Internal Architecture and Adsorption Sites of Violet Lander Molecules Assembled on Native and KBr‐Passivated InSb(001) Surfaces

The adsorption of individual Violet Lander molecules self‐assembled on the c(8×2) reconstructed InSb(001) surface in its native form and on the surface passivated with one to three monolayers of KBr is investigated by means of low‐temperature scanning tunneling microscopy (STM). Preferred adsorption sites of the molecules are found on flat terraces as well as at atomic step edges. For molecules immobilized on flat terraces, several different conformations are identified from STM images acquired with submolecular resolution and are explained by the rotation of the 3,5‐di‐tert‐butylphenyl groups around σ bonds, which allows adjustment of the molecular geometry to the anisotropic substrate structure. Formation of ordered molecular chains is found at steps running along substrate reconstruction rows, whereas at the steps oriented perpendicularly no intermolecular ordering is recorded. It is also shown that the molecules deposited at two or more monolayers of the epitaxial KBr spacer do not have any stable adsorption sites recorded with STM. Prospects for the manipulation of single molecules by using the STM tip on highly anisotropic substrates are also explored, and demonstrate the feasibility of controlled lateral displacement in all directions.     

Synthesis,spectroscopic and thermodynamic studies of new transition metal complexes with N,N′-bis(2-hydroxynaphthalin-1-carbaldehydene)-1,2-bis(m-aminophenoxy)ethane and their determination by spectrophotometric methods

A novel tetradentate N₂O₂-type Schiff base, synthesized from 1,2-bis(m-aminophenoxy)ethane and 2-hydroxynaphthalin-1-carbaldehyde, forms stable complexes with transition metal ions such as Cu(II), VO(IV) and Zn(II) in DMF. Microanalytical data, elemental analysis, magnetic measurements, UV, visible and IR spectra as well as conductance measurements were used to confirm the structures. The stability constants of these complexes in 60% (v/v) DMF–water were determined at different ionic strengths (0.07,?0.13,?0.2?M) and at different temperatures (45,?50,?55,?60?±?0.1°C) using a spectrophotometric method. From these constants, thermodynamic stability constants and thermodynamic parameters (ΔG?⁰, ΔH?⁰, ΔS?⁰) were calculated. The values of enthalpy change are negative for all systems. The acid dissociation constant of the ligand, investigated in 60% (v/v) DMF–water, has also been calculated at different temperatures.     

Metal complexes derived from hydrazoneoxime ligands: II. Synthesis,electrospray mass spectra and magnetochemical studies of some copper(II) complexes derived from p-substituted aroylhydrazoneoximes

Mono- and binuclear copper(II) complexes derived from substituted aroylhydrazoneoximes of the general formulae [Cu(H₂LR)Cl₂]·nH₂O, [Cu(HLR)Cl], [{Cu(HLR)}₂]·2NO₃·nH₂O and [{Cu(LR)}₂]·nH₂O have been prepared and characterized, where H₂LR, HLR and LR refer, respectively, to the neutral, monoanionic and dianionic ONN tridentate aroylhydrazoneoxime ligands. Electrospray ionization (ESI) mass spectra revealed the formation of tri- and tetranuclear copper(II) complexes in dimethylformamide (DMF) or dimethysulphoxide (DMSO) solutions. The effect of substitution in the aroylhydrazone residue on the degree of deprotonation of the ligand and the energies of d–d transitions of the copper(II) complexes have been studied. Tuning of the antiferromagnetic exchange coupling by different substituents in [{Cu(HLR)}₂]·2NO₃·nH₂O and [{Cu(LR)}₂]·nH₂O complexes have been discussed.     

Lanthanide complexes of D-penicillamine: formation constants,spectral and thermal properties

The complex-formation of lanthanide(III) elements with D-penicillamine have been investigated in acidic and neutral media. The macroscopic protonation constants of the ligand and the formation constants of [Ln.Pen]⁺, [Ln.Pen₂]^?, [Ln.Pen.OH] and [Ln.Pen.(OH)₂]^? complexes were determined from pH-metric data using the BEST computer program. Elemental analyses of the solid complexes indicate formation of 1?:?1 metal?:?ligand species. The binding sites in the complexes with the possible role of –COO^?, –NH₂ and –SH groups in the coordination have been discussed using infrared data. The complexes decompose in four steps as shown by their t.g. and d.t.a. analyses. A mechanism of decomposition is proposed which is supported by mass spectral data.     

Spectral characterization and biocidal activity of organotin(IV) (E)-3-[(2′,6′-dichlorophenylamido)]propenoates

Biocidal and spectroscopic aspects of organotin(IV) complexes with (E)-3-[(2′,6′-dichlorophenylamido)]propenoic acid are described with support of elemental analysis. IR, ¹H, ¹³C, ¹¹⁹Sn NMR and mass spectral data suggest that the ligand is bidentate, coordinating through oxygen atoms and that diorganotin(IV) complexes are six-coordinate. Triorganotin(IV) carboxylates exist as pentacoordinated trigonal bipyramidal complexes in the solid state and tetrahedral ones in solution. The complexes have been screened against bacteria, fungi and brine-shrimp larvae to assess their biological activity.     

Synthesis,characterization, thermal and redox behavior,and biological activity of Ni(II), Cu(II), and Zn(II) complexes containing pyridoxine and imidazole moieties

Several mixed ligand complexes [M(II)(PN)(B)] [M(II) = Ni(II), Cu(II), and Zn(II)] derived from pyridoxine (PN) and imidazoles (B), namely imidazole (him), benzimidazole (bim), histamine (hist), and L-histidine (his), were synthesized. The complexes are characterized by elemental analysis, IR, UV-Vis ¹H NMR, and ESR spectroscopy. In [M(II)(PN)B], the monovalent anion of PN is bidentate to M(II) (–O, –OH), him, bim monodentate (–N), hist bidentate (–N, –N), and his tridentate (–O, –N, –N). Magnetic moment studies showed that the Ni(II) complexes and Cu(II)–PN–his have octahedral configuration while the other Cu(II) complexes have distorted tetrahedral geometry. The g _∥/A _∥ values calculated from the X-band ESR spectra of Cu(II) complexes in DMSO at 300 and 77 K supports the geometry. The thermal behavior (TG/DTA) of the synthesized complexes indicates the presence of lattice as well as coordinated water in the complexes. The in vitro biological activity of the mixed ligand complexes was tested against common bacteria, yeast, and fungi. The results in comparison with the control indicate that most of the complexes exhibit higher biological activities. The oxidative DNA cleavage studies of the mixed ligand complexes were performed using gel electrophoresis.     

Metal-containing polyurethanes from tetradentate Schiff bases: synthesis,characterization, and biocidal activities

N,N′-bis(salicylidene)thiosemicarbazide Schiff base has been synthesized by the reaction of thiosemicarbazide with salicylaldehyde and then reacted with formaldehyde to generate phenolic groups, resulting in the formation of Schiff-base monomeric ligand. It was further incorporated with transition metals, Mn⁺², Co⁺², Ni⁺², Cu⁺², and Zn⁺², to form Schiff-base metal complex, which was then polymerized with toluene 2,4-diisocyanate to form metal-chelated polyurethanes. Monomeric ligand, its metal complexes, and its metal polychelates were characterized and compared by elemental analysis, FT-IR, ¹H NMR, thermal, and biocidal activities to evaluate the enhancement in physical and chemical properties on coordination with metal and on polymerization. SEM images of ligand and polymer metal complexes showed changes in surface morphology, while electronic spectra of polymer metal complexes were used to predict the geometry. Antimicrobial activities were determined by using agar-diffusion method with Staphylococcus aureus, Escherichia coli, Bacillus subtilis (bacteria), Aspergillus niger, Candida albicans, and Aspergillus flavus (yeast). The polymeric ligand had varied antibacterial and antifungal activities, enhanced after chelation and polymerization. Comparative results show that coordination of metal to the ligand enhances its physical and chemical properties which were meliorated on polymerization.     

Synthesis,spectroscopic, thermal,and biological activities of mixed ligand complexes containing E-N′-(3,4,5-trimethoxybenzylidene)benzofuran-2-carbohydrazide and 2-aminothiophenol

Complexes [M(L)(L′)Cl?·?H₂O], where M?=?Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II), L?=?ligand derived from reaction between benzofuran-2-carbohydrazide and 3,4,5-trimethoxybenzaldehyde (TMeOBFC) and L′?=?2-aminothiophenol (2-atp), have been synthesized. The structures of the complexes have been proposed from analytical data, IR, UV-Vis, ¹H NMR, direct analysis in real time-mass spectra, ESR spectral data, magnetic, and thermal studies. The complexes are soluble in DMF and DMSO. Molar conductance values indicate that the complexes are non-electrolytes. Antibacterial and antifungal activities of the ligands and their metal complexes have been obtained against bacteria Escherichia coli and Staphylococcus aureus and against fungi Aspergillus niger and Aspergillus flavus.     

Polymer complexes. LV. Spectroscopic,thermal studies,and coordination of metal ions N-[3-(5-amino-1,2,4-triazolo)] acrylamide polymer complexes

Novel polymeric complexes with a potentially bidentate ligand formed by amidation of 3,5-diamino-1,2,4-triazole with acryloyl chloride were synthesized and characterized on the basis of elemental analyses, IR, ¹H-NMR, UV-Vis, magnetic susceptibility measurements, molar conductance, and thermal analyses. The molar conductance data reveal that all the polymer complexes are non-electrolytes. Spectral studies reveal that the free ligand coordinates bidentate to the metal ion through the oxygen of the carbonyl and azomethine of the heterocyclic ring. Elemental analyses of the polychelates indicate the metal to ligand ratio of 1?:?1/1?:?2. On the basis of electronic spectral data and magnetic susceptibility measurements, suitable geometry has been proposed for each polymeric complex. The electron spin resonance spectral data of the Cu(II) complex showed that the metal–ligand bonds have considerable covalent character. The thermal behavior of these chelates shows that the polymer complexes lose coordinated water in the first step immediately followed by decomposition of the anions and ligand molecules in a subsequent step.