Norbani Abdullah

Organocatalysis by p-sulfonic acid calix[4]arene: a convenient and efficient route to 2,3-dihydroquinazolin-4(1H)-ones in water

An efficient and eco-friendly method is reported for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones from the direct cyclocondensation of anthranilamide with aldehydes using p-sulfonic acid calix[4]arene (p-SAC) as a recyclable organocatalyst in excellent yields in water at room temperature. The catalyst was reusable without significant loss of catalytic efficiency. Operational simplicity, the compatibility with various functional groups, non-chromatographic purification technique, high yields and mild reaction conditions are the notable advantages of this procedure. Large scale reaction demonstrated the practical applicability of this methodology.

Spin-crossover, mesomorphic and thermoelectrical properties of cobalt(II) complexes with alkylated N3-Schiff bases

Three new cobalt(II) complexes, [Co(L12)2](BF4)2 (1), [Co(L14)2](BF4)2·H2O (2) and [Co(L16)2](BF4)2·H2O (3), where L12–16 are N3-Schiff bases appended with linear C12–16 carbon chains at the nitrogen atoms, were obtained in good yields by facile one-pot reactions. The single crystal X-ray structure of complex 1 shows a tetragonally compressed CoN6 coordination geometry. The melting temperatures of 1–3 were lower than 373 K, while their decomposition temperatures were above 473 K. All complexes have high-spin Co(II) centres at 300 K and exhibit a columnar mesophase above 383 K. Complexes 1 and 3 showed normal thermal spin-crossover behaviour with weak hysteresis loops at about 320 K. Hence, these complexes showed uncoupled phase transitions (class iiia). The values for the Seebeck coefficient (Se) of the cobalt redox couples formed from 1 and 2 were 1.89 ± 0.02 mV K−1 and 1.92 ± 0.08 mV K−1, respectively, identifying them as potential thermoelectrochemical materials.

Ionic liquid entrapment by an electrospun polymer nanofiber matrix as a high conductivity polymer electrolyte

Through external doping, novel conductive polymer nanofibers were successfully fabricated using ionic liquids. In this study, a polymer blend of polyvinyl alcohol (PVA) and chitosan (CS) in a 4 : 1 weight ratio was fabricated in the form of nanofibers through electrospinning and used as a scaffold membrane to capture room-temperature ionic liquids (RTILs), such as 1-ethyl-3-methylimidazolium chloride (EMIMCl) and 1-butyl-3-methylimidazolium bromide (BMIMBr). Morphological analysis using scanning electron microscopy (SEM) showed that the scaffold structure of the electrospun membrane facilitated sufficient trapping of RTILs. This membrane demonstrated significantly increased conductivity from 6 × 10−6 S cm−1 to 0.10 S cm−1, interestingly surpassing the value of pure ionic liquids, where the polymer chain breathing model has been suggested as a hypothesis to explain this phenomena. The dominance of ions as charge carriers was explained using an ionic transference number measurement. The interaction between the polymer nanofiber matrix and an ionic liquid has been explained using Fourier-transform infrared spectroscopy (FTIR), where the ionic liquid was found to be physically dispersed in the polymer nanofiber matrix. These materials have also shown some thermoelectric (TE) activity, by demonstrating Seebeck coefficients up to 17.92 μV K−1. The existence of freely movable ions in this type of membrane shows their applications as energy storage/conversion devices such as organic thermoelectrics (TEs), sensors, and dye-sensitised solar cells.

Structural, mesomorphic, photoluminescence and thermoelectric studies of mononuclear and polymeric complexes of copper(II) with 2-hexyldecanoato and 4,4′-bipyridine ligands

[Cu(R)2(bpy)2]·2RH (1) and [Cu2(R)4(bpy)]x (2) were obtained from the reaction of [Cu2(R)4(RH)2] (R = 2-hexyldecanoato) with 4,4′-bipyridine (bpy) using different work-up procedures. Complex 1 consisted of single crystals and its molecular structure showed a distorted octahedral Cu(II) with two chelating bidentate R. Complex 2 has a similar structure as crystals of a linear-chain coordination polymer, [Cu2(CH3(CH2)5COO)4(bpy)]x (3). Both 1 and 2 were thermally stable (Tdec = 240 °C for 1; 220 °C for 2), have low melting temperatures (Tm = 52.3 °C for 1; Tm = 48.3 °C for 2) and exhibited temperature-dependent mesomorphisms. For 1, the mesomorphism arose from the change in the binding mode of R from chelating to bridging during isotropization, while for 2, the mesomorphism arose from the breaking of the Cu–Nbpy bonds. The mesophases for 2 were cubic columnar (Cub, P4332) and rectangular columnar (ColR, space group p2gg) on cooling from 150 °C, Cub and hexagonal columnar (ColH) on cooling from 184 °C (isotropic liquid phase), and ColH and nematic columnar (ColN) on cooling from 190 °C. These complexes also exhibited photoluminescence upon charge transfer and d–d excitation. Finally, the Seebeck coefficient value (Se) for 2 was −0.47 mV K−1, identifying it as a potential thermoelectric material.

The Effect of Stabiliser’s Molarity to the Growth of ZnO Nanorods

A wet chemical approach, originating from sol-gel preparation, was adopted with the intention to develop a low-temperature benign method of preparation. ZnO nanorods are successfully grown in an aqueous medium. The precursor, zinc nitrate hexahydrate (Zn(NO3)2.6H2O), is stabilized by hexamethylene tetraamine (HMTA). The effect of changing the molarity of HMTA to the structural orientation of ZnO nanorods is investigated. X-ray diffraction of the synthesized ZnO shows hexagonal zincite structure. The structural features of the nanocrystalline ZnO were studied by SEM. Structural features, surface morphology and differences in lattice orientation are seemingly influenced by varying the Zn2+: HMTA molar ratio. The formation of ZnO nanorods with blunt and sharp tips is found to be significantly affected by this ratio.

Thermal stability and electrochemical behaviour of Tetrakis-μ-benzoatodicopper(II)

AbstractCopper(II) benzoate (CuB) was synthesized and structurally characterized to have a binuclear, paddle-wheel structure. The complex was found to be thermally stable up to 230°C, and underwent four stages of decomposition, loss of CO2, C6H6, CH3CH2-OCH2CH3 and some aliphatic unsaturated organic materials. The DSC curve shows two endotherms at 80.0°C and 230.0°C respectively, indicating that the initial weight loss can be attributed to solvated molecules and the starting of the major decomposition process, (shown in the TG analysis). Cyclic voltammetry studies in a mixed-solvent system of methanol and ethanoic acid (20:1 v/v) show three cathodic peaks, at −0.13 V, −0.35 V and −0.74 V, representing a step-wise electron transfer process, and two overlapping anodic peaks at +0.31 V and +0.46 V. The high value of ΔE ranging from 400 mV to 1200 mV indicates that the redox process is accompanied by an extensive structural reorganization of the complex in the solution creating a different geometrical environment around the central copper ion.

Covalent and ionic Cu(II) complexes with cyclam and substituted benzoato ligands: structural, thermal, redox and mesomorphic properties

Abstract A covalent mononuclear complex, [Cu(p–HOC6H4COO)2(cyclam)] (1), and two ionic mononuclear complexes, [Cu(cyclam)(H2O)2](p–CH3OC6H4COO)2 (2) and [Cu(cyclam)(H2O)2](p–CH3(CH2)15OC6H4COO)2·H2O (3), were formed from reaction of cyclam with [Cu2(p–HOC6H4COO)4(H2O)2], [Cu2(p–CH3OC6H4COO)4(H2O)2] and [Cu2(p-CH3(CH2)15OC6H4COO)4(H2O)2], respectively. These complexes were isolated as purple crystals with molecular structures showing distorted octahedral N4O2 geometry. Complexes 1 and 2 were irreversibly reduced to Cu(I) and oxidized to Cu(III), while 3 was redox inactive. Complex 2 reacted with N-(hexadecyl)isonicotinamide (L) to form [Cu(cyclam)(L)2](p–CH3OC6H4COO)2 (4). These complexes were thermally stable (Tdec > 200 °C for 1–3 and 174 °C for 4). Complexes 3 and 4 behaved as ionic liquids (melting temperatures lower than 100 °C) and exhibited mesomorphism.

Structures and mesomorphism of complexes of tetrakis(4-chlorobenzoate-μ-O,O′)bis(ethanol)dicopper(II) with different N-donor ligands

Dimeric [Cu2(4-ClC6H4COO)4(EtOH)2] (1) reacted with pyridine (pyr), 2,2′-bipyridine (bpy), and 1,4,8,11-tetraazacyclotetradecane (cyclam) to form mononuclear covalent complexes, [Cu(4-ClC6H4COO)2(pyr)2(H2O)] (2) and [Cu(4-ClC6H4COO)2(bpy)(H2O)] (3), and mononuclear ionic, [Cu(cyclam)(H2O)2](4-ClC6H4COO)2 (4), respectively. The molecular structures of 2 and 3 were determined by single-crystal X-ray crystallography. Complexes 1 and 4 then reacted with 4-hexadecyloxypyridine (L) to form mesomorphic complexes, [Cu(4-ClC6H4COO)2(L)2(H2O)] (5) and [Cu(cyclam)(L)2](4-ClC6H4COO)2 (6), respectively. These complexes are potential molecular magnetic materials with tunable properties. This article reports the synthesis and paddle-wheel structure of [Cu2(4-ClC6H4COO)4(EtOH)2], and its reaction with pyridine (pyr), 2,2′-bipyridine (bpy), and 1,4,8,11-tetraazacyclotetradecane (cyclam) to form mononuclear covalent complexes, [Cu(4-ClC6H4COO)2(pyr)2(H2O)] and [Cu(4-ClC6H4COO)2(bpy)(H2O)], and mononuclear ionic complex, [Cu(cyclam)(H2O)2](4-ClC6H4COO)2, respectively. Also reported are the mesomorphic properties of [Cu(4-ClC6H4COO)2(L)2(H2O)] and [Cu(cyclam)(L)2](4-ClC6H4COO)2, where L = 4-hexadecyloxypyridine. These complexes are potential molecular magnetic materials with tunable properties.

Magnetic, thermal, mesomorphic and thermoelectric properties of mononuclear, dimeric and polymeric iron(II) complexes with conjugated ligands

Three iron(II) complexes with conjugated multidonor ligands (L1 and L2) studied as thermally stable magnetic and thermoelectric materials were [Fe2(CH3COO)4(L1)2] (1), [Fe(L1)3](BF4)2·4H2O (2), and {[Fe2(CH3COO)4(L2)]·2H2O}n (3). These complexes have low optical band gaps (1.9 eV for 1 and 2, and 2.2 eV for 3) and were magnetic with 57% high-spin Fe(II) in 1, 33% in 2, and 100% in 3 at 25 °C. Complex 1 melted at 57.2 °C and exhibited mesomorphism, while 2 melted at 96.9 °C, defining it as an ionic liquid. The thermal stabilities of 1 (Tdec = 199 °C) and 3 (Tdec = 191 °C) were lower than 2 (Tdec = 248 °C). Their Seebeck coefficients, Se (in mV K−1) were −0.65 for 1, −0.54 for 2, and +0.25 for 3, identifying them as potential thermoelectric materials. Complex 1 formed stable thin films on quartz by the spin coating technique. The films formed at aging time t = 0 (F1) and t = 7 days (F2) were made up of monomers of 1. The optical band gaps of the films (1.39 eV for F1 and 1.57 eV for F2) were lower than 1. The films were free of cracks and have a fairly homogeneous morphology. The films with the best morphology were F1 annealed at 40 °C and F2 annealed at 60 °C.

ZnO Nanostructures – Nanorods and Flower-Like on Si/Au Substrates by Solution-Immersion Method in Different pH of Precursor

Low-temperature solution immersion growth of low-dimensional ZnO nanostructures on gold-seeded Si substrate has been demonstrated. pH environment of the precursor solution, Zn(NO3)2.6H2O (zinc nitrate hexahydrate) and C6H12N4 (HMTA) was found to have considerable effect to ZnO morphology and photoluminescence. Structural, morphological and photoluminescence (PL) properties of the samples were obtained from XRD, SEM and PL-Raman characterisation. A near neutral (pH = 6.8) and acidic (pH = 5) precursor solution aided a dense near-aligned ZnO nanorods growth with smallest rods diameter of 30 and 20 nm respectively. Whereas alkaline precursor solution (pH = 9) gave rise to flower-like structures of ZnO. Chemical equations for the reactions and the role of H+ and OH- ions role in affecting the XRD diffraction peaks and morphology, are suggested. Room temperature PL emission spectra of ZnO were collected after excitation at 325 nm. UV and visible emission distinctive of ZnO were formed and the rationale for significant shifts of the visible emission was also discussed.