Anion directed template synthesis of Cu(II) complexes of a N,N,O donor mono-condensed Schiff base ligand: A molecular scaffold forming highly ordered H-bonded rectangular grids

Anion directed, template syntheses of two dinuclear copper(II) complexes of mono-condensed Schiff base ligand Hdipn (4-[(3-aminopentylimino)-methyl]-benzene-1,3-diol) involving 2,4-dihydroxybenzaldehyde and 1,3-diaminopentane were realized in the presence of bridging azide and acetate anions. Both complexes, [Cu₂(dipn)₂(N₃)₂] (1) and [Cu₂(dipn)₂(OAc)₂] (2) have been characterized by X-ray crystallography. The two mononuclear units are joined together by basal-apical, double end-on azido bridges in complex 1 and by basal-apical, double mono-atomic acetate oxygen-bridges in 2. Both complexes form rectangular grid-like supramolecular structures via H-bonds connecting the azide or acetate anion and the p-hydroxy group of 2,4-dihydroxybenzaldehyde. Variable-temperature (300-2 K) magnetic susceptibility measurements reveal that complex 1 has antiferromagnetic coupling (J = −2.10 cm⁻¹) through the azide bridge while 2 has intra-dimer ferromagnetic coupling through the acetate bridge and inter-dimer antiferromagnetic coupling through H-bonds (J = 2.85 cm⁻¹, J′ = −1.08 cm⁻¹).     

Dinuclear triply bridged copper(II)-carboxylato compounds with different bischelating ligands: Synthesis, crystal structure, spectroscopic and magnetic properties

Three new triply bridged dinuclear copper(II) compounds containing carboxylato bridges, [Cu₂(μ-CH₃COO-κ-O¹,O²)₂(μ-CH₃COO-κ-O¹)(dpyam)₂](BF₄) (1), [Cu₂(μ-CH₂CH₃COO-κ-O¹,O²)(μ-OH)(μ-OH₂)(bpy)₂](ClO₄)₂ (2) and [Cu₂(μ-CH₃COO-κ-O¹,O²)(μ-OH)(μ-OH₂)(phen)₂](ClO₄)₂ (3) (in which dpyam = di-2-pyridylamine, bpy = 2,2-bipyridine, phen = phenanthroline), have been synthesized in order to investigate the magnetic super-exchange pathway between coupled copper(II) centres. All three compounds display a distorted square-pyramidal arrangement around each copper(II) ion with a CuN₂O₃ chromophore. Compound 1 has three acetato bridges, two of which connect each square pyramid at two equatorial sites in a triatomic bridging mode and the third acetato bridge acts at the apical site in the monoatomic bridging mode. The structures of compounds 2 and 3 are mutually similar. In each dinuclear unit, both copper(II) ions are linked at two equatorial positions through a hydroxo bridge and a triatomic carboxylato bridge and at the axial position through a water molecule.The magnetic susceptibility measurements, measured from 5 to 300 K, revealed an antiferromagnetic interaction between the Cu(II) ions in compound 1 and a ferromagnetic interaction for compounds 2 and 3 with singlet-triplet energy gaps (J) of −56, 149 and 120 cm⁻¹, for compounds 1, 2 and 3, respectively.     

Syntheses, crystal structures, and magnetic properties of two cyclic dimer M2L2 complexes constructed from a new nitronyl nitroxide ligand and M(hfac)2 (M = Cu, Mn)

Two new binuclear radical complexes derived from a new long nitronyl nitroxide ligand, 2-[4-(5-pyrimidyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (4-NITPhPyrim), and M(hfac)₂ (M²⁺ = Cu²⁺, Mn²⁺; hfac⁻ = hexafluoroacetylacetonato), [Cu(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (1) and [Mn(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (2), were synthesized as well as characterized structurally and magnetically. X-ray analysis indicates that 1 and 2 are rectangle-like centrosymmetric dimer M₂L₂ complexes. Magnetic measurements indicate that there are two types of magnetic exchanges in 1: the ferromagnetic (FM) exchange between the Cu(II) ion and the directly bonded nitroxide unit (J₁ = 24.20 cm⁻¹) and the weak FM exchange of Cu-NIT through the pyrimidine and phenyl rings (J₂ = 0.62 cm⁻¹). Besides the strong antiferromagnetic (AFM) coupling between the Mn(II) ion and the directly bonded nitroxide unit (J = −87.61 cm⁻¹), there is a weak FM interaction between the two Mn-NIT pairs (θ = 0.39 K) in 2.     

Magnetic properties and circular dichroism of 1D chains built from chiral mononuclear and non-chiral trinuclear Cu(II) complexes with α-aminocarboxylates

Coordination polymers Cu(l-Pro)(ClO₄)(H₂O)₂ (1) and Cu₃(Gly)₄(H₂O)₂(NO₃)₂ (2) were synthesized and characterized structurally. Compound 1 possesses the structure of 1D chain, where Cu(II) ions are linked by carboxyl-group in syn-anti conformation in equatorial-equatorial mode. Compound 2 is polymeric chain, consisting from trinuclear blocks Cu₃(Gly)₄(H₂O)₂²⁺. In each of these units Cu(II) ions are linked by carboxyl-group in the same way as in 1, while trinuclear units Cu₃(Gly)₄(H₂O)₂²⁺ are linked by NO₃⁻ ions, acting as the bridges between Cu(II) ions of neighboring trinuclear units. Circular dichroism properties of 1 were studied in solid state and solution. Magnetic measurements revealed that there were ferromagnetic exchange interactions between Cu(II) ions in 1 (J = +1.22(1) cm^-1 for Hamiltonian ) and 2 (J = +1.17(2) cm^-1 for Hamiltonian ).     

Oxidative nuclease activity of ferromagnetically coupled μ-hydroxo-μ-propionato copper(II) complexes [Cu3(L)2(μ-OH)2(μ-propionato)2] (L = N-(pyrid-2-ylmethyl)R-sulfonamidato, R = benzene, toluene, naphthalene)

Three doubly-bridged, trinuclear copper(II) compounds with hydroxo and carboxylato bridges, ^∞₁[Cu₃(L1)₂(μ-OH)₂(μ-propionato)₂](1), [Cu₃(L2)₂(μ-OH)₂(μ-propionato)₂(DMF)₂] (2) and ^∞₁{[Cu₃(L3)₂(μ-OH)₂(μ-propionato)₂]} [Cu₃(L3)₂(μ-OH)₂(μ-propionato)₂(DMF)₂]} (3) [HL1 = N-(pyrid-2-ylmethyl)benzenesulfonylamide, HL2 = N-(pyrid-2-ylmethyl)toluenesulfonylamide, HL3 = N-(pyrid-2-ylmethyl)naphthalenesulfonylamide], have been synthesized and characterized. 1 is built from [Cu₃(L1)₂(μ-OH)₂(μ-propionato)₂] clusters. Each unit contains three copper(II) with two different coordination environments: the terminal centers are square-base pyramidal whereas the central copper is square planar. 2 presents a similar square-base pyramidal geometry in the terminal centers, but the central copper is six-coordinate. 3 shows an unusual 1D coordination polymer comprised of two distinct building blocks: one similar to that found in 1 and the other similar to that found in 2. The magnetic susceptibility measurements (2-300 K) reveal a ferromagnetic interaction between the Cu(II) ions with J values of 76.0, 55.0, and 48.0 cm⁻¹ for 1, 2, and 3, respectively. Emission spectroscopy, thermal denaturation, viscosimetry and cyclic voltammetry show an interaction of the complexes with DNA through the sugar-phosphate backbone. All three Cu(II) complexes were found to be very efficient agents of plasmid DNA cleavage in the presence of ascorbato or mercaptopropionic acid. Both the kinetics and the mechanism of the cleavage reaction have also been examined.     

EPR and magnetic properties of [Mn(μ-Cl)2(bpy)]n: An unusual ferromagnetic interaction in a Mn(II) chloro-bridged polymer

The study of the magnetic properties and EPR spectra of the one-dimensional bis(μ-chloro) Mn(II) polymer [Mn(μ-Cl)₂(bpy)]_n (1) (bpy = 2,2′-bipyridine) is reported. Magnetic susceptibility measurements reveal a weak ferromagnetic interaction between the Mn(II) ions (J = +0.19 cm⁻¹). This is the first polymer of six-coordinated Mn(II) ions with a [Mn₂(μ-Cl)₂]²⁺ magnetic repeating unit, showing a ferromagnetic interaction. The coordination octahedra are elongated in the Cl?Cl direction and the elongation axes are parallel along the chain. Extended Hückel calculations show that the octahedra share an equatorial-apical edge, with the equatorial plane being parallel, and perpendicular to the Mn₂(μ-Cl)₂. Due to this disposition, the overlap through the chloride bridges is small, so the antiferromagnetic contribution must also be small and, therefore, a ferromagnetic behaviour is observed. The EPR spectra of a polycrystalline sample of 1 at different temperatures are also reported. A variation of the bandwidth with temperature is observed, which could be because this ferromagnetic interaction is weak: above 150 K the dipolar interaction is the predominant effect, while below 150 K the magnetic exchange interaction dominates.     

Chlorido-bridged polymeric and dinuclear copper(II) complexes with tridentate Schiff base: Synthesis, crystal structure and magnetic properties

Two copper(II) complexes, [Cu(qsal)Cl](DMF) (1) and [Cu₂(qsalBr)₂Cl₂](DMF) (2), with tridentate Schiff base ligands, 8-(salicylideneamino)quinoline (Hqsal) and 8-(5-bromo-salicylideneamino)quinoline (HqsalBr), respectively, were synthesised and structurally characterized. Each copper(II) ion in the two complexes is in a distorted square pyramidal N₂OCl₂ environment. Complex 1 exists as a polymeric species via equatorial-apical chloride bridges, whereas 2 is a di-chlorido-bridged dinuclear complex, where each bridging chloride simultaneously occupies an in-plane coordination site on one copper(II) ion and an apical site on the other copper(II) ion. Variable-temperature magnetical susceptibility measurements on the two complexes in the temperature range 2-300 K indicate the occurrence of intrachain ferromagnetic (J = +6.58 cm⁻¹) and intramolecular antiferromagnetical (J = −6.91 cm⁻¹) interactions.     

Structures and magnetic properties of dicopper(II) and dinickel(II) complexes with end-on azido bridges

An asymmetric single EO azido bridged dinuclear copper(II) complex, [Cu₂(dmterpy)₂(μ-1,1-N₃)(N₃)₂] · NO₃ · (H₂O)₂1 [dmterpy = 5,5″-dimethyl-2,2′:6′,2″-terpyridine], and a double EO azido bridged dinuclear nickel(II) complex, [Ni₂(pbdiim)₄(μ-1,1-N₃)₂] · 2(N₃) · 6(H₂O) 2 [pbdiim = 2-(2′-pyridyl)benzo[1,2-d:4,5-d′]diimidazole], have been synthesized and characterized structurally and magnetically. Compound 1 consists of a single EO azido bridged Cu^II dimer in which each Cu^II ion is five-coordinated in the form of a distorted square-based pyramid. The N_(μ−1,1) atom holds on the apical position of one Cu^II pyramid with an elongated bond length of 2.305 Å and on the basal plane of another distorted Cu^II pyramid with a bond length of 1.991 Å. The Cu-N_(μ−1,1)-Cu angle is 117.4 (2)°. The copper(II) dimer forms a 1 D zig-zag chain via hydrogen bondings between azide ions, water molecules and the nitrate anion. Compound 2 consists of a double EO azido bridged Ni^II dimer with the Ni-N_(μ−1,1)-Ni bond angle of 102.96 (13)°. The coordination geometry of Ni^II is octahedral. Their magnetic properties have been measured in the range from 300 to 2 K and correlated with the molecular structures. Compound 1 shows weak ferromagnetic interactions within the copper(II) dimer (J = 2.88 cm⁻¹), despite the large EO azide bridge angle (117.4 (2)°). The intramolecular coupling between the Ni^II (S = 1) ions in compound 2 was found to be ferromagnetic (J = 27.87 cm⁻¹).     

1D/2D coordination polymers of copper(II) having two superexchange pathways: syntheses, crystal structures and magnetic properties

Two new polynuclear complexes of Cu(II), [(μ-1,1,3-N₃)₂{Cu₂(me₂tn)₂(N₃)₂}]_n (1) (me₂tn=2,2-dimethylpropane-1,3-diamine) and [Cu₂(μ-C₂O₄)(μ-N₃)(ipr₂en)₂]_n(ClO₄)_n (2) (ipr₂en=N,N^′-di-isopropylethane-1,2-diamine) have been synthesized and structurally characterized by X-ray crystallography. The crystal structure of 1 displays a 2D network in which distorted octahedral copper(II) centers, chelated by a me₂tn ligand and bound to a terminal azide, are connected through μ-1,1,3 bridging azide anions. The structure of 2 shows 1D chains comprising alternating [(ipr₂en)Cu-Ox-Cu(ipr₂en)] units and end-to-end azide ligand. The chains on mutual H-bonding interaction through ClO₄⁻, give rise to a 2D supramolecular architecture. The magnetic data of complexes were recorded in the temperature range, 300-2 K. In case of complex 1, the magnetic data are consistent with a ferromagnetic interaction through the end-on azide bridge (J_FM=10 cm⁻¹) and a weak antiferromagnetic interaction (zj=−0.8 cm⁻¹) between the ferromagnetically coupled dimers and an average g-value of 2.05. The susceptibility data of 2 were fitted using an alternating AF-AF chain spin 1/2 law which leads to the following parameters J_oxalate=−180 cm⁻¹, J_azide=−43 cm⁻¹ and g=2.25 cm⁻¹.     

A new Cu-Mn heterobinuclear complex exhibiting magnetization relaxation

A new heterometallic complex [CuMn(5-Brsap)₂(MeOH)(Ac)] ⋅ CH₃OH (1) (5-Brsap = 5-bromo-2-salicylideneamino-1-propanol) has been synthesized and characterized structurally as well as magnetically. Complex 1 has an alkoxo-bridged Cu(II) and Mn(III) heterobinuclear core, where the Mn(III) and Cu(II) ions have elongated octahedral and square-pyramidal geometries, respectively. In dc magnetic susceptibility measurements reveal that there is strong ferromagnetic interaction between the Mn(III) and Cu(II) ions with an exchange coupling constant J = 67.64 cm⁻¹. The ac magnetic susceptibility measurements, frequency dependence in both the real and imaginary signals is observed, which indicates slow relaxation of magnetization. An Arrhenius plot gave the effective anisotropy barrier Δ/k_B = 11.58 K and the pre-exponential factor ι₀ = 1.28 × 10⁻⁶ s.     

[{Cu(pz)(Opo)}2(μ-Cl)2]: A new dinuclear copper(II) complex with a chloride bridge and mixed blocking ligands

A new copper(II) complex with chloride bridges and mixed blocking ligands, [{Cu(pz^Ph)(Opo)}₂(μ-Cl)₂] (1), whereby pz^Ph = 3-phenyl-pyrazolyl, and OpoH = 2-hydroxypyridine-N-oxide, has been obtained by degrading tris(pyrazolyl)borate in the presence of hydrated CuCl₂ salt and the ligand Opo⁻. The molecular structure of 1 was solved by X-ray diffraction. The two Cu(II) atoms of the dinuclear complex have a pyramidal arrangement in which the two pyramids share one base-to-apex edge with parallel basal planes. Magnetic susceptibility measurements revealed ferromagnetic coupling between the Cu atoms, with J = +8.72 cm⁻¹. X-band EPR spectra of CH₂Cl₂ solutions of 1 were recorded at different temperatures.     

[Cu4(H2O)4(dmapox)2(btc)]n · 10nH2O: The first two-dimensional polymeric copper(II) complex with bridging μ-trans-oxamidate and μ4-1,2,4,5-benzentetracarboxylato ligands: Synthesis, crystal structure and DNA binding studies

A two-dimensional copper(II) polymer with formula of [Cu₄(H₂O)₄(dmapox)₂(btc)]_n · 10nH₂O, where dmapox is the dianion of N,N′-bis[3-(dimethylamino)propyl]oxamide and btc is the tetra-anion of 1,2,4,5-benzenetetracarboxylic acid, was synthesized and characterized by elemental analysis, conductivity measurement, IR and electronic spectral studies. The crystal structure of the complex has been determined by X-ray single-crystal diffraction. The structure consists of crystallized water molecules and neutral two-dimensional copper(II) coordination polymeric networks constructed both by the bis-tridentate μ-trans-dmapox and tetra-monodentate μ₄-btc bridging ligands. Each btc ligand links four trans-dmapox-bridged binuclear copper(II) building blocks [Cu₂(H₂O)₂(trans-dmapox)]²⁺ and each binuclear copper(II) building block attaches to two btc ligands forming an infinite 2D layer which consists of 4+4 grids with dimensions of 13.563(5) × 15.616(5) Å. The environment around the copper(II) atom can be described as a distorted square-pyramid and the Cu?Cu separations through μ-trans-dmapox and μ₄-btc bridging ligands are 5.225 Å (Cu1-Cu1ⁱ), 5.270 Å (Cu2-Cu2ⁱⁱ), 6.115 Å (Cu1-Cu2), 9.047 Å (Cu1-Cu2ⁱⁱⁱ) and 10.968 Å (Cu1-Cu1ⁱⁱⁱ), respectively. Abundant hydrogen bonds among the crystallized, the coordinated water molecules, and the uncoordinated carboxyl oxygen atoms cross-link the two-dimensional layers into an overall three-dimensional channel-like framework. The interaction of the copper(II) polymer with calf thymus DNA (CT-DNA) has been investigated by using absorption, emission spectral and electrochemical techniques. The results indicate that the copper(II) polymer interacts with DNA strongly (K_b = 4.8 × 10⁵ M⁻¹ and K_sv = 1.1 × 10⁴) and the interaction mode between the copper(II) polymer and DNA may be the groove binding. To the best of our knowledge, this is the first report about the crystal structure and DNA-binding studies of a two-dimensional copper(II) polymer bridged both by the trans-oxamidate and btc ligands.     

Synthesis, spectroscopy and magnetism of novel metal complexes of 3-aminoflavone (3-af). X-ray crystal structure of 3-af and [Cu(3-af)2(NO3)2]

The synthesis and characterization of four new complexes with the bioactive ligand 3-aminoflavone (3-af) are reported. The complexes of general formula [M(3-af)₂(H₂O)₂](NO₃)₂ · nH₂O], where M = Co(II), Ni(II), and Zn(II), and n = 0, 2, 0, respectively, and [Cu(3-af)₂(NO₃)₂] compound were prepared and studied. In particular, to investigate the binding in detail, the crystal structures of the free ligand (3-af) and [Cu(3-af)₂(NO₃)₂] (1) were determined. The new coordination compounds were identified and characterized by elemental analysis, magnetic measurements, and infrared and ligand-field spectra. The crystal structure of the Cu(II) complex reveals that the ligand acts as a N,O-bidentate chelate ligand forming a five-membered ring with the copper(II) ion. The copper(II) ion is octahedrally surrounded by the two amino nitrogens and two carbonyl oxygens from two chelating organic ligands in trans arrangement. Two molecules of coordinated nitrate anions occupy axial positions. The spectral and magnetic properties are in accordance with the structural data of the copper(II) compound. From X-ray powder-diffraction patterns and IR spectra, the complexes of nickel(II) (2) and cobalt(II) (3) were found to be mutually isomorphous. The results of the spectroscopic studies suggest a mononuclear structure of 2 and 3 complexes. The variable-temperature (1.8-300 K) magnetic susceptibility data of 2 indicate a weak ferromagnetic interaction. The magnetic behavior of complex 3 is characteristic of cobalt(II) systems with an important orbital contribution via spin-orbit-coupling and also suggests a weak ferromagnetic interaction.     

Chemistry at the apical position of square-pyramidal copper(II) complexes: Synthesis, crystal structures, and magnetic properties of homopolynuclear complexes with azido bridges containing [Cu(AA)(BB)] moieties (AA = acetylacetonate; BB = 1,10-phenanthroline, bipy = 2,2′-bipyridine)

Three new homopolynuclear complexes with azido bridges have been obtained by using [Cu(AA)(BB)]⁺ building-blocks (AA = acetylacetonate; BB = 1,10-phenanthroline or 2,2′-bipyridine). The reaction between [Cu(acac)(phen)(H₂O)](ClO₄) and NaN₃ leads to a mixture of two compounds: a binuclear complex, [{Cu(acac)(phen)}₂(μ_1,3-N₃)](ClO₄) · 2H₂O (1), and a linear tetranuclear one, [{Cu(acac)(phen)(ClO₄)}₂{Cu(phen)(μ_1,1-N₃)₂}₂] (2). The reaction between [Cu(acac)(bipy)(H₂O)](ClO₄) and NaN₃ affords also a mixture of two compounds: [{Cu(acac)(bipy)}₂(μ_1,3-N₃)]₃(ClO₄)₃ · 3.75H₂O (3) and [Cu(acac)(bipy)(N₃)][Cu(acac)(bipy)(H₂O)](ClO₄) (4). The X-ray crystal structures of compounds 1-4 have been solved (for compound 4 the crystal structure was previously reported). In compounds 1 and 3, two {Cu(AA)(BB)} fragments are bridged by the azido anion in an end-to-end fashion. Two isomers, cis and trans with respect to azido bridge, were found in crystal 3. The structure of compound 2 consists of two Cu(II) central cations bridged by two μ_1,1-azido ligands, each of them being also connected to a {Cu(acac)(phen)} fragment through another μ_1,1-azido ligand. The cryomagnetic properties of the compounds 1 and 2 have been investigated and discussed. The magnetic behaviour of compound 1 shows the absence of any interactions between the metallic ions. In the tetranuclear complex 2, the magnetic interactions between the external and central copper(II) ions(J₁), and between the central metallic ions (J₂) were found ferromagnetic (J₁ = 0.36 cm⁻¹, J₂ = 7.20 cm⁻¹).     

Synthesis, structure and magnetic studies of two-dimensional network of Cu(II) polymer using malonate and 4,4′-azobispyridine ligands

The malonato-bridged copper(II) complex [Cu(mal)(H₂O)(azpy)_1/2] · H₂O (1) (mal = malonate, azpy = 4,4′-azobispyridine) has been synthesized and characterized by X-ray diffraction. The structure of 1 consists of malonato-bridged uniform copper(II) chains which are covalent connected through azpy to form two-dimensional wavelike network. The magnetic pathway of complex 1 is through a single syn-anti carboxylate bridge connecting equatorial and equatorial positions of adjacent copper(II) atoms, and have the value of the intrachain ferromagnetic coupling (J = 8.73(3) cm⁻¹) and interchain antiferromagnetic coupling (zJ′ = − 1.31(1) cm⁻¹) through a numerical expression for a ferromagnetic uniform chain.     

Synthesis, crystal structure, magnetism and electrochemical properties of two copper(II) furoyltrifluoroacetonate complexes with nitroxide radical

Two new magnetic copper compounds were obtained using the 4,4,4-trifluoro-1-furoylbutane-1,3-dione (Ftfac) ligand and two nitroxide radicals: 3-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITmPy) and 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-N-oxy (Tempol). The complexes with formula [Cu(Ftfac)₂(NITmPy)₂] (1) and [Cu(Ftfac)₂(Tempol)] (2) were structurally characterized by single-crystal X-ray diffraction. In compound 1, the copper ion has a distorted octahedral environment, bound to two NITmpPy ligands through the nitrogen atom of the pyridine ring. In compound 2, the copper ion has a distorted pyramidal environment in which the apical position is occupied by the oxygen atom of the Tempol hydroxyl group. The temperature dependence of the magnetic susceptibility of the two compounds was investigated. It was found that compound 1 presents ferromagnetic interaction (J = 9.1 cm⁻¹) among copper(II) ions and NITmPy radicals. As a result of the interconnection between molecular moieties through H-bonds, compound 2 presents an unusual magnetic behavior with alternating ferro- and antiferromagnetic interactions.     

Structure and magnetic properties of polynuclear copper(II) compounds with syn-anti carboxylato- and bromo-bridges

Synthesis, spectroscopic and magnetic properties, and X-ray crystal structures of two copper(II) polymers Cu(2-qic)Br (2-qic = quinoline-2-carboxylate) (1) and Cu(2-pic)Br (2-pic = pyridine-2-carboxylate) (2) are described. These compounds are isostructural with Cu(2-qic)Cl and Cu(2-pic)Cl, respectively, the X-ray crystal structures of which were reported recently. Both complexes are polynuclear copper(II) compounds (1D and 2D, respectively) based on syn-anti carboxylate bridges and additionally on linear monobromo- (in 1) and dibromo-bridging (in 2) motifs. The magnetic properties were investigated in the temperature range 1.8-300 K. They reveal the occurrence of strong antiferromagnetic coupling (J₁ = −102.5 cm⁻¹) through the single bromo-bridge in 1, which is much stronger than that transmitted by the single chloro-bridge (J = −57.0 cm⁻¹). Very weak ferromagnetic interaction through the syn-anti carboxylate bridge J₂ is expected as it was observed in isomorphous Cu(2-qic)Cl (J = 0.37 cm⁻¹). For 2 a weak ferromagnetic couplings through the syn-anti carboxylate (zJ′ = 1.35 cm⁻¹) and dibromo-bridges (J = 8.31 cm⁻¹) were found. The experimental results indicate that the observed ferromagnetic exchange through dibromo-bridge is weaker than that in the chloride analog (J = 15.0 cm⁻¹). The magnitude of magnetic interactions is discussed on the basis of structural data of compounds 1 and 2 and their halide analogues.     

Mono, di and polynuclear Cu(II)-azido complexes incorporating N,N,N reduced schiff base: syntheses, structure and magnetic behavior

Three kinds of copper(II) azide complexes have been synthesised in excellent yields by reacting Cu(ClO₄)₂ · 6H₂O with N,N-bis(2-pyridylmethyl)amine (L¹); N-(2-pyridylmethyl)-N′,N′-dimethylethylenediamine (L²); and N-(2-pyridylmethyl)-N′,N′-diethylethylenediamine (L³), respectively, in the presence of slight excess of sodium azide. They are the monomeric Cu(L¹)(N₃)(ClO₄) (1), the end-to-end diazido-bridged Cu₂(L²)₂(μ-1,3-N₃)₂(ClO₄)₂ (2) and the single azido-bridged (μ-1,3-) 1D chain [Cu(L³)(μ-1,3-N₃)]_n(ClO₄)_n (3). The crystal and molecular structures of these complexes have been solved. The variable temperature magnetic moments of type 2 and type 3 complexes were studied. Temperature dependent susceptibility for 2 was fitted using the Bleaney-Bowers expression which led to the parameters J = −3.43 cm⁻¹ and R = 1 × 10⁻⁵. The magnetic data for 3 were fitted to Baker’s expression for S = 1/2 and the parameters obtained were J = 1.6 cm⁻¹ and R = 3.2 × 10⁻⁴. Crystal data are as follows. Cu(L¹)(N₃)(ClO₄): Chemical formula, C₁₂H₁₃ClN₆O₄Cu; crystal system, monoclinic; space group, P2₁/c; a = 8.788(12), b = 13.045(15), c = 14.213(15) Å; β = 102.960(10)°; Z = 4. Cu(L²)(μ-N₃)(ClO₄): Chemical formula, C₁₀H₁₇ClN₆O₄Cu: crystal system, monoclinic; space group, P2₁/c; a = 10.790(12), b = 8.568(9), c = 16.651(17) Å; β = 102.360(10)°; Z = 4. [Cu(L³)(μ-N₃)](ClO₄): Chemical formula, C₁₂H₂₁ClN₆O₄Cu; crystal system, monoclinic; space group, P2₁/c; a = 12.331(14), b = 7.804(9), c = 18.64(2) Å; β = 103.405(10)°; Z = 4.     

Structure and magnetic properties of polynuclear chloro- and hydroxo-bridged copper(II) complexes formed by a tetramacrocyclic derivative of 1,4,7-triazacyclononane

Two new copper(II) complexes of the ligand 1,2,4,5-tetrakis(1,4,7-triazacyclononan-1-ylmethyl)benzene (L^dur) have been synthesized and characterized by single crystal X-ray studies. The first, [Cu₄L^dur(μ₂-OH)₄]Cl₂(PF₆)₂ · 8H₂O (1), was isolated from a solution of L^dur and Cu²⁺ at pH 9. Under acidic conditions (pH 3), a polymeric complex, {[Cu₄L^dur(μ₂-Cl)₆](PF₆)₂ · 10H₂O}_n (2), crystallized from solution. In both complexes, each of the four triazacyclononane (tacn) rings of the L^dur ligand facially coordinate to separate metal centres. Pairs of Cu(II) centres are then doubly-bridged by hydroxo groups in 1, leading to tetranuclear complex cation units featuring pairs of isolated copper(II) dimers with Cu₂(μ₂-OH)₂ cores folded at the O?O lines. Two forms of the tetranuclear units, featuring slightly different Cu₂(μ₂-OH)₂ core geometries, are present in equal amounts within the crystal lattice. In complex 2, chloro bridging ligands link pairs of Cu(II) centres from neighbouring tetranuclear units, forming a 1D helical polymeric structure. Variable-temperature magnetic susceptibility measurements suggest that the hydroxo-bridged copper(II) centres within one of the tetranuclear units in 1 are weakly antiferromagnetically coupled (J = −27 cm⁻¹), whilst those in the other interact ferromagnetically (J = +19 cm⁻¹). Similar measurements indicate weak ferromagnetic coupling (J = +16 cm⁻¹) for the chloro-bridged copper(II) centres in 2.     

Topological control of the spin coupling in dinuclear copper(II) complexes with meta- and para-phenylenediamine bridging ligands

A novel series of copper(II) complexes of formula [Cu(tren)(mpda)](ClO₄)₂ · 1/2H₂O (1), [Cu₂(tren)₂(mpda)](ClO₄)₄ · 2H₂O (2), and [Cu₂(tren)₂(ppda)](ClO₄)₄ · 2H₂O (3) containing the tetradentate tris(2-aminoethyl)amine (tren) terminal ligand and the potentially bridging 1,n-phenylenediamine [n = 3 (mpda) and 4 (ppda)] ligand have been prepared and spectroscopically characterized. X-ray diffraction on single crystals of 1 and 3 show the presence of mono- (1) and dinuclear (3) copper(II) units where the mpda (1) and ppda (3) ligands adopt terminal monodentate (1) and bridging bis(monodentate) (3) coordination modes toward [Cu(tren)]²⁺ cations with an overall non-planar, orthogonal disposition of the phenylene group and the N-Cu-N threefold axis of the trigonal bipyramid of each copper(II) ion [values of the Cu-N-C-C torsion angle (?) in the range of 50.8(3)-79.2(2) (1) and 80.9(2)-86.5(2)° (3)]. Variable-temperature magnetic susceptibility measurements on the dinuclear complexes 2 and 3 show the occurrence of moderate ferromagnetic (J = +8.3 cm⁻¹, 2) and strong antiferromagnetic (J = −51.4 cm⁻¹, 3) couplings between the two copper(II) ions across the meta- and para-phenylenediamine bridges, leading to S = 1 (2) and S = 0 (3) ground spin states [H = −JS₁ · S₂ with S₁ = S₂ = S_Cu = 1/2]. Density functional theory (DFT) calculations on the triplet (2) and broken-symmetry (BS) singlet (3) ground spin states, support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction through the predominantly π-type orbital pathway of the 1,n-phenylenediamine bridge. Finally, a new magneto-structural correlation between the magnitude of the magnetic coupling (J) and the Cu-N-C-C torsion angle (?) has been found which reveals the role of σ- versus π-type orbital pathways in the modulation of the magnetic coupling for m- and p-phenylenediamine-bridged dicopper(II) complexes.