Isolation of the first ferromagnetically coupled Mn(III/IV) complex

Binuclear manganese complexes Mn2(III/IV)(dtsalpn)2DCBI, 1, Mn2(III/III)(dtsalpn)2HDCBI, 2, containing the ligand dicarboxyimidazole (DCBI) have been prepared in order to address the issue of imidazole bridged and ferromagnetically coupled Mn sites in high oxidation states of the OEC in Photosystem II (PS II). Temperature dependent magnetic susceptibility studies of 1 indicates that the interaction between the two Mn(III)/Mn(IV) ions is ferromagnetic (J = +1.4 cm(-1)). Variable temperature EPR spectra of 1 shows that a g = 2 multiline is as an excited state signal corresponding to S = 1/2.     

Structures and magnetic properties of an antiferromagnetically coupled polymeric copper(II) complex and ferromagnetically coupled hexanuclear nickel(II) clusters

Reactions between 2,6-diformyl-4-methylphenol (DFMF) and tris(hydroxymethyl) aminomethane (THMAM = H(3)L2) in the presence of copper(II) salts, CuX(2) (X = CH(3)CO(2)(-), BF(4)(-), ClO(4)(-), Cl(-), NO(3)(-)) and Ni(CH(3)CO(2))(2) or Ni(ClO(4))(2)/NaC(6)H(5)CO(2), sodium azide (NaN(3)), and triethylamine (TEA), in one pot self-assemble giving a coordination polymer consisting of repeating pentanuclear copper(II) clusters {[Cu(2)(H(5)L(2-))(μ-N(3))](2)[Cu(N(3))(4)]·2CH(3)OH}(n) (1) and hexanuclear Ni(II) complexes [Ni(6)(H(3)L1(-))(2)(HL2(2-))(2)(μ-N(3))(4)(CH(3)CO(2))(2)]·6C(3)H(7)NO·C(2)H(5)OH (2) and [Ni(6)(H(3)L1(-))(2)(HL2(2-))(2)(μ-N(3))(4)(C(6)H(5)CO(2))(2)]·3C(3)H(7)NO·3H(2)O·CH(3)OH (3). In 1, H(5)L(2-) and in 2 and 3 H(3)L1(-) and HL2(2-) represent doubly deprotonated, singly deprotonated, and doubly deprotonated Schiff-base ligands H(7)L and H(4)L1 and a tripodal ligand H(3)L2, respectively. 1 has a novel double-stranded ladder-like structure in which [Cu(N(3))(4)](2-) anions link single chains comprised of dinuclear cationic subunits [Cu(2)(H(5)L(2-))(μ-N(3))](+), forming a 3D structure of interconnected ladders through H bonding. Nickel(II) clusters 2 and 3 have very similar neutral hexanuclear cores in which six nickel(II) ions are bonded to two H(4)L1, two H(3)L2, four μ-azido, and two μ-CH(3)CO(2)(-)/μ-C(6)H(5)CO(2)(-) ligands. In each structure two terminal dinickel (Ni(2)) units are connected to the central dinickel unit through four doubly bridging end-on (EO) μ-azido and four triply bridging μ(3)-methoxy bridges organizing into hexanuclear units. In each terminal dinuclear unit two nickel centers are bridged through one μ-phenolate oxygen from H(3)L1(-), one μ(3)-methoxy oxygen from HL2(2-), and one μ-CH(3)CO(2)(-) (2)/μ-C(6)H(5)CO(2)(-) (3) ion. Bulk magnetization measurements on 1 show moderately strong antiferromagnetic coupling within the [Cu(2)] building block (J(1) = -113.5 cm(-1)). Bulk magnetization measurements on 2 and 3 demonstrate that the magnetic interactions are completely dominated by ferromagnetic coupling occurring between Ni(II) ions for all bridges with coupling constants (J(1), J(2), and J(3)) ranging from 2.10 to 14.56 cm(-1) (in the ? = -J(1)(?(1)?(2)) - J(1)(?(2)?(3)) - J(2)(?(3)?(4)) - J(1)(?(4)?(5)) - J(1)(?(5)?(6)) - J(2)(?(1)?(6)) - J(3)(?(2)?(6)) - J(3)(?(2)?(5)) - J(3)(?(3)?(5)) convention).     

Peculiarity in the electronic structure of Cu(II) complex ferromagnetically coupled with bisimino nitroxides

By means of the electron spin resonance (ESR) technique, we have investigated the electronic structures of the tridentate imino nitroxyl diradical complex with copper(II) (Cu-bisimpy), which has a square planar structure and a ground quartet state with an extremely strong ferromagnetic exchange interaction, and its related compounds (bisimpy = 2,6-bis(1'-oxyl-4',4',5',5'-tetramethyl-4',5'-dihydro-1' H-imidazol-2'-yl)pyridine). It was clarified that Cu-bisimpy had unique magnetic orbitals, compared with the biradical ligand (bisimpy), a zinc(II) biradical complex (Zn-bisimpy) and a copper(II) terpyridine complex (Cu-tpy) (tpy = 2,2';6',2'-terpyridine). Multifrequency ESR spectroscopy provided a reliable set of magnetic parameters of Cu-bisimpy, which has a small g anisotropy ( g x = 2.02, g y = 2.01, g z = 2.08) and small hyperfine coupling with Cu (|A x| = 42.0 MHz, |A y|相似文献   

Magnetostructural studies on ferromagnetically coupled copper(II) cubanes of Schiff-base ligands

Three cubane copper(II) clusters, namely [Cu(4)(HL')4] (1), [Cu4L2(OH)2] (2), and [Cu4L2(OMe)2] (3), of two pentadentate Schiff-base ligands N,N'-(2-hydroxypropane-1,3-diyl)bis(acetylacetoneimine) (H3L') and N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) (H3L), are prepared, structurally characterized by X-ray crystallography, and their variable-temperature magnetic properties studied. Complex 1 has a metal-to-ligand stoichiometry of 1:1 and it crystallizes in the cubic space group P43n with a structure that consists of a tetranuclear core with metal centers linked by a mu(3)-alkoxo oxygen atom to form a cubic arrangement of the metal and oxygen atoms. Each ligand displays a tridentate binding mode which means that a total of eight pendant binding sites remain per cubane molecule. Complexes [Cu4L2(OH)2] (2) and [Cu4L2(OMe)2] (3) crystallize in the orthorhombic space group Pccn and have a cubane structure that is formed by the self-assembly of two {Cu2L}+ units. The variable-temperature magnetic susceptibility data in the range 300-18 K show ferromagnetic exchange interactions in the complexes. Along with the ferromagnetic exchange pathway, there is also a weak antiferromagnetic exchange between the copper centers. The theoretical fitting of the magnetic data gives the following parameters: J1 = 38.5 and J2 = -18 cm(-1) for 1 with a triplet (S = 1) ground state and quintet (S = 2) lowest excited state; J1 = 14.7 and J2 = -18.4 cm(-1) for 2 with a triplet ground state and singlet (S = 0) lowest excited state; and J1 = 33.3 and J2 = -15.6 cm(-1) for 3 with a triplet ground state and quintet lowest excited state, where J1 and J2 are two different exchange pathways in the cubane {Cu4O4} core. The crystal structures of 2 * 6 H2O and 3 * 2 H2O * THF show the presence of channels containing the lattice solvent molecules.     

Metamorphosis of a butterfly: synthesis, structural, thermal, magnetic and DFT characterisation of a ferromagnetically coupled tetranuclear copper(II) complex

The reaction in water of Cu(OH)(2) with 2,2'-bipyridine (bipy) and (NH(4))(2)HPO(4) in a 4 : 4 : 2 molar ratio under an inert atmosphere leads to the formation of a tetranuclear copper(II) complex of formula {[(H(2)O)(2)Cu(4)(bipy)(4)(mu(4)-PO(4))(2)(mu(2)-OH)] x 0.5 HPO(4) x 15.5 H(2)O}, 1, with butterfly topology. The structure of the tetranuclear core in 1 consists of four crystallographically unique copper(II) ions in approximate square-pyramidal geometry with each coordinated to a bipy ligand and interacting through two mu(4)-O,O',O'-phosphate bridges. Additional bridging between Cu(3) and Cu(4) is provided by a hydroxide ligand, whereas two water molecules cap the Cu(1) and Cu(2) square pyramids to yield a N(2)O(3) chromophore at each copper atom. Adjacent tetranuclear units align in anti-parallel fashion where proximate metal-bound water molecules interact with each other through both intra- and inter-molecular H-bonding to link two such clusters. These pairs then further associate through pi[...]pi interactions between bipy ligands to form a 2D sheet with neighbouring sheets separated by H-bonded lattice water molecules, which form a 2D H-bonded network. Variable-temperature magnetic susceptibility measurements performed upon 1 reveal net intramolecular ferromagnetic coupling between the copper(II) ions and this is supported and rationalized by a DFT study.     

The first metamagnetic thiocyanato-bridged one-dimensional nickel(II) complex

A novel single thiocyanato-bridged one-dimensional polymer, [NiL(NCS)(micro-NCS)]n (L = N1-(1-pyridin-2-yl-ethylidine)propane-1,3-diamine) has been synthesized and characterized by X-ray crystallography and a variable temperature magnetic study; the compound is a metamagnet with a Neél temperature (T(N)) of 3.5 K.     

Na(THF)2Cr(N3N)]: The first trigonal monopyramidal chromium(II) complex

Reduction of [Cr(N(3)N)] (1) [(N(3)N)(3)(-) = ((SiMe(3)NCH(2)CH(2))(3)N)(3)(-)] with sodium powder in THF affords the yellow, extremely air-sensitive amidochromate(II) [Na(THF)(2)Cr(N(3)N)] (2) in good yield. Complex 2 has an effective magnetic moment of 5.1 mu(B) indicative of a d(4) high-spin electronic configuration. (1)H NMR spectroscopy in solution and single-crystal X-ray crystallography show that compound 2 is composed of idealized C(s) symmetric contact ion pairs, in which trigonal-monopyramidal [Cr(II)(N(3)N)](-) anions are linked to the [Na(THF)(2)](+) countercations by two bridging amide ligands. DFT calculations of 1, 2, and the anion [Cr(N(3)N)](-) at the RI-BP86/TZVPP level of theory provide in combination with extended Hückel calculations a rationale for the observed structural changes from 1 to 2.     

High-pressure spin-crossover in a dinuclear Fe(II) complex

The effect of pressure on the dinuclear spin crossover material [{Fe(bpp)(NCS)(2)}(2)(4,4'-bipy)]·2MeOH (where bpp = 2,6-bis(pyrazol-3-yl)pyridine and 4,4'-bipy = 4,4'-bipyridine, 1) has been investigated with single crystal X-ray diffraction and Raman spectroscopy using diamond anvil cell techniques. The very gradual pressure-induced spin crossover occurs between 7 and 25 kbar, and shows no evidence of crystallographic phase transitions. The pressure-induced spin transition leads to a complete LS state which is not thermally accessible. This structural evolution under pressure is in stark contrast to the previously reported thermal spin crossover behaviour, in which a symmetry-breaking, purely structural phase transition results in only partial conversion to the low spin state. This observation is attributed to the symmetry-breaking phase transition becoming unfavourable under pressure.     

Trinuclear, antiferromagnetically coupled Cu(II) complex with an EPR spectrum of mononuclear Cu(II): effect of alcoholic solvents

A rigid trinuclear copper pyrazolato framework supports the solvolytic exchange of mu3-X by mu3-OR ligands (X = Cl and Br; R = alkyl group), converting the trinuclear ferromagnetically coupled S = 3/2 system to antiferromagnetically coupled S = 1/2 in the solid state. In contrast, we propose that, in alcoholic solutions, solvolysis results in unsymmetrical coordination of the Cu3 cluster, magnetically decoupling one Cu center from the other two. This disguises the intact triangular Cu(II)3 system as a mononuclear Cu(II) complex in its electron paramagnetic resonance spectrum.     

A rare ferromagnetically coupled asymmetric doubly azido bridged copper(II) dimer with an N,N, O donor Schiff base

A new end-to-end (EE) doubly azido bridged dinuclear complex [Cu₂L₂(μ_1,3-N₃)₂] (1) [where L = (E)-4-(2-(dimethylamino)ethylimino)-1,1,1-trifluoropentan-2-one)] has been synthesized and characterized by elemental and spectroscopic techniques. Single crystal X-ray diffraction analysis reveals that the dimeric complex possesses a center of inversion. Each copper atom in 1 is in a distorted square pyramidal geometry with a CuN₄O chromophore as revealed from the τ value, 0.19. The four basal positions are occupied by two imine N and one keto O atom of the Schiff base and one N atom from the azide anion. Another N atom from a coordinated azide occupies the apical position. Temperature dependent magnetic susceptibility of 1 was fitted using the Bleaney–Bowers expression which led to the parameters J = 13.6 cm⁻¹ and R = 3.4 × 10⁻⁵. It indicates a ferromagnetic interaction through the double azido bridges connecting the individual copper Schiff base units.     

Synthesis, structure, and properties of an Fe(II) carbonyl [(PaPy3)Fe(CO)](ClO4): insight into the reactivity of Fe(II)-CO and Fe(II)-NO moieties in non-heme iron chelates of N-donor ligands

An Fe(II) carbonyl complex [(PaPy3)Fe(CO)](ClO4) (1) of the pentadentate ligand N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide (PaPy3H, H is the dissociable amide proton) has been synthesized and structurally characterized. This Fe(II) carbonyl exhibits its nu(CO) at 1972 cm(-1), and its 1H NMR spectrum in degassed CD3CN confirms its S = 0 ground state. The bound CO in 1 is not photolabile. Reaction of 1 with an equimolar amount of NO results in the formation of the {Fe-NO}7 nitrosyl [(PaPy3)Fe(NO)](ClO4) (2), while excess NO affords the iron(III) nitro complex [(PaPy3)Fe(NO2)](ClO4) (5). In the presence of [Fe(Cp)2]+ and excess NO, 1 forms the {Fe-NO}6 nitrosyl [(PaPy3)Fe(NO)](ClO4)2 (3). Complex 1 also reacts with dioxygen to afford the iron(III) mu-oxo species [{(PaPy3)Fe}2O](ClO4)2 (4). Comparison of the metric and spectral parameters of 1 with those of the previously reported {Fe-NO}6,7 nitrosyls 3 and 2 provides insight into the electronic distributions in the Fe(II)-CO, Fe(II)-NO, and Fe(II)-NO+ bonds in the isostructural series of complexes 1-3 derived from a non-heme polypyridine ligand with one carboxamide group.     

Chemiluminescence flow system for the determination of Fe(II) and Fe(III) in water

A novel chemiluminescence (CL) flow system has been developed for the sequential determination of Fe(II) and Fe(III) in water. Fe(II) was detected by its catalytic effect on the CL reaction between luminol immobilized on an anion exchange resin column and dissolved oxygen; Fe(III) was determined by difference measurement after on-line conversion to Fe(II) in a reducing mini-column packed with Cu plated Zn granules. For both ions, the calibration graph was linear in the range 1 × 10^–9 to 1 × 10^–6 g/mL, and the detection limit was 4 × 10^–10 g/mL. A complete analysis could be performed in 1.5 min with a relative standard deviation of less than 5%. The system could be reused for over 200 times and has been applied successfully to the determination of Fe(II) and Fe(III) in natural water samples.     

Chemiluminescence flow system for the determination of Fe(II) and Fe(III) in water

A novel chemiluminescence (CL) flow system has been developed for the sequential determination of Fe(II) and Fe(III) in water. Fe(II) was detected by its catalytic effect on the CL reaction between luminol immobilized on an anion exchange resin column and dissolved oxygen; Fe(III) was determined by difference measurement after on-line conversion to Fe(II) in a reducing mini-column packed with Cu plated Zn granules. For both ions, the calibration graph was linear in the range 1 × 10^–9 to 1 × 10^–6 g/mL, and the detection limit was 4 × 10^–10 g/mL. A complete analysis could be performed in 1.5 min with a relative standard deviation of less than 5%. The system could be reused for over 200 times and has been applied successfully to the determination of Fe(II) and Fe(III) in natural water samples. Received: 13 March 1997 / Revised: 3 June 1997 / Accepted: 6 June 1997     

The first ruthenium(II) complex with benzotriazole and pyridylcarboxylato ligands

The reaction of [RuCl₂(PPh₃)₃] with 1-(2-pyridylcarbonyl)benzotriazole has been examined. A new ruthenium(II) complex–[RuCl(PPh₃)₂(C₆H₅N₃)(C₅H₄NCO₂)] has been obtained and characterized by IR and UV–Vis measurements. The crystal structure of the complex has been determined. The electronic spectrum of the complex has been calculated by TDDFT method.     

Studies on Fe complexes produced by yeast. V. Role of the ligand in Fe absorption from an Fe(II)-oligosaccharide complex

The role of the ligand (oligosaccharide) of an Fe(II) complex (B1-c) produced in wine by Saccharomyces cerevisiae in gastrointestinal Fe absorption was examined. B1-c was found to consist of Fe(II) and an oligosaccharide having the composition of Ara: Xyl: Man: Glc: GalUA (1:1:1:5:1), and the sequence of these constituent monosaccharides was presumed by means of partial hydrolysis of B1-c with glycosidases and a diluted acid. The physicochemical comparison of the partially hydrolyzed, Fe(II)-containing products (Fe-containing fragments) obtained by glycosidase treatment indicated that the Man and GalUA residues of the ligand should be essential for stabilization of the complex form at the physiological pH in the digestive tract. The intestinal Fe absorption in vivo showed marked differences among the Fe-containing fragments having different ligands (sugar chains). Furthermore, the inhibitory effects of the Fe-containing fragments on B1-c uptake by brush border membrane vesicles of the small intestine varied with the ligand, probably being related to the composition of the sugar chain. These results suggest that the sugar chain of the ligand of B1-c may be involved, through its coordination with Fe(II), in (i) high stability and Fe solubility of B1-c at the physiological pH in the digestive tract and (ii) recognition of B1-c molecules in its transport system on the intestinal brush border membrane and, thereby, may contribute to excellent intestinal Fe absorption from B1-c.     

The first Pd(II) complex of a non-heteroatom stabilised carbene ligand

Di(p-tolyl)diazomethane reacts with the tripyrrinate TrpyPdOAc(F) 1 after activation with NaBAr(F) to yield the first stable Pd(II) complex 2 of a non-Arduengo type carbene ligand, which could be characterised by X-ray crystallography.     

Asynchronous merging zones system: spectrophotometric determination of Fe(II) and Fe(III) in pharmaceutical products

An asynchronous merging zones was proposed with simultaneous introduction of the sample and of the modifier reagent, ascorbic acid in the studied case, for sequential determination of Fe(II) and Fe(III) in pharmaceutical products. The sample and reagent attained a merging point at different times owing to the use of a delay reactor in the reagent channel. By inserting a large sample and controlling the dispersion in the flow system, Fe(II) and Fe(III) were sequentially measured in the front and in the rear of the sample zone, respectively. The results obtained for Fe redox speciation in pharmaceutical products are in agreement at a 95% confidence level with those obtained with a manual spectrophotometric procedure. The analytical frequency with the proposed flow analysis system was 54 samples h(-1), i.e. 108 determinations h(-1).