Search for: All records

A molecular rotor is created when a 2,1,3‐benzothiadiazole rotator is incorporated into a rigid arylene ethynylene framework supported by pyridine coordination to a metal (Ag⁺or PdCl₂) guest. Comparisons to a similarly sized naphthyl rotator via¹H NMR spectroscopy provide insights into the movement of these bicyclic rotators relative to the rigid stator framework. Chemical shift increases of 0.3 ppm, or more, upon metal complexation are consistent with through‐space interaction of the central arene with a bound PdCl₂guest. Further study via X‐ray crystallography illustrates that rotation of the 2,1,3‐benzothiadiazole unit in the solid state is likely hampered by relatively strong chalcogen bonding (N⋅⋅⋅S distance of 2.93 Å), forming 2S‐2N squares between benzothiadiazoles of neighboring complexes. Strong π–π interactions (3.29–3.36 Å) between neighboring complexes likewise restrict solid‐state rotation of the potential benzothiadiazole rotator. Modest changes to UV–vis spectra upon metal coordination suggest that electronic properties are mostly independent of stator configuration.

 

Macrocycle formation that relies upontransmetal coordination of appropriately placed pyridine ligands within an arylene ethynylene construct provides rapid and reliable access to molecular rotators encapsulated within macrocyclic stators. Showing no significant close contacts to the central rotators, X‐ray crystallography of Ag^I‐coordinated macrocycles provides plausibility for unobstructed rotation or wobbling of rotators within the central cavity. Solid‐state¹³C NMR of Pd^II‐coordinated macrocycles supports the notion of unobstructed movement of simple arenes in the crystal lattice. Solution¹H NMR studies indicate complete and immediate macrocycle formation upon the introduction of Pd^IIto the pyridyl‐based ligand at room temperature. Moreover, the formed macrocycle is stable in solution; a lack of significant changes in the¹H NMR spectrum upon cooling to −50 °C is consistent with the absence of dynamic behavior. The synthetic route to these macrocycles is expedient and modular, providing access to rather complex constructs in four simple steps involving Sonogashira coupling and deprotection reactions.

 

The treatment of 5-{[4-(dimethylamino)phenyl]ethynyl}pyrimidine with a threefold excess of 1,2,3,5-tetrafluoro-4,6-diiodobenzene in dichloromethane solution led to the formation of the unexpected 1:2 title co-crystal, C 14 H 13 N 3 ·2CF 4 I 2 . In the extended structure, two unique C—I...N halogen bonds from one of the 1,2,3,5-tetrafluoro-4,6-diiodobenzene molecules to the pyrimidine N atoms of the 5-{[4-(dimethylamino)phenyl]ethynyl}pyrimidine molecule generate [110] chains and layers of these chains are π-stacked along the a- axis direction. The second 1,2,3,5-tetrafluoro-4,6-diiodobenzene molecule resides in channels formed parallel to the a -axis direction between stacks of 5-{[4-(dimethylamino)phenyl]ethynyl}pyrimidine molecules and interacts with them via C—I...π(alkyne) contacts. 

Co‐crystallization of a pyridyl‐containing arylethynyl (AE) moiety with 1,4‐diiodotetrafluorobenzene leads to unique, figure‐eight shaped helical motifs within the crystal lattice. A slight twist in the AE backbone allows each AE unit to simultaneously interact with haloarene units that are stacked on top of one another. Left‐handed (M) and right‐handed (P) helices are interspersed in a regular pattern throughout the crystal. The major driving forces for assembly are 1) halogen bonding between the pyridyl nitrogen atoms and the iodine substituents of the haloarene, with N⋅⋅⋅I distances between 2.81 and 2.84 Å, and 2) π‐π stacking of the haloarenes, with distances of approximately 3.57 Å between centroids. Halogen bonding and π‐π stacking not only work in concert, but also seem to mutually enhance one another. Calculations suggest that the presence of π‐π stacking modestly intensifies the halogen bonding interaction by <0.2 kcal/mol; likewise, halogen bonding to the haloarene enhances the π‐π stacking interaction by 0.59 kcal/mol.

 

[Bis(pyridine)iodine(I)]⁺complexes offer controlled access to halonium ions under mild conditions. The reactivity of such stabilized halonium ions is primarily determined by their three‐center, four‐electron [N−I−N]⁺halogen bond. We studied the importance of chelation, strain, steric hindrance and electrostatic interaction for the structure and reactivity of halogen bonded halonium ions by acquiring their¹⁵N NMR coordination shifts and measuring their iodenium release rates, and interpreted the data with the support of DFT computations. A bidentate ligand stabilizes the [N−I−N]⁺halogen bond, decreasing the halenium transfer rate. Strain weakens the bond and accordingly increases the release rate. Remote modifications in the backbone do not influence the stability as long as the effect is entirely steric. Incorporating an electron‐rich moiety close by the [N−I−N]⁺motif increases the iodenium release rate. The analysis of the iodine(I) transfer mechanism highlights the impact of secondary interactions, and may provide a handle on the induction of stereoselectivity in electrophilic halogenations.

 

The present study evaluates the potential combination of charge-transfer electron-donor–acceptor π–π complexation and C—H hydrogen bonding to form colored cocrystals. The crystal structures of the red 1:1 cocrystals formed from the isomeric pyridines 4- and 3-{2-[4-(dimethylamino)phenyl]ethynyl}pyridine with 1-[2-(3,5-dinitrophenyl)ethynyl]-2,3,5,6-tetrafluorobenzene, both C 14 H 4 F 4 N 2 O 4 ·C 15 H 14 N 2 , are reported. Intermolecular interaction energy calculations confirm that π-stacking interactions dominate the intermolecular interactions within each crystal structure. The close contacts revealed by Hirshfeld surface calculations are predominantly C—H interactions with N, O, and F atoms. 

1,3-Diiodo-5-nitrobenzene, C₆H₃I₂NO₂, and 1,3-dibromo-5-nitrobenzene, C₆H₃Br₂NO₂, crystallize in the centrosymmetric space groupP2₁/m, and are isostructural with 1,3-dichloro-5-nitrobenzene, C₆H₃Cl₂NO₂, that has been redetermined at 100 K for consistency. While the three-dimensional packing in all three structures is similar, the size of the halogen atom affects the nonbonded close contacts observed between molecules. Thus, the structure of 1,3-diiodo-5-nitrobenzene features a close Type 1 I...I contact, the structure of 1,3-dibromo-5-nitrobenzene features a self-complementary nitro-O...Br close contact, while the structure of 1,3-dichloro-5-nitrobenzene also has a self-complementary nitro-O...Cl interaction, as well as a bifurcated C—H...O(nitro) close contact. Notably, the major energetically attractive intermolecular interaction between adjacent molecules in each of the three structures corresponds to a π-stacked interaction. The self-complementary halogen...O(nitro) and C—H...O(nitro) interactions correspond to significant cohesive attraction between molecules in each structure, while the Type 1 halogen–halogen contact is weakly cohesive.

 

The rapid evaporation of 1:1 solutions of diethynylpyridines and N -halosuccinimides, that react together to form haloalkynes, led to the isolation of unreacted 1:1 cocrystals of the two components. The 1:1 cocrystal formed between 2,6-diethynylpyridine and N -iodosuccinimide (C 4 H 4 INO 2 ·C 9 H 5 N) contains an N -iodosuccinimide–pyridine I...N halogen bond and two terminal alkyne–succinimide carbonyl C—H...O hydrogen bonds. The three-dimensional extended structure features interwoven double-stranded supramolecular polymers that are interconnected through halogen bonds. The cocrystal formed between 3,5-diethynylpyridine and N -iodosuccinimide (C 4 H 4 INO 2 ·C 9 H 5 N) also features an I...N halogen bond and two C—H...O hydrogen bonds. However, the components form essentially planar double-stranded one-dimensional zigzag supramolecular polymers. The cocrystal formed between 3,5-diethynylpyridine and N -bromosuccinimide (C 4 H 4 BrNO 2 ·C 9 H 5 N) is isomorphous to the cocrystal formed between 3,5-diethynylpyridine and N -iodosuccinimide, with a Br...N halogen bond instead of an I...N halogen bond. 

This study expands and combines concepts from two of our earlier studies. One study reported the complementary halogen bonding and π-π charge transfer complexation observed between isomeric electron rich 4-N,N-dimethylaminophenylethynylpyridines and the electron poor halogen bond donor, 1-(3,5-dinitrophenylethynyl)-2,3,5,6-tetrafluoro-4-iodobenzene while the second study elaborated the ditopic halogen bonding of activated pyrimidines. Leveraging our understanding on the combination of these non-covalent interactions, we describe cocrystallization featuring ditopic halogen bonding and π-stacking. Specifically, red cocrystals are formed between the ditopic electron poor halogen bond donor 1-(3,5-dinitrophenylethynyl)-2,4,6-triflouro-3,5-diiodobenzene and each of electron rich pyrimidines 2- and 5-(4-N,N-dimethyl-aminophenylethynyl)pyrimidine. The X-ray single crystal structures of these cocrystals are described in terms of halogen bonding and electron donor-acceptor π-complexation. Computations confirm that the donor-acceptor π-stacking interactions are consistently stronger than the halogen bonding interactions and that there is cooperativity between π-stacking and halogen bonding in the crystals.