We report the structure and characterization of 3,4,5-triiodo-2-methylthiophene, obtained as an unexpected, unreported, and significant side product from the iodination of 2-methylthiophene using ...iodine and iodic acid. Identity of this unexpected product was confirmed by X-ray crystallography and
1
H and
13
C NMR. The compound crystallizes in the P2
1
/c space group with unit cell parameters
a
= 16.4183(10) Å,
b
= 4.1971(3) Å,
c
= 14.3888(9) Å, β = 111.4442(14),
Z
= 4, and D
calc
= 3.425 g cm
−3
. Analysis of residual electron density maps indicated the presence of crystallographic disorder between the 2-methyl and 5-iodo positions leading to a model of two distinct molecules of 3,4,5-triiodo-2-methylthiophene where the atoms of these two groups were exchanged. Non-covalent iodine–iodine and sulfur–iodine interactions are observed.
Graphical Abstract
Three products, two of which are constitutional isomers, are possible when installing multiple iodine atoms on 2-methylthiophene; X-ray structural analysis and spectral characterization show that the 4,5-diiodo isomer is not formed and that the 3,4,5-triiodo isomer is unexpectedly obtained. Halogen and chalcogen bonding are clearly observed.
In situ single‐crystal diffraction experiments provide researchers with the opportunity to study the response of crystalline systems, including metal–organic frameworks and other nanoporous ...materials, to changing local microenvironments. This paper reports a new environmental control cell that is remarkably easy to use, completely reusable, and capable of delivering static or dynamic vacuum, liquids or gases to a single‐crystal sample. Furthermore the device is nearly identical in size to standard single‐crystal mounts so a full unrestricted range of motion is expected for most commercial goniometers. In situ single‐crystal X‐ray diffraction experiments performed under dynamic gas‐flow conditions revealed the cell was capable of stabilizing a novel metastable intermediate in the dehydration reaction of a previously reported metal–organic framework.
We have synthesized a new class of highly efficient nonlinear optical (NLO) chromophores based on the novel tricyanopyrroline (TCP) electron acceptor. Molecular linear and nonlinear optical ...properties of the prototypical chromophores were measured and calculated to understand structure−property relationships. One such chromophore showed molecular first hyperpolarizability (β) of (8700 ± 702) × 10-30 esu at excitation wavelengths of 1.9 μm, and another showed macroscopic electro-optic (EO) coefficients (r 33) of 51 pm/V at 1.55 μm with 20 wt % chromophore loading when poled with 65 V/μm in amorphous polycarbonate film. Synthetic strategies for extending the utility of the acceptor and chromophores are discussed.
In the title 1:2 co-crystal, C
H
N
·(C
H
O
·C
H
O
)
, l-ascorbic acid (LAA) and 4,4'-bi-pyridine (BPy) co-crystallize in the chiral space group
2
with two mol-ecules of LAA, and one mol-ecule of bpy ...in the asymmetric unit. The structure was modeled in two parts due to possible proton transfer from LAA to the corresponding side of the bpy mol-ecule having an occupancy of approximately 0.25 and part 2 with an occupancy of approximately 0.75. In this structure, LAA forms hydrogen bonds with neighboring LAA mol-ecules, forming extended sheets of LAA mol-ecules which are bridged by bpy mol-ecules. A comparison to a related and previously published co-crystal of LAA and 3-bromo-4-pyridone is presented.
Mesoscale Chiroptics of Rhythmic Precipitates Gunn, Erica; Sours, Ryan; Benedict, Jason B. ...
Journal of the American Chemical Society,
11/2006, Volume:
128, Issue:
44
Journal Article
Peer reviewed
Rhythmic precipitates of centrosymmetric phthalic acid were analyzed by a square-wave mechanically modulated circular extinction imaging microscope. Spherulites were bisected into square-millimeter ...sized heterochiral domains that are a consequence of circular intensity differential scattering of left and right circularly polarized light. The dissymmetry and chiral amplification indicated optically was confirmed in the microtexture established by atomic force and scanning electron microscopies.
Superoxide reductases (SORs) are cysteine-ligated, non-heme iron enzymes that reduce toxic superoxide radicals (O2 -). The functional role of the trans cysteinate, as well as the mechanism by which ...SOR reduces O2 -, is unknown. Herein is described a rare example of a functional metalloenzyme analogue, which catalytically reduces superoxide in a proton-dependent mechanism, via a trans thiolate-ligated iron-peroxo intermediate, the first example of its type. Acetic-acid-promoted H2O2 release, followed by Cp2Co reduction, regenerates the active Fe(II) catalyst. The thiolate ligand and its trans positioning relative to the substrate are shown to contribute significantly to the catalyst's function, by lowering the redox potential, changing the spin state, and dramatically lowering the ν Fe - O stretching frequency well-below that of any other reported iron-peroxo, while leaving ν O - O high, so as to favor superoxide reduction and Fe−O, as opposed to O−O, bond cleavage. Thus we provide critical insight into the relationship between the SOR structure and its function, as well as important benchmark parameters for characterizing highly unstable thiolate-ligated iron-peroxo intermediates.
The behavior of excitons and excess electrons in the confined space of a molecular polyoxotitanate cluster Ti17(μ4-O)4(μ3-O)16(μ2-O)4(OPr i )20 (in short Ti17) was studied using femtosecond ...pump–probe transient absorption, pulse radiolysis, and fluorescence spectroscopy. Due to pronounced quantum size effects, the electronic spectra of the exciton, Ti17*, and the excess electron carrying radical anion, Ti17 •– , are blue-shifted in comparison with bulk TiO2 and have maxima at 1.91 and 1.24 eV, respectively. The 0.7 eV difference in the position of the absorption maxima of Ti17 * and Ti17 •– indicates the presence of strong Coulomb interaction between the conduction band electron and the valence band hole in the ∼1 nm diameter cluster. Ground state Raman spectra and the vibronic structure of the fluorescence spectrum point to the importance of the interfacial ligand modes in the stabilization and localization of the fully relaxed exciton. Four pentacoordinate Ti sites near the surface of the cluster appear to play a special role in this regard. Solvent polarity has only a minor influence on the spectral behavior of Ti17 *. Exciton recombination in Ti17 is faster than in anatase nanoparticles or mesoporous films. The kinetics exhibits three components, ranging from less than 1 ps to 100 ps, which are tentatively assigned to the geminate recombination within the core of the cluster and to the decay of the surface stabilized charge transfer exciton. A persistent long-lived component with τ > 300 ps may indicate the involvement of intraband dark states, i.e., triplet excitons 3 Ti17 *.
The title compound systematic name: benzoic acid-pyrrolidin-1-ium-2-carboxyl-ate (1/1), C
H
O
·C
H
NO
, is an example of the application of non-centrosymmetric co-crystallization for the growth of a ...crystal containing a typically centrosymmetric component in a chiral space group. It co-crystallizes in the space group
2
2
2
and contains benzoic acid and l-proline in equal proportions. The crystal structure exhibits chains of l-proline zwitterions capped by benzoic acid mol-ecules which form a
(5)
(11) hydrogen-bonded network along 100. The crystal structure is examined and compared to that of a similar co-crystal containing l-proline zwitterions and 4-amino-benzoic acid.
The advent of X-ray diffraction in the early twentieth century transformed crystallography from an area of scientific inquiry largely limited to physics, mineralogy, and mathematics, to a highly ...interdisciplinary field which now includes nearly all life and physical sciences as well as materials science and engineering. This book is a collection of works showcasing some of the most recent developments in the field of crystallography.
A pair of organoplatinum(II) metallacycles, M1 and M2, was self-assembled by combining one of two donor molecules, cis-Pt(dhim)
2
(C≡CC
5
H
4
N)
2
(D1; dhim = 1,3-dihexyl-2-H-imidazole-2-yelidene) ...and Pt(tbbpy)(C≡CC
5
H
4
N)
2
(D2; tbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine), with an acceptor precursor, Pt(tbbpy)(OTf)
2
(A1; OTf = CF
3
SO
3
−
), respectively. Both donor molecules exhibit an idealized 90° angle between the coordination vectors of their ethynylpyridine moieties. When mixed with A1, coordination-driven self-assembly occurs at 50 °C (4 days in acetonitrile for M1 and 18 h in CH
2
Cl
2
for M2). Both metallacycles were characterized by
1
H NMR, FT-IR, and FT-ICR-MS techniques that support D
2
A
2
self-assembly of molecular squares. The structure of building block D1 was determined by X-ray diffraction, confirming the expected square coordination geometry and 90° orientation of the pyridyl coordination vectors. Photophysical studies of M1 and M2 reveal that the metallacycles display triplet emission bands at 466 and 469 nm, respectively, that originate from transitions localized on building blocks D1 and D2. This phosphorescent behavior is assigned to
3
ILCT and
3
LLCT (π
C≡C
* → π
C≡C
; ILCT = intraligand charge transfer, LLCT = ligand-to-ligand charge transfer) transitions based on previous studies of phenyl analogs to D1 and D2 that indicate that the ethynyl moieties dominate in their contributions to the molecular orbitals involved in absorption and emission.
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