III)Ni Research Articles

Novel Cofacial Porphyrin-Based Homo- and Heterotrimetallic Complexes of Transition Metals.

We present a straightforward and generally applicable synthesis route for cofacially linked homo‐ and heterotrimetallic trisporphyin complexes. The protocol encompasses synthesising the first aryl‐based, trans‐o‐phenylene trisporphyrin starting from pyrrole and benzaldehyde with an overall yield of 3.6 %. It also allows investigating the respective cis‐isomer as the first conformationally restricted planar‐chiral trisporphyrin. The free‐base ligand was used in subsequent metalation reactions to afford the corresponding homotrimetallic Mn(III)‐, Fe(III)‐, Ni(II)‐, Cu(II)‐, Zn(II)‐ and Pd(II) complexes – additionally, a small adaptation of the protocol resulted in the defined Ni(II)Fe(III)Ni(II) complex in a total yield of 2.3 %. By monitoring Ni(II) insertion into the empty trimeric ligands, we affirmed that the outer porphyrin rings are filled before the internal ring. The molecular species were characterised by 1H NMR, UV‐Vis, photoluminescence, IR, MS, CID, and high‐resolution IMS measurements.

Reciprocating thermal behavior in the family of single ion magnets

Among the mononuclear transition metal and lanthanide complexes showing the slow magnetic relaxation, as a prerequisite of the single ion magnetism, there are examples of a non-traditional thermal behavior when at the low temperature the relaxation time, referring to the high-frequency relaxation channel, is shortened on further cooling instead of an expected prolongation. This reciprocating thermal behavior has been identified in a number of examples: for the Mn(II), Co(II), Ni(II), Cu(II), {Co(II)Co(III)}, {Gd(III)Ni(II)} and Dy(III) systems. The relaxation time in the low-temperature range can be recovered by applying equation τ–1 = CpbTl + FT–k where the phonon bottleneck process (rather than Raman process) and the “strange” process participate in the inverse relaxation time. The exponents of the temperature variable typically vary as l = 2–4 and k = 0.5–1.

Syntheses, Crystal Structures, and Fluorescence Properties of 3d–4f Coordination Polymers LnNi (Ln = Er, Eu)

Two novel 3d–4f coordination polymers [Ln(NiL)(Nipt)(C2O4)0.5 · H2O] · H2O (Ln = Er (I), Eu (II) (H2L = 2,3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclopentadeca-7,13-dien; H2Nip = 5-nit-roisophthalic acid) were obtained by using 5-nitroisophthalate and mononuclear macrocyclic oxamide complex NiL as co-ligand to react with Ln(NO3)3 ⋅ 6H2O (Ln = Er, Eu) under solvothermal condition, and characterized by single crystal X-ray diffraction (CIF files CCDC nos. 1587618 (I) and 1587619 (II)). Two complexes are isostructural structure and exhibit a two-dimensional network architecture formed by [Ln(III)Ni(II)] units via the oxamide, 5-nitroisophthalate and oxalate bridges, and adjacent 2D structures are linked together with C–H⋅⋅⋅O and O–H⋅⋅⋅O intermolecular hydrogen bonds to form a 3D superamolecular architectures. The fluorescence properties of I and II are also characterized.

Multi-component adsorption of Pb(II), Cd(II), and Ni(II) onto Egyptian Na-activated bentonite; equilibrium, kinetics, thermodynamics, and application for seawater desalination

The adsorption potential of the Egyptian Na-activated bentonite (Na-AB) to remove Pb(II), Cd(II), and Ni(II) from synthetic ternary-ion solutions and contaminated seawater, was investigated for the first time. In this study, natural Egyptian Ca-bentonite was activated to Na-AB, which then was characterized using XRF, XRD, FT-IR, and BET. The adsorption process was strongly influenced by pH, contact time, adsorbent dose, metal concentration, agitation speed, and temperature. The isotherm equations due to Langmuir and Freundlich isotherm models showed good fits with the experimental data. Na-AB has a Langmuir monolayer capacity in a decreasing order of; Pb(II) (5.43mg/g)>Cd(II) (3.14mg/g)>Ni(II) (2.77mg/g), these are considered high capacity values relative to the initial concentration (10mg/L of each metal). The adsorption selectivity was interpreted by means of atomic radii, charge density and hydration enthalpy. The multi-component adsorption kinetics was more accurately described by pseudo-second-order model. The intraparticle diffusion model gave multi-linear curves, so more than one-step controlled the adsorption process. Activation energy was calculated as 17.54, 13.73, and 28.66kJmol−1 for Pb(II), Cd(II), and Ni(II) respectively, suggesting physical adsorption. Thermodynamic parameters at different temperatures (290–328)K showed that (i) Pb(II) adsorption was spontaneous and exothermic, (ii) Cd(II) adsorption was non-spontaneous and endothermic, (iii) Ni(II) adsorption was non-spontaneous and exothermic. Application study on polluted seawater, showed removal efficiency within range of 92–100% not only for Pb(II), Cd(II), and Ni(II) but also for other co-existing metals like Cu(II), Mn(II), Cr(III), and Zn(II).

Syntheses, Structures, Magnetic Properties, and Density Functional Theory Magneto-Structural Correlations of Bis(μ-phenoxo) and Bis(μ-phenoxo)-μ-acetate/Bis(μ-phenoxo)-bis(μ-acetate) Dinuclear FeIIINiII Compounds

The bis(μ-phenoxo) Fe(III)Ni(II) compound [Fe(III)(N3)2LNi(II)(H2O)(CH3CN)](ClO4) (1) and the bis(μ-phenoxo)-μ-acetate/bis(μ-phenoxo)-bis(μ-acetate) Fe(III)Ni(II) compound {[Fe(III)(OAc)LNi(II)(H2O)(μ-OAc)](0.6)·[Fe(III)LNi(II)(μ-OAc)2](0.4)}(ClO4)·1.1H2O (2) have been synthesized from the Robson type tetraiminodiphenol macrocyclic ligand H2L, which is the [2 + 2] condensation product of 4-methyl-2,6-diformylphenol and 2,2'-dimethyl-1,3-diaminopropane. Single-crystal X-ray structures of both compounds have been determined. The cationic part of the dinuclear compound 2 is a cocrystal of the two species [Fe(III)(OAc)LNi(II)(H2O)(μ-OAc)](+) (2A) and [Fe(III)LNi(II)(μ-OAc)2](+) (2B) with weights of 60% of the former and 40% of the latter. While 2A is a triply bridged bis(μ-phenoxo)-μ-acetate system, 2B is a quadruply bridged bis(μ-phenoxo)-bis(μ-acetate) system. Variable-temperature (2-300 K) magnetic studies reveal antiferromagnetic interaction in 1 and ferromagnetic interaction in 2 with J values of -3.14 and 7.36 cm(-1), respectively (H = -2JS1·S2). Broken-symmetry density functional calculations of exchange interaction have been performed on complexes 1 and 2 and also on previously published related compounds, providing good numerical estimates of J values in comparison to experiments. The electronic origin of the difference in magnetic behavior of 1 and 2 has been well understood from MO analyses and computed overlap integrals of BS empty orbitals. The role of acetate and thus its complementarity/countercomplementarity effect on the magnetic properties of diphenoxo-bridged Fe(III)Ni(II) compounds have been determined on computing J values of model compounds by replacing bridging acetate and nonbridging acetate ligand(s) by water ligands in the model compounds derived from 2A,B. The DFT calculations have also been extended to develop several magneto-structural correlations in these types of complexes, and the correlations focus on the role of Fe-O-Ni bridge angle, average Fe/Ni-O bridge distance, Fe-O-Ni-O dihedral angle, and out-of-plane shift of the phenoxo group.

Synthesis and Antimicrobial Activity of Aluminium(III), Nickel(II) and Zinc(II) Schiff base Complexes Derived from o-Phenylenediamine and Salicylaldehyde

N2O2 tetradentate Schiff base ligand-was synthesized from salicylaldehyde and o-phenylenediamine. This ligand was reacted with Al(III), Ni(II) and Zn(II) ions to yield the corresponding complexes. The ligand and its complexes have been :characterized by IR, H-1 NMR, and elemental analysis. The spectral data of these compounds are discussed. in connection with the structural changes due to complexation. The complexes prepared showed good antibacterial activities. The activity data show that the Al(III) Ni(II) and Zn(II) complexe are more potent antibacterial than the parent Schiff base ligand and among all Al(III), complex was the highest.

Slow magnetic relaxation in a cyano-bridged ferromagnetic {FeIIINiII} alternating chain

A cyano-bridged ferromagnetic {Fe(III)Ni(II)} alternating chain {[Fe(pzTp)(CN)3][Ni(chxn)2]}·ClO4·H2O (1) (pzTp = tetrakis(pyrazolyl)borate, chxn = (1R,2R)-1,2-diaminocyclohexane) was synthesized via rational design. Crystal structure analysis and magnetic studies demonstrated that compound had a one-dimensional zigzagging chain-like structure and slow magnetic relaxation.

The Dilemma of CrIIINiII Exchange Interactions: Ferromagnetism versus Antiferromagnetism

The sign of the exchange interaction in dinuclear Cr(III)Ni(II) complexes was analyzed using theoretical methods based on density functional theory. This approach allowed us to reproduce the experimental J values correctly. In addition, the Kahn-Briat model, which uses the square of the sum of the overlaps between the magnetic orbitals to correlate with the exchange coupling constant, provided a reasonable correlation between the different types of Cr(III)Ni(II) complexes when using biorthogonalized orbitals. We also examined the exchange interactions in two polynuclear Cr(III)Ni(II) complexes: a Cr(7)Ni ring and an S-shaped Cr(12)Ni(3) complex. We concluded that both systems exhibit antiferromagentic interactions, and that the Cr(III)···Ni(II) interactions are similar in value to the C(III)···Cr(III) exchange couplings.

Thermodynamic and Kinetic Studies for the Adsorption of Fe(III) and Ni(II) Ions From Aqueous Solution Using Natural Bentonite

In this study, the adsorption behavior of natural bentonite with respect to Fe(III) and Ni(II) has been studied in order to consider its application to purity metal finishing wastewaters. During the adsorption process, batch technique is used, and the effects of pH, bentoite amount, temperature, heavy metal concentration, bentonite treatment (calcinations of natural bentonite at 700°C, washing by deionized water to remove the excess salt from bentonite surface), and agitation time on adsorption efficiency are studied. The washed and calcined bentonite samples were labeled by WB and CB, respectively. The pH-dependence of Fe(III) and Ni(II) sorption on the bentonite is significantly more noticeable, indicating a major contribution of surface complexation at the edge sites. It was determined that adsorption of Fe(III) and Ni(II) is well fitted by the second order reaction kinetic. Furthermore, the sorption rate of Fe(III) was higher than the sorption rate of Ni(II). Adsorption of Fe(III) and Ni(II) on NB appeared to follow Langmuir isotherm. In addition, calculated and experimental adsorbed amounts of Fe(III) by the unit NB mass are very higher than Ni(II). The paper also discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. Also the adsorption capacity of bentonite for Fe(III) Ni(II) and increases with increased bentonite dose. According to the equilibrium studies, the selectivity sequence can be given as Fe(III) > Ni(II). The adsorbed amount of Fe(III) and Ni(II) on washed bentonite (WB) were very higher compared to NB and CB. Our results show that bentonite could especially WB be considered as a potential adsorbent for Fe(III) and Ni(II) removal from aqueous solutions.

Three‐Dimensional Antiferromagnetic Order of Single‐Chain Magnets: A New Approach to Design Molecule‐Based Magnets

Two one-dimensional compounds composed of a 1:1 ratio of Mn(III) salen-type complex and Ni(II) oximato moiety with different counter anions, PF(6)(-) and BPh(4)(-), were synthesized: [Mn(3,5-Cl(2)saltmen)Ni(pao)(2)(phen)]PF(6) (1) and [Mn(5-Clsaltmen)Ni(pao)(2)(phen)]BPh(4) (2), where 3,5-Cl(2)saltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene)bis(3,5-dichlorosalicylideneiminate); 5-Clsaltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene)bis(5-chlorosalicylideneiminate); pao(-) = pyridine-2-aldoximate; and phen = 1,10-phenanthroline. Single-crystal X-ray diffraction study was carried out for both compounds. In 1 and 2, the chain topology is very similar forming an alternating linear chain with a [-Mn(III)-ON-Ni(II)-NO-] repeating motif (where -ON- is the oximate bridge). The use of a bulky counteranion, such as BPh(4)(-), located between the chains in 2 rather than PF(6)(-) in 1, successfully led to the magnetic isolation of the chains in 2. This minimization of the interchain interactions allows the study of the intrinsic magnetic properties of the chains present in 1 and 2. While 1 and 2 possess, as expected, very similar paramagnetic properties above 15 K, their ground state is antiferromagnetic below 9.4 K and paramagnetic down to 1.8 K, respectively. Nevertheless, both compounds exhibit a magnet-type behavior at temperatures below 6 K. While for 2, the observed magnetism is well explained by a Single-Chain Magnet (SCM) behavior, the magnet properties for 1 are induced by the presence in the material of SCM building units that order antiferromagnetically. By controlling both intra- and interchain magnetic interactions in this new [Mn(III)Ni(II)] SCM system, a remarkable AF phase with a magnet-type behavior has been stabilized in relation with the intrinsic SCM properties of the chains present in 1. This result suggests that the simultaneous enhancement of both intrachain (J) and interchain (J') magnetic interactions (with keeping J >> J'), independently of the presence of AF phase might be an efficient route to design high temperature SCM-based magnets.

Metal-Complexes As Ligands to Generate Asymmetric Homo- and Heterodinuclear MAIIIMBIISpecies: a Magneto-Structural and Spectroscopic Comparison of Imidazole-N versus Pyridine-N

Ten hetero- and homodinuclear M(A)(III)M(B)(III) complexes, 1-10, containing the metal centers Fe(III)Zn(II) (1), Fe(III)Cu(II) (2), Fe(III)Ni(II) (3), Fe(III)Fe(II) (4), Fe(III)Mn(II) (5), Cr(III)Ni(II) (6), Cr(III)Zn(II) (7), Ga(III)Ni(II) (8), Co(III)Fe(II) (9), and Mn(III)Mn(II) (10) are described. The tridentate ligation property of the divalent metal complexes tris(1-methylimidazole-2-aldoximato)metal(II) with three facially disposed pendent oxime O-atoms has been utilized to generate the said complexes. Complexes were characterized by various physical methods including MS, IR, UV-vis, Mossbauer and EPR spectroscopy, cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, and X-ray diffraction techniques. Binuclear complexes 1-10 contain three oximato anions as bridging ligands and are isostructural in the sense that they all contain a metal(III) ion, LM(A)(III) (L = 1,4,7-trimethyl-1,4,7-triazacyclononane), in a distorted octahedral environment M(A)(III)N(3)O(3) and a second six-coordinated divalent metal ion, M(B)(II), in a trigonally distorted M(B)(II)N(6) geometry. A comparison of the cyclic voltammograms of the complexes with those of similar systems reveal both ligand-centered and metal-centered redox processes. Complexes 2, 3, 5, and 6 display antiferromagnetic exchange coupling of the neighboring metal centers in the order Fe(III)Mn(II) (5) < Fe(III)Ni(II) (3) < Fe(III)Cu(II) (2) whereas Fe(III)Ni(II) (3) > Cr(III)Ni(II) (6). On the contrary, complex 10, containing high-spin Mn(III) and Mn(II) centers, exhibits ferromagnetic coupling yielding a "high-spin" molecule with an S(t) = (9)/(2) ground state. X-band electron paramagnetic resonance (EPR) spectroscopy for 6, Cr(III)Ni(II) and 3, Fe(III)Ni(II) has been used to establish the electronic ground state in great detail and to complement the magnetic susceptibility measurements. Moreover, computational results have been included to compare the sigma-bonding character of the nitrogen lone pair in imidazole-containing ligand and the analogous pyridine-containing oxime.

Probing the role of the divalent metal ion in uteroferrin using metal ion replacement and a comparison to isostructural biomimetics

Purple acid phosphatases (PAPs) are a group of heterovalent binuclear metalloenzymes that catalyze the hydrolysis of phosphomonoesters at acidic to neutral pH. While the metal ions are essential for catalysis, their precise roles are not fully understood. Here, the Fe(III)Ni(II) derivative of pig PAP (uteroferrin) was generated and its properties were compared with those of the native Fe(III)Fe(II) enzyme. The kcat of the Fe(III)Ni(II) derivative (approximately 60 s(-1)) is approximately 20% of that of native uteroferrin, and the Ni(II) uptake is considerably faster than the reconstitution of full enzymatic activity, suggesting a slow conformational change is required to attain optimal reactivity. An analysis of the pH dependence of the catalytic properties of Fe(III)Ni(II) uteroferrin indicates that the mu-hydroxide is the likely nucleophile. Thus, the Ni(II) derivative employs a mechanism similar to that proposed for the Ga(III)Zn(II) derivative of uteroferrin, but different from that of the native enzyme, which uses a terminal Fe(III)-bound nucleophile to initiate catalysis. Binuclear Fe(III)Ni(II) biomimetics with coordination environments similar to the coordination environment of uteroferrin were generated to provide both experimental benchmarks (structural and spectroscopic) and further insight into the catalytic mechanism of hydrolysis. The data are consistent with a reaction mechanism employing an Fe(III)-bound terminal hydroxide as a nucleophile, similar to that proposed for native uteroferrin and various related isostructural biomimetics. Thus, only in the uteroferrin-catalyzed reaction are the precise details of the catalytic mechanism sensitive to the metal ion composition, illustrating the significance of the dynamic ligand environment in the protein active site for the optimization of the catalytic efficiency.

Tridentate Facial Ligation of Tris(pyridine-2-aldoximato)nickel(II) and Tris(imidazole-2-aldoximato)nickel(II) To Generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiIIand the Electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIIISpecies: A Magnetostructural, Electrochemical, and EPR Spectroscopic Study

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction. Complexes were characterized by various physical methods including cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, electron paramagnetic resonance (EPR) measurements, and X-ray diffraction methods. Binuclear complexes 2-6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 complexes, 3a-c, and 4, demonstrates the effects of the remote substituents on the spin coupling. The electrochemical measurements CV and square wave voltammograms (SQW) reveal two reversible metal-centered oxidations, which have been assigned to the Ni center ligated to the oxime N atoms, unless a Mn ion is present. Complex 2, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) to the corresponding higher states. These assignments of the redox processes have been complemented by the X-band EPR measurements. That the electrooxidized species [3a]+, [3b]+, [3c]+, and [4]+ contain the localized mixed-valent NiIINiIII system resulting from the spin coupling, a spin quartet ground state, S(t) = 3/2, has been confirmed by the X-band EPR measurements.

Synthesis and characterization of unusual heterotrinuclear Co(III)Ni(II)Co(III) hydrotris(3,5-dimethylpyrazolyl)borate complex with mixed 1,1-azide and pyrazolate bridges

An unusual heterotrinuclear complex [LCo(μ-L1, 1-N3)2(μ-L1)Ni(μ-1, 1-N3)2(μ-L1)CoL] (1) was obtained by the reaction of the precursor of half-sandwich nickel(II) complex [LNi(HL1)2(N3)] (2) and CoCl2·6H2O (L=hydrotris(3,5-dimethylpyrazolyl)borate; L1=3,5-dimethylpyrazolate), the complex 1 was characterized by X-ray single-crystal diffraction, elemental analysis, IR, UV–vis spectra and magnetic properties.

Square Planar versus Tetrahedral NiS4 Cores in the Coordination Spheres of (HMB)Ru(II) and Cp*Ru(III) and a Related CuS4 Complex. Synthetic, Single-Crystal X-ray Diffraction, and Magnetic Studies {HMB = η6-C6Me6 and Cp* = η5-C5Me5}

The reaction of [LRu(κ3SSS‘-tpdt)] (L = η6-C6Me6 (HMB), (1); L = η5-C5Me5 (Cp*), (2); tpdt = S(CH2CH2S-)2) with Cl2Ni(PPh3)2 gave diamagnetic trinuclear complexes, [{(HMB)RuII(μ-1κ3SSS‘:2κ2SS-tpdt)}2NiII]2+ (3) and [{Cp*RuIII(μ-1κ3SSS‘:2κ2SS-tpdt)}2NiII]2+ (4), isolated as hexafluorophosphate salts in 96 and 61% yields, respectively. A similar reaction of 2 with CuSO4 in excess gave a dinuclear species, [Cp*RuIII(μ-1κ3SSS‘:2κ2SS-tpdt)CuII-(CH3CN)2]2+ (5) (73% yield, as PF6- salt), which further reacted with 1 molar equiv of 2 to give a paramagnetic complex, [{Cp*RuIII(μ-1κ3SSS‘:2κ2SS-tpdt)}2CuII]2+ (6) (81% yield, as PF6- salt), or 1 molar equiv of 1 to give the “mixed-ring” tpdt dithiolate-bridged diamagnetic complex [{Cp*RuIII(μ-1κ3SSS‘:2κ2SS-tpdt)}CuII{(HMB)RuII(μ-1κ3SSS‘:2κ2SS-tpdt}]2+ (7) (89% yield, as PF6- salt). The molecular structures of complexes 3−7 were determined by single-crystal X-ray diffraction analysis. Notably it was observed that the trimetallic array Ru−M−Ru possesses a M−M bond between the central metal atom (Ni(II) or Cu(II)) and terminal Ru atoms in +3 oxidation state, i.e., Ru atoms bearing a Cp* ligand. Thus, while Ni is in a square planar environment in 3, in the other trinuclear complexes, viz., 4, 6, and 7, Ni/Cu is in a slightly distorted tetrahedral environment with respect to the four thiolate S donors, but is formally five- or six-coordinate, in the presence of one or two M−M bonds, respectively. Variable-temperature magnetic susceptibility studies on neat powders of representative compounds 2, 3, 4, and 6 show S = 1/2 Curie-like behavior for mononuclear Ru(III) complex 2, as expected, and also for the trinuclear {Ru(III)Cu(II)Ru(III)} complex 6, the behavior of the latter being ascribed either to a 19e electron count on Cu, involving Ru−Cu bonding, or to a strongly antiferromagnetically coupled {Ru(III)(S = 1/2)Cu(II)(S = 1/2)Ru(III)(S = 1/2)} sulfur-bridged moiety. Complexes 3 and 4, having oxidation states Ru(II)Ni(II)Ru(II) and Ru(III)Ni(II)Ru(III), respectively, are close to being diamagnetic but display very weak paramagnetism between 4.2 and 300 K.

Magnetic coupling in oxalato-bridged hetero-bimetallic compounds: an ab initio study

Multiconfigurational perturbation theory (CASPT2) and difference dedicated configuration interaction are applied to study the ferromagnetic coupling in oxalato-bridged Cr(III)Cu(II) molecular species, where the external ligands of the Cr(salen)C2O4Cu(acpy) complex, with salen=N,N′-ethylenebis(salicylideneaminate) and acpy=N-acetylacetonylidene-N-(2-pyridylethyl)aminate, are modeled by simple H2O or NH3 groups. The results show little dependence on the external ligand modeling. The experimental coupling is very well reproduced at both calculation levels when the model nearly reproduces the experimental geometrical structure. CASPT2 calculations on an oxalato-bridged Cr(III)Ni(II) model of Cr(salen)C2O4Ni(taea)BPh4, where taea=tris(2-aminoethyl)amine, are also in good agreement with experiment.

(μ-Hydroxo)bis(μ-acetato)dimetal complexes: structural and magnetochemical characterization of the Cr(III)Ni(II) and the Cr(III)Cr(III) species

The perchlorate salts of the cations [LCr(μ-OH)(μ-OOC·CH3)2NiL] 2+ (1) and [LCr(μ-OH)(μ-OOC·CH3)2CrL] 3+ (2), where L represents the macrocyclic tridentate amine 1,4,7-trimethyl-1,4,7-triazacyclononane have been characterized by X-ray crystallography. The core-structures consist of bioctahedra in which the metal ions (CrIII, NiII in 1 and CrIII, CrIII in 2) are bridged by one hydroxo and two acetate groups. A moderate antiferromagnetic coupling (J=−18.5 cm−1; H=−2J S1·S2) has been evaluated for the CrIIINiII pair 1 from the variable-temperature (2–290 K) SQUID measurements, thus revealing a spin doublet ground state. The doublet ground state has also been confirmed by EPR measurements (2–50 K). In 2 the Cr(III) centers are also antiferromagnetically coupled.

Tris(pyridinealdoximato)metal complexes as ligands for the synthesis of asymmetric heterodinuclear Cr(III)M species [M = Zn(II), Cu(II), Ni(II), Fe(II), Mn(II), Cr(II), Co(III)]: a magneto-structural study.

Reactions of the LCr(III) unit with an in situ prepared M(PyA)(3)(n-) ion, where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane and PyA(-) is the monoanion of pyridine-2-aldoxime, yield heterodinuclear complexes of general formula [LCr(III)(PyA)(3)M](2+/3+) as perchlorate salts, where M = Cr(II) (1), Mn(II) (2), low-spin Fe(II) (3), Ni(II) (4), Cu(II) (5), Zn(II) (6), and low-spin Co(III) (7). These compounds contain three oximato anions as bridging ligands. The hexadentate ligand with the identical donor atoms, tris(2-aldoximato-6-pyridyl)phosphine, P(PyA)(3), has been employed to prepare a second Cr(III)Ni(II) species 8, whose magnetic properties differ significantly from those of 4. Complexes 1-8 have been characterized on the basis of elemental analysis, mass spectrometry, IR, UV-vis, Mössbauer, and EPR spectroscopies, and variable-temperature (2-295 K) magnetic susceptibility measurements. They are isostructural in the sense that they all contain a terminal Cr(III) ion in a distorted octahedral environment, CrN(3)O(3), and a second six-coordinated metal ion M in a mostly trigonal prismatic MN(6) geometry. The crystal structures of the perchlorate salts of 2-5, 7, and 8 have been determined by X-ray crystallography at 100 K. The structures consist of mixed-metal Cr(III)M(II) and Cr(III)Co(III) complexes with a geometry in which two pseudooctahedral polyhedra are joined by three oximato (=N-O(-)) groups, with an intramolecular Cr.M(Co) distance in the range of 3.4-3.7 A. The cyclic voltammograms of the complexes reveal ligand oxidation and reduction processes, and in addition, metal-centered oxidation processes have been observed. X-band EPR spectroscopy has been used to establish the electronic ground state of the heterodinuclear complexes. Analysis of the susceptibility data indicates the presence of weak exchange interactions, both ferro- and antiferromagnetic, between the paramagnetic centers. A qualitative rationale on the basis of the Goodenough-Kanamori rules is provided for the difference in magnetic behaviors.

Interaction of manganese(II), cobalt(II) and nickel(II) with DNA oligomers studied by 1H NMR spectroscopy

The metal binding properties of three different oligodeoxyribonucleotides, one decamer and two dodecamers, have been studied by 1D and 2D 1H NMR spectroscopy. The sequential composition of the oligomers was chosen so as to provide a multitude of different binding site contexts: 5′-GACGGCCGTC ( I), 5′-CGCGAATTCGCG ( II), and 5′-ATGGGTACCCAT ( III). Salts of three different metal ions: Mn(II), Co(II) and Ni(II), were used in titration experiments. The binding studies were carried out under duplex conditions. The influence of paramagnetic metal ions on protons adjacent to the binding site were followed by measuring line broadening and T 1 relaxation times. We have previously proposed a rule for sequence-selective metal binding to G-N7 in oligodeoxyribonucleotides where the metal prefer the 5′-guanine residue in the order: 5′-GG ≥ GA > GT ≫ GC. This binding pattern is also observed in the present study for Mn( II) and Co(II). However, in sequence I Ni(II) does not follow the established selectivity rule showing greater affinity for 5′-G in the context 5′-GC than in the context 5′-GA. For II and III Ni(II) ions are seen to follow the selectivity rule. Fluctuation in the nucleophilicity of G-N7 along the duplex is probably a consequence of sequence-dependent variation in π-stacking interaction between base residues.

Textural and electrochemical properties of Watts nickel-deposited titanium electrodes

The surface morphologies and crystalline structures of Watts nickel-deposited titanium electrodes obtained for different plating times or plating solutions with various pH values were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). These textural results indicate that the Ni grains with Ni(111) and Ni(200) preferred orientations have spherical/paddy-like and cubic morphologies, respectively. The XRD results indicate that Ni(111) is the preferred orientation of a newly grown grain or a deposit from a plating solution with pH > 5.0. Voltametric behavior of the Ni(III) Ni(II) transition as well as that in the hydrogen region and the ability for hydrogen evolution of these electrodes were compared by cyclic voltametry (CV) and log( i) — E relationships. These electrochemical results revealed that deposits with Ni(111) preferred orientation exhibit higher active sites/activities for both the hydrogen responses and the Ni(III) Ni(II) transition.