Trans-trans Forms Research Articles

Synthesis, Photophysics, and Switchable Luminescence Properties of a New Class of Ruthenium(II)-Terpyridine Complexes Containing Photoisomerizable Styrylbenzene Units.

We report here the synthesis and structural characterization of a new class of homoleptic terpyridine complexes of Ru(II) containing styrylbenzene moieties to improve room-temperature luminescence properties. Solid-state structure determination of 2 was done through single-crystal X-ray diffraction. Tuning of photophysical properties was done by incorporating both electron-donating and electron-withdrawing substituents in the ligand. The complexes exhibit strong emission having lifetimes in the range of 10.0–158.5 ns, dependent on the substituent and the solvent. Good correlations were also observed between Hammett σp parameters with the lifetimes of the complexes. Styrylbenzene moieties in the complexes induce trans–trans to trans–cis isomerization accompanied by huge alteration of their spectral profiles upon treating with UV light. Reversal of trans–cis to trans–trans forms was also achieved on interacting with visible light. Change from trans–trans to the corresponding trans–cis form leads to emission quenching, whereas trans–cis to the corresponding trans–trans form leads to restoration of emission. In essence, “on–off” and “off–on” photoswitching of luminescence was observed. Calculations involving density functional theory (DFT) and time-dependent-DFT methods were performed to understand the electronic structures as well as for appropriate assignment of the absorption and emission bands.

IR induced photochemistry of glycolaldehyde in nitrogen matrix

The conformational equilibria and IR isomerisation processes of glycolaldehyde (HOCH2CHO) conformers have been studied at low temperature in nitrogen cryogenic matrix. The effects of selective IR irradiation, in the νOH and νCH domains, have been followed by FTIR spectroscopy. After deposition the main form is the most stable one, CC (Cis-Cis), which features an intramolecular hydrogen bond. Upon selective IR irradiation, this latter form is able to interconvert into two open forms, those called TT (Trans–Trans), and TG (Trans-Gauche). From TT and TG forms, no recovering (by tunneling, dark process, irradiation, annealing, etc.) of the initial state (i.e. CC regeneration) has been observed. However, a TT⇌TG thermal equilibrium is observed with a standard reaction enthalpy about 0.37kJmol−1.

Acetic acid dimers in a nitrogen matrix: Observation of structures containing the higher-energy conformer.

Acetic acid (AA) dimers are studied experimentally by infrared spectroscopy in a N2 matrix and theoretically at the MP2/6-311++G(2d,2p) level of approximation. This work is focused on the first preparation and characterization of structures containing the higher-energy (cis) conformer of AA. Nine trans-trans, fourteen trans-cis, and six cis-cis dimers are theoretically predicted. Five trans-trans and a number of trans-cis dimers are identified in the experiments, but no indication of cis-cis dimers is found. Two trans-trans dimers and the trans-cis dimers are reported for the first time. One trans-cis dimer is prepared by selective vibrational excitation of the structurally related trans-trans dimer, which converts one of the trans subunits to the cis form. Several trans-cis dimers are obtained by annealing of a matrix containing both trans and cis monomers of AA. Tunneling-induced conversion of the trans-cis dimers into trans-trans forms (including two new trans-trans forms) is observed at low temperatures.

Raman spectra and conformational analyses for a series of diethyl ether and its organosilicon derivatives, CH 3MH 2OM′H 2CH 3 (M, M′=C and Si), by density functional theory

The molecular structures of a series of diethyl ether and its organosilicon derivatives of CH 3MH 2OM′H 2CH 3 (M, M′=C and Si) have been studied by Raman spectroscopy and density functional theory (DFT) with the B3LYP/6-31G* and 6-311+G** methods. Raman spectra for these molecules were measured in the liquid and solid states. Normal vibrations and calculated Raman spectra were also obtained by using the Raman activities and the scaled wavenumbers from the B3LYP/6-311+G** method. For diethyl ether, CH 3CH 2OCH 2CH 3, the trans– trans ( TT) and trans– gauche ( TG) forms were the stable conformers in the liquid state, while only the TT form existed in the solid state. Additionally, two solid states were obtained and the conformer in both the stable and metastable solids was the TT. For bis(methylsilyl) ether, CH 3SiH 2OSiH 2CH 3, geometry optimization and the DFT calculation showed that only the TT and skew– skew ( SS) forms existed in the liquid state and the SS form existed in the solid state. While, for ethyl methylsilyl ether, CH 3CH 2OSiH 2CH 3, the TT, TG and GT forms coexisted in the liquid state and only the TT form existed in the solid state.

Vibrational analysis of 3-chloropropylsilane

Abstract Raman and IR spectra of 3-chloropropylsilane, ClCH 2 CH 2 CH 2 SiH 3 , and its Si-deuterated analogues were measured in their liquid and solid states. The normal coordinate treatment was carried out and the fundamental vibrations were assigned. The rotational isomerism was investigated by comparing the results for 1-chlorobutane and butylsilane reported in the literature with those obtained from the normal coordinate calculation. All the rotational isomers, e.g., trans-trans (TT), trans-gauche (TG), gauche-trans (GT) and gauche-gauche (GG) forms, except for gauche-gauche′ (GG′) form coexist in the liquid state and only the TT form is found to exist in the solid state. From the temperature dependent measurement of the Raman spectra in the liquid state, the stability of the rotational isomers in the liquid state is found to be in the order of GT > TT > GG > TG.

Molecular vibrations and conformational analysis of methylphosphorodichloridate and ethylphosphorodichloridate

The Raman spectra of methylphosphorodichloridate, CH 3OP(O)Cl 2, and ethylphosphorodichloridate, CH 3CH 2OP(O)Cl 2, have been measured in the liquid and solid states. Rotational isomerism about the COP(O) bond has been investigated on the basis of normal coordinate treatment. CH 3OP(O)Cl 2 has two rotational isomers, trans (T) and gauche (G) forms, in the liquid state and the T form persists in the solid state. Two different spectra have been obtained in this state and the molecular conformation is the same as T form in both the solid phases. For CH 3CH 2OP(O)Cl 2, trans-trans (TT) and trans-gauche (TG) forms are present in the liquid state and only the TT form exists in the solid state. The enthalpy differences between the isomers for both the molecules are measured.

The crystal and molecular structure of γ-hydroxy-β-amino butyric acid

The crystal structure of γ-hydroxy-β-aminobutyric acid was determined byMULTAN system with X-ray intensity data on a diffractometer and refined by the least-squares method to an Rvalue 0.034 for 711 reflections. The crystals were orthorhombic, space group P212121, Z=4, with a=10.220, b=8.257 and c=6.556A. The molecule takes the zwitterionic form and skeletal conformation is trans-trans form. The molecules are held together by intra-and intermolecular NH---O and OH---O hydrogen bonds.

ChemInform Abstract: INTERNAL ROTATION IN PROPYL MERCAPTAN BY MICROWAVE SPECTROSCOPY

Abstract The microwave spectra of propyl mercaptan and its six deuterated species were assigned for two rotational isomers, the trans-gauche and trans-trans forms, where the first refers to the isomerism around the central CC bond, and the second, to the one around CS bond. The double minimum splittings of the gauche isomers were directly observed for the species having the symmetry plane in the frame. The rotational constants and the torsional splitting of the gauche isomers of the normal species were determined to be A = 23 907.47 ± 0.09, B = 2345.597 ± 0.006, C = 2250.338 ± 0.009, and Δ ν = 1613.01 ± 0.04 MHz. From the torsional splittings of the normal and SD species and the energy difference of two isomers, the Fourier coefficients of the thiol internal rotation potential function were determined to be V 2 = −353 ± 6, and V 3 = 1310 ± 9 cal/mol on the assumption that V 1 was the same as that of ethyl mercaptan. The dipole moments and their components were also obtained from the Stark effect measurements of the two isomers of the normal and SD species. The directions of the dipole moments were discussed.

CONFIGURATION OF OCTADECYL TETRASULFIDE

Abstract Open-chain organic tetrasulfides can exist in three distinct conformations known as cis-cis, cis-trans, and trans-trans forms. Previously, the structure of only one other open chain organic tetrasulfide, benzylidenimine tetrasulfide, has been established and this compound has a cis-cis configuration. Now we can report that octadecyl tetrasulfide crystallizes in the trans-trans form, is nonbranched, nonplanar, and has two different sulfur-sulfur bondings. Its central S-S bond (2.060Å) is longer than the terminal S-S bond (2.018Å). The central bond length of 2.060Å is close to the average value of 2.08Å selected by Pauling as a normal S-S single bond. Terminal bond lengths of 2.018Å represent another type of S-S bonding that displays some double bond character. A central torsion angle (dihedral angle) is 65.3 (±2)° and this is considerably less than the optimum value of 90° postulated by Pauling. Octadecyl tetrasulfide crystallizes in the monoclinic space group C2/c with a = 5.44Å, b = 9.43Å, c = 78.3Å, β = 90.6°, and z = 4. The compound is stable at ordinary laboratory temperatures under indirect lighting.

Internal rotation in propyl mercaptan by microwave spectroscopy

The microwave spectra of propyl mercaptan and its six deuterated species were assigned for two rotational isomers, the trans-gauche and trans-trans forms, where the first refers to the isomerism around the central CC bond, and the second, to the one around CS bond. The double minimum splittings of the gauche isomers were directly observed for the species having the symmetry plane in the frame. The rotational constants and the torsional splitting of the gauche isomers of the normal species were determined to be A = 23 907.47 ± 0.09, B = 2345.597 ± 0.006, C = 2250.338 ± 0.009, and Δ ν = 1613.01 ± 0.04 MHz. From the torsional splittings of the normal and SD species and the energy difference of two isomers, the Fourier coefficients of the thiol internal rotation potential function were determined to be V 2 = −353 ± 6, and V 3 = 1310 ± 9 cal/mol on the assumption that V 1 was the same as that of ethyl mercaptan. The dipole moments and their components were also obtained from the Stark effect measurements of the two isomers of the normal and SD species. The directions of the dipole moments were discussed.

Infrared spectra and configurations of dialkylureas

Infrared spectra of 30 dialkylureas of the type [ RHNCONH R'] have been investigated in the solid state in the 4000-400 cm −1 region. The interpretation of the spectra and the assignments of the bands have been made on the basis of the frequency shift by deuteration and of the information from the previous study on sym-dimethylurea ( s-DMU) including a normal coordinate analysis. From the positions of the amide characteristic bands, the molecular configuration of the dialkylureas is concluded to be trans-trans form just as in s-DMU.

Complexes of diacetamide and divalent transition metal salts

Thirty complexes of diacetamide with divalent transition metal salts have been isolated. Some of the more unusual features of these complexes are: complexation of diacetamide in both the cis-trans and trans-trans forms and the formation of the unusual tetrahedral anionic species Co 2Br = 6 and Co 2Cl = 6. The greatest number of complexes were prepared with CoBr = 2: [Co(DA) 4(H 2O) 2]Br 2, [Co(DA) 3]Br 2, [Co(DA) 3][CoBr 4] and [Co(DA) 3][Co 2Br 6]. All of the configurations in these and the other compounds were deduced from visible spectra and were supported via infra-red and magnetic susceptibility data. The complexes of other Co(II), Ni(II), Fe(II), and Mn(II) salts all contain octahedrally co-ordinated central metal ions.