CuN4 Plane Research Articles

Bis- and mixed-ligand copper(II) complexes of nalidixic acid the antibacterial drug: Mode of nalidixate coordination determines DNA binding and cleavage and cytotoxicity

The new complexes [Cu(nal)2]∙2H2O 1 and [Cu(en)2(nal)2] 2, where H(nal) is the antibacterial drug nalidixic acid, have been isolated and their X-ray structures successfully determined. The complex 1 possesses a square planar CuO4 chromophore constituted by the pyridone and carboxylate oxygen atoms of nalidixate anion. Complex 2 contains a CuN4O2 chromophore with a tetragonally distorted octahedral geometry, and the trans-axial coordination of two nalidixate anions at longer distances to the CuN4 plane constituted by ethylenediamine is stabilized by a network of H-bonding. DFT studies illustrate the structures and stabilities of complexes. The DNA binding affinity of 2 (Kb, 9.2 (±0.2) × 104 M−1) is higher than that of [Cu(en)2]2+ [Kb, 2.0 (±0.2) × 104 M−1], illustrating that bound nal¯ enhances the DNA binding affinity. DNA docking studies reveal that 2 bound to DNA undergoes interesting coordinative distortions more than 1, causing more significant changes in DNA host. Thus, 2 displays oxidative DNA cleavage (ascorbic acid) more prominent than [Cu(en)2]2+, by generating OH radicals, and shows poor cytotoxicity towards A549 lung cancer cell lines.

Evaluating the Conformational Role of an Allosteric CuII Ion in Anion Recognition and Catalysis by a Tricopper Complex

Structural and anion binding studies have provided an insight into the conformational role of an allosteric CuII ion in the trinuclear catalyst (L 2–2H). L 2 is a novel trinucleating ligand with pyridyl, pyrimidyl and amide donor groups. (L 2–2H)Cu (1) has been characterized by X-ray crystallography. The Cu ion is located at the allosteric site and coordinated by two amide N and two pyrimidine N atoms, the CuN4 plane is tetrahedrally distorted, and the complex adopts a helically twisted conformation. In contrast, the (L 2–2H)Cu3(μ4-C2O4) subunit of the dodecanuclear complex [(L 2–2H)4Cu12(μ4-C2O4)2(μ-OH)4(μ-Cl)4Cl4(H2O)2] (5) is roof-shaped, and the allosteric Cu is located on the top of a square-based pyramid. The oxalate coligand is coordinated by the two catalytic Cu ions in an unusual 1,4-μ-O,O bridging mode with an O ⃛O “bite length” of 2.6 Å and a Cu ⃛Cu distance of 6.4 Å. Intramolecular transesterification of the phosphodiester 2-(hydroxypropyl)-p-nitrophenyl phosphate (HPNP) by [(L 2–2H)Cu3]4+ was investigated, in comparison with the closely related complex [(L 3–2H)Cu3]4+ in which the ligand framework is somewhat less flexible. From a kinetic analysis of cleavage rate at varying HPNP concentrations, K HPNP (the equilibrium constant for binding of HPNP to the complex) and k cat (first-order rate constant for cleavage of HPNP when bound to the complex) parameters were derived: K HPNP=190 M-1 ([(L 2–2H)Cu3]4+) and 305 M-1 ([(L 3–2H)Cu3]4+), k cat=10×10-3 s-1 ([(L 2–2H)Cu3]4+) and 3.3×10-3 s-1 ([(L 3–2H)Cu3]4+). Anion binding constants of the complexes were determined by monitoring competitive inhibition of HPNP cleavage. The complexes have a high affinity to , , and , which appear to be of the appropriate size for bridging coordination, while “smaller” anions and are bound less efficiently. [(L 3–2H)Cu3]4+ has a higher affinity than [(L 2–2H)Cu3]4+ to HPNP but a lower affinity to the rather large anion . This is interpreted as a consequence of the reduced flexibility of [(L 3–2H)Cu3]4+, which slightly disfavours widening of the Cu ⃛Cu distance for incorporation of perrhenate. Similarly, the somewhat lower reactivity of [(L 3–2H)Cu3]4+ is attributed to the larger energy gap between the ground state and sterically more demanding (and less efficiently stabilized) transition state.

Tetrakis(2-methylimidazolo)bis(trifluoromethylsulfonato)copper(II)

The title complex, [Cu(C4H6N2)4(CF3SO3)2], was prepared by reaction of Cu(CF3SO3)2·6H2O and 2-methyl­imidazole in aceto­nitrile. The central Cu atom is coordinated by four 2-methyl­imidazole ligands forming an equatorial plane (average Cu—N 2.007 A) and two tri­fluoro­methyl­sulfonate anions at the axial sites, with long Cu—O bonds of 2.651 (4) and 3.069 (6) A; thus, the Cu atom has the octahedral environment typical for CuII complexes, with a tetragonal distortion. All four 2-methyl­imidazole rings are tilted out of the CuN4 plane by about 50°.

On the Structure, Electrochemistry, and Spectroscopy of the (N,N‘-Bis(2‘-(dimethylamino)ethyl)-N,N‘-dimethylpropane-1,3- diamine)copper(II) Ion

The synthesis, spectroscopy, and electrochemistry of the acyclic tertiary tetraamine copper(II) complex [CuL(1)](ClO4)(2) (L(1) = N,N-bis(2'-(dimethylamino)ethyl)-N,N'-dimethylpropane-1,3-diamine) is reported. The X-ray crystal structure of [CuL(1)(OClO3)(2)] reveals a tetragonally elongated CuN4O2 coordination sphere, exhibiting relatively long Cu-N bond lengths for a Cu-II tetraamine, and a small tetrahedral distortion of the CuN4 plane. The [CuL(1)](2+) ion displays a single, reversible, one-electron reduction at -0.06 V vs Ag/AgCl. The results presented herein illustrate the inherent difficulties associated with the separation and characterization of Cu-II complexes of tertiary tetraamines, and some previously incorrect assertions and unexplained observations of other workers are discussed.

Synthesis, structure, spectra and redox interconversions in copper(II) complexes of 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine

Copper(II) complexes of 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine (dppt) with ClO4–, BF4–, NO3–, Cl– and Br– as counter ions have been prepared. The crystal structure of the complex [Cu(dppt)2(H2O)2][ClO4]2 has been determined. The co-ordination geometry of the copper ion is elongated octahedral, the equatorial plane being formed by the N(2) nitrogens of both the triazine units and two pyridyl nitrogens and the axial positions being occupied by water molecules. The copper ion can be best described as centrosymmetric with the two dppt ligands being strictly coplanar to each other. The electronic and EPR spectral properties illustrate the strong axial interaction by solvent molecules with the weakly ligated CuN4 plane. The markedly positive redox potential (0.57–0.34 V vs. NHE) of these complexes is ascribed to the π-acceptor properties of the ligand rather than to steric effects of the phenyl substituents. The E½ and ΔEp values are significantly dependent on the solvent and the anions. The spectral and electrochemical behaviour of the copper(II) complex of 3-(2-pyridyl)-5,6-bis(p-sulfonatophenyl)-1,2,4-triazine, the sulfonato derivative of dppt, in aqueous solution at various pH revealed that it could not act as an effcient catalytically active redox agent.

L-Band ESR Spectra of Copper(II) Complexes with CuN4 Configurations

L-band ESR spectrometry has been developed for detecting free radicals or paramagnetic metal ions in intact animals or biological samples which contain much water. Several studies by L-band ESR on free radicals have been reported, but few on paramagnetic elements such as copper(II) or iron(III). We measured L-band ESR spectra of Cu(II) for the first time to investigate the coordination structure around the metal ion in aqueous solution. In X- and L-band ESR, both spectral patterns and parameters have been found to reflect the coordination structure of Cu(II)-polyamine complexes depending on the structures such as square-planar, axially coordinate square-planar, tetrahedral and distorted square-planar (Cu(II) ion is displaced from CuN4 plane). In addition, in L-band ESP, the coordination structures of Cu(II) complexes relate with spectral pattern, ESR parameter (LA-value), stability constants and halfwave potentials in terms of the electron density on Cu(II). Thus, L-band ESR spectrometry was indicated to be useful to know the coordination structure of Cu(II) proteins or enzymes in aqueous solution.

BONDING PROPERTIES OF Cu(II)-IMIDAZOLE CHROMOPHORES: ELECTRONIC AND MOLECULAR STRUCTURE OF Cu(IMIDAZOLE)4(CF3SO3)2

Abstract The crystal and molecular structure of [Cu(imidazole)4(CF3SO3)2] has been determined using three-dimensional X-ray diffraction data. The complex crystallizes in the monoclinic space group P21/n with Z = 2, a = 9.116(4), b = 9.560(1), c = 14.664(5) A, and β = 106.19(3)°. Least-squares refinement of the structure yields a final R value of 0.041 and Rw of 0.052 for 1607 independent reflections at 298 K. The copper(II) ion is coordinated centrosymmetrically by four imidazole ligands forming an equatorial plane, mean Cu-N 2.010 A, and by two trifluoromethanesulfonate ions at the axial sites, Cu-O 2.593(5) A. The dihedral angles between the imidazoles and the CuN4 plane are 88.6° and 59.4°. Gaussian analyses of the electronic spectra of four tetrakis(imidazole)copper(II) complexes having O-donor counter ions yield the d orbital sequences as d x2−y 2 ≫ d z 2 > d xy > d xz ≧ d yz, depending on the orientations of the imidazole nuclei. Energy differences between the antibonding d z 2 and non-bonding d xy ...

Bonding properties of copper(II)?N chromophores: Preparation, structure, and spectroscopic properties of ethylenediaminecopper(II) complexes. Molecular structure of [Cu(ethylenediamine)(pyridine)2(ClO4)2

Ethylenediaminecopper(II) perchlorate complexes of the [Cu(ethylenediamine)L2(ClO4)2] type, where L = imidazole, N-methylimidazole, 2-methylimidazole, 4-methylimidazole, and pyridine, have been prepared and characterized by elemental analyses, and electronic, vibrational, and e.p.r. spectroscopic measurements. The molecular structure of [Cu(ethylenediamine)(pyridine)2(ClO4)2] has been determined by three-dimensional X-ray diffraction data. The CuII ion is coordinated by one ethylenediamine and two pyridine ligands forming an equatorial plane, and by two perchlorate anions located on the z axis. The pyridine ligands incline at 54.9 ° to the CuN4 plane suggesting virtually no π -interaction in the complex. Similar structures with a CuN4 coordination plane are proposed for other complexes based on the spectroscopic data. The bonding properties of these complexes are elucidated and discussed with reference to the electronic structures deduced from Gaussian analyses of their LF spectra.

X-Ray crystal structure of [(1SR,4RS,7RS,8SR,11RS,14RS)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane]thiocyanatocopper(II) perchlorate dihydrate

The crystal structure of [CuL(SCN)]ClO4·2H2O (L = C-rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane) has been determined by X-ray crystallography: space group P21/n, a= 8.01 6(3), b= 30.109(8), c= 10.865(2)A, β= 104.93(2)°, Z= 4, and R= 0.084 for 3 751 observed reflections [I 2.5σ(I)]. The co-ordination about CuII is a distorted square pyramid with the macrocycie equatorial and the sulphur atom of the thiocyanato group axial. The four NH groups are on the same side of the CuN4 plane and are close to the S-bonded thiocyanato group. The two six-membered chelate rings exhibit a stable chair form and the two five-membered rings an unstable twist form. Intermolecular hydrogen bonds play an important role.

Synthesis and spectroscopic properties of some thermochromic copper(II) complexes ofN(2-aminoethyl) heterocyclic derivatives

Compounds of the type CuL2X2, where L =N(2-aminoethyl)piperazine [N(2-amet)pipz],N(2-aminoethyl)-pyrrolidine [N(2-amet)pyrr] andN(2-aminoethyl)morpholine [N(2-amet)morph] and X = BF 4 − , ClO 4 − and NO 3 − , have been prepared and characterized by means of magnetic moments, e.s.r., electronic and i.r. spectra. Only forN(2-amet)pyrr and Cu[N(2-amet)morph]2(NO3)2 complexes, do the electronic and i.r. spectra suggest polyanion coordination. In particular, as their electronic and i.r. spectra in the 293–393K range are temperature-dependent, it may be ascribed to the presence of a reversible continuous thermochromism arising from a temperature-dependent axial interaction between the anion and the CuN4 plane, which diminishes as the temperature increases. In all the other complexes, the thermochromism may be associated with a geometry which is more planar forN(2-amet)morph than forN(2-amet)pipz derivatives.

X-Ray Structures of Cu(II) Chelates of cis-1,3-Cyclohexanediamine

Abstract The crystal structures of wine-red [Cu(1,3-chxn)2]Br2 (1), [Cu(1,3-chxn)2](NO3)2 (2), and blue-violet [CuCl(1,3-chxn)2]ClO4 (3) (1,3-chxn=cis-1,3-cyclohexanediamine) have been determined from the diffractometer data measured by the use of Mo Kα radiation. The structures were solved by the Patterson–Fourier method and refined by the least-squares method to R=0.042 (1), 0.033 (2), and 0.057 (3) for 1309, 1210, and 776 nonzero reflections respectively. The Cu atoms in 1 and 2 have a square-planar coordination by 4 N atoms, while the complex ion in 3 has a 5-coordinate square-pyramidal geometry, with the Cl atom at the apical position. The 6-membered chelate rings in 1, 2, and 3 are of the chair, flattened-chair, and envelope conformations respectively. The complex ions in 1 and 2 have virtually a C2h symmetry, the two-fold axis of which lies on the CuN4 plane. The virtual symmetry for [CuCl(1,3-chxn)2]+ is C2v, the approximate two-fold axis being coincident with the Cu–Cl bond. The cyclohexane rings (chair conformation) in 2 and 3 are roughly perpendicular to the coordination plane, but that in 1 leans toward the central Cu(II) atom. The formation of such coordinatively unsaturated Cu(II) complexes as 1–3 is attributable to the steric hindrance of the bulky cyclohexane ring to the axial coordination site.

Synthesis, spectroscopic and structural properties of 2,2-dimethylpropane-1,3-diaminecopper(II) complexes. Temperature-dependent tetragonal distortion in some thermochromic complexes. Crystal and molecular structure of bis(2,2-dimethylpropane-1,3-diamine)diperchloratocopper(II)

Some compounds of the type [Cu(dmpd)2X2](dmpd = 2,2-dimethylpropane-1,3-diamine and X = Cl, Br, or ClO4) have been prepared and characterized by means of magnetic moments, e.s.r., electronic, and i.r. spectra. For one of them, bis(2,2-dimethylpropane-1,3-diamine) diperchloratocopper(II), the crystal structure has been determined by three-dimensional X-ray diffraction. Crystals are monoclinic, space group P21/c, with unit-cell dimensions: a= 9.724(2), b= 6.287(1), c= 16.191(3)A, β= 97.66(1)°, and Z= 2. The structure has been refined to R= 0.036 8. Co-ordination around the copper is distorted tetragonal bipyramidal; two centrosymmetric chelate ligands form the base [Cu–N(1) 2.028(3), Cu–N(2) 2.021 (3)A], and the two centrosymmetric unidentate perchlorate ions form the apices [Cu–O(1) 2.602(3)A]. The electronic and i.r. spectra of the [Cu-(dmpd)2X2] complexes are temperature-dependent suggesting reversible continuous thermochromism arising through a temperature-dependent axial interaction between the anion and the CuN4 plane, with a more square form being favoured at higher temperature. Other complexes of the types [Cu(dmpd)X2] and [Cu(H2dmpd)X4](X = Cl or Br) were also prepared and investigated and their possible stereochemistries discussed.

ChemInform Abstract: SIX‐COORDINATE COPPER(II) COMPLEXES DERIVED FROM THE REACTIONS OF BIS(ACETYLACETONATO)‐ AND BIS(ETHYL ACETOACETATO)‐COPPER(II) WITH SOME BIDENTATE NITROGEN BASES

AbstractDie Reaktion der Titeldiketonate mit entsprechenden Diaminen im molaren 1:1‐Verhältnis in Methylenchlorid führt zu den sechsfach‐koordinierten Komplexen (I).

Six-coordinate Copper(II) Complexes Derived from the Reactions of Bis(acetylacetonato)- and Bis(ethyl acetoacetato)-copper(II) with Some Bidentate Nitrogen Bases

Abstract Green-to-blue six-coordinate mixed complexes, Cu(acac)2(en) and Cu(etac)2(diamine)(acac=acetylacetonate anion; etac=ethyl acetoacetate anion; diamine=ethylenediamine, trimethylenediamine, 2,2′-bipyridine or 1,10-phenanthroline) have been isolated by the reactions of the respective parent β-diketonate with the corresponding diamine in dry dichloromethane. On the other hand, the reaction of Cu(acac)2 with en in the mole ratio of one-to-two in dichloromethane saturated with water has resulted in purple crystals of Cu(acac)2(en)2·2H2O. This compound has been shown by X-ray analysis to consist of a square-planar copper(II) cation, coordinated by two ethylenediamine molecules, and two planar acetylacetonate anions, the plane of which is not perpendicular to, but slanted against, the CuN4 plane. One oxygen atom of the anion participates in the N–H···O hydrogen bonding with an NH2 group of the ethylenediamine molecule, while the other occupies the axial position of Cu(en)22+ (Cu···O: 2.79(1) Å). Therefore, the compound can be designated by the formula [Cu(en)2]·(acac)2·2H2O. The water hydrogen atoms seem to take part in the hydrogen bonding with the anion oxygen atoms.