The Crucial Role of Polyatomic Anions in Molecular Architecture: Structural And Magnetic Versatility of Five Nickel(II) Complexes Derived from A N,N,O-Donor Schiff Base Ligand

A series of five Ni(II)-complexes containing the same tridentate Schiff base but different monoanionic ligands (N-3(-), NO3-, PhCOO- and NO2-)reveals that the competitive as well as the cooperative role of the monoanions and phenoxo group in bridging the metal ions play the key role in the variation of molecular architecture.

Facile strategies for the synthesis and crystallization of linear trinuclear nickel(II)-Schiff base, complexes with carboxylate bridges: Tuning of coordination geometry and magnetic properties

Three new linear trinuclear nickel(II) complexes, [Ni-3(salpen)(2)(OAc)(2)(H2O)(2)]center dot 4H(2)O (1) (OAc = acetate, CH3COO-), [Ni-3(salpen)(2)(OBz)(2)] (2) (OBz=benzoate, PhCOO-) and [Ni-3(salpen)(2)(OCn)(2)(CH3CN)(2)] (4) (OCn = cinnamate, PhCH=CHCOO-), H(2)salpen = tetradentate ligand, N,N'-bis(salicylidene)-1,3-pentanediamine have been synthesized and characterized structurally and magnetically. The choice of solvent for growing single crystal was made by inspecting the morphology of the initially obtained solids with the help of SEM study. The magnetic properties of a closely related complex, [Ni-3(salpen)(2)(OPh)(2)(EtOH)] (3) (OPh = phenyl acetate, PhCH2COO-) whose structure and solution properties have been reported recently, has also been studied here. The structural analyses reveal that both phenoxo and carboxylate bridging are present in all the complexes and the three Ni(II) atoms remain in linear disposition. Although the Schiff base ligand and the syn-syn bridging bidentate mode of the carboxylate group remain the same in complexes 1-4, the change of alkyl/aryl group of the carboxylates brings about systematic variations between six- and five-coordination in the geometry of the terminal Ni(II) centres of the trinuclear units. The steric demand as well as hydrophobic nature of the alkyl/aryl group of the carboxylate is found to play a crucial role in the tuning of the geometry. Variable-temperature (2-300 K) magnetic susceptibility measurements show that complexes 1-4 are antiferromagnetically coupled (J = -3.2(1), -4.6(1). -3.2(1) and -2.8(1) cm(-1) in 1-4, respectively). Calculations of the zero-field splitting parameter indicate that the values of D for complexes 1-4 are in the high range (D = +9.1(2), +14.2(2), +9.8(2) and +8.6(1) cm(-1) for 1-4, respectively). The highest D value of +14.2(2) and +9.8(2) cm(-1) for complexes 2 and 3, respectively, are consistent with the pentacoordinated geometry of the two terminal nickel(II) ions in 2 and one terminal nickel(II) ion in 3. (C) 2009 Elsevier Ltd. All rights reserved.

Synthesis and crystal structure characterization of iron(II), cobalt(II) and nickel(II) complexes with 1,3-bis(2-pyridylmethylthio)propane

Three new mononuclear complexes of nitrogen-sulfur donor sets, formulated as (Fe-II(L)Cl-2] (1), [Co-II(L)Cl-2] (2) and [Ni-II(L)Cl-2] (3) where L = 1,3-bis(2-pyridylmethylthio)propane, were synthesized and isolated in their pure form. All the complexes were characterized by physicochemical and spectroscopic methods. The solid state structures of complexes I and 3 have been established by single crystal X-ray crystallography. The structural analysis evidences isomorphous crystals with the metal ion in a distorted octahedral geometry that comprises NSSN ligand donors with trans located pyridine rings and chlorides in cis positions. In dimethylformamide solution, the complexes were found to exhibit Fe-II/Fe-III, co(II)/co(III) and Ni-II/Ni-III quasi-reversible redox couples in cyclic voltammograms with E-1/2 values (versus Ag/AgCl at 298 K) of +0.295, +0.795 and +0.745 V for 1, 2 and 3, respectively. (C) 2009 Elsevier Ltd. All rights reserved.

Antitumour activity of [1,2-di(cyclopentadienyl)-1,2-di(p-N,N-dimethylaminophenyl)-ethanediyl] titanium dichloride in xenografted Ehrlich's ascites tumour

The effects of a new titanocene compound with an ansa ligand in the cyclopentadienyl rings, the 1,2-di(cyclopentadienyl)-1,2-di(p-NNdimethylaminophenyl)-ethanediyl] titanium dichloride (TITANOCENE X), on the growth and differentiation of granulocyte-macrophage progenitor cells [colony-forming unit-granulocyte-macrophage (CFU-GM)] and Natural killer (NK) cell activity in Ehrlich's ascites tumour (EAT)-bearing mice were studied. Myelosuppression concomitant with increased numbers of spleen CFU-GM was observed in tumour-bearing mice. Treatment of these animals with TITANOCENE X (2.5-50mg/kg/day) produced an increase in myelopoicsis, in a dose-dependent manner, and reduced spleen colony formation. In addition, the treatment of EAT-bearing mice with 3 doses of 20 or 50 mg/kg TITANOCENE X restored to normal values the reduced Natural killer cell function observed during tumour growth. In parallel, TITANOCENE X prolonged, in a dose-dependent manner, the survival of mice inoculated with Ehrlich's ascites tumour. The highest dose of 50 mg/kg prolonged in 50% the survival time of EAT-bearing mice, compared to non-treated tumour-bearing controls. In comparison with previous results from our laboratory addressing the effects of titanocenes on haematopoiesis, we observed with TITANOCENE X a similar effective profile as for bis(cyclopentadienyl) dithiocyanate titanium(IV), being both less effective than di(cyclopentadienyl) dichloro titanium(IV), since the latter not only prolonged, but also increased the rate of survival. These differences in efficacy may be due to the nature of the ansa-cyclopentadienyl ligand used in TITANOCENE X, since the C, bridge between the two cyclopentadienyl groups will increase the hydrolytic stability by an organometallic chelate effect. Also, the introduction of two dimethylamino substituents increases the water solubility of TITANOCENE X when compared to titanocene dichloride itself (c) 2006 Elsevier B.V. All rights reserved.

A square-planar nickel(II) monoradical complex with a bis(salicylidene)diamine ligand

The new square-planar Ni-II-N2O2 complex [Ni(L-Me)] (1(Me)), where L-Me, stands for the dianionic phenolato form of N,N'bis(3,5-di-tert-butyl-salicylidene)-4,5-dimethyl-1,2-phenyl- enediamine ((LH2)-L-Me), has been synthesised and fully characterised. X-ray crystallography was also used for the characterisation. The electrochemical one-electron oxidation of 1(Me) produces the thermally stable (within the temperature range 10-295 K) cationic species (1(Me))(+). The UV/Vis and X-band EPR experimental data, supported by DFT calculations, indicate that (1(Me))(+), is best described as a Ni-II monoradical complex and, thus, does NOT exist in a Ni-III ground state, in contrast to its demethylated counterpart [Ni(L-H)](+) (1(H))(+) below 170 K.

Palladium-coated nickel nanoclusters: new Hiyama cross-coupling catalysts

The advantages of bimetallic nanoparticles as C - C coupling catalysts are discussed, and a simple, bottom- up synthesis method of core - shell Ni - Pd clusters is presented. This method combines electrochemical and 'wet chemical' techniques, and enables the preparation of highly monodispersed structured bimetallic nanoclusters. The double- anode electrochemical cell is described in detail. The core - shell Ni - Pd clusters were then applied as catalysts in the Hiyama cross- coupling reaction between phenyltrimethoxysilane and various haloaryls. Good product yields were obtained with a variety of iodo- and bromoaryls. We found that, for a fixed amount of Pd atoms, the core - shell clusters outperform both the monometallic Pd clusters and the alloy bimetallic Ni - Pd ones. THF is an excellent solvent for this process, with less than 2% homocoupling by-product. The roles of the stabiliser and the solvent are discussed.

Hydrogen-bond assisted stabilization of the less favored conformation of a tridentate Schiff base ligand in dinuclear nickel(II) complex: an experimental and theoretical study

The Schiff base ligand, HL (2-[1-(3-methylamino-propylimino)-ethyl]-phenol), the 1:1 condensation product of 2-hydroxy acetophenone and N-methyl-1,3-diaminopropane, has been synthesized and characterized by X-ray crystallography as the perchlorate salt [H2L]ClO4 (1). The structure consists of discrete [H2L](+) cations and perchlorate anions. Two dinuclear Ni-II complexes, [Ni2L2(NO2)(2)] (2), [Ni2L2(NO3)(2)] (3) have been synthesized using this ligand and characterized by single crystal X-ray analyses. Complexes 2 and 3 are centrosymmetric dimers in which the Ni-II ions are in distorted fac- and mer-octahedral environments, respectively, bridged by two mu(2)-phenolate ions of deprotonated ligand, L. The plane of the phenyl rings and the Ni2O2 basal plane are nearly coplanar in 2 but almost perpendicular in 3. We have studied and explained this different behavior using high level DFT calculations (RI-BP86/def2-TZVP level of theory). The conformation observed in 3, which is energetically less favorable, is stabilized via intermolecular non-covalent interactions. Under the excitation of ultraviolet light, characteristic fluorescence of compound 1 was observed; by comparison fluorescence intensity decreases in case of compound 3 and completely quenched in compound 2.

Synthesis, structure and magnetic properties of mono- and di-nuclear nickel(II) thiocyanate complexes with tridentate N3 donor Schiff bases

The 1:1 condensation of N-methyl-1,3-diaminopropane and N,N-diethyl-1,2-diminoethane with 2-acetylpyridine, respectively at high dilution gives the tridentate mono-condensed Schiff bases N-methyl-N'-(1-pyridin-2-yl-ethylidene)-propane-1,3-diamine (L-1) and N,N-diethyl-N'-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine (L-2). The tridentate ligands were allowed to react with methanol solutions of nickel(II) thiocyanate to prepare the complexes [Ni(L-1)(SCN)(2)(OH2) (1) and [{Ni(L-2)(SCN)}(2)] (2). Single crystal X-ray diffraction was used to confirm the structures of the complexes. The nickel(II) in complex 1 is bonded to three nitrogen donor atoms of the ligand L-1 in a mer orientation, together with two thiocyanates bonded through nitrogen and a water molecule, and it is the first Schiff base complex of nickel(II) containing both thiocyanate and coordinated water. The coordinated water initiates a hydrogen bonded 2D network. In complex 2, the nickel ion occupies a slightly distorted octahedral coordination sphere, being bonded to three nitrogen atoms from the ligand L-2, also in a mer orientation, and two thiocyanate anions through nitrogen. In contrast to 1, the sixth coordination site is occupied by a sulfur atom from a thiocyanate anion in an adjacent molecule, thus creating a centrosymmetric dimer. A variable temperature magnetic study of complex 2 indicates the simultaneous presence of zero-field splitting, weak intramolecular ferromagnetic coupling and intermolecular antiferromagnetic interactions between the nickel(II) centers.

Nickel(II) and copper(II) complexes of unsymmetrical tetradentate reduced Schiff base ligands

Two new reduced Schiff base ligands, [HL1 = 4-(2-[(pyridin-2-ylmethyl)-amino]-ethylimino)-pentan-2-one and HL2 =4-[2-(1-pyridin-2-yl-ethylamino)-ethylimino]-pentan-2-one] have been prepared by reduction of the corresponding tetradentate unsymmetrical schiff bases derived from 1.1: 1 condensation of 1,2-ethanediamine, acetylacetone and pyridine-2-carboxaldehyde/2-acetyl pyridine. Four complexes, [Ni(L-1)]ClO4 (1), [Cu(L-1)]ClO4 (2). [Ni(L-2)]ClO4 (3). and [Cu(L-2)]ClO4 (4) with these two reduced Schiff base ligands have been synthesized and structurally characterized by X-ray crystallography. The mono-negative ligands L-1 and L-2 are chelated in all four complexes through the four donor atoms to form square planar nickel(II) and copper(II) complexes Structures of 3 and 4 reveal that enantiomeric pairs are crystallized together with opposite chirality in the nitrogen and carbon atoms. The two Cu-II complexes (2 and 4) exhibit both irreversible reductive (Cu-II/Cu-II, E-pc. -1.00 and -1.04 V) and oxidative (Cu-II/CUII, E-pa, + 1.22 and + 1.17 V, respectively) responses in cyclic voltammetry. The electrochemically generated Cu-1 species for both the complexes are unstable and undergo disproportionation.

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, H2Lm (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 MLm (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.

Fulvalene titanium and zirconium complexes: synthesis and NMR study of phosphanido-, alkyl-, and alkynyl-derivatives. X-ray crystal structures of [{Ti(η5−C5H5)(μ−PPH2)}2{μ−(η5−C5H4−η5−C5H4)}] and [{Zr(η5−C5H5)(μ−C≡CSiMe3)}2{μ−(η5−C5H4−η5−C5H4)}]

Reaction of with one or two equivalents of LiPPh2 afforded the new phosphanidometal(III) complexes . Reaction of 2 with LiC≡CSiMe3 led to the diamagnetic zirconium(III) alkynyl derivative [{Zr(C5H5)(μ−C≡CSiMe3)}2(μ−η5−C5H4−η5−C5H4], 7. Alkylation of 6 with LiCH2CMe2Ph gave [{Zr(η5−C5H5)(CH2CMe2Ph)2}2{μ−(η5−C5H4)}], 8. A detailed NMR study of complexes 3 and 4 allowed the observation of the spectral behaviour of the eight different fulvalene protons through their coupling to the 31P nucleus. The fluxional behaviour of complex 7 was studied by dynamic DNMR, and kinetic parameters for the σ-π-conversion of the alkynyl ligand were determined. The molecular structures of complexes 3 and 7 were determined by X-ray diffraction methods.

Fulvalene cyclopentadienyl titanium and zirconium(III) and -(IV) complexes. X-Ray crystal structure of [{Ti(η5-C5H5) Cl}2 (μ-O)(μ-η5-η5-C10H8)]

The reaction of the fulvalene titanium(III) hydride [{Ti(η5-C5H5)(μ-H)}2(μ-η5-η5-C10H8)] (1) with chlorine leads to [{Ti(η5-C5H5)(μ-Cl)}2(μ-η5-η5-C10H8)] (3) and [{Ti(η5-C5H5)Cl2}2(μ-η5-η5-C10H8)] (4). The reaction of 3 with azobenzene, in wet toluene, gives [{Ti(η5-C5H5)Cl}2(μ-O)(μ-η5-η5-C10H8)] (5) and 1,2-diphenyl hydrazine. The alkylation of 4 and the analogous zirconium complex [{Zr(η5-C5H55)Cl2}2(μ-η5-η5-C10H8)] (2) with LiCH2SiMe3 or LiCH3 permits isolation of the tetraalkyl derivatives [{M(η5-C5H5)(CH2SiMe3)2}2(μ-η5-η5-C10H8)] (M  Ti (6); Zr (8)) and [{Ti(η5-C5H5)(CH3)2}2(μ-η5-η5C10H8)] (7). All the new fulvalene compounds were characterized by IR, and 1H and 13C NMR spectroscope, and mass spectra and 5 by X-ray diffraction. The structure of 5 is very similar to that of the comparable TiIV compound [{Ti(η5-C5H5)2Cl}2(μ-O)] except for the smaller TiOTi angle (159.4° against 173.81°) and a significant deviation from linearity.

Hetero-metallic trinuclear nickel(II)–cadmium(II) complexes of a salicylaldimine ligand with thiocyanate, cyanate and azide ions: isolation of a pair of polymorphs with thiocyanate ion

Four new trinuclear hetero-metallic nickel(II)-cadmium(II) complexes [(NiL)(2)Cd(NCS)(2)] (1A and 1B), [(NiL)(2)Cd(NCO)(2)] (2) and [(NiL)(2)Cd(N-3)(2)] (3) have been synthesized using [NiL] as a so-called "ligand complex" (where H2L = N,N'-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Crystal structure analyses reveal that all four complexes contain a trinuclear moiety in which two square planar [NiL] units are bonded to a central cadmium(II) ion through double phenoxido bridges. The Cd(II) is in a six-coordinate distorted octahedral environment being bonded additionally to two mutually cis nitrogen atoms of terminal thiocyanate (in 1A and 1B), cyanate (in 2) and azide (in 3). Complexes 1A and 1B have the same molecular formula but crystallize in very different monoclinic unit cells and can be considered as polymorphs. On the other hand, the two isoelectronic complexes 2 and 3 are indeed isomorphous and crystallize only in one form. Their conformation is similar to that observed in 1A.

Synthesis, crystal structures, magnetic properties and catecholase activity of double phenoxido-bridged penta-coordinated dinuclear nickel(II) complexes derived from reduced Schiff-base ligands: mechanistic inference of catecholase activity

Three double phenoxido-bridged dinuclear nickel(II) complexes, namely [Ni-2(L-1)(2)(NCS)(2)] (1), [Ni-2(L-2)(2)(NCS)(2)] (2), and [Ni-2(L-3)(2)(NCS)(2)] (3) have been synthesized using the reduced tridentate Schiff-base ligands 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL1), 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL2), and 2-[1-(3-dimethylarnino-propylamino)-ethyl]-phenol (HL3), respectively. The coordination compounds have been characterized by X-ray structural analyses, magnetic-susceptibility measurements, and various spectroscopic methods. In all complexes, the nickel(II) ions are penta-coordinated in a square-pyramidal environment, which is severely distorted in the case of 1 (Addison parameter tau = 0.47) and 3 (tau = 0.29), while it is almost perfect for 2 (tau = 0.03). This arrangement leads to relatively strong antiferromagnetic interactions between the Ni(II) (S = 1) metal centers as mediated by double phenoxido bridges (with J values of -23.32 (1), -35.45 (2), and -34.02 (3) cm(3) K mol(-1), in the convention H = -2JS(1)S(2)). The catalytic activity of these Ni compounds has been investigated for the aerial oxidation of 3,5-di-tert-butylcatechol. Kinetic data analysis following Michaelis-Menten treatment reveals that the catecholase activity of the complexes is influenced by the flexibility of the ligand and also by the geometry around the metal ion. Electrospray ionization mass spectroscopy (ESI-MS) studies (in the positive mode) have been performed for all the coordination compounds in the presence of 3,5-DTBC to characterize potential complex-substrate intermediates. The mass-spectrometry data, corroborated by electron paramagnetic resonance (EPR) measurements, suggest that the metal centers are involved in the catecholase activity exhibited by the complexes.