Crystal Structure Determination of the Nonclassical 2-Norbornyl Cation

Science ◽  
2013 ◽  
Vol 341 (6141) ◽  
pp. 62-64 ◽  
Author(s):  
F. Scholz ◽  
D. Himmel ◽  
F. W. Heinemann ◽  
P. v. R. Schleyer ◽  
K. Meyer ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Data Collection ◽  
Quantum Chemical ◽  
Molecular Structures ◽  
X Ray ◽  
Disorder Phase Transition ◽  
Carbonium Ion ◽  
Phase Data

After decades of vituperative debate over the classical or nonclassical structure of the 2-norbornyl cation, the long-sought x-ray crystallographic proof of the bridged, nonclassical geometry of this prototype carbonium ion in the solvated [C7H11]+[Al2Br7]–• CH2Br2salt has finally been realized. This achievement required exceptional treatment. Crystals obtained by reacting norbornyl bromide with aluminum tribromide in CH2Br2undergo a reversible order-disorder phase transition at 86 kelvin due to internal 6,1,2-hydride shifts of the 2-norbornyl cation moiety. Cooling with careful annealing gave a suitably ordered phase. Data collection at 40 kelvin and refinement revealed similar molecular structures of three independent 2-norbornyl cations in the unit cell. All three structures agree very well with quantum chemical calculations at the MP2(FC)/def2-QZVPP level of theory.

Crystal structure determination of the conformation of two bicyclo[3.3.1]nonan-ones

1985 ◽  
Vol 63 (6) ◽  
pp. 1166-1169 ◽  
Author(s):  
John F. Richardson ◽  
Ted S. Sorensen
Keyword(s):  
Crystal Structure ◽  
Direct Methods ◽  
Chair Conformation ◽  
Molecular Structures ◽  
Boat Conformation ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Final Agreement

The molecular structures of exo-7-methylbicyclo[3.3.1]nonan-3-one, 3, and the endo-7-methyl isomer, 4, have been determined using X-ray-diffraction techniques. Compound 3 crystallizes in the space group [Formula: see text] with a = 15.115(1), c = 7.677(2) Å, and Z = 8 while 4 crystallizes in the space group P21 with a = 6.446(1), b = 7.831(1), c = 8.414(2) Å, β = 94.42(2)°, and Z = 2. The structures were solved by direct methods and refined to final agreement factors of R = 0.041 and R = 0.034 for 3 and 4 respectively. Compound 3 exists in a chair–chair conformation and there is no significant flattening of the chair rings. However, in 4, the non-ketone ring is forced into a boat conformation. These results are significant in interpreting what conformations may be present in the related sp2-hybridized carbocations.

Gilded Chalices: Tetra-aurated Calix[4]arenes

2014 ◽  
Vol 69 (11-12) ◽  
pp. 1061-1072 ◽  
Author(s):  
Ulf H. Strasser ◽  
Beate Neumann ◽  
Hans-Georg Stammler ◽  
Raphael J. F. Berger ◽  
Norbert W. Mitzela
Keyword(s):  
Crystal Structure ◽  
Mass Spectrometry ◽  
Quantum Chemical ◽  
Molecular Structures ◽  
X Ray Diffraction ◽  
X Ray ◽  
H Nmr ◽  
Elemental Analyses ◽  
One Step ◽  
Energy Of Formation

Abstract 5,11,17,23-Tetrakis(trimethylsilylethynyl)-25,26,27,28-tetra-n-propoxycalix[4]arene (1) was synthesised in two steps starting from 25,26,27,28-tetra-n-propoxycalix[4]arene, and the structure of 1 was determined by X-ray diffraction. Compound 1 was desilylated (K2CO3) to give 5,11,17,23- tetrakis(ethynyl)-25,26,27,28-tetra-n-propoxycalix[4]arene (2), which was tetra-aurated under basic conditions (NaOEt, THF) with a series of phosphane-gold chlorides (o-Tol3PAuCl, Ph3PAuCl, Ph2MePAuCl, PhMe2PAuCl, Me3PAuCl, Cy3PAuCl, t-Bu3PAuCl) to afford in good to excellent yields the tetra-aurated tetraethynylcalix[4]arene species 3-9 in one step [with phosphane ligands o-Tol3P (3), Ph3P (4), Ph2MeP (5), PhMe2P (6), Me3P (7), Cy3P (8), t-Bu3P (9)]. All compounds were characterised by 1H NMR and infrared spectroscopy, mass spectrometry and by elemental analyses, additionally 3, 4, 5, 8 and 9 by 13C{1H}, and 3-6, 8 and 9 by 31P{1H} NMR spectroscopy. The molecular structures of complexes 3 and 9 were determined by X-ray diffraction and show pinched-cone conformations, but neither intra- nor intermolecular attractive aurophilic Au···Au contacts. The acceptor ability of complexes 3 and 9 was investigated by complexation attempts with various phosphane-gold chlorides and xenon gas under pressure, but interactions could not be determined experimentally. The formation of a complex between xenon and gilded calix[4]arene could, however, be predicted for fluorine-substituted species and with very small phosphane ligands (PH3) on the basis of quantum-chemical calculations; the energy of formation is 9:6 kJ mol-1. The crystal structure of Ph2MePAuCl was also determined and shows Au···Au-bonded dimers.

Molecular and Crystal Structure of Two Anthracene Derivatives and their 1,4-Endoperoxides. Influence of the Aromatic Ring Distortion upon the Steric Acceleration of the 1,4-Addition of Singlet Oxygen

1999 ◽  
Vol 52 (3) ◽  
pp. 213
Author(s):  
Nacer Lahrahar ◽  
Henri Bouas-Laurent ◽  
Jean-Pierre Desvergne ◽  
Pierre Marsau ◽  
Jean Rigaudy
Keyword(s):  
Crystal Structure ◽  
Singlet Oxygen ◽  
Aromatic Ring ◽  
Structure Determination ◽  
Molecular Structures ◽  
X Ray ◽  
Anthracene Derivatives ◽  
Oxygen Addition ◽  
Ring Distortion

The X-ray structure determination of two anthracene derivatives, namely 1,2,3,4-tetramethylanthracene (TMA) and 1,2,3,4-tetramethyl-9,10-diphenylanthracene (TMDPA), and of their endoperoxides, 1,2,3,4- tetramethyl-1,4-dihydro-1,4-epidioxyanthracene (TMAPO) and 1,2,3,4-tetramethyl-9,10-diphenyl-1,4-dihy- dro-1,4-epidioxyanthracene (TMDPAPO), has been performed. The compared analysis of the conformations of the four molecular structures strongly suggests that the steric acceleration observed for singlet oxygen addition to TMDPA should be attributed to the important distortion of the anthracene nucleus.

Pressure-Induced Order–Disorder Phase Transition of Spinel Single Crystals

1998 ◽  
Vol 54 (6) ◽  
pp. 714-721 ◽  
Author(s):  
J. Wittlinger ◽  
S. Werner ◽  
H. Schulz
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Single Crystal ◽  
Structural Changes ◽  
X Ray ◽  
Disorder Phase Transition ◽  
X Ray Scattering ◽  
Structure Investigations ◽  
Pressure Phase ◽  
Oxygen Framework

The present study deals with single-crystal structure investigations by means of X-ray scattering of a pressure-induced phase transition of Mg0.4Al2.4O4. The compressibility of the substance is very small, whereas the structural changes are surprisingly high. A non-identified high-pressure phase turns out to be reversible considering the existence of a spinel single crystal, but not reversible with regard to the ordering of the cations in the oxygen framework. The pressure-induced disordering of the cations is preserved on abrupt pressure decrease and can be detected in a recovered specimen.

Simple Method for the Handling of Crystals at Low Temperature: Application to the X-Ray Structure Determination of But2P(=NSiMe3)NHSiMe3 and [But2P(NSiMe3)2]Li·(thf)2

2002 ◽  
Vol 55 (4) ◽  
pp. 249 ◽  
Author(s):  
A. J. Edwards ◽  
E. Wenger
Keyword(s):  
Low Temperature ◽  
Data Collection ◽  
Structure Determination ◽  
Molecular Structures ◽  
Simple Method ◽  
Dry Ice ◽  
X Ray ◽  
Temperature Application

Crystals of the very soluble iminophosphonamide species But2P(=NSiMe3)NHSiMe3 (1) and [But2P(NSiMe3)2]Li�(thf)2 (2) have been obtained and were mounted at dry-ice temperature using a propan-2-ol matrix for X-ray data collection at 100 K. This very simple method for handling the crystals at low temperature is described together with the resulting molecular structures of (1) and (2).

Trioxorhenium(VII) Complexes with Imidazolin-2-iminato Ligands

2004 ◽  
Vol 59 (11-12) ◽  
pp. 1497-1504 ◽  
Author(s):  
Matthias Tamm ◽  
Stephan Beer ◽  
Eberhardt Herdtweck
Keyword(s):  
Crystal Structure ◽  
Heterocyclic Carbenes ◽  
Molecular Structures ◽  
Staudinger Reaction ◽  
X Ray ◽  
Trimethylsilyl Azide ◽  
Twofold Excess ◽  
Nitrogen Bond ◽  
Boiling Toluene

The Staudinger reaction of the N-heterocyclic carbenes 1,3-di-tert-butylimidazolin-2-ylidene (1a), 1,3-dimesitylimidazolin-2-ylidene (1b) and 1,3-diisopropyl-4,5-dimethylimidazolin-2- ylidene (1c) with trimethylsilyl azide in boiling toluene furnishes the corresponding 2- (trimethylsilylimino)imidazolines 2a - c. Treatment of Re2O7 with a twofold excess of these N-silylated imines results in the formation of the imidazolin-2-iminato trioxorhenium(VII) complexes 3a - c and hexamethyldisiloxane, Me3SiOSiMe3. The molecular structures of 2a, 3a and 3b are reported. In addition, the X-ray crystal structure determination of complex 3c · H2O is presented, which has formed by hydrolysis and cleavage of the metal-nitrogen bond in 3c. 3c · H2O consists of 2-aminoimidazolium cations and tetraoxorhenate(VII) anions, which are linked by N-H-O hydrogen bonds.

Single Crystal Growth of High-Pressure Phases of Ice and Salt Hydrate Far Below the Original Melting Point by Mixing Alcohol: Crystal Structure Determination of Magnesium Chloride Heptahydrate

2020 ◽  
Author(s):  
Keishiro Yamashita ◽  
Kazuki Komatsu ◽  
Hiroyuki Kagi
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Crystal Growth ◽  
Single Crystal ◽  
Room Temperature ◽  
Growth Technique ◽  
Salt Hydrate ◽  
X Ray

An crystal-growth technique for single crystal x-ray structure analysis of high-pressure forms of hydrogen-bonded crystals is proposed. We used alcohol mixture (methanol: ethanol = 4:1 in volumetric ratio), which is a widely used pressure transmitting medium, inhibiting the nucleation and growth of unwanted crystals. In this paper, two kinds of single crystals which have not been obtained using a conventional experimental technique were obtained using this technique: ice VI at 1.99 GPa and MgCl<sub>2</sub>·7H<sub>2</sub>O at 2.50 GPa at room temperature. Here we first report the crystal structure of MgCl2·7H2O. This technique simultaneously meets the requirement of hydrostaticity for high-pressure experiments and has feasibility for further in-situ measurements.

The protonation of the ethylenediphosphinetetraacetate anion and the crystal structure of the bis (hydrogen bromide) of ethylenediphosphinetetraacetic acid

1981 ◽  
Vol 46 (12) ◽  
pp. 3063-3073 ◽  
Author(s):  
Jana Podlahová ◽  
Bohumil Kratochvíl ◽  
Vratislav Langer ◽  
Josef Šilha ◽  
Jaroslav Podlaha
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Structure Determination ◽  
Free Acid ◽  
Hydrogen Bromide ◽  
Carboxyl Groups ◽  
Spectroscopic Methods ◽  
X Ray ◽  
Partial Formation

The equilibria and mechanism of addition of protons to the ethylenediphosphinetetraacetate anion (L4-) were studied in solution by the UV, IR, 1H and 31P NMR spectroscopic methods. A total of six protons can be bonded to the anion. They are added stepwise, first with partial formation of zwitterions containing P-H bonds, which then dissociate with formation of the free acid, H4L, where all four protons are bonded in carboxyl groups. The formation of zwitterions is strongly dependent on the concentration. In the final stage, the acid bonds two additional protons to form the bis-phosphonium cation, H6L2+. A number of isostructural salts containing this cation, H4L.2 HX (X = Cl, Br, I), have been prepared. The X-ray crystal structure determination of the bromide confirmed the expected arrangement. The bromide crystals are monoclinic, a = 578.2, b = 1 425.0, c = 1 046.7 pm, β = 103.07° with a space group of P21/c, Z = 2. The final R factor was 0.059 based on 1 109 observed reflections. The structure consists of H6L2+ cations containing protons bonded to phosphorus atoms (P-H distance 134 pm) and of bromide anions, located in gaps which are also sufficiently large for I- anions in the isostructural iodide. The interbonding of phosphonium cations proceeds through hydrogen bonds, C-OH...O=C, in which the O...O distance is 275.3 pm.

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