Julio Zukerman-Schpector

Luminescence and structure of europium compounds

Abstract Europium complexes in the +3 oxidation state, with coordination numbers six, seven, eight, nine and ten are under consideration. In most cases, single crystals or isomorphous compounds were studied by X-ray structural analyses. An attempt is made to correlate the results with the emission spectrum interpretation. Only articles containing both aspects are included in this review. Some general remarks concerning different coordination numbered complexes are also presented.

The importance of Pi-interactions in crystal engineering : frontiers in crystal engineering

Crystal engineers aim to control the way molecules aggregate in the crystalline phase and are therefore concerned with crystal structure prediction, polymorphism, and discovering the relative importance of different types of intermolecular forces and their influence on molecular structure. In order to design crystal structures, knowledge of the types, strengths, and nature of possible intermolecular interactions is essential. Non-covalent interactions involving p-systems is a theme that is under extensive investigation as these interactions can be inductors for the assembly of a vast array of supramolecular architectures.

Tellurium⋯π-aryl interactions: a new bonding motif for supramolecular self-assembly and crystal engineering

A search of the Cambridge Structural Database (CSD) was performed to identify Te⋯π-aryl interactions not reported before in the literature. The examination of the distance between tellurium atoms and aryl group centroids and the analysis of crystal packing, using deposited crystal structure data, produced a list of organotellurium compounds which showed a variety of Te⋯π bonding interactions. These include inter-ionic Te⋯π interactions in anion–cation ion pairs, intramolecular Te⋯π-aryl interactions in mono- and di-nuclear covalent molecular compounds, as well as in dimeric and tetrameric supermolecules or in supramolecular polymeric arrays formed through secondary bonds. Most interesting was the finding that intermolecular Te⋯π aryl interactions can connect molecular tectons, leading to supramolecular self-assembly with formation of dimeric and polymeric superstructures. Finally, Te⋯π aryl interactions may interconnect polymeric chains formed through Te⋯X secondary bonds into 2D and perhaps 3D networks. Thus, the Te⋯aryl interactions appear as a new bonding motif for supramolecular self-assembly, which could be exploited for crystal engineering in organotellurium chemistry, i.e. for the design of new materials with attractive useful properties.

Gold⋯π aryl interactions as supramolecular synthons

Au⋯π interactions whereby the electron-rich π-system of C6-aromatic rings interact with gold are shown to exist in the crystal structures of both gold(I) and gold(III) complexes, and have been revealed to occur between neutral/neutral, cationic/cationic, and cationic/anionic systems. Supramolecular aggregation facilitated by Au⋯π interactions leads to the formation of 0-dimensional aggregates, e.g. arising from an interaction between a gold complex and a solvent molecule, loosely associated spherical aggregates, e.g. cooperative interactions between centrosymmetrically related gold complexes, and even extended supramolecular polymeric chains of variable topology (e.g. linear, step ladder, and helical). The described Au⋯π interactions represent a new synthon in structural gold chemistry that should be considered in any complete analysis of their crystal structures.

Supramolecular architectures based on As(lone pair)⋯π(aryl) interactions

As(lone pair)···π interactions provide stability to their crystal structures often leading to supramolecular chains and prevailing over As···X secondary contacts. The interaction (ca 8 kJ mol(-1)) arises from polarisation induced in the aryl ring by the As-lone pair plus the weak sharing of these electrons with the ring-C atoms.

Supramolecular Self-Assembly Through Secondary Bonds in Organotellurium Chemistry

Abstract The solid state structures of organotellurium compounds, associated through secondary bonds, are presented in the light of supramolecular chemistry principles. Supramolecular self-assembly through secondary bonds occurs in organotellurium-nitrogen. -oxygen, -sulfur and -halogen compounds and leads to the formation of discrete supermolecules (e.g. dimers or tetramers) or infinite supramolecular arrays.

A Novel Asymmetric Total Synthesis of (+)-Artemisinin

Abstract A 12-step synthesis of the natural product (+)-Artemisinin, very active against malaria, is described. (-)-Isopulegol, which already contains two of the asymmetric centers of (+)-Artemisinin in the correct absolute configuration, was used as starting material.

What is a co-crystal?

Abstract What might very well be classified as a revolution in chemical crystallography is the emergence of crystal engineering as a discipline and the pivotal role X-ray crystallography plays in this [1]. Although dating back to the 1950s, the field has exploded in the last decade or so, and now is at the forefront of contemporary chemical and cognisant research. One of the areas in crystal engineering of greatest potential impact relates to the pharmaceutical industry – drug formulation and intellectual property – where issues relating to crystallisation, polymorphism, etc. are paramount [2]. A focus of these crystal engineering studies relates to the preparation of multi-component crystals, often referred to as co-crystals, where, for example utilizing hydrogen bonding synthons, active pharmaceutical ingredients are co-crystallised with other molecules [2]. The motivation for such studies is to improve stability (e.g. shelf-life), bioavailability (e.g. solubility), etc. [3].

The metal–carbonyl⋯π(aryl) interaction as a supramolecular synthon for the stabilisation of transition metal carbonyl crystal structures

M-carbonyl(lone pair)···π(aryl) interactions provide stability to their transition metal crystal structures. This supramolecular synthon usually leads to zero- or one-dimensional aggregation patterns; a rare example of a three-dimensional architecture based on the M-CO(lone pair)···π(aryl) synthon has also been revealed.

A structural survey of metal⋯π heteroaromatic supramolecular synthons for metal = tellurium, tin, and gold

A survey of tellurium, tin and gold structures containing metal⋯π heteroaromatic interactions has been conducted, and their occurrence correlated with previously described metal⋯π aryl interactions. Metal⋯π heteroaromatic interactions are found for all three metals when the heteroaromatic ring was a pyridine/pyridine-derivative, and these contacts lead usually to 0-D or 1-D aggregates with rare examples of 2-D and 3-D architectures. For each of tellurium and tin, metal⋯π aryl interactions are more likely to form over metal⋯π pyridine interactions, while the reverse is true in the case of gold. These observations are readily correlated with the influence of increasing electron density in the pyridine compared with an aryl ring. In the case of tellurium and tin, for which the metal⋯π interaction involves a metal-based lone pair of electrons being donated to the LUMO of the aryl group, increasing the electron density of the aromatic ring naturally decreases the probability of forming this type of interaction. In the case of gold, where the metal⋯π interaction involves the donation of electron density from the aromatic ring to the gold centre, increasing the electron density of the aromatic ring favours such an interaction. At least for the metals surveyed, metal⋯π interactions are observed in a significant number of their crystal structures, for example up to 6% of all tellurium structures feature Te⋯π aryl interactions as a supramolecular synthon.