The structural information collected by X-ray (or neutron) diffraction studies of metallic, ionic, molecular and macromolecular crystals has increased beyond any previously imagined limit. Data are presently compiled in computer-based crystal structure databases. Making particular reference to molecular crystals, it is shown that the information collected may possess a great heuristic value, that is a great potential for guiding the discovery of new chemical facts or the formulation of new chemical theories, provided systematic methods of database analysis and crystal structure interpretation are made available. It is suggested that such methods consist of systematic correlations of structural data pertaining to single molecular fragments as found in many different crystal structures and can be collectively called (crystal) structure correlation methods (SCMs). SCMs are based on the search for and recognition of correlations among the geometrical descriptors of the fragment (structural correlations) and other physical properties of the fragment itself or of the molecule the fragment belongs to (structure-properties correlations). SCMs are systematically reviewed from the point of view of their chemical applications. Chemical themes so far investigated include chemical bonding, molecular interactions, reaction pathways and transition states, conformational interconversions, and reversible or irreversible transformations occurring in the crystalline state. Methodological aspects of SCMs are treated by means of a formalization of the structural correlation concept based on simple analytical mechanics considerations. The meaning of structural correlations, is dicussed in terms of chemical bond theories and potential energy hypersurfaces (principle of structure correlation) and their degree of applicability to chemical kinetics is analyzed in the frame of the Marcus rate-equilibrium theory. In the final section a number of selected SCM applications are discussed in detail, paying particular attention to the chemical relevance of the results obtained.
Structure Correlation Methods in Chemical Crystallography
FERRETTI, Valeria;GILLI, Paola;BERTOLASI, Valerio;GILLI, Gastone
1996
Abstract
The structural information collected by X-ray (or neutron) diffraction studies of metallic, ionic, molecular and macromolecular crystals has increased beyond any previously imagined limit. Data are presently compiled in computer-based crystal structure databases. Making particular reference to molecular crystals, it is shown that the information collected may possess a great heuristic value, that is a great potential for guiding the discovery of new chemical facts or the formulation of new chemical theories, provided systematic methods of database analysis and crystal structure interpretation are made available. It is suggested that such methods consist of systematic correlations of structural data pertaining to single molecular fragments as found in many different crystal structures and can be collectively called (crystal) structure correlation methods (SCMs). SCMs are based on the search for and recognition of correlations among the geometrical descriptors of the fragment (structural correlations) and other physical properties of the fragment itself or of the molecule the fragment belongs to (structure-properties correlations). SCMs are systematically reviewed from the point of view of their chemical applications. Chemical themes so far investigated include chemical bonding, molecular interactions, reaction pathways and transition states, conformational interconversions, and reversible or irreversible transformations occurring in the crystalline state. Methodological aspects of SCMs are treated by means of a formalization of the structural correlation concept based on simple analytical mechanics considerations. The meaning of structural correlations, is dicussed in terms of chemical bond theories and potential energy hypersurfaces (principle of structure correlation) and their degree of applicability to chemical kinetics is analyzed in the frame of the Marcus rate-equilibrium theory. In the final section a number of selected SCM applications are discussed in detail, paying particular attention to the chemical relevance of the results obtained.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
