Search

The reaction of uranyl nitrate hexahydrate with the maleonitrile containing Schiff base 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile (salmnt(Et2N)2H2) in methanol produces [UO2(salmnt(Et2N)2)(H2O)] (1) where the uranyl equatorial coordination plane is completed by the N2O2tetradentate cavity of the (salmnt(Et2N)2)2−ligand and a water molecule. The coordinated water molecule readily undergoes exchange with pyridine (py), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF) and triphenylphosphine oxide (TPPO) to give a series of [UO2(salmnt(Et2N)2)(L)] complexes (L = py, DMSO, DMF, TPPO; 2–5, respectively). X-Ray crystallography of 1–5show that the (salmnt(Et2N)2)2−ligand is distorted when coordinated to the uranyl moiety, in contrast to the planar structure observed for the free protonated ligand (salmnt(Et2N)2H2). The Raman spectra of 1–5only display extremely weak bands (819–828 cm−1) that can be assigned to the typically symmetric OUO stretch. This stretching mode is also observed in the infrared spectra for all complexes 1–5(818–826 cm−1) predominantly caused by the distortion of the tetradentate (salmnt(Et2N)2)2−ligand about the uranyl equatorial plane resulting in a change in dipole for this bond stretch. The solution behaviour of 2–5was studied using NMR, electronic absorption and emission spectroscopy, and cyclic voltammetry. Complexes 2–5exhibit intense absorptions in the visible region of the spectrum due to intramolecular charge transfer (ICT) transitions and the luminescence lifetimes (< 5 ns) indicate the emission arises from ligand-centred excited states. Reversible redox processes assigned to the {UO2}2+/{UO2}+couple are observed for complexes 2–5(2: E1/2= −1.80 V; 3,5: E1/2= −1.78 V; 4: E1/2= −1.81 V : vs.ferrocenium/ferrocene {Fc+/Fc}, 0.1 M Bu4NPF6) in dichloromethane (DCM). These are some of the most negative half potentials for the {UO2}2+/{UO2}+couple observed to date and indicate the strong electron donating nature of the (salmnt(Et2N)2)2−ligand. Multiple uranyl redox processes are clearly seen for [UO2(salmnt(Et2N)2)(L)] in L (L = py, DMSO, DMF; 2–4: 0.1 M Bu4NPF6) indicating the relative instability of these complexes when competing ligands are present, but the reversible {UO2}2+/{UO2}+couple for the intact complexes can still be assigned and shows the position of this couple can be modulated by the solvation environment. Several redox processes were also observed between +0.2 and +1.2 V (vs.Fc+/Fc) that prove the redox active nature of the maleonitrile-containing ligand. [ABSTRACT FROM AUTHOR]

The synthesis and structural characterization of two families of low-valent vanadium(III) {V6P4} and vanadium(III/IV) {V13P8} phosphonate complexes are reported. Magnetic characterization is reported for representative examples. [ABSTRACT FROM AUTHOR]

The reaction of cobalt salts with phosphonic acids in the presence of 6-chloro-2-hydroxypyridine as a co-ligand, using sodium methoxide as a base, leads to a series of new polymetallic cobalt cages. Variation of the phosphonate present and the cobalt salt leads to {Co6Na8}, {Co12}, {Co13Na14}, {Co6Na4} and {Co15Na} cages, all of which have been characterized by X-ray crystallography. Using lithium methoxide produces a sixth cage with a {Co6Li9} core. The structures are, in general, extremely irregular with no structural motifs common to the six cages. Magnetic studies of these cages show a general decline in the product cmT with T, but for {Co13Na6}, {Co15Na} and {Co12} there are maxima at low temperature, which suggest non-diamagnetic ground states. Investigation of the dynamic behaviour of the magnetisation of these complexes shows that the {Co13Na6}, and possibly the {Co12} cage, appear to display slow relaxation of magnetisation. [ABSTRACT FROM AUTHOR]

Examines the temperature-resolved structural behavior of nickel octahexyl phthalocyanine. Phase transitions; Differential scanning calorimetry measurements; Increase in the mobility of hexyl groups as a function of temperature.

We report the structural, spectroscopic and preliminary magnetic characterisation of a tri-metallic plutonyl(vi) polyoxometalate complex, K11[K3(PuO2)3(GeW9O34)2]·12H2O. [ABSTRACT FROM AUTHOR]

The reaction of 1,2-diacetoxycyclooctane-5,6-dione with ortho-phenylenediamine in acetic acid gave trans-6,7,8,9,10,11-hexahydrocycloocta[ b]quinoxaline-8,9-diyl diacetate, C18H20N2O4. The saturated H atoms in the structure display almost perfect gauche orientations and the two acetoxy groups are oriented almost perfectly antiperiplanar. There are C—H...N bonding interactions linking the molecules into chains and intermolecular π–π stacking interactions between pyrazine rings [centroid–centroid distance = 3.6569 (9) Å and perpendicular distance = 3.426 Å]. [ABSTRACT FROM AUTHOR]

The geometry around the Sn atom of the title compound, [Sn(C6H5)3(C7H2ClN2O6)], is distorted tetra­hedral, with Sn—C distances lying in the range 2.124 (2)–2.119 (2) Å and an Sn—O distance of 2.0645 (15) Å. [ABSTRACT FROM AUTHOR]

Abstract: Eleven new complexes of the form cis-[RuII(bpy)2(LA)]4+ (bpy=2,2′-bipyridyl; LA =a pyridinium-substituted bpy derivative) have been prepared and isolated as their PF6 − salts. Characterisation involved various techniques including 1H NMR spectroscopy and MALDI mass spectrometry. The UV–Vis spectra show intense intraligand π → π ∗ absorptions and metal-to-ligand charge-transfer (MLCT) bands with two distinct maxima in the visible region. Small shifts in the MLCT bands correlate with the electron-withdrawing strength of the ligand LA. Cyclic voltammograms show quasi-reversible or reversible RuIII/II oxidation waves, and two or more ligand-based reductions with varying degrees of reversibility. The variations in the redox potentials correlate with changes in the structure of LA, and also with the MLCT energies. Differential pulse voltammetry allows the first reduction process for two of the complex salts to be resolved into two peaks. Single-crystal X-ray structures have been solved for three of the new complex salts and also for a pro-ligand salt. Two carboxylate-functionalised compounds have been tested as photosensitizers on TiO2-coated electrodes, but show only negligible efficiencies, in accord with expectations. [Copyright &y& Elsevier]

Abstract: A series of oligo-m- and p-benzanilides were made and their conformations in solution were studied by NMR. In most cases, conformational mixtures were observed as soon as three or more monomers were incorporated into the oligomer. Some crystal structures were obtained, which indicated that helical conformations were adopted in the solid state. [ABSTRACT FROM AUTHOR]

Highlights: [•] Preparation and solid state study of a novel member of an interesting structural class. [•] This modeling studies show that the E-isomer is the global minimum isomer. [•] A rationale for the observed E-selectivity is based on strong E–E dimerization. [ABSTRACT FROM AUTHOR]

Abstract: Two new lanthanide carboxylato complexes [Ln(3,5-DNBA)3(H2O)2] n , (Ln=LaIII in 1 and GdIII in 2, DNBA=dinitrobenzoic acid) have been synthesized hydrothermally and characterized structurally by single crystal X-ray analysis. Alternate (μ-η1:η1)4 and (μ-η1:η1)2 type bridging modes by carboxylate ligands provide eightfold coordination around the Ln center in both complexes, which result in two different LnLn distances, with polymeric chains propagating along the [100] direction. Intermolecular O–HO hydrogen bonds and π–π stacking interactions form (20), (40) rings, thus generating three-dimensional supramolecular frameworks in 1 and 2. Density functional theory (DFT) calculations were carried out using the hybrid exchange–correlation functional, PBE. The HOMO–LUMO energy gap of 2.63eV in 1 is found to be greater than that of 1.86eV in 2. [Copyright &y& Elsevier]

Abstract: One Mg(II) malonate complex with protonated 2-aminopyridine and hexafluoridophosphate as counterions, (C5H7N2)4[Mg(C3H2O4)2(H2O)2](PF6)2 (1) [C5H7N2 =protonated 2-aminopyridine, C3H4O4 =malonic acid] has been synthesized from purely aqueous media just by mixing the reactants in their stoichiometric proportion and its crystal structure has been determined by single-crystal X-ray diffraction. The role of weak forces like lone pairπ and anionπ interactions in influencing the self-assembly process appears to be of importance. A rare combination of lone pairπ and anionπ interactions in 1, of the type lone pairπ/ππ/πanion, is observed, and this unusual supramolecular network is fully described here. [Copyright &y& Elsevier]

Abstract: The mixed ligand copper(II) complex of succinate and 2,2′-bipyridyl was synthesized from disodium succinate, 2,2′-bipyridine and copper nitrate. The structure of the synthesized complex was determined by micro-analysis, IR, thermogravimetric analysis and X-ray crystallography. The thermal decomposition of the complex under an inert atmosphere has been studied. The crystal structure is monoclinic space group P21/n with parameters a =15.080(9)Å, b =22.406(13)Å, c =15.138(9)Å, β =91.539°, V =5113(5)Å3, Z =4, 1.534Mg/m3, R =0.0911 and Mr=1181.08. The geometry around copper atom is distorted octahedral. The complex consists of a dimer in which each Cu atom is linked through two carboxylate–oxygen atoms from a tetradentate succinate ligand and four nitrogen atoms from two chelating 2,2′-bipyridyl groups. The succinate ligand bridges between the two Cu atoms. [Copyright &y& Elsevier]

Abstract: Three metal complexes containing malonate as primary ligand and 4-aminopyridine as secondary ligand (counter ion) namely, {(ampyH)2[Cu(mal)2]} n (1), (ampyH)2[Ni(mal)2(H2O)2] (2) and (ampyH)2[Co(mal)2(H2O)2] (3) [ampyH=protonated 4-aminopyridine, malH2 =malonic acid] have been synthesized from purely aqueous media and their crystal structures have been determined by single crystal X-ray diffraction. The copper complex is polymeric, whereas the nickel and cobalt complexes are monomeric in nature. The most striking feature of the present study is the observed ligand induced topological variations of the [Cu(mal)2]2− unit, which is the building block not only for 1, but for several other copper–malonate complexes previously synthesized by us. It is also observed that this influence of the ligand is not reflected in the primary coordination of the analogs Ni(II) and Co(II) complexes, as the same monomeric unit [M(II)(mal)2(H2O)2]2−, [M=Ni/Co] exists not only in 2 and 3, but also in other Ni and Co complexes prepared by us, although there are subtle differences in the overall supramolecular arrangements in the solid state of these complexes (Ni and Co). Starting with 2-amino-4-picoline molecule as an auxiliary ligand [S. Ray Choudhury, A.D. Jana, E. Colacio, H.M. Lee, G. Mostafa, S. Mukhopadhyay, Cryst. Growth Des. 7 (2007) 212], we have found that protonated heterocyclic bases (2-amino-4-picoline and 2-aminopyridine) have a preferred hydrogen bonded recognition motif with metal carboxylate frameworks, which has an important role in guiding the crystal packing in the solid state. In the present study, we have extended our investigation by choosing 4-aminopyridine as an auxiliary ligand and discuss its effect in the overall self-assembly. A comprehensive comparison of the present complexes with our previously reported related complexes revealed the delicate nature of the self-assembly process. [Copyright &y& Elsevier]

Describes the synthesis of a undecametallic iron cluster. Molecular structure; Magnetic properties; Spin ground state; Quantum mechanical tunneling; Low-temperature single-crystal magnetic measurements.