Formation Of Binuclear Complexes Research Articles

Phytochelatins Bind Zn(II) with Micro- to Picomolar Affinities without the Formation of Binuclear Complexes, Exhibiting Zinc Buffering and Muffling Rather than Storing Functions.

Phytochelatins (PCs) are poly-Cys peptides containing a repeating γ-Glu-Cys motif synthesized in plants, algae, certain fungi, and worms by PC synthase from reduced glutathione. It has been shown that an excess of toxic metal ions induces their biosynthesis and that they are responsible for the detoxification process. Little is known about their participation in essential metal binding under nontoxic, basal conditions under which PC synthase is active. This study presents spectroscopic and thermodynamic interactions with the PC2-PC5 series, mainly focusing on the relations between Zn(II) complex stability and cellular Zn(II) availability. The investigations employed mass spectrometry, UV-vis spectroscopy, potentiometry, competition assays with zinc probes, and isothermal titration calorimetry (ITC). All peptides form ZnL complexes, while ZnL2 was found only for PC2, containing two to four sulfur donors in the coordination sphere. Binuclear species typical of Cd(II)-PC complexes are not formed in the case of Zn(II). Results demonstrate that the affinity for Zn(II) increases linearly from PC2 to PC4, ranging from micro- to low-picomolar. Further elongation does not significantly increase the stability. Stability elevation is driven mainly by entropic factors related to the chelate effect and conformational restriction rather than enthalpic factors related to the increasing number of sulfur donors. The affinity of the investigated PCs falls within the range of exchangeable Zn(II) concentrations (hundreds of pM) observed in plants, supporting for the first time a role of PCs both in buffering and in muffling cytosolic Zn(II) concentrations under normal conditions, not exposed to zinc excess, where short PCs have been identified in numerous studies. Furthermore, we found that Cd(II)-PC complexes demonstrate significantly higher metal capacities due to the formation of polynuclear species, which are lacking for Zn(II), supporting the role of PCs in Cd(II) storage (detoxification) and Zn(II) buffering and muffling. Our results on phytochelatins' coordination chemistry and thermodynamics are important for zinc biology and understanding the molecular basis of cadmium toxicity, leaving room for future studies.

Luminescent polymorphism of mononuclear Cu(I) complexes with pyrazolo[1,5-a][1,10]phenanthrolines

Six copper(I) complex compounds with new bidentate phenanthroline-like ligands, pyrazolo[1,5-a][1,10]phenanthroline-3-carbonitrile (L1) and 1-(pyrazolo[1,5-a][1,10]phenanthrolin-3-yl)ethan-1-one (L2), have been synthesized. A reaction of copper(I) iodide with L1 or L2 leads to the formation of binuclear complexes [Cu2(Ln)2I2]·Solv, which have rhomboid binuclear fragment {Cu2I2} according to the single crystal X-ray diffraction. These complexes are gradually oxidized on air and do not show any photoluminescence. At the same time, reaction between the ligand (L1 or L2), triphenylphosphine and copper(I) iodide produces mononuclear coordination compounds [CuLn(PPh3)I]. It has been discovered that the [CuL1(PPh3)I] complex can be isolated as two polymorph modifications. The mononuclear complexes demonstrate microsecond red luminescence: λmax = 700 nm for [CuL2(PPh3)I], λmax = 640 nm for the first polymorph of [CuL1(PPh3)I] (2a) and λmax = 700 nm for the second polymorph (2b). Also for [CuL1(PPh3)I] polymorphs excitation-dependent emission has been detected at 77 K.

Synthesis, Spectral Characterization, Antioxidant, Antimicrobial and Anticancer Activities of New Binuclear Copper and Rhodium Complexes

AbstractTwo novel binuclear complexes of Cu (II) and Rh (III) with Bis [4‐hydroxy‐6‐methyl‐3‐{(1E)‐N‐[2‐(ethylamino) ethyl] ethanimidoyl}‐2H‐pyran‐2‐one] (L) were prepared and characterized by elemental analysis, electrospray ionization‐mass spectrometry (ESI‐MS), conductivity, nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT‐IR), ultraviolet‐visible spectrophotometry, fluorescence, thermogravimetric analysis ( TGA), scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX) and cyclic voltammetry (CV). The spectral data indicate that the ligand binds the metal ions via the oxygen atom of the phenolic group, the nitrogen atoms of the azomethine and NH groups. These characterizations suggested the formation of binuclear complexes with octahedral geometry around each metal ion. For a better understanding of the response of complexes to biological activities, the stability constants, potential zeta and size of the complexes were determined. From the results, we can deduce that the complexes have more significant activities than their corresponding ligand. Moderate antioxidant activity recorded with both complexes, superior antibacterial and antifungal activities with Rh (III) complex with MIC value of 0.3125 mg. mL−1 and interesting anticancer activity towards Hep2 cells (IC50=13.77 μM) with Rh (III) and towards Hep2 (IC50=28.35 μM) and K562 cells (IC50=26.34 μM) with Cu (II) complex.

COMPLEXATION OF CIS-Pd(NH3)2Cl2 AND Pd(en)Cl2 WITH 1-AMINOPROPYLIDENE­DIPHOSPHONIC ACID

The complexation of cis-Pd(NH3)2Cl2 and Pd(en)Cl2 (en – ethylenediamine) with 1-aminopropylidene-1,1-diphosphonic acid (APrDP, H4L) in solutions with extracellular concentration of chloride ions (0.15 mol/L) at the rations Pd(II):APrDP=1:1, 1:2 and 2:1 has been stu­di­ed by pH-potentiometry, electron and NMR spectroscopy.
 It has been found that upon interaction in the system cis-Pd(NH3)2Cl2:AprDP=1:1, complexes of the equimolar composition [PdHL(NH3)Cl]2- (lgβ=38.84(4)), [PdHL(NH3)2]- (lgβ=43.14(2)) and [PdL(NH3)2]2- (lgβ=34.91(2)) are formed depending on pH, in which the APrDP molecule is coordinated in a bidentate fashion to the cent­ral ion by the nitrogen atom of the amine group and oxygen atom of the phosphonic group. In the case of twofold excess of ligand, bisligand complexes [PdH4L2]2- (lgβ=59.64(9)), [PdH3L2]3- (lgβ=57.39(19), [PdH2L2]4- (lgβ=52.37(17), [PdHL2]5- (lgβ=44.71(9)) [PdL2]6- (lgβ=36.57(6)) are formed, in which two APrDP molecules are coordinated in a bidentated fashion. At pH>6, complexes [PdHL2(NH3)]5- (lgβ=48.57(6)) and [PdL2(NH3)2]6- (lgβ=42.76(8)) are formed, in which the coordinated phosphonic groups of APrDP are sequentially replaced upon coordination by NH3. molecules.
 In the systems Pd(en)Cl2:APrDP=1:1 and 1:2, complexes only of equimolar composition: [Pd(en)(H2L)] (lgβ=28.88(9)), [Pd(en)(HL)]- (lgβ=24.67(8)) and [Pd(en)L]2- (lgβ=16.84(9)) are formed, whose coordination sphere contains the nitrogen atom of the amine group and oxygen atom of the phosphonic group of APrDP and two nitrogen atoms of the amine groups of an ethylenediamine.
 At the ratio Pd(II):APrDP=2:1, the formation of binuclear complexes {[Pd(NH3)2]2L} (lgβ=63.58(22)) and {[Pd(en)]2L} (lgβ= 25.18(4)), in which two palladium atoms have a different coordination environment. The coordination sphere of one of the palladium contains a nitrogen atom of the amine group and an oxygen atom of the phospho­nic group of APrDP, and two NH3 molecules or two amine groups of ethylenediamine. The other palladium coordinates two oxygen atoms of phoshonic groups of APrDP and two NH3 molecules or two amine groups of ethylenediamine.

The Solution Behavior of Dopamine in the Presence of Mono and Divalent Cations: A Thermodynamic Investigation in Different Experimental Conditions.

The interactions of dopamine [2-(3,4-Dihydroxyphenyl)ethylamine, (Dop−)] with methylmercury(II) (CH3Hg+), magnesium(II), calcium(II), and tin(II) were studied in NaCl(aq) at different ionic strengths and temperatures. Different speciation models were obtained, mainly characterized by mononuclear species. Only for Sn2+ we observed the formation of binuclear complexes (M2L2 and M2LOH (charge omitted for simplicity); M = Sn2+, L = Dop−). For CH3Hg+, the speciation model reported the ternary MLCl (M = CH3Hg+) complex. The dependence on the ionic strength of complex formation constants was modeled by using both an extended Debye–Hückel equation that included the Van’t Hoff term for the calculation of enthalpy change values of the formation and the Specific Ion Interaction Theory (SIT). The results highlighted that, in general, the entropy is the driving force of the process. The sequestering ability of dopamine towards the investigated cations was evaluated using the calculation of pL0.5 parameter. The sequestering ability trend resulted to be: Sn2+ > CH3Hg+ > Ca2+ > Mg2+. For example, at I = 0.15 mol dm−3, T = 298.15 K and pH = 7.4, pL0.5 = 3.46, 2.63, 1.15, and 2.27 for Sn2+, CH3Hg+, Ca2+ and Mg2+ (pH = 9.5 for Mg2+), respectively. For the Ca2+/Dop− system, the precipitates collected at the end of the potentiometric titrations were analyzed by thermogravimetry (TGA). The thermogravimetric calculations highlighted the formation of solid with stoichiometry dependent on the different metal:ligand ratios and concentrations of the starting solutions.

Versatile Reactivity of MnII Complexes in Reactions with N-Donor Heterocycles: Metamorphosis of Labile Homometallic Pivalates vs. Assembling of Endurable Heterometallic Acetates.

Reaction of 2,2′-bipyridine (2,2′-bipy) or 1,10-phenantroline (phen) with [Mn(Piv)2(EtOH)]n led to the formation of binuclear complexes [Mn2(Piv)4L2] (L = 2,2′-bipy (1), phen (2); Piv− is the anion of pivalic acid). Oxidation of 1 or 2 by air oxygen resulted in the formation of tetranuclear MnII/III complexes [Mn4O2(Piv)6L2] (L = 2,2′-bipy (3), phen (4)). The hexanuclear complex [Mn6(OH)2(Piv)10(pym)4] (5) was formed in the reaction of [Mn(Piv)2(EtOH)]n with pyrimidine (pym), while oxidation of 5 produced the coordination polymer [Mn6O2(Piv)10(pym)2]n (6). Use of pyrazine (pz) instead of pyrimidine led to the 2D-coordination polymer [Mn4(OH)(Piv)7(µ2-pz)2]n (7). Interaction of [Mn(Piv)2(EtOH)]n with FeCl3 resulted in the formation of the hexanuclear complex [MnII4FeIII2O2(Piv)10(MeCN)2(HPiv)2] (8). The reactions of [MnFe2O(OAc)6(H2O)3] with 4,4′-bipyridine (4,4′-bipy) or trans-1,2-(4-pyridyl)ethylene (bpe) led to the formation of 1D-polymers [MnFe2O(OAc)6L2]n·2nDMF, where L = 4,4′-bipy (9·2DMF), bpe (10·2DMF) and [MnFe2O(OAc)6(bpe)(DMF)]n·3.5nDMF (11·3.5DMF). All complexes were characterized by single-crystal X-ray diffraction. Desolvation of 11·3.5DMF led to a collapse of the porous crystal lattice that was confirmed by PXRD and N2 sorption measurements, while alcohol adsorption led to porous structure restoration. Weak antiferromagnetic exchange was found in the case of binuclear MnII complexes (JMn-Mn = −1.03 cm−1 for 1 and 2). According to magnetic data analysis (JMn-Mn = −(2.69 ÷ 0.42) cm−1) and DFT calculations (JMn-Mn = −(6.9 ÷ 0.9) cm−1) weak antiferromagnetic coupling between MnII ions also occurred in the tetranuclear {Mn4(OH)(Piv)7} unit of the 2D polymer 7. In contrast, strong antiferromagnetic coupling was found in oxo-bridged trinuclear fragment {MnFe2O(OAc)6} in 11·3.5DMF (JFe-Fe = −57.8 cm−1, JFe-Mn = −20.12 cm−1).

Ethylene polymerization by binuclear chromium complex with tetrakis(pyrazolyl-methyl)benzene ligand

The reaction of one equivalent of 1,2,4,5-tetrakis(pyrazolyl-methyl)benzene ligand (L) with two equivalents of Cr(THF)3Cl3 in tetrahydrofuran has produced a binuclear neutral complex of general formula [Cr2L(THF)2Cl6] (1). It was characterized by mass spectrometry, Fourier-transformed infrared, X-ray photoelectron spectroscopy, and magnetic susceptibility. Theoretical calculations supported the formation of binuclear complex (1) with each hexacoordinate metal center. This complex was active in ethylene polymerization employing methylaluminoxane as cocatalyst, with moderate activities (5.7–20.8 kg polymer/(mol precat.) (bar) (h)). The reaction parameters such as temperature, monomer pressure, and Al/Cr ratio were studied. An increase of reaction temperature produced a decreasing of catalytic activity. However, an increase in the monomer pressure did not produce a significant increase in catalytic activity. The Al/Cr ratios used to activate this complex are smaller than those reported for the tris(pyrazolyl)borate chromium complex. This system produced high-density polyethylenes with wide molecular weight, Mw, distributions between 42,280 and 74,346 and polydispersity index from 2.3 to 6.6.

An X-ray Spectral Study of the Electronic Structure of Non-Innocent Mono- and Binuclear Platinum Complexes with N-Phenyl-o-Benzosemiquinonediimine

The electronic structure of mono- and binuclear platinum complexes with N-phenyl-o benzosemiquinondiimine ligands was studied using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and the density functional theory. The oxidation state of the central platinum ion corresponds to that of Pt(II). Upon the transition from the trans-complex 1 to the cis-complex 2 and to the binuclear complex 3, the electron density on platinum and nitrogen atoms decreases thus testifying the participation of platinum and nitrogen atoms in the oxidation processes and in the formation of binuclear complex 3.

Influence of Pb(II) in the sorption of As(V) by a Ca-polygalacturonate network, a root mucilage model

ABSTRACT In this study, the role of lead [Pb(II)] in the sorption of arsenate [As(V)] by a Ca-polygalacturonate network (CaPGA), i.e. a model of root mucilage, was determined in acidic conditions (pH 4.5) commonly occurring at the soil–root interface. Sorption isotherms and kinetics showed that CaPGA was able to sorb As(V) (~0.89 mmol g−1 CaPGA) only in the presence of Pb(II). The concurrent sorption of Pb(II) by CaPGA (~2.30 mmol g−1), and the FT-IR spectra, suggested the formation of binuclear complexes involving one As(V) anion and two Pb(II) cations, which were in turn involved in bridging complexes with two carboxylate groups of CaPGA. The As(V) sorption by the Pb(II)-PGA system followed a pseudo-second-order kinetic model, while the sorption isotherms data fitted the Langmuir model better than the Freundlich one. The release of As(V) and Pb(II) from the As(V)-Pb(II)-PGA system, following treatment with environmentally relevant organic acids, i.e. citric and malic acids (0.0–24 mM concentration range), showed that As(V) was strongly retained and that both organic acids were able to mobilize similar As(V) and Pb(II) pools. Plant growth experiments showed that CaPGA was effective at reducing the As(V) phytotoxicity toward triticale plants (×Triticosecale Wittm.) in the presence of Pb(II), highlighting the environmental relevance of the interactions reported in this study.

Application of periodic density functional theory calculations for exploring copper(II) coordination effects on the mesophase behavior of p-n-alkoxybenzoic acids

Copper(II) benzoates ([Formula: see text]OBA-Cu) with various terminal alkoxy carbon numbers, [Formula: see text]–12, were prepared from [Formula: see text]-[Formula: see text]-alkoxy benzoic acids (nOBAs). Fourier transform infrared (IR) experiments suggested that dimerization through copper(II) chelating bidentate coordination created [Formula: see text]OBA-Cu with a linear rod-like structure, similar to the hydrogen-bonded structure of its parent [Formula: see text]OBA. However, the coordination structure of [Formula: see text]OBA-Cu changed during heating. Periodic density functional theory calculations provided valuable insight into the possible arrangement of the parent and copper(II)-coordinated [Formula: see text]OBAs. The formation of binuclear complexes between two adjacent [Formula: see text]OBA-Cu dimers forced [Formula: see text]OBA-Cu to arrange itself in a layer and exhibit smectic A mesophase. Accordingly, four types of IR stretching absorption of benzoyl carbonyl were observed in binuclear [Formula: see text]OBA-Cu complexes, replacing the original symmetric and asymmetric vibrations of benzoyl carboxylate in chelating bidentate coordination. The lateral association by [Formula: see text]–[Formula: see text] interactions between adjacent parent [Formula: see text]OBA dimers preferred a progressive smectic C arrangement. The origin of the odd–even effect was understood from the consideration of the molecular structure.

Design of amino-functionalized chelated macroporous copolymer [poly(GMA-EDGMA)] for the sorption of Cu (II) ions

Polymer-based, highly porous nanocomposites with functionalized ligands attached to the core structure are extremely efficient in the detection, removal and recovery of metals through the process of sorption. Quantumchemical models could be helpful for sorption process analyses. The sorption of Cu(II) ions by amino-functionalized chelating macroporous copolymers poly(GMA-co-EGDMA)-amine and sorption selectivity of the subject copolymers, ethylenediamine (en), diethylenetriamine (dien) and triethylenetetramine (trien), were successfully modelled by quantum chemical calculations. Considering the crystal structures from CSD and experimental conditions during the formation of metal complexes, the most frequent mononuclear complexes are those with the tetradentate teta ligand, while binuclear complexes are formed when the metal ion is in large excess. Although the en-copolymer was the most effective functionalized one, higher maximum sorption capacities (Qmax) were observed for the dien- and trien-copolymers, due to their abilities to form binuclear complexes. The enthalpy term has the greatest contribution to the total Gibbs energy change of reaction for the formation of mononuclear Cu(II) complexes (?Gaq), while the solvation energy of the reaction has the greatest contribution in the formation of binuclear complexes. The results of the study indicate that small amines with the ability to form binuclear complex are the best choice for functionalization of the considered copolymer.

Heteroleptic complexes of silver(I) featuring 4′-hydroxy- and 4′-(2-furyl)-2, 2′:6′, 2″-terpyridine: An easy route for synthesis of silver nanoparticles

New coordination complexes of silver(I) containing triphenylphosphine and 4′-hydroxy-2,2′:6′,2″-terpyridine (tpyOH) or 4′-(2-furyl)-2,2′:6′,2″-terpyridine (ftpy) have been synthesized to afford the new compounds [Ag(tpyOH)(PPh3)](NO3) (1) and [Ag(ftpy)(PPh3)](NO3) (2). In addition, the reaction of silver(I) nitrate with ftpy in the presence of excess of 4,4′-bipyridine (bpy) and NH4PF6 led to the formation of binuclear complex [Ag2(ftpy)2(μ-bpy)](PF6)2 (3). The products have been characterized by elemental analysis, IR, UV–Vis, NMR (1H, 31P) spectroscopy and single crystal X-ray diffraction in the case of 3. The 31P NMR data reveal that the interaction of PPh3 with silver(I) is maintained in solution in 1–2. The crystal structure of 3 shows that each Ag+ ion is coordinated by three N-atoms of ftpy and a nitrogen from the bridging ligand of bpy in a slightly distorted square planar geometry. There are some strong noncovalent interactions of hydrogen bonding and Ag-η2-furyl in the crystal structure, connecting molecules to form a supramolecular network. The thermal decomposition of 1–3 has also been investigated. The thermal stabilities of all complexes, as determined by thermogravimetric analysis (TGA), are almost the same and they are thermally stable up to 220 °C. The complex 3 was used for the preparation of Ag nanoparticles by simple calcination method at two different temperatures of 400 and 600 °C resulting in the formation of silver nanoparticles, crystalline in nature with the size of 66 and 52 nm, respectively, using Scherrer’s equation. The nano-sized silver particles have also been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDX).

Thermolabile Organotitanium Monoalkyl Phosphates: Synthesis, Structures, and Utility as Epoxidation Catalysts and Single-Source Precursors for TiP2O7.

The reaction of [Cp*TiCl3] (Cp* = C5Me5) with monoalkyl phosphates (RO)PO3H2 (R = Me, Et, and iPr) in tetrahydrofuran (THF) at 25 °C leads to the formation of binuclear complexes [Cp*2Ti2(μ-O2P(OH)OR)2(μ-O2P(O)OR)2] [R = Me (1), Et (2), and iPr (3)]. On the other hand, the reaction of ( tBuO)2PO2K with [Cp*TiCl3] in acetonitrile or THF results in isolation of either the dinuclear [Cp*2Ti2(μ-O2P(OH)O tBu)2(μ-O2P(O)O tBu)2] (4) or the trinuclear titanophosphate [Cp*3Ti3(μ-O3PO tBu)2(μ-O)2(μ-O2P(O tBu)2)] (5), respectively. The formation of compounds 4 and 5 is facilitated by partial hydrolysis of the tert-butoxy groups of ( tBuO)2PO2K. New titanophosphates 1-5 have been characterized by spectroscopic and analytical methods, and the molecular structures have further been confirmed by single-crystal X-ray diffraction studies. Thermal decomposition studies of 1-5 reveal the initial loss of thermally labile alkyl substituents of the organophosphate ligands, followed by the loss of C5Me5 groups to form an organic-free amorphous titanophosphate in the temperature range 300-500 °C. This material transforms to highly crystalline titanium pyrophosphate TiP2O7 at 800 °C. Compounds 1-5 and the TiP2O7 materials obtained at 300, 500, and 800 °C through the thermal decomposition of 3 have been employed as efficient homogeneous catalysts for the alkene epoxidation reaction. Using hydrogen peroxide as the oxidant in an acetonitrile medium, these catalysts exhibit >90% alkene conversion with >90% epoxide selectivity in 4 h at temperatures below 100 °C.

Inorganically modified clay minerals: Preparation, characterization, and arsenic adsorption in contaminated water and soil

The use of modified clay minerals for adsorbing arsenic (As) in contaminated soils is an underexplored area of research. The adsorption behavior of As onto inorganically modified smectite and kaolinite both in aqueous and soil media was studied. X-ray diffraction, infra-red spectroscopy, scanning and transmission electron microscopy studies confirmed successful modification of smectite through Fe-exchange and Ti-pillaring, and kaolinite through phosphate binding. The modified smectites were more efficient than phosphate-bound kaolinite in adsorbing As both in water and soil systems. Kinetic study revealed that the clay products reached adsorption equilibrium within 3h, and the data well fitted to the power function and simple Elovich equation (R2>0.90). The Freundlich isotherm model best described the As adsorption data (R2>0.86) of the modified clay products in both the systems. The Ti-pillared smectite exhibited the highest As adsorption capacity (156.54μgg−1) in the aqueous medium, while the Fe-exchanged smectite was the best material in the soil system (115.63μgg−1). The partition coefficient (Kd) and adsorption efficiency (%) data also maintained the similar trend. Precipitation of As and binuclear complex formation also took place in the soil system which made the metalloid non-labile as the time passed. The inorganically modified clay products reported here hold a great potential to adsorb As in contaminated groundwater, drinking water as well as soil.

Experimental and theoretical studies of new rhenium carbonyls containing 4,5-bis(chalcogenodiphenylphosphinoyl)-1,2,3-triazolates

The novel binuclear complexes [Re(CO)3-μ-{κ3-N,N′,E-LT-E2}2]2 E = S and Se were prepared upon reaction of the corresponding potassium bis(chalcogenodiphenylphosphinoyl)triazolate, K[LT−E2], and [ReBr(CO)5]. 31P{1H}-NMR monitoring studies showed that formation of the binuclear complexes was preceded by the corresponding mononuclear complex [Re(CO)4{κ2-N,E-LT-E2] (E = S, Se). Theoretical calculations indicated that a faster reaction time for the formation of the sulfur binuclear complex in comparison with its selenium analog stems from thermodynamic considerations. The new complexes herein reported were characterized by standard spectroscopic techniques and single crystal X-ray analysis.

Synthesis of first representatives of 46-membered P,N,O-containing cyclophanes and their transition metal complexes

A condensation of phenyl- or l-menthylphosphine with formaldehyde and 4,4´-bis-(4´-aminophenoxy)biphenyl proceeding as a covalent self-assembly gave rise to the first representatives of 46-membered P,N,O-containing cyclophanes, namely, 13,17,83,87-tetra-R-3,6,10,13-tetraoxa-1,8(1,5)-di(1,5-diaza-3,7-diphosphacyclooctana)-2,4,5,7,9,11,12,14(1,4)-octabenzenacyclotetradecaphanes (R = Ph (1), l-Ment (2)). The cage macrocyclic tetraphosphine 2 reacted with (cyclooctadiene)dichloroplatinum(ii) and -palladium(ii), as well as with (tetrahydrofuran)pentacarbonyltungsten(0) with the formation of binuclear complexes, in which the metal atoms are coordinated to 1,5-diaza-3,7-diphosphacyclooctane fragments by the P,P-chelate mode.

New examples of chelating triketone-like ligands that promote formation of binuclear complexes

The present work is to investigate of binding properties of chelating triketone-like ligands, which are able to forming of binuclear complexes. The studied compounds are able to exist in cyclic or ‘close form’ (phenyl substituted or unsubstituted 2-hydroxy-2-(trifluoromethyl)chroman-4-ones) as well as in their associated ‘open form’ (phenyl substituted or unsubstituted 1,1,1-trifluoro-4-(2-hydroxyphenyl)butan-2,4-diones). In this paper there is good evidence for the compounds are being in solid in ‘close form’ (pre-ligands), whereas in basic solutions and when involved in metal ion coordination sphere they are being in ‘open form’ (ligands). Protolytic equilibria of the compounds in aqueous ethylene glycol solutions were studied. Schemes of acid-base equilibria of these compounds were proposed. Apparent ionization constants of compounds containing electron-donor and electron-acceptor substituents in the benzene ring were determined using spectrophotometric method. The binding properties of 1,1,1-trifluoro-4-(2-hydroxyphenyl)butan-2,4-dione towards Cu(II), Ni(II) and Co(II) were studied. The formation of 2:2 metal–ligand complexes was observed. X-ray analysis gives evidence the formation of complexes in which the ratio metal to ligand can be 1:2 and 2:2. Similar to β-triketones the studied ligands tends to formation of binuclear complexes with transition metal ions.

Organometallic macrocycles and cages based on bis(amidinate) ligands

Abstract A series of half-sandwich iridium-based complexes bearing 1,4-benzenebis (N,N′-dicyclohexylamidine) (H2 L 1) or 4,4′-bisphenylbis(N,N′-dicyclohexylamidine) (H2 L 2) has been synthesized and characterized. Treatment of [Cp*IrCl2]2 (Cp* = η5 -pentamethyl-cyclo pentadienyl) with deprotonated H2 L 1 or H2 L 2 at low temperature resulted in formation of binuclear complexes [Cp*IrCl]2 (L 1) and [Cp*IrCl]2(L 2). They were chosen as precursors to construct macrocycles and cages. Tetranuclear metallamacrocycles [(Cp*Ir)4(L 1)2 (pyrazine)2][OTf]4 and [(Cp*Ir)4(L 2)2(pyrazine)2][OTf]4 were assembled by the reaction of complex [Cp*IrCl]2 (L 1) or [Cp*IrCl]2(L 2) with pyrazine after the removal of chloride from the iridium centers with silver salt AgOTf (OTf = O2SCF3). When 2,4,6-tri(4-pyridyl)-1,3,5-triazine (tpt) is used instead of pyrazine under the same conditions, hexanuclear metallacages [(Cp*Ir)6(L1 )3(tpt)2][OTf]6 and [(Cp*Ir)6(L 2)3(tpt)2][OTf]6 were formed. Single-crystal X-ray analysis indicated that the cation of complex [(Cp*Ir)4(L 1)2 (pyrazine)2][OTf]4 is a rectangular structure, while the cation of complex [(Cp*Ir)4(L 2)2(pyrazine)2][OTf]4 is seriously distorted, nearly to a tetrahedral state. Moreover, complexes [(Cp*Ir)6(L1 )3(tpt)2][OTf]6 and [(Cp*Ir)6(L 2)3(tpt)2][OTf]6 are prism-like cages with large cavity size, which can be prepared in very high yield in the absence of templates. Surprisingly, solutions of multinuclear complexes are very sensitive to carbon monoxide, in which the frameworks were destroyed, giving the binuclear complexes [(Cp*Ir)2(CO)2(L 1)][OTf]2 and [(Cp*Ir)2(CO)2(L 2)][OTf]2.

Stepwise formation of organometallic macrocycles and triangular prisms containing 2,2′-bisbenzimidazole ligands

A series of organometallic macrocycles have been constructed by an efficient “bottom-up” assembly methodology at ambient temperature. Treatment of [Cp*MCl2]2 (1a: M = Ir, 1b: M = Rh) with pyrazine or 4,4′-bipyridine (bpy) (1:1; Cp* = pentamethylcyclopentadienyl) at room temperature resulted in the formation of binuclear complexes [Cp*MCl2]2(pyrazine) and [Cp*MCl2]2(bpy) (M = Ir or Rh), which were then further reacted with AgOTf (Tf = O2SCF3) and 2,2′-bisbenzimidazole ligand (BiBzIm). Four organometallic macrocyclic complexes formulated as [Cp*4Ir4(BiBzIm)2(pyrazine)2](OTf)4 (2a), [Cp*4Rh4(BiBzIm)2(pyrazine)2](OTf)4 (2b), [Cp*4Ir4(BiBzIm)2(bpy)2](OTf)4 (2c) and [Cp*4Rh4(BiBzIm)2(bpy)2](OTf)4 (2d) each bearing 2,2′-bisbenzimidazole ligand and the half-sandwich Ir, Rh fragments were finally obtained in good yields. In a similar process, if a rigid ligand L (3-pyridyl-bian) was used as the linker, two novel metallacycles (3a and 3b) which enchased a silver atom in the centre were obtained. Organometallic triangular prisms 4a were synthesized via methods similar to those of the rectangles. [Cp*IrCl2]2 reacted with tridentate ligand 2,4,6-tri(4-pyridyl)-1,3,5-triazine (tpt) to give the corresponding trinuclear complexes [Cp*IrCl2]3(tpt), then further reacted with AgOTf and 2,2′-bisbenzimidazole ligand, leading to the formation of the prism-like complexes formulated as [Cp*6M6(BiBzIm)6(tpt)2](OTf)6 (3a: M = Ir, 3b: M = Rh). All complexes were well characterized by 1H NMR and IR spectroscopy, as well as elemental analyses. The molecular structures of 2a, 2b, 2c, 3a, 3b and 4a were characterized by single-crystal X-ray crystallography. We found that the prism-like hexanuclear complexes 4a displayed interesting host–guest chemistry.

DFT Study of Oxo-Functionalized Pentavalent Dioxouranium Complexes: Structure, Bonding, Ligand Exchange, Dimerization, and U(V)/U(IV) Reduction of OUOH and OUOSiH3 Complexes

The structural and electronic properties of model oxo-functionalized pentavalent dioxouranium complexes have been studied using scalar relativistic density functional theory (DFT) calculations. The electronic structures of these complexes are compared to those of their hexavalent and pentavalent counterparts with free axial oxo groups while paying particular emphasis on the effect of oxo-functionalization on the formation of binuclear complexes, the U(V)/U(IV) redox potentials, as well as ligand exchange between the axial and equatorial regions of the dioxouranium moiety. The stabilization of the σ(d) orbitals of the UO(2) moiety is one of the major effects of oxo-functionalization. The origin of this effect is the mixing of the σ(d) orbital of the uranyl group with the σ(OH)/σ(OSiH(3)) orbitals of the axial OH/OSiH(3) group. The 6p atomic orbitals of the uranium center are mixed to a greater extent with the σ(d) orbital after stabilization caused by oxo-functionalization. The asymmetric nature of the oxo-functionalization has dramatic effects not only on the U-O bond lengths (elongation by up to 0.24 Å) and U-O bond orders (loss of a full bond order) but also on the formation and type of U(2)O(4) core found in binuclear complexes. The loss of a full bond order upon oxo-functionalization means the axial U-OH/U-OSiH(3) bonds are only slightly stronger than they would be if they were found in the equatorial region of the uranyl moiety. This raises the possibility of ligand exchange between the axial and equatorial regions as well as increasing the stability of the binuclear complexes with butterfly-shaped U(2)O(4) cores relative to those with diamond U(2)O(4) cores. Reductive oxo-functionalization results in complexes with lower electron density at their U(V) centers in comparison to UO(2)(+) complexes. This has dramatic effects on the calculated U(V)/U(IV) redox potentials.