Two complexes of CuBr2 with 5-tert-butyl­pyrazole

trans-Di­bromo­bis(5-tert-butyl­pyrazole-N²)copper(II), trans-[CuBr₂(Hpz^tBu)₂] (Hpz^tBu is 5-tert-butyl­pyrazole, C₇H₁₂N₂), ex­hibits a distorted square-planar geometry with a significant tetrahedral twist, while trans-di­bromo­tetrakis(5-tert-butyl­pyrazole-N²)copper(II), trans-[CuBr₂(Hpz^tBu)₄], adopts a distorted octahedral geometry across a crystallographic inversion centre. Both compounds exhibit intramolecular N—H⋯Br hydrogen-bonding interactions.     

Design of an oscillating flow apparatus for the study of low Reynolds number particle dynamics

An apparatus was designed and built to explore the effects of transient flow fluctuations on the dynamic behavior of particles in low Reynolds number (LRN) flows. While many experiments have been performed on LRN particle flows, relatively few have investigated periodic oscillations on the flow dynamics. The apparatus was oscillated at a frequency of 10 Hz with peak-to-peak displacements on the order of 10 mm. Particles of varying densities and diameters were placed into the oscillating flow. Video images of the particle dynamics were captured with both a personal video camcorder and high-speed digital camera. In parallel, computations were performed for the particle system in order to validate the experimental method and apparatus. Received: 25 February 2000/Accepted: 5 September 2000     

Crystal Engineering Using Polyiodide Halogen and Chalcogen Bonding to Isolate the Phenothiazinium Radical Cation and Its Rare Dimer, 10-(3-Phenothiazinylidene)phenothiazinium

Utilizing facile one-electron oxidation of 10H-phenothiazine by molecular diiodine, the solid-state structure of the 10H-phenothiazinium radical cation was obtained in three cation:iodide ratios, as well as its THF and acetone solvates. Oxidation of 10H-phenothiazine with molecular diiodine in DMSO or DMF provided the structure of the radical coupling product 10-(3-phenothiazinyldene)phenothiazinium, which has not been crystallographically characterized to date. The radical cations were balanced by a mixture (I₇)⁻, (I₅)⁻, (I₃)⁻, and I⁻ anions, where a variety of chalcogen, halogen, and hydrogen bonding interactions stabilize the structures to reveal these interesting cationic species.