oxygen atoms are in a tetrahedral environment indicative of negative charge localisation on each. The metal ions also show a highly irregular form of six-coordination, while the biphenyl units are planar, seemingly as a result of attractive interactions between the ortho hydrogen atoms.

Alkali Metal and Alkaline Earth Metal Complexes with the Bis(borane‐diphenylphosphanyl)amido Ligand – Synthesis, Structures, and Catalysis for Ring‐Opening Polymerization of ϵ‐Caprolactone

AbstractThe syntheses of lithium and alkaline earth metal complexes with the bis(borane‐diphenylphosphanyl)amido ligand (1‐H) of molecular formulas [{κ2‐N(PPh2(BH3))2}Li(THF)2] (2) and [{κ3‐N(PPh2(BH3))2}2M(THF)2] [(M = Ca (3), Sr (4), Ba (5)] are reported. The lithium complex 2 was obtained by treatment of bis(borane‐diphenylphosphanyl)amine (1‐H) with lithium bis(trimethylsilyl)amide in a 1:1 molar ratio via the silylamine elimination method. The corresponding homoleptic alkaline earth metal complexes 3–5 were prepared by two synthetic routes – first, the treatment of metal bis(trimethylsilyl)amide and protio ligand 1‐H via the elimination of silylamine, and second, through salt metathesis reaction involving respective metal diiodides and lithium salt 2. The molecular structures of lithium complex 2 and barium complex 5 were established by single‐crystal X‐ray diffraction analysis. In the solid‐state structure of 2, the lithium ion is ligated by amido nitrogen atoms and hydrogen atoms of the BH3 group in κ2‐coordination of the ligand 1 resulting in a distorted tetrahedral geometry around the lithium ion. However, in complex 5, κ3‐coordination of the ligand 1 was observed, and the barium ion adopted a distorted octahedral arrangement. The metal complex 5 was tested as catalyst for the ring opening polymerization of ϵ‐caprolactone. High activity for the barium complex 5 towards ring opening polymerization (ROP) of ϵ‐caprolactone with a narrow polydispersity index was observed. Additionally, first‐principle calculations to investigate the structure and coordination properties of alkaline earth metal complexes 3–5 as a comparative study between the experimental and theoretical findings were described.

Study of complexation between two 1,3-alternate calix[4]crown derivatives and alkali metal ions by electrospray ionization mass spectrometry and density functional theory calculations

Complexation of two 1,3-alternate calix[4]crown ligands with alkali metals (K+, Rb+ and Cs+) has been investigated by electrospray ionization mass spectrometry (ESI-MS) and density functional theory calculations. The binding selectivities of the ligands and the binding constants of their complexes in solution have been determined using the obtained mass spectra. Also the percentage of each formed complex species in the mixture of each ligand and alkali metal has been experimentally evaluated. For both calix[4]crown-5 and calix[4]crown-6 ligands the experimental and theoretical selectivity of their alkali metal complexes found to follow the trend K+ > Rb+ > Cs+. The structures of ligands were optimized by DFT-B3LYP/6-31G method and the structures of complexes were obtained by QM-SCF-MO/PM6 method and discussed in the text.

Probing the selective separation of potassium ion from sodium ion with cyclopentadienyl anion as receptor: a computational study.

A systematic computational study has been carried out using post-Hartree-Fock and density functional theory methods on half sandwich (M-Cp), sandwich (Cp-M-Cp), inversed sandwich (M-Cp-M), and multi-decker chain complexes of alkali metal ions (Na(+), and K(+)). The binding affinity of cyclopentadienyl anion (Cp) with K(+) and Na(+) ions has been studied in half sandwich, sandwich, inversed sandwich, and multi-decker chain complexes. These complexes have been examined in the aqueous phase. The calculated results show that Cp anion can preferentially bind with Na(+) ion over K(+) ion in aqueous phase. The results obtained from DFT calculations have been compared with the crystal structures of Cp-Na and Cp-K complexes. The Bader's atoms in molecule (AIM) analysis were performed to characterize the non-covalent cation-π interactions in the Cp-M complexes. The calculated electron density at cage critical point indicates the strength of the Cp-M complexes. Energy decomposition analysis (EDA) has also been performed to investigate the origins of these interactions. The electrostatic interaction contributes significantly to the total interaction energy in Cp-M complexes. The relative stability difference of cyclopentadienyl anion (Cp) with K(+) and Na(+) ions in aqueous phase can be exploited for the separations from mixture such as sea bittern. The lower stability of K-Cp complex can induce to precipitate the K(+) ions more easily than the corresponding Na(+) ions. Graphical Abstract Potassium ion from sodium ion with cyclopentadienyl anion as receptor.

Negative Ion Laser Desorption/Ionization Time-of-Flight Mass Spectrometric Analysis of Small Molecules Using Graphitic Carbon Nitride Nanosheet Matrix.

Ultrathin graphitic carbon nitride (g-C3N4) nanosheets served as a novel matrix for the detection of small molecules by negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was described for the first time. In comparison with conventional organic matrices and graphene matrix, the use of g-C3N4 nanosheet matrix showed free matrix background interference and increased signal intensity in the analysis of amino acids, nucleobases, peptides, bisphenols (BPs), and nitropolycyclic aromatic hydrocarbons (nitro-PAHs). A systematic comparison of g-C3N4 nanosheets with positive and negative ion modes revealed that mass spectra produced by g-C3N4 nanosheets in negative ion mode were featured by singly deprotonated ion without matrix interference, which was rather different from the complicated alkali metal complexes in positive ion mode. Good salt tolerance and reproducibility allowed the determination of 1-nitropyrene (1-NP) in sewage, and its corresponding detection limit was lowered to 1 pmol. In addition, the ionization mechanism of the g-C3N4 nanosheets as matrix was also discussed. The work expands its application scope of g-C3N4 nanosheets and provides an alternative approach for small molecules.

Third order nonlinear optical properties and optical limiting behavior of alkali metal complexes of p-nitrophenol

Abstract Optical nonlinearity of metal complexes of p-nitrophenolate (M=Li, Na and K) in ethanol is studied by using a continuous wave (cw) diode pumped Nd:YAG laser (532 nm, 50 mW). The predominant mechanism of observed nonlinearity is thermal in origin. The nonlinear refractive index and the nonlinear absorption coefficient of the samples were found to be in the order of 10 −8 cm 2 /W and 10 −3 cm/W respectively. Magnitude of third-order optical parameters varies according to the choice of alkali metal chosen for metal complex formation of p-nitrophenolate. The third-order nonlinear susceptibility was found to be in the order of 10 −6 esu. The observed saturable absorption and the self-defocusing effect were used to demonstrate the optical limiting action at 532 nm by using the same cw laser beam.

Alkali-Metal Monophenolates with a Sandwich-Type Catalytic Center as Catalysts for Highly Isoselective Polymerization of rac-Lactide.

Highly isoselective ring-opening polymerization (ROP) of rac-lactide is a challenge for sodium and potassium complexes under mild conditions. In this work, three sodium and potassium complexes with a sandwich-type catalytic center are highly active catalysts for the polymerization of rac-lactide and show high isoselectivities with Pm values of 0.72-0.82. The best isoselectivity of Pm = 0.82 is the highest value for alkali-metal complexes under mild conditions. The molecular weights of the obtained PLA are close to the theoretical values, and the molecular weight distributions are narrow.

ChemInform Abstract: Podand‐Based Dimeric Chromium(III)—Salen Complex for Asymmetric Henry Reaction: Cooperative Catalysis Promoted by Complexation of Alkali Metal Ions.

AbstractA new kind of podand‐based dimeric salen ligand is synthesized, and its association with potassium cations is investigated by 1H NMR spectroscopy.

Thermal and spectral properties of alkali metal complexes of vitamin K3 analogue phthiocol

Hydroxynaphthoquinones, alkali, and alkali metal salts were used to synthesize several biologically important molecules. As hydroxynaphthoquinones act also as potential ligands, it is possible that alkali metal complexes may be formed as intermediates in such reactions. To ensure this, the reactions of 2-hydroxy-3-methyl-1,4-naphthoquinone (phthiocol, a vitamin K3 analogue) with sodium metal, alkali such as NaOH and KOH, and alkali metal salts such as CH3COONa, Na2CO3 and K2CO3 were studied in the present investigation. The products were characterized by various analytical techniques, namely elemental analysis, FT-IR, 1H NMR, UV–Vis, thermogravimetric (TG) analysis, GC–MS, and DSC studies. 100 % reduction of the ligand was observed in Phth-1 with sodium metal as reducing agent. The solution of CH3COONa, NaOH, KOH, and K2CO3 in methanol facilitates the reduction of phthiocol ligand. The reduction of the ligands may be probably due to disproportionate reaction of the ‘catechol’ form and the fully oxidized naphthoquinone form of the ligand. The radical signatures of the ligands in complexes were detected by EPR studies and also by carbonyl frequencies in FT-IR spectra. Non-isothermal TG studies confirm the presence of adsorbed and coordinated water molecules. Residue formed after complete decomposition was observed to be 1/2 Na2O in Phth-1 to Phth-3, K2O in Phth-4, and 1/2 K2O in Phth-5. Based on GC–MS and TG studies, three decomposition mechanisms are being proposed for all complexes.

Tuning electron donor-acceptor hybrids by alkali metal complexation.

A zinc phthalocyanine endowed with four [18]-crown-6 moieties, ZnPcTeCr, has been prepared and self-assembled with either pyridyl-functionalized perylenebisimides (PDI-Py) or fullerenes (C60-Py) to afford a set of novel electron donor-acceptor hybrids. In the case of ZnPcTeCr, aggregation has been circumvented by the addition of potassium or rubidium ions to lead to the formation of monomers and cofacial dimers, respectively. From fluorescence titration experiments, which gave rise to mutual interactions between the electron donors and the acceptors in the excited state, the association constants of the respective ZnPcTeCr monomers and/or dimers with the corresponding electron acceptors were derived. Complementary transient-absorption experiments not only corroborated photoinduced electron transfer from ZnPcTeCr to either PDI-Py or C60-Py within the electron donor-acceptor hybrids, but also the unexpected photoinduced electron transfer within ZnPcTeCr dimers. In the electron donor-acceptor hybrids, the charge-separated-state lifetimes were elucidated to be close to 337 ps and 3.4 ns for the two PDI-Pys, whereas the longest lifetime for the photoactive system that contains C60-Py was calculated to be approximately 5.1 ns.

Complex formation of phthalocyanine derivatives substituted by polyethylene oxide with alkali metal ions in methanol

Amphiphilic bifunctional phthalocyanine (Pc) derivatives (protonated compound: EO–H2Pc and copper(II) complex: EO–CuPc) having methylhexaethylene oxide (EO: –O(CH2CH2O)6–CH3) have been synthesized. Dimerization equilibria of EO–H2Pc in alcohols and complex formation with alkali metal ion (Li+, Na+, and K+) in methanol have been studied by means of absorption and fluorescence spectrophotometry. EO–H2Pc in methanol exists predominantly as a dimer, (EO–H2Pc)2. By the reaction with alkali metal hydroxide, the dimer dissociates to monomer and forms complexes at the Pc moiety and/or EO moiety. Lithium ion is captured inside the cavity of the Pc ring and forms a stable complex, EO–LiPc−. Sodium ion and potassium ion, the ion sizes of which are larger than the cavity size of Pc, form “sitting a top” (SAT) complex, that is, the metal ion in the complex with Pc moiety is located on the outside of the Pc ring. By the reaction with NaOH, sodium ion is inserted between the dimeric Pc ring, (EO–Na1/2Pc)2 at the first step, then forms a monomeric 1:1 complex, EO–NaPc−. In the case of reaction with KOH, the monomeric complex, in which potassium ion is coordinated at the EO moiety, (KEO)+H2Pc, is formed as the first step. Then, the Pc moiety coordinates to the potassium ion, (KEO)+–KPc−. The structures of complexes were confirmed by the reaction of EO–CuPc. The order of stability of alkali metal ion complex is obtained as Li+ > > Na+ > K+ for Pc moiety and Li+ < Na+ < < K+ for EO moiety.

Low-dimensional coordination polymeric structures in alkali metal complex salts of the herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D).

The Li, Rb and Cs complexes with the herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D), namely poly[[aqua[μ3-(2,4-dichlorophenoxy)acetato-κ(3)O(1):O(1):O(1')]lithium(I)] dihydrate], {[Li(C8H5Cl2O3)(H2O)]·2H2O}n, (I), poly[μ-aqua-bis[μ3-(2,4-dichlorophenoxy)acetato-κ(4)O(1):O(1'):O(1'),Cl(2)]dirubidium(I)], [Rb2(C8H5Cl2O3)2(H2O)]n, (II), and poly[μ-aqua-bis[μ3-(2,4-dichlorophenoxy)acetato-κ(5)O(1):O(1'):O(1'),O(2),Cl(2)]dicaesium(I)], [Cs2(C8H5Cl2O3)2(H2O)]n, (III), respectively, have been determined and their two-dimensional polymeric structures are described. In (I), the slightly distorted tetrahedral LiO4 coordination involves three carboxylate O-atom donors, of which two are bridging, and a monodentate aqua ligand, together with two water molecules of solvation. Conjoined six-membered ring systems generate a one-dimensional coordination polymeric chain which extends along b and interspecies water O-H...O hydrogen-bonding interactions give the overall two-dimensional layers which lie parallel to (001). In hemihydrate complex (II), the irregular octahedral RbO5Cl coordination about Rb(+) comprises a single bridging water molecule which lies on a twofold rotation axis, a bidentate O(carboxy),Cl-chelate interaction and three bridging carboxylate O-atom bonding interactions from the 2,4-D ligand. A two-dimensional coordination polymeric layer structure lying parallel to (100) is formed through a number of conjoined cyclic bridges, including a centrosymmetric four-membered Rb2O2 ring system with an Rb...Rb separation of 4.3312 (5) Å. The coordinated water molecule forms intralayer aqua-carboxylate O-H...O hydrogen bonds. Complex (III) comprises two crystallographically independent (Z' = 2) irregular CsO6Cl coordination centres, each comprising two O-atom donors (carboxylate and phenoxy) and a ring-substituted Cl-atom donor from the 2,4-D ligand species in a tridentate chelate mode, two O-atom donors from bridging carboxylate groups and one from a bridging water molecule. However, the two 2,4-D ligands are conformationally very dissimilar, with one phenoxyacetate side chain being synclinal and the other being antiperiplanar. The minimum Cs...Cs separation is 4.4463 (5) Å. Structure extension gives coordination polymeric layers which lie parallel to (001) and are stabilized by intralayer water-carboxylate O-H...O hydrogen bonds.

Precipitation and surface adsorption of metal complexes during electropolishing. Theory and characterization with X-ray nanotomography and surface tension isotherms.

Electropolishing of metals often leads to supersaturation conditions resulting in precipitation of complex compounds. The solubility diagrams and Gibbs adsorption isotherms of the electropolishing products are thus very important to understand the thermodynamic mechanism of precipitation of reaction products. Electropolishing of tungsten wires in aqueous solutions of potassium hydroxide is used as an example illustrating the different thermodynamic scenarios of electropolishing. Electropolishing products are able to form highly viscous films immiscible with the surrounding electrolyte or porous shells adhered to the wire surface. Using X-ray nanotomography, we discovered a gel-like phase formed at the tungsten surface during electropolishing. The results of these studies suggest that the electropolishing products can form a rich library of compounds. The surface tension of the electrolyte depends on the metal oxide ions and alkali-metal complexes.

Alkali and alkaline-earth metal complexes with tetraoxa[8]circulene sheet: a computational study by DFT and QTAIM methods

The optimized structure of the sandwich-type complexes [M(TOC)2]n+(M = K+, Ca2+).

Differential response of cholesterol based pyrimidine systems with oxyethylene type spacers to gelation and mesogen formation in the presence of alkali metal ions.

A new series of lipophilic cholesteryl derivatives of 2,4,6-trichloro-pyrimidine-5-carbaldehyde has been synthesized. Oxyethylene spacers of variable lengths were inserted between the hydrogen bonding promoting pyrimidine core and the cholesteryl tail in order to understand their effect on the self-assembly of these compounds. Only compound 1a with the shortest spacer formed a gel in organic solvents such as n-butanol and n-dodecane. While other members (1b and c) having longer spacers led to sol formation and precipitation in n-butanol and n-dodecane respectively. The self-assembly phenomena associated with the gelation process were investigated using temperature-dependent UV-Vis and CD-spectroscopy. The morphological features of the freeze-dried gels obtained from different organic solvents were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The solid phase behaviours of these molecules and their associated alkali metal ion complexes were explored using polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The molecular arrangements in the xerogel and in the solid state were further probed using a wide-angle X-ray diffraction (WAXD) technique. Analysis of the wide-angle X-ray diffraction data reveals that this class of molecules adopts a hexagonal columnar organization in the gel and in the solid state. Each slice of these hexagonal columnar structures is composed of a dimeric molecular-assembly as a building block. Significant changes in the conformation of the oxyethylene chains could be triggered via the coordination of selected alkali metal ions. This led to the production of interesting metal ion promoted mesogenic behaviour.

MPW1PW91‐Calculated Structures, IR Spectra, and Frontier Orbitals of Benzoylmethoxythiacalix[4]arene Complexed with Alkali Metal Ions

The molecular structures of four conformers [cone (CONE), partial cone (PACO), 1,2‐alternate (12A), and 1,3‐alternate (13A)] of benzoylmethoxythiacalix[4]arene 1 and the corresponding alkali metal ion complexes were optimized by using a mPW1PW91/6‐31G(d,p) (hybrid Hartree–Fock density functional) calculation method. The 13A conformer was the most stable among the various conformers of 1 because of less steric hindrance. The total electronic and Gibbs free energies, complexation energies, and the gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) frontier orbitals of the complexes of 1 with the sodium and potassium ions were analyzed. Among the ditopic complexes, the 13A‐type 1•2Na+ complex exhibited the strongest binding efficiency. The binding efficiency of the CONE‐type 1•Na+ complex was much stronger than that of the 12A‐type 1•Na+ complex. However, the 1•K+ complexes were relatively insensitive to the conformation of host 1. The calculated binding preference of the various conformers is consistent with the empirical solution data. The infrared spectra of the conformers of 1 and their exo complexes with the alkali metal ions were calculated by mPW1PW91 and analyzed.

Tris(borane) Adducts of Diphosphanylmethanides: The [H 3 BCH(PPh 2 BH 3 ) 2 ] – Anion and Its Alkali Metal Complexes

The reactivity of lithium complexes that contain the borane-modified diphoshanylmethanide ligand [CH(PPh2BH3)2]– towards different Lewis base adducts of BH3 was studied to gain further insight into the mechanism of the isomerization of this derivative, which formally proceeds through a shift of one BH3 group from the phosphorus atom to the carbon atom. Whereas the use of BH3·THF in THF only resulted in the thf adduct of the starting material, [Li{CH(PPh2BH3)2}(thf)2] (1), the application of BH3·SMe2 in toluene resulted in the formation of the novel compound [(Li{H3BCH(PPh2BH3)2})∞] (2). The subsequent addition of ethereal ligands led to the isolation of [Li{H3BCH(PPh2BH3)2}(Me4thf)] (3) and [Li{H3BCH(PPh2BH3)2}(thf)3] (4). Treatment of these complexes with stronger Lewis bases such as N,N,N′,N′-tetramethylethane-1,2-diamine (tmeda) results in the removal of one phosphorus-bound BH3 molecule and the formation of the [Ph2PCH(BH3)PPh2BH3]– anion. These results indicate that the isomerization of [CH(PPh2BH3)2]– requires an additional BH3 source and a rather strong Lewis base. Complexes 1–4 and the related derivatives [Li{CH(PPh2BH3)2}(Me4THF)] (5) and [K{H3BCH(PPh2BH3)2}(dme)2] (6; dme = 1,2-dimethoxyethane) were characterized by multinuclear NMR spectroscopy and by single-crystal X-ray diffraction analysis.

Highly Iso-Selective and Active Catalysts of Sodium and Potassium Monophenoxides Capped by a Crown Ether for the Ring-Opening Polymerization of rac-Lactide

Sodium and potassium complexes supported by a bulky monophenoxy with one xanthenyl group at the ortho-position and 18-crown-6 or 15-crown-5 as an auxiliary ligand were synthesized and characterized. These complexes are highly iso-selective and active catalysts for the controlled ring-opening polymerization of rac-lactide. The best isotacticity (Pm) achieved was 0.86, which is the highest iso-selectivity reported to date for an alkali-metal complex. In addition, the corresponding polymer exhibited a high Tm of 182 °C. Furthermore, the polymerization looks like an anti-Arrhenius reaction, which is slower at high temperatures than at low temperatures.