Search results for "Spectroscopy."

Tuning the Electronic Properties of Nonplanar exTTF-Based Push–Pull Chromophores by Aryl Substitution

2012

International audience; A new family ofπ-extended tetrathiafulvalene (exTTF) donor−acceptorchromophores has been synthesized by [2 + 2] cycloaddition of TCNE with exTTF-substituted alkynes and subsequent cycloreversion. X-ray data and theoretical calculations,performed at the B3LYP/6-31G**level, show that the new chromophores exhibit highlydistorted nonplanar molecular structures with largely twisted 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) units. The electronic and optical properties, investigated by UV/visspectroscopy and electrochemical measurements, are significantly modified when theTCBD acceptor unit is substituted with a donor phenyl group, which increases the twistingof the TCBD unit…

Structural studies of homoisoflavonoids: NMR spectroscopy, X-ray diffraction, and theoretical calculations

2010

Abstract In this article we present a detailed structural investigation for five homoisoflavonoids, molecules important from the pharmacological point of view. For studying the electron distribution as well as its influence on the physicochemical properties, NMR spectroscopy, X-ray diffraction, and theoretical calculations have been used. Nuclear magnetic shieldings obtained by using DFT calculations for optimized molecular geometries are correlated with the experimentally determined chemical shifts. The theoretical data are well in agreement with the experimental values. The single crystal X-ray structures of homoisoflavonoid derivatives 1, 3, and 4 have been solved. The molecular geometri…

Novel Stannatrane N(CH2CMe2O)2(CMe2CH2O)SnO-t-Bu and Related Oligonuclear Tin(IV) Oxoclusters. Two Isomers in One Crystal

2016

The syntheses of the alkanolamine N(CH2CMe2OH)2(CMe2CH2OH) (1), of the stannatrane N(CH2CMe2O)2(CMe2CH2O)SnO-t-Bu (2), and of the trinuclear tin oxocluster 3 consisting of the two isomers [(μ3-O)(O-t-Bu){Sn(OCH2CMe2)(OCMe2CH2)2N}3] (3a) and [(μ3-O)(μ3-O-t-Bu){Sn(OCH2CMe2)(OCMe2CH2)2N}3] (3b) as well as the isolation of a few crystals of the hexanuclear tin oxocluster [LSnOSn(OH)3LSnOH]2 [L = N(CH2CMe2O)2(CMe2CH2O)] (4) are reported. The compounds were characterized by 1H, 13C, 15N, and 119Sn (1–3) nuclear magnetic resonance and infrared spectroscopy, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction analysis (1–4). A graph set analysis was performed for compoun…

Structural Tuning and Conformational Stability of Aromatic Oligoamide Foldamers

2017

A series of aromatic oligoamide foldamers with two or three pyridine-2,6-dicarboxamide units as their main folding motifs and varying aromatic building blocks as linkers have been synthetized to study the effects of the structural variation on the folding properties and conformational stability. Crystallographic studies showed that in the solid state the central linker unit either elongates the helices and more open S-shaped conformations, compresses the helices to more compact conformations or acts as a rigid spacer separating the pyridine-2,6-dicarboxamide units, which for their part add the predictability of the conformational properties. Multidimensional NMR studies showed that, even in…

A trigonal prismatic anionic iron(iii) complex of a radical o-iminobenzosemiquinonate derivative: structural and spectral analyses

2017

A new iron(III) complex, [Et3NH][FeIII(L2−˙)2] (1) with a substituted o-aminophenol based ligand is reported. Complex 1 is an anionic complex with a triethylammonium cation in the lattice. It contains two O,O,N-coordinated o-iminobenzosemiquinonate(2−) radical anions with an Fe(III) centre in a high-spin configuration. The crystal structure of 1 was determined by X-ray diffraction, which revealed a trigonal prismatic coordination environment whose electronic structure was established by various physical methods including EPR, Mossbauer spectroscopy and variable-temperature (2–300 K) magnetic susceptibility measurements. Electrochemical analysis indicated primarily ligand-centred redox proce…

Preparative and Electrochemical Investigations on the Electron Sponge Behavior of Cobalt Telluride Clusters: CO Substitution in[Co11Te7(CO)10]n− Ions…

2003

The reaction of the cluster salts [Cp* 2 Nb(CO) 2 ] n [Co 1 1 Te 7 (CO) 1 0 ] (Cp* = C 5 Me 5 ; n = 1, 2) with excess PMe 2 Ph gave the neutral, dark brown clusters [Co 1 1 Te 7 (CO) 6 (PMe 2 Ph) 4 ] (5) and [Co 1 1 Te 7 (CO) 5 (PMe 2 Ph) 5 ] (6) with 147 metal valence electrons. The new compounds were characterized by IR spectroscopy, elemental analyses, and mass spectrometry. The molecular structure of 6 was determined by X+ray crystallography. Like its precursor anion, it consists of a pentagonal-prismatic [Co 1 1 Te 7 ] core, but with a ligand sphere composed of five CO and five PMe 2 Ph ligands. Detailed electrochemical studies of both reactions reveal that a stepwise substitution of C…

NMR T1-Relaxation Measurements on Paramagnetic Organolanthanides: An Alternative Tool for Structure Determination in Solution

2005

1H NMR investigations were conducted on four paramagnetic organolanthanides, all bearing the tetraisopropylcyclopentadienyl ligand Cp4i (HC5iPr4) in order to verify whether or not interactions observed in the solid state are maintained in solution. In some cases variable-temperature experiments were necessary to enhance the resolution and determine the best conditions for the study. The 1D NMR spectrum could be interpreted in every case. Complementary 2D COSY experiments allowed the full attribution of the signals. T1 (1H) relaxation values were determined for all the paramagnetic complexes at the most suitable temperature, and compared with those of the diamagnetic KCp4i. The same tendency…

2021

A nickel complex incorporating an N2 O ligand with a rare η2 -N,N'-coordination mode was isolated and characterized by X-ray crystallography, as well as by IR and solid-state NMR spectroscopy augmented by 15 N-labeling experiments. The isoelectronic nickel CO2 complex reported for comparison features a very similar solid-state structure. Computational studies revealed that η2 -N2 O binds to nickel slightly stronger than η2 -CO2 in this case, and comparably to or slightly stronger than η2 -CO2 to transition metals in general. Comparable transition-state energies for the formation of isomeric η2 -N,N'- and η2 -N,O-complexes, and a negligible activation barrier for the decomposition of the lat…

Three‐in‐One Crystal: The Coordination Diversity of Zinc Polypyridine Complexes

2017

The synthesis, structural and photophysical properties of two novel zinc(II) complexes bearing the tridentate ddpd (N,N' dimethyl N,N' dipyridin 2 ylpyridine 2,6 diamine) ligand are presented. Structural investigations have been carried out by single crystal X-ray diffractometry, NMR spectroscopy and Density Functional Theory calculations, revealing a diverse coordination behavior depending on the counter ion. Spectroscopic (UV-VIS and emission spectroscopy) and theoretical techniques (density functional theory and time dependent DFT calculations) have been employed to explore the photophysical properties of the complexes.

Thermo-Chromium: A Contactless Optical Molecular Thermometer.

2017

The unparalleled excited-state potential-energy landscape of the chromium(III)-based dye [1]3+ ([Cr(ddpd)2 ]3+ ; ddpd=N,N'-dimethyl-N,N'-dipyridin-2-yl-pyridin-2,6-diamine) enables a strong dual emission in the near infrared region. The temperature dependence of this dual emission allows the use of [1]3+ as an unprecedented molecular ratiometric thermometer in the 210-373 K temperature range in organic and in aqueous media. Incorporation of [1]3+ in biocompatible nanocarriers, such as 100 nm-sized polystyrene nanoparticles and solutol micelles, provides nanodimensional thermometers operating under physiological conditions.