Feature article

Member Profile and Favorite Crystal

[Gautam Desiraju] Gautam Desiraju

I was trained as a physical organic chemist before I studied crystallography. My research has always been influenced by these two subjects during my independent career that has so far lasted 33 years. I have tried to look at what determines the crystal structure of a small organic molecule and whether or not one can predict such crystal structures using experimental, computational, or database-related methods. These goals constitute a part of the subject of crystal engineering. This subject today also has come to include an understanding of the process of crystallization. Crystal nucleation is not studied as well as crystal growth. How and why do crystals nucleate? I do believe that such challenging themes will play a natural part in the future of crystallography.

After the landmark studies of Max von Laue and the Braggs, father and son, 100 years ago, crystallography changed from being a subject pertaining to the study of crystals to a study of the determination of the internal structures of crystals from their diffraction patterns. I believe that the phase of research that dealt with structure determination of crystals from their diffraction patterns is now coming to a close. Crystallography will undoubtedly see newer avenues for its progress. One of these will be the study of the crystallization event itself. How does long-range order enter the crystal nucleus? Does a crystal nucleate from an amorphous precursor? Clearly these are questions that cannot be answered with diffraction alone. We also need spectroscopy and computation in big ways to solve these problems. One might also want to redefine what a crystal is to include all species with some degree of order.

My personal goals for the International Year of Crystallography (IYCr) are that it should allow crystallographers to reinforce a sense of group identity and to convey their enthusiasm for this remarkable subject to the larger scientific community. Science brings people together and I believe that the IYCr should be an occasion for us to try and foster relationships between scientists in different countries or in different regions of the world. Because of the universality of science it is natural that scientists from different parts of the world come together, setting aside cultural, social, religious and economic differences that may be otherwise prevalent, and which tend to separate people. The IYCr I believe should also be an occasion when scientists are able to explain to the general public, and also to students and younger people, about the excitement and importance of crystallography as a scientific endeavor.

[Srirangam Temple] Srirangam Temple
[Orlov diamond] The Orlov diamond

I and others have been asked by the Editor of the IUCr Newsletter to mention what I consider to be the most important crystal ever found or grown and why it is important. Any such choice will quite necessarily be subjective and therefore it is difficult to provide a justification beyond a certain level. Anyway, my choice of a favorite crystal is diamond, for both scientific and personal reasons. Till a few hundred years ago all the diamonds in the world were mined in my country. A great number of very famous diamonds like the Koh-i-Noor and the Hope, which intertwine history, geopolitics and intrigue, originate from the famous mines of Golconda, which is not very far from the campus of the University of Hyderabad, where I lived and worked for 30 years. Diamond is one of the earliest crystals whose crystal structure was determined from its diffraction pattern. It was a crystal that greatly impressed C. V. Raman, who referred to it as the prince of solids. I am fascinated by what might, in the end, be called its 'fearful symmetry'. Many questions can be posed about this remarkable crystal. Why is hexagonal diamond, or Lonsdaleite, so uncommon compared to its cubic counterpart? Why is its thermal conductivity so high? Why is it so hard? Why and how do trace gases get occluded in this crystal, giving rise to the remarkable range of color that is observed? As an organic chemist, I could call diamond the 'ultimate cyclohexane' and in this regard its topology is an attractive target for supramolecular synthesis. The diamond network is actively pursued by crystal engineers who work both with pure organics and with metal-organic framework (MOF) compounds.

Ancient Indian writings refer to diamonds as crystals and the ancient Hindu word for diamond is related to the words for thunder and lightning. As early as the third century BC, the octahedral shape of the diamond crystal was noted in India and archeologists have found evidence of diamond-tipped drills from around that time. I have enclosed a picture of the famous Orlov diamond, presently in the Kremlin in Moscow but located till the early 18th century in the Ranganathaswamy temple in Srirangam, Tamil Nadu, India, where it was once one of the eyes of the presiding deity. The Orlov diamond was also mined in Golconda and is preserved in its, currently rare, original cutting that was a specialty in medieval India.

G. R. Desiraju