Debashis Ray

Self-assembly of an azido-bridged [NiII6] cluster featuring four fused defective cubanes.

The cluster [Ni6(H2L)2(HL1)2(N3)8].2C2H5OH.2H2O [1.2C2H5OH.2H2O], featuring four fused defective cubanes, has been obtained via azido-bridge-driven dimerization of two phenolate-centered trinuclear Ni3 fragments.

New μ4-Oxido-Bridged Copper Benzoate Quasi-Tetrahedron and Bis-μ3-Hydroxido-Bridged Copper Azide and Copper Thiocyanate Stepped Cubanes: Core Conversion, Structural Diversity, and Magnetic Properties

[Cu(2)(mu(4)-O)Cu(2)] and [Cu(2)(mu(3)-OH)(2)Cu(2)] geometrical arrangements are found in a new family of tetranuclear complexes: [Cu(4)(mu(4)-O)(mu-bip)(2)(mu-O(2)CPh)(4)].0.5CH(2)Cl(2) (1.0.5CH(2)Cl(2)), [Cu(4)(mu(3)-OH)(2)(mu-bip)(2)(N(3))(4)] (2), and [Cu(4)(mu(3)-OH)(2)(mu-bip)(2)(NCS)(4)(DMF)(2)] (3.2DMF) [Hbip = 2,6-bis(benzyliminomethyl)-4-methylphenol; DMF = dimethylformamide]. These complexes have been characterized by X-ray crystallography, and their magnetic properties have been studied. Complex 1 reacts with azide and thiocyanate anions, leading to 2 and 3 with a change of the [Cu(4)(mu(4)-O)] core into [Cu(4)(mu(3)-OH)(2)] units. These compounds are new examples of [Cu(4)] complexes where Cu(II) ions are connected by two types of water-derived ligands: oxide and hydroxide. Formation of these [Cu(4)] complexes can be controlled by changing the bridging ligands, which allows an effective tuning of the self-assembly. The study of the magnetic properties reveals that these complexes exhibit strong intramolecular antiferromagnetic interactions to yield a S(T) = 0 ground state. For the three complexes, the temperature dependence of the magnetic susceptibility was fitted using a model with two isolated S = 1/2 dimers based on the H = -2J{S(Cu,1).S(Cu,2)} spin Hamiltonian with J/k(B) = -289 K for 1; J/k(B) = -464 and -405 K for 2 and 3, respectively (where J is the exchange constant through the oxido-phenoxido or hydroxido-phenoxido bridges, respectively).

Tetranuclear Cu(II) complex supported by a central μ4-1,1,3,3 azide bridge

The new cluster [Cu4L2(N3)]Cl.16H2O has been synthesized and characterized; it features a unique mu4-1,1,3,3 bridging mode for azide, whose capacity to mediate magnetic coupling has been examined through bulk magnetic measurements and numeric fitting procedures.

Interaction with DNA of a heteronuclear [Na2Cu4] coordination cluster obtained from the assembly of two hydroxo-bridged [CuII2] units by a dimeric sodium nitrate template

The heteronuclear [Na(2)Cu(4)(bemp)(2)(OH)(2)(NO(3))(2)(OH(2))(4)] x 5 H(2)O (1 x 5H(2)O; H(3)bemp: 2,6-bis-[(2-hydroxyethylimino)-methyl]-4-methyl-phenol) cluster has been synthesized in aqueous-methanol at room temperature and structurally characterized. The water soluble complex is obtained from the template assembly of two [Cu(2)(bemp)(OH)] neutral fragments through their weak oxophillic interactions with two interconnected NaNO(3) units as core. Four [Na(2)Cu(4)] units form a metal-organic cage arrangement in the crystal lattice that traps a (H(2)O)(7) cluster. Variable-temperature magnetic susceptibility measurements (2-300 K) reveals a strong antiferromagnetic coupling between the Cu(II) ions within the dimers with J = -124.1 cm(-1) (in the H = -2JS(1)S(2) convention). The interaction of complex 1 x 3H(2)O with calf thymus DNA (binding constant K(b), 4.6 x 10(4) M(-1)) in Tris buffer was studied by UV-visible and emission titration, and cyclic voltammetry. The hexanuclear Na(2)Cu(4) complex also binds double-stranded supercoiled plasmid pBR322 DNA and displays efficient hydrolytic cleavage. The hydrolytic mechanism is supported by evidence from DNA relegation employing T4 ligase assay and reactive oxygen species (ROS) quenching cleavage experiments.

New Phenoxido-Bridged Quasi-Tetrahedral and Rhomboidal [Cu4] Compounds Bearing μ4-Oxido or μ1,1-Azido Ligands: Synthesis, Chemical Reactivity, and Magnetic Studies

[Cu(2)(μ(4)-O)Cu(2)] and [Cu(2)(μ(1,1)-N(3))(4)Cu(2)] geometrical arrangements are found in a new family of tetranuclear copper(II) complexes: [Cu(4)(μ(4)-O)(μ-cip)(2)Cl(4)] (1), [Cu(4)(μ(4)-O)(μ-cip)(2)(μ(1,3)-O(2)CPh)(4)]·2CH(3)OH (2·2CH(3)OH), and [Cu(4)(μ(1,1)-N(3))(4)(μ-cip)(2)(N(3))(2)]·DMF (3·DMF) [Hcip = 2,6-bis(cyclohexyliminomethylene)-4-methylphenol; CH(3)OH = methanol; DMF = dimethylformamide]. These complexes have been characterized by X-ray crystallography, and their magnetic properties have been studied. 1 and 2 form quasi-tetrahedral [Cu(4)(μ(4)-O)] complexes, and 3 is the first example of a rhomboidal [Cu(4)(μ(1,1)-N(3))] compound. Formation of the [Cu(4)] compounds is achieved via ligand-exchange reactions. The relative binding strength of the three ancillary ligands as N(3)(-) > PhCO(2)(-) > Cl(-) has been demonstrated from the core-conversion and peripheral ligand-exchange reactions. For the three complexes, the magnetic susceptibility measurements in the range of 1.8-300 K have been performed and modeled using two isolated S = (1)/(2) dimers based on the spin Hamiltonian H = -2J{S(Cu,1)·S(Cu,2)} with J/k(B) = -513, -340, and -315 K for 1-3, respectively (where J is the exchange constant through the oxido-phenoxido and azido-phenoxido bridges, respectively).

Double-CO32− Centered [CoII5] Wheel and Modeling of Its Magnetic Properties

A high-spin Co(II) cluster with a rare pentagonal molecular structure and formula [Co(5)(CO(3))(2)(bpp)(5)]ClO(4) (1; Hbpp is 2,6-bis(phenyliminomethyl)-4-methylphenolate) has been synthesized and characterized by single-crystal X-ray diffraction. This topology arises from fusing five [Co(2)(bpp)] moieties in a cyclic manner around two CO(3)(2-) central ligands, resulting in propeller-like configuration. The irregular coordination of the carbonate ions to the metal centers results in a combination of coordination numbers (CNs) of the Co(II) ions of five and six. The bulk magnetization of this complicated magnetically exchanged system has been modeled successfully by employing a matrix diagonalization technique. For this, the combination of S=3/2 ions (CN=5) with ions exhibiting strong spin-orbit coupling (CN=6) has been considered and a perturbative approach to handle the data in the whole studied range of temperatures (2-300 K) yielding parameters of g and D (for the five-coordinate Co(II) ions), of A, κ, λ, and Δ (for the metals with spin-orbit coupling) and of the exchange constants J. The agreement with results from DFT calculations, also presented here, is remarkable.

Self-Assembled Tetra- and Pentanuclear Nickel(II) Aggregates From Phenoxido-Based Ligand -Bound {Ni2} Fragments: Carboxylate Bridge Controlled Structures

Three different carboxylato bridges (R = C2H5, CF3, and PhCH2 in RCO2(-)) have been used to obtain the supramolecular aggregates [Ni5(μ-H2bpmp)2(μ3-OH)2(μ1,3-O2CC2H5)6]·2H2O·4DMF (1·2H2O·4DMF), [Ni4(μ3-H2bpmp)2(μ3-OH)2(μ1,3-O2CCF3)2](CF3CO2)2·H2O (2·H2O), and [Ni4(μ3-H2bpmp)2(μ3-OH)2(μ1,3-O2CCH2Ph)2](PhCH2CO2)2·4H2O (3·4H2O) (H3bpmp =2,6-bis-[(3-hydroxy-propylimino)-methyl]-4-methyl-phenol) from the hydroxido-bridged dinuclear motif [Ni2(μ-H2bpmp)(OH)](2+). These complexes have been characterized by X-ray crystallography and magnetic measurements. A change from propanoate group to trifluoroacetate and phenylaceate groups provided different course of cluster assembly based on Ni2(μ-H2bpmp)2 fragments. The {Ni5(μ3-OH)2(μ1,3-O2CC2H5)6}(2+) core in 1 contains five Ni(II) ions in an hourglass (pentanuclear vertex-shared double cubane) arrangement. These compounds are new examples of [Ni5] and [Ni4] complexes where aggregation of the building motifs are guided by the nature of the carboxylate anions, which allows an effective tuning of the self-aggregate process within same ligand environment. The study of the magnetic properties reveals that 1 exhibits an S = 3 ground state. Nevertheless, the magnetization increases above the expected saturation value of 6 μB at higher fields, because of the suppression of antiferromagnetic exchange between the central and peripheral Ni(II) ions. Complexes 2 and 3 exhibit ferromagnetic exchange interactions that result in the S = 4 ground state. Examination of AC magnetic susceptibility showed that complex 2 in finely ground form behaves as spin glass with the spin-freezing temperature of ∼5.5 K. This behavior was attributed to the collapse of the structure upon the loss of interstitial solvent. Such property was not observed for complex 3, in which the bulkier carboxylate ligands provide for a more robust crystal packing and larger separation between the [Ni4O4] clusters.

Synthesis and structural characterization of a triply bridged copper(II)–zinc(II) Schiff base complex with N,O coordination

Abstract The μ -bis(tetradentate) Schiff base ligand H 3 L ( 1 ), formed from salicylaldehyde and triethylenetetramine, affords [CuZn(OAc)(L)]·2H 2 O. It represents a new type of imidazolidine bridged heterodinuclear complex of copper(II)–zinc(II) as they are similar to the arrangement present in Cu,Zn superoxide dismutase.

A New Family of Ni4 and Ni6 Aggregates from the Self-Assembly of [Ni2] Building Units: Role of Carboxylate and Carbonate Bridges

Carboxylato (R = (t)Bu and Et) and carbonato bridges have been utilized for nickel(II)-based aggregates [Ni4(μ-H2L)2(μ3-OH)2(μ1,3-O2CBu(t))2](NO3)2·H2O·2DMF (1·H2O·2DMF), Ni4(μ-(hy)HL)2(μ3-OMe)2(μ1,1-N3)2(μ1,3-O2CEt)2]·4H2O (2·4H2O), and Ni6(μ4-L)(μ3-L)2(μ6-CO3)(H2O)8](ClO4)·9H2O (3·9H2O). Building blocks [Ni2(μ-H2L)](3+), [Ni2(μ-(hy)HL)](3+), and [Ni2(μ-L)](+) originating from [Ni2(μ-H2L)](3+) have been trapped in these complexes. The complexes have been characterized by X-ray crystallography, magnetic measurements, and density functional theory (DFT) analysis. In 1, the magnetic interactions are transmitted through the μ3-phenoxido/μ3-hydroxido/syn-syn-(t)BuCO2(-), μ3-phenoxido/μ3- hydroxido, and double μ3-phenoxido/double μ3-hydroxido bridges with J = +11.4 cm(-1), J1 = -2.1 cm(-1), and J2 = -2.8 cm(-1), respectively. In 2, the interactions are ferromagnetic, with J1 = +27.5 cm(-1), J2 = +20.62 cm(-1), and J3 = +1.52 cm(-1) describing the magnetic couplings through the μ-phenoxidoo/μ3-methoxido, μ-azido/μ3-methoxido, and μ3-methoxido/μ3-methoxido exchange pathways, respectively. Complex 3 gives J1 = -3.30 cm(-1), J2 = +1.7 cm(-1), and J3 = -12.8 cm(-1) for exchange pathways mediated by μ-phenoxido/μ-carbonato, μ-alkoxido/μ-alkooxido/μ-syn-syn-carbonato, and the μ-phenoxido/μ-carbonato, respectively. Interestingly, 1 and 3 below 20 K and 35 K, respectively, show an abrupt increase of the χMT product to reach a magnetic-field-dependent maximum, which is associated with a slightly frequency-dependent out-of-phase alternating-current peak. DFT calculations have also been performed on 1-3 to explain the exchange interaction mechanisms and to support the magnitude and sign of the magnetic coupling constants between the Ni(II) ions.

Design, synthesis and crystal structure determination of dinuclear copper-based potential chemotherapeutic drug entities; in vitro DNA binding, cleavage studies and an evaluation of genotoxicity by micronucleus test and comet assay

Copper-based potential chemotherapeutic complexes 1 and 2 were designed, synthesized and evaluated for in vitro DNA binding, cleaving capability and in vivo genotoxicity. The structural elucidation of complexes was done using elemental and spectroscopic data while the (R)-enantiomer of Cu(II) complex 1 was studied by single crystal diffraction. In vitro DNA binding profiling of both (R)- and (S)-enantiomers of complexes 1 and 2 was carried out to evaluate their enantioselectivity, exhibiting a remarkable degree of enantioselectivity in their interaction with DNA, with the (R)-enantiomer exhibiting greater DNA binding propensity. Interaction between complexes and pBR322 DNA was evaluated by agarose gel electrophoresis assay; both the (R)-enantiomeric complexes exhibit effective DNA cleavage and proceed via an oxidative pathway. Furthermore, the in vivo genotoxicity of the (R)-enantiomer of complex 1 was evaluated by micronucleus testing on bone marrow cells and comet assay in peripheral blood lymphocytes. These results support our contention that the (R)-enantiomer of complex 1 is a suitable chemotherapeutic drug candidate showing reduced toxic effects on normal cells as compared to cisplatin and an antioxidant (EVOO).