Crystal structures of 1,1 ',1"-trimethyl-4,4',4"-(1,3,5-triazin-2,4,6-triyl)tripyridinium trisiodide (m.p. 383C) and 4-cyano-1-methylpyridinium triiodide (m.p.118C) are described. These red salts were obtained unexpectedly from yellow 4-cyano-1methylpyridinium iodide in either water or methanol solution in contact with insoluble heavy metal chlorides under ambient conditions. Neither compound is widely described in the chemical literature.
Three dipeptides bearing alkynes on their side chains (9 (derived from dilysine), 14 (derived from dicysteine) and 17 (derived from diglycine)) were prepared and reacted with W(CO) 3 (dmtc) 2 [dmtc = dimethyldithiocarbamate] to afford, respectively, three metallacyclicpeptides, 18, 19 and 20. The metallacyclicpeptides were characterized by HPLC, ES-MS, and 1 H NMR. The conformational behavior of the alkynes about the tungsten center was assessed using 1 H NMR. It was found that all three metallacyclicpeptides adopt multiple conformations of the alkynes relative to the tungsten. Both 18 and 19 appear to adopt all 8 possible conformations, while 20 adopts a limited number of conformations. The ability of the alkynes to equilibrate between the syn and anti conformations was assessed by examining the alkyne hydrogen resonances using variable temperature 1 H NMR. It was found that the alkyne ligands in 18 and 19 will equilibrate between the syn and anti conformations. The alkyne hydrogen resonances in 18 coalesce to one signal around 343K, while the alkyne hydrogen resonances in 19 do not completely coalesce even by 360K. Complex 18 has a larger ring than complex 19, and the higher temperature of coalescence for 19 is attributed to its smaller ring size. In contrast, complex 20, which has the smallest ring size, cannot equilibrate between the syn and anti conformations, even at elevated temperatures. The results show that cyclic tungsten-bis(alkyne) complexes will form ring systems with ring sizes of approximately 10 atoms, that ring sizes of approximately 10 atoms are rigid, and that rigidity is lost as the ring size is increased.
An update to the thermochromic cobalt(II) chloride equilibrium demonstration is described. Filter paper that has been saturated with aqueous cobalt(II) chloride is heated for seconds in a microwave oven, producing a color change. The resulting pink and blue map is used to colorfully demonstrate Le Chatelier's principle and to illuminate the hot spots in the microwave oven. The demonstration is a quick, easy, and colorful way to introduce Le Chatelier's principle to students in high school or general chemistry courses.
In the crystal of the title molecular salt, C7H7N2
+·ClO4
−, the components are linked by C—H⋯O and C—H⋯N interactions, generating zigzag chains running parallel to [100].
In the title molecular salt, C7H7N2
+·Br−, all the non-H atoms lie on crystallographic mirror planes. The packing consists of (010) cation–anion layers, with the cations forming dimeric units via very weak pairwise C—H⋯N interactions. Weak C—H⋯Br interactions link the cations to the anions.
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