Thomas F. Koetzle

SINGLE CRYSTAL NEUTRON DIFFRACTION FOR THE INORGANIC CHEMIST – A PRACTICAL GUIDE

Advances and upgrades in neutron sources and instrumentation are poised to make neutron diffraction more accessible to inorganic chemists than ever before. These improvements will pave the way for single crystal investigations that currently may be difficult, for example due to small crystal size or large unit cell volume. This article aims to highlight what can presently be achieved in neutron diffraction and looks forward toward future applications of neutron scattering in inorganic chemistry.

Topaz: a single-crystal diffractometer for the spallation neutron source

A single-crystal, time-of-flight Laue diffractometer, Topaz, is under development for the SNS (Spallation Neutron Source). The Topaz instrument design is optimized for studying samples with unit cell repeats up to 50 A. An innovative bent, focusing neutron guide on an 18 m flight path will produce enhanced flux on sample, while an array of highly pixilated Anger camera detectors will provide coverage over a large volume of reciprocal space. Because the crystal volumes required on Topaz are expected to approach those of typical ’’X-ray size’’ samples, the instrument promises to revolutionize the application of singlecrystal neutron diffraction as we know it, particularly from the viewpoint of the practicing synthetic chemist. Besides conventional structure analysis, Topaz will support the measurement of diffuse scattering to study disorderedmaterials and a polarized beam option to study magnetic systems. Topaz is expected to come on line in 2009. The instrument will be operated in a broadly based usermode, and theTopaz IDT (InstrumentDevelopment Team) accordingly welcomes inquiries from all interested parties. Acknowledgement. The Office of Science, United States Department of Energy, provides financial support for this work. SNS is managed byUT-Batelle, LLC, under contract DE-AC0500OR22725. m44.o04

TOPAZ: a new time-of-flight Laue diffractometer for new science

(iBIX)”, which is now constructing at Materials and Life-science Facility (MLF) of J-PARC. STARGazer has several functional components; 1) peak search from the raw data, 2) determination of the UB matrix, 3) finding the Bravais lattice, 4) refinement of the UB matrix, 5) calculate the intensities of all Bragg reflections, and 6) data visualization. The algorithms of crystallographic fundamental functions of those components referred the algorithms of program ISAW, which is a data processing software package developed on Argonne National Laboratory. In addition, STARGazer has some additional functions optimized for the measurement of protein crystals on the iBIX; real-space indexing technique to find UB matrix, refinement of the detector position simultaneously in UB matrix refinement, and finding the Bragg reflections which are overlapping with neighboring reflections. In the near future, a function to deconvolute the overlapping Bragg reflections will be added. STARGazer was developed based on a software library “Manyo-Lib”, which is a framework software for data analysis at MLF developed by J. Suzuki and co-workers. Each component of STARGazer works independently as a part of Manyo-Lib, and users of other instruments in MLF and other pulsed neutron facilities can easily use the components for their data processing.

Single-crystal neutron diffraction on sigma complexes: recent results from IPNS

E-mail: tkoetzle@anl.gov For a number of years we have been employing single-crystal neutron diffraction to investigate structures of sigma complexes of transition metals. Sigma complexes are of special interest because they are ubiquitous intermediates in metal-catalyzed reactions including hydrogenations, activation and functionalization of hydrocarbons, and hydroborations. Here we will report on some recent results obtained using the SCD instrument at Argonne’s Intense Pulsed Neutron Source, which has been upgraded with two new position-sensitive Anger detectors to achieve increased data collection efficiency. In the future, we hope to be able to dramatically extend these studies at the Spallation Neutron Source (SNS) using the single-crystal diffractometer (Topaz) that is currently under development there.

Scientific Review: Single Crystal Analyses of the Structure and Bonding in Transition-Metal σ-Complexes

Transition-metal _σ-complexes [2] are coordination compounds in which two electrons in an X-H _σ-bond form a dative bond with a transition metal as illustrated in Figure 1. This bond can be further stabilized by π-backbonding from the metal to the X-H σ* antibonding orbital. Transition-metal σ-complexes are typically reactive intermediates that precede oxidative addition of substrates having an X-H bond. σ-complexes are, therefore, intermediates in catalytic hydrogenation (X = H), activation and functionalization of hydrocarbons (X = C), hydro-silylation (X = Si), and hydroboration (X = B) reactions.