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Relevant academic research and scientific papers

Probing the reactivity of oxomanganese-salen complexes: An electrospray tandem mass spectrometric study of highly reactive intermediates

Electrospray ionization in combination with tandem mass spectrometric techniques has been employed to study the formation of oxomanganese-salen complexes upon oxidation of [MnIII(salen)]+ cations as well as the properties and reactions of the oxidized species in the gas phase. Two species could be characterized as the principal oxidation products: the oxomanganese(V) complex, [Mn=O(salen)]+, which is the actual oxygen-transfer agent in epoxidation reactions, and the dinuclear, μ-oxo bridged [L(salen)Mn-Q-Mn-(salen)L]2+ with two terminal ligands L; the latter acts as a reservoir species. The effects of various substituents in the 5-and 5′-positions, respectively, of the salen ligand on the reactivity of the epoxidation catalyst were determined quantitatively from CID (collision-induced dissociation) experiments and B3LYP density functional calculations. Accordingly, the effect of axial donor ligands on the reactivity of the epoxidation catalyst was studied. Electron-withdrawing substitutents on the salen ligand and additional axial ligands decrease the stability and thus enhance the reactivity of the Mn=O moiety, while electron-donating salen substituents have a strong stabilizing effect. WILEY-VCH Verlag GmbH, 2001.

Synthesis and crystal structures of N,N'-bis(5-fluoro-2-hydroxybenzylidene) ethane-1,2-diamine and its dinuclear manganese(III) complex with antibacterial activities

A new dinuclear manganese complex, [Mn2L2(N 3)2], was prepared by reaction of bis-Schiff base N,N'-bis(5-fluoro-2-hydroxybenzylidene)ethane-1,2-diamine (H2L) with manganese acetate and sodium azide in methanol. Both the Schiff base and the complex were characterized by physico-chemical methods and single crystal X-ray determination. The Schiff base crystallized in the orthorhombic space group Pbca with unit cell dimensions a = 7.3191(7) A, b = 6.0948(6) A, c = 35.382(3) A, V = 1578.3(3) A3, Z = 4, R1 = 0.0481, wR2 = 0.1488. The manganese complex crystallized in the monoclinic space group P21/c with unit cell dimensions a = 8.802(1) A, b = 14.928(2) A, c = 14.478(2) A, β = 105.517(2)°, V = 1833.0(4)A3, Z = 2, R1 = 0.0768, wR2 = 0.1640. There are crystallographic inversion centers in both the ligand and the complex. The ligand coordinates to Mn through all the phenolate oxygens and imino nitrogens. The two Mn in the complex are bridged by two phenolate oxygens with separation of 3.549(1) A. Each Mn is octahedral with four donors of the Schiff base ligand defining the equatorial plane, and with one azido nitrogen and one phenolate oxygen of an adjacent Schiff base ligand occupying the axial positions. The Schiff base and the complex were tested in vitro for their antibacterial activities.

Synthesis, X-ray structural characterization, and catalytic property of an end-to-end azido-bridged polymeric manganese(III) complex derived from N,N?-bis(5-fluorosalicylidene)-1,2-diaminoethane

A new end-to-end azido-bridged polymeric manganese(III) complex [MnL(μ1,3-N3)]n with the Schiff base ligand N,N?-bis(5-fluorosalicylidene)-1,2-diaminoethane (H2L), has been synthesized and structurally characterized by physicochemical methods and single-crystal X-ray determination. Crystal of the complex crystallizes in orthorhombic space group Pca21, with a=10.8211(5), b=13.4644(6), c=11.1811(5)?, V=1629.08(13)?3, Z=4, R1=0.0255, wR2=0.0653, GOOF=1.053. X-ray analysis indicates that the complex is an end-to-end azido-bridged polymeric manganese species. The Mn atom is coordinated in an octahedral coordination by two phenolate O and two imine N atoms from the Schiff base ligand, and two azido N atoms. The catalytic property for epoxidation of styrene by the complex was evaluated.

Manganese(III) complexes derived from bis-Schiff bases: Synthesis, structures, and antimicrobial activity

Manganese(III) complexes derived from the bis-Schiff bases N,N′-bis(5-fluorosalicylidene)-1,2-diaminoethane (H2La) and 3,4-bis(2-hydroxybenzylideneamino)pyridine (H2Lb), respectively, have been prepared and characterized by elemental analyses, IR, and single crystal X-ray crystallographic determination (CIF files CCDC nos. 997243 (I), 995896 (II)). The crystal of [MnLa(μ1,3-N3)] n (I) is orthorhombic: space group Pca21, a = 10.723(1), b = 13.430(1), c = 11.112(1) ?, V = 1600.2(2) ?3, Z = 4, R 1 = 0.0264, wR 2 = 0.0649. The crystal of [MnLb(N3)(CH3OH)] (II) is monoclinic: space group C2/c, a = 22.792(1), b = 14.4442(7), c = 12.8637(6) ?, β = 119.262(1)°, V = 3694.5(3) ?3, Z = 8, R 1 = 0.0367, wR 2 = 0.0776. The bis-Schiff base ligands coordinate to the metal atoms through phenolate O and imine N atoms. Each metal atom in the complexes is in octahedral coordination. The effects of the complexes on the antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans were studied.

Synthesis, Structures, and Antibacterial Activities of Two Methanol Coordinated Zinc Complexes with Tetradentate Bis-Schiff Bases

Two methanol coordinated zinc(II) complexes, [Zn(L1)(MeOH)] (I) and [Zn(L2)(MeOH)] (II), where L1 and L2 are the dianionic form of N,N'-bis(5-fluorosalicylidene)ethane-1,2-diamine and N,N'-bis(5-fluorosalicylidene)propane-1,2-diamine, respectively, have been synthesized and characterized by physical chemical methods and single crystal X-ray diffraction (CIF files CCDC nos. 950907 (I) and 950908 (II)). Crystallographic data for I: triclinic, P1 ˉ , a = 8.8765(8), b = 9.6577(9), c = 10.5117(9) ?, α = 114.590(2)°, β = 91.648(3)°, γ = 97.114(3)°, V = 809.87(13) ?3, Z = 2, R1 = 0.0307, wR2 = 0.0698. Crystallographic data for II: orthorhombic, Pca21, a = 22.946(2), b = 7.6942(7), c = 9.6234(8) ?, V = 1699.0(2) ?3, Z = 4, R1 = 0.0320, wR2 = 0.0676. X-ray crystal structural study indicated that the coordination environment around each zinc(II) atom in the complexes is a five-coordinated distorted pyramid in which the apical position is occupied by a methanol oxygen atom, and the basal plane is defined by the nitrogen and oxygen donor atoms of the Schiff base ligand. The antibacterial activities of the complexes were assayed.

Influences of polarizability effect of alkyl group and homoring competition effect of substituents on the NMR spectra of salen-type Schiff base

Salen-type Schiff bases are a kind of important compounds and are widely used. In order to explore the effect of alkyl groups and substituents attached to aromatic ring on the chemical shifts, 63 title compounds were synthesized. Their 1H NMR and 13C NMR spectra were obtained; and the effects of the alkyl chain length and substituents on the chemical shifts (δH(CH=N), δC(CH=N), δH(OH), and δC(C-OH)) were studied. The results show that (1) the alkyl polarizability effect index (PEI) has an important influence on the chemical shifts of the above four atoms, with the increase of PEI, the values of δH(CH=N) and δc(CH=N) decrease, and the values of δH(OH) and δC(C-OH) increase. (2) The influence of substituent X attached to aromatic ring on the chemical shift is related to its position by taking OH or CH=N as reference. As for the effect of substituent on the chemical shifts, the effect of Hammett constant σ(X)-OH and excited-state substituent parameter (Formula presented.) with OH as reference are different from that ofσ(X)-CH=N and (Formula presented.) with CH=N as reference, and there is a “homoring competition effect” of the substituent. (3) The effect of the cross-interaction between X and OH on the chemical shift is also significantly different due to the different position of X. Quantitative correlation equations against chemical shifts were built for the four atoms, and the stability and prediction ability of the obtained equations were confirmed by leave-one-out cross validation.

Enhancing single-molecule magnet behaviour through decorating terminal ligands in Dy2 compounds

The utilization of two isomorphic ligands with different substituents leads to two centrosymmetric DyIII dimers, namely, [Dy2(bfbpen)2(H2O)2]·2I- (1) and [Dy2(bcbpen)2

Synthesis, structural characterization, and antibacterial activity of Cu(II) and Zn(II) complexes with tetradentate Schiff bases

Biological activity study on Cu(II) and Zn(II) complexes is a challenging issue because of the activity of ligands could be modulated by complexation. A new dinuclear copper(II) complex, [Cu2(L1)2]·2CH3OH (1), a