Syntheses and crystal structures of mono-, di- and trinuclear cobalt complexes of a salen type ligand

Three cobalt complexes containing the salen type ligand, bis(salicylidene)-meso-1,2-diphenylethylenediaminato (mdpSal²⁻), are reported. The complexes differ in nuclearity and include the mononuclear, Co(mdpSal) (1), which contains a Co(II) metal center bound to one mdpSal⁻² ligand frame in a square planar geometry. The second complex is the dinuclear [Co(mdpSal)Cl]₂ (2) in which both cobalt ions have been oxidized to the +3 oxidation state. The overall geometry of complex 2 is an edge-sharing bioctahedron with the coordination sphere around each cobalt metal center consisting of one mdpSal⁻² ligand and one Cl⁻ ion. The shared edge between the Co(III) ions contains two bridging phenolate groups, one from each ligand frame. Complex 3 is a linear, mixed valence, trinuclear species, [Co(mdpSal)(OAc)(μ-OAc)]₂Co, with the oxidation states of the metal centers assigned as Co(III)-Co(II)-Co(III). The terminal Co(III) centers are equivalent with the central Co(II) lying on the inversion center of the molecule. Each cobalt ion in 3 adopts an octahedral geometry with the terminal Co(III) ions being bound to one mdpSal²⁻ ligand each. All phenolate groups bridge to the central Co(II). The coordination sphere about each metal center in the trinuclear complex is completed by four acetate groups, two of which bind in a μ-fashion bridging from the terminal Co(III) metal centers to the central Co(II). The complexes have been characterized by X-ray crystallography as well as UV-Vis and IR spectroscopy.     

Synthesis of camphecene derivatives using click chemistry methodology and study of their antiviral activity

A series of seventeen tetrazole derivatives of 1,7,7-trimethyl-[2.2.1]bicycloheptane were synthesized using click chemistry methodology and characterized by spectral data. Studies of cytotoxicity and in vitro antiviral activity against influenza virus A/Puerto Rico/8/34 (H1N1) in MDCK cells of the compounds obtained were performed. The structure-activity relationship analysis suggests that to possess virus-inhibiting activity, the compounds of this group should bear oxygen atom with a short linker (C2-C4), either as a hydroxyl group (18, 19, 29), keto-group (21) or as a part of a heterocycle (24). These compounds demonstrated low cytotoxicity along with high anti-viral activity.     

Synthesis and structural diversity of 2-pyridylmethylideneamine complexes of zinc(II) chloride

The addition reactions of zinc(II) chloride to N-substituted pyridine-2-carbaldimines [Py-CHNR, R = Me (1a), Ph (1b), Bz (1c), allyl (1d)] lead to different complexes dependent on the N-bound substituent R. The 1:1 complexes show molecular structures of the type [(Py-CHNR)ZnCl₂] for R = methyl (2a), phenyl (2b), and allyl (2d) with a distorted tetrahedral environment for the zinc atom. The zinc complex with the N-methylated pyridine-2-carbaldimine also forms a dimer of the type [(Py-CHNR)ZnCl₂]₂ (2a)₂ with a square pyramidal coordination sphere of zinc. A 3:2 stoichiometry is observed for R = benzyl and an ion pair of the type [Zn(Py-CHNR)₃]²⁺ [ZnCl₄]²⁻ (2c) is found in the solid state.     

Synthesis and characterization of 2-quinoxalinol Schiff-base metal complexes

The reaction of uranyl acetate with (2,2′-(1E,1′E)-(2-benzyl-3-hydroxyquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene) diphenol) (H₂L1) at room temperature in methanol and chloroform yields the UO₂L1 complex. Crystals were grown through solvent diffusion of the ligand-metal complex in dimethyl formamide with diethyl ether to prepare: UO₂L1 · DMF (1). Complexes with 2,2′-(1E,1′E)-(2-benzyl-3-hydroxyquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dibenzene-1,4-diol (H₂L2) and 2,2′-(1E,1′E)-(2-hydroxy-3-isopropylquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)diphenol (H₂L3) were also prepared, and crystals of the uranyl complexes (UO₂L2 · DMF (2) and (3)) grown from DMF/ether. A fourth complex UO₂L4 · H₂O (4) was prepared through layering a solution of the tetra-tert-butyl substituted 2-quinoxalinol salen ligand H₂L4 in acetone with an aqueous solution containing uranyl acetate. The complexes exhibit a symmetric core featuring a slightly distorted bicapped pentagonal geometry around the uranium center with two oxo-groups and two imine groups from the ligand chelating the ligand and the fifth site in the coordination plane of the ligand occupied by a solvent molecule. These compounds have been characterized using solution (NMR and UV-Vis) and solid-state (IR, X-ray crystallography) techniques. Complexes of H₂L4 with early transition metals; Mn²⁺, Co²⁺, Ni²⁺, and Cu²⁺ are also prepared and characterized for comparison of solution and spectroscopic characteristics.