Two-dimensional Supramolecular Assemblies Research Articles

Supramolecular Nanostructure of Porphyrin Diacid on Sulfate/Bisulfate Adlayer Formed on Au(111)

Cationic tetraphenyl porphyrin with two carboxyphenyl moieties in cis-position (cis-H4DCPP2+) was investigated to control the structure of the two-dimensional supramolecular assembly in 0.05 M H2SO4. In situ scanning tunneling microscopy (STM) images revealed the formation of supramolecularly organized nanostructures of cis-H4DCPP2+ such as dimer, trimer, and tetramer on the (√3 × √7) sulfate/bisulfate (SO42-/HSO4-) adlayer, suggesting the importance of both electrostatic interaction between cationic porphyrin core and SO42-/HSO4- adlayer and the hydrogen bond formation between carboxyl groups of the nearest neighbor cationic porphyrins. In contrast, when 0.1 M HClO4 was used as an electrolyte solution, only a disordered array was observed. The results indicate that the (√3 × √7) SO42-/HSO4- adlayer formed on Au(111) plays a significant role as a template in the control of electrostatically assembled cis-H4DCPP2+.

Synthesis, crystal structures and luminescent properties of phenylmercury(II) complexes with thiohydrazone ligands having weak Hg····π and Hg····Hg interactions

The Reaction of phenylmercury(II) acetate with salicylaldehyde morpholine N-thiohydrazone (H 2smth) and 2-hydroxyacetophenone morpholine N-thiohydrazone (H 2apmth) in dry ethanol under gentle refluxing condition form light yellow complexes [PhHg(Hsmth)] ( 1) and [PhHg(Hapmth)] ( 2) involving formation of Hg-S bond from the thiol form of the ligands after deprotonation of the SH proton. The structures of the complexes as determined by X-ray crystallography shows that the complex ( 1) has a distorted T-shaped geometry while the complex ( 2) adopts familiar linear coordination geometry. Complex ( 2) has two independent molecules comprising the asymmetric unit. Both the complexes form two-dimensional supramolecular assemblies due to a combination of weak intermolecular Hg····π and Hg····Hg interactions. The Hg····π and Hg····Hg distances are 3.937 and 4.0216(10) Å, respectively, possibly indicating weak mercuriophilic interactions. The luminescent properties of the complexes in solution and in the solid state at room temperature are also described.

Two-dimensional supramolecular assembly of phenylmercury(II) and cadmium(II) complexes with a tridentate thiohydrazone NNS donor ligand: Synthesis, coordination behavior and crystal structure

The reaction of phenylmercury(II) acetate and cadmium(II) acetate with a refluxed solution of diacetylmonoxime and morpholine N-thiohydrazide formed a novel phenylmercury(II) complex, [PhHg(Hdammthiol)] ( 1) and a cadmium(II) complex, [Cd(Hdammthiol) 2] ( 2), respectively (where H 2dammthiol is the thiol form of diacetylmonoximemorpholine N-thiohydrazone (Hdammth) formed by the condensation of diacetylmonoxime and morpholine N-thiohydrazide in the presence of phenylmercury(II) and cadmium(II) ions). The complexes were characterised by elemental analyses and spectral data (electronic, infrared and 1H NMR) and also by X-ray crystal structure analysis. The X-ray crystallography shows that the phenylmercury(II) complex attained a tricoordinated distorted T-shaped structure, while the cadmium(II) complex attained a trapezoidal bipyramidal geometry. The phenylmercury(II) complex forms a two-dimensional sheet via C–H⋯O and O–H⋯N hydrogen bonding and also forms a two-dimensional supramolecular dimer, having C–H⋯π synthons. Intermolecular C–H⋯O and O–H⋯O hydrogen bonding of the cadmium(II) complex forms a two-dimensional supramolecular sheet along the bc plane and posses an impressively short intermolecular C(sp 3)⋯O(sp 3) contact.

Halogen bonded two-dimensional supramolecular assemblies studied by high resolution scanning tunneling microscopy

We described the formation of self-organized two-dimensional (2D) assemblies of N-(2,3,5,6-tetrafluoro-4-iodophenyl)hexadecylamine and 1-dodecyl-imidazole at the liquid/HOPG interface. The two-dimensional assemblies showed a fishbone-like pattern structure as revealed by high-resolution scanning tunneling microscopy. Although different interactions can drive the formation of 2D assemblies, as far as we know, this is the first report on halogen bond-driven 2D assemblies.

The nature of supramolecular interactions in tetrakis(4-iodophenyl)porphyrin and its zinc(II) complex

Crystals of tetrakis(4-iodophenyl)porphyrin chloroform 0.85-solvate, C(44)H(26)I(4)N(4) x 0.85CHCl(3), (I), and [tetrakis(4-iodophenyl)porphyrinato]zinc(II), [Zn(C(44)H(24)I(4)N(4))], (II), reveal different modes of supramolecular organization. I...I attractions provide a significant contribution to the layered interporphyrin arrangement in (I), wherein all molecules have the same orientation. Weak axial coordinations of the I atoms to the Zn centres appear to have a dominant effect on the formation of two-dimensional supramolecular assemblies in (II), with a herring-bone arrangement of the metalloporphyrin species. Both molecules are located on inversion centres.

Nucleoside-based organogelators: gelation by the G–G base pair formation of alkylsilylated guanosine derivatives

2′,3′- O-Isopropylideneguanosine derivatives 1a– c having a bulky alkylsilyl moiety showed excellent gelation ability in alkane solvents. IR spectra of the gel clearly showed the absence of hydrogen bonding interaction at the C(6) O position and, together with a CD study, a G–G base pair formation by double N(2)H⋯N(3) and additional N(2)H⋯O(2′) hydrogen bonds was indicated. X-ray diffraction and SEM studies of the xerogel and AFM observation of the transferred gel suggested the formation of a two-dimensional supramolecular assembly 2 nm in thickness. The G–G base pair formation is discussed in terms of the molecular packing in the two-dimensional assemblies.

Coexistence of one- and two-dimensional supramolecular assemblies of terephthalic acid on Pd(111) due to self-limiting deprotonation

The adsorption of terephthalic acid [C(6)H(4)(COOH)(2), TPA] on a Pd(111) surface has been investigated by means of scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy, and near-edge x-ray absorption fine structure spectroscopy under ultrahigh vacuum conditions at room temperature. We find the coexistence of one- (1D) and two-dimensional (2D) molecular ordering. Our analysis indicates that the 1D phase consists of intact TPA chains stabilized by a dimerization of the self-complementary carboxyl groups, whereas in the 2D phase, consisting of deprotonated entities, the molecules form lateral ionic hydrogen bonds. The supramolecular growth dynamics and the resulting structures are explained by a self-limiting deprotonation process mediated by the catalytic activity of the Pd surface. Our models for the molecular ordering are supported by molecular mechanics calculations and a simulation of high resolution STM images.

Palladium(II) Complexes of the Thiosemicarbazone andN-Ethylthiosemicarbazone of 3-Hydroxypyridine-2-carbaldehyde: Synthesis, Properties, and X-Ray Crystal Structure

Two novel, stable PdII complexes, compounds 3 and 4, of two 3-hydroxypyridine-2-carbaldehyde thiosemicarbazones, 1 and 2, resp., were prepared from Li2PdCl4. The single-crystal X-ray structure of complex 3 (= [Pd(2)Cl]) shows that the ligand monoanion coordinates in a planar conformation to the metal via the pyridyl N-, the imine N-, and the thiolato S-atoms. Intermolecular H-bonds, π–π, and CH ⋅ ⋅ ⋅ π interactions lead to a two-dimensional supramolecular assembly. The electronic, IR, UV/VIS, and NMR spectroscopic data of the two complexes are reported, together with their electrochemical properties. A sophisticated experimental procedure was used to determine the multiple dissociation constants of the ligands 1 and 2 by UV/VIS titration.

Intra and intermodular exchange interactions in bis(α-aminoisobutyrato)oxalamidodicopper(Aib-COCO-Aib)Cu 2

Magnetic susceptibility and electron paramagnetic resonance (EPR) spectra of exquisite two-dimensional supramolecular assembly of [bis(α-aminoisobutyrato)oxalamidodicopper](Aib-COCO-Aib)Cu 2 were studied. The temperature dependent magnetic susceptibility studies reveal temperature dependency of the exchange coupling constant. Single crystal EPR studies both at X- and Q-bands show the two-dimensional nature of magnetic lattice and yield the weak intermodular exchange coupling constant in presence of strong intramodular exchange. The intermodular coupling is about five orders of magnitude smaller than the intramodular coupling but it produces a broadening and coalescence of the EPR lines. The temperature dependence of exchange coupling constant reflects dynamical properties of the crystal lattice.

Platinum(II) complexes with 2-acetyl pyridine thiosemicarbazone. Synthesis, crystal structure, spectral properties, antimicrobial and antitumour activity.

An interesting series of new platinum complexes has been synthesized by the reaction of Na(2)PtCl(4) with 2-acetyl pyridine thiosemicarbazone, HAcTsc. The new complexes, [Pt(AcTsc)Cl], [Pt(HAcTsc)(2)]Cl(2) and [Pt(AcTsc)(2)], have been characterized by elemental analyses and spectroscopic studies. The crystal structure of the complex [Pt(AcTsc)Cl] has been solved by single-crystal X-ray diffraction. The anion of HAcTsc coordinates in a planar conformation to the central platinum(II) through the pyridyl N, azomethine N and thiolato S atoms. Double intermolecular hydrogen bonds (NH-Cl), pi-pi and weak Pt-Pt and Pt-pi contacts lead to aggregation and to a two-dimensional supramolecular assembly. The antibacterial and antifungal effect of the novel platinum(II) complexes and the related palladium(II) complexes, [Pd(AcTsc)Cl], [Pd(HAcTsc)(2)]Cl(2) and [Pd(AcTsc)(2)], were studied in vitro. The complexes were found to have a completely lethal effect on Gram+ bacteria, while the same complexes showed no bactericidal effect on Gram- bacteria. Additionally, the complexes [Pt(AcTsc)(2)] and [Pd(AcTsc)(2)] showed effective antifungal activity towards yeast. Among these compounds [33], the most effective in inducing antitumour and cytogenetic effects are the complexes [Pt(AcTsc)(2)] and [Pd(AcTsc)(2)] while the rest, display marginal cytogenetic and antitumour effects.

Two-Dimensional Supramolecular Assemblies of a Polydiacetylene. 1. Synthesis, Structure, and Third-Order Nonlinear Optical Properties

A diacetylene monomer with a rigid backbone and capable of forming hydrogen bonds was synthesized and found to polymerize forming two-dimensional supramolecular assemblies. The two-dimensional structure self-assembles when UV light generates polydiacetylene comb polymers, and hydrogen bonds are established within molecular layers. The two-dimensional assemblies have been characterized by X-ray diffraction and infrared spectroscopy and found to consist of highly ordered bilayers. The material forms blue solid thin films which generate third-order nonlinear optical signals and have remarkable photochemical stability to 1064 nm radiation from a Q-switched Nd:YAG laser. Upon heating to 62 °C, the material turns bright red reversibly while maintaining its two-dimensional structure, and this thermochromic process is accompanied by endothermic and exothermic signatures detected by differential scanning calorimetry. Most importantly, however, variable temperature sum frequency generation experiments show that the...

Tailoring of stacked π-electron arrays from electron—and/or energy donor—acceptor molecules based on two-dimensional supramolecular assemblies

A newly proposed ‘crystal engineering’ based on two-dimensional supramolecular assemblies, e.g. bilayer membranes, is shown to be quite useful for tailoring stacked π-electron arrays which are applicable to molecular photonics devices of long-range energy and/or electron transportation. Formation and migration of single excitons through π-electron arrays of stilbene chromophores and failoring of charge transfer complexes of viologen amphiphiles are described as successful examples of the two—dimensional ‘crystal engineering’ for constructing stacked π-electron arrays directing photoinduced electron transfer. Molecular-recognition-directed assembling of nucleic acid—base pairs at the air/water interface is shown to be another method of tailoring stacked π-electron arrays.

Two-dimensional assembly of functionalized 4-aryl-1-alkenyl-3,5-dioxo-1,2,4-triazolidines

Acid functionalized derivatives of 4-aryl-1-alkenyl-3,5-dioxo-1,24-triazolidines (4-arylurazoles), i.e. 4-(-but-1-en-3-yl-3, 5-dioxo-1,2,4-triazolidin-4-yl) benzoic acid ( 1), 4-urazoyl benzamide, i.e. 4-(1-but-1-en-3-yl-3, 5-dioxo-1,2,4-triazolidin-4-yl) benzamide ( 2), and 4-urazoylphenylazobenzoic acid, i.e. 4-(1-but-1-en-3-yl-3, 5-dioxo-1,2,4-triazolidin-4-yl) phenylazobenzoic acid ( 3), organize into two-dimensional supramolecular assemblies via intermolecular hydrogen bonding. Hydrogen bonds are formed between two acid (or amide) and two urazole groups, as well as between a carbonyl group of the urazole heterocycle and a hydrogen atom of the phenyl ring. These two-dimensional layers also persist if the polar groups are attached randomly to flexible polybutadiene chains.