The perfect pairing (PP) approximation from generalized valence bond theory is formulated in an unrestricted fashion for both closed- and open-shell systems using a coupled cluster ansatz. In the model chemistry proposed here, active electron pairs are correlated, but the unpaired or radical electrons remain uncorrelated, leading to a linear number of decoupled cluster amplitudes which can be solved for analytically. The alpha and beta spatial orbitals are variationally optimized independently. This minimal treatment of electron-electron correlation noticeably improves upon symmetry-breaking problems and other pathologies in Hartree-Fock (HF) theory and may be computed using the resolution of the identity approximation at only a factor of several times more effort than HF itself. PP also generally predicts improved molecular structures over HF. This compact, correlated wave function potentially provides a useful starting point for dynamical correlation corrections. 相似文献
The perfluoroalkyliodine (V) fluorides CF3IF4 and CF3IOF2 react with many alcohols, acids and anhydrids in solution to give fluorine exchange. In all these reactions we observed equilibria, e.g.: These reactions depend strongly on the kind of the reacting compounds and on the conditions, and they can be followed by n.m.r. spectroscopy. When trying to isolate the new derivatives always decomposition takes place.These reactions, the n.m.r. spectra, the properties of the new compounds and the decomposition reactions will be reported. 相似文献
Zusammenfassung Eine Methode zur potentiometrischen Titration von Sulfid mit Natriumplumbat(II)lösung an einer sulfidsensitiven Membranelektrode wird beschrieben. Sie eignet sich zur Bestimmung von 10–4% Sulfid in Gegenwart von Cl–, Br–, J–, SCN–, SO32–, S2O32–
Titration of sulphide with a sulphide-ion sensitive electrode
A method is described for the titration of sulphide with sodium plumbate(II) solution using a sulphide-sensitive electrode. The method is suitable for the determination of 10–4% of sulphide in the presence of Cl–, Br–, J–, SCN–, SO32–, S2O32–.
Wir danken Herrn Dr. K. Obst für wertvolle Hinweise und Diskussionen. 相似文献
Perfluoroorgano tin and lead compounds can be prepared in high yields from the reactions of (CH3)3SnOCOCF3 and (CH3)3Pb(OCOCF3) with perfluoroorgano cadmium complexes. (CH3)3SiOCOCF3 reacts with (CF3)2Cd complexes — probably via the intermediate (CH3)3SiCF3 and CF2 elimination — to form (CH3)3SiF and CF3CdOCOCF3 complexes. While the reaction of (CF3)2Cd·D with (CH3)3SnONO2 yields CF3NO as the only volatile product, (Rf)2Cd·D (Rf C2F5, iC3F7) forms RfCdONO2·D and (CH3)3SnRf. The preparations and properties of the partly new compounds as well as the n.m.r. spectra are described. 相似文献
CF3I(NO3)2 is formed from the reactions of CF3IF2 or CF3IO with N2O5 as well as CF3I with ClNO3. During the reactions of CF3IF2 with N2O5 or CF3I with ClNO3 the intermediate products CF3IF(NO3) or CF3ICl(NO3) can be identified. The preparations, properties, 19F-nmr spectra and the thermal decomposition of CF3I(NO3)2 are described. 相似文献
Zusammenfassung Eine Methode zur kathodenstrahlpolarographischen Bestimmung von Spuren Kobalt und Zink in Nickel und Nickelsalzen wird beschrieben. Die Spuren werden untereinander und von der Matrix über den Anionenaustauscher Dowex 1X8 getrennt. Die Nachweisgrenzen betragen für Kobalt 5·10–4% und für Zink 4·10–4%.
Summary A method is described for the cathode-ray polarographic determination of cobalt and zinc traces in nickel and nickel salts after separation by the anionexchange resin Dowex 1X8. Traces are detectable as low as 5·10–4% and 4·10–4%, respectively.
DTA, DSC and X-ray investigations of Mg(NO3)2 · 6H2O revealed a lattice transformation at (71±2) C withH=12.5 J/g, and congruent melting at 90 C withH=150.3 J/g. The results of the DTA investigations on different Mg(NO3)2-H2O samples are in good agreement with those of solubility investigations. The melting enthalpy of Mg(NO3)3 · 6H2O is lowered considerably by deviation from the stoichiometric water content of the compound. The results allow conclusions as to the application of this salt hydrate as a latent heat-storage material.
Zusammenfassung DTA-, DSC- und röntgenographische Untersuchungen von Mg(NO3)2 · 6H2O zeigten die Existenz einer Gitterumwandlung bei (71±2) C mitH=12.5 J/g und ein kongruentes Schmelzen bei 90 C mitH=150.3 J/g. Die Ergebnisse der DTA-Untersuchungen an verschiedenen Mg(NO3)2-H2O Proben stehen in guter übereinstimmung mit denen von Löslichkeitsuntersuchungen. Durch ein Abweichen vom stöchiometrischen Wassergehalt der Verbindung wird die Schmelzenthalpie von Mg(NO3)2 · 6H2O beträchtlich vermindert. Die Ergebnisse ermöglichen Aussagen zur Anwendbarkeit dieses Salzhydrates als Wärmespeichermedium.
Zusammenfassung Eine Methode wird beschrieben, die die kathodenstrahlpolarographische Bestimmung von Spuren Ni, Pb, Mn, Co, Cu, Fe, Mo in Zinnchloriden in den Bereichen 10–4% (Ni, Pb, Mn, Cu, Fe) und 10–5% (Mo, Co) gestattet. Über den stark basischen Anionenaustauscher AG 1×8 wird das Zinn von den Spurenelementen getrennt.
Cathode-ray polarographic determination of trace elements in tin chlorides
A method is described for the cathode-ray polarographic detemination of traces of Ni, Pb, Mn, Co, Cu, Fe, and Mo in tin chlorides. Tin is separated from the trace metals by ion exchange on the strong basic anion-exchange resin AG 1×8. The detection limits are within the ranges of 10–4% and 10–5%.
DTA and DSC methods and quasi-isothermal and quasi-isobaric thermogravimetry are of great importance in the investigation of salt hydrates as latent heat-storage materials. However, the transferability of the DTA and DSC results is given only for application in static latent heatstorage units. Special calorimetric methods adapted to the storage principle are preferred for the study of salt hydrates under dynamic storage conditions. The findings are discussed in connection with the examples of Na2SO4·10H2O, CH3COONa·3H2O, Na2S·9H2O, Na2S·5H2O, Mg(NO3)2·6H2O, MgCl2·6H2O and the eutectic mixture of Mg(NO3)2·6H2O-MgCl2·6H2O.
Zusammenfassung Bei der Untersuchung von Salzhydraten als Latentwärmespeichermaterialien besitzen DTA-, DSC-Methoden und die quasi-isotherme und quasi-isobare Thermogravimetrie eine wesentliche Bedeutung. Die Übertragbarkeit der DTA- und DSC-Ergebnisse ist jedoch nur für den Einsatz in statischen latentwärmespeichern gegeben. Für das Studium der Salzhydrate under dynamischen Speicherbedingungen werden spezielle, dem Speicherprinzip angepaßte kalorimetrische Methoden bevorzugt. Die Aussagen werden an den Beispielen Na2SO4·10H2O, CH3COONa·3H2O, Na2S·9H2O, Na2S·5H2O, Mg(NO3)2·6H2O, MgCl2·6H2O und der eutektischen Mischung von Mg(NO3)2·6H2O-MgCl2·6H2O diskutiert.
