The word as a unit of meaning. The role of context in words meaning

A unit of meaning is a word plus all those words within its contextual context that are needed to disambiguate this word to make it monosemous. A lot of research were made to study the influence of the context. They testify that there is usually in each word a hard core of relatively stable meaning and can be modified by the context within certain limits

Why Is Uranyl Formohydroxamate Red?

The complexation of UO₂²⁺ by formohydroxamate (FHA^–) creates solutions with dark red coloration. The inherent redox activity of formohydroxamate leads to the possibility that these solutions contain U­(V) complexes, which are often red. We demonstrate that the reaction of U­(VI) with formohydroxamate does not result in reduction, but rather in formation of the putative <i>cis</i>-aquo UO₂(FHA)₂(H₂O)₂, whose polymeric solid-state structure, UO₂(FHA)₂, contains an unusually bent UO₂²⁺ unit and a highly distorted coordination environment around a U­(VI) cation in general. The bending of the uranyl cation results from unusually strong π donation from the FHA^– ligands into the 6<i>d</i> and 5<i>f</i> orbitals of the U­(VI) cation. The alteration of the bonding in the uranyl unit drastically changes its electronic and vibrational features

Spontaneous Partitioning of Californium from Curium: Curious Cases from the Crystallization of Curium Coordination Complexes

The reaction of ²⁴⁸CmCl₃ with excess 2,6-pyridinedicarboxylic acid (DPA) under mild solvothermal conditions results in crystallization of the tris-chelate complex Cm­(HDPA)₃·H₂O. Approximately half of the curium remains in solution at the end of this process, and evaporation of the mother liquor results in crystallization of the bis-chelate complex [Cm­(HDPA)­(H₂DPA)­(H₂O)₂Cl]­Cl·2H₂O. ²⁴⁸Cm is the daughter of the α decay of ²⁵²Cf and is extracted in high purity from this parent. However, trace amounts of ^249,250,251Cf are still present in all samples of ²⁴⁸Cm. During the crystallization of Cm­(HDPA)₃·H₂O and [Cm­(HDPA)­(H₂DPA)­(H₂O)₂Cl]­Cl·2H₂O, californium­(III) spontaneously separates itself from the curium complexes and is found doped within crystals of DPA in the form of Cf­(HDPA)₃. These results add to the growing body of evidence that the chemistry of californium is fundamentally different from that of earlier actinides

Covalency in Americium(III) Hexachloride

Developing a better understanding of covalency (or orbital mixing) is of fundamental importance. Covalency occupies a central role in directing chemical and physical properties for almost any given compound or material. Hence, the concept of covalency has potential to generate broad and substantial scientific advances, ranging from biological applications to condensed matter physics. Given the importance of orbital mixing combined with the difficultly in measuring covalency, estimating or inferring covalency often leads to fiery debate. Consider the 60-year controversy sparked by Seaborg and co-workers (Diamond, R. M.; Street, K., Jr.; Seaborg, G. T. J. Am. Chem. Soc. 1954, 76, 1461) when it was proposed that covalency from 5<i>f</i>-orbitals contributed to the unique behavior of americium in chloride matrixes. Herein, we describe the use of ligand K-edge X-ray absorption spectroscopy (XAS) and electronic structure calculations to quantify the extent of covalent bonding inarguablyone of the most difficult systems to study, the Am–Cl interaction within AmCl₆^3–. We observed both 5<i>f</i>- and 6<i>d</i>-orbital mixing with the Cl-3<i>p</i> orbitals; however, contributions from the 6<i>d</i>-orbitals were more substantial. Comparisons with the isoelectronic EuCl₆^3– indicated that the amount of Cl 3<i>p</i>-mixing with Eu^III 5d-orbitals was similar to that observed with the Am^III 6<i>d</i>-orbitals. Meanwhile, the results confirmed Seaborg’s 1954 hypothesis that Am^III 5<i>f-</i>orbital covalency was more substantial than 4<i>f</i>-orbital mixing for Eu^III

A Pseudotetrahedral Uranium(V) Complex

A series of uranium amides were synthesized from <i>N</i>,<i>N</i>,<i>N</i>-cyclohexyl­(trimethylsilyl)lithium amide [Li]­[N­(TMS)­Cy] and uranium tetrachloride to give U­(NCySiMe₃)_<i>x</i>(Cl)_4–<i>x</i>, where <i>x</i> = 2, 3, or 4. The diamide was isolated as a bimetallic, bridging lithium chloride adduct ((UCl₂(NCyTMS)₂)₂-LiCl­(THF)₂), and the tris­(amide) was isolated as the lithium chloride adduct of the monometallic species (UCl­(NCyTMS)₃-LiCl­(THF)₂). The tetraamide complex was isolated as the four-coordinate pseudotetrahedron. Cyclic voltammetry revealed an easily accessible reversible oxidation wave, and upon chemical oxidation, the U^V amido cation was isolated in near-quantitative yields. The synthesis of this family of compounds allows a direct comparison of the electronic structure and properties of isostructural U^IV and U^V tetraamide complexes. Spectroscopic investigations consisting of UV–vis, NIR, MCD, EPR, and U L₃-edge XANES, along with density functional and wave function calculations, of the four-coordinate U^IV and U^V complexes have been used to understand the electronic structure of these pseudotetrahedral complexes