Search results for " Crystal"
showing 10 items of 3073 documents
Multivalent N-donor ligands for the construction of coordination polymers and coordination polymer gels
2018
This work describes the synthesis and characterisation of several multivalent N-donor ligands and their coordination compounds and the use of these ligands in the construction of coordination polymers and coordination polymer gels. The project can be divided into two parts. The first part of the research is focused on the coordination chemistry of ring-substituted biimidazoles in acidic media. The dependence of the formation of ion pairs and zwitterionic, especially zinc and copper containing coordination compounds on the pH of the reaction medium and ring-substituents of the ligand were examined. The second part of the study deals with the preparation of Ag, Zn and Cu coordination polymers…
The Effect of the Side Chain on Gelation Properties of Bile Acid Alkyl Amides
2021
Abstract Six bile acid alkyl amide derivatives were studied with respect to their gelation properties. The derivatives were composed of three different bile acids with hexyl or cyclohexyl side chains. The gelation behaviour of all six compounds were studied for 36 solvents with varying polarities. Gelation was observed mainly in aromatic solvents, which is characteristic for bile‐acid‐based low molecular weight gelators. Out of 108 bile acid‐solvent combinations, a total of 44 gel systems were formed, 28 of which from lithocholic acid derivatives, only two from deoxycholic acid derivatives, and 14 from cholic acid derivatives. The majority of the gel systems were formed from bile acids with…
Structure and optical properties of a monolayer single crystal of a cyanine dye
1992
Abstract Molecularly thin single crystals of a cyanine dye prepared by adsorption at a charged surfactant monolayer are studied by polarized optical spectroscopy and electron diffraction. Both techniques independently show a herringbone arrangement of the dye with the long axes of translationally inequivalent molecules forming an angle of 80°. The dye arranges in a primitive rectangular unit cell (a=21.2 A, b=6.14 A) adjacent to an epitaxially related hexagonal cell of the aliphatic tails of the surfactant.
Iodine(I) and Silver(I) Complexes of Benzoimidazole and Pyridylcarbazole Derivatives
2021
The synthesis of iodine(I) complexes with either benzoimidazole or carbazole-derived sp 2 N -containing Lewis bases is described, as well as their corresponding silver(I) complexes. The addition of elemental iodine to the linear two-coordinate Ag(I) complexes produces iodine(I) complexes with a three-center four-electron (3c-4e) [N — I — N] + bond. The 1 H and 1 H- 15 N HMBC NMR studies unambiguously confirm the formation of the complexes in all cases via the [N — Ag — N] + → [N — I — N] + cation exchange, with the 15 N NMR chemical shift change between 94 to 111 ppm when compared to the free ligand. The single crystal X-ray crystallographic studies on four I + complexes revealed highly sym…
Design and construction of halogen-bonded capsules and cages
2017
This thesis describes the design, synthesis and characterization of supramolecular halogen-bonded capsules and cages from multivalent ligands. In the first part of the thesis, an overview to halogen bonding is provided. After discussing the general features of the halogen bonding, the most frequently used halogen bond donors are introduced and examples of their utilization in halogen-bonded systems are discussed. The chapter also presents recent advances made in the field of halogen-bonded supramolecular capsules. The first part of the thesis also includes a review of halogen-bonded complexes involving halonium ions, and a brief introduction to [N···X+···N] halogen bonds is provided along w…
Very strong −N–X+⋯−O–N+ halogen bonds
2016
A new (-)N-X(+)(-)O-N(+) paradigm for halogen bonding is established by using an oxygen atom as an unusual halogen bond acceptor. The strategy yielded extremely strong halogen bonded complexes with very high association constants characterized in either CDCl3 or acetone-d6 solution by (1)H NMR titrations and in the solid-state by single crystal X-ray analysis. The obtained halogen bond interactions, RXB, in the solid-state are found to be in the order of strong hydrogen bonds, viz. RXB ≈ RHB.
Low temperature heat capacity of phononic crystal membranes
2016
Phononic crystal (PnC) membranes are a promising solution to improve sensitivity of bolometric sensor devices operating at low temperatures. Previous work has concentrated only on tuning thermal conductance, but significant changes to the heat capacity are also expected due to the modification of the phonon modes. Here, we calculate the area-specific heat capacity for thin (37.5 - 300 nm) silicon and silicon nitride PnC membranes with cylindrical hole patterns of varying period, in the temperature range 1 - 350 mK. We compare the results to two- and three-dimensional Debye models, as the 3D Debye model is known to give an accurate estimate for the low-temperature heat capacity of a bulk sam…
Comment on "Crystallographic Snapshot of an Arrested Intermediate in the Biomimetic Activation of CO2"
2015
Out of focus: A recent Communication published in this journal describes the synthesis of [nBu4N]HCO3. The authors performed a single-crystal X-ray study that revealed a putative species described as an incipient hydroxide ion engaging in a long, and presumably weak, interaction with CO2. Our recent exploration of the coordination chemistry of CO2 with small ions leads us to believe that such an exceptional bonding situation is unlikely. Instead, we argue that the crystal structure is that of [nBu4N]O2CCH3 and therefore not representative of the bulk powder from the synthesis. peerReviewed
Comment on “Crystallographic Snapshot of an Arrested Intermediate in the Biomimetic Activation of CO2”
2015
Out of focus: A recent Communication published in this journal describes the synthesis of [nBu4 N]HCO3 . The authors performed a single-crystal X-ray study that revealed a putative species described as an incipient hydroxide ion engaging in a long, and presumably weak, interaction with CO2 . Our recent exploration of the coordination chemistry of CO2 with small ions leads us to believe that such an exceptional bonding situation is unlikely. Instead, we argue that the crystal structure is that of [nBu4 N]O2 CCH3 and therefore not representative of the bulk powder from the synthesis.
Recognition of alkali metal halide contact ion pairs by uranyl-salophen receptors bearing aromatic sidearms. The role of cation-pi interactions.
2005
Hard anions have long been known to bind strongly to the uranium of uranyl-salophen complexes. Upon functionalization of the salophen framework with one or two benzyloxy substituents, efficient ditopic receptors for alkali metal ions are obtained. The solid-state structures of complexes formed by the two-armed receptor 1 with CsF and with the chlorides of K+, Rb+, and Cs+ reported here reveal the existence of dimeric supramolecular assemblies in which two receptor units assemble into capsules fully enclosing (MX)2 ion quartets. In addition to the strong coordinative binding of the anion to the uranyl center and to electrostatic cation-anion interactions, stabilizing interactions arise from …