Stabilization of the trivalent oxidation state of copper by tetradentate imine–oxime ligands

Copper(III) complexes stabilized by tetradentate imine–oxime ligands were characterized by elemental analysis, cyclic voltammetry, u.v.–visible, and e.s.r. spectra. Electrode potentials of copper(III/II) couples having five-, six-, five-membered chelate rings are pH-dependent. Copper(III/II) couples with five-, five-, five-membered chelate rings were independent of pH. The magnitude of E _1/2 ⁰ is affected by both the size and electron-donor ability of substituent groups.     

Transition metal complexes with thiosemicarbazide-based ligands,Part II,Synthesis and characterisation of nickel(II), cobalt(II), manganese(II) and zinc(II) complexes with the pentadentate ligand, 2,6-diacetylpyridine bis(S-methylisothiosemicarbazone)

Summary The reaction of warm alcoholic solutions of acetates of Co^II, Mn^II, Zn^II and Ni^II with 2, 6-diacetylpyridine andS-methylisothiosemicarbazide hydrogen iodide yielded the complexes: [Co(H₂L)I₂]·H₂O, [Mn(H₂L)(MeOH)₂]I₂, [Zn(H₂L)(MeOH)I]I and [Ni(HL)]I, (H₂L=the pentadentate pentaaza-ligand 2, 6-diacetylpyridine bis(S-methylisothiosemicarbazone)). The reaction of methanolic solutions of [Ni(HL)]I and NH₄NCS or LiOAc.2H₂O, give [Ni(HL)]NCS and NiL, respectively. For the complexes of Co^II, Mn^II and Zn^II, a pentagonal bipyramidal configuration is proposed, with H₂L in the equatorial plane and two unidentate ligands (I and/or MeOH) in the axial positions. The complexes [Ni(HL)]X (X=I or NCS) and NiL probably have monomeric five- and dimeric six-coordinate structures, respectively, in which only the chelate ligand is involved in coordination.     

Theoretical predictions of the structures and electronic spectra of C60NH with comparisons with the isoelectronic molecules C60O and C60CH2

Intermediate neglect of differential overlap (INDO ) calculations were used to study two structures of C₆₀NH: one of C_2ν, geometry with a bridging NH across the bond between two fused six-membered rings in C₆₀ and the other of C_s geometry with a bridging NH across the bond between a five- and a six-membered ring. We calculated the most stable isomer of C₆₀NH to be of C_2ν, symmetry. It was found that the C_2ν isomer has a protonated aziridine structure with a bridging C? C bond length of 0.1520 nm. The electronic spectra of both isomers of C₆₀NH were calculated. Comparisons were made with the isoelectronic molecules C₆₀O and C₆₀CH₂, cases in which the calculated electronic spectra for the most stable isomers C₆₀O (C_2ν) and C₆₀CH₂ (C_2ν) are in good agreement with recent experimental results. © 1995 John Wiley & Sons, Inc.     

Crossover Sorption of C2H2/CO2 and C2H6/C2H4 in Soft Porous Coordination Networks

Porous sorbents are materials that are used for various applications, including storage and separation. Typically, the uptake of a single gas by a sorbent decreases with temperature, but the relative affinity for two similar gases does not change. However, in this study, we report a rare example of “crossover sorption,” in which the uptake capacity and apparent affinity for two similar gases reverse at different temperatures. We synthesized two soft porous coordination polymers (PCPs), [Zn₂(L1)(L2)₂]_n (PCP-1) and [Zn₂(L1)(L3)₂]_n (PCP-2) (L1= 1,4-bis(4-pyridyl)benzene, L2=5-methyl-1,3-di(4-carboxyphenyl)benzene, and L3=5-methoxy-1,3-di(4-carboxyphenyl)benzene). These PCPs exhibits structural changes upon gas sorption and show the crossover sorption for both C₂H₂/CO₂ and C₂H₆/C₂H₄, in which the apparent affinity reverse with temperature. We used in situ gas-loading single-crystal X-ray diffraction (SCXRD) analysis to reveal the guest inclusion structures of PCP-1 for C₂H₂, CO₂, C₂H₆, and C₂H₄ gases at various temperatures. Interestingly, we observed three-step single-crystal to single-crystal (sc-sc) transformations with the different loading phases under these gases, providing insight into guest binding positions, nature of host–guest or guest-guest interactions, and their phase transformations upon exposure to these gases. Combining with theoretical investigation, we have fully elucidated the crossover sorption in the flexible coordination networks, which involves a reversal of apparent affinity and uptake of similar gases at different temperatures. We discovered that this behaviour can be explained by the delicate balance between guest binding and host–guest and guest-guest interactions.     

Palladium(II) and Platinum(II) Complexes with Bisphosphanes, [S2C=C(CN)2]2– and [Se2C=C(CN)2]2– as Chelating Ligands

The palladium(II) and platin(II) 1, 1‐dicyanoethylene‐2, 2‐dithiolates [(L–L)M{S₂C=C(CN)₂}] (M = Pd: L–L = dppm, dppe, dcpe, dpmb; M = Pt: dppe, dcpe, dpmb) were prepared either from[(L–L)MCl₂] and K₂[S₂C=C(CN)₂] or from [(PPh₃)₂M{S₂C=C(CN)₂}] and the bisphosphane. Moreover, [(dppe)Pt{S₂C=C(CN)₂}]was obtained from [(1, 5‐C₈H₁₂)Pt{S₂C=C(CN)₂}] and dppeby ligand exchange. The 1, 1‐dicyanoethylene‐2, 2‐diselenolates[(dppe)M{Se₂C=C(CN)₂}] (M = Pd, Pt) were prepared from[(dppe)MCl₂] and K₂[Se₂C=C(CN)₂]. The oxidation potentials of the square‐planar palladium and platinum complexes were determined by cyclic voltammetry. The reaction of [(dcpe)Pd(S₂C=O)] with TCNE led to a ligand fragment exchange and gave the 1, 1‐dicyanoethylene‐2, 2‐dithiolate [(dcpe)Pd{S₂C=C(CN)₂}] in good yield.     

Asymmetric Core-Expanded BOPYOs: Facile Synthesis and Optical Properties

N,O-bidentate BF₂ complexes with five- and six-membered core rings have been thoroughly investigated. However, the development of seven-membered N,O-boron complexes is still an area to be explored. We have developed BF₃ ⋅ OEt₂-induced self-condensation and coordination reactions based on a single starting material, which had been elucidated by experiment and calculation. This parent asymmetric core-expanded borondifluoride-(Z)-1,3-di(1H-pyrrol-2-yl)but-2-en-1-one (BOPYO) showed reactivity with a wide range of aldehydes, thus providing a series of conjugation BOPYOs. Moreover, a BOPYO derivative with a dimethylamino group was developed as a new NIR dye that responds to acid with favorable photophysical properties based on intramolecular charge transfer effect.     

Synthesis of unsaturated dibasic acid esters from five-, six-, and seven-membered cycloalkanones

A new route to diesters of symmetrical octene-, decene-, and dodecenedioic acids was proposed. The ratio of the cis/trans-isomers was 1: 4. The synthesis involved oxidative splitting of five-, six-, and seven-membered cycloalkanones with hydrogen peroxide into the corresponding ω-alkenoic acids followed by esterification and metathesis over Re₂O₇/B₂O₃-Al₂O₃-SnMe₄. Dedicated to Academician O. M. Nefedov on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1942–1944, November, 2006.     

Reactions of 1,3-dioxacycloalkanes and their 2-arsena, 2-bora, 2-germa, 2-sila,and 2-thia analogs with nitriles

New reactions of five-, six-, and seven-membered 1,3-dioxacycloalkanes and their 2-arsena, 2-bora, 2-germa, 2-sila, and 2-thia analogs with nitriles giving rise to 1,3-oxazacycloalkanes and then to amino alcohols are surveyed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1499–1507, July, 2005.     

First-principles investigation of structural,electronic, and optical properties of transition metal-doped C40 CrSi2

Although CrSi₂ silicide is an attractive advanced functional material, the improvement of electronic and optical properties is still a challenge for its applications. Here, we apply the first-principles calculations to investigate the influence of transition metals (TMs) on the electronic and optical properties of C40 CrSi₂ silicide. Five possible TMs, Ti, V, Pd, Ag, and Pt, are considered in detail. The calculated results show that the additive metals Ti, V, Pd, and Pt are thermodynamically stable in C40 CrSi₂ because the calculated impurity formation energy of TM-doped C40 CrSi₂ is lower than zero. In particular, the V dopant is more thermodynamically stable than that of the other TMs. The calculated electronic structure shows that the band gap of C40 CrSi₂ is 0.391 eV, which is in good agreement with the other results. In particular, the additive TMs improve the electronic properties of C40 CrSi₂ due to the role of the d-state of TMs. Naturally, the additive TMs result in band migration (Cr-3d state and Si-3p state) from the valence band to the conduction band. Interestingly, the additive TMs lead to a red shift for optical adsorption of C40 CrSi₂ silicide.     

Cyclization of diols with ammonia over CuO-ZnO-Al2O3 catalyst in the presence of H2

Cyclization of diols with ammonia in an H₂ atmosphere over an industrial CuO-ZnO-Al₂O₃ catalyst for the synthesis of methanol (SNM-1) gives nitrogen-containing five-, six-, or seven-membered heterocyclic compounds. The yields of cyclic amines in the 180–230 °C temperature range are 46 to 97 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2046–2048, October, 1995.     

Cationic copolymerization of cyclic ketene acetals: The effect of substituents on reactivity

Cationic copolymerizations of 4-methyl-2-methylene-1,3-dioxane, 2 (M₁), with 2-methylene-1,3-dioxane, 1 (M₂); of 4,4,6-trimethyl-2-methylene-1,3-dioxane, 3 (M₁), with 2-methylene-1,3-dioxane, 1 (M₂); of 4-methyl-2-methylene-1,3-dioxolane, 5 (M₁), with 2-methylene-1,3-dioxolane, 4 (M₂); and of 4,5-dimethyl-2-methylene-1,3-dioxolane, 6 (M₁), with 2-methylene-1,3-dioxolane, 4 (M₂) were conducted. The reactivity ratios for these four types of copolymerizations were r₁ = 1.73 and r₂ = 0.846; r₁ = 2.26 and r₂ = 0.310; r₁ = 1.28 and r₂ = 0.825; r₁ = 2.23 and r₂ = 0.515, respectively. The relative reactivities of these monomers towards cationic polymerization are: 3 > 2 > 1; and 6 > 5 > 4. With both five- and six-membered ring cyclic ketene acetals, the reactivity increased with increasing methyl substitution on the ring. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 861–871, 1998     

Formation of substituted pyrazolines in the reaction of C,N-diphenylnitrilimine with a zwitterion derived from triisopropylphosphine and ethyl 2-cyanoacrylate

The reaction of C,N-diphenylnitrilimine with a P-zwitterion derived from Prⁱ ₃P and H₂C=C(CN)CO₂Et afforded the first representative of 2-pyrazolines containing the phosphonium group and products of the addition of nitrilimine to Prⁱ ₃P and H₂C=C(CN)CO₂Et. The reaction of the P-zwitterion with C-4-nitrophenyl-N-phenylnitrilimine gave rise to a condensation product of one Prⁱ ₃P molecule and two nitrilimine molecules. The three-dimensional structures of the compounds synthesized were established by X-ray diffraction analysis.     

Organodiphosphines in cis-Pt(η2-P2L)(SR)2 derivatives – structural aspects

Abstract

This review covers 30?Pt(II) complexes in which the inner coordination of PtP₂S₂ is created by organodiphosphines and a pair of S-donor ligands. The organodiphosphines generate four-(PCP), five-(PC₂P), six-(PC₃P) and seven-(PC₄P) membered metallocyclic rings. These complexes crystallize in three crystal systems: orthorhombic (four examples), triclinic (nine examples) and monoclinic (seventeen examples). The respective metallocyclic rings open in the sequence: (mean values): 73.2° (PCP) < 86.0° (PC₂P) < 94.5° (PC₃P) < 97.5° (PC₄P). The mean values of Pt-P and Pt-S bond distances are 2.247 and 2.350?Å, respectively. The structure parameters are analyzed and discussed with attention to any trans-influence.     

Homoleptic Ti[ONO]2 type complexes of amino-acid-tethered phenolato Schiff-base ligands: Synthesis,characterization, time-resolved fluorescence spectroscopy,and cytotoxicity against ovarian and colon cancer cells

Six homoleptic Ti (IV) compounds of dianionic tridentate ONO Schiff base ligands with various substitutions were prepared from chiral amino acids, 2-hydroxybenzaldehyde, which were generated in situ, and Ti (OⁱPr)₄. The compounds were spectroscopically characterized and the molecular geometries of five complexes were established by X-ray crystallography; for two structures, two independent molecules compose the asymmetric units. The di-anionic, tridentate ligands coordinate the titanium centers via the carboxylate-O-, imine-N- and phenoxide-O atoms to form five- and six-membered chelate rings. The molecules are based on a trans-N₂O₄ donor with each carboxylate-O atom trans to a phenoxide-O atom. For the smallest derivative with Me substitution, racemization occurs during repeated recrystallization. Photophysical profiles of the titanium compounds in the solid phase and in solution are discussed. Marked cytotoxicities were recorded toward human ovarian A2780 and colon HT-29 cancer cells with IC₅₀ values ranging between 23 ± 2 and 103 ± 3 μM. Comparative hydrolytic stability of the complexes were studied by NMR in 10% D₂O solutions which provided t_1/2 values of up to 15 ± 2 hr.     

Disorder in the crystal structure of NaNi4(PO4)3

NaNi₄(PO₄)₃ crystallizes in the space group Amam, a = 9.892(1), B = 14.842(2), and c = 6.3576(2) Å. For Z = 4, the calculated density is 3.862 g/cm³ (V = 933.3ų). The presence of several weak reflections (of the class 2k0 and 6k0) which should be systematically absent in this space group has been attributed to a partial disorder of one of the phosphate tetrahedra. Two half-occupied P(2) sites related by a mirror normal to the a axis result in a column of phosphate tetrahedra pointing either up or down in this direction. Nickel atoms occupy five- and six-coordinated sites while sodium is six-coordinated.     

Contacted Ion Pairs in Aqueous CuCl2 by the Combination of Ratio Spectra,Difference Spectra,Second Order Difference Spectra in the UV-Visible Spectra

The microstructure of aqueous CuCl₂ has been studied through lots of technologies for many years; however, it remains a controversial subject. In this study, a new spectroscopic method has been proposed to analyze the UV-visible spectra of thin film of CuCl₂/H₂O solutions at different concentrations. This method is the combination of ratio spectra, difference spectra and second order difference spectra. By using this method, two new bands at ~230 and ~380 nm are obviously observed. The bands are assigned as the contacted ion pairs[CuCl₃(H₂O)_n]^- or[CuCl₄(H₂O)_n]^2-, which demonstrates that ion pairs exist in the CuCl₂/H₂O solution. Such finding agrees with the recent theoretical spectra obtained by time-dependent density functional theory. Furthermore, the populations of the contacted ion pairs are discussed. This study not only offers the direct spectroscopic evidence of[CuCl₃(H₂O)_n]^- or[CuCl₄(H₂O)_n]^2- in aqueous CuCl₂, but also suggests that the spectroscopic analysis method is powerful to extract the weak bands in a strong overlapping spectrum.     

Formation of Cyclic Ketals from Hydroxyalkyl Enol Ethers,a stereoelectronically controlled endo-trig-cyclization process

Acid-catalyzed cyclic ketal formation vs. hydrolysis of a series of hydroxyalkyl cyclic enol ethers in the presence of 1 equiv. of H₂O, and acid-catalyzed cyclic-ketal formation (same ketals as above) vs. methanolysis of a series of mixed pent-4-enyl hydroxyalkyl ketals with N-bromosuccinimide in the presence of 4 equiv. of MeOH led to the same result: the intramolecular cyclization processes occur at similar rates as the intermolecular H₂O or MeOH attacks independently of the size of the rings formed (five-, six-, or seven-membered), by cyclizations. These results can be explained by the facts that, due to stereoelectronic effects which impose a torsional strain to the sp² hybridized O-atom, the cyclization activation enthalpy decreases, as the length of the hydroxyalkyl chain increase (ease of cyclization: 7 > 6 > 5), whereas the entropy factor favors the cyclization in the reverse fashion (ease of cyclization: 5 > 6 > 7). The various reaction pathways have been examined using the semi-empirical Hamiltonian AM1, and the results obtained confirm that large-ring formation is enthalpically much favored over the cyclization processes leading to small rings (ease of cyclization: 7 > 6 > 5).     

Ring contractions of dihydro- and tetrahydro-1,5-benzodiazepines in electron ionization mass spectrometry

Electron ionization mass spectra of a series of 2,4-disubstituted dihydro- and tetrahydro-1,5-benzodiazepines are discussed. The fragmentation of these compounds is dominated by ring contractions of diazepine, which give both five- and six-membered rings, benzimidazoles and quinoxalines. Tetrahydro compounds showed a tendency to eliminate one nitrogen from the ring system and give quinoline rings through NH₂ and NH₄ eliminations. The electron ionization spectra of cis and trans isomers of tetrahydro compounds are identical.     

Magnesium and Cadmium in Covalently‐Bonded Lonsdaleite Networks: Synthesis,Structure, and Bonding of AETMg2 and SrTCd2 (AE = Ca,Sr; T = Pd,Ag, Pt,Au)

The alkaline earth metal compounds AETMg₂ and AETCd₂ (AE = Ca, Sr; T = Pd, Ag, Pt, Au) were synthesized by induction‐melting (or in muffle furnaces) of the elements in sealed niobium ampoules. The new phases were characterized by powder X‐ray diffraction. The structures of SrPdMg₂ and SrPdCd₂ were investigated by X‐ray diffraction on single crystals: MgCuAl₂ type, Cmcm, a = 436.42(4), b = 1130.1(1), c = 820.54(7) pm, wR₂ = 0.0115, 511 F² values for SrPdMg₂ and a = 443.5(2), b = 1063.0(2), c = 810.2(2) pm, wR₂ = 0.0296, 386 F² values for SrPdCd₂ with 16 variables for each refinement. The magnesium and cadmium atoms build up [TMg₂] and [TCd₂] polyanionic networks, which leave cavities for the calcium and strontium atoms. The bonding variations within the polyanions, which are mainly influenced by the length of the b axis are discussed. Ab initio calculations of electronic structure, charge densities, and chemical bonding, characterize SrPdMg₂ with a larger cohesive energy than SrPdCd₂. This is illustrated by larger bonding Pd–Mg interactions, opposite to compensating Pd–Cd between bonding and antibonding states.     

Binuclear Ru(III) Schiff base complexes: synthesis,spectral characterization,oxidation, C?C coupling reactions and antibacterial activities

New hexa‐coordinated binuclear Ru(III) Schiff base complexes of the type {[(B)₂X₂Ru]₂L} (where B = PPh₃ or AsPh₃; X = Cl or Br; L = binucleating N₂O₂ Schiff bases) were synthesized and characterized by elemental analysis, magnetic susceptibility measurement, FT‐IR, UV–vis, ¹³C{¹H}‐NMR, ESR at 300 and 77 K, cyclic voltammetric technique, powder X‐ray diffraction pattern and SEM. The new complexes were used as catalysts in phenyl–phenyl coupling reaction and the oxidation of alcohols to their corresponding carbonyl compounds using molecular oxygen atmosphere at room temperature. Further, the new Schiff base ligands and their Ru(III) complexes were also screened for their antibacterial activity against K. pneumoniae, Shigella sp., M. luteus, E. coli and S. typhi. From this study, it was found that the activity of the ruthenium(III) Schiff base complexes almost reaches the effectiveness of the conventional bacteriocide standards. Copyright © 2009 John Wiley & Sons, Ltd.