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).

4,4′-Bithiazoles as Ligands: Crystal and Molecular Structure of bis(O,O′-Nitrato)(2,2′-diphenyl-4,4′-bithiazole)copper(II) (Two Polymorphs)

2003 ◽  
Vol 56 (9) ◽  
pp. 949 ◽  
Author(s):  
S. Ali Asghar Torabi ◽  
Fahimeh Jamali ◽  
George A. Koutsantonis ◽  
Ali Morsali ◽  
Brian W. Skelton ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Low Temperature ◽  
Molecular Complex ◽  
Structure Determination ◽  
Crystal And Molecular Structure ◽  
Plane Angle ◽  
Asymmetric Unit ◽  
X Ray ◽  
Crystallographic Symmetry

A low-temperature single-crystal X-ray structure determination of the 1 : 1 adduct of copper(II) nitrate with 2,2′-diphenyl-4,4′-bithiazole (L) shows it to be a molecular complex with L behaving as a symmetrical N,N′ chelate, and the nitrate groups as unsymmetrical O,O′ chelates: [LCu(O2NO)2]. Two polymorphs, both monoclinic P21/c, have been obtained from acetonitrile (‘α’) and methanol (‘β’), respectively, with one molecule, devoid of crystallographic symmetry, in the asymmetric unit of each structure. The copper environments are distorted planar four-coordinate, cis-N2CuO2 (Cu–N 2.011(1), 1.973(1), Cu–O 1.995(1), 1.962(1) Å), ‘in-plane’ angle sum Σ 369.5°, with longer trans, axial contacts (Cu–O 2.455(1), 2.458(2) Å) for the α-form; respective values are 1.995(5), 1.991(4), 1.997(4), 1.973(3) Å, 360.4°, 2.500(4), and 2.396(4) Å for the β-form.

Contribution to the Chemistry of 2,2,6,6-Tetramethylpiperidino Aluminium Compounds

2005 ◽  
Vol 60 (10) ◽  
pp. 1027-1035 ◽  
Author(s):  
Klaus Knabel ◽  
Heinrich Nöth
Keyword(s):  
Nmr Spectroscopy ◽  
Elevated Temperatures ◽  
Molecular Structures ◽  
High Yield ◽  
Dry Ice ◽  
X Ray ◽  
Unexpected Reaction

tmpAlBr2 (tmp = 2,2,6,6-tetramethylpiperidino) was prepared from AlBr3 and tmp2AlBr at 90 °C in the absence of a solvent, but could not be crystallised from toluene or hexane because it reacted with the solvents to form tmpH·AlBr3 in high yield. tmpH·AlMeCl2, obtained from the components, decomposes at elevated temperatures but no tmpAlCl2 could be isolated. Attempts to generate the cation [tmp-Al-tmp]+ from tmp2AlBr or tmp2AlCl by halide abstraction with B(C6F5)3, Ph3C(SnCl5) or SbCl5 or from tmp2AlR (R = Me, Ph) and B(C6F5)3 have failed. An unexpected reaction occurred on treatment of tmp-B=P(tBu)AlBr3 with BH3 in THF which led to the formation of [AlBr2(thf)4][AlBr4]. The attempted synthesis of tBu2Al(tmp) from tBu2AlBr and Li(tmp) gave a product which, on exposure to CO2 at dry ice temperature, yielded the salt [(tBuAl)2(O2C(tmp))3][tBu3Al-Br-AltBu3] in low yield. All isolated products were characterized by NMR spectroscopy and by X-ray determination of their molecular structures.

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.

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.

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