Hydrates of Weak and Strong Bases. 12. 18-Crown-6 and Water: Crystal Structure of a Binary Hydrate.

Mootz, D.; Albert, A.; Schaefgen, Sigrid; Staeben, Dieter

doi:10.1021/ja00105a052

Cited by 58 publications

(41 citation statements)

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“…Among these, the hydrogen bonded species are of particular interest. For the prototypic crown ether [18]-crown-6, a large number of watercontaining, hydrogen-bonded solvates with the common formula [18]-crown-6 Á x H 2 O (x ¼ 4, 4.5, 6,8,12) are known [1][2][3][4]. Another sub-class of supramolecular compounds of cyclic polyethers with neutral molecules are complexes with Lewis acids like [SbF 3 ([18]-crown-6)] [5] or [SbF 3 ([14]-crown-4)] [6].…”

Section: Introductionmentioning

confidence: 99%

Crystal structures of the [18]-crown-6 ammoniate C₁₂H₂₄O₆ · 2 NH₃ and the cryptand [2.2.2] ammoniate C₁₈H₃₆O₆N₂ · 2 NH₃

Suchentrunk¹,

Rossmeier²,

Korber³

2006

Zeitschrift Für Kristallographie - Crystalline Materials

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Supramolecular chemistry / Hydrogen bond / Low temperature crystal structure analysis / Ammonia / Crown ether / Cryptand / X-ray diffraction / Single crystal structure analysis Abstract. The crystal structures of the new polyether ligand-ammoniates C 12 H 24 O 6 Á 2 NH 3 (1) and C 18 H 36 O 6 N 2 Á 2 NH 3 (2) have been elucidated at 123 K by single crystal X-ray structure analysis. Compound 1 crystallizes as yellow plate-like crystals in the monoclinic space group P2 1 /c (no. 14) with unit cell parameters a ¼ 7.572(4) A, b ¼ 7.724(4) A and c ¼ 14.448(7) A with an angle b ¼ 91.79(6) . It consists of a molecule of [18]-crown-6 to which two ammonia molecules of crystallisation are bound by three hydrogen bonds each. The ammonia molecules reside below and above the plane of the crown ether oxygen atoms. Compound 2 crystallizes as colourless isometric crystals in the space group P6 3 22 (no. 182) with unit cell parameters a ¼ 8.2568(5) A and c ¼ 18.992(2) A. It consists of molecules of cryptand [2.2.2] which are connected by hydrogen bonds via ammonia molecules of crystallisation, resulting in two-dimensional layers parallel to the ab-plane.

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Section: Introductionmentioning

confidence: 99%

Crystal structures of the [18]-crown-6 ammoniate C₁₂H₂₄O₆ · 2 NH₃ and the cryptand [2.2.2] ammoniate C₁₈H₃₆O₆N₂ · 2 NH₃

Suchentrunk¹,

Rossmeier²,

Korber³

2006

Zeitschrift Für Kristallographie - Crystalline Materials

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“…OA and OC are oriented 1,3 to each other, in the central 18c6 ring, and th$ir inner hydrogen interaction peaks are near 2 A, indicating near ideal H bonds. It is well known from both X-ray crystal data [65] and theoretical studies [24,39,41] that water hydrogens generally interact 1,3 with regard to oxygens of 18c6, rather than 1,2 (i.e., adjacent oxygens). Thus, we see the first hydrogen peak for OB is at a slightly longer distance than OA or OC since OB is "down" relative to OA and OC, due to the gauche( + )/gauche( -1 alternating OCCO angles around the 18~6-core ring.…”

Section: Molecular Dynamics Results For S18c6 In Homentioning

confidence: 99%

Molecular dynamics study of a new rigidified 18-crown-6 derivative using a QM / MM method

Thompson

1996

Int. J. Quantum Chem.

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We present results of the first molecular dynamics study of a new rigidified 18-crown-6 derivative, recently synthesized by Li and Still. We refer to this new crown as s18c6, which contains a central 18-crown-6 core locked into a D,, configuration by the addition of six exocyclic saturated hydrocarbon rings, two of which also contain a single exocyclic heteroatom (X), peripheral to the central cation binding ring. X can be either a hemiacetal (X = oxygen) or hemithioacetal (X = sulfur). The enhanced rigidity and the exocyclic heteroatoms are thought to be involved in the novel cation binding properties of s18c6 in aqueous solutions; it is more ionophoric than 18c6, and it is selective for Na+ over K + when X = oxygen but is selective for K + over Na+ when X = sulfur. In the present communication, we report results for the X = oxygen isomer of s18c6. We use a hybrid quantum mechanical/molecular mechanical (QM/MM) approach to study the solvation properties of the uncomplexed crown in H,O. The QM/MM method described here is based on our previous QM/MM study of K+/18c6 which employs the semiempirical AM1 method for s18c6 and the SPC/E model for H,O. Both AM1 and HF/6-31 +G* optimized geometries give similar results for the gas-phase structure of s18c6. The a,b initio results show that s18c6 has a slightly smaller cavity than 18c6 (5.681 vs. 5.802 A, respectively) based on the average transannular oxygen-oxygen distances. A 100-ps equilibrium molecular dynamics simulation shows that the s18c6 core remains in a rigid D,, configuration. S18c6 avidly binds two solvent waters, one on either side of the macrocycle plane. The simulation average binding energy per bound water is -14.8 kcal/mol, which is greater than our previously reported result of -12.3 kcal/mol for H,O bound by 18c6. Both of the sl8c6-bound waters maintain multiple hydrogen bonds to the oxygens of the macrocycle, and there is evidence for involvement of the exocyclic oxygens in this binding. 0

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“…It was also predicted that the dissolution of crystals of 18C6 in water would lead to conformational changes from C i to D 3d . 21 This hydration scheme was confirmed experimentally by X-ray structures of 18C6 hydrates 22,23 or of adducts with other species 24,25 by Raman or IR spectroscopic studies of 18C6 hydrates [26][27][28][29] as well as by molecular dynamics [30][31][32] or Monte Carlo 33 simulations in aqueous solution. It was found that the D 3d structure becomes increasingly preferred over C i as the solvent polarity increases.…”

Section: Introductionmentioning

confidence: 83%

18-Crown-6 and Its Hydrates: Bridging but Versatile Hydrogen Bonding. A Theoretical Study of Static and Dynamic Properties

2003

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Quantum chemical (QM), classical molecular dynamics (MD), and Car-Parrinello (CP-MD) studies are reported for 18-crown-6 (18C6) and its first 18C6(H 2 O) n hydrates, focusing on the D 3d and C i forms of the crown. They reveal the importance of dynamics and the surrounding medium on its conformational and hydrogen-bonding properties. In the gas phase, the two forms of the free crown are found to be quasi-isoenergetic at several computational levels, but during CP-MD simulations, the D 3d form is more mobile than C i and undergoes conformational changes in such a way as "to fill its own cavity". Among several forms of the monohydrate, the one with a D 3d -type crown and a bridging water molecule is most stable. Along its 10-ps CP-MD trajectory, the H 2 O molecule undergoes a "merry-go-round" dynamics, exchanging between the three "top" oxygens of the deformed crown, and is thus more often instantaneously monodentate than bidentate. The static and dynamic results of different forms of the mono-and dihydrates confirm the importance of dynamic bridging coordination to 18C6. These results solve the apparent contradiction between IR spectroscopic results in humid CCl 4 or supercritical-CO 2 solutions that hint at an equilibrium between monodentate and bidentate hydrogen bonds, whereas in other humid phases (solid-state structures, liquid hydrates, simulated aqueous solutions), the hydrated crown is always D 3d -like and the first coordinated H 2 O molecules are bridging. IntroductionLike (poly)cyclic complex-forming molecules, 1,2 18-crown-6 (18C6) was early recognized to act as a selective host for charged atoms and small molecules and to display fundamental features of molecular recognition: preorganization and macrocyclic effects, flexibility, induced fit upon ligand binding, and a solvent effect on its recognition properties. 3-5 From a basic point of view, it is important to understand the structure of 18C6 as a function of its environment. In the solid state, 18C6 alone is of an elongated shape of C i symmetry (no cavity), and the D 3d form (Figure 1) with a cavity is commonly observed with cationic guests (e.g., K + , R-NH 3 + , H 3 O + , NH 4 + ) as well as in interaction with dipolar molecules (e.g., acetonitrile, water). 6-8 Other symmetries are observed for 18C6 itself (e.g., C 1 within the Na + complex, another C i form in the benzene-sulfonamide adduct) or its derivatives (e.g., dicyclohexyl, dibenzo). 6 These data and computer simulations in the gas phase 9-12 and in solution [13][14][15][16][17][18] show that the structure of 18C6 is highly versatile and depends on its environment.The present study was motivated by spectroscopic IR results on 18C6 hydrates formed in humid organic phases such as CCl 4 19 or supercritical CO 2 (SC -CO 2 ), 20 according to which there is an equilibrium between the monodentate and bidentate coordination of water in the 1:1 adduct with 18C6 ( Figure 2). The corresponding conformation of 18C6 was not established. However, early theoretical simulations on 18C6 in aqueous soluti...

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Hydrates of Weak and Strong Bases. 12. 18-Crown-6 and Water: Crystal Structure of a Binary Hydrate.

Cited by 58 publications

References 0 publications

Crystal structures of the [18]-crown-6 ammoniate C₁₂H₂₄O₆ · 2 NH₃ and the cryptand [2.2.2] ammoniate C₁₈H₃₆O₆N₂ · 2 NH₃

Crystal structures of the [18]-crown-6 ammoniate C₁₂H₂₄O₆ · 2 NH₃ and the cryptand [2.2.2] ammoniate C₁₈H₃₆O₆N₂ · 2 NH₃

Molecular dynamics study of a new rigidified 18-crown-6 derivative using a QM / MM method

18-Crown-6 and Its Hydrates: Bridging but Versatile Hydrogen Bonding. A Theoretical Study of Static and Dynamic Properties

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Hydrates of Weak and Strong Bases. 12. 18-Crown-6 and Water: Crystal Structure of a Binary Hydrate.

Cited by 58 publications

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Crystal structures of the [18]-crown-6 ammoniate C12H24O6 · 2 NH3 and the cryptand [2.2.2] ammoniate C18H36O6N2 · 2 NH3

Crystal structures of the [18]-crown-6 ammoniate C12H24O6 · 2 NH3 and the cryptand [2.2.2] ammoniate C18H36O6N2 · 2 NH3

Molecular dynamics study of a new rigidified 18-crown-6 derivative using a QM / MM method

18-Crown-6 and Its Hydrates: Bridging but Versatile Hydrogen Bonding. A Theoretical Study of Static and Dynamic Properties

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Crystal structures of the [18]-crown-6 ammoniate C₁₂H₂₄O₆ · 2 NH₃ and the cryptand [2.2.2] ammoniate C₁₈H₃₆O₆N₂ · 2 NH₃

Crystal structures of the [18]-crown-6 ammoniate C₁₂H₂₄O₆ · 2 NH₃ and the cryptand [2.2.2] ammoniate C₁₈H₃₆O₆N₂ · 2 NH₃