Search results for "Catalysis"
showing 10 items of 5944 documents
Electronic, vibrational, and structural properties of a spin-crossover catecholato-iron system in the solid state: theoretical study of the electroni…
2005
As a functional model of the catechol dioxygenases, [(TPA)Fe(Cat)]BPh4 (TPA = tris(2-pyridylmethyl)amine and Cat = catecholate dianion) exhibits the purple-blue coloration indicative of some charge transfer within the ground state. In contrast to a number of high-spin bioinspired systems, it was previously shown that, in the solid state, [(TPA)Fe(Cat)]BPh4 undergoes a two-step S = 1/2 = S = 5/2 spin-crossover. Therefore, the electronic and vibrational characteristics of this compound were investigated in the solid state by UV/Vis absorption and resonance Raman spectroscopies over the temperature range of the transition. This allowed the charge-transfer transitions of the low-spin (LS) form …
The prediction of the nuclear quadrupole splitting of 119Sn Mössbauer spectroscopy data by scalar relativistic DFT calculations.
2006
The electric field gradient components for the tin nucleus of 34 tin compounds of experimentally known structures and Sn-119 Mossbauer spectroscopy parameters were computed at the scalar relativistic density functional theory level of approximation. The theoretical values of the electric field gradient components were used to determine a quantity, V, which is proportional to the nuclear quadrupole splitting parameter (Delta E). In a subsequent linear regression analysis the effective nuclear quadrupole moment, Q, was evaluated. The value of (11.9 +/- 0.1) fm(2) is a significant improvement over the non-relativistic result of (15.2 +/- 4.4) fm(2) and is in agreement with the experimental val…
Cover Picture: Solid-State Molecular Nanomagnet Inclusion into a Magnetic Metal-Organic Framework: Interplay of the Magnetic Properties (Chem. Eur. J…
2015
Breaking the semi-quinoid structure: spin-switching from strongly coupled singlet to polarized triplet state.
2014
2,7-TMPNO (4,5,9,10-tetramethoxypyrene-2,7-bis(tert-butylnitroxide)) was found to exist in semi-quinoid form with unprecedented strong intramolecular magnetic exchange interaction of 2 J/kB = 1185 K operating over a distance of 10 A. Structural transformations with the activation energy of ΔEeq = 949 K were observed by varying the temperature, from more quinoid structure at low temperature to more biradicaloid structure at higher temperature. Moreover, this molecule undergoes a transient spin transition from singlet to polarized triplet state upon photoexcitation revealed by TREPR spectroscopy. The spin Hamiltonian parameters were determined to be S = 1, g = 2.0065, D = -0.0112 cm(-1), and …
Die dimerisierung von endständigen α-hydroxyacetylenen mit rhodiumkomplexkatalysatoren
1978
Abstract The dimerisation of monosubstituted α-hydroxyacetylenes, which is catalysed by rhodium complexes, yields 1,4-disubstituted vinylacetylenes. The catalyst has been optimized for 3-methylbut-1-yn-3-ol as the substrate by using different ligands. Kinetic measurements were carried out with the monomers 3-methylbut-1-yn-3-ol, 3-methylpent-1-yn-3-ol and 1-ethynylcyclohexan-1-ol. In addition the rates of the dimerisation have been compared with those for a further series of α-hydroxyacetylenes. The by-products from the reaction of 3-methylbut-1-yn-3-ol with [(C 6 H 5 ) 3 P] 3 RhCl as catalyst were determined and the yields of the products compared with those of but-1-yn-3-ol and prop-1-yn-…
Density functional theory study of the Lewis acid-catalyzed Diels-Alder reaction of nitroalkenes with vinyl ethers using aluminum derivatives
2002
The inverse electron demand Diels–Alder reaction of nitroalkenes with vinyl ethers catalyzed by Lewis acids based on aluminum metal, AlMe3, Al(OMe)3 and AlCl3 was studied using density functional theory methods. A continuum model was selected to represent the effects of dichloromethane used as solvent. For this cycloaddition reaction two reactive channels corresponding to the endo and exo approach modes of the vinyl ether to the Lewis acid-coordinated nitroalkene were studied. Coordination of the aluminum metal to an oxygen atom of the nitroalkene increases the electrophilicity of the heterodiene, decreasing the activation energy of the cycloaddition. The substitution effect on the aluminum…
Initial Radical Cation Pathway in the Mo2Cl10-Mediated Dehydrogenative Arene Coupling
2015
Experimental (EPR) and theoretical (DFT) evidence is provided for radical cation formation as initial step in the Mo2Cl10-mediated dehydrogenative arene coupling. The initial electron transfer from methoxyarenes to molybdenum proceeds via an inner sphere mechanism.
Impact of the synergistic collaboration of oligothiophene bridges and ruthenium complexes on the optical properties of dumbbell-shaped compounds.
2012
The linear and non-linear optical properties of a family of dumbbell-shaped dinuclear complexes, in which an oligothiophene chain with various numbers of rings (1, 3, and 6) acts as a bridge between two homoleptic tris(2,2'-bipyridine)ruthenium(II) complexes, have been fully investigated by using a range of spectroscopic techniques (absorption and luminescence, transient absorption, Raman, and non-linear absorption), together with density functional theory calculations. Our results shed light on the impact of the synergistic collaboration between the electronic structures of the two chemical moieties on the optical properties of these materials. Experiments on the linear optical properties …