Exogenous Bridge Research Articles

Facile synthesis of imidazolidinyl phenolate supported Dicopper(II/II) Complexes: Activation and fixation of atmospheric CO2 as MeOCO2− showing exogenous bridge modulating magnetic exchange coupling

Two imidazolidine grafted Schiff bases H3L2 and H3L3 have been utilized to fasten the Cu2 core in four new complexes [Cu2(μ-L2)(μ-O2CMe)]·H2O (1·H2O), [Cu2(μ-L2)(μ-O2COMe)]·H2O (2·H2O), [Cu2(μ-L2)(μ-NO3)]·H2O (3·H2O) and [Cu2L3(μ-OAc)]·5H2O (4·5H2O). Room temperature solution reaction of H3L2 with Cu2(OAc)4·2H2O provided 1·H2O in good yield. Follow-up reaction of 1·H2O with Et4NOH in air replaces μ-O2CMe (acetato) bridge by MeOCO2− (monomethyl carbonato) linker in 2·H2O. Single crystal X-ray structure established the individual complexes and confirmed the fixation of atmospheric CO2. Variable temperature (2 to 300 K) magnetic susceptibility measurements recognized the antiferromagnetic exchange interactions between the adjacent copper(II) centers in complexes 2 and 3. The amount of spin–spin interactions are found to be higher for ancillary NO3− bridge (−284 cm−1) compared to the in situ transformed MeOCO2− bridged (−1.64 cm−1).

Enoxaparin augments alpha-1-antitrypsin inhibition of TMPRSS2, a promising drug combination against COVID-19

The cell surface serine protease Transmembrane Protease 2 (TMPRSS2) is required to cleave the spike protein of SARS-CoV-2 for viral entry into cells. We determined whether negatively-charged heparin enhanced TMPRSS2 inhibition by alpha-1-antitrypsin (AAT). TMPRSS2 activity was determined in HEK293T cells overexpressing TMPRSS2. We quantified infection of primary human airway epithelial cells (hAEc) with human coronavirus 229E (HCoV-229E) by immunostaining for the nucleocapsid protein and by the plaque assay. Detailed molecular modeling was undertaken with the heparin–TMPRSS2–AAT ternary complex. Enoxaparin enhanced AAT inhibition of both TMPRSS2 activity and infection of hAEc with HCoV-229E. Underlying these findings, detailed molecular modeling revealed that: (i) the reactive center loop of AAT adopts an inhibitory-competent conformation compared with the crystal structure of TMPRSS2 bound to an exogenous (nafamostat) or endogenous (HAI-2) TMPRSS2 inhibitor and (ii) negatively-charged heparin bridges adjacent electropositive patches at the TMPRSS2–AAT interface, neutralizing otherwise repulsive forces. In conclusion, enoxaparin enhances AAT inhibition of both TMPRSS2 and coronavirus infection. Such host-directed therapy is less likely to be affected by SARS-CoV-2 mutations. Furthermore, given the known anti-inflammatory activities of both AAT and heparin, this form of treatment may target both the virus and the excessive inflammatory consequences of severe COVID-19.

Homodinuclear Ni (II) and Cu (II) Schiff base complexes derived from O-vanillin with a pyrazole bridge: Preparation, crystal structures, DNA and protein (BSA) binding, DNA cleavage, molecular docking and cytotoxicity study

Two homodinuclear complexes [Ni2(L)(μ-pz)] (C1) and [Cu2(L)(μ-pz)] (C2) (L = N,N′-bis(3-methoxysalicylidene)-1,3-diamino-2-propanol) were synthesized and characterized by elemental analysis, spectroscopic methods (UV–vis, 1H NMR and IR) and single crystal X-ray crystallography. The crystal structure of both complexes revealed that two metal atoms were doubly bridged by one alkoxo group as an endogenous bridge and one pyrazolate as exogenous bridge. The arrangement around each metal atom was square planar. Interaction of C1 & C2 with HS-DNA and protein (BSA) was investigated by UV–vis and fluorescence spectroscopy. Viscosity measurements, cyclic voltammetry (CV), circular dichroism (CD) and agarose gel electrophoresis were used in the interaction with DNA. The main mode of binding of the complexes with DNA was intercalation and the affinity of C2 (Kb = 9.73 × 105) to DNA was higher than C1 (Kb = 7.41 × 105). These complexes were also investigated in the interaction with BSA. The calculated binding constants of 1478 for C1 and 39012 for C2 revealed that the binuclear complexes strongly bound to protein (BSA). Beside the experimental investigations, the theoretical calculations of molecular docking were performed to obtain detailed binding information of the complexes to DNA and BSA. Finally, cytotoxic activities were assayed by MTT assay. C2 possesses a prominent cytotoxicity against MCF-7 (human breast cancer) (IC50: 19.45 ± 3.61 μM at 24 h; IC50: 17.07 ± 1.88 μM at 48 h) and LNCaP (human prostate cancer) (IC50: 34.55 ± 7.75 μM at 24 h; IC50: 24.93 ± 6.03 μM at 48 h) cell lines.

The magnetic exchange interaction in bi- and tetranuclear copper(II) complexes with the bis-azomethine of 1,3-diaminopropanol-2 and 4-hydroxy-3-formylcoumarin with an azide exogenous bridge

By the reaction of Cu(II) perchlorate with the condensation product of 1,3-diamino-2-propanol and 4-hydroxy-3-formylcoumarin (H3L) in the presence of sodium azide, a tetranuclear copper(II) complex with the composition [Cu2L(μ2-1,1-N3)]2 (I) was obtained. On crystallization from a pyridine solution, the crystalline adduct [Cu2L(μ2-N3)(py)2] (II) (py=pyridine) was obtained and further characterized by XRD. The copper ions in (II) are coordinated by ONO’NO donor atoms of the triply deprotonated pentadentate ligand and the azide anion is coordinated in an asymmetric µ2-1,1 fashion, favoring a “roof”-like conformation of the molecule. The pyridine molecules are coordinated to each copper center, completing the distorted square-pyramidal coordination environment, but in a different way – for one copper ion the solvent molecule populates an apical position, for the other – a position in the basal plane. The tetranuclear complex is formed by linking two binuclear [Cu2L] units by two bridging μ2–1,1–N3 groups in a head-to-tail fashion. The temperature dependence of the magnetic susceptibility was studied for both I and II samples, showing a medium strength overall antiferromagnetic exchange for I and a weak ferromagnetic one with 2J=+5cm−1 for II. Two major superexchange pathways in I – through an alkoxide oxygen atom of the polydenate ligand and through the bridging azide-anion are characterized by opposite magnetic interaction characters – antiferromagnetic (2JO=−328cm−1) and ferromagnetic (2JN=+132cm−1), correspondingly. Quantum-chemical modeling using the broken symmetry approach was performed for II and possible binuclear isomers of I, differing in the azide-anion coordination mode and conformation of the polydentate ligand, and for two possible tetranuclear dimers.

Binuclear copper(ii) and nickel(ii) complexes based on N,N′-bis(3-formyl-5-tert-butylsalicylidene)-1,3-diaminopropan-2-ol: physicochemical and theoretical study

Binuclear CuII and NiII complexes with exogenous acetate and pyrazolate bridges were synthesized and studied. It was shown that the μ2-coordination of the DMSO molecule in an acetate-bridged CuII complex leads to the inversion of the sign of the exchange interaction parameter. Quantum chemical calculations of the geometry of the complexes and the magnetic exchange parameters showed that the role of the DMSO molecule is to stabilize the “distorted” conformation of metallocycles.

Di-μ-chlorido-bis{[2-({[2-(2-pyridyl)ethyl](2-pyridylmethyl)amino}methyl)phenol]zinc(II)} bis(perchlorate) dihydrate

The title compound, [Zn2Cl2(C20H21N3O)2](ClO4)2·2H2O, consists of a dinuclear ZnII cationic complex, two disordered perchlorate anions and two water mol­ecules as solvate. The [Zn2(μ-Cl)2(HL)2]2+ cation [HL is 2-({[2-(2-pyrid­yl)eth­yl](2-pyridylmeth­yl)amino}meth­yl)phenol] has a centrosymmetric structure with the ZnII ions in a distorted octa­hedral environment surrounded by an N3OCl2 donor set. HL acts as a tetra­dentate ligand through three N atoms from one amine group and two pyridyl arms and one O atom from the phenolic arm. The three N-donor sites of the HL ligand are arranged in meridional fashion, with the pyridine rings coordinated in trans positions with respect to each other. Consequently, the amine and phenol groups are trans to the asymmetric di-μ-chlorido exogenous bridges. A polymeric chain is formed along [010] by C(12)R 4 2(8) inter­molecular hydrogen bonding. The perchlorate anion is disordered and was modelled by two sites in a 0.345 (18):0.655 (18) ratio. Water–perchlorate O—H⋯O inter­actions form cyclic structures, while phenol–water O—H⋯O inter­actions generate an infinite chain. In addition, weak inter­molecular C—H⋯π(Ph) inter­actions between pyridine donor and phenol acceptor groups of neighboring cations build a two-dimensional polymeric structure parallel to (110).

Synthesis and spectral characterization of some binuclear complexes designed from N4O and N2O3 donor Schiff-base ligands of 2,6-diformyl-4-methylphenol

New pentadentate binucleating ligands containing phenoxide as an endogenous bridging group, 2,6-diformyl-4-methylphenol bis(carbohydrazone) (L1H), and 2,6-diformyl-4-methylphenol bis(semicarbazone) (L2H), and their binuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes of general formula [M2LCl3] · nH2O with chloride as an exogenous bridge have been synthesized. The complexes were characterized on the basis of elemental analysis, conductivity measurements, thermal analysis, IR, Far-IR, NMR, UV–Vis, EPR, FAB-mass and magnetic data. The coordination mode (N4O, N2O3), as well as endogenous phenoxide bridge and an exogenous chloride bridge have been established on the basis of IR, Far-IR and 1H-NMR spectral data. Electronic spectral data of the complexes indicate square-pyramidal geometry. EPR spectra show line broadening, which is further supported by weak antiferromagnetic interaction from the room temperature magnetic moment data. All compounds show appreciable antimicrobial activity.

A new [Ni II4] distorted cubane assembly on four solvent derived μ 3-OMe corners: Solvent dependent formation and cleavage of exogenous bridges

A new Ni 4 distorted cubane complex [Ni 4(μ 3-OMe) 4Q 4(MeOH) 4] ( 1) (where Q − is the anion of 8-quinolinol) is obtained from the reaction of NaQ with Ni(OAc) 2 · 4H 2O in refluxing MeOH via solvent derived μ 3-OMe assisted self-assembly of four nickel(II) centres. The periphery of [Ni 4(OMe) 4] cubane is covered by four Q − and four MeOH molecules. This methanol specific reaction is not supported in solvent glycinol (Hgl; NH 2(CH 2) 2OH), an amine substituted ethanol, producing monomeric [NiQ 2(Hgl) 2] · 2H 2O ( 2 · 2H 2O) instead and is able to cleave 1 to yield 2 · 2H 2O. The cryomagnetic susceptibility data of powdered 1 can be modeled by a two J equation yielding J 1 = −1.8(1) cm −1, J 2 = 3.9(1) cm −1 and g = 2.24.

Binuclear copper(II) and oxovanadium(IV) complexes with 2,6-diformyl-4- tert -butylphenol- bis -(1′-phthalazinylhydrazone). Synthesis, properties and quantum chemical study

Four binuclear transition metal complexes: [Cu2L(μ-OCH3)] · CH3OH, [Cu2H2L(μ-Cl)Cl2] · (CH3OH), [Cu2H2L(μ-Br)Br2] · (CH3OH), [(VO)2H2L(μ-Cl)]Cl2 · (CH3OH) were synthesized by reaction of the Robson-type binucleating ligand H3L (2,6-diformyl-4-tert-butylphenol-bis-(1′-phthalazinylhydrazone)) with Cu(II) acetate, CuCl2, CuBr2 and VOCl2, correspondingly. IR and ESR spectra, elemental analysis, conductivity measurements, magnetochemical study and DFT calculations were used to characterize the ligand and isolated complexes. The ligand is a NNONN donor and its degree of deprotonation varies with the metal salt used for reaction (triply deprotonated form L−3 is observed in reaction with copper(II) acetate, while monodeprotonated form H2L− is found in complexes obtained from metal halides). All complexes contain an endogenous phenoxide bridge and an exogenous methoxide, chloride or bromide bridge. Magnetic data reveal existence of antiferromagnetic interactions between the metal ions (experimental 2J values are −700, −73, −50 and −190 cm−1, correspondingly). Broken symmetry approach at the UB3LYP/6-31G(d) level was used to theoretically calculate spin-spin coupling between metal centers. Obtained values −570, −62, −53 and −214 cm−1 are rather close to experimental ones and reproduce their counterrelation. Spin density distribution in the singlet and triplet states of the complexes is discussed.

Spectroscopic studies of bridged binuclear complexes of Co(II), Ni(II), Cu(II) and Zn(II)

Binuclear cobalt(II), nickel(II), copper(II) and zinc(II) complexes of general composition [M2L1-2(μ-Cl)Cl2] · nH2O with the Schiff-base ligands (where L1H and L2H are the potential pentadentate ligands derived by condensing 2,6-diformyl-4-methylphenol with 4-amino-3-antipyrine and 2-hydroxy-3-hydrazinoquinoxiline, respectively) have been synthesized and characterized. Analytical and spectral studies support the above formulation. 1H-NMR and IR spectra of the complexes suggest they have an endogenous phenoxide bridge, with chloride as the exogenous bridge atom. The electronic spectra of all the complexes are well characterized by broad d–d and a high intensity charge-transfer transitions. The complexes are chloro-bridged as evidenced by two intense far-IR bands centered around 270–280 cm−1. Magnetic susceptibility measurements show that complexes are antiferromagnetic in nature. The compounds show significant growth inhibitory activity against fungi Aspergillus niger and Candida albicans and moderate activity against bacteria Bacillus cirroflagellosus and Pseudomonas auresenosa.

Synthesis, spectral, electrochemical and magnetic properties of new asymmetric dicopper(II) complexes bearing chemically distinct coordination sites

Two new unsymmetrical binucleating ligands, 2-[bis(3-N,N-dimethylaminopropyl)-aminomethyl]-6-[prolin-1yl)methyl]-4-bromophenol [H2L 1 ] and 2-[bis(3-N,N-dimethylaminopropyl)aminomethyl]-6-[prolin-1-yl)methyl]-4methylphenol [H2L 2 ], and their dicopper(II) complexes with different exogenous bridging motifs (OAc, Br and Cl) have been prepared and characterized by spectral, electrochemical, magnetic and e.p.r. studies. Electrochemical studies indicate the presence of two irreversible reduction peaks in the cathodic region. Variable temperature magnetic susceptibility studies of the complexes show that the extent of antiferromagnetic coupling increases in the order: OAc ) <C l ) <B r ) . Broad isotropic or axial symmetric spectral features are observed in powder e.p.r. spectra of the complexes at 77 K. A comparison of the electrochemical and magnetic behaviour of the complexes derived from the ligands is discussed on the basis of an exogenous bridge as well as the substituent at the para position of the phenolic ring.

Synthesis, characterization and structure of a new dinickel(II) complex as model for urease

A new dinuclear nickel(II) complex [Ni 2(L)(OAc) 2(H 2O)]·ClO 4·H 2O 1 with the unsymmetrical N 5O donor ligand 2-{[bis(2-pyridylmethyl)amino]methyl}-4-methyl-6-{[2-pyridylmethyl)amino]methyl}phenol (HL) has been synthesized and characterized by conductivity, UV–Vis–NIR and IR spectroscopy, electrochemical methods and X-ray crystallography. Complex 1 crystallizes as blue crystals in monoclinic crystal system, space group I2/ a with a=21.171(4) Å, b=12.147(2) Å, c=29.771(6) Å, β=99.67(3)°, V=7547(2) Å 3 and Z=8. In this complex both nickel ions have a distorted octahedral geometry. The nickel centers are endogenously bridged by the phenolic oxygen atom of the deprotonated ligand and also bridged by the two acetate groups as exogenous bridge. A water molecule as terminal ligand is coordinated to a Ni II ion.

Structural diversity in dinickel(II) complexes of thiosemicarbazones

2,6-Diformyl- p-cresol serves as a starting point for the generation of multidentate N/O/S chelating agents. Condensation with 4-(X-phenyl) thiosemicarbazide yields the pentadentate ligand having SNONS donor sequences, capable of holding two metal ions in close proximity. The ligands behave as mono/di/tri basic depending on the pH of the medium. Stereochemical diversity in the reaction product of such ligands with nickel(II) chloride at different pH is observed. Sterically demanding substituted ligands in association with various exogenous bridges dictate the geometry and coordination number of such complexes. The compounds were investigated by elemental analysis, molar conductivities, electronic spectra, IR, NMR, FAB mass spectra, TG-DTG, magnetic susceptibility measurements. Varieties of geometries such as square planar, square pyramidal, octahedral and square planar–square pyramidal are observed. Cryomagnetic data for the complexes (79–296 K) can be reproduced by an equation based on the Heisenberg model ( H=−2 JS 1 S 2, S 1= S 2=1). The singlet–triplet splitting, J varies systematically with the coordination geometry about the Ni 2(SNONS) core, with the hydroxo bridged complex exhibiting the greatest degree of antiferromagnetic coupling. The coupling is somewhat weaker for the chloro-bridged complexes. None of the complexes have shown any appreciable antimicrobial activity.

Catecholase activity of dinuclear copper(II) complexes with variable endogenous and exogenous bridge

A group of a diverse family of dinuclear copper(II) complexes [Cu2(L1O)(μ-OH)][ClO4]2 (1), [Cu2(L2O)(μ-OH)][ClO4]2 (2), [Cu2(L3O)(μ-C3H3N2)(OClO3)(H2O)][ClO4]·H2O (3), [Cu2(L4)(μ-OH)2][ClO4]2·H2O (4), [Cu2(L5O)2(OClO3)2] (5) and [Cu2(bpy)2(μ-OH)(μ-OH2)(μ-O2CMe)][ClO4]2 (6) has been chosen to investigate their potential as catalysts for the aerial oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) (catecholase activity) [L1OH, 2,6-[N-methyl-N-(2-pyridylethyl)aminomethyl]phenol; L2OH, 2,6-bis[N-(2-pyridylethyl)iminomethyl]phenol; L3OH, 1,3-bis[N-methyl-N-(2-pyridylethyl)amino]propan2-ol; L4, α,α′-bis[N-(6-methyl-2-pyridylmethyl)-N-(pyrazol-1-ylmethyl)amino]m-xylene; L5OH, 4-methyl-2,6-bis(pyrazol-1-ylmethy)phenol; bpy, 2,2′-bipyridine; C3H3N2, pyrazolate ion; H, dissociable hydrogen atom]. The synthesis of a new m-xylyl-based dinucleating ligand L4 is described. Using this ligand a new dihydroxy-bridged copper(II) complex 4 has been synthesised and characterised by elemental analysis and physicochemical measurements. The types of bridges present are endogenous phenoxo- and exogenous hydroxo- (1 and 2), endogenous alkoxo- and exogenous pyrazolate- (3), exogenous hydroxo- (4), endogenous diphenoxo-bridge (5) and exogenous hydroxo-, aqua- and acetate- (6). Barring complex 6, which is ferromagnetically coupled, all other complexes are antiferromagnetically coupled and all reported complexes are structurally characterised. The reaction between the dicopper(II) complexes and tetrachlorocatechol was investigated spectrophotometrically to investigate whether or not, during catalysis, binding of 3,5-DTBC is occurring to the copper centre(s). Kinetic experiments have been performed to determine initial rate of reactions and the activity order follows: 1>2≫3>4≫6 (for 5 initial rate could not be determined). For a fixed 3,5-DTBC concentration, a linear relationship for the initial rates and the complex concentration is obtained, suggestive of a first-order dependence on the catalyst concentration. Analysis of Michaelis–Menten kinetic treatment has been done for complexes 1, 2, 3 and 4. Complex 1 is the most active catalyst to show catecholase activity.

The stereochemical diversity of a new SNONS binucleating ligand towards 3d metal ions

A new binucleating ligand containing phenoxide as an endogenous bridging group, 2,6-diformyl- p-cresol bis(2-furanthiocarboxyhydrazone) and its binuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes with chloride ion as an exogenous bridge, have been obtained. The complexes were characterized by elemental analysis, molar conductivities, magnetic moment measurements at room temperature, electronic, IR, 1H-NMR, EPR, FAB spectral studies and thermal data. The copper complex assumes a tetranuclear structure composed of two binuclear units related by a center of symmetry. The dimeric nature of copper(II) complex is supported by FAB. This complex is EPR silent. Room temperature magnetic moment reveals the operation of a significant antiferromagnetic spin exchange between the metal centers. Ligand and its copper and zinc complexes exhibit fluorescence at room temperature in DMF. All the compounds show an appreciable antimicrobial activity.

Bimetallic complexes of a potentially pentadentate, acyclic, symmetrical compartmental Schiff base ligand that provides suitable topology for an exogenous bridge

The binucleating ligand LH3, 2,6-diformyl-p-cresol-bis(phenylthioacetyldrazone), a Schiff base condensation product of 2,6-diformyl-p-cresol and phenylthioacetyldrazide forms complexes of the [M2ClL] type with CoII, NiII and CuII ions, which were characterized by elemental analysis, magnetic susceptibility, electronic spectra, molar conductance, i.r., n.m.r., e.p.r., t.g. and FAB mass spectral measurements. Sub-normal magnetic moments indicate the operation of antiferromagnetic coupling between the metal centres. The ligand and its copper complex show a pronounced fungistatic activity.

Synthesis and physiochemical studies on binuclear Cu(II) complexes derived from 2,6-[(N-phenylpiperazin-1-yl)methyl]-4-substituted phenols

Preparation of the ligands HL1 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-ethylphenol; HL2 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-methoxyphenol and HL3 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-nitrophenol are described together with their Cu(II) complexes with different bridging units. The exogenous bridges incorporated into the complexes are: hydroxo [Cu2L(OH)(H2O)2](ClO4)2.H2O (L1=1a, L2 =1b, L3 =1c), acetato [Cu2L(OAc)2]ClO4.H2O (L1 =2a, L2 =2b, L3 =2c) and nitrito [Cu2L1(NO2)2(H2O)2]ClO4.H2O (L1=3a, L2 =3b, L3 =3c). Complexes1a,1b,1c and2a,2b,2c contain bridging exogenous groups, while3a,3b,3c possess only open μ-phenolate structures. Both the ligands and complexes were characterized by spectral studies. Cyclic voltammetric investigation of these complexes revealed that the reaction process involves two successive quasireversible one-electron steps at different potentials. The first reduction potential is sensitive to electronic effects of the substituents at the aromatic ring of the ligand system, shifting to positive potentials when the substituents are replaced by more electrophilic groups. EPR studies indicate very weak interaction between the two copper atoms. Various covalency parameters have been calculated.

Binuclear Copper(II) Complexes with Robsori‐Type Ligands. Synthesis, characterization, crystal structure, and magnetic properties

AbstractThree binuclear copper(II) complexes, [Cu2(μ‐L)(μ‐N3)](ClO4)2′ 1‐5 EtOH (1), [Cu2(μ‐L)(μ‐MeO)(ClO4)]‐ClO4 ‐ EtOH (2) and [Cu2(μ‐L)(μ‐C3H3N2)](ClO4)2 · 2H2O, (3) where L is the pentadentale bridging ligand derived from 5‐(tert‐butyl)‐2‐hydroxybenzene‐1, 3‐dicarbaldehyde bis(benzoylhydrazone) (HL) were synthesized and characterized. The crystal‐structure determination of complex 2 provided the following crystal data: monoclinic, space group P21}/a, a = 11.412(2), b = 24.509(4), c = 14.833(4) Å, β = 104.41(2)°, K = 4018(3) Å3, Z = 4. The structure shows that the CuII ions are bridged by the endogenous phenolato O‐atom and by an exogenous bridge CH3O−. The analysis of variable‐temperature magnetic susceptibility data (4‐300 K.) indicates that there is an antiferromagnetic interaction between the CuII ions in these complexes with an exchange parameter (2J) of −119.1 cm−1 for complex 1 and −361.8 cm−1 for complex 3. The effect of some exogenous bridging ligands on magnetic coupling for this type of complex is suggested.

Synthesis, magnetism and electrochemistry of tetranuclear nickel(II) and copper(II) complexes of an unsymmetrical bis-pentadentate Schiff-base ligand

A new unsymmetrical tetranucleating ligand, H 6L, containing salicylideneimine and acetyl-acetoneimine end groups attached to a propan-2-ol backbone, has been synthesized. The ligand results from the Schiff-base condensation of 1-(1-methyl-3-oxobut-1-enylamino)-3-(amino)propan-2-ol and the dialdehyde, 5,5′-methylene-bis-salicylaldehyde (2:1). Tetranuclear nickel(II) and Copper(II) complexes of this ligand, of the type [M 4L(X) 2], containing either μ-pyrazolate (X = pz) or μ-3,5-dimethylpyrazolate (X = Me 2pz) exogenous bridges in conjunction with μ-alkoxo endogenous bridges, have been synthesized. Magnetic susceptibility studies on powdered samples of [Cu 4L(pz) 2] ( 3) show medium-strength antiferromagnetic coupling ( J 12 = −108 cm −1) within each half of the tetranuclear complex together with a weaker antiferromagnetic coupling ( J intermol. = −55 cm −1) between the molecules. Cyclic (CV), Osteryoung square wave (OSWV) and Normal pulse (NPV) voltammetric studies on dimethylformamide solutions of [Ni 4L(Me 2pz) 2] ( 2) revealed waves attributable to two sequential one-electron metal centred reduction processes (×2) to yield [Ni 4L(Me 2pz) 2] 2− and [Ni 4L(Me 2pz) 2] 4−.

Paramagnetic and diamagnetic binuclear copper(II) complexes with different bidentate exogenous bridges: synthesis, spectroscopy and magnetic properties

Four binuclear CuII complexes, [Cu2(L)(μ-X)], have been prepared and characterized, where H3L is a 2:1 Schiff base derived from 2-hydroxy-1-naphthaldehyde and 1,3-diamino-2-propanol and X = 1,3-N3(1), C3H3N2 (pyrazolate) (2), AcO (3) and PhCO2(4). The CuIIions are bridged by endogenous alkoxide and bidentate exogenous bridges. The variable-temperature magnetic analyses show that complexes (2)–(4) exhibit antiferro-magnetic coupling with the exchange integrals, 2J, from- 188 to -158 cm-1. The μ-1,3-azide-bridged binuclear CuII complex (1) shows the essential features of diamagnetism through measurements of its variable-temperature susceptibility and e.p.r. spectra. The results suggest that (1) can act as a diamagnetic model for metazidohemocyanin.