A carefully designed strategy is presented for the construction of ternary cocrystals, based on the orthogonality of two supramolecular interaction modes: hydrogen bonding between crown ethers and ...thioureas and the halogen bonding between thioureas and perfluorohalocarbons. Tested on a set comprising two crown ethers, two thioureas and five halogen bond donors, the strategy resulted in a high, 75% success rate, with 15/20 component combinations yielding at least one cocrystal. Crystal structure analysis revealed the interplay between the hydrogen and halogen bonding motifs, also shedding light on the variables affecting their formation.
Alternative Motifs for Halogen Bonding Troff, Ralf W.; Mäkelä, Toni; Topić, Filip ...
European journal of organic chemistry,
March 2013, Letnik:
2013, Številka:
9
Journal Article
Recenzirano
The halogen‐bonding interaction is one of the rising stars in supramolecular chemistry. Although other weak interactions and their influence on the structure and chemistry of various molecules, ...complexes and materials have been investigated thoroughly, the field of halogen bonding is still quite unexplored and its impact on chemistry in general is yet to be fully revealed. In principle, every Y–X bond (Y = electron‐withdrawing atom or moiety, X = halogen atom) can act as a halogen‐bond donor when the halogen is polarized enough by Y. Perfluorohalocarbons are iconic halogen‐bond donor molecules in which Y is a perfluorinated aryl or alkyl moiety and X is either iodine or bromine. In this article, alternative halogen‐bond motifs such as X2···A and Ar–X···A A = Lewis basic halogen‐bond‐accepting atom of a molecule or ion; Ar = neutral or charged (hetero)aromatic system are reviewed. In addition, haloalkenes, haloalkynes, N‐haloamides and other non‐metallic halogen‐bond donors and their respective halogen‐bonded structures will also be described. Although purely organic halogen‐bonding motifs are very prominent, the role of metal complexes in halogen bonding is becoming increasingly evident as well, which is also reflected in this review. Finally, halogen bonding in solution is briefly highlighted. Contemporary research is proving that halogen bonding is more than a solid‐state phenomenon and is now a well‐recognized weak interaction in chemistry.
Halogen bonding is an attractive non‐covalent interaction between an electrophilic halogen donor atom and a nucleophilic acceptor atom. The figure depicts halogen bonds between the electrophilic iodine atoms of four N‐iodosuccinimide (NIS) molecules and the nucleophilic nitrogen atoms of hexamethylenetetraamine (HMTA).
Two novel heterobimetallic complexes, a trigonal-bipyramidal and a cubic one, have been synthesized and characterized using the same C 3-symmetric metalloligand, prepared by a simple subcomponent ...self-assembly strategy. Adopting the molecular library approach, we chose a mononuclear, preorganized iron(II) complex as the metalloligand capable of self-assembly into a trigonal-bipyramidal or a cubic aggregate upon coordination to cis-protected C 2-symmetric palladium(II) or unprotected tetravalent palladium(II) ions, respectively. The trigonal-bipyramidal complex was characterized by NMR and UV–vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and single-crystal X-ray diffraction. The cubic structure was characterized by NMR and UV–vis spectroscopy and ESI-MS.
The first enantiomerically pure members of the cucurbituril family, (all-S)- and (all-R)-cyclohexylhemicucurbit6urils (cycHC), were synthesized in good yield (up to 85%). The crystal structure of ...this new macrocycle clearly shows its ball-like shape. CycHC monomers adopt a “zigzag” conformation, having apolar cyclohexyls around the openings and polar ureas in the middle. Cyclohexylhemicucurbit6urils formed complexes with halides, carboxylic acids and amines and diastereomeric complexes with methoxyphenylacetic acid in organic media. The association constants of cycHC with small organic compounds were evaluated by diffusion NMR in chloroform.
An enantiomerically pure BINOL‐based bis(3‐pyridyl) ligand 1 assembles into a homochiral Pd4(1)8 complex upon coordination to tetravalent PdII ions. The formation of this aggregate is templated by ...two tetrafluoroborate counterions that are encapsulated in two peripheral cavities. The resulting structure is a new structural motif for this kind of metallosupramolecular assemblies that arranges the palladium ions in a distorted tetrahedral fashion and forces ligand 1 to adopt two different conformations. Both phenomena are unique and cause an overall three‐dimensional structure that has another confined, chiral, and hydrophilic central cavity.
Close association: A BINOL‐based bis(3‐pyridyl) ligand assembles into a Pd4L8 complex upon coordination to PdII ions. The formation of the aggregate is templated by two BF4− ions that are encapsulated in peripheral cavities. The palladium ions are arranged in a distorted tetrahedral fashion, which forces the ligand to adopt two different conformations (see picture).
Cocrystallization of a cis-azobenzene dye with volatile molecules, such as pyrazine and dioxane, leads to materials that exhibit at least three different light-intensity-dependent responses upon ...irradiation with low-power visible light. The halogen-bond-driven assembly of the dye cis-(p-iodoperfluorophenyl)azobenzene with volatile halogen bond acceptors produces cocrystals whose light-induced behavior varies significantly depending on the intensity of the light applied. Low-intensity (<1 mW·cm–2) light irradiation leads to a color change associated with low levels of cis → trans isomerization. Irradiation at higher intensities (150 mW·mm–2) produces photomechanical bending, caused by more extensive isomerization of the dye. At still higher irradiation intensities (2.25 W·mm–2) the cocrystals undergo cold photocarving; i.e., they can be cut and written on with micrometer precision using laser light without a major thermal effect. Real-time Raman spectroscopy shows that this novel photochemical behavior differs from what would be expected from thermal energy input alone. Overall, this work introduces a rational blueprint, based on supramolecular chemistry in the solid state, for new types of crystalline light-responsive materials, which not only respond to being exposed to light but also change their response based on the light intensity.
Metallosupramolecular systems heavily rely on the correct choice of ligands to obtain materials with desired properties. Engaging this problem, we present three ligand systems and six of their mono- ...and dinuclear complexes, based on the subcomponent self-assembly approach using electron-deficient pyridylcarbaldehyde building blocks. The properties are examined in solution by NMR and UV–vis spectroscopy and CV measurements as well as in solid state by single crystal X-ray diffraction analysis. Ultimately, the choice of ligands allows for fine-tuning of the electronic properties of the metal centers, complex-to-complex transformations, as well as establishing distinct anion−π-interaction motifs.
As long as 50 years ago theoretical calculations predicted that Möbius annulenes with only one π surface and one edge would exhibit peculiar electronic properties and violate the Hückel rules. ...Numerous synthetic attempts notwithstanding, the first singly twisted Möbius annulene was not prepared until 2003. Here we present a general, rational strategy to synthesize triply or even more highly twisted cyclic π systems. We apply this strategy to the preparation of a triply twisted 24dehydroannulene, the structure of which was confirmed by X-ray analysis. Our strategy is based on the topological transformation of 'twist' into 'writhe'. The advantage is twofold: the product exhibits a lower degree of strain and precursors can be designed that inherently include the writhe, which, after cyclization, ends up in the Möbius product. With our strategy, triply twisted systems are easier to prepare than their singly twisted counterparts.
A tris(bipyridine) ligand 1 with two BINOL (BINOL = 2,2′-dihydroxy-1,1′-binaphthyl) groups has been prepared in two enantiomerically pure forms. This ligand undergoes completely diastereoselective ...self-assembly into D 2-symmeteric double-stranded trinuclear helicates upon coordination to copper(I) and silver(I) ions and to D 3-symmetric triple-stranded trinuclear helicates upon coordination to copper(II), zinc(II), and iron(II) ions as demonstrated by mass spectrometry, NMR and CD spectroscopy in combination with quantum chemical calculations and X-ray diffraction analysis. According to the calculations, the single diastereomers that are formed during the self-assembly process are strongly preferred compared to the next stable diastereomers. Due to this strong preference, the self-assembly of the helicates from racemic 1 proceeds in a completely narcissistic self-sorting manner with an extraordinary high degree of self-sorting that proves the power and reliability of this approach to achieve high-fidelity diastereoselective self-assembly via chiral self-sorting to get access to stereochemically well-defined nanoscaled objects. Furthermore, mass spectrometric methods including electron capture dissociation MS n experiments could be used to elucidate the redox behavior of the copper helicates.
Two isostructural ligands with either nitrile (Lnit) or isonitrile (Liso) moieties directly connected to a 2.2paracyclophane backbone with pseudo‐meta substitution pattern have been synthesized. The ...ligand itself (Lnit) or its precursors (Liso) were resolved by HPLC on a chiral stationary phase and the absolute configuration of the isolated enantiomers was assigned by XRD analysis and/or by comparison of quantum‐chemical simulated and experimental electronic circular dichroism (ECD) spectra. Surprisingly, the resulting metallosupramolecular aggregates formed in solution upon coordination of (dppp)Pd(OTf)2 differ in their composition: whereas Lnit forms dinuclear complexes, Liso exclusively forms trinuclear ones. Furthermore, they also differ in their chiral self‐sorting behavior as (rac)‐Liso undergoes exclusive social self‐sorting leading to a heterochiral assembly, whereas (rac)‐Liso shows a twofold preference for the formation of homochiral complexes in a narcissistic self‐sorting manner as proven by ESI mass spectrometry and NMR spectroscopy. Interestingly, upon crystallization, these discrete aggregates undergo structural transformation to coordination polymers, as evidenced by single‐crystal X‐ray diffraction.
Two isostructural ligands with either nitrile (Lnit) or isonitrile (Liso) moieties attached to a 2.2paracyclophane backbone have been synthesized. Surprisingly, the resulting discrete metallosupramolecular aggregates formed in solution upon coordination of (dppp)Pd(OTf)2 differ in their composition and in their chiral self‐sorting behavior. Upon crystallization these discrete aggregates undergo structural transformation to coordination polymers.
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