Crystal Structures of and Polarized Absorption-Spectroscopy in Racemic and Resolved [Ru(bpy)3] (ClO4)2 and [Zn(bpy)3] (ClO4)2Bpy=2,2'-Bipyridine

1995 ◽  
Vol 48 (5) ◽  
pp. 929 ◽  
Author(s):  
E Krausz ◽  
H Riesen ◽  
AD Rae
Keyword(s):  
Room Temperature ◽  
Energy Difference ◽  
Temperature Structure ◽  
Asymmetric Unit ◽  
Threefold Axis ◽  
Crystal Forms ◽  
The Third ◽  
Racemic Form ◽  
Ligand Charge Transfer ◽  
Dominant Influence

[Zn( bpy )3] (ClO4)2 and [ Ru ( bpy )3] (ClO4)2 are isomorphous in both their racemic and resolved crystal forms. The resolved materials are monohydrates and have a C 2, Z = 8, structure with two independent formula units on general sites in the asymmetric unit. The cations have the same chirality. The inherent threefold axis of each cation lies approximately parallel to the c axis. The unrelated racemic form has a C2/c, Z = 4, structure which is a commensurate modulation of a P3c1, Z = 2, parent structure, typified by the room-temperature structure of [ Ru ( bpy )3] (PF6)2. A primary, secondary and tertiary axis of P3c1 become the c, b and a axes respectively of C2/c, retaining a third of the symmetry elements of P3c1. The crystals grow as multiply contacted twins. This structure bas just one spectroscopic site with the cation lying on a twofold axis that passes through the metal and one of the bidendate ligands and relates the other two ligands to each other. This feature is particularly useful in the study of the optical spectroscopy of the metal-to- ligand charge transfer excitations of [ Ru ( bpy )3]2+ and related systems. A comparison of structural and spectral data indicates that the positions of the anions have a dominant influence on the relative energies of the metal-to- ligand excitations. An energy difference between excitations involving the two (lower-energy) equivalent ligands and the third ligand of the order of 800 cm-1 is indicated in both singlet and triplet regions for the racemic perchlorate. The absorption spectra of [ Ru ( bpy )3]2+and [Os( bpy )3]2+ in a number of crystalline hosts are compared and discussed.

The Crystal Structures of Thermomyces (Humicola) Lanuginosa Lipase in Complex with Enzymatic Reactants

2020 ◽  
Vol 16 (3) ◽  
pp. 199-213 ◽  
Author(s):  
Alexander McPherson ◽  
Steven B. Larson ◽  
Andrew Kalasky
Keyword(s):  
Active Form ◽  
Water Interface ◽  
Asymmetric Unit ◽  
Threefold Axis ◽  
Crystal Forms ◽  
Space Groups ◽  
Interfacial Activation ◽  
X Ray Crystallography ◽  
Fatty Acid Chain ◽  
Chain Lengths

Aim: To understand the details of the action of fungal lipase and the mechanism for its observed interfacial activation. Background: Fungal lipase, crucial to biotechnology, functions at the lipid - water interface where it undergoes a poorly understood interfacial activation. Biochemical factors influencing its activation and inhibition are also poorly understood. This study provides a basis for its activity and a plausible mechanism for interfacial activation. Objective: To determine the structures of fungal lipase in different crystal forms in complex with their enzymatic reactants and inhibitors. Method: X-ray crystallography. Results: Thermomyces lanuginosa lipase was visualized in three crystal forms, of space groups H32, P21 and I222 at 1.3 to 1.45 Å resolution. Rhombohedral crystals have one molecule, lacking segment 241 to 252, as an asymmetric unit, with molecules organized as two trimers. Monoclinic crystals’ asymmetric unit is six intact molecules organized as two, nearly identical trimers, each exhibiting an NCS threefold axis. The “lid” helix was consistently closed. Oligomerization into trimers creates an internal hydrophobic cavity where catalysis occurs. In monoclinic and orthorhombic crystals, active site serines were esterified to fatty acids. Lipase had bound within their trimeric, hydrophobic cavities 1,3-diacylglycerols with fatty acid chain lengths of about 18 carbons. Conclusions: Results suggest trimers are likely the active form of the enzyme at the lipid-water interface. Formation of trimers may provide an explanation for “interfacial activation”.

scholarly journals Structural investigation of homonuclear Pt2 and heteronuclear PdPt complexes containing a metal–metal bond bridged by hydrido and sulfido ligands

1996 ◽  
Vol 52 (2) ◽  
pp. 270-276 ◽  
Author(s):  
W. Clegg ◽  
M. Capdevila ◽  
P. González-Duarte ◽  
J. Sola
Keyword(s):  
Nmr Spectroscopy ◽  
Room Temperature ◽  
Structural Investigation ◽  
Temperature Structure ◽  
Asymmetric Unit ◽  
Rotation Symmetry ◽  
Space Group ◽  
Metal Metal ◽  
Hydride Ligand ◽  
Heteronuclear Complex

The complex [Pt2(μ-H)(μ-S)(dppe)2](PF6) undergoes a displacive order–disorder transformation at ca 230 K. The low-temperature structure is ordered with one cation–anion pair as the asymmetric unit in space group P21/n. At room temperature the b axis is halved and the space group is P2/n, imposing crystallographic twofold rotation symmetry on both ions; the anion shows major disorder and there is probably minor disorder in the cation, but its internal geometry remains essentially unchanged. The heteronuclear complex [PdPt(μ-H)(μ-S)(dppe)2](PF6) is isostructural with the Pt2 complex at room temperature. All three structures have been determined crystallographically and both complexes have been extensively characterized by NMR spectroscopy, unambiguously confirming the genuine heteronuclear nature of the mixed-metal complex and the presence of the bridging hydride ligand.

Vibrational Spectra and Crystal Structures of Tris- and Tetrakis(ethylenethiourea)copper(I) Systems

1994 ◽  
Vol 47 (1) ◽  
pp. 15 ◽  
Author(s):  
GA Bowmaker ◽  
C Pakawatchai ◽  
BW Skelton ◽  
P Thavornyutikarn ◽  
Y Wattanakanjana ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Far Infrared ◽  
The Other ◽  
Infrared And Raman Spectra ◽  
Asymmetric Unit ◽  
Sulfate Ion ◽  
Threefold Axis ◽  
Space Group ◽  
Axial Bond

A room-temperature redetermination of the crystal structure of [Cu(SC(NHCH2)2)3]2 (SO4) has been carried out. The original determination, recorded in communication format in space group Ic , Z = 4, seemingly with the full formula as the asymmetric unit, is at variance with our findings which describe the structure in space group R3c, a 12.741(7), c 35.59(1) Ǻ (hexagonal setting), Z = 6, with one-third of each of two independent cations , each lying on a threefold axis, comprising the asymmetric unit. The sulfate ion also lies on a threefold axis in proximity to only one of the two cations , the S-O axial bond approaching the copper atom normal to the planar CuS3 array [Cu-S, O 2.269(2), 2.834(8)Ǻ]; in the other cation, unperturbed by any sulfate approach, Cu-S is appreciably shorter [2.246(2)Ǻ]. R was 0.029 for 905 'observed' reflections. A redetermination of the structure of tetrakis ( ethylenethiourea )copper(I) nitrate is also recorded; crystals are triclinic, Pī , a 13.211(2), b 11.2167(4), c 7.566(3) Ǻ, α 81.93(2), β 78.35(3), γ 87.22(1)°, Z = 2, R being 0.031 for 3861 independent 'observed' reflections. The copper environment is quasi-tetrahedral, Cu-S ranging between 2.3322(9) and 2.3658(12) Ǻ, and S-Cu-S 98.76(3)-117.83(3)°. The vibrational (far-infrared and Raman) spectra are recorded for these CuSn systems, and discussed and assigned in the light of the structural results.

Two phases of C9H12O4: why is the structure at 295 K so complicated?

2002 ◽  
Vol 58 (3) ◽  
pp. 502-511 ◽  
Author(s):  
Laura L. Duncan ◽  
Brian O. Patrick ◽  
Carolyn Pratt Brock
Keyword(s):  
Carboxylic Acid ◽  
Low Temperature ◽  
Room Temperature ◽  
Mirror Plane ◽  
Temperature Structure ◽  
Ordered Structure ◽  
Asymmetric Unit ◽  
Packing Problems ◽  
Thin Electron ◽  
Two Phases

Molecules of 4,4′-dimethyl-2-hydroxy-6-oxocyclohexene-1-carboxylic acid, C9H12O4, crystallize at 295 K in a modulated superstructure with five half-molecules in the asymmetric unit; each molecule is located on one of the mirror planes of the space group Cmc21. Reflections with k ≠ 5n are systematically weak; a satisfactory refinement can be obtained in a Cmcm pseudocell having b′ = b/5. The important modulation involves small rotations of the molecules around axes perpendicular to the mirror plane; there is also an up/down disorder of the CMe2 fragment in four of the five molecules (two molecules with occupancy factors ca 4:1; two with occupancy factors ca 3:2). The modulation is a response to packing problems that can be traced to the differences between the thin, electron- and oxygen-rich `head' of the molecule and the thicker, methyl-rich `tail'. At 130 K the length of b is reduced by 2/5 and the Pmnb structure is ordered. Both structures can be described as modulated variants of the Cmcm substructure; the wavevectors are 2b′*/5 for the room-temperature structure and b′*/2 for the low-temperature structure, where b′* is the reciprocal axis of the subcell. The structure at room temperature can also be understood as a hybrid of the fully disordered pseudocell structure and the ordered structure that is found at low temperature.

scholarly journals Crystal structure of the thermochromic bis(diethylammonium) tetrachloridocuprate(II) complex

2016 ◽  
Vol 72 (1) ◽  
pp. 40-43 ◽  
Author(s):  
Emily P. Aldrich ◽  
Katherine A. Bussey ◽  
Jennifer R. Connell ◽  
Erin F. Reinhart ◽  
Kayode D. Oshin ◽  
...  
Keyword(s):  
Room Temperature ◽  
Complex Salt ◽  
Title Complex ◽  
Asymmetric Unit ◽  
Orthorhombic Space Group ◽  
Coordination Environment ◽  
The Third ◽  
Square Planar ◽  
Deep Green ◽  
Hydrogen Bonded

In the structure of the title complex salt, (Et2NH2)2[CuCl4], the asymmetric unit consists of four unique diethylammonium cations and three unique tetrachloridocuprate anions. Two of the three anions are located with their copper atoms on independent crystallographic twofold axes, while the remaining tetrachloridocuprate is located at a general position of the orthorhombic space groupP21212. Two of the three Cu atoms adopt a distorted square-planar/disphenoidal geometry and the third Cu atom has a regular square-planar coordination environment. The diethylammonium cations form an extensive hydrogen-bonded network through N—H...Cl interactions with the tetrachloridocuprate anions, resulting in a two-dimensional sheet-like hydrogen-bonded network parallel to theabdirection. The complex was observed to undergo a color shift from deep green at room temperature to pale yellow at temperatures above 328 K.

scholarly journals Polyimide mesh-based sample holder with irregular crystal mounting holes for fixed-target serial crystallography

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ki Hyun Nam ◽  
Jihan Kim ◽  
Yunje Cho
Keyword(s):  
Data Collection ◽  
Room Temperature ◽  
Picosecond Laser ◽  
Temperature Structure ◽  
Sample Holder ◽  
Fixed Target ◽  
Random Orientation ◽  
Physical Damage ◽  
Crystal Sample ◽  
Serial Crystallography

AbstractThe serial crystallography (SX) technique enables the determination of the room-temperature structure of a macromolecule while causing minimal radiation damage, as well as the visualization of the molecular dynamics by time-resolved studies. The fixed-target (FT) scanning approach is one method for SX sample delivery that minimizes sample consumption and minimizes physical damage to crystals during data collection. Settling of the crystals on the sample holder in random orientation is important for complete three dimensional data collection. To increase the random orientation of crystals on the sample holder, we developed a polyimide mesh-based sample holder with irregular crystal mounting holes for FT-SX. The polyimide mesh was fabricated using a picosecond laser. Each hole in the polyimide mesh has irregularly shaped holes because of laser thermal damage, which may cause more crystals to settle at random orientations compared to regular shaped sample holders. A crystal sample was spread onto a polyimide-mesh, and a polyimide film was added to both sides to prevent dehydration. Using this sample holder, FT-SX was performed at synchrotron and determined the room-temperature lysozyme structure at 1.65 Å. The polyimide mesh with irregularly shaped holes will allow for expanded applications in sample delivery for FT-SX experiments.

Room temperature structure of LaAlO3

2000 ◽  
Vol 215 (3) ◽  
Author(s):  
H. Lehnert ◽  
Hans Boysen ◽  
P. Dreier ◽  
Y. Yu
Keyword(s):  
Room Temperature ◽  
Temperature Structure

Owing to some recent confusion in the literature the room temperature structure of LaAlO

Single-Crystal X-Ray Scattering Study of Superstructures and Phase Transitions in Graphite-Hno3 and Graphite-Br2 Intercalation Compounds

1982 ◽  
Vol 20 ◽  
Author(s):  
R. Moret ◽  
R. Comes ◽  
G. Furdin ◽  
H. Fuzellier ◽  
F. Rousseaux
Keyword(s):  
Phase Transitions ◽  
Low Temperature ◽  
Room Temperature ◽  
Temperature Phase ◽  
Temperature Structure ◽  
X Ray ◽  
X Ray Scattering ◽  
Scattering Study ◽  
Temperature Liquid ◽  
Low Temperature Phase

ABSTRACTIn α-C5n-HNO3 the condensation of the room-temperature liquid-like diffuse ring associated with the disorder-order transition around 250 K is studied and the low-temperature. superstructure is examined.It is found that β-C8n-HNO3 exhibits an in-plane incommensurate order at room temperature.Two types of graphite-Br2 are found. Low-temperature phase transitions in C8Br are observed at T1 ≍ 277 K and T2 ≍ 297 K. The room-temperature structure of C14Br is reexamined. Special attention is given to diffuse scattering and incommensurability.

The prediction of the cyclic mechanical behavior of stainless steel 304L at room temperature

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Hala Messai ◽  
Salim Meziani ◽  
Athmane Fouathia
Keyword(s):  
Stainless Steel ◽  
Design Methodology ◽  
Room Temperature ◽  
Type Model ◽  
Good Prediction ◽  
304L Stainless Steel ◽  
Content Type ◽  
The Third ◽  
Chaboche Model

Purpose The purpose of this paper is to highlight the performance of the Chaboche model in relation to the database identification, tests with imposed deformations were conducted at room temperature on 304L stainless steel specimens. Design/methodology/approach The first two tests were performed in tension-compression between ±0.005 and ±0.01; in the third test, each cycle is composed of the combination of a compression tensile cycle between ±0.01 followed by a torsion cycle between ±0.01723 (non-proportional path), and the last, uniaxial ratcheting test with a mean stress between 250 MPa and −150 MPa. Several identifications of a Chaboche-type model were then performed by considering databases composed of one or more of the cited tests. On the basis of these identifications, the simulations of a large number of ratchet tests in particular were carried out. Findings The results present the effect of the optimized parameters on the prediction of the behavior of materials which is reported in the graphs, Optimizations 1 and 2 of first and second tests and Optimization 4 of the third test giving a good prediction of the increasing/decreasing pre-deformation amplitude. Originality/value The quality of the model's predictions strongly depends on the richness of the database used for the identification of the parameters.

A 35-year-old mystery solved: a facile synthetic route and structural confirmation of tetrachlorobis(diethyl ether)tungsten(IV)

2021 ◽  
Vol 77 (4) ◽  
Author(s):  
Thomas E. Shaw ◽  
Alfred P. Sattelberger ◽  
Titel Jurca
Keyword(s):  
Crystal Structure ◽  
Diethyl Ether ◽  
Thermal Instability ◽  
Room Temperature ◽  
Surface Characteristics ◽  
Hirshfeld Surface ◽  
Asymmetric Unit ◽  
Synthetic Route ◽  
X Ray ◽  
Elemental Analyses

The true identity of the diethyl ether adduct of tungsten(IV) chloride, WCl4(Et2O) x , has been in doubt since 1985. Initially postulated as the bis-adduct, WCl4(Et2O)2, questions arose when elemental analyses were more in line with a mono-ether adduct, viz. WCl4(Et2O). It was proposed that this was due to the thermal instability of the bis-adduct. Here, we report the room-temperature X-ray crystal structure and Hirshfeld surface characteristics of trans-tetrachloridobis(diethyl ether)tungsten(IV), trans-WCl4(Et2O)2 or trans-[WCl4(C4H10O)2]. The compound crystallizes, with half of the molecule in the asymmetric unit, in the centrosymmetric space group P21/n. The W—O distance is 2.070 (2) Å, while the W—Cl distances are 2.3586 (10) and 2.3554 (10) Å.

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