Synthesis, crystal structure and spectroscopic behaviors of Co(II) and Cu(II) complexes with Salen-type bisoxime ligands

Two Salen-type ligands (H₂L¹, 4,4′-dichloro-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol and H₂L², 4,4′-dinitro-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) and their corresponding complexes ({[CoL¹(MeOH)]₂(OAc)₂Co} · 2MeOH and [CuL²]₂) have been synthesized and characterized by element analyses, ¹H NMR, FT-IR and UV-Vis spectra, TG-DTA and single crystal X-ray crystallography. Crystallographic data suggests the octahedral geometry for Co(II) complex and square-pyramidal geometry for Cu(II) complex. Furthermore, the fluorescence behavior of Cu(II) complex in DMSO is discussed.     

ESR evidence of the formation of a new superoxide complex of tetra-p-tolyporphyrinatocobalt(II) in aprotic solvents

The reactions of the superoxide ion (O₂⁻) with tetra-p-tolyporphyrinatocobalt(II) [Co(II)TTP] in dimethyl sulfoxide(DMSO) have been investigated by use of electron spin resonance (ESR) spectroscopy. In the absence of oxygen, Co(II)TTP in DMSO gives the DMSO adduct, Co(II)(TPP)(DMSO). When this DMSO adduct is exposed to air, an oxygen complex, Co(II)(TTP)(DMSO)(O₂), is formed in which the binding state between Co(II) and O₂ has been considered formally as Co(III)O₂⁻. When the superoxide ion (O₂⁻ is added to this oxygen complex, a new superoxide complex, Co(II)(TTP)(O₂⁻)₂, is formed. The same superoxide adduct is formed by the reaction of O₂⁻ with Co(II)TTP in the absence of oxygen.     

Cobalt(II) and nickel(II) complexes with nitrogen-sulfur tripod ligands. Crystal and molecular structure of the five-coordinate complex bromotris(2-tert-butylthioethyl)aminecobalt(II) hexafluorophosphate (NS3Br donor set)

The tripod ligands tris(2-alkylthioethyl)amine, with alkyl = ethyl, iso-propyl, and tert-butyl, give with cobalt(II) and nickel(II) halides high-spin complexes with formulae [MLX₂], [MLX]Y, and [MLX]₂[MX₄] (where X = Cl, Br, I; Y = BPh₄, PF₆). The nickel complexes are either six- or five-coordinate: the coordination number decreases as the bulkiness of the alkyl group bound to the sulfur is increased. All the cobalt complexes contain the five-coordinate cation [CoLX]⁺. The crystal and molecular structure of the [Co(NS₃-t-Bu)Br]PF₆ complex has been determined by standard X-ray methods, and refined to R = 0.061. The crystals are monoclinic, space group P2¹/n. The unit cell dimensions are: a = 27.420 (2), b = 11.923 (4), c = 17.082 (1) Å, β = 102.40 (1)°, Z = 8. The complex cation has a trigonal bipyramidal geometry with the nitrogen and bromine atoms at the apexes, and the three sulfur atoms in the equatorial plane. The tetrahedral distortion is relatively small (mean BrCoS angle = 98.5°), and similar to that found for the [Co (Me₆tren)Br]Br complex [Me₆tren = tris(2-dimethylaminoethyl)amine).     

Synthesis and characterization of tris(heteroleptic) diimine complexes of chromium(III)

A preparative procedure of potentially wide applicability is described for the synthesis of previously unreported tris(heteroleptic) [Cr(diimine)₃]³⁺ complexes. The synthetic scheme involves the sequential addition of three different diimine ligands, and employs CrCl₃ · 6H₂O as the initial Cr(III) reagent. The synthesis and characterization of the complexes [Cr(TMP)(phen)(diimine′)]³⁺ are reported (where TMP = 3,4,7,8-tetramethyl-1,10-phenanthroline, phen = 1,10-phenanthroline; and diimine′ is either bpy = 2,2′-bipyridine, Me₂bpy = 4,4′-dimethyl-2,2′-bipyridine, 5-Clphen = 5-chloro-1,10-phenanthroline, or DPPZ = dipyridophenazine). Chiral capillary electrophoresis and electrospray mass spectrometry were essential aids in determining the presence or absence of diimine ligand scrambling. Utilizing emission and electrochemical data obtained on these compounds, the oxidizing power of the lowest lying excited state (²E_g(O_h)) was calculated, and was found to vary in a systematic fashion with diimine ligand type.     

Complexes of (CH3)2AuIII: synthesis,PMR and IR spectra

The syntheses and reactivity of dimethylgold(III) complexes with multidentate ligands as TRIPHOS (i.e., 1,1,1-tris(diphenylphosphinomethyl)ethane) and TREN (i.e. 2,2′,2″-triaminotriethylamine) have been examined. I.r. spectra for the compounds in the solid state, conductivity and PMR data for solutions, lead to the assignment of an ionic formula [CH₃)₂Au TRIPHOS]⁺[(CH₃)₂AuCl₂]⁻ where the gold(III) atoms are presumably four-coordinate. The complex (CH₃)₂ AuCl TREN in DMSO solution undergoes a reductive elimination reaction, as found for analogous dimethylgold(III) derivatives.     

Synthesis, characterization, electrochemical and spectroscopic investigation of cobalt(III) Schiff base complexes with axial amine ligands: The layered crystal structure of [Co(salophen)(4-picoline)2]ClO4 · CH2Cl2

Cobalt(III) complexes with potentially tetradentate salophen (H₂salophen = N,N′-bis(salicylidene)-1,2-phenylenediamine) as equatorial ligand and with different axial amine ligands (NH₃, cyclohexylamine, aniline, 4-picoline and pyridine) were synthesized and characterized by IR, ¹H NMR, elemental analysis. Electronic spectra and electrochemical properties of the complexes were studied in DMF solutions. The lowest energy transitions, which occur between 464.8 and 477 nm, are attributed mainly to the intraligand charge transfer, confirmed by Zindo/S electronic structure calculations. The reduction potentials of Co(III)/Co(II) are more affected than those of Co(II)/Co(I) by the axial amine ligands. The crystal structure of the [Co^III(salophen)(4- picoline)₂]ClO₄ · CH₂Cl₂ was determined, indicating that the cobalt(III) center is six coordinated surrounded by the tetradentate salophen ligand and two 4-picoline ligands. The crystal packing of the complex shows a layered structure, in which the perchlorate counter ions and also the lattice solvent molecules are intercalated between the bc planes of the complex cations.     

Prochelators triggered by hydrogen peroxide provide hexadentate iron coordination to impede oxidative stress

Prochelators are agents that have little affinity for metal ions until they undergo a chemical conversion. Three new aryl boronate prochelators are presented that are responsive to hydrogen peroxide to provide hexadentate ligands for chelating metal ions. TRENBSIM (tris[(2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzylidene)-2-aminoethyl]amine), TRENBSAM (tris[(2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzoyl)-2-aminoethyl]amine), and TB (tris[(2-boronic acid-benzyl)2-aminoethyl]amine) convert to TRENSIM (tris[(salicylideneamino)ethyl]amine), TRENSAM (tris[(2-hydroxybenzoyl)-2-aminoethyl]amine), and TS (tris[2-hydroxybenzyl)2-aminoethyl]amine), respectively. The prochelators were characterized by ¹¹B NMR, and the structures of TRENBSAM, TRENBSIM, and the Fe(III) complex of TS were determined by X-ray crystallography. Of the three prochelator/chelator pairs, TB/TS was identified as the most promising for biological applications, as they prevent iron and copper-induced hydroxyl radical generation in an in vitro assay. TB has negligible interactions with metal ions, whereas TS has apparent binding constants (log K′) at pH 7.4 of 15.87 for Cu(II), 9.67 Zn(II) and 14.42 for Fe(III). Up to 1 mM TB was nontoxic to retinal pigment epithelial cells, whereas 10 μM TS induced cell death. TS protected cells against H₂O₂-induced death, but only within a 1-10 μM range. TB, on the other hand, had a much broader window of protection, suggesting that it may be a useful agent for preventing metal-promoted oxidative damage.     

Reduction chemistry of the mixed ligand metallocene [(C5Me5)(C8H8)U]2(μ-C8H8) with bipyridines

The U⁴⁺ cyclooctatetraenyl complex, [(C₅Me₅)(C₈H₈)U]₂(μ-C₈H₈), 1, reacts with two equiv of 4,4′-dimethyl-2,2′-bipyridine (Me₂bipy) and 2 equiv of 2,2′-bipyridine (bipy) to form 2 equiv of (η⁵-C₅Me₅)(η⁸-C₈H₈)U(Me₂bipy-κ²N,N′) and (η⁵-C₅Me₅)(η⁸-C₈H₈)U(bipy-κ²N,N′), respectively. X-ray crystallography, infrared spectroscopy, and density functional theory calculations indicate that the products are best described as U⁴⁺ complexes of bipyridyl radical anions. Hence, only one of the (C₈H₈)²⁻ ligands in 1 acts as a reductant and delivers 2 electrons per equiv of 1. Since the reduction potentials of uncomplexed (C₈H₈)²⁻, Me₂bipy, and bipy are −1.86, −2.15, and −2.10 V vs SCE, respectively, it is likely that prior coordination of the bipyridine reagents enhances the electron transfer.     

Synthesis and electrochemistry of Co(III) and Co(I) complexes having C5Me5 auxiliary

The synthesis and electrochemistry of half-sandwich type of Co(III) complexes [(C₅Me₅)Co(bidentate)(CH₃CN)](BF₄)₂ {bidentate = dppe (1,2-bis(diphenylphosphino)ethane), dppp (1,3-bis(diphenylphosphino)propane), bpy (2,2′-bipyridine), en (ethylenediamine)) are reported. Cyclic voltammograms of [(C₅Me₅)Co(bidentate)(CH₃CN)](BF₄)₂ in CH₃CN s showed two redox couples assignable to Co(II)/Co(III) and Co(I)/Co(II). The Co(I) complex having C₅Me₅ and dppe was also prepared. Two redox couples of this Co(I) complex, (C₅Me₅)Co(dppe), in CH₃CN coincided with those of [(C₅Me₅)Co(dppe)(CH₃CN)](BF₄)₂ in spite of the structural change around the metal center.     

Synthesis, characterization and properties of series coordination polymers constructed from a biphenyl dicarboxylate and nitrogen-containing mixed ligands

A series of coordination polymers have been prepared by the combination of flexible ligand 1,1′-biphenyl-2,2′-dicarboxylic acid (H₂dpa) and different types of nitrogen-containing ligands, with various metal ions such as Co(II), Zn(II) and Cd(II). The single-crystal structure analyses reveal that the above complexes possess different structure features with the introduction of different nitrogen-containing ligands. When auxiliary linear ligand 4,4′-bipyridine (4,4′-bpy) is introduced, two-dimensional layered complex, [Co₂(dpa)₂(4,4′-bpy)₂(H₂O)]_n (1) is formed. Whereas if chelating ligand, 1,10-phenanthroline (1,10′-phen) and 2,2′-bipyridine (2,2′-bpy) are introduced, one-dimensional complex [Zn(dpa)(1,10′-phen)]_n (2) and discrete complexes [Co₂(dpa)₂(2,2′-bpy)₂(H₂O)₂] (3), [Co₃(dpa)₃(1,10′-phen)₆(H₂O)₂] (4), [Cd(dpa)(1,10′-phen)₂][(H₂dpa)₂(H₂O)₂] (5) are synthesized. To our interest, 1 and 2 crystallize in homochiral spacegroup. Furthermore, the magnetic property of complex 1 and the fluorescent properties of complexes 2 and 5 are studied.     

A new tris(2-furyl) substituted pyrazolylborate ligand and its zinc complex chemistry

The new ligand hydrotris(3-(2′-furyl)-5-methylpyrazolyl)borate (Tp^Fu,Me) was prepared by the usual procedure. With zinc salts, it forms the Tp^Fu,MeZn-X complexes (X = Cl, Br, I, NCS, CH₃COO, CF₃COO). With zinc perchlorate, the bis-ligand complex Zn(Tp^Fu,Me)₂ is formed preferrably, but by carefully controlling the reaction conditions, the “enzyme model” Tp^Fu,MeZn-OH could be obtained. The latter models carbonic anhydrase by inserting CO₂ and CS₂ in methanol producing Tp^Fu,MeZn-OCOOMe and Tp^Fu,MeZn-SCSOMe. It models hydrolases by the hydrolytic cleavage of tris(p-nitrophenyl)phosphate and γ-thiobutyrolactone. It does not hydrolyse trifluoroacetamide, but instead deprotonates it, yielding Tp^Fu,MeZn-NHCOCF₃.     

Syntheses, crystal structures and magnetic properties of 1D and 2D cobaltous coordination polymers with mixed ligands

Two new Co(II) coordination polymers with mixed ligands, {[Co(BTA)_0.5(DBI)₂]·DBI·H₂O}_n (1) and [Co(PDA)(DBI)(H₂O)]_n (2) (H₄BTA = benzene-1,2,4,5-tetracarboxylic acid; H₂PDA = 2,2′-(1,2-phenylene)diacetic acid; DBI = 5,6-dimethyl-1H-benzoimidazole) have been synthesized under hydrothermal conditions, respectively. Both of them are characterized by elemental analyses, powder X-ray diffraction, thermogravimetric analysis, single-crystal X-ray diffraction, and magnetic susceptibilities. In 1, the Co(II) ions are four-coordinated and lie in distorted tetrahedron coordination environment. 1D ladder-like chain structure is formed by the bridging BTA⁴⁻ ligand. In 2, the Co(II) ions are in slightly distorted octahedral coordination geometry, and linked by PDA²⁻ ligand exhibiting a 2D layer structure. Temperature-dependent magnetic susceptibility measurements of 1 and 2 revealed that there are antiferromagnetic interactions between Co(II) ions.     

Imidazole-based nickel(II) and cobalt(II) coordination complexes for potential use as models for histidine containing metalloproteins

It has been established that small molecule model complexes have been useful in studying more complex biological systems of metalloproteins. Because many metalloproteins have active sites that contain multiple histidine residues bound to a metal center, a series of imidazole-containing scorpionate ligands and the associated Co and Ni complexes have been developed to investigate the bonding parameters of histidine containing active sites. The tris(2-imidazolyl) carbinol (2-TIC, 6) and tris[2-(N-methylimidazolyl)] carbinol (2-^MeTIC, 7) complexes of Ni²⁺ and Co²⁺, namely [Co(2-^MeTIC)₂]Cl₂ (8), [Co(2-^MeTIC)₂](NO₃)₂ (9), [Ni(2-^MeTIC)₂]Cl₂ (10), [Ni(2-^MeTIC)₂](NO₃)₂ (11), [Co(2-TIC)₂](NO₃)₂ (12), and [Ni(2-TIC)₂](NO₃)₂ (13), have been prepared from the reaction of the appropriate ligand and appropriate metal salt in polar solvent. These complexes have been characterized by single crystal X-ray diffraction, spectroscopic techniques, and magnetic susceptibility. In each solid-state structure the metal center in the cation coordinates to three N atoms from two ligands and adopts a pseudo-octahedral coordination geometry. The X-ray characterization of tris[2-(N-methylimidazolyl)] carbinol is also reported.     

Synthesis, properties and crystal structures of new binuclear lead(II) complexes based on phenyl, naphthyl-containing fluorine β-diketones and substituted 2,2′-bipyridines

Four lead(II) complexes with substituted 2,2′-bipyridine adducts and β-diketonates ligands, [Pb(5,5′-dm-2,2′-bpy)(tfpb)₂]₂1, [Pb(4,4′-dmo-2,2′-bpy)(tfpb)₂]₂2, [Pb(4,4′-dm-2,2′-bpy)(tfnb)₂]₂3 and [Pb(5,5′-dm-2,2′-bpy)(tfnb)₂]₂4, (“4,4′-dm-2,2′-bpy”, “5,5′-dm-2,2′-bpy”, “4,4′-dmo-2,2′-bpy”, “Htfpb” and “Htfnb” are the abbreviations of 4,4′-dimethyl-2,2′-bipyridine, 5,5′-dimethyl-2,2′-bipyridine, 4,4′-dimethoxy-2,2′-bipyridine, 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione, respectively) have been synthesized and characterized by elemental analysis, IR, ¹H NMR and ¹³C NMR spectroscopy and also studied by thermal and electrochemical as well as X-ray crystallography. The supramolecular features in these complexes are guided/controlled by weak directional intramolecular interactions.     

Behavior of human immunoglobulin G adsorption onto immobilized Cu(II) affinity hollow‐fiber membranes

Iminodiacetic acid (IDA) and tris(2‐aminoethyl)amine (TREN) chelating ligands were immobilized on poly(ethylene vinyl alcohol) (PEVA) hollow‐fiber membranes after activation with epichlorohydrin or butanediol diglycidyl ether (bisoxirane). The affinity membranes complexed with Cu(II) were evaluated for adsorption of human immunoglobulin G (IgG). The effects of matrix activation and buffer system on adsorption of IgG were studied. Isotherms of batch IgG adsorption onto finely cut membranes showed that neither of the chelates, IDA‐Cu(II) or TREN‐Cu(II), had a Langmuirean behavior with negative cooperativity for IgG binding. A comparison of equilibrium and dynamic maximum capacities showed that the dynamic capacity for a mini‐cartridge in a cross‐flow filtration mode (52.5 and 298.4 mg g^?1 dry weight for PEVA‐TREN‐Cu(II) and PEVA‐IDA‐Cu(II), respectively) was somewhat higher than the equilibrium capacity (9.2 and 73.3 mg g^?1 dry weight for PEVA‐TREN‐Cu(II) and PEVA‐IDA‐Cu(II), respectively). When mini‐cartridges were used, the dynamic adsorption capacity of IDA‐Cu(II) was the same for both mini‐cartridge and agarose gel. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis, crystal structure, antibacterial assay and DNA binding activity of new binuclear Cu(II) complexes with bridging oxamidate

Two new binuclear copper complexes, [Cu₂(oxpn)(bpy)(pic)(H₂O)](pic) (1) and [Cu₂(oxpn)(Me₂bpy)(pic)](pic) (2) [H₂oxpn = N,N′-bis(3-aminopropyl)oxamide; Hpic = 2,4,6-trinitrophenol; bpy = 2,2′-bipyridine; Me₂bpy = 4,4′-dimethyl-2,2′-bipyridine], have been synthesized and characterized by elemental analyses, conductivity measurements, IR, UV-visible spectroscopy and single crystal X-ray analyses. Both complexes have similar molecular structures. In complex 1, the central two Cu(II) atoms are bridged by cis-oxpn²⁻ with the Cu1-Cu2 separation of 5.221 Å and the polyhedron of each copper atom is a square-pyramid. Similarly, complex 2 is a cis-oxpn²⁻-bridged binuclear complex with the Cu1-Cu2 separation of 5.196 Å. Cu1(II) central atom situated in a tetrahedral geometry is four-coordinated and Cu(II) atom situated in a square-pyramidal geometry is five-coordinated. Hydrogen bonding interactions and π-π stacking interactions link the binuclear copper complex 1 or 2 into a 2D infinite network. The antibacterial assays indicate that the two complexes showed better activities than their ligands. The interactions of the two binuclear complexes with herring sperm DNA (HS-DNA) have been studied by UV absorption titration, fluorescence titration and viscosity measurements. The results suggest that the two binuclear complexes bind to HS-DNA via an intercalative mode.     

Pt(II) compounds with sulfoxide ligands and crystal structures of complexes of the types I(R2SO)Pt(μ-I)2Pt(R2SO)I and trans-Pt(R2SO)(L)X2 (L = amine,pyridine and pyrimidine)

The crystal structures of several Pt(II) complexes containing sulfoxide ligands are described. The two iodo bridged dimers of the type I(R₂SO)Pt(μ-I)₂Pt(R₂SO)I (where R is ethyl or n-butyl) are twinned structures. The dinuclear species are the trans isomers. Two compounds of the type trans-Pt(DMSO)(amine)X₂ were studied by X-ray diffraction methods. The diiodo MeNH₂ compound forms H-bonded chains, formed by maximizing the H-bonds between the amine group with the O atom of DMSO and one iodo ligand. The H-bonding pattern is quite different in the dichloro t-BuNH₂ complex. In the latter crystal, there are two independent molecules which are H-bonded in pairs. The methyl groups of DMSO and the t-butyl group of the amine are oriented towards the outside of the pairs of molecules, while the H-bonds link the two independent molecules. Again, the amino group forms the maximum H-bonds with the O atom of DMSO and one chloro ligand. The crystal structures of trans-Pt(DMSO)(pyridine)I₂ and of trans-Pt(MeBzSO)(pyrimidine)I₂ (Bz = benzyl) were also studied. In the pyridine complex, the O atom of DMSO is in the Pt(II) plane by symmetry, while in the pyrimidine compound, the C atom of the –CH₃ group is in the Pt(II) plane. The pyridine and the pyrimidine ligands are perpendicular to the Pt(II) square plane. The trans influence of the different ligands is discussed.     

Nickel-quinolones interaction. Part 5-Biological evaluation of nickel(II) complexes with first-, second- and third-generation quinolones

The nickel(II) complexes with the quinolone antibacterial agents oxolinic acid, flumequine, enrofloxacin and sparfloxacin in the presence of the N,N′-donor heterocyclic ligand 2,2′-bipyridylamine have been synthesized and characterized. The quinolones act as bidentate ligands coordinated to Ni(II) ion through the pyridone oxygen and a carboxylato oxygen. The crystal structure of [(2,2′-bipyridylamine)bis(sparfloxacinato)nickel(II)] has been determined by X-ray crystallography. UV study of the interaction of the complexes with calf-thymus DNA (CT DNA) has shown that they bind to CT DNA with [(2,2′-bipyridylamine)bis(flumequinato)nickel(II)] exhibiting the highest binding constant to CT DNA. The cyclic voltammograms of the complexes have shown that in the presence of CT DNA the complexes can bind to CT DNA by the intercalative binding mode which has also been verified by DNA solution viscosity measurements. Competitive study with ethidium bromide (EB) has shown that the complexes can displace the DNA-bound EB indicating that they bind to DNA in strong competition with EB. The complexes exhibit good binding propensity to human or bovine serum albumin protein having relatively high binding constant values. The biological properties of the [Ni(quinolonato)₂(2,2′-bipyridylamine)] complexes have been evaluated in comparison to the previously reported Ni(II) quinolone complexes [Ni(quinolonato)₂(H₂O)₂], [Ni(quinolonato)₂(2,2′-bipyridine)] and [Ni(quinolonato)₂(1,10-phenanthroline)]. The quinolones and their Ni(II) complexes have been tested for their antioxidant and free radical scavenging activity. They have been also tested in vitro for their inhibitory activity against soybean lipoxygenase.     

Synthesis, spectral and structural studies of water soluble arene ruthenium (II) complexes containing 2,2′-dipyridyl-N-alkylimine ligand

A series of water soluble complexes of general formula [(η⁶-arene)Ru{(C₅H₄N)₂CNRi}Cl]PF₆ have been prepared by the reaction of [{(η⁶-arene)RuCl₂}₂] with appropriate 2,2′-dipyridyl-N-alkylimine ligands (dpNRi) in the presence of NH₄PF₆ (where; R = Me or Et; arene = p-cymene, C₆Me₆, C₆H₆). The 2,2′-dipyridyl-N-alkylimine ligands are prepared by reaction of 2,2′-dipyridyl ketone with the corresponding alkylamine. The complexes are readily obtained as air stable yellow to dark brown solids by simple stirring at room temperature. The complexes are isolated as their hexafluorophosphate salts and characterized on the basis of spectroscopic data. The molecular structure of representative complex [(η⁶-C₆Me₆)Ru{(C₅H₄N)₂CN-Me}Cl]PF₆ has been determined by single crystal X-ray diffraction studies.     

Square-planar copper(II) complexes with tetradentate amido-carboxylate ligands. Crystal structure of Na2[Cu(obap)]2 · 2H2O. Strain analysis and spectral assignments of complexes

Novel N-N-N-O-type of tetradentate ligands H₃obap (H₃obap = oxamido-N-aminopropyl-N′-benzoic acid) and H₃maeb (H₃maeb = malamido-N-aminoethyl-N′-benzoic acid) and the corresponding square-planar copper(II) complexes have been prepared and characterized. The obap³⁻ and maeb³⁻ ligands coordinate to the copper(II) ion via four ligating atoms (three deprotonated atoms: one carboxylate oxygen and two deprotonated amide nitrogens; one amine nitrogen) with in-plane square chelation. A four coordinate, square-planar geometry has been established crystallographically for the binuclear Na₂[Cu(obap)]₂ · 2H₂O complex. Structural data correlating the square-planar geometry of the [Cu(obap)]⁻ unit and an extensive strain analysis are discussed in relation to the information obtained for similar complexes. The infrared and electronic absorption spectra of the complexes are discussed in comparison to the related complexes of known geometries. Antibacterial activity of ligands and copper(II) complexes towards common Gram-negative and Gram-positive bacteria are reported as well.