click ON this photo if you wish to see a decent enlargement 


A Report


Strength from Weakness :
Structural Consequences of Weak Interactions in Molecules,
Supermolecules and Crystals.

the 32nd crystallographic course at the E. Majorana Centre, Erice, Trapani, Sicily, Italy
sponsored by the International Union of Crystallography

a EuroSummerSchool, supported by the European Commission, Research DG, Human Potential Programme,
High Level Scientific Conferences, contract no. HPCF-CT-1999-00006

23 May (arrival) to 3 June (departure day) 2001


Directors : A. Domenicano, L'Aquila and I. Hargittai, Budapest


Since their inception, crystallographic meetings in Erice have striven to explore frontier topics.
photos of Erice and surroundings have been made available by Michael Quayle and Gareth Lewis, Bristol, participants at Erice 1998





The broad range of topics  was the  most relevant  scientific highlight of this School.  This aspect is expressed symbolically as "Strength from Weakness"; however, its content is  accurately defined by the subtitle "Structural Consequences of Weak Interactions in Molecules, Supermolecules, and Crystals". 


The purpose was approached along two lines.  One was the methodology: all techniques that are important in revealing the molecular structure  were presented, including both computation, such as ab initio calculations and the density functional theory, and the experimental techniques (gas-phase electron diffraction, rotational and  vibrational spectroscopy, X-ray and neutron crystallography, solid-state NMR spectroscopy).   The second foresaw lectures on  the materials under investigation, such as inorganic systems, hydrogen-bonded systems, supermolecules, catalysts, and high-technology materials.


Another highlight was in the panel discussion on the relationship between experimental and computational results and the related discussions.    Six world renowned scientists, equally distributed among experimentalists and  computer experts made their statements: then a broad based discussion was started including the full  audience.


Six microsymposia analysed  few selected areas related to the main theme. The structural changes were discussed that accompany transition from molecule to molecule, from molecule to supermolecule, from molecule to crystal, and from crystal to crystal.    By mixing invited  lecturers and  selected participants, these events broadened the topics and gave the possibility to highlight such important areas as conformational analysis, crystal engineering, and the physical meaning of the parameters yielded by computations and experiments, besides many others.




Lectures and the microsymposia are mainly finalized to  training.   However,  several additional means proved most effective.   Firstly,  the isolated location forced the interaction between lecturers and participants: the meals, coffee breaks, and other social events provided ample opportunity for such interaction.  Secondly,  two poster sessions, followed by an informal buffet dinner in the same space  - a total time of eight hours - gave a further opportunity for interaction.  The lecturers quite willingly visited most posters – a prize has later been assigned to a young researcher from India – and  engaged in direct discussion about  participants' results and objectives.  Thirdly, a dozen  participants volunteered to give brief oral presentations, stimulating the sense of pride and self-awareness in youngsters who were presenting their research for the first time to a highly qualified, international public.    By reporting the results – often quickly retrieved, due to the unexpected event,  from home labs by internet link -  several  participants made reference to the subject matter of the EuroSummerSchool and to various aspects of the lectures attended during the  previous days.




     The School was primarily a European event.  Only nine (out of total 93) non-Europeans  attended the School and their presence was stimulating and conducive to future collaboration.  The presence of nationals from  30 countries generated interactions and fostered future cooperation.  The Europeans who came from their overseas residence gave  successful lectures ( the German Peter Schwerdtfeger, from Auckland, New Zealand,  and the Polish Jerzy Leszczynski, from Jackson, Mississippi, USA)  or  short, highly technological presentation ( the Polish  Dorota Pawlak,  from Sendai, Japan) and computer instructions ( the british John Irwin, from Chicago, Illinois, USA).  They all started useful contacts, facilitated also by the large Polish community present.




Twenty invited speakers and seventythree selected (out of 170 applicants) scientists came from 30 different nations.  


To stimulate discussion and questions during the scientific sessions, crystallography organisers assign yearly the  Erice Vaciago Prize to the most dynamic young (under 35) “student” in the lecture hall :  Ms Agnes Szabados, age 25, Budapest got a certificate and a modest monetary award.  


Since 1978, questionnaires are distributed near the end of the meeting, enquiring about the scientific and organisational aspects of the meeting. The answers by all participants, students and speakers, have produced a figure of merit, 3.21 (out of 4.00), the highest ever recorded:   nine years were gone, in June 2000,  when the 1991 meeting score, 3.17  was beaten of just one point.  Amongst the most enthusiastic answers Erice was indicated at 80% level as the location for a future meeting with similar content. Critics for the few unreadable transparencies were accompanied by general approval for  power point projection of texts and drawings, realized this year at the Majorana Centre under pressure by crystallographers and absolutely necessary for a discipline based on three dimensionality.




Everyone has been told at various level of education about the nature of the chemical bond in the substances under our reach.   A strong electrostatic interaction between opposite charged atoms is defined an ionic bond, the share of a couple of electrons between neutral atoms is called a covalent bond and – more rarely occurring – a moving cloud of free electrons along close-packed metal atoms is defined a metallic bond.


This meeting intended to show why and how accuracy in gas and solid state structure determination has revealed the mechanisms by which both nature and modern technology  relay essentially  on  weak bonds, mostly due to partial charges on atoms or group of atoms in a neutral molecule.


Cell duplication, growth,  drug action, and  also a variety of phenomena in the living organisms, are based on the hydrogen bond, a weak interaction which can easily be broken and reconstructed in biological environments. On another side,  the properties of catalysts, supraconductors, supermolecules, and several materials common to modern technology are due to weak interactions between non charged atoms and molecules.

The synthesis,  modification and behaviour of the inorganic and organic matter has been thoroughly examined by both computational and experimental experts.  Both techniques are shown to explain the most intimate aspects of several types of weak interactions.


As an example, one single phenomenon, polymorphism, can be easily brought to public attention.

Specially for organic and pharmaceutical compounds,  a wealth of weak interactions cause equal molecules to assemble themselves in different ways in the solid state.  Two or more modifications of the same substance, called polymorphs,  show  marked differences in melting point, density, solubility, and several physico-chemical properties producing, as illustrated in two brilliant lectures by Joel Bernstein, Israel, very critical situation for the pharmaceutical companies when they submit a documentation towards patenting a drug.  The presence of medicines with the same active product is therefore explained, and polymorphism is often at the centre of legal battles about huge financial interests.



Based on text provided by the directors, and modified by

Lodovico Riva di Sanseverino on June 18, 2001

Email, fax +390 51 209 4904