Valency

About: Valency is a(n) research topic. Over the lifetime, 1632 publication(s) have been published within this topic receiving 26141 citation(s).

Mixed Valence Chemistry-A Survey and Classification

Abstract: Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.

Class-Based Construction of a Verb Lexicon

Abstract: We present an approach to building a verb lexicon compatible with WordNet but with explicitly stated syntactic and semantic information, using Levin verb classes to systematically construct lexical entries. By using verb classes we capture generalizations about verb behavior and reduce the effort needed to construct the lexicon. The syntactic frames for the verb classes are represented by a Lexicalized Tree Adjoining Grammar augmented with semantic predicates, which allows a compositional interpretation.

Natural resonance theory: II. Natural bond order and valency

Abstract: Resonance weights derived from the Natural Resonance Theory .NRT , introduced in the preceding paper are used to calculate ''natural bond order,'' ''natural atomic valency,'' and other atomic and bond indices reflecting the resonance composition of the wave function. These indices are found to give significantly better agreement with observed properties empirical valency, . bond lengths than do corresponding MO-based indices. A characteristic feature of the NRT treatment is the description of bond polarity by a ''bond ionicity'' . index resonance-averaged NBO polarization ratio , which replaces the ''covalent-ionic resonance'' of Pauling-Wheland theory and explicity exhibits the complementary relationship of covalency and electrovalency that underlies empirical assignments of atomic valency. We present ab initio NRT applications . to prototype saturated and unsaturated molecules methylamine, butadiene , . polar compounds fluoromethanes , and open-shell species: hydroxymethyl . radical to demonstrate the numerical stability, convergence, and chemical reasonableness of the NRT bond indices in comparison to other measures of valency and bond order in current usage. Q 1998 John Wiley & Sons, Inc. J Comput Chem 19: 610)627, 1998

Mn 3s exchange splitting in mixed-valence manganites.

Abstract: We present Mn $3s$ x-ray photoelectron spectra of manganese oxides with the Mn formal valency from $2+$ to $4+.$ We found that the ${\mathrm{Sr}}^{2+}$ doping or cation deficiency in manganites do not change the Mn $3s$ splitting in manganites with the Mn formal valency from $3.0+$ to $3.3+.$ We suggest that doping holes are localized in O $2p$ states.