The structure of μ-oxo dimer of aluminium(III) porphyrin: a theoretical study

The gas-phase molecular structure of μ-oxo dimer of aluminium(III) porphyrin, (AlP)₂O, has been studied for the first time by density functional theory calculations using the B3LYP and M06 functionals and triple-ζ valence basis sets. The molecule has two conformers with equilibrium structures of D _4d and D _4h symmetries with parallel macrocycles and aluminium-oxygen distances of 1.680–1.684 Å (M06/cc-pVTZ). The aluminium atom lies out of the plane of the four central nitrogen atoms and forms a square-based pyramid with them, with the following parameters (M06/cc-pVTZ): r(Al–N) = 2.030–2.031 Å, r(N···N) = 2.803–2.804 Å (the side of the pyramid base), z(Al)–z(N) = 0.434–0.446 Å (the height of the pyramid).     

A μ(1,1)- or μ(1,3)-carboxylate bridge makes the difference in the magnetic properties of dinuclear Mn(II) compounds

Six new dinuclear Mn(II) compounds with carboxylate bridges have been synthesized and characterized by X-ray diffraction: [{Mn(phen)(2)}(2)(μ-RC(6)H(4)COO)(2)](ClO(4))(2) with R = 2-Cl (1), 2-CH(3) (2), 3-Cl (3), 3-CH(3) (4), 4-Cl (5) and 4-CH(3) (6). Compounds 1 and 2 show two μ(1,3)-carboxylate bridges in a syn-anti mode while compounds 3-6 present a very uncommon coordination mode of the carboxylate ligand: the μ(1,1)-bridge. The magnetic properties of these compounds are very sensitive to the bridging mode of the carboxylate ligands. While compounds 1 and 2 (μ(1,3)-bridge) display antiferromagnetic interactions, with J values of -1.41 and -1.66 cm(-1), respectively, compounds 3-6 (μ(1,1)-bridge) show ferromagnetic interactions, with J values of 1.01, 0.98, 1.04 and 1.06 cm(-1), respectively. It is worth noting that compounds 3-6 are the first of their class to be magnetically characterized. The EPR spectra at 4 K for compounds with antiferromagnetic coupling (1 and 2) are more complex than those for compounds with a ferromagnetic interaction (3-6). Quite good simulations can be obtained with the ZFS parameters of the Mn(II) ion D(Mn) ~ 0.095 cm(-1) and E(Mn) ~ 0.025 cm(-1) for compounds 1 and 2 and D(Mn) ~ 0.060 cm(-1) and E(Mn) ~ 0.004 cm(-1) for compounds 3-6.     

Syntheses of (imidazole)pentaamminemetal(III) and μ-imidazolatodecaamminedimetal(III) complexes from trifluoromethanesulfonato precursors

The [M(NH₃)₅(imidH)]³⁺ complex ions (M = Co, Rh or Ir; imidH = imidazole) can be readily prepared by reaction of [M(NH₃)₅(OSO₂CF₃)]²⁺ ions with imidazole in sulfolane. Subsequent reaction of [M′(NH₃)₅(OSO₂CF₃)]²⁺ with [M(NH₃)₅(imidH)]³⁺ in sulfolane in the presence of a non-coordinating base permits synthesis of the binuclear imidazolate-bridged complexes [(NH₃)₅M(imid)M′(NH₃)₅]⁵⁺ (M = M′= Co or Rh; M = Co, M′ = Rh), characterized by spectroscopic, chromatographic and voltammetric methods, and by reactivity.     

Crystal structure of a μ-oxo-bridged dimeric iron(III) complex

A dimeric [{Fe(5-ClL1)}₂(μ-O)], [H₂-5-ClL1 = N,N′-bis(5-chloro-2-hydroxybenzylidene)-2-methylpropane-1,2-diamine] tetradentate Schiff-base complex, 1, has been synthesized and its crystal structure has been determined by single crystal X-ray diffraction analysis. Structural analysis of complex 1 shows that the complex is a centrosymmetric dimer. Each of the Fe(III) ions has a five-coordinate geometry and one oxygen atom bridges two Fe(III) ions to form a μ-oxo structure. The geometry around iron atom can be described as a square based pyramid with the FeN₂O₂ coordination plane and oxo ligand.     

Formation of nitridotechnetium (VI) μ-oxo dimer complexes with EDTA and EDDA

Reactions of [⁹⁹TcNCl₄]^– with ethylenediaminetetraacetic acid (EDTA) and ethylenediamine-N, N-diacetic acid (EDDA) in a mixture of water and acetone gave Tc^VIN-EDTA and Tc^VIN-EDDA complexes. The infrared spectra of both reaction products showed the existence of the TcN and C=O groups. The elemental analysis indicated the 11 TcN-ligand ratio in the EDTA and EDDA complexes. Electrophoresis showed that the Tc^VI-EDTA complex was an anionic species in a perchlorate solution. For the Tc^VIN-EDDA complex, neutral and anionic species were formed, depending on the pH of the solution. Formation of the -oxo dimer complexes was suggested from the UV-Vis absorption spectra.     

Coordination chemistry of 1,4-bis(carboxymethyl)-1,4,7-triazacyclononane: Synthesis and characterization of mononuclear and binuclear μ-oxo-bridged iron(III) complexes,and a 1D-helical copper(II) chain

The syntheses of the pentadentate ligand 1,4-bis(carboxymethyl)-1,4,7-triazacyclononane (LH₂) and its use in the preparation of [LHCu]ClO₄ (1), and a mononuclear iron(III) complex ([LFeCl] (2)) are reported. The hydrolysis of 2 in the presence of an excess of NaClO₄ resulted in the crystallization of a binuclear complex, [Fe₂(μ-O)L₂] · (NaClO₄)₃ · CH₃OH · 3H₂O (3). The crystal structures of 1–3 have been determined by single-crystal X-ray crystallography. In complex 1, the Cu(II) centre is in square based pyramidal environment, with two nitrogen atoms from the tacn ring and two oxygen atoms from two different carboxylate groups lying in the basal plane and the third nitrogen atom occupying the apical position. One pendant acetic acid group is protonated and, instead of coordinating to the copper(II) centre, participates in hydrogen bonding interactions with the perchlorate counter-ion. The coordinated carboxylate group forms a bridge to the copper atom of an adjacent [LHCu]⁺ molecule, thus generating 1D-helical chains. The compound exhibits weak ferromagnetic coupling probably due to weak interactions between [LHCu]⁺ molecules. In complex 2, the iron(III) centre is in a distorted octahedral geometry, with the fac-coordinated triamine ring, two carboxylate groups and one chloride ligand occupying the coordination sphere. In the binuclear complex 3, two iron(III) centres are bridged by one oxygen atom to form a μ-oxo-diiron(III) complex with an Fe?Fe distance of 3.423(3) Å and a non-linear Fe–O–Fe angle of 144.4°. This binuclear complex features strong antiferromagnetic coupling between the two iron(III) centres.     

Synthesis and characterization of a novel Mn(III)-(γ-diketone) complex with catalytic and antifungal activity

Abstract

A novel Mn(III) complex with γ-diketone having general formula [Mn(hdo)₃], where hdo?=?hexane-2,5-dione ligand, has been synthesized and characterized using UV–vis, FT-IR, ESI-mass and EPR spectra, elemental analysis, powder X-ray diffraction, SEM, and magnetic susceptibility measurements. The X-ray diffraction studies reveal that it has monoclinic lattice system with C₂/C space group and the unit cell dimensions are a?=?9.92245 Å, b?=?10.50696 Å, and c?=?9.80835 Å. The particle size of this complex has been found to be 32.1?nm. The complex was evaluated for its antifungal activity against Aspergillus flavus, Aspergillus niger, and Aspergillus terreus fungal species. The results indicate that the minimum inhibitory concentration of the synthesized complex was 8?ppm for A. niger while for A. flavus and A. terreus it was 6?ppm. β-Diketone Mn(III) complexes inhibit the fungal growth only partially. This communication is the first report of transformation of a keto-group to an ester group catalyzed by a metal complex.     

Structure and magnetic properties of a decanuclear Mn(II)₂Mn(III)₂Dy₆ aggregate

Using glycerol (H?gly) as a primary ligand, the decanuclear aggregate [Mn(II)?Mn(III)?Dy?(μ?-OH)?(Hgly)?(H?gly)?-(PhCO?)??(H?O)?]·10CH?CN (1) has been synthesised; it has a structure built up from two Mn?Dy? heterocubane units linked through a central Dy?(μ-benzoate)? paddle-wheel dimer and shows slow relaxation of its magnetisation.     

Jahn-Teller distortion,ferromagnetic coupling,and electron delocalization in a high-spin Fe–Fe bonded dimer

Fe₂(N,N’-diphenylformamidinate)₄, 1, first synthesized in 1994, is one of very few non-organometallic compounds with Fe–Fe distances, (2.46 Å) suggestive of an Fe–Fe bond. The electronic structure of 1 has been unclear because of its distorted D₂ geometry, as well as its reported S = 4 ground state. Computational investigations using DFT methods have shown that the D₂ geometry is the result of a Jahn-Teller distortion away from D₄ symmetry, in which the ground state would be orbitally degenerate. Broken symmetry methods have shown that ferromagnetic coupling between the two high-spin Fe(II) ions in 1 is a consequence of spin delocalization caused by a three-electron σ bond and a weaker three-electron δ bond between the Fe atoms. The relationship between ferromagnetic coupling and an Fe–Fe bond is established from results using hybrid functionals having variable amounts of Hartree-Fock exchange, which is found, surprisingly, to mitigate Fe–Fe bonding.     

3D Heterometallic (3d–4f) coordination polymers: A ferromagnetic interaction in a Gd(III)–Cu(II) couple

Four 3d–4f heterometallic coordination polymers, [Cu₃(IDA)₆Ln₂] · n(H₂O) [IDA =  iminodiacetate dianion; Ln = Gd, n = 3 (1); Ln = Nd, n = 6 (2); Ln = Sm, n = 6 (3)] and [Cu(Cl)(NTA)Sm(H₂O)₆] · (ClO₄) · (H₂O) (4) [NTA = nitrilotriacetate trianion], have heen synthesized and characterized by single crystal X-ray diffraction analysis. Complexes 1–3 are isomorphous, showing a 3D coordination framework having tubular channels filled by lattice water molecules running parallel to the c axis. Whereas complex 4 is a 1D polymer of alternating copper and samarium ions connected by NTA, and the chains get involved in H-bonding interactions resulting in a 3D network. A low temperature magnetic study reveals ferromagnetic interactions for complex 1. Thermogravimetric and X-ray powder diffraction analyses of 1, 2 and 3 show that the covalently bonded 3D network remains almost unaffected after deaquation.     

Cyanide-bridged bi- and trinuclear heterobimetallic Fe(III)–Mn(III) complexes: Synthesis,crystal structures and magnetic properties

By employing trans-dicyano or pentacyanometalate as building block and using a bicompartimental Schiffbase based manganese(III) compound as assemble segment, two new cyanide-bridged heterometallic Fe(III)–Mn(III) complexes {[Mn(L)(H₂O)][Febpb(CN)₂]}·2CH₃OH (1) and {[Mn(L)(H₂O)]₂··[Fe(CN)₅NO]} (2) (bpb^2– = 1,2-bis(pyridine-2-carboxamido)benzenate, L = N,N'-ethylene-bis(3-ethoxysalicylideneiminate) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis reveals binuclear FeMn and trinuclear FeMn₂ structure, respectively, in which the cyanide precursor acts as mono- or bidentate ligand to connect the Mn(III) Schiff-base unit(s). Furthermore, these two complexes are self-complementary through coordinated aqua ligands from one complex and the free O₄ compartments from the neighboring complex, giving dimeric and 1D single chain supramolecular structure. Investigation of the magnetic susceptibility of 1 reveals weak antiferromagnetic coupling between the adjacent Mn(III) ions. Based on the binuclear FeMn model, best fit of the magnetic susceptibilities of 1 leads to the magnetic coupling constants J =–1.37 cm^–1 and zJ′ =–0.72 cm^–1 (1).     

Crystal structure and thermal stability of A μ1,1-(OMe)-bridged dimeric Schiff base iron(III) complex

A new μ_1,1-OMe-bridged dimeric iron(III) complex, [Fe₂L₂(μ_1,1-OMe)₂(NCS)₂], where L is the deprotonated form of 2-[(2-ethylaminoethylimino)methyl]-5-methoxyphenol, has been prepared and structural characterized by elemental analysis, IR spectrum, and single crystal X-ray crystallography. The complex crystallizes in the monoclinic space group P2₁/c, with unit cell dimensions a = 10.156(1) Å, b = 11.972(1) Å, c = 14.256(2) Å, β = 102.643(3)°, V = 1691.3(3) ų, Z = 2, R ₁ = 0.0394, and wR ₂ = 0.0922. Each Fe atom in the complex is in an octahedral coordination. The Fe...Fe distance is 3.102(1) Å. The thermal stability of the complex was studied.     

Synthesis, characterization and magnetism of μ-chloranilato bi-nuclear chromium (III) complexes

Five new chloranilato-bridged binuclear chromium (III) complexes have been synthesized and identified as [Cr2(CA)L4]-(ClO4)4[L denotes 5-methyl-1,10-phenanthroline (Me-phen); 2,9-dimethyl-1, 10-phenanthroline ( Me2-phen); 5-chloro-1,10-phenanthroline(Cl-phen); diaminoethane (en) or 1,3-diaminopropane (pn)], where CA represents the dianion of chloranilic acid. Based on elemental analyses, molar conductivity and magnetic moment of room-temperature measurements, and IR and electronic spectral studies, it is proposed that these complexes have CA-bridged structures and consist of two chromium (III) ions, each in an octahedral environment. The complexes [Cr2(CA)(Me-phen)4](ClO4)4(1) and [Cr2(CA)(Me2-phen)4](ClO4)4(2) were further characterized by variable temperature (4.2-300 K) magnetic susceptibility measurements and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, , giving the exchange parameter J = -7.8 cm-1 for (1) and J= -6.5 cm*1 for (2). This result     

Synthesis,crystal structure,and properties of a μ3-oxo-trichromium(III) propionate cluster with pyrazole

A new μ₃-oxo trinuclear chromium(III) propionate cluster, [Cr₃(μ₃-O)(O₂CCH₂CH₃)₆(pyr)₃]NO₃·0.25(H₂O) (1), has been synthesized by reaction of a μ₃-oxo trinuclear chromium(III) propionate precursor [Cr₃(μ₃-O)(O₂CCH₂CH₃)₆(H₂O)₃]NO₃ with a pyrazol ligand (pyr) and characterized by IR spectroscopy, single-crystal X-ray structure determination, and thermal analysis. Magnetic susceptibility and magnetization studies revealed antiferromagnetic exchange interactions within the trinuclear Cr(III) cluster (J = ?11.9 cm^?1) and determined the electronic ground state (S = ½) of the compound.     

Synthesis and crystal structures of bis(cyclopentyl)gallium phenoxide dimer and bis (cyclopentyl) gallium naphthoxide dimer

Tricyclopentylgallium reacted with phenol, naphthol respectively to yield phenox-ide (or naphthoxide) of biscyclopentylgallium which have been characterized by elemental analysis, IR, 1H NMR and mass spectrometry. X-ray diffraction analysis of compound 1 indicated that it belongs to the monoclinic system, space groups P21/c, with cell constants 0=9.602(3), 6=14.365(7), c=11.256(4)A, and β=97.54(3)°, Z=2(dimers), R=0.0706. Compound 2 assigned to the triclinic system, space groups P1 with cell constants a=9.392(4), 6=9.928(7), c=11.263(7) A, a=112.48(5), β=104.74(4), γ=99.95(5)°, and Z=l(dimers), R=0.0526. The molecule of 1 or 2 contains an oxygen-bridged coplanar Ga2O2 four-membered ring respectively.     

A Kagomé layer-based 3D Mn(II) framework showing coexistence of spin-canting, spin-frustration, field-induced metamagnetic and spin-flop transitions

A novel 3D Mn(II) coordination framework with Kagomé sublattice, [Mn(3)(py)(2)(nip)(2)](n) (py(-) = 2-((1H-tetrazol-5-yl)methyl)pyridine and nip(2-) = 5-nitroisophathalate), was in situ solvothermally synthesized and shows the coexistence of spin-canting, spin-frustration as well as field-induced metamagnetic and spin-flop transitions at 2.9 K.     

Comparative ONIOM modeling of 1,3-butadiene polymerization using Nd(III) and Gd(III) Ziegler–Natta catalyst systems

On the base of structural and thermodynamic data using modern methods of quantum chemistry, a comparative theoretical study of the elementary acts of initiation and growth of a polymer chain during the polymerization of 1,3-butadiene was carried out. Ziegler–Natta catalysts based on Nd(III) and Gd(III) were used as polymerization initiators. It was shown that the higher stereospecificity of the action of gadolinium catalytic complexes in comparison with neodymium complexes is due to the increased stability of the anti-form of the π-allylic terminal structure of the growing polymer chain, and the reduced activity is due to the higher activation energy of the processes of initiation and chain growth.     

Structural Diversity in Cyclometalated Diiridium(III) Complexes with Bridging syn and anti μ2-Oxamidato and μ2-Dithioxamidato Ligands

Six new diiridium complexes containing 2-methyl-6-phenylpyridyl as the cyclometalating ligand with a μ₂-oxamidato or a μ₂-dithioxamidato ligand as the bridge have been synthesized in 60–73 % yields. These complexes were revealed by multinuclear NMR spectroscopy to contain inseparable mixtures of diastereomers (rac, ΔΔ/ΛΛ and meso, ΔΛ) with bridges in anti and syn configurations. The remarkable variety of isomers present was confirmed by X-ray crystallography on single crystals grown from mixtures of each complex. In one complex with a N,N’-bis(4-trifluoromethylphenyl)-μ₂-oxamidato bridge, two single crystals of anti and syn isomers were structurally determined. Two single crystals of the μ₂-dithioxamidato bridge complex were found to contain rac and meso forms of the syn isomer. Hybrid DFT computations on the four isomers of each diiridium complex revealed negligible energetic preferences for one isomer despite the methyl groups in the 2-methyl-6-phenylpyridyl cyclometalating ligands being close to the neighboring methyl groups and the bridge, thus supporting the experimental findings of isomer mixtures. Two distinct broad emissions with maxima at 522–529 nm and at 689–701 nm observed in these complexes in dichloromethane are attributed to mixed metal-ligand to ligand charge transfer (MLLCT) excited states involving the pyridyl and bridge moieties respectively with the aid of electronic structure computations.