Formation Of Polynuclear Complexes Research Articles

Reaction of a Bulky β‐Diketiminato Magnesium Hydride with CO2 Yielding a Polynuclear Magnesium Cage Compound

The reaction of a sterically shielded Mg hydride complex, bearing a bulky β‐diketiminato (BDI) ligand, with CO2 leads to the formation of polynuclear complexes. CO2 not only inserts into the metal hydride bond yielding formate ions, but also adds onto the γ‐C of the BDI ligand. This reactivity gives rise to the formation of tri‐ and tetranuclear structures in THF, leading to a hexameric structure associated with a change in the coordination mode of the BDI ligand at 60 °C in THF within four days. The hexameric complex was isolated in high reproducible yield from the solution and characterized by X‐ray diffraction analysis. The reaction affording the hexameric complex was shown to be completed within 1 h at room temperature in toluene. Similar reactions of CO2 with a BDI calcium hydride complex proceeds less cleanly and a pure product could not be isolated.

A novel chitosan and polyferric sulfate composite coagulant for biogas slurry pretreatment by simultaneous flocculation and floatation: Performance and underlying mechanisms

Biogas slurry from anaerobic digestion is rich in nutrients but has not been fully utilized due to a high content of suspended solids (SS) causing clogging during agricultural irrigation. This study aimed to evaluate the performance of a novel chitosan and polyferric sulfate (CTS-PFS) composite coagulant for simultaneous flocculation and floatation to enhance SS removal while preserving nutrients in biogas slurry. Orthogonal method was used for experimental design to determine the optimal synthesis and operational conditions of CTS-PFS. Results show that CTS-PFS outperformed individual CTS and PFS coagulant in terms of SS removal and nutrient (nitrogen, phosphorus, and potassium) preservation. Compared to individual CTS and PFS coagulation, the combination of CTS and PFS at the mass ratio of 1:6 showed significantly higher performance by 41.5 % increase in SS removal and 5.2 % reduction in nutrient loss. The improved performance of CTS-PFS was attributed to its formation of polynuclear hydroxyl complexes with ferric oxide groups (e.g. Fe-OH, Fe-O-Fe, Fe-OH-Fe and COO-Fe) to strengthen charge neutralization and adsorption bridging. Data from this study further confirm that CTS-PFS enhanced the removal of small suspended particles and dissolved organic matter in the molecular weight range of 0.4–2.0 kDa and preserved ammonia and potassium better in biogas slurry. Bubbles were generated as hydrogen ions from coagulant hydrolysis interacted with bicarbonate and carbonate in biogas slurry for removing the produced flocs by floatation. Floc flotation was more effective in CTS-PFS coagulation due to the significant production of uniform bubbles, evidenced by the reduction in the viscosity of biogas slurry.

Synthesis, X-ray crystal structure and photophysics of butterfly shape orange and red emanating polynuclear complexes of tris(dibenzoylmethanato)Ln(III) (Ln = Sm/Eu) and exo-bidentate 4,4'-bipyridine.

Reaction of two equivalents of [Ln(dbm)3(H2O)] (Ln = Sm/Eu/Gd) with one equivalent of 4,4'-bipyridine (4,4'-bpy) led to the formation of rare polynuclear complexes of the type [Ln(dbm)3(4,4'-bpy)]n (dbm is the anion of 1,3-diphenyl-1,3-propanedione) instead of symmetrically bridged dinuclear complexes. The structure of the complexes has been established by the single crystal X-ray diffraction (SC-XRD) method and shows that the coordination sphere is composed of a LnO6N2 core (octacoordinated). Shape analysis further revealed that the geometry around Ln(III) is distorted square anti-prismatic with SHAPE value 0.738 and 25.719 for [Sm(dbm)3(4,4'-bpy)]n and [Eu(dbm)3(4,4'-bpy)]n, respectively. Photoluminescence (PL) properties of [Sm(dbm)3(4,4'-bpy)]n and [Eu(dbm)3(4,4'-bpy)]n are discussed in the solid-state and PMMA hybrid film (w/w 6%). By employing theoretical modelling in conjunction with the experimental PL data and crystal structure and an energy transfer (ET) mechanism for the sensitized PL of [Eu(dbm)3(4,4'-bpy)]n is proposed and discussed in detail. Finally, the role of each ligand in sensitized PL of [Eu(dbm)3(4,4'-bpy)]n is calculated and discussed by the chemical partitions of the radiative decay.Graphical abstract.

Boron cluster anions [BnHn]2– (n = 10, 12) in design of polynuclear silver(I) and copper(II) complexes

The role of boron cluster anions [BnHn]2– (n = 10, 12) in the stabilization of polynuclear compounds was shown. Tetranuclear silver(I) complex [Ag4(bipy)4[B12H12]2] (1) (bipy is 2,2ʹ-bipiridyl) and hexanuclear copper(II) complex [[CuII2(bipy)4(μ–CO3)]2[(CuII2(bipy)2(μ–OH)2]][Ag[B10H10]2]2∙5DMF (2∙5DMF) stabilized by first complex trianion [Ag[B10H10]2]3– were isolated and their structures were determined by single crystal X-ray diffraction. Based on the data of physicochemical methods of analysis (IR, Raman spectroscopy, as well as X-ray diffraction data for the polymer complex {[Ag(CH3CN)3][Ag[B10H10]]}n (3) possible mechanisms for the formation of polynuclear complexes were proposed.

Application of Fe(II)/peroxymonosulfate for efficient alkali lignin wastewater treatment: Insight into the synergistic interactions between redox reactions and coagulation

In this work, Fe(II)/Peroxymonosulfate (PMS) treatment with dual functionality of pre-oxidation and coagulation was applied to enhance the removal of alkali lignin in water. The removal efficiency of alkali lignin (2 g/L) could reach ∼ 99% at an optimal dosage of [Fe(II)] = 2.4 mM and [PMS] = 7.8 mM, which was efficiently superior than that using ferric and polymeric coagulant individually. Pre-oxidation, involving hydroxyl radical (•OH) and sulfate radical (SO4•−), has been demonstrated to play a crucial role in both oxidative degradation (∼30%) and reducing the molecular weight and hydrophilicity of lignin. Meanwhile, the formation of polynuclear Fe-hydroxide complexes was also fostered, which in turn greatly contribute to the removal of lignin through an enhanced coagulation mechanism. The reductive units present in alkali lignin was demonstrated to initiate a dynamic transition between Fe(III) and Fe(II) by donating electrons. This redox activity is anticipated to continuously promote the formation of electro-neutral and loose flocs, thereby resulting in an enhanced coagulation performance. Furthermore, ultrafiltration (UF) was also demonstrated as a viable liquid/solid separation method following Fe(II)/PMS treatment, effectively promoting membrane flux recovery rate to ∼90%. This highlights the remarkable potential of this method when combined with other treatment processes. This study aims to offer a complementary strategy for remediating alkali lignin wastewater while advancing the fundamental understanding of redox-reaction enhanced in-situ coagulation in water treatment applications.

Hexanuclear and octanuclear metal complexes of octadecaazamacrocycle based on diaminocyclohexane and pyridine units

An extended macrocyclic amine L derived from the [6+6] condensation of trans-1,2-diaminocyclohexane and 2,6-diformylpyridine contains 18 nitrogen atoms in its main cycle. All of these atoms can be engaged in the formation of polynuclear complexes with transition metal ions and the macrocycle L is able to bind six Cu(II), Ni(II) or Zn(II) ions within its interior. X-ray crystal structures of these complexes indicate variable coordination numbers of metal ions as well as various conformations adopted by the macrocyclic ligand. In the hexanuclear Cu(II) complex with coordinated nitrate anions Cu(II) ions are hexacoordinate and exhibit highly distorted octahedral geometry, while in analogous complexes with coordinated sulphate anions Cu(II) ions are pentacoordinate of distorted square pyramid geometry. Both complexes are relatively symmetric having (approximate) S6 axis and adopt a circular doughnut shape with a central void not occupied by metal ions. The NMR spectrum of the zinc(II) derivative also reflects the symmetrical coordination. In contrast, the macrocycle L is squeezed and less symmetric in the octanuclear chloride derivative where two additional Cu(II) ions are linked to a hexanuclear macrocyclic unit via chloride bridges. The macrocycle is also squeezed in the hexanuclear Ni(II) complex containing metal ions of approximate octahedral geometry. In all three Cu(II) complexes the macrocycle provides N3 donor set for each metal ion, while in the Ni(II) complex alternating N3 and N4 environments of the metal ions are observed.

Bromoantimonates(III) vs. Bromobismuthates(III): Differences in the Tendency for the Formation of Polynuclear Complexes

Pyridine-based Sb(III) bromide complexes with doubly charged cations, (PyC3)3[Sb2Br9]2 (I), (PyC4)[Sb2Br8] (II), (PyC5)2[α-Sb4Br16] (III), (PyC6)2[Sb2Br10] (IV), (4-MePyC2)2[Sb2Br10] (V), (4‑MePyC3)2[α-Sb4Br16] (VI), and (4-MePyC5)2[α-Sb4Br16] (VII), were synthesized and characterized by X-ray diffraction (CCDC nos. 2204718–2204724). The structures of these compounds were compared with the structures of related bromobismuthates(III).

Bromoantimonates(III) vs. Bromobismuthates(III): Differences in the Tendency for the Formation of Polynuclear Complexes

Bromoantimonates(III) vs. Bromobismuthates(III): Differences in the Tendency for the Formation of Polynuclear Complexes

Comparative Study of Macrocyclic and Acyclic Picolinate Derivatives for Chelation of Copper Cations

AbstractIn this work we presented a synthesis and investigation of relative acyclic and macrocyclic polyamines with picolinate pendant arms as potential chelators for copper radiopharmaceuticals. It has been shown that linear chelators lacking bisamide moiety are much more basic and form complexes with higher stability constants compared to macrocyclic ones. Both types of ligands possess many donor sites due to picolinate groups enabling formation of polynuclear complexes in the solution and solid state. According to crystal structures metal cations coordinates with studied ligands through the binding with aminogroups and picolinates donor atoms, while terminal aminogroups of acyclic ligands do not take part in the complex formation. Tripicolinate azacrown ligand coordinates cations outside the macrocyclic cavity in non‐equivalent positions. However this out‐cage location as well as a moderate logK value do not induce fast release of cation from this complex in the challenging medium of serum proteins.

Iron Stearate Structures: An Original Tool for Nanoparticles Design.

Iron carboxylates are widely used as iron precursors in the thermal decomposition process or considered as in situ formed intermediate precursors. Their molecular and three-dimensional (3D)-structural nature has been shown to affect the shape, size, and composition of the resulting iron oxide nanoparticles (NPs). Among carboxylate precursors, stearates are particularly attractive because of their higher stability to aging and hydration and they are used as additives in many applications. Despite the huge interest of iron stearates, very few studies aimed up to now at deciphering their full metal-ligand structures and the mechanisms allowing us to achieve in a controlled manner the bottom-up NP formation. In this work, we have thus investigated the molecular structure and composition of two iron stearate precursors, synthesized by introducing either two (FeSt2) or three (FeSt3) stearate (St) chains. Interestingly, both iron stearates consist of lamellar structures with planes of iron polynuclear complexes (polycations) separated with stearate chains in all-trans conformation. The iron content in polycations was found very different between both iron stearates. Their detailed characterizations indicate that FeSt2 is mainly composed of [Fe3-(μ3-O)St6·xH2O]Cl, with no (or few) free stearate, whereas FeSt3 is a mixture of mainly [Fe7(μ3-O(H))6(μ2-OH)xSt12-2x]St with some [Fe3(μ3-O)St6·xH2O]St and free stearic acid. The formation of bigger polynuclear complexes with FeSt3 was related to higher hydrolysis and condensation rates within the iron(III) chloride solution compared to the iron(II) chloride solution. These data suggested a nucleation mechanism based on the condensation of polycation radicals generated by the catalytic departure of two stearate chains from an iron polycation-based molecule.

PRECIPITATION OF METAL HYDROXIDES FROM AQUEOUS SOLUTIONS AS A RESULT OF SPONTANEOUS CONDENSATION OF POLYNUCLEAR HYDROXOCOMPLEXES

Background. Generally, it is assumed that the formation of a solid phase (precipitate) happens when the activities of the involved ions would exceed those defined by the thermodynamic solubility product. However, in case of precipitation of metal hydroxides, this is a simplification, and the real pattern is more complicated, since metal ions form strong mono- and polynuclear hydroxocomplexes in a solution. Formation of such complexes, especially those with zero charge, should result in the deviation from the common solubility product rule. Objective. The aim of this paper is to develop a precipitation model, which takes into account the effect of the formation of the hydroxocomplexes on the solubility of a metal hydroxide. Eventually, this solubility includes the sum of the concentrations of metal ions, and all neutral, positively and negatively charged hydroxocomplexes involved in all equilibria in aqueous solution. Methods. We assume that formation of the solid precipitate is the result of spontaneous condensation of polynuclear neutral hydroxocomplexes when their concentrations in a solution exceed a certain critical value. These critical concentrations can be estimated from the consideration of all equilibria with the assumption that the equilibrium constants for the formation of neutral polynuclear complexes when their nuclearity increases by one are approximately equal and do not significantly depend on the size of the particle. Results. Using this approach, we developed the model, which predicts spontaneous condensation with formation of a precipitate. Also, we calculated the dependencies of pH-logCM for precipitation of various divalent cation hydroxides. It was shown that there exist minimal concentrations, below which no precipitates are formed at any pH value. Conclusions. Such approach also explains the nature of linear correlations between logarithms of solubility products and stability constants of neutral complexes described in literature. These results are important for the development and optimization of industrial wastewater treatment processes.

Optical Fingerprints of Polynuclear Complexes in Lead Halide Perovskite Precursor Solutions.

Solvent-solute interactions in precursor solutions of lead halide perovskites (LHPs) critically impact the quality of solution-processed materials, as they lead to the formation of a variety of poly-iodoplumbates that act as building blocks for LHPs. The formation of [PbI2+n]n- complexes is often expected in diluted solutions, while coordination occurring at high concentrations is not yet well understood. In a combined ab initio and experimental work, we demonstrate that the optical spectra of the quasi-one-dimensional iodoplumbate complexes PbI2(DMSO)4, Pb2I4(DMSO)6, and Pb3I6(DMSO)8 formed in dimethyl sulfoxide solutions are compatible with the spectral fingerprints measured at high lead iodide concentrations. This finding suggests that the interpretation of optical spectra of LHP precursor solutions should account for the formation of polynuclear lead halide complexes.

A two-dimensional metallosupramolecular framework design based on coordination crosslinking of helical oligoamide nanorods

Coordination crosslinking of oligoamide nanorods yields two dimensional metallosupramolecular framework.

ПОЛИЯДЕРНЫЕ КОМПЛЕКСЫ ПЛАТИНЫ (II) И ПАЛЛАДИЯ (II) С БИОЛОГИЧЕСКИ АКТИВНЫМИ ЛИГАНДАМИ

The interaction of platinum (II) and palladium (II) salts under certain conditions with such ligands as cysteamine- (mercamine) HSCH2CH2NH2 and 2-mercaptoethanol - HSCH2CH2OH results in the formation of polynuclear complexes: [Pt6(SCH2CH2NH2)8]Cl4, [Pd6)8]Cl4·5H2O, [Pd6(SCH2CH2OH)12]Cl4·3H2O and [Pt6(NH2CH2CH2S)8]Cl4·3H2O. Based on a comparison of the IR and X-ray spectra of the synthesized complexes and ligands, as well as the X-ray results, it was found that in palladium (II) complex sulfur atoms of 2-mercaptoethanol occupy a bridging position with a displaced coordination of ligands. In the platinum (II) complexes, the bidentate coordination of ligands with sulfur and nitrogen atoms is realized. The synthesized complexes in spite of having the same compositions but differ greatly in structure.

Mechanism of Goethite Precipitation on Magnetite and Maghemite Nanoparticles Studied by Surface Complexation/Precipitation Modeling

Precipitation of goethite on magnetic nanoparticles (MNPs) has been proposed as an effective means to separate goethite from calcium sulfate in the iron removal process of zinc hydrometallurgy, which allows reuse of the hazardous residues. This study focuses on investigating the underlying mechanisms of goethite precipitation on magnetite and maghemite MNPs, providing insights on Fe(III)aq adsorption and nucleation of goethite on MNPs. A predictive surface complexation/precipitation model of the system was developed based on the results from two different types of experiments: the potentiometric titration of MNPs to calculate proton binding constants ( Ka) of discrete MNP surface functional groups and the corresponding site concentrations; and adsorption of Fe(III)aq onto MNP surfaces to determine metal binding constants ( Kf). The composition of the surface complexes on MNPs was determined by time-of-flight secondary ion mass spectrometry. The results indicated the formation of polynuclear surface complexes. The content of polynuclear surface complexes was found to be significantly higher on maghemite MNPs than on magnetite MNPs. This trend is consistent with our experimental results of a greater goethite precipitation on maghemite than on magnetite. Overall, the formation of Fe(III) polynuclear surface complexes correlates directly to the nucleation and precipitation of goethite on the surfaces of both types of MNPs.

Expressions for Enthalpies of Concurrent Polynuclear Complex Formation Reactions in Two-Phase Aqueous Systems

The paper presents a new thermodynamic approach to studying polynuclear complex formation reactions in multicomponent two-phase systems, solid phase plus saturated aqueous solution, under real conditions. The quintessence of this developed approach consists in the thermodynamic analysis of concurrent reactions on the basis of the introduced notion of a generalized reaction equation. The formation of complex polynuclear species is characterized by certain peculiarities in the behavior of studied two-phase heterogeneous systems. The formation of polynuclear complexes of the metal ion with a complexing agent leads to expressions for the enthalpy ∆H and heat capacity ∆Cp as certain concentration functions, which are normative multipliers, referring these thermochemical quantities to one mole of the metal ion. It is shown that one of these functions, Φ, characterizes the degree of formation of polynuclear complexes. In the case of concurrent formation of mono- and polynuclear complexes, the derived expressions are useful in distinguishing separate contributions of individual complex formation reactions to the ∆H and ∆Cp of the overall process.

Molecular Deformation, Charge Flow, and Spongelike Behavior in Anion–π {[M(CN)4]2−;[HAT(CN)6]}∞ (M=Ni, Pd, Pt) Supramolecular Stacks

AbstractInvited for the cover of this issue is the group of Robert Podgajny at Jagiellonian University. The image depicts the concept of the anion–π interactions between multisite anion receptors and cyanido‐complexes, in respect to the possible control of the formation of future polynuclear complexes. Read the full text of the article at 10.1002/chem.201802933.

Irreversibility of sorption of cobalt to goethite (α-FeOOH) and disparities in dissolution of aged synthetic Co-goethite

The behaviours of incorporated cobalt in goethite during desorption and dissolution is fundamental to our understanding of the best extraction techniques for maximum cobalt recovery. Here, Surface Complexation Modelling, desorption and dissolution of aged synthetic Co-goethite was investigated to demonstrate the transition between surface complexion, surface precipitation and structural incorporation in goethite with different amounts of cobalt found in oxic laterites. Surface Complexation Modelling of cobalt sorption on goethite reveals existence of both surface complexation and polynuclear complexes. Surface complexation starts at a low surface loading (≥0.004wt% Co) to form Fe(OH)2Co, and as uptake (0.03 to 0.2wt% Co) increases, two surfaces complexes, Fe(OH)2Co and (>FeOH)2Co, are formed. Additional increases in concentration (0.45 to 1.7wt%) leads to the formation of poly-nuclear complexes (e.g., (>FeOH)3Co2) co-existing with other complexes. Structural incorporation would be manifest if Co sorption was irreversible. We find that after four weeks of sorption about 55 to 70% of cobalt is reversible and the retention capacity increases with decreasing concentration. Samples formed at low loading show strong evidence of structural incorporation relative to those formed at high loading. In particular, the sample with 0.004wt% Co needs a 20% dissolution of goethite before 64% of its incorporated cobalt is released while samples with 1.74wt% Co requires a dissolution of 7.8% of goethite before liberating 66% of adsorbed cobalt. All the grades of Co-goethite dissolves incongruently with iron, however, the mode of formation should be considered when determining the leaching conditions for maximum recovery. In addition, the mixed Co-goethite grades show strong deviation from congruent dissolution and have a negative effect on the amount of cobalt and iron released during extraction.

Synthesis of pyridine-alkoxide ligands for formation of polynuclear complexes

A series of novel polydentate N,O-donor ligands strongly favour formation of polynuclear complexes.

Tailoring the local environment around metal ions: a solution chemical and structural study of some multidentate tripodal ligands.

Manganese(ii), copper(ii) and zinc(ii) complexes of four polydentate tripodal ligands (tachpyr (N,N',N''-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane), trenpyr (tris[2-(2-pyridylmethyl)aminoethyl]amine, tach3pyr (N,N',N''-tris(3-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane) and tren3pyr (tris[2-(2-pyridylmethyl)aminoethyl]amine)) were characterized in both solution and solid states. A combined evaluation of potentiometric, UV-VIS, NMR and EPR data allowed the conclusion of both thermodynamic and structural information about the complexes formed in solution. The four tailored polydentate tripodal ligands studied here exhibit a high thermodynamic stability, and a variety of coordination environments/geometries for the studied transition metal ions. Our data indicate that tachpyr is a more efficient zinc(ii) chelator and a similar copper(ii) chelator compared to trenpyr. Considering the higher number of N-donors and conformational flexibility of trenpyr, as well as the energy demanding switch to the triaxial conformation required for metal ion binding of tachpyr, the above observation is surprising and is very likely due to the encapsulating effect of the more rigid tachpyr skeleton. This relative binding preference of tachpyr for zinc(ii) may be related to the observation that zinc(ii) is one of the principal metals targeted by tachpyr in cells. In contrast, trenpyr is a considerably more efficient manganese(ii) chelator, since it acts as a heptadentate ligand in the aqueous Mn(trenpyr) complex. The crystal structures of copper(ii) and zinc(ii) complexes of tachpyr indicated important differences in the ligand conformation, induced by the position of counter ions, as compared to earlier reports. The closely related new ligands, tach3pyr and tren3pyr, have been designed to form oligonuclear complexes. Indeed, we obtained a three dimensional polymer with a copper(ii)/tren3pyr ratio of 11/6. Within this metal-organic framework, three distinctly different copper geometries can be identified: square pyramidal, trigonal bipyramidal and tetrahedral. Two square pyramidal and four trigonal bipyramidal copper centres create a hexanuclear subunit with a large inside cavity. These moieties are linked by tetrahedral copper(ii) centres, constructing the three-dimensional polymer structure. The formation of such polynuclear complexes was not detected in solution. Both tach3pyr and tren3pyr form only mononuclear complexes with square pyramidal and trigonal bipyramidal geometries, respectively.