Topic
Valence (chemistry)
About: Valence (chemistry) is a research topic. Over the lifetime, 24937 publications have been published within this topic receiving 645252 citations. The topic is also known as: valency.
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TL;DR: In this paper, a quantitative study of hole-transfer superexchange in Class II mixed-valence complexes is presented, where the free energy of resonance exchange was calculated from metal−metal coupling elements derived from Hush and CNS models and compared to experimental values that were factored from the free energies of comproportionation.
Abstract: A quantitative study of hole-transfer superexchange in Class II mixed-valence complexes is presented. The free energy of resonance exchange was calculated from metal−metal coupling elements derived from Hush and CNS models and compared to experimental values that were factored from the free energy of comproportionation. The Hush model gave acceptable results for only the most weakly coupled systems while the CNS model gave reasonable predictions throughout the range of coupling studied (valence trapped to nearly delocalized behavior).
142 citations
TL;DR: In this paper, the electron attachment to gas-phase isolated uracil molecules and mixed Uracil−argon clusters is examined in a crossing beam experiment. But the electron-binding process is strongly influenced by solvation, as demonstrated by field-detachment measurements.
Abstract: Rydberg electron attachment to gas-phase isolated uracil molecules and mixed uracil−argon clusters is examined in a crossing beam experiment. By means of reproducible uracil beam conditions, it is possible to control the electron-binding process, which is strongly influenced by solvation. Attachment followed by evaporation of a single argon atom is already sufficient to switch from dipole-bound to valence monomer uracil anions, as demonstrated by field-detachment measurements. The existence of both types of anions is in good agreement with two separate previous theoretical predictions. A DFT calculation of the valence adiabatic electron affinity of uracil provides a small but positive value of 70 meV, close to the measured value of the dipole-bound electron affinity.
142 citations
TL;DR: It is demonstrated that magnetic double exchange can be sustained by simple imidazolate bridging ligands, known to be well suited for the construction of coordination clusters and solids.
Abstract: The field of molecular magnetism has grown tremendously since the discovery of single-molecule magnets, but it remains centred around the superexchange mechanism. The possibility of instead using a double-exchange mechanism (based on electron delocalization rather than Heisenberg exchange through a non-magnetic bridge) presents a tantalizing prospect for synthesizing molecules with high-spin ground states that are well isolated in energy. We now demonstrate that magnetic double exchange can be sustained by simple imidazolate bridging ligands, known to be well suited for the construction of coordination clusters and solids. A series of mixed-valence molecules of the type [(PY5Me(2))V(II)(micro-L(br)) V(III)(PY5Me(2))](4+) were synthesized and their electron delocalization probed through cyclic voltammetry and spectroelectrochemistry. Magnetic susceptibility data reveal a well-isolated S = 5/2 ground state arising from double exchange for [(PY5Me(2))(2)V(2)(micro-5,6-dimethylbenzimidazolate)](4+). Combined modelling of the magnetic data and spectral analysis leads to an estimate of the double-exchange parameter of B = 220 cm(-1) when vibronic coupling is taken into account.
142 citations
TL;DR: In this paper, the effect of K and K-Na substitution for Pb atoms in the rocksalt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power.
Abstract: The effect of K and K-Na substitution for Pb atoms in the rocksalt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power. We combined high-temperature Hall-effect, electrical conductivity, and thermal conductivity measurements to show that K-Na codoping do not form resonance states but can control the energy difference of the maxima of the two primary valence subbands in PbTe. This leads to an enhanced interband interaction with rising temperature and a significant rise in the thermoelectric figure of merit of p-type PbTe. The experimental data can be explained by a combination of a single- and two-band models for the valence band of PbTe depending on hole density that varies in the range of 1-15 x 10{sup 19} cm{sup -3}.
142 citations
TL;DR: An analysis of hot-carrier lifetimes from electron-phonon interaction in lead iodide perovskites using first-principles calculations shows that the holes in CsPbI3 have very long lifetimes in the valence band region situated 0.6 eV below the top of theValence band, while no long lifetime is predicted in PbI 3(-).
Abstract: We report on an analysis of hot-carrier lifetimes from electron–phonon interaction in lead iodide perovskites using first-principles calculations. Our calculations show that the holes in CsPbI3 have very long lifetimes in the valence band region situated 0.6 eV below the top of the valence band. On the other hand, no long lifetime is predicted in PbI3–. These different results reflect the different electronic density of states (DOSs) in the valence bands, that is, a small DOS for the former structure while a sharp DOS peak for the latter structure. We propose a reduction of the relaxation paths in the small valence DOS as being the origin of the slow hot-hole cooling. Analyzing the generalized Eliashberg functions, we predict that different perovskite A-site cations do not have an impact on the carrier decay mechanism. The similarity between the DOS structures of CsPbI3 and CH3NH3PbI3 enables us to extend the description of the decay mechanism of fully inorganic CsPbI3 to its organic–inorganic counterpart...
142 citations