which would be in agreement with the (irregular) increase in the differences A6=16(x)-6(x+ 1)1 in the series [P7 -x A~x ] 3 ~ with increasing x. It is also possible, however, that this heteroanion is unstable and decomposes into As: -and, for example, [P2Ass]37, because incorporation of the small P atom into the large As, cage is unfavorable. The "P-NMR spectra of solutions of mixtures of the pure compounds Rb3P7 and Rb3As, exhibit, even after several weeks, only the signal of P;-, so that no exchange between P:-and As:-occurs in solution.The intensities of the 3'P-NMR signals-after correction with respect to the number of P atoms involved in the heteroanion-indicate a preference for the groups [P6AsI3and [P,As,]'-, but none for [P4As3I3-, as would have been expected based on the concept of topological charge stabilization. With increasing content of arsenic, the valence tautomerism becomes slower, as shown by the increasing halfwidths of the signals. The question remains open, therefore, whether As:-also has a fluxional structure in solution.
K4Nb6Cl18 läßt sich in kristalliner Form durch Erhitzen von Nb6Cl14 mit KCl oder einfacher aus KCl, Nb3Cl8 und Nb darstellen. Die Verbindung wird durch ihr chemisches, thermisches und optisches Verhalten charakterisiert. K4Nb6Cl18 kristallisiert monoklin in der Raumgruppe C 32h—C 2/m (a0 = 9,97; b0 = 16,51; c0 = 9,47 Å β = 115°). Die Struktur wurde durch optische Nachbildung der FOURIER. Transformierten und rechnerisch ausgeführte Verfeinerung bestimmt. Neuartig ist das Auftreten des anionischen Komplexes {[Nb6Cl12]Cl6}4−. Die darin enthaltene oktaedrische Nb6−=Gruppe ist regulär (dNb−Nb = 2,915Å K4Nb6Cl18) zeigt schwachen, von der Temperatur unabhängigen Paramagnetismus.
Although the diselane 1 is stable upon exposure to air, it is attacked rapidly by iodine, resulting in the formation of 2,4,6‐tri‐tert‐butylphenyl(iodo)selenide 2. Compound 2, which forms anthracite‐black crystals melting at 156°C, is also monomeric in the solid state, the SeI bond being 252.9 pm long. Upon dissolving, 2 decomposes to the starting materials.
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