Small-molecule chemical crystallography–from three to four dimensions: a personal perspective

Abstract

The instrumentation and methodology associated with chemical crystallography has developed extensively over the last 25 years. Data collection times have been reduced from days to hours and even minutes as serial diffractometers have been replaced by area detector systems. The increase in reliability of rotating anode generators and the advent of synchrotron radiation has meant that the available X-ray flux has increased by factors of between 100 to 10,000. These advances coupled with the development of new cryogenic systems and high pressure cells has allowed a range of new types of crystallographic experiment to be undertaken that had not been possible previously. One area that has benefited from these advances is stroboscopic photocrystallography, where it is possible to determine the structure of molecules in a crystalline environment that have lifetimes of only a few microseconds or to monitor reactions as they occur in real time. These experiments originate from technical easier experiments, which include studies of metastable structural states and solid state phase transition. As photocrystallographic techniques in small molecule crystallography develop further it is expected that it will be possible to determine the structures of species that have lifetimes of the order of only nanoseconds.