Heteropolymetallic Complexes Research Articles

Role of the Environment Polarity on the Photophysical Properties of Mesogenic Hetero-Polymetallic Complexes.

New hetero-polynuclear coordination complexes based on a pentacoordinated Zn(II) metal center with tridentate terpyridine-based ligands and monoanionic gallates functionalized with long alkyl chains containing ferrocene units were designed, synthesized and characterized using spectroscopic and analytical methods. The complexes are mesomorphic, exhibiting columnar hexagonal mesophases. The photophysical properties in a solution and in an ordered condensed state were accurately investigated and the influence of the polarity of the solvent was evidenced.

Phosphite Bearing [(μ-ADT)RFe2(CO)6] (ADT = Azadithiolate) Moieties: A Tool for the Building of Multimetallic [FeFe]-Hydrogenase Mimics

A new phosphite ligand having three [(μ-ADT)RFe2(CO)6] (R= p-HOC6H4) moieties (2) has been prepared in good yield by the reaction of complex [(μ-ADT)RFe2(CO)6] (R= p-HOC6H4) 1a with PCl3. Coordination of this phosphite to [PdCl2(MeCN)2] or [PtCl2(DMSO)2] forms heterometallic square planar complexes 5 (C84H48Cl2Fe12N6O42P2MS12) (M = Pt, Pd) in excellent yields. Three-legged piano stool complexes 6 (C52H39Cl2Fe6N3O21PMS6) (M = Rh, Ir) were obtained by the reaction of phosphite 2 with [MCl2Cp*]2 (M = Rh, Ir) in good yields. The formation of complexes 5 and 6 demonstrates the versatility of this new ligand for forming different heteropolymetallic complexes under mild reaction conditions. Moreover, the open-chain derivatives [(μ-ADT)RFe2(CO)6] (R= HOCH2CH2, o-HOC6H4) (1b and 1c, respectively) form cyclic complexes 4 by spontaneous intramolecular CO substitution by the P atom in one of the three [FeFe] fragments. The electrocatalytic behavior of complexes 2 and 4 upon the addition of AcOH is similar to that of related [(μ-ADT)Fe2(CO)6] derivatives. The successive additions of AcOH cause an increase in the current intensity in the wave at about −1.80 V for heteropolymetallic complexes 5 and 6. However, the appearance of a new wave around −1.40 V in complexes 5 points to an acid-promoted side reaction in the electrochemical process.

Heterometallic 3d-4f Complexes as Air-Stable Molecular Precursors in Low Temperature Syntheses of Stoichiometric Rare-Earth Orthoferrite Powders.

Four 3d-4f hetero-polymetallic complexes [Fe2Ln2((OCH2)3CR)2(O2CtBu)6(H2O)4] (where Ln = La (1 and 2) and Gd (3 and 4); and R = Me (1 and 3) and Et (2 and 4)) are synthesized and analyzed using elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, and SQUID magnetometry. Crystal structures are obtained for both methyl derivatives and show that the complexes are isostructural and adopt a defective dicubane topology. The four heavy metals are connected with two alkoxide bridges. These four precursors are used as single-source precursors to prepare rare-earth orthoferrite pervoskites of the form LnFeO3. Thermal decomposition in a ceramic boat in a tube furnace gives orthorhombic LnFeO3 powders using optimized temperatures and decomposition times: LaFeO3 formed at 650 °C over 30 min, whereas GdFeO3 formed at 750 °C over 18 h. These materials are structurally characterized using powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray map spectroscopy, and SQUID magnetometry. EDX spectroscopy mapping reveals a homogeneous spatial distribution of elements for all four materials consistent with LnFeO3. Magnetic measurements on complexes 1-4 confirm the presence of weak antiferromagnetic coupling between the central Fe(III) ions of the clusters and negligible ferromagnetic interaction with peripheral Gd(III) ions in 3 and 4. Zero-field-cooled and field-cooled measurements of magnetization of LaFeO3 and GdFeO3 in the solid-state suggest that both materials are ferromagnetic, and both materials show open magnetic hysteresis loops at 5 and 300 K, with Msat higher than previously reported for these nanomaterials. We conclude that this is a new and facile low temperature route to these important magnetic materials that is potentially universal, limited only by what metals can be programmed into the precursor complexes.

Small molecule activation by multimetallic uranium complexes supported by siloxide ligands.

The synthesis and reactivity of uranium compounds supported by the tris-tert-butoxysiloxide ligand is surveyed. The multiple binding modes of the tert-butoxysiloxide ligand have proven very well suited to stabilize highly reactive homo- and heteropolymetallic complexes of uranium that have shown an unusual high reactivity towards small molecules such as CO2, CS2, chalcogens and azides. Moreover, these ligands have allowed the isolation of dinuclear nitride and oxide bridged complexes of uranium in various oxidation states. The ability of the tris-tert-butoxysiloxide ligands to trap alkali ions in these nitride or oxide complexes leads to unprecedented ligand based and metal based reduction and functionalization of N2, CO, CO2 and H2.

Selective Encapsulation and Separation of Dihalobenzene Isomers with Discrete Heterometallic Macrocages.

A series of metallosupramolecular architectures have been prepared, including rectangles, prisms and cages, that feature half-sandwich rhodium(III) fragments at the vertices. Remarkably, a stable cage-like heteropolymetallic complex possessing eight rhodium(III) and two silver(I) metal ions (3) has been obtained following a multistep procedure. The RhIII /AgI mixed macrocage enables the separation of dihalogenated benzene derivatives with high selectivity. Furthermore, a detailed X-ray crystallographic study confirmed that the discriminative encapsulation of para-dihalobenzene (dichlorobenzene, dibromobenzene and diiodobenzene) is favored by Ag-π interactions and steric effects.

Pt–M Complexes (M=Ag, Au) as Models for Intermediates in Transmetalation Processes

Heteropolynuclear complexes [(CNC)(PPh3 )PtM(PPh3 )]ClO4 [M=Au (1), Ag (2)] and [{Pt(CNC)(PPh3 )}2 M]ClO4 [M=Ag (3), Au (4); CNC=2,6-diphenylpyridinate] were prepared and studied by X-ray crystallography, spectroscopic techniques, and DFT calculations. The X-ray crystal structures of 1, 3, and 4 confirmed the existence of Pt-M bonds and M⋅⋅⋅Cipso interactions involving one of the phenyl fragments of CNC. Their NMR spectra showed the persistence of the Pt-M interactions in solution and also revealed an intramolecular metronome-like dynamic process consisting of back-and-forth motion of the acidic M fragments along the C-Pt-C axis. DFT calculations on these complexes identified two main orbital interactions between the [PtCNC] and [M]+ fragments, namely, donation from the former to a vacant orbital of the latter and much weaker backdonation from the acidic M to the Pt fragment. Overall, the strength of the [Pt]⋅⋅⋅M interactions is higher for the gold compounds than for their silver counterparts. The interaction between the acidic center (silver or gold) and the carbon atom of one of the phenylene rings in these heteropolymetallic complexes can be envisaged as the first step in a process of interchange of aryl ligands. However, the ligand exchange cannot progress further due to the polydentate nature of the CNC ligand, and therefore these structures can be considered as frozen snapshots of a transmetalation reaction that has been arrested at different stages of the process.

Post-coordination backbone functionalization of an imidazol-2-ylidene and its application to synthesize heteropolymetallic complexes incorporating the ambidentate IMes(CO2(-)) ligand.

Backbone functionalization of the pre-coordinated, emblematic IMes ligand with the COOH moiety was achieved upon treatment of Cp(CO)2Mn(IMes) with n-BuLi followed by CO2 and HCl to afford Cp(CO)2Mn(IMes(COOH)). The latter reacts with (1,10-phen)M(OAc)2 (M = Cu, Zn) to obtain M3Mn4 polymetallic complexes exhibiting the ambidentate IMes(CO2(-)) moiety as a key structural unit.

Uniting Ruthenium(II) and Platinum(II) Polypyridine Centers in Heteropolymetallic Complexes Giving Strong Two-Photon Absorption.

New trinuclear RuPt2 and heptanuclear RuPt6 complex salts are prepared by attaching Pt(II) 2,2':6',2"-terpyridine (tpy) moieties to Ru(II) 4,4':2',2":4",4"'-quaterpyridine (qpy) complexes. Characterization includes single crystal X-ray structures for both polymetallic species. The visible absorption bands are primarily due to Ru(II) → qpy metal-to-ligand charge-transfer (MLCT) transitions, according to time-dependent density functional theory (TD-DFT) calculations. These spectra change only slightly on Pt coordination, while the orange-red emission from the complexes shows corresponding small red-shifts, accompanied by decreases in intensity. Cubic molecular nonlinear optical behavior has been assessed by using Z-scan measurements. These reveal relatively high two-photon absorption (2PA) cross sections σ2, with maximal values of 301 GM at 834 nm (RuPt2) and 523 GM at 850 nm (RuPt6) when dissolved in methanol or acetone, respectively. Attaching Pt(II)(tpy) moieties triples or quadruples the 2PA activities when compared with the Ru(II)-based cores.

Heteropolymetallic Complexes Linked to a 9,10-Dihydroanthracenyl Frame. Ruthenium as Active Spectator for Palladium Reactivity

New monometallic Pd(II) (3, 4) and heteropolymetallic Pd(II)/Ru(II) complexes (5, 6) linked to an original 9,10-dihydroanthracenyl–pyrrolidine scaffold were synthesized and fully characterized. For monometallic complexes, exo-3 and endo-4 conformers were exclusively obtained from Pd(OAc)2 and [PdCl2(COD)], respectively. The formation of the sterically hindered endo-4 was justified by the positive noncovalent intramolecular Cl−π interaction, observed by X-ray diffraction. The reaction of endo-4 with 1 and 2 equiv of [RuCp(NCMe)3]PF6 led to complexes 5 and 6, respectively. It is worth noting that lower conversions in the Suzuki–Miyaura coupling were found using 5 and 6 as catalysts, in comparison to those with monometallic palladium complexes. This behavior could be related to the higher stabilization of Pd(II) species for the heteropolymetallic complexes, as proven by electrochemical analyses.

Controlled Synthesis of a Novel Heteropolymetallic Complex with Selectively Incorporated Lanthanide(III) Ions

A novel synthetic strategy toward a heteropolymetallic lanthanide complex with selectively incorporated gadolinium and europium ions is outlined. Luminescence and relaxometric measurements suggest possible applications in bimodal (magnetic resonance/optical) imaging.

Homo- and heteropolymetallic 3-(2-pyridyl)pyrazolate manganese and rhenium complexes

fac-[MBr(CO)3(pypzH)] (M = Mn, Re; pypzH = (3-(2-pyridyl)pyrazole) complexes are prepared from fac-[MBr(CO)3(NCMe)2] and pypzH. The result of their deprotonation depends on the metallic substrate: the rhenium complex affords cleanly the bimetallic compound [fac-{Re(CO)3(μ(2)-pypz)}]2 (μ(2)-pypz = μ(2)-3-(2-pyridyl-κ(1)N)pyrazolate-2κ(1)N), which was crystallographically characterized, whereas a similar manganese complex was not detected. When two equivalents of pyridylpyrazolate are used, polymetallic species [fac-M(CO)3(μ(2)-pypz)(μ(3)-pypz)M'] (μ(3)-pypz = μ(3)-3-(2-pyridyl-κ(1)N)pyrazolate-1κ(2)N,N:2κ(1)N:; M = Mn, M' = Li, Na, K; M = Re, M' = Na) are obtained. The crystal structures of the manganese carbonylate complexes were determined. The lithium complex is a monomer containing one manganese and one lithium atom, whereas the sodium and potassium complexes are dimers and reveal an unprecedented coordination mode for the bridging 3-(2-pyridyl)pyrazolate ligand, where the nitrogen of the pyridyl fragment and the nitrogen-1 of pyrazolate are chelated to manganese atoms, and each nitrogen-2 of pyrazolate is coordinated to two alkaline atoms. The polymetallic carbonylate complexes are unstable in solution and evolve spontaneously to [fac-{Re(CO)3(μ(2)-pypz)}]2 or to the trimetallic paramagnetic species [Mn(II)(μ(2)-pypz)2{fac-{Mn(I)(CO)3(μ(2)-pypz)}2}]. The related complex cis-[MnCl2(pypzH)2] was also synthesized and structurally characterized. The electrochemical behavior of the new homo- and heteropolymetallic 3-(2-pyridyl)pyrazolate complexes has been studied and details of their redox properties are reported.

Heteropolymetallic complexes containing ReO4−: Catalytic oxidation of sulfide

Heteropolymetallic complexes [(salen)Ti(ReO4)2] (1) and [{(salen)Ti(ReO4)}2(μ-O)] (2) are easily obtained in high yields via reaction of [(salen)TiCl2] and [{(salen)TiCl2}2(μ-O)] with (Me3SiO)ReO3, respectively (where, salen=(S,S)-N,N′-bis(3,5-di-tert-butylsalicylidene)cyclohexane-1,2-diamine dianion). The structure of complex 2 was established by single-crystal X-ray diffraction. The tetrahedral geometry of the ReO4− anion links the dititanium unit of {(salen)Ti}2(μ-O) in the axial positions. The Re–O–Ti bridge angles range from 146.1(2) to 162.6(2) with a Re⋯Ti separation of 3.780Å. Complexes 1 and 2 are capable of catalytic oxidation of sulfides with tBuOOH.

1,3-Bis(thiophosphinoyl)indene: A Unique and Versatile Scaffold for Original Polymetallic Complexes

The coordination of tridentate ligands featuring lateral coordination sites prone to acting as bridging ligands was explored with the aim of obtaining original polymetallic species in a straightforward and controlled manner. Accordingly, the 2-indenylidene chloropalladate [{Ind(Ph(2)P═S)(2)}PdCl](-) was found to behave as a κ(2)-C,S bidentate ligand toward metal fragments, giving access to homo- and heteropolymetallic complexes. X-ray diffraction analyses reveal the presence of short metal-metal contacts in all of these complexes. Density functional theory calculations unambiguously substantiate that the metals engage in unusual d(8)···d(8) interactions with a quasi-perpendicular arrangement of their coordination planes.

Special features of photolytic transformation of tin heteropolymetallic catecholate complexes

The photolysis of bis(dicarbonylcyclopentadienyliron)(3,6-di-tert-butylcatecholato)tin(IV), bis(dicarbonylcyclopentadienylmolybdenum)(3,6-di-tert-butylcatecholato)tin(IV), and bis(dicarbonylcyclopentadienyltunsten)(3,6-di-tert-butylcatecholato)tin(IV) in solutions of saturated hydrocarbons was studied. Kinetic parameters of the transformation of these compounds under the action of a monochromatic radiation with a wavelength of 313 nm were determined. Products of their transformation formed in the course of the irradiation were identified, and the probable mechanism of their photodecomposition was proposed.

Synthesis and Photophysical Properties of LnIII–DOTA–Bipy Complexes and LnIII–DOTA–Bipy–RuII Coordination Conjugates

AbstractThe synthesis and the systematic and comparative photophysical study of a series of visible (EuIII, TbIII) and NIR‐emitting (NdIII, YbIII) lanthanide complexes (Ln2L) and ruthenium–lanthanide coordination conjugates (Ln2LRu) are reported. The GdIII complex, the GdIII–RuII coordination conjugate, as well as the RuII complex of the ligand H6L have also been synthesized and photophysically studied as control systems. The ligand H6L, composed of a central bipyridine binding unit and functionalized on each 5′‐position with a DOTA macrocycle, has been successfully synthesized from cyclen, 5,5′‐dimethyl‐2,2′‐bipyridine and 1,2‐ethylendiamine in a nine‐step process. Detailed luminescence studies of all complexes, including the determination of the quantum yield and lifetime, were carried out on finely powdered microcrystalline samples as well as in water, deuterated water and [D6]DMSO at ambient (295 K) and low temperature (77 K). The photophysical data corroborate the existence of energy transfer in the Ln2L complexes and in the Nd2LRu coordination conjugate. However, no (or at most, very little) energy transfer is takes place from the Ru(bipy)3 chromophore to the LnIII ion in the other Ln2LRu heteropolymetallic complexes. Moreover, the photophysical studies reveal that all the complexes and coordination conjugates adopt different conformations and hydration states in solution and in the solid state, which influences the efficiency of the energy transfer between the bipy and/or Ru(bipy)3 antennae and the LnIII ions.

Quasi-Planar Homopolymetallic and Heteropolymetallic Coordination Arrays. Surface-Like Molecular Clusters of Magnesium and Aluminum

The sterically isolated preorganized tetradentate ligand systems, tetrakis(2-hydroxy-3-n-propylphenyl)ethene and tetrakis(5-tert-butyl-2-hydroxy-3-trimethylsilylphenyl)ethene, nucleate the formation of quasi-planar raft-like polymetallic coordination complexes with high selectivity, providing topologically consistent structural models for metal coordination to the "oxo-surface" of silica- and alumina-supported heterogeneous catalysts. The coordination of magnesium salts to these systems yields trimetallic magnesium halide and alkyl complexes arrayed on the oxygen "surface" of the ligand, regardless of the steric profile of the ortho-substituents. The magnesium complexes, characterized in the solid state by X-ray crystallography, contain two chemically distinct metal environments, a relatively inert central magnesium bis(alkoxide) and two more labile pseudotetrahedral "wing" magnesium atoms. The central metal coordination is pseudo-octahedral; crystallography strongly suggests the presence of an unprecedented dative magnesium-olefin bonding interaction from the metal to ethene bridge of the ligand. Consistent with the chemistry proposed for typical magnesium-treated catalyst supports, the labile wing magnesium centers can be cleanly and sequentially exchanged for aluminum with retention of the surface-like coordination array. Thus, treatment with diethylaluminum chloride provides heterotrimetallic magnesium-aluminum complexes containing one aluminum and two magnesium sites or two aluminum and one magnesium site, respectively. All four heteropolymetallic complexes have been characterized by X-ray crystallography.

Oligonuclear 3d–4f Complexes as Tectons in Designing Supramolecular Solid‐State Architectures: Impact of the Nature of Linkers on the Structural Diversity

Heteronuclear cationic complexes, [LCuLn]3+ and [(LCu)2Ln]3+, were employed as nodes in designing high-nuclearity complexes and coordination polymers with a rich variety of network topologies (L is the dianion of the Schiff base resulting from the 2:1 condensation of 3-methoxysalycilaldehyde with 1,3-propanediamine). Two families of linkers have been chosen: the first consists of exo-dentate ligands bearing nitrogen-donor atoms (bipyridine (bipy), dicyanamido (dca)), whereas the second consists of exo-dentate ligands with oxygen-donor atoms (anions derived from the acetylenedicarboxylic (H2acdca), fumaric (H2fum), trimesic (H3trim), and oxalic (H2ox) acids). The ligands belonging to the first family prefer copper(II) ions, whereas the ligands from the second family interact preferentially with oxophilic rare-earth cations. The following complexes have been obtained and crystallographically characterized: [LCu(II)(OH2)Gd(III)(NO3)3] (1), [{LCu(II)Gd(III)(NO3)3}2(mu-4,4'-bipy)] (2), 1infinity[LCu(II)Gd(III)(acdca)(1.5)(H2O)2].13H2O (3), 2infinity[LCu(II)Gd(III)(fum)(1.5)(H2O)2].4H2O.C2H5OH (4), 1infinity[LCu(II)Sm(III)(H2O)(Hfum)(fum)] (5), 1infinity[LCu(II)Er(III)(H2O)2(fum)]NO3.3H2O (6), 2infinity[LCu(II)Sm(III)(fum)(1.5)(H2O)2].4H2O.C2H5OH (7), [{(LCu(II))2Sm(III)}2fum2](OH)2 (8), 1infinity[LCu(II)Gd(III)(trim)(H2O)2].H2O (9), 2infinity[{(LCu(II))2Pr(III)}(C2O4)(0.5)(dca)]dca.2H2O (10), [LCu(II)Gd(III)(ox)(H2O)3][Cr(III)(2,2'-bipy)(ox)2].9H2O (11), and [LCuGd(H2O)4{Cr(CN)6}].3H2O (12). Compound 1 is representative of the whole family of binuclear Cu(II)-Ln(III) complexes which have been used as precursors in constructing heteropolymetallic complexes. The rich variety of the resulting structures is due to several factors: 1) the nature of the donor atoms of the linkers, 2) the preference of the copper(II) ion for nitrogen atoms, 3) the oxophilicity of the lanthanides, 4) the degree of deprotonation of the polycarboxylic acids, 5) the various connectivity modes exhibited by the carboxylato groups, and 6) the stoichiometry of the final products, that is, the Cu(II)/Ln(III)/linker molar ratio. A unique cluster formed by 24 water molecules was found in crystal 11. In compounds 2, 3, 4, 9, and 11 the Cu(II)-Gd(III) exchange interaction was found to be ferromagnetic, with J values in the range of 3.53-8.96 cm(-1). Compound 12 represents a new example of a polynuclear complex containing three different paramagnetic ions. The intranode Cu(II)-Gd(III) ferromagnetic interaction is overwhelmed by the antiferromagnetic interactions occurring between the cyanobridged Gd(III) and Cr(III) ions.

Novel hetero-polymetallic derivatives of palladium bearing pyridylthioether fragments incorporating a Fe 2(CO) 6 cluster core as ligand

The complexation of poly(pyridylthioether) incorporating a Fe 2(CO) 6 cluster core with palladium derivatives in different oxidation states afforded novel hetero-polymetallic complexes.

195Pt NMR of Heteropolymetallic Complexes Containing Secondary Dithiooxamides as Binucleating Ligands

Monometallic [Pt{S-S2C2(NR)2H}2] (S-S2C2(NR)2H = kappa2-S,S-S2C2(NR)2H = bis-dialkyl-dithioxamidate, R = methyl, isoamyl, benzyl) and binuclear and trinuclear heterobimetallic complexes [Pt{S-S2C2(NR)2H}{mu-S2C2(NR)2}MLn] (mu-S2C2(NR)2 = kappa2-S,S(Pt)-kappa2-N,N(M)-S2C2(NR)2) and [Pt{{mu-S2C2(NR)2}MLn}2] (MLn+ = [(eta3-allyl)palladium]+, [bis-(2-phenylpyridine)rhodium]+, [(eta6-p-cymene)(chloro)ruthenium]+, [(1,4-cyclooctadiene)rhodium]+, [(pentamethylcyclopentadienyl)(chloro)rhodium]+) have been prepared and characterized. The progressive substitution of the residual amidic hydrogen in the [Pt{S-S2C2(NR)2H}2] complexes with a MLn+ metal fragment results in the deshielding of platinum nuclei, a red shift of the MLCT absorption maximum, and a decrease in the oxidation potential. Such behavior has been interpreted as a progressive electron shift from platinum to the binucleating ligands, the extent of which depends on the nature of MLn+ metal fragment.

The bis-molybdenum(0) trianion [1,3,6-{Mo(CO)3}-3,6-(µ-H)2-1,1,1-(CO)3-2-Ph-closo-1,2-MoCB9H7]3– and its use as a scaffold in the assembly of heteropolymetallic complexes

The title trianion reacts successively with cationic transition-metal fragments to afford a heterotrimetallic Mn-Mo-Pt species.