Christo Balarew receives Presidential Honors

Professor Christo Balarew is a prominent Bulgarian scientist. During most of his professional career he has worked at the Institute of General and Inorganic Chemistry of the Bulgarian Academy of Sciences in Sofia. Some of his scientific achievements can be summarized by the following:

According to Balarew, inorganic salts are considered ionic coordination compounds. In their crystal structures the metal ions are coordinated by anions or water molecules and in this way coordination polyhedra are formed. They are linked with one another, with other ions, or with water molecules through ionic (electrostatic) or hydrogen bonds. To prognose the composition and structure of the most probable complexes, not only the geometrical factor (Pauling rules), but also Pearson’s concept of hard and soft Lewis acids and bases (HSAB) and crystal field stabilization energy are involved. A procedure for predicting the complexes in the crystal structures was elaborated. On this basis double salts formation was explained and a theory for the isomorphous and isodimorphous co-crystallization was created. This allows theoretical calculations of the distribution coefficients of admixtures between the crystals and the solution and of the free energy of phase transitions to be performed on the basis of solubility data.

Balarew also elaborated a model for explaining the nucleation and the kinetics of crystallization of highly soluble salts.. Nucleation starts when some of the complexes existing in the solution display high activity sufficient to reach and surpass the solubility product of the crystallizing salt. These complexes or some of their directly derivable forms (e.g. those obtained by condensation) together with other ions or molecules form the crystal structure. This means that the activity of definite species in the solution (complexes, molecules or simple hydrated ions) that are able to be incorporated directly or with minor changes into the crystal structure is of primary importance for the crystallization process . The lowest critical supersaturation needed for nucleation and the highest rate of crystallization are displayed by those salts whose complexes in the solution have analogues in the crystal structure of the crystallizing salt. The knowledge of the type and composition of the species in the solution is of crucial significance for the elucidation of the ability for supersaturation and for the crystallochemical explanation of the Ostwald step rule.

The experience accumulated during these scientific studies was applied by Prof. Balarew to the elaboration of technologies for producing reagent-grade chemicals, synthesizing new materials, and developing methods for hydrometallurgical extraction of useful components from natural raw materials or from industrial waste products, including technologies for utilization of marine chemical resources.

Prof. Balarew is an active IUPAC participant, and has been since 1979, mostly in the Analytical Chemistry Division. In 1999 he has been President of the National Committee of Chemistry of Bulgaria for IUPAC. Prof. Balarew is coauthor of many publications in the field of Pure and Applied Chemistry. He was Chair of the 10th ISSP International Symposium on Solubility Phenomena, Varna, 22-26 July 2002. He is a member of the Editorial Boards of many IUPAC - Solubility Data Series Volumes since 1989.