“...crystal engineering attracts scientists with occasionally distant interests: chemists, physicists, mathematicians; both theoreticians and engineers.”

The subject of our paper lies in the interdisciplinary field of crystal engineering that has been intensively developing during the last decade. This field deals with the design of new materials which have many useful properties. Thus, interpenetrating metal-organic framework substances are being used as porous materials or catalysts; some of which have important magnetic, optical, or electronic properties. The field of crystal engineering attracts scientists with occasionally distant interests: chemists, physicists, mathematicians—both theoreticians and engineers. The main problem in obtaining new materials with a desired behavior lies in discovering the relations between chemical composition, structure, and the properties of a particular substance. It is crystal engineering that solves this problem. At the same time, it is a new branch of science, and its theory and methods are still being developed. Therefore, the investigations which result in progress in the theoretical description of crystal structures of new substances attract a great deal of attention across a wide scientific community.

We have proposed a new approach to classify interpenetrating networks and have developed a strict algorithm to recognize them in any crystal structures. This algorithm was implemented in the software package TOPOS that allows any user (even someone having no special grounding) to find and easily investigate interpenetrating arrays of any complexity. The other important result is that we have obtained a comprehensive list of metal-organic interpenetrating frameworks, and a number of them are newly discovered.

  Could you summarize the significance of your paper in layman's terms?

Firstly, the paper gives a strict algorithm of how one can discover new properties (in particular, interpenetration) in newly investigated or even well-known substances. Indeed, many of the metal-organic frameworks in our list (49 of 301) were obtained years ago, but nobody knew that they contained entangled nets. Secondly, we have developed user-friendly software that functions in an automatic mode, which makes procedures which previously would have required exhaustive work from an expert in crystal topology accessible. This is an important step in allowing the wider scientific community, not only crystal engineers, to be involved in the design of new materials. Thirdly, our comprehensive list of interpenetrating frameworks can serve as a directory for our colleagues.

  How did you become involved in this research, and were there successes or failures along the way?

V.A.Blatov:

I graduated from university in 1987 with a diploma in chemistry and over about four years was engaged in the synthesis and crystal chemistry of inorganic compounds. But I always liked mathematics and strict theoretical approaches in science. Crystal chemistry (the term "crystal engineering" was not used at that time) was not a highly developed field in theoretical aspects, and I was dreaming of automating all stages of an analysis of crystal structures. To me, the value of any particular scientific approach can be tested by its ease of realization as an algorithm or a computer program. Thus I began to develop computer programs for crystal chemistry. A real stroke of good fortune was my acquaintance, in 2003, with my future friend and co-author Prof. Davide M. Proserpio, who introduced me to the particular problems of crystal engineering. It turned out that my software, TOPOS, might be very useful in solving many of them, but some refinements in TOPOS were required.

V.A.Blatov & D.M.Proserpio:

At that time we did not think that this rather narrow undertaking, that of programming TOPOS to recognize interpenetrating arrays, would lead us into a close collaboration and an array of many other interesting tasks, new methods, and new computer programs. During the three years of our common research work, we were faced with myriad problems which we always overcame. The primary reason for our effective collaboration is that we complement one other and possess quite similar scientific outlooks.

We think the most important social outcome of our investigations could be a real joining of researchers from different countries and from among different branches of science. We hope that our approach, which can best be described as a "computer analysis of entanglements in extended polymeric structures" will become a competent part of crystal engineering and materials science, and will also attract many researchers across many different disciplines, particularly among younger scientists worldwide.