Terminal Copper Atoms Research Articles

A Tetranuclear copper(II) Complex with a Pyridine‐2,6‐dicarboxamide Ligand: Structural and Magnetic Properties and In vitro Antiproliferative Activity Against Human Cancer Cells

AbstractA pentadentate diamide ligand, N,N′‐di(pyridine‐2‐yl)pyridine‐2,6‐dicarboxamide (L1H2) and its tetranuclear Cu(II) complex [Cu4(L1)2(μ3‐OH)2(H2O)3(ClO4)](ClO4) ⋅ H2O are reported. X‐ray crystal structure of the complex reveals that it has an open‐book type architecture. Two central copper atoms are connected to each other by two hydroxo bridges. Each of these two hydroxo bridges also connects the two central copper atoms to one of the two terminal copper atoms. Variable temperature susceptibility measurements show that χMT decreases with the temperature, indicating a strong antiferromagnetic behavior. With the help of DFT calculations the magnetic data was analyzed using the spin Hamiltonian H=−2 J1S3 ⋅ S4 −2 J2(S3 ⋅ S1+ S3 ⋅ S2+ S4 ⋅ S1+ S4 ⋅ S2)−2 J3S1 ⋅ S2 (where subscripts 1 and 2 refer to the terminal copper atoms and 3 and 4 refer to the central copper atoms). The best fit was obtained with 2 J1=−322 cm−1, 2 J2=+34.8 cm−1, 2 J3=−8.8 cm−1 and g=2.18, indicating a δ‐type interaction between terminal copper atoms. The complex proves to be an avid binder of ct‐DNA, with apparent binding constant (Kapp) value estimated as 1.536×107 M−1. In vitro experiments indicate that the Cu(II) complex reduced the proliferation of HCT116 cells among other cell lines. This reduction of cell proliferation may be attributed to the enhancement of intracellular ROS, along with modulation and disruption of cell cycle associated proteins. SKC conceptualized the project, arranged funding and involved in overall coordination among collaborators, analyzing the data, and writing the paper. AM was involved in doing the experimental work on synthesis of the compounds, carrying out analytical and spectroscopic measurements, collecting X‐ray crystallographic data and DNA binding experiments. MS, SM and KDS were involved in study of anticancer activities of the complex. SS helped in refining X‐ray structure of the complex. MC did the magnetic measurements and analysis whereas AF did the DFT calculations.

Novel Trinuclear Copper(II) Complex: Crystal Structure at 100 K and Magnetic Properties of (R, S)-di[(6,7-dimethoxy-isoquinolin-1-yl)-(3,4-dimethoxy-phenyl)-methanolato]-tetra(2-hydroxybenzoato)-diaqua-tricopper dihydrate, [Cu3(C7H5O3)4(C20H20NO5)2(H2O)2]·2(H2O)

The crystal structure of [Cu3(C7H5O3)4(C20H20NO5)2(H2O)2]·2(H2O) (1) and analysis of temperature and field dependence of magnetic susceptibility is reported in this work. The structure of 1 is composed of trinuclear complex units and water molecules. The middle copper atom occupies the center of symmetry. N, O-bonded (6,7-dimethoxy-isoquinolin-1-yl)-(3,4-di­methoxy-phenyl)-methanolato ligands, 2-hydroxybenzoates with bridging carboxylic groups, and oxo-bridged water molecules connect the middle Cu(II) atom with the terminal copper atoms. Two 2-hydroxybenzoates coordinate the terminal copper atoms via one carboxylic oxygen and an O atom of the hydroxyl group. The analysis of copper coordination by bond-valence sum approach and relevant structural correlation is consistent with hexacoordinated Cu(II) centers. Cu···Cu separation is 3.0269(3) Å. The magnetism of 1 shows a strong ferromagnetic interaction between the neighboring metallic centers accompanied by very weak antiferromagnetic intermolecular interactions. The complex units are mutually held by π···π stack interactions of 2-hydroxybenzoates and hydrogen bonds.Graphical A new N,O bonded ligands, (R, S)-[(6,7-dimethoxy-isoquinolin-1-yl)-(3,4-dimethoxy-phenyl)-methanolate] coordinate the terminal atoms of the trinuclear copper(II) complex.

Searching for stable copper borozene complexes in CuB7- and CuB8.

Copper has been shown to be an important substrate for the growth of borophenes. Copper-boron binary clusters are ideal platforms to study the interactions between copper and boron, which may provide insight about the underlying growth mechanisms of borophene on copper substrates. Here we report a joint photoelectron spectroscopy and theoretical study on two copper-doped boron clusters, CuB7- and CuB8-. Well resolved photoelectron spectra are obtained for the two clusters at different wavelengths and are used to understand the structures and bonding properties of the two CuBn- clusters. We find that CuB8- is a highly stable borozene complex, which possesses a half-sandwich structure with a Cu+ species interacting with the doubly aromatic η8-B82- borozene. The CuB7- cluster is found to consist of a terminal copper atom bonded to a double-chain B7 motif, but it has a low-lying isomer composed of a half-sandwich structure with a Cu+ species interacting with an open-shell η7-B72- borozene. Both ionic and covalent interactions are found to be possible in the binary Cu-B clusters, resulting in different structures.

Structure and Magnetic Properties of a Trinuclear Copper(II) Complex with Bridging Carboxy-Phenyl Nitronyl Nitroxides

A new complex {(NITPBAH)2[Cu(hfac)2]3} 1 derived from carboxy-phenyl-substituted nitronyl nitroxide radical (NITPBAH) and Cu(hfac)2(H2O)2 (NITPBAH = 2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, hfac = hexafuoroacetylacetonato) has been synthesized as well as characterized structurally and magnetically. The single-crystal X-ray diffraction analyses indicated that the complex {(NITPBAH)2[Cu(hfac)2]3} 1 consists of trinuclear five-spin molecule system. Each NITPBAH ligand is bound to two copper atoms with its two oxygen atoms from ONCNO group. Copper atoms display two different coordination types. The central copper atom lies on an inversion center and is six-coordinated in an elongated octahedron using two hfac molecules and two oxygen atoms of ONCNO group from two different NITPBAH ligands. Two terminal copper atoms are five-coordinated in a distorted square-pyramidal environment formed by two hfac molecules and one oxygen atom of ONCNO group from one NITPBAH ligand. The magnetic susceptibility study of the complex {(NITPBAH)2[Cu(hfac)2]3} 1 shows strong antiferromagnetic interactions between Cu(II) ion and NITPBAH radical ligand.

H-bond assisted coordination bond formation in the 1D chains based on azido and phenoxido bridged tetranuclear Cu(II) complexes with reduced Schiff base ligands

Two new 1D chains [(CuL1R)2Cu2(N3)2(μ1,1,3-N3)2]n (1) and [{(CuL2R)2Cu2(N3)2(μ1,1,3-N3)2}·(CH3)2CO]n (2) based on rare μ1,1,3-N3 bridged tetranuclear Cu(II) complexes, have been synthesized using [CuL1R] and [CuL2R] as “metalloligands” [where H2L1R = N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine and H2L2R = N,N′-bis(2-hydroxybenzyl)-1,2-ethylenediamine]. Both complexes have been characterized by elemental analysis, spectroscopic methods, single crystal XRD, and magnetic study. In case of chain 1, the basic building block is a centrosymmetric tetranuclear unit whereas for 2, it is an asymmetric tetranuclear unit containing two types of square pyramidal Cu(II) centers (terminal and central). The μ1,1-N3 bridged central copper atoms of one tetranuclear unit are connected weakly to the axial position of the terminal copper atoms of neibouring units via the azide ions forming a rare μ1,1,3-N3 bridged novel 1D polymeric chain structure. Variable temperature magnetic susceptibility measurements show the presence of an overall strong antiferromagnetic exchange interactions mediated through the double phenoxido bridges with J values of −123.8 and −144.6 cm−1 for 1 and 2, respectively.

The First Characterized Coordination Compounds of Macrocyclic Ligands Including Incorporated Tetrazole Rings

The macrocyclic binuclear tetrazole, 2,2,5,5-tetramethyl-12-oxa-1,6,7,8,16,17,18,19-octaazatricyclo[13.2.1.16,9]nonadeca-7,9(19),15(18),16-tetraene (L), reacts with copper(II) chloride or copper(II) tetrafluoroborate hexahydrate to give complexes [Cu3Cl6L2] (1) or [CuL2(H2O)2](BF4)2(H2O) (2), respectively. According to single crystal X-ray analysis, both complexes were found to be coordination polymers. In the crystal structure of complex 1, there are neutral linear bibridged trinuclear units Cu3Cl6, in which the copper atoms are linked together by double chlorine bridges. Neighboring Cu3Cl6 units are bonded to each other by two bridging macrocyclic ligands L due to coordination bonds Cu–N between terminal copper atoms of Cu3Cl6 units and the tetrazole ring nitrogen atoms of ligands L to form polymeric chains. In complex 2, the copper atom is bonded to three ligands L via the tetrazole ring nitrogen atoms, and to two water molecules, with formation of a square-pyramidal coordination of the metal. In this complex, one of two independent ligands L shows monodentate coordination, whereas another ligand plays the role of a bridge between two neighboring copper atoms being responsible for formation of polymeric cationic chains [CuL2(H2O)2]n2n+. A complex system of hydrogen bonds connects the chains and the anions BF4– into a three-dimensional network. The temperature-dependent magnetic susceptibility measurements of complex 1 revealed that the copper(II) ions were ferromagnetically coupled showing a coupling constant J of 50 cm–1.

Design of end-on cyanato bridged trinuclear Cu(II) Schiff base complex with salen type Schiff base ligand: synthesis, structural investigation and DFT study

One ONNO-donor tetradentate Schiff base ligand LH2 was derived from the condensation of salicylaldehyde and 1,3-diaminopropane and reacted with Cu(NO3)2·6H2O and NaNCO to yield one trinuclear complex with molecular formula [Cu3L2(µ1,1-NCO)2]. The synthesized complex was characterized by IR, UV–vis spectroscopy, and electrochemical analysis. Single-crystal X-ray diffraction study explores that the two terminal copper atoms adopt square pyramidal geometry, whereas the central copper atom situated at the inversion center is surrounded by four phenoxo oxygens and two end-on cyanato anions to adopt an octahedral geometry. The ONNO-tetradentate Schiff base ligand coordinates with the copper(II) ion via two oxygen atoms of the phenoxo-group and two nitrogen atoms from the imine moiety. A theoretical density functional theory (DFT) calculation was also carried out to supplement the experimental results. All the DFT calculations were done in gas phase.

A new linear double phenoxide-bridged trinuclear Cu(II) Schiff base complex: Synthesis, crystallographic elucidation, magneto-structural correlation and DFT Study

The tetradentate (ONNO) donor Schiff base ligand LH2, derived from the condensation of salicylaldehyde and 1,3-diaminopropane, has been synthesized and reacted with CuBr2 to yield a trinuclear complex with the molecular formula [Cu3L2Br2]. Single crystal X-ray diffraction study reveals that the two terminal copper atoms adopt a square pyramidal geometry, whereas the central copper atom, situated at the inversion centre, is surrounded by four phenoxide oxygen atoms in a square planar fashion. Variable temperature magnetic susceptibility measurement study shows strong antiferromagnetic intra-trimer interactions between the copper centers with a J value of −302cm−1. EPR study of the complex depicts that, due to the exchange coupling between the copper ions, the EPR spectra were unresolved, having very broad resonances with g=2.133. A theoretical DFT calculation was also carried out to supplement the experimental results.

Synthesis, X-ray crystal structure, and electrochemistry of polynuclear azido-bridged manganese(III) and copper(II) Schiff base complexes

Abstract New azido-bridged [MnIII(salabza)(μ-1,3-N3)]n (1), and [CuII4(salabza)2(μ-1,1-N3)2(N3)2(HOCH3)2],(2) complexes with an unsymmetrical Schiff base ligand, {H2salabza = N,N’-bis(salicylidene)-2-aminobenzylamine}, have been synthesized, characterized by spectroscopic and electrochemical methods, and their crystal structures have been determined by X-ray diffraction. In complex 1, each manganese(III) atom is coordinated with N2O2 donor atoms from salabza and two adjacent Mn(III) centers are linked by an end-to-end (EE) azide bridge to form a helical polymeric chain with octahedral geometry around the Mn(III) centers. Complex 2 is a centrosymmetric tetranuclear compound containing two types of Cu(II) centers with square pyramidal geometry. Each terminal copper atom is surrounded by N2O2 atoms of a salabza ligand, and the oxygen atom of the methanol molecule. Each central copper(II) ion is coordinated with two phenoxo oxygen atoms from one salabza, one terminal azido, and two end-on (EO) bridging azido ligands. The central copper(II) ions are linked to each other by the two end-on (EO) azido groups.

Differences in Nuclearity, Molecular Shapes, and Coordination Modes of Azide in the Complexes of Cd(II) and Hg(II) with a “Metalloligand” [CuL] (H2L =N,N′-Bis(salicylidene)-1,3-propanediamine): Characterization in Solid and in Solutions, and Theoretical Calculations

Two new heterometallic copper(II)-mercury(II) complexes [(CuL)Hg(N3)2]n (1) and [(CuL)2Hg(N3)2] (2) and one copper(II)-cadmium(II) complex [(CuL)2Cd(N3)2] (3) have been synthesized using "metalloligand" [CuL] (where H2L = N,N'-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Complex 1 is a one-dimensional (1D) helical coordination polymer constructed by the joining of the dinuclear [(CuL)Hg(N3)2] units through a single μ-l,l azido bridge. In the dinuclear unit the Hg(II) is bonded with two phenoxido oxygen atoms of "metalloligand" [CuL] and two nitrogen atoms of azido ligands. Complex 2 is a linear trinuclear entity, in which two terminal "metalloligands" [CuL] are coordinated to central Hg(II) through double phenoxido bridges. The azido ligands link the central mercury atom with the terminal copper atoms via μ-l,3 bridges. In contrast, the trinuclear complex 3 is bent. Here, in addition to two double phenoxido bridges, central Cd(II) is bonded to two mutually cis nitrogen atoms of two terminal azido ligands. The variation in the coordination modes of the azido ligand seems to be responsible for the different molecular shapes of 2 and 3. Interestingly, bond distances between the Hg atoms and the central nitrogen atom of the azido ligands are 2.790(4) and 2.816(5) Å in 1 and 2.823(4) Å in 2. These bond distances are significantly less than the sum of van der Waals radii of mercury (2.04 Å) and nitrogen (1.55 Å) and considerably longer than the sum of their covalent radii (2.03 Å). However the distances are similar to reported Hg-N bond distances of some Hg(II) complexes. Therefore, we have performed a theoretical density functional theory study to know whether there is any interaction between the central nitrogen atom of the azido ligand and the mercury atoms. We have used the Bader's "atoms-in-molecules", energetic and orbital analyses to conclude that such interaction does not exist. The probable reason for different molecular shapes observed in trinuclear complexes of 2 and 3 also has been studied and explained by theoretical calculations and using the CSD. Electronic spectra, EPR spectra and ESI mass spectra show that all three complexes lose their solid state identity in solution.

Synthesis and structure of photoluminescent di- and trinuclear copper(I) complexes assembled from alkane-bridged bis-imidazole

[Cu 2Br 2L 1(PPh 3) 4] 2 · 2CH 2Cl 2 · 3H 2O ( 1) (L 1 = bis( N-imidazolyl)butane) and [Cu 3I 2(PPh 3) 6(L 2) 2] · 2DMSO · Br · H 2O ( 2) (L 2 = bis( N-imidazolyl)methane) have been synthesized and characterized by X-ray diffraction analysis and elemental analysis. Compound 1 is a tetracoordinated dinuclear complex, it consists of two Cu(PPh 3) 2 units bridged by a bis( N-imidazolyl)butane ligand. While compound 2 is a trinuclear copper(I) complex, in the compound copper atoms are located in two kinds of coordination spheres, for the two terminal copper(I) atoms, they are surrounded by two P, one N, and one iodine atoms to complete their tetrahedron geometry. While the middle copper(I) atom is surrounded by two P and two nitrogen atoms, the bromide anion exists as free counter anion. The photoluminescent studies show that the two complexes display intense blue emissions.

Synthesis of Two New Linear Trinuclear CuII Complexes: Mechanism of Magnetic Coupling through Hybrid B3LYP Functional and CShM Studies

Two new Cu(II) linear trinuclear Schiff base complexes, [Cu3(L)2(CH3COO)2] (1) and [Cu3(L)2(CF3COO)2] (2), have been prepared using a symmetrical Schiff base ligand H2L [where H2L = N,N'-bis(2-hydroxyacetophenone)propylenediimine]. Both of the complexes have been characterized by elemental analyses, Fourier transform IR, UV/vis, and electron paramagnetic resonance spectroscopy. Single-crystal X-ray structures show that the adjacent Cu(II) ions are linked by double phenoxo bridges and a mu(2)-eta(1):eta(1) carboxylato bridge. In each complex, the central copper atom is located in an inversion center with distorted octahedral coordination geometry, while the terminal copper atoms have square-pyramidal geometry. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit a distinct antiferromagnetic interaction of J = -36.5 and -72.3 cm(-1) for 1 and 2, respectively. Density functional theory calculations (B3LYP functional) and continuous-shape measurement (CShM) studies have been performed on the trinuclear unit to provide a qualitative theoretical interpretation of the antiferromagnetic behavior shown by the complexes.

An antiferromagnetically coupled trinuclear Cu(II) complex containing μ( O, O′), μ( O) carboxylates and μ( O) phenoxide bridges

The trinuclear complex [L 2Cu 3(CF 3CO 2) 4] ( 1) has been synthesized and its crystal structure determined. It consists of a linear arrangement of Cu(II) centers. The central copper atom is bonded to six oxygen atoms and has a tetragonally distorted octahedral geometry, while the terminal copper atoms are bonded to three oxygen and two nitrogen atoms and show a distorted square pyramidal geometry. The complex shows di-μ( O, O′) syn– syn carboxylate bridging as well as monoatomic (μ-O) bridging, along with phenolate (μ-O) oxygen bridging. Cryomagnetic investigations in the range 2–300 K revealed an antiferromagnetic spin exchange interaction with J = −95.7 cm −1, based on the isotropic exchange model H ex = −2 J[ S 1 · S 2 + S 2 · S 3].

Synthesis, crystal structure, magnetic property and oxidative DNA cleavage activity of an octanuclear copper(II) complex showing water–perchlorate helical network

A new octanuclear copper(II) complex has been synthesized and structurally characterized by X-ray crystallography: [Cu 8(HL) 4(OH) 4(H 2O) 2(ClO 4) 2] · (ClO 4) 2 · 2H 2O ( 1) (H 3L = 2,6-bis(hydroxyethyliminoethyl)-4-methyl phenol). The complex is formed by the linkage of two terminal bimetallic cationic units and a tetranuclear μ 3-hydroxo bridged dicubane core by a very short intramolecular hydrogen bond (O–H ⋯ O, 1.48(3) Å and the angle 175°). The coordination sphere of the terminal copper atoms is square pyramidal, the apical positions being occupied by water and a perchlorate ion. Complex 1 self-assembles to form a new type of water–perchlorate helical network [(H 2O) 2(ClO 4)] ∞ involving oxygen atoms of coordinated perchlorate ion and the two lattice water molecules through hydrogen-bonding interaction. The variable temperature-dependent susceptibility measurement (2–300 K) of 1 reveals a strong antiferromagnetic coupling, J 1 = −220 cm −1 and J 2 = −98 cm −1 ( J 1 and J 2 representing the exchange constant within [Cu 2+] 4 and [Cu 2+] 2 units, respectively). The complex binds to double-stranded supercoiled plasmid DNA giving a K app value of 1.2 × 10 7 M −1 and displays efficient oxidative cleavage of supercoiled DNA in the presence of H 2O 2 following a hydroxyl radical pathway.

Synthesis, structure and redox properties of an unexpected trinuclear copper(II) complex with aspartame: [Cu(apm) 2Cu(μ-N,O:O′-apm) 2(H 2O)Cu(apm) 2(H 2O)] · 5H 2O

Structural, magnetic and spectroscopic data of a new trinuclear copper(II) complex with the ligand aspartame (apm) are described. [Cu(apm) 2Cu(μ-N,O:O′-apm) 2(H 2O)Cu(apm) 2(H 2O)] · 5H 2O crystallizes in the triclinic system, space group P1 (#1) with a = 7.3300(1) Å, b = 15.6840(1) Å, c = 21.5280(1) Å, α = 93.02(1)°, β = 93.21(1)°, γ = 92.66(1)° and Z = 1. Aspartame coordinates to Cu(II) through the carboxylate and β-amino groups. The carboxylate groups of the two central ligands act as bidentate bridges in a syn–anti conformation while the carboxylate groups of the four peripheral ligands are monodentate in a syn conformation. The central copper ion is in a distorted square pyramidal geometry with the apical position being occupied by one oxygen atom of the water molecule. The two terminal copper(II) atoms are coordinated to the ligands in the same position but their coordination sphere differs from each other due to the fact that one copper atom has a water molecule in an apical position leading to an octahedral coordination sphere while the other copper atom is exclusively coordinated to aspartame ligands forming a distorted square pyramidal coordination sphere. Thermal analysis is consistent with the X-ray structure. EPR spectra and CV curves indicate a rupture of the trinuclear framework when this complex is dissolved in ethanol or DMF, forming a mononuclear species, with a tetragonal structure.

Copper(II) Mediated Anion Dependent Formation of Schiff Base Complexes

A tetranuclear mixed ligand copper(II) complex of a pyrazole containing Schiff base and a hydroxyhexahydropyrimidylpyrazole and copper(II) and nickel(II) complexes of the Schiff base having N-donor atoms have been investigated. A 2 equiv amount of 5-methyl-3-formylpyrazole (MPA) and 2 equiv of 1,3-diamino-2-propanol (1,3-DAP) on reaction with 1 equiv of copper(II) nitrate produce an unusual tetranuclear mixed ligand complex [Cu4(L1)2(L2)2(NO3)2] (1), where H2L1 = 1,3-bis(5-methyl-3-formylpyrazolylmethinimino)propane-2-ol and HL2 = 5-methyl-3-(5-hydroxyhexahydro-2-pyrimidyl)pyrazole. In contrast, a similar reaction with nickel(II) nitrate leads to the formation of a hygroscopic intractable material. On the other hand, the reaction involving 2 equiv of MPA and 1 equiv each of 1,3-DAP and various copper(II) salts gives rise to two types of products, viz. [Cu(T3-porphyrinogen)(H2O)]X2 (X = ClO4, NO3, BF4 (2)) (T3-porphyrinogen = 1,6,11,16-tetraza-5,10,15,20-tetrahydroxy-2,7,12,17-tetramethylporphyrinogen) and [Cu(H2L1)X]X x H2O (X = Cl (3), Br (4)). The same reaction carried out with nickel(II) salts also produces two types of compounds [Ni(H2L1)(H2O)2]X2 [X = ClO4 (5), NO3 (6), BF4 (7)] and [Ni(H2L1)X2] x H2O [X = Cl (8), Br (9)]. Among the above species 1, 3, and 5 are crystallographically characterized. In 1, all four copper atoms are in distorted square pyramidal geometry with N4O chromophore around two terminal copper atoms and N5 chromophore around two inner copper atoms. In 3, the copper atom is also in distorted square pyramidal geometry with N4Cl chromophore. The nickel atom in 5 is in a distorted octahedral geometry with N4O2 chromophore, where the metal atom is slightly pulled toward one of the axial coordinated water molecules. Variable-temperature (300 to 2 K) magnetic susceptibility measurements have been carried out for complex 1. The separations between the metal centers, viz., Cu(1)...Cu(2), Cu(2)...Cu(2)A, and Cu(2)A...Cu(1)A are 3.858, 3.89, and 3.858 A, respectively. The overall magnetic behavior is consistent with strong antiferromagnetic interactions between the spin centers. The exchange coupling constants between Cu(1)...Cu(2) and Cu(2)...Cu(2A) centers have turned out to be -305.3 and -400.7 cm(-1), respectively, resulting in a S = 1/2 ground state. The complexes are further characterized by UV-vis, IR, electron paramagnetic resonance, and electrochemical studies.

Synthesis and characterization of copper(II) azide complexes containing polyamines as co-ligands

Two new copper(II) azide complexes Cu 2(pn) 2(N 3) 4 ( 1) and Cu 3(dien) 2(N 3) 6 ( 2) (pn=1,3-diaminopropane and dien=diethylenetriamine) have been synthesized and characterized by single crystal X-ray diffraction. In complex 1 each copper(II) atom is coordinated to six nitrogen atoms from four azide anions and one 1,3-diaminopropane molecule in a distorted octahedral geometry. Successive pairs of copper(II) atoms are linked by two end-on azide bridges to form a polymeric chain. In centrosymmetric complex 2 the central copper(II) is coordinated by two monodentate azide anions and linked to two terminal copper atoms by double end-on azide bridges to give a linear trinuclear unit. The coordination geometry around each of the terminal copper atoms is square pyramidal, being surrounded by two nitrogen atoms of the bridging azide anions and three nitrogen atoms of the diethylenetriamine ligand. Magnetic susceptibility measurement of complex 2 in the range 2–300 K showed weak antiferromagnetic exchange between the copper(II) ions ( J=−2.09(8) cm −1) through the double end-on azide bridges.

Trinuclear Cu(II) complex with tetrazolyl-pyridine units as a bridging ligand: synthesis, characterization and X-ray structure

Reaction of 5-(2-pyridyl)tetrazole with 1,3-dibromopropane afforded three regioisomeric multidentate ligands L 1 , L 2 and L 3 containing two tetradentate pyridyl/tetrazolyl units linked by a flexible propylene spacer. These compounds were fully characterized by IR, 1H and 13C NMR spectroscopy and elemental analysis. The crystal structure of L 1 was determined. With Cu(II), L 1 formed a trinuclear complex Cu 3(L 1) 2Cl 6. Its structure was determined crystallographically. In the complex, the three copper atoms are found to be in a strict linear arrangement, with the ligand bridging two adjacent copper atoms. The central copper ion is six-co-ordinated. The co-ordination spheres of the terminal copper atoms are distorted square pyramidal. Inter and intramolecular π,π-stacking interactions are observed in the free ligand and in complex 1.

Covalent linkage of the type-2 and type-3 structural mimics to model the active site structure of multicopper oxidases: synthesis and magneto- structural properties of two angular trinuclear copper(II) complexes.

Two new angular trinuclear copper(II) complexes of formulation [Cu(3)(HL)LL'](ClO(4)), where L' is imidazole (Him, 1) or 1-methylimidazole (1-MeIm, 2) and H(3)L is a Schiff base obtained from the condensation of salicylaldehyde and 1,3-diaminopropan-2-ol (2:1 mole ratio), are prepared from a reaction of [Cu(2)L(mu-Br)] and [Cu(HL)] in the presence of L' and isolated as perchlorate salts. The crystal structures of 1 and 2 consist of a trinuclear copper(II) unit formed by the covalent linkage of monomeric type-2 mimic and dimeric type-3 mimic precursor complexes to give an angular arrangement of the metal atoms in the core which is a model for the active site structure of blue multicopper oxidases. In 1 and 2, the coordination geometry of two terminal copper atoms is distorted square-planar. The central copper has a distorted square-pyramidal (4 + 1) geometry. The mean Cu...Cu distance is approximately 3.3 A. The complex has a diphenoxo-bridged dicopper(II) unit with the phenoxo oxygen atoms showing a planar geometry. In addition, the complex has an endogenous alkoxo-bridged dicopper(II) unit showing a pyramidal geometry for the oxygen atom. The 1:1 electrolytic complexes show a d-d band at 607 nm. Cyclic voltammetry of the complexes in MeCN containing 0.1 M TBAP using a glassy carbon working electrode displays a Cu(3)(II)/Cu(2)(II)Cu(I) couple near -1.0 V (vs SCE). The variable temperature magnetic susceptibility measurements in the range 300-18 K show antiferromagnetic coupling in the complexes giving magnetic moments of approximately 3.0 mu(B) at 300 K and approximately 2.1 mu(B) at 18 K for the tricopper(II) unit. The experimental susceptibility data are theoretically fitted using a model with Heisenberg spin-(1)/(2) Hamiltonian for a trimer of spin-(1)/(2) copper(II) ions having two exchange parameters involving the alkoxo-bridged dicopper(II) (J1) and the diphenoxo-bridged dicopper(II) (J2) units, giving J1 and J2 values of -82.7, -73 cm(-1) for 1 and -98.3, -46.1 cm(-1) for 2, respectively. The structural features indicate a higher magnitude of anitiferromagnetic coupling in the alkoxo-bridged unit based on the greater value of the Cu-O-Cu angle in comparison to the diphenoxo-bridged unit. The core structures of 1 and 2 compare well with the first generation model complexes for the active site structure of multicopper oxidases in the oxidized form. The crystal structure of 1 exhibits a lamellar structure with a gap of approximately 7 A containing water molecules in the interlamellar space. Complex 2 forms a hexanuclear species due to intermolecular hydrogen bonding interactions involving two trimeric units. The crystal packing diagram of 2 displays formation of a three-dimensional framework with cavities containing the perchlorate anions.

Oxidative cleavage of DNA by a new ferromagnetic linear trinuclear copper(II) complex in the presence of H2O2/sodium ascorbate.

A new trinuclear copper(II) complex has been synthesized and structurally characterized: [Cu(3)(L)(2)(HCOO)(2)(OH)(2)](infinity) (HL = (N-pyrid-2-ylmethyl)benzenesulfonylamide). In the complex, the central copper ion is six-coordinated. The coordination spheres of the terminal copper atoms are square pyramidal, the apical positions being occupied by a sulfonamido oxygen of the contiguous trimer. As a consequence, the complex can be considered a chain of trinuclear species. The three copper atoms are in a strict linear arrangement, and adjacent coppers are connected by a hydroxo bridge and a bidentate syn-syn carboxylato group. The mixed bridging by a hydroxide oxygen atom and a bidentate formato group leads to a noncoplanarity of the adjacent basal coordination planes with a dihedral angle of 61.4(2) degrees. Susceptibility measurements (2-300 K) reveal a strong ferromagnetic coupling, J = 79 cm(-1), leading to a quartet ground state that is confirmed by the EPR spectrum. The ferromagnetic coupling arises from the countercomplementarity of the hydroxo and formato bridges. The trinuclear complex cleaves DNA efficiently, in the presence of hydrogen peroxide/sodium ascorbate. tert-Butyl alcohol and sodium azide inhibit the oxidative cleavage, suggesting that the hydroxyl radical and singlet oxygen are involved in the DNA degradation.