Coordination modes of N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine with copper (I) and (II) halides

The title ligand, N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine, was prepared via a condensation-reduction synthetic route. The compounds, CuCl(C₁₉H₁₉N₃O) and [CuBr(C₁₉H₁₉N₃O)]⁺Br⁻ · 3H₂O, were readily synthesized from the reaction of CuCl or CuBr₂ and the ligand in acetonitrile. The title copper(I) compound is an O-H ? Cl hydrogen-bonded linear chain of tetrahedrally coordinated copper centers, and the title copper(II) compound exists as two strongly tetragonally distorted dibromide bridged metal cations in a dimer with the phenol hydroxyl groups weakly bound in a trans-fashion to one of the bridging bromides. In the copper(I) complex the phenoxy group acts only as a hydrogen bond donor, whereas in the copper(II) complex it acts both as a ligand and a hydrogen bond donor.     

Spectroscopic, magnetic, and electrochemical studies of a dimeric N-substituted-sulfanilamide copper(II) complex. X-ray and molecular structure of the Cu2(N-(pyridin-2-yl)biphenyl-4-sulfonamidate)4 complex

A dinuclear copper(II) complex with a N-substituted sulfonamide as ligand has been investigated. The new N-(pyridin-2-yl)biphenyl-4-sulfonamide ligand has been prepared and structurally characterized. The copper(II) complex has been synthesized and its crystal structure, magnetic properties and EPR spectra were studied in detail. The metal centers are bridged by four nonlinear triatomic NCN groups. The coordination geometry of the copper(II) ions in the dinuclear entity is distorted square planar with two N-pyridyl and two N-sulfonamido atoms. Magnetic susceptibility data show a moderate antiferromagnetic coupling, with −2 J = 284 cm⁻¹. The EPR spectrum of the polycrystalline sample of the title compound has been measured at the X-band frequency at different temperatures.     

Coordination compounds of Cd(II) with several bidentate-NN′ and tridentate-NN′N nitrogen donor ligands. Cd NMR studies of monomeric compounds containing nitrogen donor atoms

Reaction of CdCl₂ with N-alkylaminopyrazole ligands 1-[(2-ethylamino)ethyl]-3,5-dimethylpyrazole (deae), 1-[(2-(tert-butylamino)ethyl)]-3,5-dimethylpyrazole (deat), bis-[(3,5-dimethylpyrazolyl)methyl]ethylamine (bdmae), and bis-[(3,5-dimethylpyrazolyl)ethyl]ethylamine (ddae) in absolute ethanol yields [CdCl₂(NN′)] (NN′ = deae (1), deat (2)), [CdCl₂(bdmae)] (3), and [CdCl(ddae)]₂[CdCl₄] (4). The Cd(II) complexes have been characterised by elemental analyses, conductivity measurements, IR, ¹H, ¹³C{¹H} and ¹¹³Cd NMR spectroscopies, and X-ray diffraction methods. ¹H and ¹¹³Cd NMR experiments at variable temperature for 3 and 4 show that dynamic processes are taking place in solution. We report the measurements of ¹¹³Cd NMR chemical shift data for complexes 1-4 in solution. X-ray crystal structures for complexes 2 and 3 have been determined. The Cd(II) is coordinated to the deat ligand, in 2, by one nitrogen atom of the pyrazolyl group and one nitrogen atom of the amine. It finishes a tetrahedral geometry with two chlorine atoms. The bdmae ligand is linked to Cd(II), in 3, by two nitrogens atoms of the pyrazolyl groups and one amine nitrogen, along with two chlorine atoms, in a distorted trigonal bipyramidal geometry.     

Coordination versatility of 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane: Co(II) and Ni(II) complexes

The ligand 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane (L⁸) has afforded six-coordinate monomeric and dimeric complexes [(L⁸)Co^II(H₂O)₂][ClO₄]₂ (1), [(L⁸)Ni^II(MeCN)₂][BPh₄]₂ (2), [(L⁸)Ni^II(O₂CMe)][BPh₄] (3), and . The crystal structures of 1, 2 · MeCN, 3, and 4 revealed that the ligand L⁸ is flexible enough to expand its coordinating ability by fine-tuning the angle between the chelating fragments and hence folds around cobalt(II)/nickel(II) centers to act as a tetradentate chelate, allowing additional coordination by two trans-H₂O, cis-MeCN, and a bidentate acetate affording examples of distorted octahedral , , and coordination. The angles between the two CoN₂/NiN₂ planes span a wide range 23.539(1)° (1), 76.934(8)° (2), and 69.874(14)° (3). In contrast, complex 4 is a bis-μ-1,3-acetato-bridged (syn-anti coordination mode) dicobalt(II) complex [Co?Co separation: 4.797(8) Å] in which L⁸ provides terminal bidentate pyridylpyrazole coordination to each cobalt(II) center. To our knowledge, this report provides first examples of such a coordination versatility of L⁸. Absorption spectral studies (MeCN solution) have been done for all the complexes. Complexes 1-3 are uniformly high-spin. Temperature-dependent (2-300 K) magnetic studies on 4 reveal weak ferromagnetic exchange coupling between two cobalt(II) (S = 3/2) ions. The best-fit parameters obtained are: Δ (axial splitting parameter) = −765(5) cm⁻¹, λ (spin-orbit coupling) = −120(3) cm⁻¹, k (orbital reduction factor) = 0.93, and J (magnetic exchange coupling constant) = +1.60(2) m⁻¹.     

A new (μ3-carbonato)tricopper(II) complex with symmetry related equilateral triangular array of metal centers; structure and magnetism

Using an unsymmetrical N-tridentate (2-pyridyl)alkylamine ligand methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine (mpepma), a new tricopper(II) complex [{(mpepma)Cu(OClO₃)}₃(μ₃-OCO₂)][ClO₄] (1), having triply bridging μ₃-carbonate group, with three symmetry related triangular array of copper(II) centers has been synthesized. In 1, each copper ion is five-coordinate (almost perfect square pyramidal) by three nitrogens from the ligand (two pyridyl and an amine) and an oxygen atom of the carbonate group in the equatorial plane and by an oxygen atom of the perchlorate ion in the apical position. Magnetic susceptibility data (2-300 K) were fitted using the Hamiltonian: , which corresponds to a triangular array of spins, corrected with a zJ′ intertrimer interaction or zero-field splitting within the ground state, to fit low temperature data. It is concluded that the copper(II) ions in 1 are ferromagnetically coupled. The best parameters obtained are g = 2.11, J = 18 ± 1 cm⁻¹, zJ′ = −0.36 ± 0.02 cm⁻¹ or D = 0.50 ± 0.05 cm⁻¹.     

Synthesis, characterisation of a complex of Cu(II) with a multidentate macrocyclic ligand and its interactions with anions

A macrocyclic ligand possessing a donor set of {N₃S₂} synthesised via Cs⁺-templation, 4-(pyridin-2-ylmethyl)-1,7-dithia-4,10-diazacyclododecane (L) and its Cu(II) complex, [CuL(NCMe)]²⁺ (6), are described. This Cu(II) complex interacts with a range of anions, F⁻, Cl⁻, Br⁻, I⁻, HCOO⁻, AcO⁻, CO₃²⁻, NO₃⁻, C₂O₄²⁻, H₂PO₄⁻, SCN⁻, CN⁻, BF₄⁻. Of the investigated anions, I⁻, SCN⁻, and CN⁻, show strong interaction with the Cu(II) centre as indicated by their spectral variations. The iodide particularly demonstrates distinct change in colour. This change originates from a newly appeared band at 471 nm upon iodide binding, which arises from the ligand (I⁻) to Cu(II) charge transfer (LMCT) in the iodide-substituted Cu(II) complex, [CuLI]⁺ (7). All organic compounds are characterised by NMR spectroscopy and/or microanalysis. The identities of the two Cu(II) complexes are confirmed by using microanalysis and the complex 6 is crystallographically analysed.     

Nickel(II) and copper(II) complexes of Schiff base ligands containing N4O2 and N4S2 donors with pyrrole terminal binding groups: Synthesis, characterization, X-ray structures, DFT and electrochemical studies

A series of hexadentate ligands, H₂L^m (m = 1−4), [1H-pyrrol-2-ylmethylene]{2-[2-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)ethoxy]phenyl}amine (H₂L¹), [1H-pyrrol-2-ylmethylene]{2-[4-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)butoxy]phenyl}amine (H₂L²), [1H-pyrrol-2-ylmethylene][2-({2-[(2-{[1H-pyrrol-2-ylmethylene]amino}phenyl)thio]ethyl}thio)phenyl]amine (H₂L³) and [1H-pyrrol-2-ylmethylene][2-({4-[(2-{[1H-pyrrol-2-lmethylene]amino}phenyl)thio]butyl}thio) phenyl]amine (H₂L⁴) were prepared by condensation reaction of pyrrol-2-carboxaldehyde with {2-[2-(2-aminophenoxy)ethoxy]phenyl}amine, {2-[4-(2-aminophenoxy)butoxy]phenyl}amine, [2-({2-[(2-aminophenyl)thio]ethyl}thio)phenyl]amine and [2-({4-[(2-aminophenyl)thio]butyl}thio)phenyl]amine respectively. Reaction of these ligands with nickel(II) and copper(II) acetate gave complexes of the form ML^m (m = 1−4), and the synthesized ligands and their complexes have been characterized by a variety of physico-chemical techniques. The solid and solution states investigations show that the complexes are neutral. The molecular structures of NiL³ and CuL², which have been determined by single crystal X-ray diffraction, indicate that the NiL³ complex has a distorted octahedral coordination environment around the metal while the CuL² complex has a seesaw coordination geometry. DFT calculations were used to analyse the electronic structure and simulation of the electronic absorption spectrum of the CuL² complex using TDDFT gives results that are consistent with the measured spectroscopic behavior of the complex. Cyclic voltammetry indicates that all copper complexes are electrochemically inactive but the nickel complexes with softer thioethers are more easily oxidized than their oxygen analogs.     

Magnetic, spectroscopic and X-ray crystallographic structural studies on copper(II) complexes of tridentate NNS Schiff base ligands formed from 2-acetylpyrazine and S-methyl- and S-benzyldithiocarbazates

New copper(II) complexes of general empirical formula, [Cu(NNS)X] (NNS = anionic forms of the 2-acetylpyrazine Schiff bases of S-methyl- and S-benzyldithiocarbazate, Hapsme and Hapsbz) and X = Cl⁻, Br⁻, NCS⁻ and NO₃⁻ have been synthesized and characterized. X-ray crystal structures of the free ligand, Hapsbz and the complexes, [Cu(apsbz)(NO₃)]_∞, [Cu(apsme)(NCS)]₂ and [Cu(apsme)Cl]₂ have been determined. In the solid state, the Schiff base, Hapsbz remains in its thione tautomeric form with the thione sulfur atom trans to the azomethine nitrogen atom. X-ray diffraction shows that the [Cu(apsbz)(NO₃)]_∞ complex is a novel coordination polymer in which one of the nitrogen atoms of the pyrazine ring bridges two adjacent copper(II) ions. The Schiff base is coordinated to the copper(II) ion in its iminothiolate form via the thiolate sulfur atom, the azomethine nitrogen atom and one of the pyrazine nitrogen atoms, the overall geometry of each copper atom in the polymer being close to a square-pyramid. The complexes, [Cu(apsme)X]₂ (X = NCS⁻, Cl⁻) are dimers in which each copper atom adopts a five-coordinate near square-pyramidal geometry with an N₃S₂ coordination environment. The Schiff base coordinates as a uninegatively charged tridentate ligand chelating via the pyridine and azomethine nitrogen atoms and the thiolate sulfur atoms. A nitrogen atom of a unidentate thiocayanate or chloride ligand and a bridging sulfur atom from a second ligand completes the coordination sphere. Room temperature μ_eff values for the complexes in the solid state are in the range 1.70-2.0 μ_B typical of uncoupled or weakly coupled Cu(II) centres. Variable temperature susceptibility studies show that the chain complex displays weak ferromagnetic coupling across the pyrazine bridges, while the S-bridged dinuclear compounds display either weak ferromagnetic or weak antiferromagnetic coupling that relates to subtle bridging geometry differences. EPR studies of frozen DMF solutions give rather similar g and A_Cu values for all compounds indicative of Cu(d_x²-y²) ground state orbitals on the Cu centers.     

A solution thermodynamic study of the Cu(II) and Zn(II) complexes of EBTA: X-ray crystal structure of the dimeric complex [Cu2(EBTA)(H2O)3]2

The copper(II) complex of the acyclic EBTA ligand (H₄EBTA = 1,2-bis(2-aminoethoxy)benzene-N,N,N′,N′-tetraacetic acid) has been prepared and characterized by X-ray analysis. The two copper ions of the dinuclear unit present the same distorted octahedral coordination polyhedra. The EBTA ligand is shared between two copper coordination centres, with the formation of centrosymmetric dimers, which are linked in a supramolecular tridimensional structure via additional interactions through the coordinated waters molecules with adjacent carboxylic oxygen atoms. The stability and protonation constants of EBTA with Cu(II) and Zn(II) ions indicate a higher stability of these complexes with respect to the corresponding complexes with the more flexible EGTA ligand (H₄EGTA = ethyleneglycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid). On the other hand, the lower stability of [Gd(EBTA)]⁻ than [Gd(EGTA)]⁻ results in a decreased overall selectivity (lower K_sel) of EBTA towards Gd(III) and suggests that this complex may undergoes transmetallation reactions under physiological conditions.     

Palladium(II) complexes of imidazolin-2-ylidene N-heterocyclic carbene ligands with redox-active dimethoxyphenyl or (hydro)quinonyl substituents

Four novel imidazolium salts, precursors to N-heterocyclic carbene (NHC) ligands, with 2,5-dimethoxybenzyl or 2,5-dihydroxybenzyl (i.e., p-hydroquinone) substituents have been prepared. The crystal structure of the hydroquinone-substituted imidazolium salt H₃L³Br reveals Br⁻?H-O bridged chiral chains of alternating [H₃L³]⁺ cations and Br⁻ counter-ions parallel to the x-axis. Palladium(II) complexes were accessible from reactions of the dimethoxyphenyl-substituted imidazolium precursors with palladium(II) acetate, but not from reactions of imidazolium cations with hydroquinonyl substituents. The crystal structure of the bis(dimethoxybenzyl)-substituted bis(NHC)Pd complex, cis-[PdBr₂(L²)] (2), is described. Puckering of the bis(NHC) ligand leads to a cleft in which an included molecule of dimethylformamide is situated. The cleft is closed by one of the dimethoxybenzyl groups which π-stacks with the dimethylformamide; the other dimethoxybenzyl group points away from the cleft and Pd(II) centre. Reaction of complex 2 with BBr₃ afforded the targeted bis(hydroquinone)-substituted bis(NHC)Pd(II) complex 3 (97% yield) which, in turn, was oxidised by 2,3-dichloro-5,6-dicyano-benzoquinone to the corresponding p-benzoquinone-substituted bis(NHC)Pd(II) complex 4 (98% yield). The cyclic voltammograms of the Pd(II) complexes 2-4 reveal waves that are attributed to an admix of the anticipated ligand-centred and [Pd(C-NHC)₂Br₂]-centred processes.     

A MLCT-switched photochromic copper(II) coordination polymer with 1,2-bis(2′-methyl-5′-(4″-pyridyl)-3′-thienyl)perfluorocyclopentene in crystalline phase

A novel Cu(II) coordination polymer with photochromic 1,2-bis(2′-methyl-5′-(4″-pyridyl)-3′-thienyl)perfluorocyclopentene (BM-4-PTP) was prepared and crystallographically characterized. Its photochromic behavior as well as magnetic property was investigated in crystalline phase. In complex [Cu(BM-4-PTP)Br₂(DMF)₂] (1), each copper atom is bridged by two N atoms of BM-4-PTP, two Br atoms from anions and two O atoms of DMF in an slightly distorted octahedral geometry. The basal planar center is in turn linked by bidentate ligand forming a 1-D polymeric chain. Free ligand showed typical spectral changes upon appropriate optical excitation, indicating the reversible photochromism in crystalline phase. Complex 1 occurred reversible photoisomerization not only through the π-π^∗ transition but also the MLCT transition in crystalline phase. On the other hand, the magnetic property of complex 1 has been investigated by means of ESR. The spectra slightly and reversibly changed in response to UV and visible light supporting the normal photoreactivity in crystalline phase.     

Oligonuclear nickel(II) complexes sustained by intermolecular hydrogen-bonding

Reaction of Ni(OAc)₂ with the symmetric `end-off' compartmental proligand 2,6-[N,N^′-bis(2-hydroxy-phenylmethyl)-N,N^′-bis(2-pyridylmethyl)aminomethyl]-4-methylphenol (H₃L) in the presence of NaPF₆ has been found to generate a homotetranuclear nickel(II) complex [(Ni₄HL)(L)(OAc)₂(H₂O)₂(HOAc)₂]PF₆. The crystal structure of the complex reveals that the complex is donor asymmetric and that the extended supra-ligand periphery is maintained by a tight hydrogen-bond between two pendant phenol/phenoxy groups of adjacent ligands and by further tight hydrogen-bonds between coordinated acetic acid molecules and the remaining pendant phenols of the ligand, generating a double acid salt of the type [CH₃COO?H?LH?L?H?OOCCH₃]⁵⁻. Reaction of H₃L with Ni(OAc)₂ and NaClO₄ in methanol gave the complex [Ni₂(HL)(OAc)₂(OH₂)₂][ClO₄]. The structure was determined by X-ray diffraction and showed that the complex exists as a dimer promoted by intermolecular hydrogen-bonding.     

Copper(II) complexes of Neobelliera Bullata Trypsin Modulating Oostatic Factor and its analogues

The stoichiometry, stability constants and solution structure of the complexes formed in the reaction of copper(II) with hexapeptide NPTNLH, i.e. the Neobelliera Bullata Trypsin Modulating Oostatic Factor (Neb-TMOF), and its analogues DPTNLH, Ac-NPTNLH and Ac-DPTNLH have been determined by potentiometric, UV-visible, CD and EPR spectroscopic methods. Upon raising pH for Ac-NPTNLH and Ac-DPTNLH peptides, copper(II) coordination starts from the imidazole nitrogen of the His⁶; afterwards three deprotonated amide nitrogens are progressively involved in metal ions coordination. In a wide pH range of 4.5-8.5 for the NPTNLH and DPTNLH ligands the CuL complex dominates with the imidazole nitrogen of His⁶ coordinated to form a macrochelate. The N-terminal amino group of the NPTNLH and DPTNLH peptides takes part in the coordination of the metal ion in the CuL, CuH₋₁L and CuH₋₂L complexes. However, at pH above 9 the CuH₋₃L complex with the {N_Im, 3N⁻} coordination mode is formed. For the CuH₋₂L complex the spectroscopic data clearly indicate the 4N {NH₂, CO or COO⁻, 2N⁻, N_Im} bonding mode with the axial coordination of the N-terminal amine group to the metal ion.     

Crystal structures and magnetic properties of tetranuclear copper(II) complexes of N-(2-hydroxymethylphenyl)salicylideneimine with a defective double-cubane core

Tetranuclear Cu(II) complexes of N-(2-hydroxymethylphenyl)salicylideneimine (H₂L1-H) and its homologues (5-CH₃: H₂L1-Me, 5-Cl: H₂L1-Cl), [Cu(L1-H)]₄ · 3H₂O (1), [Cu(L1-Me)]₄ · 2CH₂Cl₂ (2), and [Cu(L1-Cl)]₄ · 2CH₂Cl₂ (3), have been characterized by X-ray crystal structure analyses and magnetic measurements. The structure analyses revealed that the complexes 1-3 have a defective double-cubane tetra copper(II) core connected by μ₃-alkoxo bridges. The intramolecular Cu?Cu distances are in the range from 5.251(2)-5.256(3) Å for the longest to 3.0518(9)-3.092(2) Å for the shortest. Each Cu(II) ion has a square-pyramidal geometry and the dihedral angles between adjacent Cu(II) basal planes are almost right angles. Magnetic measurements of the present complexes indicate that weak antiferromagnetic interactions (J=−15 to −19 cm⁻¹) between neighboring copper(II) ions are dominant in these tetracopper cores.     

A new tyrosinase model with 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene: Binuclear copper(I) and phenoxo/hydroxo-bridged dicopper(II) complexes

The ligand 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene (baib) reacts with [Cu(MeCN)₄][ClO₄] to form a binuclear copper(I) complex . Crystal structure analysis reveals that the distorted tetrahedral coordination of each copper(I) center is satisfied by one bidentate arm of each ligand. The complex undergoes ready aromatic ring hydroxylation at position 2 of the phenyl ring when reacted with molecular oxygen in MeCN/MeOH/CH₂Cl₂, producing a four-coordinate μ-phenoxo- and μ-hydroxo-bridged dicopper(II) complex, [Cu₂(baib-O)(OH)(OClO₃)₂] · 1.5H₂O (2) (baib-OH: 1,3-bis[(2-dimethylaminoethyl)iminomethyl]phenol). This reaction mimics the reactivity of the copper monooxygenase tyrosinase. A trend is observed for the extent of aromatic ring hydroxylation (25 °C): MeCN > MeOH > CH₂Cl₂. Cyclic voltammetric experiment of 1 in MeCN reveals an appreciably high redox potential (anodic peak potential, E_pa = 0.69 V versus SCE) for the redox process. Complex 2 has been characterized by single-crystal X-ray crystallography. Variable temperature (60-300 K) magnetic susceptibility measurements on 2 establish that the copper(II) centers in 2 are antiferromagnetically coupled (2J = −280 cm⁻¹).     

Conformational flexibility of 2,6-bis(pyrazol-1-ylmethyl)pyridine (L) in [(L)Co(H2O)3]Cl2 and [(L)Ni(H2O)2Cl]Cl·H2O. Molecular structures and non-covalent interactions

Using a non-planar tridentate ligand 2,6-bis(pyrazol-1-ylmethyl)pyridine (L⁵) two new coordination complexes [(L⁵)Co^II(H₂O)₃]Cl₂ (1) and [(L⁵)Ni^II(H₂O)₂Cl]Cl·H₂O (2) have been synthesized and structurally characterized. Complex 1 has N₃O₃ distorted octahedral environment around Co^II with coordination by L⁵ (two pyrazole and a pyridine nitrogen in a facial mode) and three water molecules. Complex 2 has N₃O₂Cl distorted octahedral geometry around Ni^II with meridional L⁵ coordination, two water molecules, and a Cl⁻ ion. Analysis of the crystal packing diagram reveals the involvement of solvent (water as metal-coordinated and as solvent of crystallization) and counteranion (Cl⁻) to play significant roles in generating 1D chains, involving O-H···Cl, and O-H···O interactions.     

New polymeric thiocyanatoiron(II) complex with N,N′-diethylnicotinamide - Synthesis, structure, magnetic and spectral properties

The iron(II) compound of formula [Fe(NCS)₂(dena)₂]_n (dena = N,N′-diethylnicotinamide) has been prepared by the reaction between iron(III) thiocyanate and dena in ethanol solution. The complex was characterized by elemental analysis, spectral and magnetic measurements. Single-crystal X-ray diffraction methods show that the complex, crystallizing in the triclinic space group, undergoes a phase transition between 220 K and 230 K, connected with the doubling of cell volume. Crystal structures at 230 K (1a; HT phase) and 150 K (1b; LT phase) are described and a transition mechanism is discussed. In both phases the compound has an extended chain structure, in which the neutral molecule of N,N′-diethylnicotinamide acts as a bridging ligand binding through pyridine N atom to one centre and through amide O atom to the neighbouring Fe centre. The Fe²⁺ ion has a slightly distorted trans-octahedral environment with FeO₂N₄ chromophore, and all Fe-O and Fe-N bonds in the typical for high-spin iron(II) compounds range. Variable-temperature magnetic susceptibility data in the temperature range 1.8-300 K show that iron(II) is high-spin S = 2(⁵T_2g) and as a result effects due to zero-field splitting are anticipated at low temperatures. The IR spectrum suggested the coordination of N,N′-diethylnicotinamide to the central atom of iron(II) as a bridging ligand and NCS group as a monodentate ligand.     

Structure and characterization of non-cyclic tetraaza complexes of copper(II) and their reactions with nitric oxide

[Cu(bapp)ClO₄]⁺ (1) and [Cu(bapp)Cl]⁺ (2) were prepared by the reaction of 1,4-bis(3-aminopropyl)piperazine (bapp) with copper acetate and copper chloride in the presence of sodium perchlorate, respectively, and structurally characterized. Complex 1 has a square-pyramidal geometry, whereas [Cu(3,2,3-tet)(ClO₄)]⁺ (A) has a polymeric octahedral geometry in its X-ray crystal structure. Complex 1 is stable against disproportionation, whereas complex A is unstable in the mono-valent Cu(I) state. An aqua ligand on complex 1 in aqueous solution is substituted by NO with kinetic constants of k_f=43±2 M⁻¹ s⁻¹ and k_b=(8.8±0.2)×10⁻² s⁻¹ at 25 °C, whereas there were no spectral changes observed for complex A in saturated NO solution.     

Synthesis, structure, cytotoxic activities and DNA-binding properties of tetracopper(II) complexes with dissymmetrical N,N′-bis(substituted)oxamides as ligands

To compare the cytotoxicities and the DNA-binding properties in tetranuclear complexes with different bridging ligands, two tetracopper(II) complexes with formulae of [Cu₄(oxbe)₂Cl₂(bpy)₂]·4H₂O (1) and [Cu₄(oxbm)₂Cl₂(bpy)₂]·2H₂O (2) were synthesized, where H₃oxbe and H₃oxbm stand for N-benzoato-N′-(2-aminoethyl)oxamide and N-benzoato-N′-(1,2-propanediamine)oxamide, respectively, and bpy is 2,2′-bipyridine. Complex 1 was characterized by elemental analyses, IR and electronic spectra and single-crystal X-ray diffraction. The crystal structure reveals the presence of the circular tetranuclear copper(II) cations which are assembled by a pair of cis-oxamido-bridged dinuclear copper(II) units through carboxyl bridges. The crystal structure of complex 2 has been reported in our previous paper. However, the bioactivities were not studied. Cytotoxicities experiments reveal that both the two complexes exhibit cytotoxic effects against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549, and complex 1 has the better activities than those of complex 2. The results of the interactions between the two complexes and herring sperm DNA (HS-DNA) suggest that the two complexes interact with HS-DNA in the mode of intercalation with the intrinsic binding constants of 3.93 × 10⁴ M⁻¹ (1) and 2.48 × 10⁴ M⁻¹ (2). These results indicated that the bridging ligands may play an important role in the cytotoxicities and the DNA-binding properties of tetranuclear complexes.     

Synthesis, characterization and structure of a new zinc(II) complex containing the hexadentate N,N′,N,N′-bis[(2-hydroxy-3,5-di-tert-butylbenzyl)(2-pyridylmethyl)]-ethylenediamine ligand: Generation of phenoxyl radical species

This work summarizes the results of our studies on the structural, spectral and redox properties of a mononuclear zinc(II) complex with the new H₂L ligand (H₂L = N,N′,N,N′-bis[(2-hydroxy-3,5-di-tert-butylbenzyl)(2-pyridylmethyl)]-ethylene diamine). The crystal structure of the complex [Zn^II(HL)] · ClO₄ (1) was determined by X-ray crystallographic analysis. The structure of this complex consists of a discrete mononuclear cation [Zn^II(HL)]⁺, in a strongly distorted geometry with a slight tendency toward a distorted square pyramidal geometry, as reflected by the structural index parameter τ of 0.44. The zinc(II) cation is coordinated to one oxygen and four nitrogen atoms: the pyridine nitrogen atoms (N22 and N32), tertiary amine nitrogen atoms (N1 and N4) and phenolate oxygen atom (O10). ¹H and ¹³C NMR spectral data show a rigid solution structure for 1 in agreement with X-ray structure. Potentiometric studies of complex 1 were also performed and revealed three titratable protons which are attributed to the protonation/deprotonation of two phenol groups (p[K]_a1 = 4.04 and p[K]_a3 = 11.34) and dissociation of a metal-bound water molecule (p[K]_a2 = 7.8). The phenolate groups in complex 1 are suitably protected by bulky substituents (tert-butyl) in the ortho- and para-positions, which through electrochemical oxidation generate a one-electron oxidized phenoxyl species in solution. This radical species was characterized by UV-Vis, EPR and electrochemical studies. The Zn(II)-phenoxyl radical species is of bioinorganic relevance, since its spectroscopic, redox and reactivity properties can be used to establish the role of phenoxyl radicals in biological and catalytical systems.