Binuclear Nature Research Articles

Experimental and Theoretical Investigation of the Mechanism of the Reduction of O2 from Air to O22- by VIVO2+-N,N,N-Amidate Compounds and Their Potential Use in Fuel Cells.

The two-electron reductive activation of O2 to O22- is of particular interest to the scientific community mainly due to the use of peroxides as green oxidants and in powerful fuel cells. Despite of the great importance of vanadium(IV) species to activate the two-electron reductive activation of O2, the mechanism is still unclear. Reaction of VIVO2+ species with the tridentate-planar N,N,N-carboxamide (ΗL) ligands in solution (CH3OH:H2O) under atmospheric O2, at room temperature, resulted in the quick formation of [VV(═O)(η2-O2)(κ3-L)(H2O)] and cis-[VV(═O)2(κ3-L)] compounds. Oxidation of the VIVO2+ complexes with the sterically hindered tridentate-planar N,N,N-carboxamide ligands by atmospheric O2 gave only cis-[VV(═O)2(κ3-L)] compounds. The mechanism of formation of [VV(═O)(η2-O2)(κ3-L)(H2O)] (I) and cis-[VV(═O)2(κ3-L)] (II) complexes vs time, from the interaction of [VIV(═O)(κ3-L)(Η2Ο)2]+ with atmospheric O2, was investigated with 51V, 1H NMR, UV-vis, cw-X-band EPR, and 18O2 labeling IR and resonance Raman spectroscopies revealing the formation of a stable intermediate (Id). EPR, MS, and theoretical calculations of the mechanism of the formation of I and II revealed a pathway, through a binuclear [VIV(═O)(κ3-L)(H2O)(η1,η1-O2)VIV(═O)(κ3-L)(H2O)]2+ intermediate. The results from cw-EPR, 1H NMR spectroscopies, cyclic voltammetry, and the reactivity of the complexes [VIV(═O)(κ3-L)(Η2Ο)2]+ toward O2 reduction fit better to an intermediate with a binuclear nature. Dynamic experiments in combination with computational calculations were undertaken to fully elucidate the mechanism of the O2 reduction to O22- by [VIV(═O)(κ3-L)(Η2Ο)2]+. The galvanic cell {Zn|VIII,VII||Id, [VIVO(κ3-L)(H2O)2]+|O2|C(s)} was manufactured, demonstrating the important applicability of this new chemistry to Zn|H2O2 fuel cells technology generating H2O2 in situ from the atmospheric O2.

Binuclear Macrocyclic Silver(I) Complex of a Bis(carbone) Pincer Ligand: Synthesis and Application as a Carbone-Transfer Agent.

A facile synthesis of a binuclear AgI complex 2 of a bis(carbone) ligand L and its application as a carbone-transfer agent for the generation of other transition-metal complexes of AuI (3), NiII (4), and PdII (5) is presented. Complex 2 was synthesized through multiple synthetic routes under mild reaction conditions using the tetracationic [LH4][OTf·Cl]2 precursor salt, the dicationic [LH2][OTf]2 ylide salt, and the free ligand L. The first two synthesis routes require no prior isolation of the air-, moisture-, and temperature-sensitive free ligand L, thus affording complex 2 with high yield and purity. Multinuclear NMR techniques, high-resolution mass spectrometry, and single-crystal X-ray diffraction analysis confirmed the identity of complex 2 as a binuclear AgI complex of L with a molecular formula of [L2Ag2][OTf]2 and a 16-membered-ring metallomacrocyclic structure. During the transmetalation reaction with AuI, the binuclear nature of complex 2 remains intact to give analogous complex 3 ([L2Au2][OTf]2). However, the dimeric structure was disrupted upon the carbone-transfer reaction with NiII and PdII, yielding mononuclear C-N-C pincer-type complexes 4 ([LNiCl][OTf]) and 5 ([LPdCl][OTf]), respectively. These results demonstrated the versatile use of complex 2 as a carbone-transfer agent to other transition metals regardless of the type or size of the metals or the geometry they prefer.

Binuclear VIV/V, MoVI and ZnII - hydroquinonate complexes: Synthesis, stability, oxidative activity and anticancer properties

Since the discovery of the anticancer properties of cis-platin the road for the development of less toxic and more specific metal ion based anticancer drugs has opened. Based on the low toxicity of VIV/V, MoVI and ZnII metal ions, their binuclear hydroquinonate complexes have been synthesized and their biological activity towards their anticancer properties on various cancerous and non-cancerous cell lines has been evaluated. The new complexes of ZnII with the ligands 2,5-bis((bis(pyridin-2-ylmethyl)amino)methyl)benzene-1,4-diol (H2bpymah) and 2,2′-(((2,5-dihydroxy-1,4-phenylene)bis(methylene))bis((carboxymethyl)ammoniumdiyl))diacetate (H6bicah) have been synthesized and characterized by X-ray crystallography in solid state and 1H NMR in aqueous solution. The binuclear nature of the complexes increases their hydrolytic stability in aqueous solutions at pD 7.0, depending on the metal ion. The most hydrolytic stable VV and ZnII hydroquinonate complexes show to activate O2 towards oxidation of mercaptoethanol in aqueous solutions at physiological pHs. Only the strongest oxidant, the VV complex with bicah6−, significantly activates the intracellular radical oxygen species (ROS) generation. Apparently, the mercaptoethanol oxidation experiment vs time can be used as a preliminary experiment for the prediction of the in vitro ROS generation activity of the complexes in aqueous solutions.

Synthesis and characterization of some binuclear alkylene dithiophosphate complexes of bis(acetylacetonato)aluminium(III)-di-(μ-isopropoxo)di-isopropoxoaluminium(III) and sol-gel synthesis of nanosized θ-alumina

Reactions of bis(acetylacetonato)aluminum(III)-di-(μ–isopropoxo)-di-isopropoxoaluminum(III) (A) with a variety of alkylenedithiophosphoric acids in different molar ratio yield products of the type [(CH3COCHCOCH3)2Al(μ-OPri)2Al{S(S)P(O-G-O)n(OPri)2-n] (1-9) {where G = C(CH3)2C(CH3)2, n=1[1], n=2[2]; -CH2CH(C2H5), n=1[3], n=2[4]; CH2CH(CH3), n=1[5], n=2[6];C(CH3)2CH2CH(CH3), n=1[7]; CH(CH3)CH(CH3) n=1[8], n=2[9]}. Progress of the reactions was monitored by estimating liberated 2-propanol in benzene-2-propanol azeotrope by oxidimetric method. All pale coloured viscous products were soluble in common organic solvents and were characterized by elemental analyses, FT-IR and NMR (1H and 13C{1H} NMR) spectral studies. Molecular weight measurements in refluxing anhydrous benzene indicated binuclear nature of the complexes. 27Al NMR spectra of two of the derivatives, (1) and (2), suggested the presence of aluminium(III) atoms in different coordination states. 31P NMR spectra of the representative derivatives (1) and (2) exhibited only a single peak at 95.71 and 90.59 ppm, respectively suggesting tetra-coordination around phosphorus atom and a bidentate mode of chelation of the dithio ligand. Sol-gel transformation of Al(OPri)3 and [(CH3COCHCOCH3)2Al(μ-OPri)2Al(OPri)2] (A) followed by sintering at ~850°C yield alumina (a) and (b), respectively. The powder X-ray diffraction patterns, SEM images and FT-IR spectral studies of (a) and (b) indicated formation of nano-crystallites of θ -Al2O3 [PDF # 110517] in both the cases. The energy band gaps of 4.78 eV and 5.01 eV for (a) and (b), respectively were obtained from the absorption spectra.

Novel VO (IV) complexes derived from a macrochelates: Synthesis, characterization, molecular modeling and in vivo insulin‐mimic activity studies

For the development of extensive investigations into a potential medicinal application of vanadium coordination compounds for the oral treatment of diabetes, new mono and bimetallic VO (IV) complexes with N,N′‐(2,2′‐(9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐dicarbonyl) bis (hydrazine‐1‐carbonothioyl)) dibenzamide (H6EBT) and 2,2′‐((9S,10S,11R,12R)‐9,10‐dihydro‐9,10‐ethanoanthracene‐11, 12‐dicarbonyl) bis (N‐phenylhydrazine‐1‐carboxamide) (H6EPH) have been isolated and characterized. The FTIR and NMR spectral data revealed that H6EBT acts as neutral tridentate and dibasic hexadentate while H6EPH as dibasic tridentate and tetrabasic hexadentate. The electronic and ESR spectra indicated that complexes has octahedral geometry. ESR spectrum of [(VO)(H6EBT)(SO4)].5H2O gives a well resolved hyperfine eight‐line pattern typical spectrum for mononuclear vanadyl complexes with g˃ g⊥ = 1.9 suggesting that the ligand donor atoms ONS are coplanar with the two chelate rings forming octahedral geometry. Also, the high parallel hyperfine splitting value, A = 0.0108, than perpendicular one (A⊥ = 0.0087) indicated that the single d‐ electron is in a σ‐nonbonding orbital and aiming away from the equatorial ligands. On the other hand, the EPR spectra of the binuclear [(VO)2(H4EBT)(SO4)]3H2O and [(VO)2(H2EPH)(H2O)2].10H2O complexes gave a single broad line centered at g = 2.05 and 2.07, respectively, without resolved hyperfine structure paramagnetic triplet (S = 1) is consistent with the anomalous value of the magnetic moment value (μeff = 1.100 and 0.99 B.M.) supporting a binuclear nature. The TG analyses confirmed the existence of solvent molecules inside and/or outside the coordination sphere. The DFT molecular modeling of ligands and its VO (IV) complexes supported the suggested geometries. Also, all compounds were screened for in vivo insulin‐mimetic activity.

SYNTHESIS, CHARACTERIZATION AND ANTIMICROBIAL ACTIVITY OF SOME TRANSITION METALS COMPLEXES DERIVED FROM BIS-PYRAZOLINE BASED LIGAND

A series of binuclear transition metal complexes with a general composition of (M2L(H2O)2Cl3) where (M=Mn(II), Co(II), Ni(II) and Cu(II), L=.5,5'-(5-(tert-butyl)-2-hydroxy-1,3-phenylene)bis(3-methyl-4,5-dihydro-1H-pyrazole-1-carbothioamide) are reported herein. The new pyrazoline ligand was synthesized via the ring closure of 4,4'-(5-(tert-butyl)-2-hydroxy-1,3-phenylene)bis(but-3-en-2-one) in an alkaline solution of thiosemicarbazide after adjusting the stoichiometric ratios of the reactants. The new bis-2-pyrazoline was fully characterized by EIMS, NMR, FT-IR and elemental analyses upon completion of the TLC technique. The metal complexes of the new ligand were isolated in their solid state after adjusting the mole ratios (M:HL) 2:1 through the reaction of the metal chlorides with the ethanolic solution of the ligand (HL). The metal complexes were fully characterized by elemental analysis, molar conductance, molecular weight determination, FT-IR, UV-Visible and magnetic measurements. Molecular weight determination of these complexes indicate a binuclear nature. The octahedral geometry was confirmed on the basics of electronic spectra and magnetic measurement together with spectral and flame atomic absorption data. The zinc (II) complex was tetrahedral geometry with the formula Zn2LCl3. The complexes are non-electrolytic in nature negligible molar conductance. The anti-microbial activities of these derivatives have been studied by screening them against bacteria such as Staphylococcus aureus and Eschericheia Coli and fungi such as Aspergillus nidulece and Condida albicance by the serial dilution method.

Controlled Sol-Gel Hydrolysis for Synthesis and Characterization of Χ-Al2O3 Nano-Powder Using New Class of Precursors of Bis (N Phenylsalicylideneiminato) Aluminum(III)-Di-(μ-Isopropoxo)-Di-Isopropoxo Aluminum(III) Modified By Mono-Carboxylic Acids

Reactions of bis(N-phenylsalicylideneiminato)aluminum(III))-di-(μ- isopropoxo)-di-isopropoxoaluminum (III) with mono-carboxylic acids yield product of the type [C6H4O{CH=N(C6H5)}]2A1(μ-OPri)2Al(OOCR) (OPri)2–n [where R=CH3, C2H5, C3H7 and n=1 or 2). Progress of the reactions was monitored by estimating liberated 2-propanol in benzene-2-propanol azeotrope by oxidimetric method. All the yellow foamy solid products are soluble in common organic solvents. They were characterized by elemental analyses, FT-IR and (1H, 13C and 27Al) NMR spectral studies. Molecular weight measurements in refluxing anhydrous benzene indicate their binuclear nature. Sol-gel hydrolysis of [C6H4O{CH=N(C6H5)}]2Al(μ-OPri)2Al(OPri)2] (A), and representative compounds [C6H4O{CH=N(C6H5)}]2Al(μ- OPri)2Al(OOCCH3)(OPri)] (1) and [C6H4O{CH=N(C6H5)}]2Al(μ- OPri)2Al(OOCCH3)2] (2) followed by sintering at 600° C yielded cubic primitive phase of nano-crystallites of χ-Al2O3 [JCPDF # 040880] in all the cases, as reflected by their powder X-ray diffraction pattern. The IR, SEM and EDX studies also support the formation of the transition alumina.

Binuclear aluminum complexes supported by linked bis(β-diketiminate) ligands for ring-opening polymerization of cyclic esters

Binuclear aluminum alkyl complexes 2a–4g supported by linked bis(β-diketiminate) ligands were synthesized via the reaction of AlEt3 or AlMe3 and the corresponding proligand in a 2:1 molar ratio with moderate yields. The isolated complexes were well-characterized by 1H-NMR, 13C-NMR and elemental analysis. The binuclear nature of aluminum complex 2b was further confirmed by an X-ray diffraction study. All complexes 2a–4g could efficiently initiate the ring-opening polymerization (ROP) of e-caprolactone in toluene. The substituents at the aromatic rings and the linker unit in the auxiliary ligands exerted significant influence on the catalytic behavior of the investigated aluminum complexes. Complex 4g (R1 = R2 = Cl) containing propylenyl bridging unit exhibited the highest catalytic activity among these complexes, which might be attributed to the increased electrophilicity of the metal center as well as more opened coordination sphere. The molecular weights of obtained poly(e-caprolactone)s deviating considerably from the theoretical values indicated that the ROP of e-caprolactone by complexes 2a–4g was not well-controlled, which was also judged from the broad molecular weight distributions (MWD = 1.47–2.47) of produced poly(e-caprolactone)s. These complexes proved to be inactive toward the polymerization of rac-lactide alone. In the presence of alcohol the polymerization occurred, which was actually initiated by the decomposition species of the aluminum complex upon the treatment with isopropanol.

Elaborated studies on Schiff base homo-binuclear Cu(II) and Co(II) complexes, spectral, thermal, P-XRD and biocidal studies

A homo-binuclear Cu(II) and Co(II) complexes were synthesized using a Schiff base ligand derived by condensation of 2,6-diaminopyridine and glyoxal. The reasonable geometry of the Schiff base and its binucleating metal complexes were examined by means of elemental and thermal analyses, molar conductance, 1HNMR, UV–Vis, IR, ESR, P-XRD and mass spectra. The ligand behaved as a polydentate, coordinating through the nitrogen atom of the azomethine group, a nearest nitrogen atom of the pyridine group and the oxygen atom of a glyoxal group. From the spectral studies, a six coordinate environment around the metal dimers was confirmed. The binuclear nature of the metal complexes was assessed from their magnetic susceptibility values. Both of the Schiff base and its metal complexes were also tested for their in vitro antimicrobial activities against some bacterial and fungal strains. Schiff base and the metal complexes were also investigated for its cytotoxic effect against human breast cancer (MCF7) cell lines.

Crystal and molecular structure of novel binuclear ten coordinated praseodymium(III) with octadentateethylenediaminetetraacetate – Synthesis, characterization and antioxidant, antiviral and anticancer activities

A novel ten coordinated binuclear hydrated praseodymium(III) ethylenediaminetetraacetate with phenyl hydrazine has been synthesized and characterized by analytical, spectral and thermal techniques. The structure of the compound determined by X-ray crystallography reveals the binuclear nature of the complex with ten coordination around Pr(III) ions. Neutral phenyl hydrazine molecules present outside the coordination sphere and four inner sphere water molecules found to occupy the coordination sites (each Pr(III) ions possessing two coordinated water molecules). Among five more water molecules, four are involved in hydrogen bonding with phenyl hydrazine and EDTA4− and hence present in the second sphere. The remaining water molecule is present as bulk water. Interestingly, in the present case EDTA4− ions act as heptadentate ligand with one acetate group from each EDTA4− ion showing novel tridentate bridging behavior. The biological studies such as antioxidantal, antiviral and cytotoxicity studies reveal that this complex indeed shows promising activity.

A DFT Study on the Binuclear CuAAC Reaction: Mechanism in Light of New Experiments

In this DFT study, the mechanism of the copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction is revisited in light of recent experimental findings that made significant contributions to unraveling this challenging and important reaction. The generally accepted binuclear mechanism was used as a framework to investigate two inquiries raised by new experiments. First, Fokin et al. have proposed ligand exchanges that can take place as possible alternative pathways to the generic path and in that way they have proved the binuclear nature of the CuAAC mechanism. In this study, the experimentally proposed ligand exchanges which deviate from the generic path were modeled with NHC as the ligand and the electronic nature of the mechanism was also investigated with the NBO analyses. The results in this study are compatible with the experimental proposals, since the ligand exchange and the generic pathways’ calculated energies are on the same order. Second, possible pathways for the formation of a recently...

Electronic structure of calix[4]arene thioethers and their complexes with palladium, as studied by X-ray emission spectroscopy, X-ray photoelectron spectroscopy, and quantum chemistry

The charge state of calix[4]arene thioethers and their complexes with palladium was studied by X-ray emission spectroscopy and X-ray photoelectron spectroscopy. Experimental data were compared with the results of quantumchemical calculations. The involvement of the sulfur lone electron pairs in the coordination to Pd atoms causes a decrease in the energies of the corresponding MOs having contributions from the sulfur 3p AOs and, consequently, a decrease in the intensity of the maximum A on going from the S(Kβ) spectra of free ligands to the spectra of complexes. The binuclear nature of the complexes does not lead to the onset of significant additional interactions between two metal centers.

Synthesis and spectral characterization of copper(II) complexes derived from 2-benzoylpyridine-N4,N4-dimethyl-3-thiosemicarbazone: Crystal structure of a binuclear complex

Six copper(II) complexes [Cu2(L)2SO4]·H2O (1), [Cu2(L)2(OAc)2]·H2O (2), [Cu(L)NO3]2 (3), [Cu(L)N3]2·H2O (4), [Cu(L)NCS]·H2O (5) and [Cu(L)I] (6) of 2-benzoylpyridine-N4,N4-dimethyl-3-thiosemicarbazone (HL) were prepared and characterized using partial elemental analysis, magnetic susceptibility, conductivity measurements, FT-IR, UV–Vis and EPR studies. The molecular structure of [Cu2(L)2(OAc)2] (2a) was resolved using single crystal X-ray diffraction studies and it was found to have distorted square pyramidal geometry with the basal plane occupied by thiosemicarbazone and the acetate oxygen O2. The compound crystallized in monoclinic space group P21/n and formed a centrosymmetric dimer, bridged through oxygen of the acetate moiety. From the physicochemical studies, it was found that thiosemicarbazone coordinates through one of the pyridyl nitrogen, azomethine nitrogen and thioiminolate sulfur atoms. Binuclear nature of some of the complexes was confirmed from EPR parameters and magnetic moment values. In all complexes g values in frozen DMF, indicate the presence of the unpaired electron residing in the dx2−y2 orbital.

Synthesis, spectroscopic characterization, electrochemistry and biological evaluation of some binuclear transition metal complexes of bicompartmental ONO donor ligands containing benzo[b]thiophene moiety

A series of new binucleating Cu(II), Co(II), Ni(II) and Zn(II) complexes of bicompartmental ligands with ONO donor were synthesized. The ligands were obtained by the condensation of 3-chloro-6-substituted benzo[b]thiophene-2-carbohydrazides and 4,6-diacetylresorcinol. The synthesized ligands and their complexes were characterized by elemental analysis and various spectroscopic techniques. Elemental analysis, IR, 1H NMR, ESI-mass, UV–Visible, TG–DTA, magnetic measurements, molar conductance and powder-XRD data has been used to elucidate their structures. The bonding sites are the oxygen atom of amide carbonyl, azomethine nitrogen and phenolic oxygen for ligands 1 and 2. The binuclear nature of the complexes was confirmed by ESR spectral data. TG–DTA studies for some complexes showed the presence of coordinated water molecules and the final product is the metal oxide. All the complexes were investigated for their electrochemical activity, only the Cu(II) complexes showed the redox property. Cu(II) complexes were square planar, whereas Co(II), Ni(II) and Zn(II) complexes were octahedral. Powder-XRD pattern have been studied in order to test the degree of crystallinity of the complexes and unit cell calculations were made. In order to evaluate the effect of antimicrobial activity of metal ions upon chelation, both the ligands and their metal complexes were screened for their antibacterial and antifungal activities by minimum inhibitory concentration (MIC) method. The results showed that the metal complexes were found to be more active than free ligands. The DNA cleaving capacities of all the complexes were analyzed by agarose gel electrophoresis method against supercoiled plasmid DNA. Among the compounds tested for antioxidant capacity, ligand 1 displayed excellent activity than its metal complexes.

Tetradentate-arm Schiff base derived from the condensation reaction of 3,3′-dihydroxybenzidine, glyoxal/diacetyl and 2-aminophenol: Designing, structural elucidation and properties of their binuclear metal(II) complexes

The novel binuclear Schiff base complexes were prepared by the reaction of 3,3′-dihydroxybenzidine, glyoxal/diacetyl and 2-aminophenol in 1:2:2M ratio. The binucleating Schiff base ligand and its complexes of Cu(II), Ni(II) and VO(II) ions were characterized by elemental analysis, molar conductance, 1H NMR, infrared, electronic spectra, cyclic voltammetry, thermal, magnetic and EPR studies. The low molar conductance values of the complexes support the non-electrolytic in nature. In IR spectra, the comparison of shift in frequency of the complexes with the ligand reveals the coordination of donor atom to the metal atom. The binuclear nature of the complexes is assessed from their magnetic susceptibility values. The electronic and EPR spectra of the metal complexes provide information about the geometry of the complexes and are in good agreement with the proposed square planar geometry for Cu(II), Ni(II) and square pyramidal for VO(II) complexes. Molecular modeling has been used to suggest the structure of the complexes. The DNA cleavage ability of the complexes was monitored by gel electrophoresis using supercoiled pUC18 DNA. The metal complexes were screened for their antibacterial activities against pathogenic bacteria like Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae and Bacillus subtilis. The activity data show that the metal complexes are more potent activity than the parent Schiff base ligand against microorganisms.

Effective binuclear Pd(II) complexes for Suzuki reactions in water

A series of new ionic binuclear Pd(II) complexes supported by water‐soluble bis(α‐diimine) ligands were prepared and employed as catalysts for the palladium‐catalyzed Suzuki reaction in aqueous media. The binuclear nature of the complexes increased the reaction rate, while electronic and steric modification of the ligand frameworks had a remarkable influence upon the catalytic activity of the palladium complexes. The catalysts were shown to be homogeneous through mercury poisoning experiments and complexes could be recycled more than 10 times without loss of catalytic activity. Copyright © 2013 John Wiley & Sons, Ltd.

Synthesis and structural characterization of some binuclear acetylacetone and Schiff’s base complexes containing aluminum(III) atoms in different coordination states

Some Schiff’s base complexes of aluminum(III) of the type (CH3COCHCOCH3)2Al(µ-OPri)2AlLn(OPri)2-n [where LH=OHC(R)=CHC(R′)=NC6H5; R=R′=CH3,C6H5; R=CH3, R′=C6H5; LH=C6H4(OH)CH=NC6H5 and n=1 or 2] were prepared and characterized by various spectroscopic techniques. The molecular weight measurements indicated their binuclear nature. The 27Al nuclear magnetic resonance spectra of representative compounds [(CH3COCHCOCH3)2Al(µ-OPri)2Al{OC(C6H5)=CHC(C6H5)=NC6H5}(OPri)] [3] and [(CH3COCHCOCH3)2 Al(µ-OPri)2Al{OC(CH3)=CHC(CH3)=NC6H5}2] [6] suggest the presence of aluminum(III) atoms in different coordination states.

XAFS investigations of copper(II) complexes with tetradentate Schiff base ligands

X‐ray absorption fine structure spectra have been investigated at the K‐edge of copper in copper(II) salen/salophen complexes: [Cu(salen)] (1), [Cu(salen)CuCl2].H2O (2), [Cu(salophen)] (3) and [Cu(salophen) CuCl2].H2O (4), where salen2− = N,N′‐ethylenebis (salicylidenaminato); salophen2− = o‐phenylenediaminebis(salicylidenaminato). Complexes 1 and 3 are supposed to have one type of copper centers (called (Cu1)) and complexes 2 and 4 two types of copper centers (called (Cu1) and (Cu2)) having different coordination environments and geometries. A theoretical model has been generated using the available crystallographic data of complex 1 and it has been used for analysis of the extended X‐ray absorption fine structure (EXAFS) data of the four complexes to obtain the structural parameters for (Cu1) center. For this center, the obtained Cu–Cu distance (3.2 Å) verifies the binuclear nature of all the complexes. For determining the coordination geometry around (Cu2) center in 2 and 4, a theoretical model has been generated using the crystal structure of a Cu(II) complex, [Cu(C16H12N2O2Cl2)]. This theoretical model has been fitted to the EXAFS data of 2 and 4 to obtain the structural parameters for (Cu2) center. The present analysis shows that (Cu1) center has square pyramidal geometry involving 2N and 3O donor atoms, whereas (Cu2) center has distorted tetrahedral geometry with 2O and 2Cl donor atoms. The values of the chemical shifts and presence of typical Cu(II) X‐ray absorption near‐edge spectroscopy features suggest that copper is in the +2 oxidation state in all these complexes. The intensity of ls → 3d pre‐edge feature has been used to investigate the geometry and binuclear nature of the complexes. Copyright © 2012 John Wiley & Sons, Ltd.

Design and characterization of Cu(II) complexes from 2-benzoylpyridine benzhydrazone: Crystallographic evidence for coordination versatility

The syntheses and characterization of six copper(II) complexes of 2-benzoylpyridine benzhydrazone in the form of [Cu(BPB)(2)], [Cu(BPB)Cl].H(2)O, [Cu(BPB)Br], [Cu(2)(BPB)(2)](ClO(4))(2).4H(2)O, [Cu(BPB)N(3)].H(2)O, and [Cu(BPB)NCS].H(2)O.CH(3)OH are reported. The analytical methods used for the characterization of complexes include partial elemental analyses, IR, electronic and EPR spectra, conductivity measurements, magnetic susceptibility measurements and single crystal X-ray diffraction. From the crystal structure, it is clear that the hydrazone adopts the E conformation about the azo bond to attach to the metal through the N(py)-N(azo)-O chelating system. In the EPR spectra of complexes in DMF at 77K four hyperfine quartets in the parallel region could be resolved and a half field signal is observed at 1500 G for complex [Cu(2)(BPB)(2)](ClO(4))(2).4H(2)O in polycrystalline state at 298 K which gives evidence for its binuclear nature indicating a weak interaction between the two Cu(II) ions.

Synthesis of rhodium(III) complexes with tris/tetrakis‐benzimidazoles and benzothiazoles—quick identification of cyclometallation by nuclear magnetic resonance spectroscopy

Reactions of rhodium(III) halides with multidentate N,S-heterocycles, (LH3) 1,3,5-tris(benzimidazolyl)benzene (L1H3; 1), 1,3,5-tris(N-methylbenzimidazolyl) benzene (L2H3; 2) and 1,3,5-tris(benzothiazolyl)benzene (L3H3; 3), in the molar ratio 1:1 in methanol-chloroform produced mononuclear cyclometallated products of the composition [RhX2(LH2)(H2O)] (X = Cl, Br, I; LH2 = L1H2, L2H2, L3H2). When the metal to ligand (1-3 or 1,2,4,5-tetrakis(benzothiazolyl)benzene [L4H2; 4]) molar ratio was 2:1, the reactions yielded binuclear complexes of the compositions [Rh2Cl5(LH2)(H2O)3] (LH2 = L1H2, L2H2, L3H2) and [Rh2X4(L4)(H2O)2] (X = Cl, Br, I). Elemental analysis, IR and 1H nuclear magnetic resonance (NMR) chemical shifts supported the binuclear nature of the complexes. Cyclometallation was detected by conventional 13C NMR spectra that showed a doublet around approximately 190 ppm. Cyclometallation was also detected by gradient-enhanced heteronuclear multiple bond correlation (g-HMBC) experiment that showed cross-peaks between the cyclometallated carbon and the central benzene ring protons of 1-3. Cyclometallation was substantiated by two-dimensional 1H-1H correlated experiments (gradient-correlation spectroscopy and rotating frame Overhauser effect spectroscopy) and 1H-13C single bond correlated two-dimensional NMR experiments (gradient-enhanced heteronuclear single quantum coherence). The 1H-15N g-HMBC experiment suggested the coordination of the heterocycles to the metal ion via tertiary nitrogen.