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.     

1-D coordination chains of Cu(hfac)2 and Mn(hfac)2 bridged by phenyl-nitronylnitroxide derivatives

Two alternating 1-D metal-radical linear [L:Cu(hfac)₂]_n and zig-zag [L:Mn(hfac)₂]_n chains (where L = 4-trimethylsilylethynyl-1-(4,4,5,5-tetramethyl-3-oxylimidazoline-1-oxide)benzene) and hfac = hexafluoroacetylacetonate) are described and characterized by X-ray diffraction of their crystals. Bulk magnetic measurements of L:Cu(hfac)₂ indicated a ferromagnetic interaction with J = 6 cm⁻¹ and L:Mn(hfac)₂ yielded ferrimagnetic interactions with J = −95 cm⁻¹. For the latter, a strong increase of their magnetic moment at lowest temperatures was observed only at very low static magnetic field, while for H_dc > 0.05 T saturation effect led to a downward slope after reaching a maximum.     

Structure and magnetic properties of Ln2[Cu(opba)]3(DMSO)6(H2O) · (H2O) compounds with LnLa-Lu exhibiting ladder-like molecular motifs

The reaction of Ln(III) ions with the precursor [Cu(opba)]²⁻ in DMSO has afforded a series of isostructural compounds of general chemical formula Ln₂[Cu(opba)]₃(DMSO)₆(H₂O) · (H₂O), where Ln(III) stands for a lanthanide ion and opba stands for ortho-phenylenebis(oxamato). The crystal structure has been solved for the Gd(III) containing compound. It crystallizes in the orthorhombic system, space group Pbn2₁ (No. 33) with a = 9.4183(2) Å, b = 21.2326(4) Å, c = 37.9387(8) Å and Z = 4. The structure consists of ladder-like molecular motifs parallel to each other. To the best of our knowledge, this is the first Ln(III)Cu(II) coordination polymer family exhibiting the same crystal structure over the whole lanthanide series. The magnetic properties of the compounds have been investigated and the magnetic behavior of the Gd(III) containing compound was studied in more detail.     

Synthesis and characterization of new lanthanide complexes with hexadentate hydrazonic ligands

In this paper, we report the synthesis and the characterization of a novel series of lanthanide (III) complexes with two potentially hexadentate ligands.The ligands contain a rigid phenanthroline moiety and two flexible hydrazonic arms with different donor atom sets (NNN′N′OO and NNN′N′N″N″, respectively for H₂L¹ (2,9-diformylphenanthroline)bis(benzoyl)hydrazone and H₂L² (2,9-diformylphenanthroline)bis(2-pyridyl)hydrazone).Both nitrate and acetate complexes of H₂L¹ with La, Eu, Gd, and Tb were prepared and fully characterized, and the X-ray crystal structure of the complex [Eu(HL¹)(CH₃ COO)₂] · 5H₂O is presented.The stability constants of the equilibria Ln³⁺ + H₂L¹ = [Ln(H₂L¹)]³⁺ and Ln³⁺ + (L¹)²⁻ = [Ln(L₁)]⁺ (Ln = La(III), Eu(III), Gd(III), and Tb(III)) are determined by UV spectrophotometric titrations in DMSO at t = 25 °C. The nitrate complexes of H₂L² with La, Eu, Gd and Tb were also synthesized, and the X-ray crystal structures of [La(H₂L²)(NO₃)₂(H₂O)](NO₃), [Eu(H₂L²)(NO₃)₂](NO₃) and [Tb(H₂ L²)(NO₃)₂](NO₃) are discussed.     

Electrochemical reduction properties of A-frame compounds and crystal structure of Pd2(dppm)2(Me)2(Br) dimer

Two series of A-frame complexes, [Pd₂(dppm)₂(R)₂(μ-X)]⁺ (R = Me and X = Cl, Br, I, H; R = Mes and X = Br, I), were investigated by cyclic voltammetry (CV). The 2-electron reduction potentials for the first series increase from I (−1.10), Br (−1.17), Cl (−1.25) to H (−1.65 V versus SCE, in CHCl₃), as well as in the second series; Br (−1.35) and I (−1.38 V versus SCE, in THF). The nature of the LUMO where the electron reduction takes place is qualitatively addressed by DFT on the corresponding model complexes [Pd₂(H₂PCH₂PH₂)₂(R)₂(μ-X)]⁺. The LUMO and (LUMO + 1) of the halide derivatives exhibit the presence of Pd d_x²-y² atomic orbitals interacting in an anti-bonding fashion with the n-donor orbitals of X⁻, P, and Me⁻, explaining in part the observed reactivity upon reduction. The X-ray structure of [Pd₂(dppm)₂(Me)₂(μ-Br)]⁺ compound exhibits the typical A-frame structure with a Pd?Pd non-bonding distance of 3.036(1) Å, and long Pd-Br bonds of 2.5623(5) and 2.5793(5) Å.     

Synthesis, characterization, and magnetic properties of new binuclear CuCu bis(oxamato) complexes

Two new neutral, binuclear Cu^IICu^II bis(oxamato) complexes with the formula [Cu₂(opba)(pmdta)(MeOH)] · 1/2MeOH · dmf (3) and [Cu₂(nabo)(pmdta)(MeOH)] (4), with opba = o-phenylene-bis(oxamato), nabo = 2,3-naphthalene-bis(oxamato), pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine and dmf = dimethylformamide have been synthesized and their crystal structures have been determined. The structure of 3 consists of dimeric [Cu₂(opba)(pmdta)(MeOH)] entities, joined together by mutual intermolecular Cu?O contacts of the Cu²⁺ ion of one [Cu(opba)]²⁻ complex fragment and one carboxylate atom of the oxamato group of a second [Cu(opba)]²⁻ complex fragment. The structure of 4 consists of neutral binuclear complexes joined together by hydrogen bonds and π-π interactions, giving rise to an unique supramolecular 1D-chain. The magnetic properties of 3 and 4 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter, identical values of (−114 ± 2) cm⁻¹ (3) and (−112 ± 2) cm⁻¹ (4) were obtained.     

Synthesis and structural characterization of copper(II) bishexafluoroacetylacetonate complexes with N-donor ligands

The reactions of Cu(hfac)₂ with different N-donor ligands such as 2-ethynylpyridine and imidazole give copper complexes Cu(hfac)₂(ethynylpyridine) (1) and Cu(hfac)₂(ImH)₂ (2), respectively. The reaction of Cu(hfac)₂ · (ethynylpyridine) (1) and ethynylpyridine with oxygen in tmeda (tmeda = N,N,N′,N′-tetramethylethylenediamine) in the presence of copper(I) chloride gives Cu(hfac)₂(tmeda) (3). Finally, [Cu(hfac)₂(H₂O)]₂(μ-TCNE) (4) was prepared by reaction of Cu₂O on the free acid β-diketone in the presence of TCNE (TCNE = tetracyanoethylene) (ratio 1.5:1:1), under an atmosphere of oxygen-free Ar. The previously synthesized Cu(hfac)TCNE proceeded further reaction by disproportionation, yielding [Cu(hfac)₂(H₂O)]₂(μ-TCNE). All new compounds have been structurally characterized and their thermal properties were examined by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC).     

Syntheses, spectroscopic characterization and X-ray structural studies of lanthanide complexes with adamantyl substituted 4-acylpyrazol-5-one

Synthesis and spectroscopic characterization of new lanthanide complexes [Ln(Q_AD)₃(EtOH)(H₂O)], (Ln = Tb, Eu; HQ_AD = 1-phenyl-3-methyl-4-adamantylcarbonyl-pyrazol-5-one), [H₃O][Tb(Q_AD)₄], [Ln(Q_AD)₃(N-N)] (Ln = Tb, Eu; N-N = 1,10-phenanthroline (Phen), 2,2′-bipyridyl (Bipy), 4,4′-dimethyl-2,2′-bipyridyl (4,4′-Me₂Bipy)) are reported. The crystal structures of the proligand HQ_AD and of complexes [H₃O][Tb(Q_AD)₄] and [Tb(Q_AD)₃(4,4′-Me₂Bipy)] have been determined. In both complexes the lanthanide ions are in a square antiprismatic environment, the H₃O⁺ cation in the former acid complex being stabilized by H-bonding. Luminescence studies have been performed on selected derivatives.     

The interesting DNA-binding properties of three novel dinuclear Ru(II) complexes with varied lengths of flexible bridges

Three binuclear Ru(II) complexes with two [Ru(bpy)₂(pip)]²⁺-based subunits {where bpy = 2,2′-bipyridine and pip = 2-phenylimidazo[4,5-f][1,10]phenanthroline} being linked by varied lengths of flexible bridges, were synthesized and characterized by ¹H NMR, elemental analysis, UV-visible (UV-vis) and photoluminescence spectroscopy. The structures of the three complexes were optimized by density functional theory calculations. The interaction of the complexes with calf thymus DNA was investigated by UV-vis and luminescence titrations, steady-state emission quenching by [Fe(CN)₆]⁴⁻, DNA competitive binding with ethidium bromide, DNA melting experiments, and viscosity measurements. The experimental results indicated that the three complexes bound to the DNA most probably in a threading intercalation binding mode with high DNA binding constant values three orders of magnitude greater than the DNA binding constant value reported for proven DNA intercalator, mononuclear counterpart [Ru(bpy)₂(p-mopip)]²⁺ {p-mopip = 2-(4-methoxylphenyl)imidazo[4,5-f][1,10]phenanthroline}.     

Synthesis, crystal structures and magnetic characterization of heterodinuclear CuGd and CuTb Schiff base complexes

Preparation, crystal structures and magnetic properties of new heterodinuclear Cu^IIGd^III (1) and Cu^IITb^III (2) complexes [CuLn(L)(NO₃)₂(H₂O)₃MeOH]NO₃·MeOH (where Ln = Gd, Tb) with the hexadentate Schiff-base compartmental ligand N,N′-bis(5-bromo-3-methoxysalicylidene)propylene-1,3-diamine (H₂L = C₁₉H₂₀N₂O₄Br₂) (0) have been described. Crystal structure analysis of 1 and 2 revealed that they are isostructural and form discrete dinuclear units with dihedral angle between the O1Cu1O2 and O1Gd1/Tb1O2 planes equal to 2.5(1)° and 2.6(1)°, respectively. The variable-temperature and variable-field magnetic measurements indicate that the metal centers in 1 and 2 are ferromagnetically coupled (J = 7.89 cm⁻¹ for 1). Crystal and molecular structure of the Schiff base ligand (0) has been also reported. The complex formation changes the conformation of Schiff base ligand molecule.     

Advances on the interaction of polypyridyl Cr(III) complexes with transporting proteins and its potential relevance in photodynamic therapy

The present study reports a detailed investigation into the interaction of [Cr(phen)₂(dppz)]³⁺ and [Cr(phen)₃]³⁺ with transferrin, the key protein for the transport of Fe³⁺ in blood plasma; its cycle holds promise as an attractive system for strategies of drug targeting to tumor tissues. This can allow us to understand further the role of both complexes as sensitizers in photodynamic therapy (PDT). Chromium(III) complexes, [Cr(phen)₂(dppz)]³⁺ and [Cr(phen)₃]³⁺, (phen = 1,10-phenanthroline and dppz = dipyridophenazine), where dppz is a planar bidentate ligand with an extended π system, have been found to bind strongly with apotransferrin (apoTf) with an intrinsic binding constant, K_b, of (1.8 ± 0.3) × 10⁵ M^− 1 and (1.1 ± 0.1) × 10⁵ M^− 1 at 299 K, for apoTf-[Cr(phen)₂(dppz)]³⁺ and apoTf-[Cr(phen)₃]³⁺, respectively. The interactions of apoTf with the different Cr(III) complexes were assessed employing UV-visible absorption, fluorescence and circular dichroism spectroscopy. The relative fluorescence intensity of the protein decreased when the increasing concentration of Cr(III) complex was added, suggesting that perturbation around the Trp and Tyr residues took place. The analysis of the thermodynamic parameters ΔG, ΔH, ΔS indicated that the presence of the Cr(III) complex stabilizes the protein with a strong entropic contribution. The binding distances and transfer efficiencies for apoTf-[Cr(phen)₂(dppz)]³⁺ and apoTf-[Cr(phen)₃]³⁺ binding reactions were calculated according to Föster theory of non-radiation energy transfer. All these experimental results suggest that [Cr(phen)₂(dppz)]³⁺ and [Cr(phen)₃]³⁺ bind strongly to apoTf indicating that this protein could act as a carrier of these complexes for further applications in PDT.     

Remarkable chiral and luminescent properties of novel Yb(III) and Eu(III) complexes containing BINAPO ligand

Lanthanide complexes are of great importance for their prospective applications in wide range of science and technology. Chiral lanthanide complexes can constitute stereo-discriminating probes in biological media, owing to the luminescent properties of the rare-earth ions. Sensitized emission with narrow bandwidth, having fast radiation rate and high emission quantum efficiency are the main perspective for synthesizing the complexes. Attention has been given on remarkable chirality with high dissymmetry factors (g = Δε_ext/ε_max) of the complexes. For this purpose, beta-diketonato ligands with chiral BINAPO (1,1′-binapthyl phosphine oxide) ligand were chosen to achieve the goal. The complexes [Ln(TFN)₃(S-BINAPO)](TFN = 4,4,4-trifluoro-1(2-napthyl)-1,3-butanedione), [Ln(HFT)₃(S-BINAPO)] (HFT = 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione) and [Ln(HFA)₃(S-BINAPO)](hfa = hexafluoroacetylacetonate) (where Ln = Yb, Eu) were synthesized. The complex, [Eu(TFN)₃(S-BINAPO)] gives strong red emission at 615 nm with narrow emission band (<10 nm) when excited by 465 nm light with quantum efficiency 86%. The dissymmetry factors (g = Δε_ext/ε_max) corresponding to the ⁷F₁ → ⁵D₀ transition at 590 nm is 0.091 for [Eu(TFN)₃(S-BINAPO)] and for [Yb(hfa)₃(S-BINAPO)](hfa = hexafluoroacetylacetonate) corresponding to the ²F_7/2 → ²F_5/2 transitions is 0.12, are among the largest values for both Eu and Yb complexes to date, respectively. The Eu complexes, [Eu(HFT)₃(S-BINAPO)] and [Eu(TFN)₃(S-BINAPO)] are found to be spontaneously emissive, showing bright red emission, when placed in sunlight or even in the laboratory when light is switched on.     

Synthesis, structure and magnetic property of μ-phenoxo-μ-acetato-bis(η-acetato)dicobalt(II, II) complexes

Dinuclear cobalt(II) complexes Co₂(bpmp)(OAc)₃ (1) and Co₂(bpcp)(OAc)₃ (2) have been synthesized by using acyclic ligands 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol [H(bpmp)] and 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol [H(bpcp)] with versatile coordination sites. X-ray analysis uncovered that complex 1 · 3H₂O contains a μ-phenoxo-μ-acetato-bis(η²-acetato) dicobalt(II, II) core. Magnetic susceptibility was measured for 1 over the temperature range 1.8-300 K, and the best theoretical fitting parameters were g = 2.12(6), J = −3.63(9) cm⁻¹ and D = −12(4) cm⁻¹.     

Syntheses, structures and antimicrobial activities of various metal complexes of hinokitiol

Metal-oxygen bonding complexes (M = Mg^II, Mn^II, Ni^II, Mo^VI, W^VI, Pd^II, Sb^III, Bi^III, Fe^III, Ti^IV, K^I, Ba^II, Zr^IV and Hf^IV) with a hinokitiol (Hhino; 2-hydroxy-4-isopropylcyclohepta-2,4,6-trienone or β-thujaplicin) ligand, which has two unequivalent oxygen donor atoms, were synthesized and characterized by elemental analysis, TG/DTA, FT-IR and solution (¹H and ¹³C) NMR spectroscopy. Single-crystal X-ray structure analysis revealed various molecular structures for the complexes, which were classified into several families of family, i.e. type A [M^II(hino)₂(L)]₂ (M = Mg^II, Mn^II, Ni^II; L = EtOH or MeOH), with a dimeric structure consisting of one bridging hino⁻ anion, one chelating hino⁻ anion and one alcohol or water molecule, type B, with the octahedral, cis-dioxo, bis-chelate complexes cis-[M^VIO₂(hino)₂] (M = Mo^VI, W^VI), type C, with square planar complex [M^II(hino)₂] (M = Pd^II), type D, with tris-chelate, 7-coordinate complexes with one inert electron pair [M^III(hino)₃] (M = Sb^III, Bi^III), type D′, with the bis-chelate, pseudo-6-coordinate complexes with one inert electron pair [M^III(hino)₂X] (M = Sb^III, X = Br), type E, with tris-chelate, 6-coordinate complexes with Δ and Λ isomers [M^III(hino)₃] (M = Fe^III), type E′ of bis-chelate, 6-coordinate complex [M^IV(hino)₂X₂] (M = Ti^IV, X = Cl), type F, with water-soluble alkali metal salts [M^I(hino)] (M = K^I), and type H, with tetrakis-chelate, 8-coordinate complexes [M^IV(hino)₄](M = Zr^IV, Hf^IV). These structural features were compared with those of metal complexes with a related ligand, tropolone (Htrop). The antimicrobial activities of these complexes, evaluated in terms of minimum inhibitory concentration (MIC; μg mL⁻¹) in two systems, were compared to elucidate the relationship between structure and antimicrobial activity.     

Reactions of pentaammineruthenium complexes with 1,2- and 1,4-dicyanobenzene and cyanobenzamides: evidences of neighboring group participation

The spectral (UV-Vis and IR) and electrochemical behavior of the nitrile bonded complexes [Ru(NH₃)₅L]²⁺ (L = 1,4-dicyanobenzene (1,4-dcb), 1,2-dicyanobenzene (1,2-dcb)), [Ru(NH₃)₅(NHC(OH)-bz-4-CN)]³⁺, [Ru(NH₃)₅(NHC(O)-bz-2-CN)]²⁺ and [Ru(NH₃)₅(NH(C)NHC(O)bz)]³⁺ (NH(C)NHC(O)-bz = 3-imino-1-oxo-isoindoline) are described. Oxidation of [Ru(NH₃)₅L]²⁺, at 0 ? pH ? 6, is followed by hydrolysis of the coordinated nitrile to give amide complexes in which the amide is through the nitrogen, with pH-dependent rate constants. The estimated values of the rate constant of hydrolysis (k_obs) at 25 °C are 2.9 × 10⁻³ s⁻¹ for [Ru(NH₃)₅(1,4-dcb)]³⁺ and 5.6 × 10⁻³ s⁻¹ for [Ru(NH₃)₅(1,2-dcb)]³⁺ at pH 4.65. Reduction of [Ru(NH₃)₅(NHC(O)-bz-4-CN)]²⁺ and [Ru(NH₃)₅(NHC(O)-bz-2-CN)]²⁺ is followed by two reactions, one is an aquation forming [Ru(NH₃)₅(OH₂)]²⁺ and free ligand, and the other an intramolecular linkage isomerization forming [Ru(NH₃)₅(NC-bz-4-NH₂C(O))]²⁺ and [Ru(NH₃)₅(NC-bz-2-NH₂C(O))]²⁺. The oxidized1,2-cyanobenzamide complex [Ru(NH₃)₅(NHC(OH)-bz-2-CN)]³⁺ undergoes an amide to nitrile intramolecular linkage isomerization, followed by a cyclization reaction resulting in [Ru(NH₃)₅(NH-(C)(HN-C(O)-2-bz))]³⁺ ((NH-(C)(HN-C(O)-2-bz)) = 3-imino-1-oxo-isoindoline bonded through the exocyclic nitrogen) (pK_a = 4.3). The rates of these reactions, which occur with neighboring group participation, increase with acidity. The reduced form, [Ru(NH₃)₅(NH-(C)(HN-C(O)-2-bz))]²⁺, is relatively substitution inert.     

EPR spectroscopic study of a dinuclear copper(II) complex of tolfenamic acid

The copper(II) complex with tolfenamic acid [Cu(tolf)₂(H₂O)]₂ was studied by X-band and K-band EPR spectroscopies in the temperature range from 90 to 300 K. The Cu²⁺ ions in dinuclear complex show a strong antiferromagnetic exchange interaction with |J| = 292 cm⁻¹. The EPR spectra, which were observed for [Cu(tolf)₂(H₂O)]₂, are typical powder spectra of the copper pairs. The spectra exhibit the hyperfine structure in low temperature range. The values of the spin-Hamiltonian parameters were determined on the basis of the best fit for the simulated spectra at both K-band (0.75 cm⁻¹) at T = 298 K and X-band (0.3 cm⁻¹) at T = 93 K as compared with the experimentally observed spectra. These values show that the local environment around the copper species is distorted tetragonal pyramid. This EPR evidence is consistent with the crystallographic data.     

Aminocarboxylate complexes of vanadium(III): Electronic structure investigation by high-frequency and -field electron paramagnetic resonance spectroscopy

Aminocarboxylate complexes of vanadium(III) are of interest as models for biologically and medicinally relevant forms of this interesting and somewhat neglected ion. The V(III) ion is paramagnetic, but not readily suited to conventional EPR, due to its integer-spin ground state (S = 1) and associated large zero-field splitting (zfs). High-frequency and -field EPR (HFEPR), however, has the ability to study such systems effectively. Three complexes, all previously structurally characterized: Na[V(trdta)] · 3H₂O, Na[V(edta)(H₂O)] · 3H₂O, and [V(nta)(H₂O)₃] · 4H₂O (where trdta stands for trimethylenediamine-N,N,N′,N′-tetraacetate and nta stands for nitrilotriacetate) were studied by HFEPR. All the investigated complexes produced HFEPR responses both in the solid state, and in aqueous solution, but those of [V(nta)(H₂O)₃] · 4H₂O were poorly interpretable. Analysis of multi-frequency HFEPR spectra yielded a set of spin Hamiltonian parameters (including axial and rhombic zfs parameters: D and E, respectively) for these first two complexes as solids: Na[V(trdta)] · 3H₂O: D = 5.60 cm⁻¹, E = 0.85 cm⁻¹, g = 1.95; Na[V(edta)(H₂O)] · 3H₂O: D = 1.4 cm⁻¹, E = 0.14 cm⁻¹, g = 1.97. Spectra in frozen solution yielded similar parameters and showed multiple species in the case of the trdta complex, which are the consequence of the flexibility of this ligand. The EPR spectra obtained in frozen aqueous solution are the first, to our knowledge, of V(III) in solution in general and show the applicability of HFEPR to these systems. In combination with very insightful previous studies of the electronic absorption of these complexes which provided ligand-field parameters, it has been possible to describe the electronic structure of V(III) in [V(trdta)]⁻ and [V(edta)(H₂O)]⁻; the quality of data for [V(nta)(H₂O)₃] does not permit analysis. Qualitatively, six-coordinate V(III) complexes with O,N donor atoms show no electronic absorption band in the NIR region, and exhibit relatively large magnitude zfs (D ? 5 cm⁻¹), while analogous seven-coordinate complexes do have a NIR absorption band and show relatively small magnitude zfs (D < 2 cm⁻¹).     

Copper(II) complexes derived from tripodal tris[(2-ethyl-(1-pyrazolyl)]amine

Three mono-nuclear copper(II) complexes [Cu(tepza)X]ClO₄ (X = Cl, 1; X = NCS, 2; X = dca, 3) and two dinuclear bridging complexes [Cu₂(tepza)₂(μ-C₄O₄)](ClO₄)₂·H₂O(4) and [Cu₂(tepza)₂(μ-C₅O₅)](ClO₄)₂(5) where tepza = tris[2-ethyl(1-pyrazolyl)]amine, dca = dicyanamide, C₄O₄²⁻ = 3,4-dihydroxycyclobut-3-ene-1,2-dionate (squarate dianion) and C₅O₅²⁻ = 4,5-dihydroxycyclopent-4-ene-1,2,3-trionate (croconate dianion) were synthesized and structurally characterized by IR and UV-Vis spectroscopy as well as by single X-ray crystallography. In the solid state, the geometry of copper(II) centers in these complexes are as follows: close to SP in 2, distorted TBP in 3, predominant SP in 4, and distorted octahedral in 5, whereas in solution distorted SP geometry was generally found. The squarato and the croconato dianions in complexes 4 and 5 are bridging the two copper(II) centers in cis-bis-monodentate and bis-bidentate bonding modes, respectively. Magnetic susceptibility measurements at variable temperatures (2-300 K) reveal the weak antiferromagnetic coupling in the two bridging dinuclear complexes 4 (J = −24.9 cm⁻¹) and 5 (J = −3.1 cm⁻¹).     

Copper(II) complexes of tetradentate thioether-oxime ligands

Two dinuclear copper(II) thioether-oxime complexes ([Cu(DtdoH)]₂(ClO₄)₂ and [Cu(DtudH)]₂(ClO₄)₂ · 2CH₃OH) have been synthesized. [Cu(DtdoH)]₂(ClO₄)₂ reacted with excess BF₃ · OEt₂ to yield [Cu(Thyclops)]ClO₄, a -macrocyclized di-oxime. [Cu(DtdoH)]₂(ClO₄)₂ and [Cu(DtudH)]₂(ClO₄)₂ · 2CH₃OH are the first representatives of copper(II) thioether oximes which exhibit the classical out-of-plane oximate oxygen-metal dimer structure. [Cu(DtdoH)]₂(ClO₄)₂ and [Cu(Thyclops)]ClO₄ have been structurally characterized by single-crystal X-ray diffraction. The geometry about each copper(II) in [Cu(DtdoH)]₂(ClO₄)₂ is a distorted square pyramid (τ = 0.14). The average copper-nitrogen(oxime) bond length is 1.984 Å longer (∼0.03 Å) than the average copper-nitrogen(oxime) bonds in copper(II) bis-glyoximates. The geometry of [Cu(Thyclops)]ClO₄ reveals an almost perfect square pyramid (τ = 0.03) of N₂S₂O donors. Solution, cryogenic glass, and powder ESR spectra show a typical axial pattern, except for the powder spectrum of [Cu(DtudH)]₂(ClO₄)₂ · 2CH₃OH which displays a small rhombic distortion. Variable-temperature magnetic susceptibility measurements indicate very weak ferromagnetic interactions in [Cu(DtdoH)]₂(ClO₄)₂, where J = +0.52 cm⁻¹ and very weak antiferromagnetic interactions in [Cu(DtudH)]₂(ClO₄)₂ · 2CH₃OH, where J = −0.59 cm⁻¹. Electrochemical measurements reveal that the mixed thioether-oxime coordination environment tends to stabilize Cu(II), as all electrochemical reductions were quasi-reversible or irreversible. [Cu(Thyclops)]ClO₄ is more oxidizing than [Cu(DtdoH)]₂(ClO₄)₂ by 0.14 V.