Search results for "Ground State"
showing 10 items of 928 documents
A Diferrous Single‐Molecule Magnet
2007
The diferrous complex [Fe2(acpypentO)(NCO)3] (1),(acpypentO– = the anion of 1,5-bis[2-pyridyl(1-ethylimino)]pentane-3-ol) was studied by spectroscopic (dual-mode X-band EPR and 57Fe-Mossbauer) and magnetic (AC magnetic susceptibility) techniques. Complex 1 (A. K. Boudalis et al., Inorg. Chem.2004, 43, 1574) was previously shown to exhibit an intramolecular ferromagnetic coupling with important single-ion anisotropies with marked differences in the single-ion electronic parameters of the two iron sites. In this contribution, additional studies are carried out to probe its dynamic magnetic properties. Mossbauer spectra recorded at liquid helium temperatures indicate slow paramagnetic relaxati…
Magnetic Study of a Pentanuclear {Co 2 III Co 3 II } Cluster with a Bent {Co II 3 } Motif
2014
We have synthesised and structurally characterised a new pentanuclear mixed-valent cobalt cluster of formula [CoII3CoIII2(OH)2(piv)6(L)2(H2O)4] (piv = trimethylacetate, H2L = salicylideneanthranillic acid) from reaction of a dinuclear cobalt pivalate precursor with a Schiff base type ligand under mild reaction conditions. The core structure can be conveniently described as two fused Co3–μ3–OH triangles with a strict unique sharing vertex point. A complete picture of the magnetic behaviour of this compound is presented. Through combined use of susceptibility, magnetisation, and EPR data as well as broken-symmetry DFT calculations, we have supported the magnetic data that show weak and anisot…
Relaxation Mechanisms of 5-Azacytosine.
2015
The photophysics and deactivation pathways of the noncanonical 5-azacytosine nucleobase were studied using the CASPT2//CASSCF protocol. One of the most significant differences with respect to the parent molecule cytosine is the presence of a dark (1)(nNπ*) excited state placed energetically below the bright excited state (1)(ππ*) at the Franck-Condon region. The main photoresponse of the system is a presumably efficient radiationless decay back to the original ground state, mediated by two accessible conical intersections involving a population transfer from the (1)(ππ*) and the (1)(nNπ*) states to the ground state. Therefore, a minor contribution of the triplet states in the photophysics o…
Solvatochromy and symmetry breaking in two quadrupolar oligophenylenevinylenes
2020
Electrooptical absorption measurements (EOAM), solvatochromic dependences and quantum chemical simulations testify to large dipole moments change of two quadrupolar oligophenylenevinylenes upon transition to Franck-Condon excited state μeFC. The values of the dipole moments μg and μeFC are in the range [(4.2 - 4.9)1030] C m and (30.8 - 47.0)1030C m, respectively. The relations of dipole moments in the ground and excited states determined by EOAM correlate well with results obtained via the solvatochromic method. Calculations carried out by density functional theory (DFT) show that optimized configuration of the ground state of these molecules is not planar. The results from all methods appl…
Extension of Walsh's rules to more general systems
1972
It is demonstrated that location of hydrogen atoms within bonding distance of a simple triatomic molecule can alter the order of energy levels relative to that of the parent system without significantly changing the behavior of the orbital energies under geometrical variation. As a result the ground state electronic configurations of H n AB2 systems often differ from those of triatomics with the same number of electrons and this fact is shown to be directly responsible for the existence of such distinctive geometrical structures as those possessed by cyclopropane, cyclopropyl and allyl cations and cyclopropene. Thus the familiar prescription of Walsh's rules which states that isoelectronic …
General occurrence of polar twisted minima in the ionic singlet excited surfaces of polyenes
1982
Except for a few cases, the lowest closed shell SCF solutions for the twisted geometries of polyenes involves delocalized nonpolarized MO’s, and represents a meaningless mixture of radicalar gound state and ionic excited states. Higher (quasi) solutions allow a realistic approach of the polarized ionic states. Orthogonality to the radicalar ground state may be imposed without important loss of energy. Further extensive CI does not modify significantly the situation. These statements are illustrated through ab initio calculations of butadiene and hexatriene. This approach allows us to show that slight distortions stablize polar minima even in ’’homosymmetric’’ molecules such as all‐trans hex…
Pairing energy effects in cyanide complexes of CpCrIII
1999
International audience; The steric and electronic factors responsible for the reactivity differences between CN and Cl complexes of CpCrIII were examined by DFT/B3LYP computational techniques. The energy difference between quadruplet and doublet [CpCr(CN)2(PH3)], ΔED–Q, was calculated to be 21.2 kcal mol−1 with the LanL2DZ basis set. Although the high-spin configuration is still the ground state for the cyanide complex, the energy gap is 8.7 kcal mol−1 less than that found for the corresponding chloride species. The difference between quadruplet [CpCr(CN)2(PH3)] and doublet [CpCr(CN)2(PH3)2] less free PH3, ΔECr–P, is also smaller than for the Cl system. The components of ΔECr–P for CN and C…
Unconventional dihydrogen-bond interaction induced cyanide-bridged chiral nano-sized magnetic molecular wheel: synthesis, crystal structure and syste…
2019
A pair of cyanide-bridged 4d–3d heterobimetallic chiral macrocyclic enantiomeric magnetic complexes have been successfully assembled from the trans-dicyanoruthenium(III) building block [PPh4][Ru(Salen)(CN)2] (Salen = N,N-ethylenebis(salicylideneaminato)dianion) and [Mn((S,S/R,R)-Salcy)(H2O)2]ClO4 (Salcy = N,N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato)dianion) with the great help of the dihydrogen bond (DHB) interaction and characterized by elemental analysis, IR spectroscopy, circular dichroism (CD) and magnetic circular dichroism (MCD) spectroscopy. Single X-ray diffraction reveals that complex 1, {[Ru(Salen)(CN)2][R,R-Mn(Salcy)]}6·PPh3·6CH3CN·6CH3OH·12H2O, is a neutral dodecan…
Theoretical description of the decays Λb→Λ(*)(12±,32±)+J/ψ
2017
We calculate the invariant and helicity amplitudes for the transitions ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}^{(*)}({J}^{P})+J/\ensuremath{\psi}$, where the ${\mathrm{\ensuremath{\Lambda}}}^{(*)}({J}^{P})$ are $\mathrm{\ensuremath{\Lambda}}(sud)$-type ground and excited states with ${J}^{P}$ quantum numbers ${J}^{P}={\frac{1}{2}}^{\ifmmode\pm\else\textpm\fi{}}$, ${\frac{3}{2}}^{\ifmmode\pm\else\textpm\fi{}}$. The calculations are performed in the framework of a covariant confined quark model previously developed by us. We find that the values of the helicity amplitudes for the ${\mathrm{\ensuremath{\Lambda}}}^{*}(1520,{\frac{3}{2}}^{\ensu…
The Ground State Electronic Energy of Benzene.
2020
We report on the findings of a blind challenge devoted to determining the frozen-core, full configuration interaction (FCI) ground state energy of the benzene molecule in a standard correlation-consistent basis set of double-$\zeta$ quality. As a broad international endeavour, our suite of wave function-based correlation methods collectively represents a diverse view of the high-accuracy repertoire offered by modern electronic structure theory. In our assessment, the evaluated high-level methods are all found to qualitatively agree on a final correlation energy, with most methods yielding an estimate of the FCI value around $-863$ m$E_{\text{H}}$. However, we find the root-mean-square devia…