Azide Bridged Dicopper and Dinickel Complexes: Structure and Magnetism

Tryptophan moiety ligand based tri/tetranuclear Ni(ii) complexes: syntheses, structure and magnetic properties

Two N-(2-(hydroxy)-3-methoxybenzylidene)tryptophan coordinated Ni(ii) complexes have been synthesized and structurally characterized. Magnetic analysis reveals antiferromagnetic behaviour for both the compounds.

Self-Assembly of Antiferromagnetically-Coupled Copper(II) Supramolecular Architectures with Diverse Structural Complexities

The self-assembly of 2,6-diformyl-4-methylphenol (DFMP) and 1-amino-2-propanol (AP)/2-amino-1,3-propanediol (APD) in the presence of copper(II) ions results in the formation of six new supramolecular architectures containing two versatile double Schiff base ligands (H₃L and H₅L1) with one-, two-, or three-dimensional structures involving diverse nuclearities: tetranuclear [Cu₄(HL²⁻)₂(N₃)₄]·4CH₃OH·56H₂O (1) and [Cu₄(L³⁻)₂(OH)₂(H₂O)₂] (2), dinuclear [Cu₂(H₃L1²⁻)(N₃)(H₂O)(NO₃)] (3), polynuclear {[Cu₂(H₃L1²⁻)(H₂O)(BF₄)(N₃)]·H₂O}_n (4), heptanuclear [Cu₇(H₃L1²⁻)₂(O)₂(C₆H₅CO₂)₆]·6CH₃OH·44H₂O (5), and decanuclear [Cu₁₀(H₃L1²⁻)₄(O)₂(OH)₂(C₆H₅CO₂)₄] (C₆H₅CO₂)₂·20H₂O (6). X-ray studies have revealed that the basic building block in 1, 3, and 4 is comprised of two copper centers bridged through one μ-phenolate oxygen atom from HL²⁻ or H₃L1²⁻, and one μ-1,1-azido (N₃⁻) ion and in 2, 5, and 6 by μ-phenoxide oxygen of L³⁻ or H₃L1²⁻ and μ-O²⁻ or μ₃-O²⁻ ions. H-bonding involving coordinated/uncoordinated hydroxy groups of the ligands generates fascinating supramolecular architectures with 1D-single chains (1 and 6), 2D-sheets (3), and 3D-structures (4). In 5, benzoate ions display four different coordination modes, which, in our opinion, is unprecedented and constitutes a new discovery. In 1, 3, and 5, Cu(II) ions in [Cu₂] units are antiferromagnetically coupled, with J ranging from −177 to −278 cm⁻¹.

Organic chelate-free and azido-rich metal clusters and coordination polymers from the use of Me3SiN3: a new synthetic route to complexes with beautiful structures and diverse magnetic properties

A new synthetic route to structurally novel and magnetically interesting 3d-metal azido clusters and coordination polymers is presented; the key reagent for the preparation of solely azido-bridged molecule-based species is the organic azide precursor Me₃SiN₃.

Mono- and di-nuclear nickel(ii) complexes derived from NNO donor ligands: syntheses, crystal structures and magnetic studies of dinuclear analogues

Ferromagnetic interaction in dinickel(ii) complexes, supported by DFT calculations, is reported. Bis(phenoxo)-bridged compound is only the second example of ferromagnetically coupled system.

Doubly end-on azido bridged mixed-valence cobalt trinuclear complex: Spectral study, VTM, inhibitory effect and antimycobacterial activity on human carcinoma and tuberculosis cells

Doubly end-on azido-bridged mixed-valence trinuclear cobalt complex, [Co3(L)2(N3)6(CH3OH)2] (1) is afforded by employing a potential monoanionic tetradentate-N2O2 Schiff base precursor (2-[{[2-(dimethylamino)ethyl]imino}methyl]-6-methoxyphenol; HL). Single crystal X-ray structure reveals that in 1, the adjacent Co(II) and Co(III) ions are linked by double end-on azido bridges and thus the full molecule is generated by the site symmetry of a crystallographic twofold rotation axis. Complex 1 is subjected on different spectral analysis such as IR, UV-vis, emission and EPR spectroscopy. On variable temperature magnetic study, we observe that during cooling, the χMT values decrease smoothly until 15K and then reaches to the value 1.56 cm(3) K mol(-1) at 2 K. Complex 1 inhibits the cell growth on human lung carcinoma (A549 cells), human colorectal (COLO 205 and HT-29 cells), and human heptacellular (PLC5 cells) carcinoma cells. Complex 1 exhibits anti-mycobacterial activity and considerable efficacy on Mycobacterium tuberculosis H37Rv ATCC 27294 and H37Ra ATCC 25177 strains.

Structures and magnetic properties of an antiferromagnetically coupled polymeric copper(II) complex and ferromagnetically coupled hexanuclear nickel(II) clusters

Reactions between 2,6-diformyl-4-methylphenol (DFMF) and tris(hydroxymethyl) aminomethane (THMAM = H(3)L2) in the presence of copper(II) salts, CuX(2) (X = CH(3)CO(2)(-), BF(4)(-), ClO(4)(-), Cl(-), NO(3)(-)) and Ni(CH(3)CO(2))(2) or Ni(ClO(4))(2)/NaC(6)H(5)CO(2), sodium azide (NaN(3)), and triethylamine (TEA), in one pot self-assemble giving a coordination polymer consisting of repeating pentanuclear copper(II) clusters {[Cu(2)(H(5)L(2-))(μ-N(3))](2)[Cu(N(3))(4)]·2CH(3)OH}(n) (1) and hexanuclear Ni(II) complexes [Ni(6)(H(3)L1(-))(2)(HL2(2-))(2)(μ-N(3))(4)(CH(3)CO(2))(2)]·6C(3)H(7)NO·C(2)H(5)OH (2) and [Ni(6)(H(3)L1(-))(2)(HL2(2-))(2)(μ-N(3))(4)(C(6)H(5)CO(2))(2)]·3C(3)H(7)NO·3H(2)O·CH(3)OH (3). In 1, H(5)L(2-) and in 2 and 3 H(3)L1(-) and HL2(2-) represent doubly deprotonated, singly deprotonated, and doubly deprotonated Schiff-base ligands H(7)L and H(4)L1 and a tripodal ligand H(3)L2, respectively. 1 has a novel double-stranded ladder-like structure in which [Cu(N(3))(4)](2-) anions link single chains comprised of dinuclear cationic subunits [Cu(2)(H(5)L(2-))(μ-N(3))](+), forming a 3D structure of interconnected ladders through H bonding. Nickel(II) clusters 2 and 3 have very similar neutral hexanuclear cores in which six nickel(II) ions are bonded to two H(4)L1, two H(3)L2, four μ-azido, and two μ-CH(3)CO(2)(-)/μ-C(6)H(5)CO(2)(-) ligands. In each structure two terminal dinickel (Ni(2)) units are connected to the central dinickel unit through four doubly bridging end-on (EO) μ-azido and four triply bridging μ(3)-methoxy bridges organizing into hexanuclear units. In each terminal dinuclear unit two nickel centers are bridged through one μ-phenolate oxygen from H(3)L1(-), one μ(3)-methoxy oxygen from HL2(2-), and one μ-CH(3)CO(2)(-) (2)/μ-C(6)H(5)CO(2)(-) (3) ion. Bulk magnetization measurements on 1 show moderately strong antiferromagnetic coupling within the [Cu(2)] building block (J(1) = -113.5 cm(-1)). Bulk magnetization measurements on 2 and 3 demonstrate that the magnetic interactions are completely dominated by ferromagnetic coupling occurring between Ni(II) ions for all bridges with coupling constants (J(1), J(2), and J(3)) ranging from 2.10 to 14.56 cm(-1) (in the Ĥ = -J(1)(Ŝ(1)Ŝ(2)) - J(1)(Ŝ(2)Ŝ(3)) - J(2)(Ŝ(3)Ŝ(4)) - J(1)(Ŝ(4)Ŝ(5)) - J(1)(Ŝ(5)Ŝ(6)) - J(2)(Ŝ(1)Ŝ(6)) - J(3)(Ŝ(2)Ŝ(6)) - J(3)(Ŝ(2)Ŝ(5)) - J(3)(Ŝ(3)Ŝ(5)) convention).

Ferromagnetic Coupling in a 1D Coordination Polymer Containing a Symmetric [Cu(μ1,1-N3)2Cu(μ1,1-N3)2Cu]2+ Core and Based on an Organic Ligand Obtained from the Solid State

Addition of rctt-tetrakis(2-pyridyl)cyclobutane (2,2'-tpcb) in a Cu(II)/N(3)- solution afforded the 1D coordination polymer [Cu(3)(N(3))(6)(2,2'-tpcb)(DMF)(2)](n) (1). The ligand 2,2'-tpcb serves as a tetradentate bis-chelating ligand by linking linear [(DMF)Cu(mu(1,1)-N(3))(2)Cu(N(3))(2)(mu(1,1)-N(3))(2)Cu(DMF)] trinuclear units to produce a zigzag chain. Within each centrosymmetric trinuclear unit there exist two irregularly asymmetric end-on double azido-bridged [Cu(mu(1,1)-N(3))(2)Cu](2+) cores, while one of the largest Cu-Nazide-Cu angles is observed. Magnetic susceptibility data, measured from 2 to 300 K, show bulk moderate ferromagnetic coupling within the magnetically isolated trinuclear units. These data were fitted to the appropriate equation derived from the Hamiltonian H = -J(1)(S(A1)S(B) + S(A2)S(B)) - J(2)S(A1)S(A2), giving the parameters J1 = +70(3) cm(-1), J2 = -3(2) cm(-1), g = 2.12(1), with an intertrimer interaction parameter theta = -0.74(2) K. The coupling constants were correlated with the structural parameters. Density functional calculations reproduce very well the experimental J values and show that ferromagnetism for this complex is mainly due to the topology of the magnetic orbitals and the different coordination spheres of two neighboring Cu(II) atoms, resulting in a small overlap of the orbitals possessing the unpaired electrons.

Alternating Spin Chains: Controlled Assembly from Bimetallic Building Blocks and QMC Simulation of Spin Correlation

By using the compartmental dinucleating pyrazolate ligand HL, dinickel(II) complexes [LNi2(micro-N3)(acetone)2]X2 (1: X = CIO4; 2: X = BPh4) and tetranickel(II) complex [{LNi2(micro-N3)(MeOH)2](CI04)4 (3) have been prepared and structurally characterized. Complexes 1 and 2 differ in the torsion along the bridging micro-1,3-azide moiety, while the azido ligands in 3 adopt an unusual micro-1,1,3 bridging mode to connect the two subunits. All three complexes show overall antiferromagnetic coupling and an S = 0 ground state, but the torsion along the azide moiety is a determining factor for the coupling strength. Compounds 1 and 2 serve as preorganized building blocks for the controlled synthesis of alternating 1D polymeric structures 4-6 by replacement of their labile acetone ligands by additional azido ligands. Due to the modular synthetic approach, 4-6 can be described as Heisenberg antiferromagnetic systems with inherent bond alternation (HABA), whereby the organic ligand framework ensures that the individual nickel/azido chains are well isolated in the crystal lattice. Like their precursors, 4-6 are mainly distinguished by torsion along the micro-1,3-azido bridges, both within and between the bimetallic constituents. Magnetic measurements confirm an overall 5 = 0 ground state for 4-6, and coupling parameters have been deduced from quantum Monte Carlo simulations. The two J values for the alternating 1D chains can be clearly assigned on the basis of the magnetostructural correlations established for the bimetallic building blocks. The alternation ratio gamma = J2J1(-1) places the three new systems in the HABA regime for a singlet-dimer ground state.

An Unprecedented Asymmetric End-On Azido-Bridged Copper(II) Imino Nitroxide Complex: Structure, Magnetic Properties, and Density Functional Theory Analysis

The dinuclear copper(II) complex [Cu2(mu(1,1)-N3)2(im-2py)2(N3)2] [im-2py = 2-(2-pyridyl)-4,4,5,5-tetramethylimidazolinyl-1-oxy] has been prepared and structurally characterized. The crystal structure consists of a dinuclear unit in which the Cu(II) ions are bridged by two azido ions in a end-on asymmetric fashion and the imino nitroxide radicals are chelating by the two imino N atoms. Accordingly, the magnetic susceptibility data were analyzed considering a linear spin-coupling scheme rad(1)-Cu(2)-Cu(3)-rad(4) (with Si = 1/2, i = 1-4), where the Heisenberg spin Hamiltonian assumes the general form -2Sigma(i)<(j)S(i)S(j). Considering only first-neighbor spin-coupling constants (J13 = J24 = J14 = 0), magnetic susceptibility measurements show that the copper(II) imino nitroxide rad-Cu-(Cu-rad)(rad-Cu)-Cu-rad exchange coupling is ferromagnetic and large (J12 = J34 = J1 > +190 cm(-1)), as is expected for copper imino nitroxide species, and the copper-copper (rad)-Cu-Cu-(rad) coupling through the asymmetric double end-on azide bridges appeared antiferromagnetic and rather large [J23 = J2 = -43(2) cm(-1)]. By contrast, a density functional theory analysis of the system through the computation of broken-symmetry-state energies resulted in J2 approximately 0 cm(-1). This apparent paradox is resolved by introducing a second-neighbor rad-(Cu)-Cu-(rad)(rad)-Cu-(Cu)-rad spin-coupling constant J13 = J24 = J3, which turns out to be antiferromagnetic both experimentally (when J2 is set equal to zero) and computationally.

Ferromagnetic vs. antiferromagnetic coupling in bis(µ2-1,1-azido)dinickel(ii) complexes with syn- and anti-conformations of the end-on azide bridges

Reaction of a 1 : 1 : 1 molar ratio of NiCl(2), NaN(3) and H(2)L, a tetradentate ligand N-(2-pyridyl)methyl)-N,N-bis(2'-hydroxy-3',5'-dimethylbenzyl)amine in methanol in presence of Et(3)N results in a turquoise precipitate, which affords deep green crystals of [Ni(2)(HL)(2)(N(3))(2)]*1.5CH(2)Cl(2) (1) and [Ni(2)(HL)(2)(N(3))(2)]*H(2)O (2) upon crystallization from CH(2)Cl(2)-MeOH or THF-MeOH, respectively. Both complexes reveal distorted octahedral NiN(4)O(2) coordination environments around the Ni(ii) centers with bis(micro-1,1-azido) bridging ligands. Complex 1 displays an unprecedented small Ni-N-Ni bridge angle of 90.4 degrees , whereas 2 contains the said angle of av. 98.7 degrees lying in the usual range observed for other comparable structures. The variable-temperature magnetic susceptibility together with the variable-field, variable-temperature (VTVH) magnetization measurements discern different ground states of S(t) = 0 for 1 and S(t) = 2 for 2. The magnetic behaviours of these compounds are discussed in the context of the known bis(end-on azido) bridging dinickel(II) complexes.

Targeted construction of azido-bridged Ni4complexes with decisive effect of µ-1,3-azide torsion on the spin ground state

Highly preorganized pyrazolate-based dinickel(II) systems are shown to constitute suitable building blocks for the targeted assembly of azido-bridged Ni4 complexes with rectangular arrangement of the metal ions. A set of such complexes has been prepared and structurally characterized. mu-1,1-Azide binding within the bimetallic sub-units is controlled by the chosen topology of the pyrazolate ligand scaffold and gives rise to the anticipated ferromagnetic intradimer coupling. Overall magnetic properties of the Ni4 array, however, are mainly determined by the Ni-NNN-Ni torsion of the interdimer mu-1,3-azido linkages. According to the crystallographic results, these torsion angles vary over a wide range, and partial disorder of the mu-1,3-azide bridge in one of the compounds indicates high structural flexibility even in the solid state. Two of the compounds represent rare examples of molecular complexes with a Ni-NNN-Ni torsion angle of almost exactly 90 degrees . The resulting magnetic ground state (neglecting zero-field splitting) is either S = 0 or S = 4 depending on the Ni-NNN-Ni torsion, and in one case a drastic change is observed upon extrusion of lattice solvent.