Cationic Metal Complexes Research Articles

Complexation of common metal cations by cyanins: Binding affinity and molecular structure

AbstractThe ability of diverse metal cations to form complexes with cyanin has been investigated by means of Density Functional Theory (DFT) and the Quantum Theory of Atoms in Molecules (QTAIM). The strongest preference is shown by trivalent metals which exceed that of Mg(II), indicating that ion replacement processes are suitable detoxification mechanisms for plants. Molecular structure analysis indicates that the larger the metal affinity of Cy− the longer the C2‐C1’ bond length and smaller ρb value. This is understood as upon metal complexation the Cy− ligand molecular structure is more compatible with a dienolate‐like structure rather than the 4′‐keto‐quinoidal‐like structure. The weight of the former increases as stronger the binding. QTAIM charges indicate that the stronger the binding energy the larger the charge transfer from Cy− to the metal, reducing its positive charge below the values indicated by the corresponding Lewis structure.

Structural diversity of metal–organic frameworks via employment of azamacrocycles as a building block

Research on incorporating macrocycles into metal–organic frameworks (MOFs) has been performed intensively due to the opportunities afforded by merging a merit of macrocycles with MOF chemistry, which lead to novel hybrid materials for potential application. Among the numerous kinds of macrocycles, azamacrocycles are used as traditional and popular chelating agents in supramolecular coordination chemistry, because they are very easily functionalized by joining pendant arms and possess a strong propensity to complex metal cations, accounting for the amine functionalities. With this as background, many types of azamacrocyclic MOFs have been synthesized, granting compositionally and topologically new MOFs. The macrocyclic rings can serve as additional adsorption sites or catalytic sites, and the pendant arms on the macrocycles can also play versatile roles such as structure-directing agents, pore-decorating moieties, or rotatable molecular gates for opening/closing pores. In this review, we comprehensively discuss the syntheses, structures, and features of azamacrocyclic MOFs reported to date. Based on representative studies, advantages of these compounds are described, such as how the azamacrocycles increase the structural diversity and complexity of the MOFs and induce novel structural properties within the architectures.

Poly(tertiary amine) as a surface-active multifunctional macro-initiator in Cu2+–amine redox-initiated radical emulsion polymerization of methyl methacrylate

Redox-initiated radical polymerization of methyl methacrylate (MMA) using poly(2-(N,N-dimethylamino)ethyl methacrylate) (PDMAEMA) or poly(N-[3-(N,N-dimethylamino)]propyl methacrylamide) (PDMAPMA) as a surface-active multifunctional reducing agent, vis-a-vis low-molecular-weight (MW) analogs, was performed in aqueous emulsion at 70 °C using CuSO4 or FeCl3 complexes as an oxidizing agent and poly(ethylene glycol) as a nonionic emulsifier, to examine their effect on emulsification, rate of polymerization and the structure of final resultants. The kinetics was followed gravimetrically, while the MW of the resultants was monitored by gel permeation chromatography. CuSO4 complexes exhibited a higher activity than FeCl3 complexes in both cases, and the polymerization evolved at a faster rate than those with low-MW tertiary amines. The MW of the resultants increased by several folds with respect to pristine PDMAEMA or PDMAPMA initially, but adversely decreased with further reaction, owing to the formation of free PMMA chains. The control experiments suggested that the transition metal cation complexes promote the hydrolysis of ester/amide moieties. CuII-catalyzed hydrolysis of PDMAEMA or PDMAPMA occurred steadily during the CuII–PDMAEMA or PDMAPMA redox-initiated radical polymerization of MMA, leading to gradual accumulation of low-MW tertiary amines. During the later stage, the radical polymerization was primarily redox-initiated by pairs of CuII complexes and low-MW tertiary amines, giving rise to the formation of free PMMA chains.

Triflimide (HNTf2) in Organic Synthesis.

Triflimide (HNTf2) is a commercially available and highly versatile super Brønsted acid. Owing to its strong acidity as well as good compatibility with organic solvents, it has been widely employed as an exceptional catalyst, promoter, or additive in a wide range of organic reactions. On many occasions, triflimide has been demonstrated to outperform triflic acid (TfOH). The uniquely outstanding performance of triflimide also benefits from the low nucleophilicity and noncoordinating property of its conjugate base (Tf2N-). Therefore, it has been employed as a precursor toward a variety of cationic metal complexes or organic intermediates with enhanced reactivity or catalytic activity. In this Review, we describe these features and applications of triflimide in organic synthesis, including its synthesis, physical properties, and role as catalyst or promoter in organic reactions. At the end of this Review, another closely related reagent, triflidic acid (HCTf3), is also briefly introduced.

Coordination of Asymmetric Diborenes towards Cationic Coinage Metals (Au, Ag, Cu).

Synthesis of a series of cationic coinage metal (Au: 2-4, Ag: 5, and Cu: 6) complexes of asymmetric diborenes (1 a, 1 b) is reported. X-ray diffraction analysis reveals that the metal center interacts unsymmetrically with the B2 moiety and the terminal boron atom exhibits pronounced pyramidal geometry. A computational study shows that in complexes 2-6, the bonding between the B2 units and the metal center is dominated by electrostatic interactions concomitant with non-negligible covalent contributions.

Alkyl Sulfate Compounds with Cationic Metal Complexes and Some Organic Reagents as Active Membrane Components of Potentiometric Sensors

A review of publications for the last 20 years devoted to the purposeful search for new ionophores ensuring the reliable, reproducible, and selective determination of analytes. The synthesis of new ionophores and optimization of sensor designs in combination with their simplicity, availability, and low cost allow the modernization of present-day sensor technologies. The constantly growing interest in metal complexes with various organic reagents favors the expansion of the areas of their use, in particular, for the development of potentiometric sensors. Potentiometric sensors are a promising tool of the quality control of surfactants (SAS) and their presence in various samples. It was shown that the introduction of alkyl sulfate compounds with cationic copper(II) complexes of some organic reagents (pyridine, 1,10-phenanthroline, 2,2'-dipyridyl) into the composition of membranes ensures the creation of sensors selective to ionic surfactants with improved electroanalytical characteristics.

Employing an Unsaturated Th4+ Site in a Porous Thorium-Organic Framework for Kr/Xe Uptake and Separation.

Actinide based metal-organic frameworks (MOFs) are unique not only because compared to the transition-metal and lanthanide systems they are substantially less explored, but also owing to the uniqueness of actinide ions in bonding and coordination. Now a 3D thorium-organic framework (SCU-11) contains a series of cages with an effective size of ca. 21×24 Å. Th4+ in SCU-11 is 10-coordinate with a bicapped square prism coordination geometry, which has never been documented for any metal cation complexes. The bicapped position is occupied by two coordinated water molecules that can be removed to afford a very unique open Th4+ site, confirmed by X-ray diffraction, color change, thermogravimetry, and spectroscopy. The degassed phase (SCU-11-A) exhibits a Brunauer-Emmett-Teller surface area of 1272 m2 g-1 , one of the highest values among reported actinide materials, enabling it to sufficiently retain water vapor, Kr, and Xe with uptake capacities of 234 cm3 g-1 , 0.77 mmol g-1 , 3.17 mmol g-1 , respectively, and a Xe/Kr selectivity of 5.7.

Employing an Unsaturated Th4+ Site in a Porous Thorium–Organic Framework for Kr/Xe Uptake and Separation

AbstractActinide based metal–organic frameworks (MOFs) are unique not only because compared to the transition‐metal and lanthanide systems they are substantially less explored, but also owing to the uniqueness of actinide ions in bonding and coordination. Now a 3D thorium–organic framework (SCU‐11) contains a series of cages with an effective size of ca. 21×24 Å. Th4+ in SCU‐11 is 10‐coordinate with a bicapped square prism coordination geometry, which has never been documented for any metal cation complexes. The bicapped position is occupied by two coordinated water molecules that can be removed to afford a very unique open Th4+ site, confirmed by X‐ray diffraction, color change, thermogravimetry, and spectroscopy. The degassed phase (SCU‐11‐A) exhibits a Brunauer–Emmett–Teller surface area of 1272 m2 g−1, one of the highest values among reported actinide materials, enabling it to sufficiently retain water vapor, Kr, and Xe with uptake capacities of 234 cm3 g−1, 0.77 mmol g−1, 3.17 mmol g−1, respectively, and a Xe/Kr selectivity of 5.7.

Distribution Control-Oriented Intercalation of a Cationic Metal Complex into Layered Silicates Modified with Organosulfonic-Acid Moieties.

A layered sodium silicate, octosilicate (Na2Si8O17· nH2O), was modified with an organosulfonic-acid moiety (sulfonated propyl (SPr) group, sulfonated phenethyl (SPhE) group, or sulfonated p-trifluoromethylphenyl (STFPh) group) for use as a host material to accommodate a cationic guest, tris(2,2'-bipyridine)ruthenium(II) cation ([Ru(bpy)3]2+). The organosulfonic-acid moiety was bound to the silicate layer via a reaction of an alkylammonium-exchanged octosilicate with a silane coupling agent, and subsequent treatment (oxidation or sulfonation) of the bound organosilyl groups; the surface densities of the organosulfonic-acid moiety were varied by controlling the added amount of silane coupling agents. Adsorption of [Ru(bpy)3]2+ onto surface-modified octosilicates was conducted to find that some surface-modified octosilicates successfully adsorbed [Ru(bpy)3]2+ in the interlayer space (intercalation), while other surface-modified octosiliates did not. In addition, the UV-vis absorption and the luminescence indicate that intercalated [Ru(bpy)3]2+ diffused in the interlayer and that the distribution of the time-averaged location varied depending on the kind and amount of the organosulfonic-acid moieties. Thus, the kind and surface density of the organosulfonic-acid moiety, which correlates to the interactions between the group and the guest species, the volume of free nanospace for adsorption and motion of guests, and the swelling properties, are the key factors not only for the intercalation ability but also for the dynamics of the guest in the interlayer space.

Competitive association of cations with poly(sodium 4-styrenesulfonate) (PSS) and heavy metal removal from water by PSS-assisted ultrafiltration

Complexing metal cations with water-soluble nano-sized ionic polyelectrolytes, combined with a separation process such as ultrafiltration (UF), is a potential strategy to remove or recover ionic heavy metals from water or wastewater. However, competition from naturally occurring cations (e.g., Na+, K+, Ca2+ and Mg2+) may adversely influence target cation removal. To investigate this competition effect, the affinities of both common aqueous cations commonly found in natural surface waters, groundwaters or wastewaters and toxic cationic metals for a typical, commercially available anionic polyelectrolyte, poly(sodium 4-styrenesulfonate) (PSS), were evaluated using a simple ion exchange model and a binary-system ultrafiltration process. Selectivity of these cations for PSS complexation decreased in the order Ba2+ > Pb2+ > Sr2+ > Ca2+ > Cu2+ > Co2+ > Ni2+ > Mg2+ > H+ > K+ > Na+ > Li+. For cations with same valence, their affinity for PSS is proportionally related to their ionic radii. Competitive interactions among different cations complexing with PSS were also investigated in a multi-ion experimental system and the results were compared with estimates obtained using a simple model based on binary-system selectivity coefficients and mass balances. The cation distribution observed in the experimental multi-ion system was consistent with the model calculations. Experimental results also indicate the model can be applied to predict heavy metal (Cu2+ and Pb2+) removal by PSS-assisted UF in a competitive multi-cation water environment. Greater removal of heavy metals was observed at higher ratios of PSS molecular weight to membrane molecular weight cut-off (MW/MWCO).

Preparation and Properties of Nanoparticles, tRNA-Bivalent Metal Cation (Me2+) Complexes, and Prospects of Their Practical Use.

The patterns of formation of RNA nanoparticles (NPs) during thermal cycling of bacterial total tRNA in the presence of cations Ca2+, Mn2+, Ni2+, Zn2+, Co2+, and Cu2+ were studied. The optimal conditions for the production of NPs were found, and it was revealed that their size depends on the ratio of the concentrations of Me2+ and tRNA. The concentration of reagents for obtaining NPs of small size (from 5 to 100 nm) was selected. It was shown that tRNA-based nanoparticles can comprise short (20-50 nt) ribooligonucleotides, including aptamers and siRNAs. The stability of NPs during storage in buffer solutions of various composition was studied. It was found that the initial suspensions of NPs are quite stable, but they are rapidly destroyed in PBS buffer (pH 7.4). A simple and effective stabilizer (polyarginine) was found, the additives of which ensure the preservation of nanoparticles in PBS buffer for more than 5 h. Nanoparticles modified with the stabilizer are resistant to blood serum nucleases and can be used for transfection.

Neutral glycoconjugated amide-based calix[4]arenes: complexation of alkali metal cations in water.

Cation complexation in water presents a unique challenge in calixarene chemistry, mostly due to the fact that a vast majority of calixarene-based cation receptors is not soluble in water or their solubility has been achieved by introducing functionalities capable of (de)protonation. Such an approach inevitably involves the presence of counterions which compete with target cations for the calixarene binding site, and also rather often requires the use of ion-containing buffer solutions in order to control the pH. Herein we devised a new strategy towards the solution of this problem, based on introducing carbohydrate units at the lower or upper rim of calix[4]arenes which comprise efficient cation binding sites. In this context, we prepared neutral, water-soluble receptors with secondary or tertiary amide coordinating groups, and studied their complexation with alkali metal cations in aqueous and methanol (for the comparison purpose) solutions. Complexation thermodynamics was quantitatively characterized by UV spectrometry and isothermal titration calorimetry, revealing that one of the prepared tertiary amide derivatives is capable of remarkably efficient (log K ≈ 5) and selective binding of sodium cations among alkali metal cations in water. Given the ease of the synthetic procedure used, and thus the variety of accessible analogues, this study can serve as a platform for the development of reagents for diverse purposes in aqueous media.

Complexation and Extraction of Transition Metal Cations by New Azodyes: Synthesis, Structure Elucidation and Binding Properties

Complexation and Extraction of Transition Metal Cations by New Azodyes: Synthesis, Structure Elucidation and Binding Properties

Perfectly isoselective polymerization of 2-vinylpyridine promoted by β-diketiminato rare-earth metal cationic complexes

Symmetric and asymmetric β-diketiminato rare-earth metal dialkyl complexes L1Ln(CH2SiMe3)2(THF) (L1 = (2,6-Et2C6H3)NC(Me)CHC(Me)N(2,6-Et2C6H3), Ln = Y (1a), Lu (1b)) and L2Ln(CH2SiMe3)2(THF) (L2 = (2,6-iPr2C6H3)NC(Me)CHC(Me)N(C6H5), Ln = Y (2a), Lu (2b)) have been synthesized by the reaction of the precursor Ln(CH2SiMe3)3(THF)2 with the corresponding pro-ligands (HL1 and HL2) in good yield. These complexes promote the polymerization of 2-vinylpyridine (2-VP) to produce isotactic-biased poly(2-vinylpyridine) (P2VP) (mm: 40%) in quantitative yield. The in situ generated cationic species with the addition of borate ([Ph3C][B(C6F5)4], [PhNHMe2][B(C6F5)4]) prior to the polymerization display distinct results, and the symmetric ones afford perfectly isotactic P2VP with an mm value up to 99%, whilst the asymmetric ones produce atactic P2VP (mm: 26%). The 1H NMR spectrum and MALDI-TOF mass analysis of an oligomer prepared with 1a/[Ph3C][B(C6F5)4] indicate that the polymerization is initiated by coordination insertion of 2-VP into the Y-CH2SiMe3 bond of the in situ generated cationic species.

Complexation of heavy metal cations on clay edges at elevated temperatures

Aiming at the complexation mechanism of heavy metals on clay edges at elevated temperatures, we carried out systematic first principles molecular dynamics (FPMD) simulations at 423K by taking Cd(II) and Ni(II) as model cations. The results show that stable surface complexes include monodentate complexes on ≡SiO site, bidentate complexes on ≡Al(OH)2 site, and tetradentate complexes on octahedral vacancy on (010) edges and monodentate complexes on ≡SiO site, bidentate complexes on ≡AlOH≡AlSiO site, and tetradentate complexes on vacancy on (110) edges. Constrained FPMD simulations were conducted to calculate the desorption free energies of the complexes of the two cations on (010) surface. The results show that the octahedral vacancy has significantly higher free energy than the other sites regardless of the coordination of Al(III), indicating that the vacancy is the most favorable complexing site at elevated temperatures. The same conclusion has been deduced for (110) edges. Computed pKa values show that only the complexes on vacancy sites can hydrolyze in the common pH range, whereas those on the other sites hardly dissociate due to the extremely high pKa values, that is, the former complexes can serve as complexing sites for more metal cations. Additional simulations show that multinuclear complexes of Cd(II) and Ni(II) hold stably at 423K, which may act as precursors for epitaxial growth of new mineral phases. This study forms a physical basis for understanding the behaviors of heavy metals in various environments of elevated temperatures, and provides fundamental data for further experimental and modelling studies.

Theoretical design on a new double functional device of 2,2′‐bipyridine‐embedded N‐(9‐pyrenyl methyl)aza‐15‐crown‐5

AbstractTheoretical design on a new molecular switch and fluorescent chemosensor double functional device of aza‐crown ether (2,2′‐dipyridine‐embedded N‐(9‐anthraceneyl(pyrenyl)methyl)aza‐15‐crown‐5) was explored. The interactions between ligands and a series of alkaline earth metal cations (Mg2+, Ca2+, Sr2+, and Ba2+) were investigated. The fully optimized geometry structures of the free ligands (L1, L2) and their metal cation complexes (L1/M2+, L2/M2+) were calculated with the B3LYP/6‐31G(d) method. The natural bond orbital analysis, which is based on optimized geometric structures, was used to explore the interaction of L1/M2+, L2/M2+ molecules. The absorption spectra of L1, L2, L1/M2+, and L2/M2+, and their excited states were studied by time‐dependent density functional theory. A new type molecular device L2(2,2′‐dipyridine‐embedded N‐(9‐pyrenyl methyl)aza‐15‐crown‐5) is designed, which not only has the selectivity for Sr2+, and construct allosteric switch, but also has fluorescent sensor performance.

Convenient synthesis of perfluoroalkyltrifluoroborates

Perfluoroalkyltrimethoxyborates were converted into the corresponding perfluoroalkyltrifluoroborates in high yield by the action of potassium bifluoride in acidic media, i.e. in hydrochloric acid (37%), glacial acetic acid, and trifluoroacetic acid as well as in acidic ionic liquids. These low-cost methods avoid the use of toxic and corrosive hydrofluoric acid or anhydrous HF (aHF). Potassium and sodium perfluoroalkyltrifluoroborates are highly valuable starting materials for the preparation of low viscosity ionic liquids and organic salts with [RFBF3]− anions, in general, and for the synthesis of further perfluoroalkylborate anions, for example perfluoroalkylcyanofluoroborates [RFBF3-n(CN)n]− (n = 1–3). Furthermore, complex metal cations are accessible with the weakly coordinating [RFBF3]− counterions, as exemplified by the synthesis of [Cu(bpy)3][C2F5BF3] (bpy = 2,2′-bipyridine).

Density Functional Theory Studies on the Stability of Alkaline Metal Complexes of Pentazole and Oxopentazole Anions

We performed calculations on alkaline metal ion complexes of pentazole and oxopentazole anions using density functional theory methods to examine the stability of the complexes in the gas phase and in solution. The complexation energies and Gibbs energies were estimated, and the structures corresponding to local and global minima were also identified. In addition, the transition states along the decomposition pathways of the metal‐complexed pentazole and oxopentazole were characterized to evaluate the kinetic stability of the complexes in the gas phase and in solution. The Gibbs energies for metal cation complexation were fairly negative in tetrahydrofuran (THF) solution. This reflected the good thermodynamic stability of the metal‐complexed pentazole and oxopentazole. The kinetic stability of pentazole and oxopentazole was increased by several kilocalories per mole in the THF solution. Upon metal complexation, in the gas phase, the decomposition barrier of the pentazole was significantly reduced, while that of the oxopentazole was little changed. This showed that the metal cation preferentially bound to the oxygen atom rather than to one of the nitrogen atoms in the ring. In the THF solution, the decomposition barriers were rarely altered, when compared to the bare anions.

Chitosan for wastewater treatment

AbstractChitosan (an amino‐polysaccharide obtained from deacetylation of chitin, the major constituent of crustaceous shells and insect cuticles) presents a cationic character in acidic media allowing its dissolution, its shaping and possible ion‐exchange interactions with anionic compounds (a property applied in adsorption and coagulation–flocculation processes). In neutral media, non‐protonated amino groups allow complexation of metal cations or organic chemicals. These different properties explain the interest taken by the scientific community in using this biopolymer. In solution it contributes to complex metals and their recovery by complexation‐assisted ultrafiltration. It can also be used to coagulate–flocculate organic compounds (as anionic dyes). In the solid state, it can be used for metal ion adsorption, as well as adsorption of organic compounds (dyes, pesticides, drugs, endocrine disruptors, etc.). The adsorption and coagulation–flocculation processes will be compared and examples considered. Moreover, it is noteworthy that the thermal degradation of this type of material is also more environmentally friendly than that of conventional synthetic resins (production of hazardous by‐products, etc.), a supplementary advantage of these biopolymer‐based sorbents. Combined with its ability to be chemically or physically modified improving the potential and phase separation of chitosan‐based materials, all these properties mean it is an excellent candidate for wastewater treatment. © 2017 Society of Chemical Industry

Solvation Effect on Complexation of Alkali Metal Cations by a Calix[4]arene Ketone Derivative.

The medium effect on the complexation of alkali metal cations with a calix[4]arene ketone derivative (L) was systematically examined in methanol, ethanol, N-methylformamide, N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile. In all solvents the binding of Na+ cation by L was rather efficient, whereas the complexation of other alkali metal cations was observed only in methanol and acetonitrile. Complexation reactions were enthalpically controlled, while ligand dissolution was endothermic in all cases. A notable influence of the solvent on NaL+ complex stability could be mainly attributed to the differences in complexation entropies. The higher NaL+ stability in comparison to complexes with other alkali metal cations in acetonitrile was predominantly due to a more favorable complexation enthalpy. The 1H NMR investigations revealed a relatively low affinity of the calixarene sodium complex for inclusion of the solvent molecule in the calixarene hydrophobic cavity, with the exception of acetonitrile. Differences in complex stabilities in the explored solvents, apart from N,N-dimethylformamide and acetonitrile, could be mostly explained by taking into account solely the cation and complex solvation. A considerable solvent effect on the complexation equilibria was proven to be due to an interesting interplay between the transfer enthalpies and entropies of the reactants and the complexes formed.