W0090: Small Molecule Single Crystal Diffraction at the Intense Pulsed Neutron Source (Ipns)

W0090

Small Molecule Single Crystal Diffraction at the Intense Pulsed Neutron Source (IPNS). Arthur J. Schultz, IPNS Division, Bldg. 360, Argonne National Laboratory, Argonne, IL 60439-4814

Small molecule crystallography using pulsed neutrons is now an established method for providing positional and thermal parameters with proven accuracy. Although data collection and reduction is different than for single wavelength experiments, refinement of the structural model is performed in the usual manner. The time-of-flight (TOF) Laue technique can routinely measure data out to (sin[theta])/[lambda] of 1.2 to 1.4 Å^-1, permitting the analysis of anharmonicity in certain cases. Data sets sufficient to provide atomic connectivity and bond lengths in crystals with more than 100 independent atoms can be obtained in a 2 weeks of beam time. Sample temperatures and pressures of 2.5 to 1000 K and of 0 to 5 kbar are easily achieved. Because the TOF Laue technique provides a sampling of a volume of reciprocal space with a stationary crystal and detector, it is also very useful for characterizing phase transitions with accompanying satellite or superlattice peaks. The types of experiments performed by users on the IPNS Single Crystal Diffractometer (SCD) have included hydrogen bonding studies, transition metal hydride and molecular dihydrogen complexes, complexes with C-H^...metal interactions, organic and high-T_c superconductors, and a variety of structural (disorder-order, Jahn-Teller switches, ferro- to paraelectric transitions) and magnetic (antiferromagnetic ordering) phase transitions due to variation of temperature and pressure. The IPNS is a national user facility with 75% of the beam time on most of the instruments available to users who are provided assistance with collecting and analyzing data. Proposal forms and other information are available from the IPNS Web site (http://www.pns.anl.gov/). A description of the single crystal TOF Laue technique, the scientific accomplishments, the procedure for obtaining beam time, and prospects at the future Spallation Neutron Source (SNS) at Oak Ridge will be presented.

This work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences, under Contract W-31-109-ENG-38.