Band Jahn-Teller instability and formation of valence bond solid in a mixed-valent spinel oxide LiRh2O4

We have synthesized a new spinel oxide LiRh2O4 with a mixed-valent configuration of Rh3+ and Rh4+. At room temperature, it is a paramagnetic metal, but on cooling, a metal-insulator transition occurs and a valence bond solid state is formed below 170 K. We argue that the formation of valence bond solid is promoted by a band Jahn-Teller transition at 230 K and the resultant confinement of t_{2g} holes within the xy band. The band Jahn-Teller instability is also responsible for the observed enhanced thermoelectric power in the orbital-disordered phase above 230 K.     

The protonation constants and 31P NMR of tetra-, penta-, hexa- and heptapolyphospates

The first and second protonation constants of linear polyphosphates at 25°C and ionic strength 0.1 have been evaluated: log K₁ = 8.91, log K₁₂ = 6.13 for P₂O₇^4?(P₂); log K₁ = 8.88, log K₁₂ = 5.86 for P₃O₁₀^5?(P₃); log K₁ = 8.40, log K₁₂ = 6.58 for P₄O₁₃^6?(P₄); log K₁ = 8.15, log K₁₂ = 7.03 for P₅O₁₆^7?(P₅); log K₁ = 8.12, log K₁₂ = 7.16 for P₆O₁₉^8?(P₆); log K₁ = 8.07, log K₁₂ = 7.18 for P₇O₂₂^9?(P₇). The variations of these values with the polyphosphate chain length have been discussed. A simple identification for polyphosphate species utilizing ¹³P NMR signal ratio of middle to end P has been proposed. By applying a micro ion-exchange technique, a rapid concentration of each polyphosphate and the subsequent preparation of the magnesium salt have been accomplished.     

Harmonicity of gradient mappings of level surfaces in a real affine space

In our previous paper [4] we have investigated level surfaces of a non-degenerate function in a real affine space A ⁿ⁺¹ by using the gradient vector field . We gave characterizations of by means of the shape operatorS, the transversal connection , and studied the difference between and the affine normal. In particular we showed that a graph defined by a non-degenerate function satisfiesS=0 and =0. In this paper we consider harmonic gradient mappings of level surfaces and apply these results to a certain problem which is similar to the affine Bernstein problem conjectured by S. S. Chern [3].     

Synthesis and biological activity of (3,5-disubstituted-1H-1,2,4-triazol-1-yl)benzophenone derivatives

The synthesis of (5-acylaminomethyl-3-carbamoyl-1H-1,2,4-triazol-1-yl)benzophenone derivatives 4a-i, 14a-d, 15a-d, 16a-c , is described. Acylation of the key intermediate, 1-benzoylphenylazo-1-aminoacetamide 7, followed by cyclization in the presence of acid afforded 1H-1,2,4-triazole derivatives. These compounds were evaluated for their central nervous system (CNS) activity. Some of these compounds exhibited high activities in anti-pentylene tetrazole and rotarod test in mice when orally administered.     

Ion-exchanger phase spectrophotometry for trace cobalt

An ion-exchanger phase spectrophotometric method with disodium 1-nitroso-2-naphthol-3,6-disulphonate (Nitroso-R salt) has been developed for the determination of cobalt(II) at 0.1 mug/l. levels in sea-water. The sensitivity is about 1000 times that for conventional spectrophotometry.     

Cubane-Type Molybdenum-Zinc or -Cadmium Mixed-Metal Clusters with Diethyldithiophosphate or Nitrilotriacetate Ligands

The reactions of sulfur-bridged clusters, [Mo₃( ₃-S)(-S)₃(-dtp)(dtp)₃(CH₃CN)] (1) in acetonitrile or [Mo₃( ₃-S)(-S)₃(Hnta)₃]^2– (2) in pure water, with zinc or cadmium metal result in the formation of three novel molybdenum-zinc or molybdenum-cadmium mixed-metal clusters, [Zn{( ₃-S)₄Mo₃(-dtp)(dtp)₃(CH₃CN)}₂] (3), [Cd{( ₃-S)₄Mo₃(-dtp)(dtp)₃(CH₃CN)}₂] (4), and [Cd{( ₃-S)₄Mo₃(Hnta)₃}₂]^4– (5), respectively. The X-ray crystal structures of 1·H₂O(1), 3, 4, and [Co(H₂O)₆]₂ 5·22H₂O (5) were determined, and the existence of the sandwich cubane-type cores Mo₃S₄MS₄Mo⁸⁺ ₃ cores (M=Zn, Cd) in 3, 4, and 5 verified. By the change of the ligands, the peak positions at the longest wavelength in the electronic spectra are distinctly different from each other between 4 (856 nm) and 6 (1235 nm). The electronic structures of 3, 4, and 5 have been calculated by Discrete Variational (DV)-X method.     

Ion-exchanger ultraviolet spectrophotometry for uranium(VI)

A sensitive method based on solid-phase spectrophotometry has been developed for the microdetermination of uranium(VI) in water samples. Uranium is sorbed on the anion-exchanger QAE-Sephadex from thiocyanate solution and the absorbance of the exchanger is measured at 300 nm. This method is about 30 times more sensitive than solution spectrophotometry. Absorption spectra of various metals in the anion-exchanger phase are presented and their interferences discussed. A procedure for the cation-exchange separation of uranium from accompanying elements before spectral measurement of uranium is proposed.     

Thiamin ylide: isolation and identification

The action of two equivalents of NaOEt on thiamin hydrochloride in EtOH gives a neutral compound. Spectroscopic data and its chemical behavior indicated that the compound is thiamin ylide $\text{1}$. The chemical behaviors of $\text{1}$ are entirely consistent with those of in situ generated thiamin ylide.     

Unbiased Rotational Motions of an Ellipsoidal Guest in a Tight Yet Pliable Host

In the design of machinery such as steel bearings, a fundamental understanding of material characteristics provides an indispensable basis for the design. Although hydrocarbon cycloarylenes have started to be used for providing unique supramolecular bearings with anomalous dynamic behaviors, their fundamental understanding is immature. A unique property of the cycloarylene host is now reported: the cyclic host is so pliable that it tracks the orientational changes of the ellipsoidal guest, that is, C₇₀ fullerene. Unique structures of the complex were revealed by spectroscopic and crystallographic analyses, and additional theoretical investigations deepened our understanding by revealing the structural changes associated with unbiased rotational motions.