Bildiing und kristallstruktur des (complexes [(18-Krone-6)(CH₂Cl₂)₂] / Formation and Crystal Structure of the Complex [(18-Crown-6)(CH₂Cl₂)₂]

Abstract

Einleitung

Geometries, interaction energies and complexation free energies of 18-crown-6 with neutral molecules

“…All have C s symmetry, with the methylene hydrogen atoms situated asymmetrically above the ring; the shortest methylene-H•••O distances are all considerably shorter than the respective sum Complexation energies for this family of guests are all substantial, those for malononitrile and dinitromethane being the greatest in the present study. Free energies are negative for this family, in agreement with the observation of the 18C6:(guest) 2 motif in crystals with dichloromethane 11 and malononitrile, 8 and indicating that the complexes with difluoromethane and dinitromethane should also be observable.…”

“…However, the ability to bind neutral molecules is one of the most important properties of crown ethers; 18-crown-6 (18C6), one of the most common crown ethers, is well known for its ability to form stable and ordered complexes with a vast number of neutral molecules possessing structural elements -OH, -CH 3 and -XH 2 (X = N, C) in the solid state. 7 These range from common solid-state neutral molecules such as malononitrile 8 and urea 9 to low vapour pressure solvents such as acetonitrile, 10 and dichloromethane, 11 and gases such as ammonia. 12 The fact that the corresponding crystals formed by these host : guest complexes are stable implies strong binding affinities, and these form the focus of the present study.…”

Supramolecular Assemblies Involving Organometallic Free Acids

“…The 18-crown-6 molecule adopts a typical crown conformation, in which the acid moieties of the Hsal ligands hydrogen bond to four of the ether oxygens in a 1,4,10,13-substitution pattern. A large number of structures of the 18-crown-6 macrocycle exist, some of which hydrogen bond to water and small organic molecules. − Typically, in structures of non-hydrogen-bonded and non-metal-coordinated 18-crown-6 molecules, dihedrals are observed to be 60° around the C−C bonds and 180° around the C−O bonds. , This lends the macrocycle its characteristic shape with the oxygen atoms oriented toward the interior of the structure. This orientation is largely maintained in the [W(η 2 -Ph 2 C 2 )Cl 3 (Hsal)···] 4 (18-crown-6) complex, in which all of the atoms in the 18-crown-6 show a 0.248(40) Å RMS deviation from planarity.…”

“…A large number of structures of the 18-crown-6 macrocycle exist, some of which hydrogen bond to water and small organic molecules. [66][67][68][69][70][71][72] Typically, in structures of non-hydrogen-bonded and non-metal-coordinated 18-crown-6 molecules, dihedrals are observed to be 60°around the C-C bonds and 180°a round the C-O bonds. 73,74 This lends the macrocycle its characteristic shape with the oxygen atoms oriented toward the interior of the structure.…”

“…This orientation is largely maintained in the [W(η 2 -Ph 2 C 2 )Cl 3 (Hsal)‚‚‚] 4 -(18-crown-6) complex, in which all of the atoms in the 18-crown-6 show a 0.248(40) Å RMS deviation from planarity. Like the hydrogen bonds in hydrates, chloroform, and chloroacetonitile adducts of 18-crown-6, 67,68,71,72 the hydrogen-bonding interactions in 5 are not bifurcated but exhibit standard O‚‚‚O distances averaging 2.51(1) Å. The hydrogen-bonding interactions pull the ether oxygens slightly farther than normal out of the interior of the ring, which may be responsible for the slight observed increase in the O-C-C-O torsional angles to 64.1°(average).…”