The preparation and crystal structure analysis of bis(L-Arginine)Cu(II)(acetate)2trihydrate

The crystal structure of bis(L-arginine)Cu(II)(acetate)₂trihydrate has been determined by X-ray analysis. The complex crystallizes in the monoclinic space group P2₁, with cell dimensions a = 15.948(2), b = 16.878(2), c = 10.378(2) Å, β = 108.47(1)°, Z = 4. There are two independent formula units in the asymmetric unit. The Cu atoms were located from a Patterson synthesis and the remaining atoms from difference Fourier syntheses. The structure was refined by least-squares to R = 0.079 and R = 0.11. Each copper atom has an essentially square planar coordination with the two arginine molecules chelated via the carboxy oxygens and the α-amino nitrogens, but with distorted six-fold coordinations completed by weak Cu…O (acetate) interactions. Electrostatic interactions between the acetates and the protonated ends of the amino acid residues link the two independent [Cu(L-arginine)₂(acetate)₂] units into dimers, which are then connected via hydrogen bonds, also involving the water molecules, into an infinite network.     

Characterization of a mononuclear copper carboxylate complex: Bis(acetylsalicylato)bis(pyridine)copper(II)

The preparation, spectral properties, and crystal structure of a mononuclear copper(II) complex of acetylsalicylate and pyridine are reported. The complex exists as bis(acetylsalicylato)bis(pyridine)copper(II) both in the solid state and in chloroform solution. The crystal is monoclinic, space group P2₁/n, with a = 17.823(5), b = 10.903(4), c = 6.598(2) Å, β = 95.74(2)°. The final refinement used 1472 observed reflections and gave an R of 0.046. The copper atom is surrounded by four atoms in a trans square planar arrangement with two short CuO distances of 1.949(3) Å and two CuN distances of 2.003(4) Å. Two longer CuO distances of 2.623(3) Å are made with the remaining oxygen atoms of the aspirin carboxylate groups.     

Intramolecular hydrogen bonding: synthesis and crystal structure of nickel(II) and copper(II) complexes of a tetradentate amine oxime

In the reaction of the tetradentate ligand 3,3′-(1,4- butanediyldiamino) bis (3-methyl-2-butanone)-dioxime (BnAO) with nickel(II) and copper(II), the monomeric [Ni(BnAO-H)]I·H₂O and a mixed monomer/dimer salt [Cu(BnAO-H)H₂O]₂[(Cu(BnAO-H))₂](ClO₄)₄, respectively, are formed, and all complexes have an intramolecular hydrogen bond between cis oxime groups. The OHO bonds give the characteristic infrared absorptions as well as the downfield proton-NMR signal (Ni complex). [Ni(BnAO-H)]I·H₂O crystallizes in space group P2₁/a with a=13.511(2), b=10.599(2), c=14.096(2) Å, β=97.52°, Z=4 and D_c=1.623 g/cm³. The structure was solved by Patterson and Fourier methods and refined by full-matrix least-squares techniques to a final R of 0.021 for 2124 reflections with I 2σ(I). The nickel(II) atom in the complex has slightly distorted square planar geometry with an intramolecular O···O contact of 2.417(7) Å. The copper(II) complex crystallizes in space group P2₁/c with a =13.425(2), b=21.446(3), c=14.349(4) Å, β= 104.4(5)°, Z=8 (monomers) and D_c=1.485 g/cm³. The final R value for this complex was 0.053 for 3033 reflections with I 2σ(I). This structure contains a monomeric [Cu(BnAO-H)H₂O]⁺ ion and a dimeric [(Cu(BnAO-H))₂]²⁺ ion, having intramolecular O···O hydrogen bonds of 2.421(5) and 2.531(5) Å, respectively. The copper(II) ions have square-pyramidal coordination with the axial positions occupied by an oxygen of the water of hydration in the monomer and by an oxime oxygen atom in the dimer. A center of symmetry relates the two halves of the dimer. The copper atom in each case is out of the plane of the four nitrogen atoms toward the axial site. The copper(II) complex is unusual in that the crystal contains both a monomer and a dimer.     

A ferromagnetically coupled tetranuclear pseudo-cubane copper(II) cluster: magnetic and ESR studies

A tetranuclear copper(II) complex [Cu₄(NSI)₄] · 2C₂H₅OH · 2H₂O (NSI=hydroxethylsalicydeneimine) has been synthesized and characterized by X-ray diffraction analysis. The compound crystallizes in the monoclinic system, space group P2(1), a=9.494(3) Å, b=18.687(5) Å, c=13.149(4) Å, β=110.162(5)°, Z=2, R₁=0.0482 and wR₂=0.0978. The crystal structure contains a tetranuclear pseudo-cubane core based on an approximately cubane array of alternating copper and oxygen atoms. Each copper atom resides in a distorted square planar coordination environment with one nitrogen and three oxygen atoms from two NSI ligands. The tetranuclear units are linked in the crystal by O-H?O hydrogen bonds and weak Cu?O co-ordination bonds into one-dimensional structure. Variable temperature (5-300 K) magnetic measurements indicate the existence of ferromagnetic interactions among copper atoms. The IR and ESR spectra have also been investigated.     

Studies on the metal—amide bond. XVII. The crystal and molecular structure of the α-form of aqua[N,N′-bis(2′-pyridinecarboxamido)-1,3-propane] copper(II) dihydrate

α-Aqua[N,N′-bis(2′-pyridinecarboxamido)-1,3-propane]copper(II) dihydrate, C₁₅H₂₀N₄O₅Cu, is monoclinic, space group P2₁/c, with a = 11.719(2), b = 13.092(2), c = 12.663(2) Å, β = 119.56(1)°, Z = 4. The structure was refined to R = 0.026 for 2398 diffractometer data using full-matrix least-squares methods. The copper atom is five-coordinate with the N₄-tetradentate ligand encompassing the base of a distorted square-based pyramid which is appreciably distorted towards a trigonal bipyramid [average Cu-N(amide) 1.950(2), Cu-N(pyridine) 2.043(2) Å, N(amide)-Cu-N(amide) 94.5(1), N(pyridine)-Cu-N(pyridine) 100.2(1)°] and with the copper atom lying 0.27 Å above the N₄ plane towards the apical water molecule [Cu-O 2.236(2) Å]. The central six-membered chelate ring adopts a skewed boat conformation and the enforced strain in the molecule results in non-planar distortions in the pyridine rings with only small distortions in the amide groups. The molecules pack in sheets parallel to (10$\text{1}$) and the hydrogen-bonding network involves the water molecules and the amide oxygen atoms of the ligand.     

Copper(II) complexes of a new N-picolylated bis benzimidazolyl diamide ligand: Synthesis, crystal structure and catechol oxidase studies

Copper(II) complexes of a new bis benzimidazole diamide ligand N-picolyl-N,N′-bis(2-methylbenzimidazolyl)hexanediamide [Pic-GBHA = L₂] have been synthesized and characterized. One of the compound [Cu(L₂)(NO₃)₂] has been structurally characterized. The copper atom is bound to two benzimidazolyl nitrogen atoms, two amide carbonyl oxygen atoms and a bidentate nitrate ion, resulting in a distorted octahedral geometry. EPR spectra obtained at low temperature indicate a tetragonal geometry in the solution state. Complexes display a quasi-reversible redox wave due to the Cu(II)/Cu(I) reduction process having fairly cathodic E_1/2. These Cu(II) complexes were utilized to carry out oxidation of ditertbutylcatechol (DTBC) in methanol using molecular oxygen as the oxidant in. Low temperature EPR study of the oxidation reaction implicates the formation of an active copper species with fairly low A_‖ value. The presence of picolyl groups on the ligand also serve as a proton sponge giving 2-3 times higher rates of reaction in comparison to the non-picolylated ligand, implying a role of free basic groups in the pH control of enzymatic oxidation of catechols by catechol oxidase and tyrosinase.     

The preparation and crystal structure analysis of a 2:1 complex between L-lysine and copper(II) chloride

The crystal structure of bis(L-lysine)Cu(II) chloride dihydrate has been determined by X-ray analysis. The complex crystallizes in the monoclinic space group P2₁, with cell dimensions a = 5.189(1), b = 16.988(3), c = 11.482(2) Å, β = 93.57(1)°. The position of the Cu atom was found from a Patterson synthesis, the remaining atoms were located with DIRDIF. The structure was refined by least-squares to R = 0.060 and R_w = 0.065 for 2637 observed reflections. The copper(II) atom has an essentially square planar coordination with the two lysine molecules chelated via the carboxy oxygen and the α-amino nitrogen. However the two chlorine atoms form weak interactions with the metal to complete a strongly tetragonally elongated six-fold coordination. The two aliphatic chains have rather different geometries and are extended in a zig-zag mode. Extensive hydrogen bonding links the complex and the water molecules together.     

Stereoelectronic properties of metalloenzymes. 10. a refined model that mimics the type II copper(II) site in galactose oxidase2

A number of copper(II) complexes of tridentate ligands with various donor atoms have been studied in an attempt to duplicate the unusual reactivity patterns and accompanying spectral changes of the copper(II) center in galactose oxidase. Results indicate that in order to match the optical and electron spin resonance spectral change observed upon CN^? binding by the enzyme, an equatorial, negative ligand must be displaced in a small molecule model. The crystal and molecular structure of the best model complex was solved by a single crystal X-ray diffraction study. The compound, monoacetato-1,3-bis(2-(4-methyl-pyridyl)imino)isoindolatocopper(II), crystallizes in the centro-symmetric triclinic space group Pī with a = 7.392(3) Å, b = 13.782(5) Å, c = 23.422(12) Å, α = 92.08(3)°, β = 104.11(5)°, γ = 109.98(4)°, V = 2156(1) ų, d(obsd.)(calc.)=(1.43)(1.44) g/cm^?3 for mol wt of 466.7 and Z = 4. Diffraction data were collected with a Syntex Pl diffractometer using graphite-monochromatized Cu radiation (λ = 1.5418 Å). The copper atoms were located from a Patterson synthesis; all other nonhydrogen atoms were located via difference. Fourier techniques, and hydrogen atoms were placed in calculated positions. Final refinement resulted in discrepancy indices of R = 0.089 and “Goodness to Fit” = 3.68 for all 3608 reflections having (I) ? 3σ(I) (5°<2θ<100°). There are two unique molecules in the asymmetric unit that are monomeric and well separated. The geometry around the copper atom is approximately square pyramidal, with the coordination sphere derived from three nitrogens of the tridentate ligand, one oxygen from the acetate unit, and an oxygen atom of a water molecule occupying an axial position. The structure is surprising both in that an axial water molecule is present and that the remaining four ligand atoms to the copper atom are rather distorted from a planar configuration. The plane defined by the copper, N5, and N3 atoms intersects the plane defined by the copper, Nl, and Ol, atoms forming a “twist angle” of 25.0° (0.0° would be ideal for a planar inner coordination sphere). The stereoelectronics of the inner coordination spheres of the type II Cu(II) enzymes galactose oxidase and superoxide dismutase are discussed and appropriate comparisons are made with emphasis on the origin of spectral changes observed upon anion binding.     

Synthetic, EPR spectroscopic, magnetic and X-ray crystallographic structural studies on copper(II) complexes of the tridentate N2S donor ligand formed from 6-methyl-2-formylpyridine and S-methyldithiocarbazate (Hmpsme)

New copper(II) complexes of general empirical formula, Cu(mpsme)X · xCH₃COCH₃ (mpsme = anionic form of the 6-methyl-2-formylpyridine Schiff base of S-methyldithiocarbazate; X = Cl, N₃, NCS, NO₃; x = 0, 0.5) have been synthesized and characterized by IR, electronic, EPR and susceptibility measurements. Room temperature μ_eff values for the complexes are in the range 1.75-2.1 μ_B typical of uncoupled or weakly coupled Cu(II) centres. The EPR spectra of the [Cu(mpsme)X] (X = Cl, N₃, NO₃, NCS) complexes reveal a tetragonally distorted coordination sphere around the mononuclear Cu(II) centre. We have exploited second derivative EPR spectra in conjunction with Fourier filtering (sine bell and Hamming functions) to extract all of the nitrogen hyperfine coupling matrices. While the X-ray crystallography of [Cu(mpsme)NCS] reveals a linear polymer in which the thiocyanate anion bridges the two copper(II) ions, the EPR spectra in solution are typical of a magnetically isolated monomeric Cu(II) centres indicating dissociation of the polymeric chain in solution. The structures of the free ligand, Hmpsme and the {[Cu(mpsme)NO₃] · 0.5CH₃COCH₃}₂ and [Cu(mpsme)NCS]_n complexes have been determined by X-ray diffraction. The {[Cu(mpsme)NO₃] 0.5CH₃COCH₃}₂ complex is a centrosymmetric dimer in which each copper atom adopts a five-coordinate distorted square-pyramidal geometry with an N₂OS₂ coordination environment, the Schiff base coordinating as a uninegatively charged tridentate ligand chelating through the pyridine and azomethine nitrogen atoms and the thiolate, an oxygen atom of a unidentate nitrato ligand and a bridging sulfur atom from the second ligand completing the coordination sphere. The [Cu(mpsme)(NCS)]_n complex has a novel staircase-like one dimensional polymeric structure in which the NCS⁻ ligands bridge two adjacent copper(II) ions asymmetrically in an end-to-end fashion providing its nitrogen atom to one copper and the sulfur atom to the other.     

Studies on dithio-o-toluate copper(I) complexes with bis(diphenylphosphino)methane. Crystal structures of {di-μ3-dithio-o-toluato-S,S′,S′-bis[μ-bis(diphenylphosphino)methane-μ-dithio-o-toluato-S,S′]} tetracopper(I) and {di[μ-bis(diphenylphosphino)methane]bis(dithio-o-toluato-S,S′)} dicopper(I)

The structures of [(CuS₂CT)₂dppm]₂ (I) (T = o-tolyl; dppm = bis(diphenylphosphino)methane) and [CuS₂CTdppm]₂ (II) have been determined by X-ray methods. Crystals of I are monoclinic, space group P2₁/n, with a = 15.163(4), b = 18.691(5), c = 13.478(4) Å, β = 96.81(3)°, Z = 2; crystals of II are orthorhombic. space group Pccn, with a = 23.267(4), b = 13.016(3), c = 20.731(5) Å, Z = 4. The structures of I and II have been solved by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.082 for I and 0.092 for II. The structure of I consists of centrosymmetric tetranuclear complexes in which two pairs of Cu atoms are triply bridged by a dppm ligand and two dithiocarboxylate groups from the dithio-o-toluate ligands. These last behave differently: one of them through a sulphur atom is also bonded to a Cu atom of the other pair so forming a tetranuclear complex. The Cu atoms of each pair show different coordination: Cu(1) displays a distorted trigonal and Cu(2) a distorted trigonal pyramidal geometry. The structure of II consists of dimers, in which each copper atom, doubly bridged by two dppm ligands, completes a distorted trigonal pyramidal coordination through two sulphur atoms from dithio-o-toluate anions acting as chelating ligands. In both compounds the phenyl group of the dithio-o-toluate anions is orthogonal to the corresponding CS₂ group. Both complexes give methyldithio-o-toluate in high yields by reaction with methyl iodide.     

Imidazole-containing ternary complexes of N-benzyloxycarbonyl-aminoacids. Crystal and molecular structure of bis(N-benzyloxycarbonyl-alaninato)bis-(N-methylimidazole)copper(II) ethanol solvate

Mixed ligand complexes of the type Cu(Z-aminoacidato)₂(B₂) (Z = benzyloxycarbonyl group, Z-aminoacidate = Z-glycinate (Zgly), Z-alaninate (Zala); Z-valinate (Zval), Z-leucinate (Zleu) ion, B = imidazole (Im), N-methylimidazole (MeIm)) were synthesized and characterized by means of electronic, infrared and EPR spectroscopies. For one of them, bis(Z-alaninato)bis(N-methylimidazole)copper(II) ethanol solvate, the crystal and molecular structure was also determined by the single crystal X-ray diffraction method. The complex crystallizes in the monoclinic space group P2₁/c, with cell dimensions a = 11.1119(6), b = 18.8398(7), c = 8.9652(5) Å, β = 105.380(2)° and Z = 2. The structure was solved by conventional Patterson and Fourier methods and refined by full-matrix least-squares to an R value of 0.045. The complex has square-planar coordination via two centrosymmetric carboxylic oxygens and two N-methylimidazole nitrogens. The second carboxylate oxygen is 2.731(5) Å from the copper atom in an ‘out of plane’ position. Packing is mainly determined by hydrogen bondings between amide nitrogen and amide carboxyl oxygen. Electronic, infrared and EPR spectra are consistent with this type of coordination geometry for anhydrous complexes, while for hydrate complexes are suggestive of tetragonal bipyramidal geometry.     

Preparation and structural characterization of di-μ-azido-bis[azido(2-aminopyridine)aquo]dicopper(II), [Cu(2-ampy)(N3)2(H2O)]2

Di-μ-azido-bis[azido(2-aminopyridine)aquo]dicopper(II), [Cu(2-ampy)(N₃)₂(H₂O)]₂, was synthesized and characterized by X-ray crystallography. The crystals are triclinic, space group P$\text{1}$, with a = 7.142(1), b = 7.812(1), c = 9.727(1) Å, a = 96.52(1), β = 95.52(1), γ = 113.47(1)°, and Z = 1. The structure was refined to R_F = 0.030 for 1960 observed MoKα diffractometer data. The dimeric molecule, which possesses a crystallographic inversion center, contains both terminal and μ(1)-bridging azido groups. Each copper(II) atom is further coordinated by a 2-aminopyridine ligand (via its ring N atom) and a water molecule to give a distorted square pyramid, with the metal atom raised by 0.17 Å above the N₄ basal plane [CuN (ring) = 2.001(2), CuN (azide) = 1.962(3)–2.018(2) Å] towards the apical aquo ligand [CuO = 2.371(2) Å]. Each water molecule forms an intramolecular O?HN (amine) acceptor hydrogen bond, and is linked by two OH?N (terminal azide) intermolecular donor hydrogen bonds to adjacent dimeric complexes to yield a layer structure parallel to (001). Infrared and electronic spectral data are presented and discussed.     

Structural comparison of (CuICH3CN4·dibenzo-18-crown-6 (I) and (CuICH3CN)x (II) fluorescent copper(I) materials

The single crystal X-ray structures of (CuICH₃CN₄·dibenzo-18-crown-6 (I) and (CuICH₃CN) (II) have been determined at room temperature [(I) C₂₈H₃₆Cu₄I₄N₄o₆, monoclinic space group P2₁/n, a = 10.116(4), b = 18.092(8), c = 22.211(9) Å, β = 98.66(3)°, Z = 4; (II) C₂H₃CuIN, orthorhombic pBN2₁, a = 13.618(8), b =8.742(2), c = 4.298(2), Z = 4]. (I) exists as a distorted cube with copper and iodine at alternate corners, the fourth coordination site copper occupied by an acetonitrile molecule coordinated through nitrogen. The cluster contains no crystallographic symmetry element and CuCu distances average 2.770(5) Å. The dibenzo-18-crown-6 displays only second sphere type interactions with cluster. (II) displays a pleated double chain type structure with distorted rectangles of alternating Cu and I atoms sharing opposite edges in infinite array. Copper displays tetrahedral geometry by coordination to three iodine atoms and a nitrogen bound acetonitrile molecule.     

Ferromagnetic trinuclear carbonato-bridged and tetranuclear hydroxo-bridged Cu(II) compounds with 4,4′-dimethyl-2,2′-bipyridine as ligand. X-ray structure, spectroscopy and magnetism

A controlled synthesis, characterisation and single-crystal X-ray analysis of two novel copper(II) compounds with the ligand 4,4′-dimethyl-2,2′-bipyridine (abbreviated dmbipy) is described. In a CO₂ atmosphere, with sodium hydroxide added, the carbonato-bridged triangular trinuclear compound [Cu₃(dmbipy)₆(μ₃-CO₃)](BF₄)₄(C₂H₅OH)(H₂O) (1) is obtained. Compound 1 crystallises in the monoclinic space group P2₁/n with a=16.169(6), b=23.351(11), c=21.312(7) Å, β=91.26(3), Z=4. The three copper ions are connected via the oxygen atoms from the symmetrically bridging carbonato group, resulting in a triangular array of copper atoms. Each copper has a distorted square-pyramidal environment with a basal plane formed by three nitrogen atoms of the two chelating bipyridine groups and the oxygen atom of the bridging carbonato group (Cu-N/O distances about 2.0 Å). The apical position at each copper is occupied by the fourth nitrogen atom of the bipyridines with distances varying from 2.100(11) to 2.146(11) Å. In all other experimental conditions the tetranuclear hydroxo-bridged compound [Cu₄(dmbipy)₄(μ₃-OH)₂(μ-OH)₂(H₂O)₂](BF₄)₄(H₂O)₄ (2) is obtained. Compound 2 crystallises in the monoclinic space group P2₁/c with a=13.274(8), b=21.685(7), c=11.266(7) Å, β=107.71(4), Z=2. The structure consists of two bis(hydroxo)-bridged dinuclear planar units which are connected with long Cu-O bonds to form a tetranuclear unit. Each Cu ion has a similar square-pyramidal coordination geometry: the equatorial plane of each Cu ion consists of two nitrogen atoms of the dmbipy ligand (Cu-N distances 1.945-2.003 Å), and two bridging hydroxo oxygen atoms (Cu-O distances 1.945-1.973 Å). The apical position of Cu1 is occupied by an oxygen atom of a water molecule with a distance of 2.262 Å. The second copper atom, Cu2, has the apical position occupied by an oxygen atom of a bridging hydroxo group at a distance of 2.349 Å; this bond is responsible for the formation of the tetranuclear unity. Compound 1 exhibits a ferromagnetic interaction between the copper ions with a J=29.3 cm⁻¹ and a very weak ferromagnetic intercluster interaction with zj′=2.4 cm⁻¹. Compound 2 also exhibits a ferromagnetic interaction between the copper ions with a J=31.1 cm⁻¹ and an overall magnetic interaction between the two dimeric units J′=8.76 cm⁻¹     

Diaquabis(3,6-dioxaheptanoato)copper(II): crystal structure and EPR characteristics

The structure of the title compound has been determined by X-ray diffraction at 190 K. The complex has an all trans configuration with an elongated tetragonally distorted octahedral CuO6 chromophore. The elongated axis corresponding to the trans-Cu–O(ether) bonds. The ligand molecules are bidentate via the carboxyl and the 3-ether O atoms; the 6-ether O atoms are not coordinated and are remote from the Cu centres. The bond lengths to the Cu centres are Cu–O(ether) 2.355 Å, Cu–O(Carboxyl) 1.933 Å and Cu–OH2 1.995 Å.The EPR spectrum of both the powder and frozen solution forms is typical of a rhombic system with a dx2−y21 electronic configuration. There were no significant differences in spectra recorded over the temperature range 77 K to room temperature. These results are discussed in relation to earlier published results on closely related oxa-carboxyl complexes.     

Synthesis and magnetic properties of the copper(II) complex derived from dimethyl aminomethylphosphine oxide ligand. X-ray crystal structure of DMAO and [Cu(NO3)2(POC3H10N)2]

The synthesis and properties of the copper(II) complex with dimethylaminomethylphosphine oxide as a ligand will be presented. The complex, with the formula [Cu(NO₃)₂(POC₃H₁₀N)₂] 1, has been characterized by elemental analysis, IR spectroscopy, SQUID and X-ray measurements. The X-ray structure was determined for the complex 1 and for the ligand dimethylaminomethylphosphine oxide (DMAO) 2. The single crystal X-ray structure of 1 shows that in the crystal the copper ions form distorted octahedral environment, consisting of two oxygen and two nitrogen atoms from the DMAO ligand. Additionally, one oxygen atom of each anion is semi-coordinated to the copper ion. The solid state magnetic measurements show that the complex 1 is paramagnetic with weak antiferromagnetic interactions in low temperatures.     

Synthetic,structural and molecular mechanics investigation of some mono- and dinuclear copper(I) and copper(II) complexes of macrocyclic and related acyclic ligands

A number of di-Cu(II) complexes of the new tetraimine macrocyclic ligand derived from the Schiff base [2 + 2] condensation of 2,5-diformylfuran with 3-oxa-pentane-1,5-diamine have been prepared by methods which employ the heavier alkaline earth metal ions as templates followed by transmetallation. The complexes have been characterised by spectroscopic and other physical methods. Several of the di-Cu(I) complexes react reversibly with CO in solution and irreversibly with O₂ in a 4:1 Cu:O₂ stoicheiometry. Depending on conditions the oxidation product may be a dinuclear Cu(II) complex of the macrocycle or a mononuclear Cu(II) complex of a new ring-opened ligand. The single crystal X-ray structure of the latter complex has been determined.[CuL](BPh₄)₂ is monoclinic, space group C2/c with a=20.12(1), b=14.48(1), c=22.37(2) Å, β=110.1(1)°, Z=4. 1389 Independent reflections above background were measured on a diffractometer and the structure refined to R=0.108. The cation has imposed C₂ symmetry. The copper atom is bonded to four nitrogen atoms in the ‘outer’ compartment of the ligand with unique CuN distances of 2.050(17) and 1.977(17) Å. The geometry of the copper atom is intermediate between square planar and tetrahedral with an angle of 39.7° between two CuN₂ planes. Molecular mechanics calculations show that this distortion is due to steric effects.     

EPR spectroscopic study of a dinuclear copper(II) complex of tolfenamic acid

The copper(II) complex with tolfenamic acid [Cu(tolf)₂(H₂O)]₂ was studied by X-band and K-band EPR spectroscopies in the temperature range from 90 to 300 K. The Cu²⁺ ions in dinuclear complex show a strong antiferromagnetic exchange interaction with |J| = 292 cm⁻¹. The EPR spectra, which were observed for [Cu(tolf)₂(H₂O)]₂, are typical powder spectra of the copper pairs. The spectra exhibit the hyperfine structure in low temperature range. The values of the spin-Hamiltonian parameters were determined on the basis of the best fit for the simulated spectra at both K-band (0.75 cm⁻¹) at T = 298 K and X-band (0.3 cm⁻¹) at T = 93 K as compared with the experimentally observed spectra. These values show that the local environment around the copper species is distorted tetragonal pyramid. This EPR evidence is consistent with the crystallographic data.     

Spectroscopic and magnetic properties of diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand with perchlorate transition metal salts. Crystal structure of [Cu(4-pmOpe)2(ClO4)2]

The perchlorate M(II) (M = Cu, Ni, Co) complexes with the diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand of the composition [M(4-pmOpe)₂ (H₂O)₂](ClO₄)₂ (M = Ni, Co) and [Cu(4-pmOpe)₂(ClO₄)₂] were prepared and studied. The ligand contains two donor atoms, i.e. pyridine nitrogen and phosphoryl oxygen atoms. In particular, the crystal structure of [Cu(4-pmOpe)₂(ClO₄)₂] was determined by the X-ray method. Its structure consists of a one-dimensional polymeric chain in which copper(II) ions are N,O-bridged by two 4-pmOpe organic ligands in a trans arrangement. Two perchlorate ions occupy the fifth and the sixth coordination sites. The Cu?Cu distance is 9.180 Å. The crystal packing is determined by the weak intermolecular C-H?O hydrogen contacts. The coordination compounds were identified and characterized by elemental analysis, spectroscopic and magnetic studies. Spectroscopic and magnetic results of the copper(II) compound are presented in the light of the crystal structure. The magnetic data indicate very weak intra- and interchain magnetic exchange interactions (J^’ = −0.43 and zJ^’ = 0.29 cm⁻¹, respectively). The spectroscopic and magnetic properties of the Co(II) and Ni(II) complexes indicate octahedral and polymeric structure of both compounds in which 4-pmOpe ligand also acts as N,O-bridge between metal ions.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.