The CUNY X-ray Facility

Louis J. Todaro, Ph.D., Facility Director

Hunter College of the City University of New York

Department of Chemistry
695 Park Avenue
New York, NY 10065
(212) 772-4992 (phone)
(212) 772-5332 (fax)
mailto:%20Louis.Todaro@hunter.cuny.edu (e-mail)

MISSION:

The mission of the CUNY X-ray Facility is to perform single-crystal analyses for the structure determination of molecules, which make up a crystal. This technique is called single-crystal X-ray crystallography. It is the ultimate method for definitive determination of molecular structures at the atomic level for both organic and inorganic compounds. Its uses range from simple identification of compounds to various exotic configuration and conformational studies.

INSTRUMENTATION:

Bruker-Nonius KappaCCD System

Instrument: Bruker-Nonius KappaCCD, equipped with a CCD detector and a liquid-nitrogen low-temperature device, on a Bruker-Nonius FR590 X-ray generator with a molybdenum sealed tube.

Capabilities: The KappaCCD, acquired in 2001, embodies the state-of-the-art technologies for rapid, precise, and accurate data collection even with small crystals. A charge-coupled device (CCD) detector allows many diffraction spots to be collected simultaneously. Molybdenum radiation with a wavelength of 0.7093 Å is energetic and better suited for inorganic compounds containing heavy atoms, such as, technetium and rhenium, to minimize absorption-correction errors.

Enraf-Nonius CAD4

Instrument: Nonius CAD4 serial diffractometer, equipped with a scintillation detector and a liquid-nitrogen low-temperature device, on a Nonius Diffractis 586 X-ray generator with a copper sealed tube.

Capabilities: A serial diffractometer collects one diffraction spot at a time. This CAD4 is an excellent instrument for teaching crystallographic methods and principles to students. It is safe, rugged, and can illustrate, display, and apply the principles of crystallography. A CAD4 diffractometer requires little maintenance.

Instrument: Nonius CAD4 serial diffractometer, equipped with a scintillation detector, liquid-nitrogen low-temperature device, and a long 2theta-detector arm, on a Nonius FR571 X-ray generator with a copper rotating anode.

Capabilities: The long 2theta-detector arm allows better resolution of diffraction spots for crystals with long unit-cell axes. Copper radiation with a wavelength of 1.54 Å matches the carbon-carbon distance of 1.50 Å in organic structures and thus it is the wavelength of choice to obtain optimal diffraction from organic crystals. The X-ray generator with the copper rotating anode has the advantage of producing a more intense X-ray beam than a sealed X-ray tube, which means that the signal-to-noise ratio is higher than for data from a sealed tube; and thus smaller crystals may be used to collect data.

The low-temperature options immensely improve the flexibility of a diffractometer. When a crystal is cooled, the single-to-noise ratio for intensity measurements of a diffracted beam is significantly enhanced, and thus data collection may be carried out at a faster rate. In Addition, low temperatures can make possible analyses of compounds whose crystallinity deteriorates at ambient temperature.