Oxime Oxygen Atoms Research Articles

Bifunctional hyper-cross-linked polymer with phosphorylated-amidoximated groups for efficient uranium extraction from water

Designing and developing a uranium adsorbent with high adsorption capacity and good selectivity is highly significant. We synthesized a novel hyper-cross-linked polymer adsorbent with bifunctional groups, (PHCP-4-AO), such as phosphate and amidoxime groups, via simple Scholl reaction and subsequent functionalization for the first time highly efficient extraction of U(VI) from aqueous solution. Due to its unique molecular structure design, it can enhance the selectivity and adsorption capacity of uranium by using two different functional groups. The maximum uranium adsorption capacity of PHCP-4-AO was 424.33 mg/g, which was higher than the single-functional group phosphorylated (PHCP-4) (315.43 mg/g) and amidoximated (HCP-4-AO) (260.38 mg/g) adsorbents. The combination of phosphate and amidoxime groups improves the adsorption effect. PHCP-4-AO has good selectivity and affinity for uranyl ions. In simulated wastewater, the Kd of PHCP-4-AO for uranium was 7266.3 mL/g, which was more than 15 times that of other ions. After three adsorption–desorption cycles, the adsorption capacity of PHCP-4-AO can still be maintained above 300.00 mg/g. Through XPS analysis, it is speculated that the sorption of uranium by PHCP-4-AO is owing to the lone pair electrons found on the oxygen atom of the phosphate groups, as well as the oxime oxygen and amino nitrogen atoms of the amidoxime groups entering the uranium’s empty orbit to form the coordination bonds. These findings demonstrated that this new hyper-cross-linked polymer could be considered as a valuable material in the extraction and recovery of uranium from uranium-containing aqueous solutions.

Arene-ruthenium(II) complexes with tetracyclic oxime derivatives: synthesis, structure and antiproliferative activity against human breast cancer cells

Six new arene-ruthenium(II) complexes containing two different η6-arene ligands – benzene and hexamethylbenzene, with indenoquinoxalinone oxime analogues (11H-indeno[1,2-b]quinoxalin-11-one oxime, 6H-indeno[1,2-b]pyrido[3,2-e]pyrazin-6-one oxime and 6–(hydroxyimino)indolo[2,1-b]quinazolin-12(6H)-one oxime (tryptanthrin-6-oxime)) as N,N’- chelating ligands are reported. The complexes were characterized by elemental analysis, IR, UV–VIS, 1H and 13C NMR spectroscopy and by single-crystal X-ray structure analysis. Complexes adopt a half-sandwich «piano-stool» geometry with oxime ligands in anionic form, the ruthenium(II) center coordinates one arene, one N,N-bidentate oximate and one chloride ligand. The computational analysis of non-covalent intermolecular interactions revealed weak attraction between the oxime oxygen atoms and the nearest hydrogen atoms of the oxime and the arene ligands. The cytotoxic activity of the complexes was evaluated against human breast cancer cell line MCF-7 and cisplatin-resistant human breast cancer cell line MCF-7CR as well as non-cancerous human breast epithelial cell line MCF10A. The cytotoxicity tests show micromolar IC50 values and tryptanthrin-6-oxime hexamethylbenzene-ruthenium(II) complex was found to exhibit the best antiproliferative activity among the studied compounds against the MCF-7 and MCF-7CR cell lines (IC50 9.0 ± 4.4 and 8.9 ± 1.5 µM, respectively).

Syntheses and Crystal Structures of a Series of Dysprosium–Manganese–Sodium 12-Metallacrown-4 Compounds with Halogenated Benzoate Bridging Anions

A series of heterotrimetallic dysprosium–manganese–sodium 12-metallacrown-4 compounds has been synthesized and characterized by single-crystal X-ray analysis: DyNaX4[12-MCMn(III)N(shi)-4], where X− = 2-fluorobenzoate (1), 3-fluorobenzoate (2), 4-fluorobenzoate (3), 2-chlorobenzoate (4), 4-chlorobenzoate (5), 3-bromobenzoate (6), and 2-iodobenzoate (7); MC is metallacrown; and shi3− is salicylhydroximate. Each 12-MC-4 framework is comprised of four ring MnIII ions and four shi3− ligands. The oxime oxygen atoms of the shi3− ligands produce a central cavity which then binds one DyIII ion and one Na+ ion on opposite sides. In each molecule four halogenated benzoate anions bridge between the central DyIII ion and the ring MnIII ions via the carboxylate groups. The identity of the halogenated benzoate anion has little effect on the structure of the [12-MCMn(III)N(shi)-4] framework as determined by several metrical parameters: the MC cavity radius, the average cross cavity MnIII–MnIII distance, the average cross cavity oxime oxygen-oxime oxygen distance, and the distance of the DyIII from the oxime oxygen mean plane. For 1–7 these metrical parameters are strikingly similar; thus, providing further reinforcement of one hallmark of metallacrown chemistry—the ability to substitute various components of the molecule without affecting the overall structure which can be used for the fine-tuning of molecular properties. Four 4-fluorobenzoate (4-Fben) anions bridge between the central DyIII ion and the ring MnIII ions in the metallacrown compound DyNa(4-Fben)4[12-MCMn(III)N(shi)-4](H2O)4·4DMF.

Pyridine-4-carboxamidoxime N-oxide.

Our work in the area of synthesis of metal-organic frameworks (MOFs) based on organic N-oxides led to the crystallization of pyridine-4-carboxamidoxime N-oxide. Herein we report the first crystal structure of the title compound, C6H7N3O2 [systematic name: (Z)-4-(N'-hy-droxy-carbamimido-yl)pyridine N-oxide]. The hy-droxy-carbamimidoyl group is essentially coplanar with the aromatic ring, r.m.s.d. = 0.112 Å. The compound crystallizes in hydrogen-bonding layers built from the formation of strong O-H⋯O hydrogen bonds between the oxime oxygen atom and the oxygen atom of the N-oxide, and the formation of N-H⋯O hydrogen bonds between one amine nitro-gen atom and the N-oxide oxygen atom. These combined build R 3 4(24) ring motifs in the crystal. The crystal structure has no π-π inter-actions.

Syntheses and Crystal Structures of Two Classes of Aluminum-Lanthanide-Sodium Heterotrimetallic 12-Metallacrown-4 Compounds: Individual Molecules and Dimers of Metallacrowns

Two series of aluminum-lanthanide-sodium 12-metallacrown-4 compounds have been synthesized and characterized by single-crystal X-ray analysis. For the individual LnNa(ben)4[12-MCAl(III)N(shi)-4] molecules, where LnIII = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6), Tm (7), Yb (8), Lu (9), and Y (10), ben− is benzoate, MC is metallacrown, and shi3− is salicylhydroximate, two independent molecules are present in each unit cell. The aluminum(III) ions and shi3− ligands comprise the MC framework, while the LnIII and Na+ ions bind opposite of each other across the central MC cavity. The benzoate anions serve to tether the LnIII ion to the MC framework. When benzoate is replaced with the dicarboxylate anion isophthalate (iph2−), two [12-MCAl(III)N(shi)-4] units are connected to form a dimer of MCs: {LnNa[12-MCAl(III)N(shi)-4]}2(iph)4, where LnIII = Eu (11), Gd (12), Tb (13), Dy (14), Ho (15), Ho (16), Er (17), Yb (18), and Lu (19). As in 1–10, the aluminum(III) ions and shi3− ligands produce the MC frameworks, and one LnIII ion binds to each central MC cavity. However, there are two binding modes for the sodium ions. For 12–15 and 18, the sodium ions bind to the central MC cavity opposite of the LnIII ions as in 1–10. For 11, 16, 17, and 19, the sodium ions bind to the side of the MC framework by bonding to the phenolate and carboxylate oxygen atoms of two shi3− ligands and to the carboxylate oxygen atom of an iph2− ligand. In these structures, the MC cavity is vacant opposite of the LnIII ions. The substitution of isophthalate for benzoate does not significantly alter the [12-MCAl(III)N(shi)-4] framework as the size of the central MC cavity is not significantly different between analogous lanthanide individual and dimer MCs. However, the identity of the central LnIII ion does determine how close the LnIII ion can approach the mean plane of the oxime oxygen atoms (OoxMP) of the MC cavity. As the ion radius of the central LnIII ion decreases, the LnIII ion is able to more closely approach the OoxMP. For the individual MCs 1–10, the EuIII of 1 is the farthest away from the OoxMP (1.55 A) and this value steadily decreases to 1.44 A for the LuIII ion of 9. This same trend is true for the dimer MCs as the EuIII ion of 11 is 1.45 A from the OoxMP and the LuIII ion of 19 is 1.36 A from the OoxMP. Though the location of the sodium ions in the dimer MCs does influence the LnIII-OoxMP distance as the absence of the sodium ion in the MC cavity allows the LnIII ion to approach the MC cavity even closer. In 15 a sodium ion is opposite the HoIII ion and the HoIII-OoxMP distance is 1.47 A, while in 16 the sodium ion is bound to the side of the MC and the HoIII-OoxMP distance is 1.40 A. The complex GdNa[12-MCAl(III)N(shi)-4]}2(iph)4(DMF)2(H2O)8 is a dimer of [12-MC-4] molecules linked by four isophthalate anions.

Unprecedented Dinuclear CuII N,O-Donor Complex: Synthesis, Structural Characterization, Fluorescence Property, and Hirshfeld Analysis

An unprecedented dinuclear CuII complex, [Cu2(L2)2], derived from a salamo-like chelating ligand H2L2, was produced by the cleavage of a newly synthesized, half-salamo-like ligand HL1 (2-[O-(1-ethyloxyamide)]oxime-3,5-dichloro-phenol). This was synthesized and characterized by elemental analyses, IR, UV–Vis and fluorescent spectra, single crystal X-ray diffraction analysis, and Hirshfeld surface analysis. X-ray crystallographic analysis indicated that the two CuII (Cu1 and Cu2) ions bore different (N2O3 and N2O2) coordination environments, the penta-coordinated Cu1 ion possessed a slightly twisted tetragonal pyramid geometry with the τ value τ = 0.004, and the tetra-coordinated Cu2 ion showed a slightly twisted square planar geometry. Interestingly, one oxime oxygen atom participated in the coordination reported previously. Moreover, an infinite two-dimensional layered supramolecular network was formed. Compared with HL1, the CuII complex possessed the characteristic of fluorescence quenching.

Synthesis, characterization, theoretical calculations and biochemical evaluation of a novel oxime ligand with complexes

A novel amine containing ketooxime ligand (HBOX) and its Cu(II) and Mn(II) complexes were synthesized, characterized and tested for some of their biological activities. Structural characterization was carried out by elemental analysis, ICP-OES, 1H and 13C NMR, UV–Vis, FT-IR, XRD, TG-DTG, magnetic susceptibility and molar conductivity measurements. Elemental analyses, stoichiometric and spectroscopic data of the metal complexes indicated that the metal:ligand ratio was found to be 1:2 and the metal ions were coordinated to the oxime oxygen and amine nitrogen atoms. Furthermore, DFT/B3LYP method with 6-311G(d,p) and LANL2DZ basis sets were used for full optimization of molecular geometries of the ligand and complexes, respectively. The vibrational frequencies, isotropic chemical shifts (1H and 13C NMR), electronic transition absorption wavelengths, HOMO and LUMO analyses and molecular electrostatic potential (MEP) properties of the synthesized molecules have been calculated. The results obtained experimentally were confirmed by the theoretical data which are in good agreement. Inhibitory capacity of the HBOX was investigated against neoangiogenic factors, vascular endothelial growth factor receptor-2 (VEGFR-2) and cyclooxygenase-2 (COX-2) by molecular docking studies. HBOX bound to COX-2 protein with 2 hydrogen bonds at the lowest energy level which indicates the most stabilized form of the protein ligand complex. Complexes were also tested for their catecholase and phenoxazinone synthase-like activities using spectrophotometric procedures. Catecholase and phenoxazinone synthase-like enzyme activities were spectrophotometrically followed by the increase in absorbance at 400 and 433nm resulted from the oxidation reaction of 3,5-di-tert-butylcatechol and 2-aminophenol to 3,5-di-tert-butylquinone and 2-aminophenoxazine-3-one, respectively. According to the calculated kobs values, the Mn(II) complex was found to be more active for both enzymes compared to Cu(II).

Synthesis of New N-Hydroxy-6-methyluracil-5-carboximidoyl Chloride Derivatives

N-Hydroxy-6-methyluracil-5-carboximidoyl chloride was synthesized for the first time, and its halogenation and reactions with amines (imidazole, aniline) were studied. The reaction of the title compound with sodium azide gave the corresponding N-hydroxycarboximidoyl azide. The Z isomer of the latter was stable, and it did not undergo isomerization to the E isomer, which prevented transformation to 1-hydroxytetrazole. 6-Methyluracil-5-carbaldehyde oxime was readily acylated at the oxime oxygen atom.

Complexation-assisted reduction: complexes of glutaroimide-dioxime with tetravalent actinides (Np(iv) and Th(iv)).

Glutaroimide-dioxime forms strong complexes with tetravalent Th(iv) and Np(iv) in aqueous solution. In conjunction with literature data on the complexation of glutaroimide-dioxime with other metal ions, it was found that the complexes become weaker as the effective charge density on the metal ions decreases: V5+ > Th4+ ≈ Fe3+ > UO22+ > Eu3+/Nd3+ > Cu2+ > Pb2+ > NpO2+ > Ca2+/Mg2+. In the glutaroimide-dioxime complexes with Th(iv) and Np(iv), deprotonation of the imide group and relocation of the two hydrogen atoms from oxygen to nitrogen of the oxime groups result in a large conjugated system (-O-N-C-N-C-N-O-) that coordinates strongly to the metal center in a tridentate mode via the central imide nitrogen atom and the two oxime oxygen atoms. Because the stability of glutaroimide-dioxime complexes with Np(iv) is much higher than those with Np(v), the redox potential of the Np(v)/Np(iv) couple is expected to be shifted significantly. As a result, crystals of glutaroimide-dioxime complexes with Np(iv) were readily obtained from initial solutions containing Np(v). A mechanism of complexation-assisted reduction integrating the thermodynamic and structural data from this work is discussed.

Antitumor activity of synthesized and characterized Cu(II), Ni(II) and Co(II) complexes of hydrazone-oxime ligands derived from 3-(hydroxyimino) butan-2-one

Mononuclear and binuclear metal complexes of hydrazone oxime resulted from the condensation of acetohydrazide and pyridyl hydrazide with 3-(hydroxyimino) butan-2-one were prepared. All compounds were characterized using elemental, spectral and thermal analyses, as well as magnetic moment and molar conductance measurements. The ligands acted as neutral/monobasic bidentate, monobasic tridentate and dibasic tetradentate ligands bonded to the metal ions via azomethine nitrogen or oxime oxygen atoms and enolic carbonyl oxygen or pyridine nitrogen atom. The spectral and magnetic studies of the complexes showed that exhibit either distorted octahedral, square planer or tetrahedral geometry. Newly complexes were tested for their anti-proliferative activity in vitro against three human cell lines; MCF-7, Hep-G2 and HL-60. The cytotoxic action of the complexes was determined and compared to that of the anticancer drug doxorubicin. Results of cytotoxicity activities indicated that the compound (6) has a wide range of cytotoxicity against the three cell lines in concentration ranges as that of doxorubicin. It shows more cytotoxic against MCF-7 (IC50=1.8μM) and HL-60 (IC50=10.6μM) cancer cell lines. Compounds (H2L1) and (11) exhibited higher cytotoxic activities rather than doxorubicin against MCF-7 and HL-60 cell line. Compounds (2) and (11) are 3.1 and 2.1 times more active than doxorubicin; respectively, against HL-60 cell line.

Synthesis and characterization of some metal complexes of isonitroso-2-acetylnaphthalene derivative

Nickel(II), copper(II), and zinc(II) complexes with the Schiff base obtained from isonitroso-2-acetylnaphthalene and 1,2-phenylenediamine were synthesized. The compounds were characterized by elemental analyses, FT-IR, UV-Vis, and 1H and 13C NMR spectra, conductance measurements, magnetic susceptibility measurements, and thermal analysis. The results suggest tetradentate coordination of the symmetrical Schiff base ligand through the two oxime oxygen atoms and two azomethine nitrogen atoms. The molar conductance data showed that the synthesized complexes are non-electrolytes.

Crystallization of the $${\text{Mn}}^{{\text{II}}}[12{\text{-MC}}_{{\text{Mn}}^{{\text{III}}}{\text{(N)shi}}}{\text{-}}4]^{2+}$$ Mn II [ 12 -MC Mn III (N)shi - 4 ] 2 + Structure with 1,2,4-Triazolate from Methanol

The metallacrown (MC) dimer complex {MnII(OAc)(1,2,4-trz) $$[12{\text{-MC}}_{{\text{Mn}}^{{\text{III}}}{\text{(N)shi}}}{\text{-}}4]$$ (CH3OH)4.46(H2O)0.54}2·1.53CH3OH·6.47H2O, 1, where −OAc is acetate, 1,2,4-trz is triazolate, and shi3− is salicylhydroximate, has been synthesized and characterized by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P21/c with a = 10.9139(17) A, b = 28.319(4) A, c = 15.675(2) A, α = 90.00°, β 93.362(3)°, γ = 90.00°, V = 4836.4(13) A3, and Z = 2. The compound is an example of a $$12{\text{-MC}}_{{\text{Mn}}^{{\text{III}}}{\text{(N)shi}}}{\text{-}}4$$ complex crystallized from methanol in the presence of a basic nitrogen-containing aromatic heterocycle. The dimer formation is a result of the two 1,2,4-triazolate anions being able to form N1, N2, N4-bridges between ring and central cavity manganese ions thus linking two neighboring MCs. An individual MC unit of 1 is nearly planar as evident from the average angle between the axial oxygen or nitrogen atoms, the ring MnIII ion, and the calculated centroid of the oxime oxygen atoms being 90.12° about the MC ring. This manuscript provides a structural description of a manganese-based MC dimer with the composition {MnII(OAc)(1,2,4-trz) $$[12{\text{-MC}}_{{\text{Mn}}^{{\text{III}}}{\text{(N)shi}}}{\text{-}}4]$$ (CH3OH)4.46(H2O)0.54}2 ·1.53CH3OH·6.47H2O, where two 1,2,4-triazolate (trz) anions bind in a N1,N2,N4 fashion and form bridges between two neighboring MCs

Theoretical study of the coordination behavior of formate and formamidoximate with dioxovanadium(V) cation: implications for selectivity towards uranyl.

Poly(acrylamidoxime)-based fibers bearing random mixtures of carboxylate and amidoxime groups are the most widely utilized materials for extracting uranium from seawater. However, the competition between uranyl (UO2(2+)) and vanadium ions poses a significant challenge to the industrial mining of uranium from seawater using the current generation of adsorbents. To design more selective adsorbents, a detailed understanding of how major competing ions interact with carboxylate and amidoxime ligands is required. In this work, we employ density functional theory (DFT) and wave-function methods to investigate potential binding motifs of the dioxovanadium ion, VO2(+), with water, formate, and formamidoximate ligands. Employing higher level of theory calculations (CCSD(T)) resolve the existing controversy between the experimental results and previous DFT calculations for the structure of the hydrated VO2(+) ion. Consistent with the EXAFS data, CCSD(T) calculations predict higher stability of the distorted octahedral geometry of VO2(+)(H2O)4 compared to the five-coordinate complex with a single water molecule in the second hydration shell, while all seven tested DFT methods yield the reverse stability of the two conformations. Analysis of the relative stabilities of formate-VO2(+) complexes indicates that both monodentate and bidentate forms may coexist in thermodynamic equilibrium in solution. Investigations of VO2(+) coordination with the formamidoximate anion has revealed the existence of seven possible binding motifs, four of which are within ∼4.0 kcal mol(-1) of each other. Calculations establish that the most stable binding motif entails the coordination of oxime oxygen and amide nitrogen atoms via a tautomeric rearrangement of amidoxime to imino hydroxylamine. The difference in the most stable VO2(+) and UO2(2+) binding conformation has important implications for the design of more selective UO2(2+) ligands.

Synthesis, characterization and molecular structure of titanium alkoxide complexes with aromatic oxime ligands

Stoichiometric reactions of pyridine-2-aldoxime (HL1) with titanium 2-propoxide and of salicylaldoxime (H2L2) with titanium 2-propoxide or titanium ethoxide in toluene at room temperature resulted in the formation of [Ti2(μ-O)(μ-L)2(OR)4] (for L1, R = iPr; for L2, R = iPr or Et). These complexes were all characterized by spectroscopic methods; in addition, the molecular structure of [Ti2(μ-O)(μ-L1)2(OiPr)4] was determined by single-crystal X-ray diffraction. The titanium atoms have distorted octahedral geometries that share an apex through a bridging oxygen. Each monoanionic L1 is chelated to one titanium atom through its pyridine and oximate nitrogen atoms and to a second titanium atom through its oximate oxygen atom.

A new linear trinuclear cobalt complex bearing oximato and azido ligands: synthesis, structure, and magnetic characterization

The reaction of CoCl2 · 6H2O, mpkoH (methyl 2-pyridyl ketone oxime), NEt3, and NaN3 in a 1 : 1 : 2 : 1 molar ratio affords a linear trinuclear complex, [CoII(mpko)4(N3)4(H2O)2] (1). Complex 1 has been characterized by single-crystal X-ray diffraction, elemental analysis, and infrared spectrum. Three cobalt ions are in the center of distorted octahedra, which are connected by two μ-1,1 azides and two oxime oxygen atoms to form a linear trinuclear structure. Discrete units of 1 are connected to form a stable 3-D supramolecular network by C–H···O and C–H···N weak interactions. Variable temperature magnetic susceptibility measurements reveal that 1 exhibits antiferromagnetic behavior.

Salicylaldoxime derivatives as new leads for the development of carbonic anhydrase inhibitors

New compounds containing a novel zinc binding group (salicylaldoxime system) were identified as effective inhibitors of carbonic anhydrases (CAs). This structural motif seems to bind the catalytic zinc ion of CAs, revealing itself as a new valid alternative to the sulfonamide group. Computational procedures were used to investigate the binding mode of this class of compounds, within the active site of CAII. This study suggests that the salicylaldoxime moiety binds the zinc ion through the oxime oxygen atom that also forms an H-bond with T199. The results herein obtained will allow the development of new CA-inhibitors bearing the salicylaldoxime moiety.

How Amidoximate Binds the Uranyl Cation

This study identifies how the amidoximate anion, AO, interacts with the uranyl cation, UO(2)(2+). Density functional theory calculations have been used to evaluate possible binding motifs in a series of [UO(2)(AO)(x)(OH(2))(y)](2-x) (x = 1-3) complexes. These motifs include monodentate binding to either the oxygen or the nitrogen atom of the oxime group, bidentate chelation involving the oxime oxygen atom and the amide nitrogen atom, and η(2) binding with the N-O bond. The theoretical results establish the η(2) motif to be the most stable form. This prediction is confirmed by single-crystal X-ray diffraction of UO(2)(2+) complexes with acetamidoxime and benzamidoxime anions.

Heterometallic Oximato‐Bridged Linear Trinuclear NiII−MIII−NiII (MIII = Mn, Fe, Tb) Complexes Constructed with the fac‐O3 [Ni(HL)3]– Metalloligand (H2L = pyrimidine‐2‐carboxamide oxime): A Theoretical and Experimental Magneto‐Structural Study

AbstractThree oximato‐bridged linear trinuclear heterobimetallic complexes of formula [{Ni(HL)3}2M]X·nS [M = Mn3+, X = ClO4–, n = 9, S = H2O (1); M = Fe3+, X = ClO4–, n = 9, S = H2O (2); M = Tb3+, X = NO3–, n = 11, S = CH3OH (3); H2L = pyrimidine‐2‐carboxamide oxime] were prepared from the reaction of the in situ generated [Ni(HL)3]– complex with the corresponding M2+ salts for 1 and 2 (which are oxidized to M3+ during the course of the reaction) and the Tb3+ salt for 3. The heterometallic trinuclear [NiMNi]+ cationic entities are formed by the coordination of two [Ni(HL)3]– metalloligands to the central M3+ metal ion through three facially arranged oxime oxygen atoms belonging to the H2L ligands. Therefore the HL– ligand acts in a κ2‐N1,N8:κ‐O9 bidentate bridging mode. Compounds 1 and 2 exhibit antiferromagnetic interactions, whereas for 3 the spin‐orbit coupling and the effects of the crystal‐field on the 2S+1LJ states of the Tb3+ ion encumbers the determination of the nature of the magnetic exchange interaction between the Ni2+ and Tb3+ ions through the oximato bridging group. DFT calculations carried out on the solid‐state structures predict J values that match well with the experimental ones. The experimental J values were compared with those observed for analogous NiMNi complexes and their differences justified on the basis of structural parameters such as the Ni–N–O–M torsional angle and the distortion from the OC‐6 octahedral to the TPR‐6 trigonal prismatic geometry.

The crystal structure of μ-Oxo-bis{diethoxy[salicylaldoximato(2-)]-tantalum(V)}

Stochiometric reaction of salicylaldoxime and tantalum or niobium ethoxide in toluene at room temperature resulted in formation of [M2O(C7H5NO2)2(C2H5O)4], M=Ta and Nb which were crystallized from CH2Cl2 at −5 °C and characterized by spectroscopic techniques. The molecular structures of [Ta2O(C7H5NO2)2(C2H5O)4] was determined by single-crystal X-ray diffraction and compared with molecular structure of [Nb2O(C7H5NO2)2(C2H5O)4]. The geometries at metal atoms are distorted octahedron which shared an apex through bridged oxygen. Each dianionic salicylaldoximate ligand chelates to the one metal ion through its phenolic oxygen and oximate nitrogen atoms, and to another metal ion through its oximate oxygen atom.

Initial use of di-2-pyridyl ketone oxime in chromium carboxylate chemistry: Triangular [formula omitted] compounds and unexpected formation of a carboxylate-free dichromium(II,II) complex

A systematic investigation of the [Cr 3O(O 2CCMe 3) 6(H 2O) 3](O 2CCMe 3)/(py) 2CNOH [(py) 2CNOH = di-2-pyridyl ketone oxime] reaction system is described, involving the determination of the influence of the Cr III:(py) 2CNOH ratio, the temperature and the presence of counterions on the identity of the reaction products. As a consequence, complexes [Cr 2{(py) 2CNO} 4] · 2H 2O ( 1 · 2H 2O), [Cr 3OCl(O 2CCMe 3) 4{(py) 2CNO} 2] · 2Me 2CO ( 2 · 2Me 2CO) and [Cr 3O(O 2CCMe 3) 4{(py) 2CNO} 2(H 2O)](NO 3) · H 2O · 0.5Me 2CO ( 3 · H 2O · 0.5Me 2CO) have been isolated and structurally characterized by single-crystal X-ray studies. (py) 2CNO − behaves as a N, N′-bidentate chelating and/or N, N′, O-tridentate bridging ligand binding through one 2-pyridyl and the oximate nitrogen atoms, and/or the oximate oxygen atom. 1 is a relatively stable air-stable dinuclear Cr(II) complex with no metal–metal bonding arising, from the ligand-assisted reduction of the ‘basic carboxylate’ Cr(III) triangle. The structures of 2 and 3 consist of similar neutral and cationic triangles of Cr III ions, respectively, centered by a triply bridging oxo ligand and with two edge-bridging oximate groups from the two 2.1110 (py) 2CNO − ligands. Variable-temperature magnetic susceptibility studies and EPR data for 2 reveal an antiferromagnetically-coupled system with an S T = 3/2 ground state. Solid-state IR and ligand field spectra of 2 are briefly discussed in terms of its structure.