Structural determination; vibration study and thermal decomposition of [C 5 H 6 N 5 ] 2 SeO 4 ⋅2H 2 O

The rise and fall of adenine clusters in the gas phase: a glimpse into crystal growth and nucleation

The emergence of a crystal nucleus from disordered states is a critical and challenging aspect of the crystallization process, primarily due to the extremely short length and timescales involved. Methods such as liquid-cell or low-dose focal-series transmission electron microscopy (TEM) are often employed to probe these events. In this study, we demonstrate that ion mobility spectrometry-mass spectrometry (IMS-MS) offers a complementary and insightful perspective on the nucleation process by examining the sizes and shapes of small clusters, specifically those ranging from n = 2 to 40. Our findings reveal the significant role of sulfate ions in the growth of adeninediium sulfate clusters, which are the precursors to the formation of single crystals. Specifically, sulfate ions stabilize adenine clusters at the 1:1 ratio. In contrast, guanine sulfate forms smaller clusters with varied ratios, which become stable as they approach the 1:2 ratio. The nucleation size is predicted to be between n = 8 and 14, correlating well with the unit cell dimensions of adenine crystals. This correlation suggests that IMS-MS can identify critical nucleation sizes and provide valuable structural information consistent with established crystallographic data. We also discuss the strengths and limitations of IMS-MS in this context. IMS-MS offers rapid and robust experimental protocols, making it a valuable tool for studying the effects of various additives on the assembly of small molecules. Additionally, it aids in elucidating nucleation processes and the growth of different crystal polymorphs.

Two new organic-selenate salts: syntheses and crystal structures of bis(di-iso-propylammonium) selenate and di-n-butylammonium hydrogenoselenate

Two new dialkyammonium selenate salts [i-Pr2NH2]2[SeO4] (1) and [n-Bu2NH2][HSeO4] (2) have been isolated and characterized by single-crystal X-ray diffraction. Salt 1 crystallizes in the monoclinic system, space group P21/n with a=8.7190(5), b=8.8500(4), c=22.5953(9) Å, β=94.6290(17)°, V=1737.84(14) Å3 and Z=4. Salt 2 crystallizes in the monoclinic system space group P21/n with a=10.9328(9), b=8.1700(6), c=13.8095(11) Å, β=97.130(3)°, V=1223.94(17) Å3 and Z=4. In both salts, dialkylammonium cations and selenate anions are connected through NH···O and OH···O hydrogen bonds. In the crystal structure, 1 and 2 are organized in layer-like arrangements. Structural characterizations were completed by infrared and 1H, 13C{1H} and 77Se NMR spectroscopy and elemental analysis which corroborate the X-ray elucidations.

A compact Raman converter for UV-VIS spectrometers

A small form factor, easily constructed converter that adapts fiber coupled UV/VIS CCD detector-based spectrometers into a right angle scattering Raman spectrometer is described. Its design philosophy and design are discussed. An example measurement, the depolarization ratio of carbon tetrachloride, a classic Raman test compound, is presented. The unique instrument features a blue-violet (405 nm wavelength) diode laser that takes advantage of the inverse fourth power wavelength dependence of Raman scattering. The converter also features Glan-Thompson polarizing prisms that enable measurement of depolarization ratios. The spectrometer is also capable of measuring a standard Raman spectrum. A fiber optic link offers flexibility when adapting the converter to any spectrometer system that accepts a fiber optic input. The performance of the instrument is critically discussed in the context of an example measurement.