Direct observation of deuterium migration in crystalline-state reaction by single-crystal neutron diffraction. II. 3–1 Photoisomerization of a cobaloxime complex

2000 ◽  
Vol 56 (2) ◽  
pp. 245-253 ◽  
Author(s):  
Takashi Ohhara ◽  
Jun Harada ◽  
Yuji Ohashi ◽  
Ichiro Tanaka ◽  
Shintaro Kumazawa ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Single Crystal ◽  
Diffraction Analysis ◽  
Crystalline State ◽  
Crystal Form ◽  
The Other ◽  
Second Step ◽  
Xenon Lamp ◽  
Disordered Structure ◽  
Cell Dimensions

Single crystal neutron diffraction analysis of photo-exposed(3-cyanopropyl-d 2 α,α)-[(R)-1-phenylethylamine-d 11]bis(dimethylglyoximato-d 14)cobalt(III) was carried out in order to clarify the mechanism of the crystalline-state photoisomerization of the 3-cyanopropyl group bonded to the Co atom in some cobaloxime complexes. Before irradiation the two H atoms bonded to the C1 atom of the 3-cyanopropyl group were exchanged with the D atoms such as —CH2CH2CD2CN. On exposure to a xenon lamp, the cell dimensions of the crystal were gradually changed. After 7 d exposure the change became insignificantly small. The structure was analyzed by neutron diffraction. The 3-cyanopropyl group was transformed to the 1-cyanopropyl group such as —CD(CN)C(H1/2,D1/2)2CH3 with retention of the single-crystal form. This indicates that one of the D atoms bonded to C1 migrates to either position bonded to C2. The other atoms of the complex remained unchanged. These results indicate that photoisomerization proceeded in two steps: the 3-cyanopropyl group was isomerized to the 2-cyanopropyl group in the first place and then the 2-cyanopropyl group was transformed to the 1-cyanopropyl group. Moreover, it was made clear that the second-step isomerization was irreversible, since one of the D atoms was retained. The disordered structure at C2 is estimated to be caused by the interconversion between the 1-cyanopropyl group produced and its dehydrogenated olefin after the photoisomerization.

Direct observation of deuterium migration in crystalline-state reaction by single-crystal neutron diffraction. III. Photoracemization of 1-cyanoethyl cobaloxime complexes

2001 ◽  
Vol 57 (4) ◽  
pp. 551-559 ◽  
Author(s):  
Takashi Ohhara ◽  
Hidehiro Uekusa ◽  
Yuji Ohashi ◽  
Ichiro Tanaka ◽  
Shintaro Kumazawa ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Single Crystal ◽  
Bond Cleavage ◽  
Cobalt Complexes ◽  
Crystal Form ◽  
Xenon Lamp ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Stereogenic Center ◽  
Cyanoethyl Group

The H atoms bonded to the chiral C atoms (stereogenic center) of the 1-cyanoethyl groups in two cobalt complexes, [(R)-1-cyanoethyl]bis(dimethylglyoximato)(pyridine)cobalt(III) (2) and [(R,S)-1-cyanoethyl]bis(dimethylglyoximato)(piperidine)cobalt(III) (3), were replaced with D atoms, such as Co—C*D(CH3)CN. The crystals of the two cobalt complexes were irradiated with a xenon lamp for 72 h and 27 d, respectively. The unit-cell dimensions were gradually changed with retention of the single-crystal form. The crystal structures after irradiation were determined by neutron diffraction. In each crystal the chiral 1-cyanoethyl group of one of the two crystallographically independent molecules was partly inverted to the opposite configuration, whereas that of the other molecule kept the original configuration. The C*—D bond in the inverted group was completely conserved in the process of the inversion of the chiral alkyl group. This suggests that the inversion of the chiral 1-cyanoethyl group proceeds with the rotation of the cyanoethyl radical after the Co—C bond cleavage by photo-irradiation so that the opposite side of the radical faces the Co atom. This is followed by recombination of the Co—C bond to form the inverted 1-cyanoethyl group.

Direct observation of arylnitrene formation in the photoreaction of arylazide crystals

2010 ◽  
Vol 66 (6) ◽  
pp. 639-646 ◽  
Author(s):  
Terufumi Takayama ◽  
Takahiro Mitsumori ◽  
Masaki Kawano ◽  
Akiko Sekine ◽  
Hidehiro Uekusa ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Uv Light ◽  
Crystal Form ◽  
The Other ◽  
Azido Group ◽  
X Rays ◽  
Butanoic Acid ◽  
Cell Dimensions ◽  
Triplet Nitrene

Seven crystal structures of arylazides, 2-azidobiphenyl (2), 4-(4-azidophenyl)butanoic acid (3), 3-azidobenzoic acid (4), N-(4-azidophenyl)acetamide (5), 2,4,6-trichlorophenyl azide (6), 2,5-dibromophenyl azide (7) and 2,4,6-tribromophenyl azide (8), have been analyzed by X-rays. When the crystals were irradiated with UV light at ≃ 80 K, only 2-azidobiphenyl gradually changed its cell dimensions with the retention of the single-crystal form. The crystal structure after photo-irradiation was analyzed by X-rays under the same conditions as those before photo-irradiation. Approximately 20% of the 2-azidobiphenyl molecule was converted to the triplet 2-biphenylnitrene and dinitrogen molecules. The existence of the triplet nitrene was confirmed by ESR and IR measurements. Although the structure of dinitrogen was clearly determined, the nitrene structure was obscure because the nitrene produced was almost superimposed on the original 2-azidobiphenyl. The other six crystals were non-reactive or easily broken when they were exposed to UV light. The different reactivity between 2-azidobiphenyl and the other compounds was successfully explained by the reaction cavity of the azido group.

Water Molecule Dispositions in the Cesium Sulfate α- and β-Alums: Single-Crystal Neutron Diffraction Studies of CsM(SO4)2.12H2O (M=V, Rh)

1993 ◽  
Vol 46 (9) ◽  
pp. 1337 ◽  
Author(s):  
JK Beattie ◽  
SP Best ◽  
FH Moore ◽  
BW Skelton ◽  
AH White
Keyword(s):  
Neutron Diffraction ◽  
Water Molecule ◽  
Single Crystal ◽  
Tilt Angle ◽  
Room Temperature ◽  
Bond Angle ◽  
Sulfate Salt ◽  
Cell Dimensions ◽  
Coordinated Water ◽  
Unit Cell Dimensions

Room-temperature single-crystal neutron diffraction studies are recorded for two alums, Cs( Rh /V)(SO4)2.12H2O [cubic, Pa3, a 12.357(5) ( Rh ), 12.434(1)Ǻ (V)], residuals 0.037 and 0.068 for 328 and 164 'observed' reflections, with the intention of defining water molecule hydrogen atom orientations. Whereas the two tervalent hexaaqua cations are similar in size [ rM -O = 2.010(6)Ǻ (M = V) and 2.006(2)Ǻ (M = Rh )] the vanadium salt adopts the β alum modification while rhodium gives an α alum. Significantly, the water coordination geometry is different in the two cases with the tilt angle between the plane of the water molecule and the M-O bond vector being 1° (M = V) and 35° (M = Rh ). The tilt angle for water coordinated to rhodium in CsRh (SeO4)2.12H2O is inferred from the unit cell dimensions to be similar to that of the corresponding sulfate salt and not that which generally pertains for caesium selenate alums. Significant differences in the H-O-H bond angle are found for trigonal planar and trigonal pyramidal water coordination, suggesting that differences in the metal(III)-water interaction are a determinant of the geometry of the coordinated water molecule in the caesium sulfate/ selenate alum lattices.

Variable-temperature neutron diffraction studies of the short, strong N...O hydrogen bonds in the 1:2 co-crystal of benzene-1,2,4,5-tetracarboxylic acid and 4,4'-bipyridyl

2003 ◽  
Vol 59 (6) ◽  
pp. 794-801 ◽  
Author(s):  
John A. Cowan ◽  
Judith A. K. Howard ◽  
Garry J. McIntyre ◽  
Samuel M.-F. Lo ◽  
Ian D. Williams
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Neutron Diffraction ◽  
Single Crystal ◽  
Variable Temperature ◽  
Intermediate Position ◽  
The Other ◽  
Tetracarboxylic Acid ◽  
Other Hand

The 1:2 adduct of benzene-1,2,4,5-tetracarboxylic acid and 4,4′-bipyridyl at 100 K has been studied by single-crystal neutron diffraction at 20, 200 and 296 K. The structure contains two short, strong N...O hydrogen bonds: one O—H...N hydrogen bond [O...N 2.6104 (17) Å at 20 K] and one short N—H...O hydrogen bond [N...O 2.5220 (17) Å at 20 K]. The N—H distance in the N—H...O hydrogen bond changes from 1.207 (3) Å at 20 K to 1.302 (4) Å at 296 K and the N...O distance increases to 2.5315 (16) Å at 296 K. At 200 K the H atom lies in an intermediate position 1.251 (6) Å from the N atom with an N...O separation of 2.520 (4) Å. The O—H...N hydrogen bond, on the other hand, does not change with temperature.

Sign in / Sign up

Export Citation Format

Share Document