Dear Users,

SAIF, IIT Madras currently houses two single crystal x-ray diffractometers. Older of them, installed in 1992, is a serial Diffractometer (CAD4 Diffractometer, make: M/S Nonius BV, The Netherlands) which can collect only one reflection at a time. This machine is no more used for intensity data collection for molecular structure determination (as it takes, on the average, 50-60 hours for data collection per crystal). The machine is effectively used for morphology measurements. The second machine (Bruker AXS Kappa Apex2 CCD Diffractometer, make: M/S Bruker AXS, Germany) installed in 2006, even though in working condition, is not able to meet the user queue and full requirements due to the following reasons:

1. User queue

X-ray structure has almost become a mandatory requirement for publication of newly synthesized crystalline compounds. This has led to multifold increase in the number of single crystal XRD users all over the country. At present, the average waiting time for a single crystal XRD user at SAIF, IIT Chennai is 2 months.

2. Light atom structures and absolute configuration.

The Diffractometer (Bruker AXS) currently housed in SAIF, IITM is custom built for molybdenum x-ray source alone. Mo-source is not the best suitable source for collecting data of light atom structures. The recommended x-ray source for light atom structures is that of Cu. The Cu source has higher photon count and hence higher incident intensity. For weakly diffracting light atom crystals, Cu source gives much better results as compared to Mo. Another problem faced with Mo source is the difficulty in finding the absolute configuration of light atom structures.

As the light atoms (atomic weight < sodium) do not have significant anomalous dispersion for Mo(Kα) radiation, it is practically impossible to determine the absolute structure of non-centrosymmetric light atom compounds with Mo source. Organic chemists doing chiral synthesis find it difficult to determine the stereo chemical configuration of their compounds using Mo-radiation. Same problem is faced by phyto-chemists and other researchers who isolate natural products. Situation being this, a Diffractometer equipped with Cu x-ray source has become an absolute requirement in a national center like SAIF, IIT Madras. At present there is no machine in south India (except IISc, Bangalore) with Cu source, which is being run as a national facility.

3. Problems with the existing machine.

The existing CCD machine is 8 years old. The machine is frequently shut down due to several technical problems. As the machine is aging, the down time for the machine is bound to increase in the future.

4. Users

SAIF, IITM single crystal xrd user group is not from south India alone. We still get lot of samples from all over India. Even though there are many other diffractometers in India, the one housed in SAIF, IIT Chennai is the main source of Single Crystal X-ray data for the ´less privileged´ users of Indian Universities. In view of the above mentioned situation, it is felt that the procurement of a new single crystal xrd with dual source (Cu and Mo) will be of great support to academic research in India. As a user of xrd facility at SAIF, IITM, your response in this regard is requested.