Self-assembled cobalt(II) Schiff base complex: synthesis, structure, and magnetic properties

Abstract  

A mononuclear complex [CoL₂Cl₂]·3.5H₂O (L = 2-[(2,2-diphenylethylimino)methyl]pyridine-1-oxide) has been synthesized and characterized by X-ray structure analysis. The crystal structure confirms the formation of an interesting porous framework with channel diameters of about 8 ? through weak C–H···π and C–H···Cl interactions. The magnetic properties of this complex have also been studied, and the susceptibility and magnetization data were analyzed in terms of the spin Hamiltonian formalism. They confirm substantial zero-field splitting, D/hc = 75 cm⁻¹.     

Base-stabilized amidodiarsenes: synthesis, structure, and theoretical studies

The guanidinato- or amidinato-bridged diarsenes [As2{mu-(ArN)2CR}2] (Ar = C6H3Pri2-2,6; R = N(C6H11)2, NPri2, or But) have been prepared by reduction of the corresponding As(III) precursors, [Cl2As{kappa2-N,N'-(ArN)2CR}]. Theoretical studies suggest that the As-As bonds of the dimers have significant double-bond character, the sigma and pi components of which are derived mainly from As p orbital overlaps.     

Alumazene adducts with pyridines: synthesis, structure, and stability studies

Lewis acid-base adducts of the alumazene [2,6-(i-Pr)2C6H3NAlMe]3 (1) with pyridine (py) and 4-dimethylaminopyridine (dmap) were synthesized and structurally characterized: 1(py)2 (2), 1(py)3 (3), 1(dmap)2 (4), and 1(py)(dmap) (5). The bisadducts 2, 4, and 5 form the trans isomers. The trisadduct 3 exhibits an unexpected cis-cis isomer and can be prepared only in the presence of excess py. The planarity of the alumazene ring is lost upon coordination of the Lewis base molecules. A comparison of the Al-N(base) bond distances and pyramidality at Al suggests the higher basicity of dmap. NMR spectroscopy confirms stability to dissociation of the bisadducts in solution while the trisadduct 3 is labile and converts to 2. The thermodynamics of the adduct formation has been investigated experimentally and theoretically. Thermodynamic characteristics of the 1(py)n (n=2, 3) dissociation reactions in the temperature range 25-200 degrees C have been derived from the vapor pressure-temperature dependence measurements by the static tensimetric method. In all experiments, excess py was employed. Quantum chemical computations at the B3LYP/6-31G* level of theory have been performed for the 1(py)n and model complexes [HAlNH]3(py)n (n=1-3). Obtained results indicate that for the gas phase adducts upon increasing the number of py ligands the donor-acceptor Al-N(py) distance increases in accord with decreasing donor-acceptor bond dissociation energies.     

Hydrothermal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba_1-xSr_xTi_1-yZr_yO₃ (0≤x≤0.5, 0≤y≤0.4) and BA_1?xZn_xTi_1?ySn_yO₃ (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr²⁺ and Zr⁴⁺ or Zn²⁺ and Sn⁴⁺ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO₃ phase at room temperature.     

Hydrotherrnal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba1-xSrxTi1-yZryO3 (0≤x≤0.5, 0≤y≤0.4) and Ba1-xZnxTi1-ySnyO3 (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by Iow-temperature/Iow-pressure hydrothermal method below 170℃, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO3. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr2+ and Zr4+ or Zn2+ and Sn4+ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO3 phase at room temperature.     

Hydrothermal synthesis, structure and property of nano-BaTiO_3based dielectric materials

A series of Ba1-xSrxTi1-yZryO3 (0≤x≤0.5, 0≤y≤0.4) and Ba1-xZnxTi1-ySnyO3 (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170℃, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO3. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr2+ and Zr4+ or Zn2+ and Sn4+ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO3 phase at room temperature.     

Thorium oxo and sulfido metallocenes: synthesis, structure, reactivity, and computational studies

The synthesis, structure, and reactivity of thorium oxo and sulfido metallocenes have been comprehensively studied. Heating of an equimolar mixture of the dimethyl metallocene [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)ThMe(2) (2) and the bis-amide metallocene [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th(NH-p-tolyl)(2) (3) in refluxing toluene results in the base-free imido thorium metallocene, [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th═N(p-tolyl) (4), which is a useful precursor for the preparation of oxo and sulfido thorium metallocenes [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th═E (E = O (5) and S (15)) by cycloaddition-elimination reaction with Ph(2)C═E (E = O, S) or CS(2). The oxo metallocene 5 acts as a nucleophile toward alkylsilyl halides, while sulfido metallocene 15 does not. The oxo metallocene 5 and sulfido metallocene 15 undergo a [2 + 2] cycloaddition reaction with Ph(2)CO, CS(2), or Ph(2)CS, but they show no reactivity with alkynes. Density functional theory (DFT) studies provide insights into the subtle interplay between steric and electronic effects and rationalize the experimentally observed reactivity patterns. A comparison between Th, U, and group 4 elements shows that Th(4+) behaves more like an actinide than a transition metal.     

Self-assembled multibilayers of europium alkanoates: structure, photophysics, and mesomorphic behavior

A series of europium alkanoates (C(n-1)H(2n-1)CO(2))(3)Eu, (n = 14, 16, 18, 20) have been synthesized and characterized in detail. X-ray diffraction and Fourier transform infrared spectroscopic measurements confirm the multibilayer structure of these homologues. In such bilayers, the europium ionic layers are well separated by the highly ordered alkyl chains which are in an all-trans conformation and perpendicular to both sides of the europium ionic layers. There is a mixed-coordination type of chelating bidentate and bridging bidentate between the carboxylate groups and the europium ions. All samples exhibit characteristic emission of europium, though the luminescent intensity has been partly quenched by the carboxylate groups. Differential scanning calorimetry (DSC) shows multiple melting points for these homologues, and temperature-dependent X-ray diffraction measurements also confirm the existence of the mesophase on heating. This mesophase is not truly liquid crystalline, but is similar to the smectic A phase of organic rodlike molecules. Meanwhile, it seems that with increasing atomic number of lanthanide ions, longer alkyl chains will be required to form such a mesophase for the corresponding lanthanide alkanoates.     

Metalloid derivatives for synthesis: Monoderivatization of symmetric diols

The monoderivatization of symmetric diols by condensation of their stannoxanes with activated halides is described.     

Coordination complexes exhibiting anion...pi interactions: synthesis, structure, and theoretical studies

The polydentate ligand 2,4,6-tris(dipyridin-2-ylamino)-1,3,5-triazine (dpyatriz) in combination with the Cu(ClO 4) 2/CuX 2 salt mixtures (X (-) = Cl (-), Br (-), or N 3 (-)) leads to the formation of molecular coordination aggregates with formulas [Cu 3Cl 3(dpyatriz) 2](ClO 4) 3 ( 2), [Cu 3Br 3(dpyatriz) 2](ClO 4) 3 ( 3), and [Cu 4(N 3) 4(dpyatriz) 2(DMF) 4(ClO 4) 2](ClO 4) 2 ( 4). These complexes consist of two dpyatriz ligands bridged via coordination to Cu (II) and disposed either face-to-face in an eclipsed manner ( 2 and 3) or parallel and mutually shifted in one direction. The copper ions complete their coordination positions with Cl (-) ( 2), Br (-) ( 3), or N 3 (-), ClO 4 (-), and N, N-dimethylformamide (DMF) ( 4) ligands. All complexes crystallize together with noncoordinate ClO 4 (-) groups that display anion...pi interactions with the triazine rings. These interactions have been studied by means of high level ab initio calculations and the MIPp partition scheme. These calculations have proven the ClO 4 (-)...[C 3N 3] interactions to be favorable and have revealed a synergistic effect from the combined occurrence of pi-pi stacking of triazine rings and the interaction of these moieties with perchlorate ions, as observed in the experimental systems.     

Hydrothermal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba_1-xSr_xTi_1-yZr_yO₃ (0≤x≤0.5, 0≤y≤0.4) and BA_1?xZn_xTi_1?ySn_yO₃ (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr²⁺ and Zr⁴⁺ or Zn²⁺ and Sn⁴⁺ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO₃ phase at room temperature.     

Self-assembled templates for polypeptide synthesis

The chemical synthesis of polypeptide chains >50 amino acids with prescribed sequences is challenging. In one approach, native chemical ligation (NCL), short, unprotected peptides are connected through peptide bonds to render proteins in water. Here we combine chemical ligation with peptide self-assembly to deliver extremely long polypeptide chains with stipulated, repeated sequences. We use a self-assembling fiber (SAF) system to form structures tens of micrometers long. In these assemblies, tens of thousands of peptides align with their N- and C-termini abutting. This arrangement facilitates chemical ligation without the usual requirement for a catalytic cysteine residue at the reactive N-terminus. We introduced peptides with C-terminal thioester moieties into the SAFs. Subsequent ligation and disassembly of the noncovalent components produced extended chains > or =10 microm long and estimated at > or =3 MDa in mass. These extremely long molecules were characterized by a combination of biophysical, hydrodynamic, and microscopic measurements.     

Self-assembled dendrimers with uniform structure

Calix[4]arenes substituted at their wide rim by four aryl urea residues (1) form hydrogen-bonded dimers in apolar solvents. Replacement of one urea residue by an acetamido moiety leads to calix[4]arene derivatives (5) which form hydrogen-bonded tetramers under the same conditions. Both self-assembly processes occur independently. Therefore, molecules have been prepared in which a tetra-urea calix[4]arene and a tri-urea mono acetamide derivative are covalently connected between their narrow rims by a long, mainly aliphatic chain [-O-(CH(2))(n)-C(O)-NH-(CH(2))(m)-O-] (7). In the presence of an equimolar amount of tetra-tosyl urea calix[4]arene () they form dendritic assemblies since the well known heterodimerization of tetra-tosyl and tetra-aryl urea calix[4]arenes prevents the formation of a cross-linked structure. Covalent connection of adjacent urea residues leads to tetra-loop derivatives (3) that cannot form homodimers, but instead form heterodimers with tetra-aryl or tetra-tosylureas. Therefore, similar dendrimers should be available using the selective dimerization observed for 3. The formation of a single, structurally uniform dendrimer from eight building blocks is confirmed by (1)H NMR spectra, showing only peaks that are also found for respective model assemblies. Translational diffusion coefficients of the assemblies have been determined using (1)H DOSY NMR.     

The synthesis,structure, and magnetic studies of one supramolecular PtS net

A new 2-D coordination polymer, Co(H₂O)₂(Hoba)₂ (1) [H₂oba?=?4,4′-oxybis(benzoic acid)], was synthesized under hydrothermal conditions. Polymer 1 has been characterized by single-crystal X-ray diffraction and TG analysis. Through hydrogen bonds 1 shows a supramolecular four-connecting 3-D matrix with 4²8⁴ PtS topology. Magnetic studies reveal antiferromagnetic interactions.     

Selective self-assembly of hexameric homo- and heteropolymetallic lanthanide wheels: synthesis, structure, and photophysical studies

A rational approach to the formation of pure heteropolymetallic lanthanide complexes that uses a two-step assembly strategy and exploits the different size requirements of the two metals included in the final structure is described. The investigation of the assembly of [LnL2](Otf) (L = 2,2':6',2' '-terpyridine-6-carboxylate) complexes into hexametallic rings hosting an additional hexacoordinated lanthanide cation was crucial for the development of this strategy. The formation and size of the cyclic assembly are controlled by the ionic radius and by the coordination number of the lanthanides. The rather high luminescence quantum yield of the heptaeuropium complex (25%) indicates that the ring structure is well adapted to include highly luminescent lanthanide complexes in nanosized architecture. The use of a stepwise synthetic strategy leads to the selective assembly of large heteropolymetallic rings. The addition of a smaller lanthanide ion to the [EuL2](Otf) complex in anhydrous acetonitrile leads selectively to heterometallic species with the Eu ions located on the peripheral sites and the smaller ion occupying only the central site. The high selectivity is the result of the different size requirements of the two metal sites present in the cyclic structure. The heterometallic structure of the isolated [Lu subset (EuL2)6](Otf)9 complex was confirmed by X-ray diffraction and by high resolution solid-state photophysical studies. The described synthetic approach allowed us to obtain the first example of selective assembly of two different lanthanide ions in a large polymetallic structure characterized in solution and in the solid state and will make the isolation of planned dimetallic combinations presenting different lanthanide emitters in the peripheral sites possible.