THE Fddd DIFFRACTOMETER: HARDWARE INNOVATIONS AND A STUDY OF [Zn(H2O)6][C6H2(COOH)2(CO)2]. R.C.B. Copley,a C.W. Lehmann,a J.A.K. Howard,a K. Wade,a G. Walker,a J.M. Archer,b and K.N. Trueblood.c aDept. of Chemistry, University of Durham, Durham DH1 3LE, UK; bInstitute Laue Langevin, BP 156X, F-38042 Grenoble, France; cDept. of Chemistry and Biochemistry, UCLA, CA, 90024, USA.
The Fddd four-circle diffractometer has been developed to collect X-ray diffraction experiments at temperatures down to 9K and here we describe some hardware innovations and a study at five different temperatures on the compound [Zn(H2O)6][C6H2(COOH)2(CO)2] (1). The diffractometer consists of: (i) a Siemens molybdenum rotating anode generator; (ii) Huber circles with offset chi; (iii) a Siemens Fast Scintillation Detector; and (iv) an APD `202' Displex cryogenic refrigerator.
The belt-driven rotating anode gives X-ray fluxes far superior to those obtained with a conventional X-ray tube. X-ray alignment requires precise movements of the 300kg circles and this is achieved using air pads attached to the base of the goniometer. When activated with compressed air, the pads `float' above the polished surface of an aluminium tabletop and allow precise movements of the circles.
The steel braided gas lines between the Displex and the helium compressor are supported by a counter balance system. The stress on these lines has been reduced by attaching them to the Displex via rotating joints and by passing them through a metal ring 50cm above the Displex. The ring is supported by a framework attached to the chi circle. A compact vacuum gauge has been mounted through one of the four ports on the top of the cryostat and gives interesting information on the vacuums obtained within the Displex during an experiment. Crystals are mounted on `sharpened' 0.3mm graphite pencil leads and a new sample mount has been designed.
X-ray diffraction data for 1 have been collected at 296, 210, 120, 50 and 9K. Full analysis of the ADPs at the different temperatures demonstrates the high resolution capabilities of the Fddd diffractometer.