The syntheses, characterizations, X-ray crystal structures and properties of Cu(I) complexes of a bis-bidentate schiff base ligand

Bis-bidentate Schiff base ligand L and its two mononuclear complexes [CuL(CH3CN)(2)]ClO4 (1)and [CuL(PPh3)(2)]ClO4 (2)have been prepared and thoroughly characterized by elemental analyses, IR, UV-Vis, NMR spectroscopy and X-ray diffraction analysis. In both the complexes the metal ion auxiliaries adopt tetrahedral coordination environment. Their reactivity, electrochemical and photophysical behavior have been studied. Complex 1 shows reversible Cu-II/I couple with potential 0.74 V versus Ag/AgCl in CH2Cl2. At room temperature L is weakly fluorescent in CH2Cl2, however in Cu(I)complexes 1 and 2 the emission in quenched. (C) 2009 Elsevier B. V. All rights reserved.

Study of (Ba3MMWO9)-M-II-W-IV (M-II = Ca, Zn; M-IV = Ti, Zr) perovskite oxides: Competition between 3C and 6H perovskite structures

We describe an investigation of (Ba3MMWO9)-M-II-W-IV oxides for M-II = Ca, Zn, and other divalent metals and M-IV = Ti, Zr. In general, a 1:2-ordered 6H (hexagonal, P6(3)/mmc) perovskite structure is stabilized at high temperatures (1300 degrees C) for all of the (Ba3MTiWO9)-Ti-II oxides investigated. An intermediate phase possessing a partially ordered 1:1 double perovskite (3C) structure with the cation distribution, Ba-2(Zn2/3Ti1/3)(W2/3Ti1/3)O-6, is obtained at 1200 degrees C for Ba3ZnTiWO9. Sr substitution for Ba in the latter stabilizes the cubic 3C structure instead of the 6H structure. A metastable Ba3CaZrWO9 that adopts the 3C (cubic, Fm (3) over barm) structure has also been synthesized by a low-temperature metathesis route. Besides yielding several new perovskite oxides that may be useful as dielectric ceramics, the present investigation provides new insights into the complex interplay of crystal chemistry (tolerance factor) and chemical bonding (anion polarization and d(0)-induced distortion of metal-oxygen octahedra) in the stabilization of 6H versus 3C perovskite structures for the (Ba3MMWO9)-M-II-W-IV series.

Studies on some metal monothiobenzoates

Monothiobenzoate (MTB) (Chemical Equation Presented) complexes with the molecular formulas Cr(MTB)3, [Ni(MTB)2]n, [Zn(MTB)2]n, [Cd(MTB)2]n, [Hg(MTB)2]n, [Cu(MTB)]n, and [Ag(MTB)]n have been prepared and studied. All the complexes are nonionic in acetonitrile. Only the chromium complex is soluble in nitrobenzene and found to be monomeric cryoscopically. The thiobenzoate ligand appears to be asymmetrically chelated in Cr(III) and Cd(II) complexes, with stronger oxygen and sulfur coordination, respectively, while practically symmetrically coordinated in Ni(II) and Zn(II) complexes. These four complexes are assigned distorted octahedral structures around the metal ion. The coordination in Hg(II), Cu(I), and Ag(I) complexes is mainly through sulfur indicating the monodentate nature of the thiobenzoate ligand in these complexes. The coordination of monothiobenzoate ion in the complexes has been rationalized in terms of "hard" and "soft" acid-base concept.

Synthesis, Structure, and Magnetic Properties of Amine-Templated Transition-Metal Phosphites

Transition-metal phosphites of cobalt and vanadium, [C4N2H12][Co(HPO3)(2)] (I), [C4N2H14][Co(HPO3)(2)] (II), [Co[C4H8N12)(H2PO3)(2)] (III),[C4N2H14][(VF)-F-III(HPO3)(2)]center dot H2O (IV), and[C3N2H5](2)[V-4(III)(H2O)(3)(HPO3)(4)(HPO4)(3)] (V), have been synthesized and characterized. Organophosphorus esters were employed to stabilize cobalt in tetrahedral coordination and also to prepare the low-dimensional structures, which are otherwise difficult to synthesize. The structures have one- (I, II, IV), two- (III) and three-dimensionally (V) extended networks built up by the linking of metal polyhedra and phosphite units. Another vanadyl phosphite, [C2N2H10][((VO)-O-IV)(3)(H2O) (HPO3)(4)]center dot H2O,([15]) was also prepared and investigated extensively by ESR, magnetic susceptibility, and other studies. All the compounds in the present study exhibit antiferromagnetic interactions. Well-established magnetic models have been used to fit the experimental data. The compounds havealso been characterized in detail by using UV/Vis spectroscopic studies.

Analysis of multiple crystal forms of Bacillus subtilis BacB suggests a role for a metal ion as a nucleant for crystallization

Bacillus subtilis BacB is an oxidase that is involved in the production of the antibiotic bacilysin. This protein contains two double-stranded beta-helix (cupin) domains fused in a compact arrangement. BacB crystallizes in three crystal forms under similar crystallization conditions. An interesting observation was that a slight perturbation of the crystallization droplet resulted in the nucleation of a different crystal form. An X-ray absorption scan of BacB suggested the presence of cobalt and iron in the crystal. Here, a comparative analysis of the different crystal forms of BacB is presented in an effort to identify the basis for the different lattices. It is noted that metal ions mediating interactions across the asymmetric unit dominate the different packing arrangements. Furthermore, a normalized B-factor analysis of all the crystal structures suggests that the solvent-exposed metal ions decrease the flexibility of a loop segment, perhaps influencing the choice of crystal form. The residues coordinating the surface metal ion are similar in the triclinic and monoclinic crystal forms. The coordinating ligands for the corresponding metal ion in the tetragonal crystal form are different, leading to a tighter packing arrangement. Although BacB is a monomer in solution, a dimer of BacB serves as a template on which higher order symmetrical arrangements are formed. The different crystal forms of BacB thus provide experimental evidence for metal-ion-mediated lattice formation and crystal packing.

Synthesis of metal oxide nanorods using carbon nanotubes as templates

Nanorods of several oxides, with diameters in the range of 10-200 nm and lengths upto a few microns, have been prepared by templating against carbon nanotubes. The oxides include V2O5, WO3, MoO3 and Sb2O5 as well as metallic MoO2, RuO2 and IrO2. The nanorods tend to be single-crystalline structures. Nanotube structures have also been obtained in MoO3 and RuO2.

A series of transition metal-azido extended complexes with various anionic and neutral co-ligands: synthesis, structure and their distinct magnetic behavior

The crystal structures and magnetic properties of five new transition metal-azido complexes with two anionic [pyrazine-2-carboxylate (pyzc) and p-aminobenzoate (paba)] and two neutral [pyrazine (pyz) and pyridine (py)] coligands are reported All five complexes were synthesized bysolvothermal methods The complex [Co-2(pyzc)(2)(N-3)(2)(H2O)(2)](n) (1) is 1D and exhibit canted antiferromagnetism, while the 3D complex [MnNa(pyzc)(N-3)(2)(H2O)(2)](n) (2) has a complicated structure and is weakly ferromagnetic in nature [Mn-2(paba)(2)(N-3)(2)(H2O)(2)](n) (3). is a 2D sheet and the Mn-II ions are found to be antiferromagnetically coupled The isostructural 2D complexes [Cu-3(pyz)(2)(N-3)(6)](n) (4) and [Cu-3(py)(2)(N-3)(6)](n) (5) resemble remarkably in their magnetic properties exhibiting moderately strong ferromagnetism. Density functional theory calculations (B3LYP functional) have been performed to provide a qualitative theoretical interpietation of the overall magnetic behavior shown by these complexes.

Mixed Azide and 5-(Pyrimidyl)tetrazole Bridged Co(II)/Mn(II) Polymers: Synthesis, Crystal Structures, Ferroelectric and Magnetic Behavior

The reaction of pyrimidine-2-carbonitrile, NaN3 in the presence of Co(NO3)(2)center dot 6H(2)O or MnCl2 center dot 4H(2)O leads to the formation of complexes Co(pmtz)(mu(1,3)-N-3)(H2O)](n) (1) and Mn(pmtz)(mu(1,3)-N-3)(H2O)](n) (2) respectively, under hydrothermal condition pmtz =5-(pyrimidyl)tetrazolate]. These two complexes have been fully characterized by single crystal X-ray diffraction. Complex 1 crystallizes in a non-centrosymmetric space group Aba2 in the orthorhombic system and is found to exhibit ferroelectric behavior, whereas complex 2 crystallizes in the P2(1)/c space group in the monoclinic system. Variable temperature magnetic characterizations in the temperature range of 2-300 K indicate that complex 1 is a canted antiferromagnet (weak ferromagnet) with T-c = 15.9 K. Complex 1 represents a unique example of a multiferroic coordination polymer containing tetrazole as a co-ligand. Complex 2 is a one-dimensional chain of Mn(II) bridged by a well-known antiferromagnetic coupler end-to-end azido ligand. In contrast to the role played by the end-to-end azido pathway in most of the transition metal complexes, complex 2 showed unusual ferromagnetic behavior below 40 K because of spin canting.

Synthesis and characterization of metal substituted AlxCr1-x(acetylacetonate)(3) single-source precursors for their application to MOCVD of thin films

A detailed study, involving the synthesis of a single-source precursor containing two metal ions sharing the same crystallographic site, has been undertaken to elucidate the use of such a single-source precursor in a CVD process for growing thin films of oxides comprising these two metals, ensuring a uniform composition and distribution of metal ions. The substituted complexes Cr1-xAlx(acac)(3), where acac = acetyl-acetonate, have been prepared by a co-synthesis method, and characterized using UV-Vis spectroscopy. TGA/DTA measurements, and single crystal X-ray diffraction at low temperature. All the studied compositions crystallize in the monoclinic space group P2(1)/c with Z = 4 in the unit cell. It was observed that the ratio (Al:Cr) of the site occupancy for the metal ions, obtained from single crystal refinement, is in agreement with the results obtained from complexometric titrations. All the solid state structures have the metal in an octahedral environment forming six-membered chelate rings. M-O acac bond lengths and disorder in the terminal carbon have been studied in detail for these substituted metal-organic complexes. One composition among these was chosen to evaluate their suitability as a single-source precursor in a LPMOCVD process (low-pressure metal-organic chemical vapour deposition) for the deposition of a substituted binary metal oxide thin film. The resulting thin films were characterized by X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. (C) 2010 Elsevier Ltd. All rights reserved.

Synthesis, crystal structures and magnetic behavior of two 3D coordination polymers using N-(4/3-arboxyphenyl)iminodiacetic acids as bridging ligands

Research on structure and magnetic properties of polynuclear metal complexes to understand the structural and chemical factors governing the electronic exchange coupling mediated by multi-atom bridging ligands is of growing interest. Hydrothermal treatment of Ni(NO3)(2)center dot 6H(2)O with N-(4-carboxyphenyl)iminodiacetic acid N-4(H(3)CPIDA)] at 150 degrees C yielded a 3D coordination polymer of general formula Ni-3{N-4( CPIDA)}(2)(H2O)(3)]center dot 6H(2)O (1). An analogous network of general formula Co-3{N-3(CPIDA)}(2)(H2O)(3)]center dot 3H(2)O (2) was synthesized using N-(3-carboxyphenyl) iminodiacetic acid N-3(H(3)CPIDA)] in combination with Co(NO3)(2)center dot 6H(2)O under identical reaction condition. Both the complexes contain trinuclear secondary building unit, and crystallized in monoclinic system with space groups C2/c (1) and P2(1)/c (2), respectively. Variable temperature magnetic characterization of these complexes in the temperature range of 2-300 K indicated the presence of overall ferromagnetic and antiferromagnetic behavior for 1 and 2, respectively. Density functional theory calculations (B3LYP functional) were performed for further insight on the trinuclear units to provide a qualitative theoretical interpretation on the overall magnetic behavior of the complexes 1 and 2. (C) 2010 Elsevier B.V. All rights reserved.

Use of 2-pyrimidineamidoxime to generate polynuclear homo-/heterometallic assemblies: synthesis, crystal structures and magnetic study with theoretical investigations on the exchange mechanism

Three new transition metal complexes using 2-pyrimidineamidoxime (pmadH(2)) as multidentate chelating and/or bridging ligand have been synthesized and characterized. The ligand pmadH(2) has two potential bridging functional groups mu-O and mu-(N-O)] and consequently shows several coordination modes. While a polymeric 1D Cu-II complex Cu(pmadH(2))(2)(NO3)](NO3) (1) was obtained upon treatment of Cu(NO3)(2)center dot 3H(2)O with pmadH(2) at room temperature in the absence of base, a high temperature reaction in the presence of base yielded a tetranuclear Cu-II-complex Cu-4(pmad)(2)(pmadH)(2)(NO3)](NO3)(H2O) (2). One of the Cu-II centers is in a square pyramidal environment while the other three are in a square planar geometry. Reaction of the same ligand with an equimolar mixture of both Cu(NO3)(2)center dot 3H(2)O and NiCl2 center dot 6H(2)O yielded a tetranuclear heterometallic (Cu2Ni2II)-Ni-II complex Cu2Ni2(pmad)(2)(pmadH)(2)Cl-2]center dot H2O (3) containing both square planar (Ni-II) and square pyramidal (Cu-II) metal centers. Complexes 1-3 represent the first examples of polynuclear metal complexes of 2-pyrimidineamidoxime. The analysis of variable temperature magnetic susceptibility data of 2 reveals that both ferromagnetic and antiferromagnetic interactions exist in this complex (J(1) = +10.7 cm(-1) and J(2) = -2.7 cm(-1) with g = 2.1) leading to a resultant ferromagnetic behavior. Complex 3 shows expected antiferromagnetic interaction between two Cu-II centers through -N-O- bridging pathway with J(1) = -3.4 cm(-1) and g = 2.08. DFT calculations have been used to corroborate the magnetic results.

Reactivity Of Pph3 Toward Ruiiruiiicl(O2car)4 - Syntheses, Molecular-Structures, And Spectroscopic And Electrochemical Properties Of Ruiiruiii(Oh2)Cl(Mecn)(O2car)4(Pph3)2 And Ruii2(Oh2)(Mecn)2(O2car)4(Pph3)2

By the reaction of Ru2Cl(O2CAr)4 (1) and PPh3 in MeCN-H2O the diruthenium(II,III) and diruthenium(II) compounds of the type Ru2(OH2)Cl(MeCN)(O2CAr)4(PPh3)2 (2) and Ru2(OH2)(MeCN)2(O2CAr)4(PPh3)2 (3) were prepared and characterized by analytical, spectral, and electrochemical data (Ar is an aryl group, C6H4-p-X; X = H, OMe, Me, Cl, NO2). The molecular structure of Ru2(OH2)Cl(MeCN)(O2CC6H4-p-OMe)4(PPh3)2 was determined by X-ray crystallography. Crystal data are as follows: triclinic, P1BAR, a = 13.538 (5) angstrom, b = 15.650 (4) angstrom, c = 18.287 (7) angstrom, alpha = 101.39 (3)-degrees, beta = 105.99 (4)-degrees, gamma = 97.94 (3)-degrees, V = 3574 angstrom 3, Z = 2. The molecule is asymmetric, and the two ruthenium centers are clearly distinguishable. The Ru(III)-Ru(II), Ru(III)-(mu-OH2), and Ru(II)-(mu-OH2) distances and the Ru-(mu-OH2)-Ru angle in [{Ru(III)Cl(eta-1-O2CC6H4-p-OMe)(PPh3)}(mu-OH2)(mu-O2CC6H4-p-OMe)2{Ru(II)(MeCN)(eta-1-O2CC6H4-p-OMe)(PPh3)}] are 3.604 (1), 2.127 (8), and 2.141 (10) angstrom and 115.2 (5)-degrees, respectively. The compounds are paramagnetic and exhibit axial EPR spectra in the polycrystalline form. An intervalence transfer (IT) transition is observed in the range 900-960 nm in chloroform in these class II type trapped mixed-valence species 2. Compound 2 displays metal-centered one-electron reduction and oxidation processes near -0.4 and +0.6 V (vs SCE), respectively in CH2Cl2-TBAP. Compound 2 is unstable in solution phase and disproportionates to (mu-aquo)diruthenium(II) and (mu-oxo)diruthenium(III) complexes. The mechanistic aspects of the core conversion are discussed. The molecular structure of a diruthenium(II) compound, Ru2(OH2)(MeCN)2(O2CC6H4-p-NO2)4(PPh3)2.1.5CH2Cl2, was obtained by X-ray crystallography. The compound crystallizes in the space group P2(1)/c with a = 23.472 (6) angstrom, b = 14.303 (3) angstrom, c = 23.256 (7) angstrom, beta = 101.69 (2)-degrees, V = 7645 angstrom 3, and Z = 4. The Ru(II)-Ru(II) and two Ru(II)-(mu-OH2) distances and the Ru(II)-(mu-OH2)-Ru(II) angle in [{(PPh3)-(MeCN)(eta-1-O2CC6H4-p-NO2)Ru}2(mu-OH2)(mu-O2CC6H4-p-NO2)2] are 3.712 (1), 2.173 (9), and 2.162 (9) angstrom and 117.8 (4)-degrees, respectively. In both diruthenium(II,III) and diruthenium(II) compounds, each metal center has three facial ligands of varying pi-acidity and the aquo bridges are strongly hydrogen bonded with the eta-1-carboxylato facial ligands. The diruthenium(II) compounds are diamagnetic and exhibit characteristic H-1 NMR spectra in CDCl3. These compounds display two metal-centered one-electron oxidations near +0.3 and +1.0 V (vs SCE) in CH2Cl2-TBAP. The overall reaction between 1 and PPh3 in MeCN-H2O through the intermediacy of 2 is of the disproportionation type. The significant role of facial as well as bridging ligands in stabilizing the core structures is observed from electrochemical studies.

Synthesis, spectral and structural studies on metal complexes of Schiff bases involving vitamin B6 and histamine

Six metal complexes of Schiff bases involving Vitamin B6 and the decarboxylated amino acid histamine have been synthesised and characterized. Crystal structures have been determined for [CuL1(H2O)Br]-NO31(L1= pyridoxylidenehistamine) and [Cu2L22(NO3)2]·6H2O 2(L2= 5′-phosphopyridoxylidenehistaminate). The crystal structure of complex 1[space group P[1 with combining macron], a= 8.161(2), b= 10.368(2), c= 11.110(2)Å, α= 105.18(1), β= 102.12(1), γ= 72.10(1)° and Z= 2; R= 0.072, R′= 0.083] consists of square-pyramidally co-ordinated copper with the tridentate Schiff base in the zwitterionic form, whereas in 2[space group P[1 with combining macron], a= 8.727(1), b= 10.308(1), c= 12.845(2)Å, α= 110.00(1), β= 78.94(1), γ= 114.35(1)° and Z= 1; R= 0.035, R′= 0.034] the copper has the same co-ordination geometry but the tetradentate Schiff-base ligand exists as a monoanion. The conformational parameters deduced from such structures are important for understanding the stereochemical aspects of Vitamin B6-catalysed model reactions involving histidine.

Studies on ß-arylhydrazone-imine nickel(II) complexes—Examples of metal template syntheses

ß-arylhydrazone-imine ligand complexes of nickel(II), namely, 4,10-dimethyl-5,9-diazatrideca-4,9-diene-2,12-dione-3,11-diphenylhydrazonato nickel(II), Ni(acacpn)(N2Ph-R)2 and 1,11-diphenyl-3,9-dimethyl-4,8-diazaun-deca-3,8-diene,1,11-dione-2,10-diphenyl hydrazonato nickel(II), Ni (beacpn) (N2Ph-R)2, [R = H, o-CH3p-CH3] have been prepared by metal template reactions and characterized. Both the azomethine nitrogens and α-nitrogens of bis-hydrazone form the coordination sites of the square-planar geometry around the nickel(II) ion. Loss of CO from the molecule and subsequently an interesting methyl group migration to the nucleus of the chelate ring have been observed in the mass spectrum. Structures are proposed based on the spectral and magnetic properties.

Crystal structures, spectral and magnetic properties of (µ-hydroxo)(µ-acetato)dicopper(II) complexes containing chelating amines

The reaction of [Cu2(O2CMe)4(H2O)2] with N, N, N′, N′-tetramethylethane- 1,2-diamine (tmen) in ethanol yielded the dicopper(II) complex [Cu2(OH)(O2CMe)(tmen)2][ClO4]21. A similar reaction with N, N- dimethylethane- 1,2-diamine (dmen) afforded a crystalline product 2 in which two dicopper(II) complexes, [Cu2(OH)(O2CMe)(dmen)2][ClO4]22a and [Cu2(OH)(O2CMe)(H2O)2(dmen)2][ClO4]22b, are cocrystallized in a 1 : 1 molar ratio along with 2NaClO4. The crystal structures of 1 and 2 have been determined. The complexes have an asymmetrically dibridged [Cu2(µ-OH)(µ-O2CMe)]2+ core. The co-ordination geometry of the metal is square planar (CuO2N2). The copper atoms in 2b have a square-pyramidal CuO3N2 co-ordination sphere. The Cu Cu distances and Cu–O–Cu angles in 1, 2a and 2b are 3.339(2), 3.368(3), 3.395(7)Å, 120.1(2), 116.4(1) and 123.6(2)°, respectively. Complex 1 exhibits an axial ESR spectrum in a methanol glass giving g∥= 2.26 (A∥= 164 × 10–4 cm–1) and g⊥= 2.04. The ESR spectra obtained from the bulk material of the dmen product are indicative of the presence of two dimers, viz. complex 2a(g∥= 2.25, A∥= 165 × 10–4 cm–1; g⊥= 2.03) and 2b(g∥= 2.19, A∥= 184 × 10–4 cm–1; g⊥= 2.0). Variable-temperature magnetic susceptibility measurements on these complexes show an intramolecular antiferromagnetic coupling in the dimeric core. The fitting parameters are J=–27.8 cm–1, g= 2.1 for complex 1 and J=–10.1 cm–1, g= 2.0 for 2. The magnetostructural properties of the complexes are discussed. There is a linear correlation of the –2J values with the Cu Cu distances among dibridged complexes having square-planar copper(II) centres.