YEARS OF LIGAND - FIELD - . THEORY Hermann Hartmann

This paper gives a short description of the historicaldevelopment of ligand field theory, including a presentationof the basic ideas and of the most important results , together with, personal remembrances out of the pioneering period. . In 1951 I published under my name and the name of my friend and cOworker F.E. use (Ref. 1) our first papers concerning a theory of the term systems of complex ions developed on the basis of the electrostatic theory of complex compounds which had been founded by A. Magnus (Ref. 2) in 1922. F.E. use was my second doctorand. His thesis (Ref. 3) was finished in 1946. He died in 1949. In the same year 1951 at the international soectroscopists' meeting held in Basel, Switzerland, I gave a report about whatwe meanwhile called "Liganden— feldtheorie". I used that word in my lecture held in Basel and I think that was the first time it was used, because all papers concerning the theory of term systems of complex ions on the basis of the electrostatic theory written by other scientists appeared at least one year later. In my talk in Basel I also mentioned the experimental results which my coworker H.L. Schlàfer (Ref. 4) had described in his thesis in 1950. Schläfer had investigated the light absorption of Ti(3+)-complex ions as the most simple cases suited to test the propositions of our liaand-field-theory. My friends in the organizing committee of this congress 25 years after our first publications have entrusted me with the task to speak about 25 years of ligand-fie,ld-theOry. . . . For me it is a bit difficult to do that, because I am quite sure that I am not the right man to take you all on a highly intensive tour d'horizon through a quarter of a century of theoretical comnlex chemistry. I resolved to do the following: at first I shall try to describe the. situation in. theoretical complex chemistry in 1945. Then I shall explain the basic idea of our ligand-field-theory. I think that will be useful because modern complex chemists work with much more advanced theoretical programs and perhaps are not so well .aware about the first steos. In that part of my talk I shall say how and why ligand-field-theory works. Then I shall pick out two typical examples and show which types of results in my opinion are the most important ones. Then .1 want to say only a few words about further developments which led to the present satisfying situation in theoretical complex chemistry, but point out the relation of ligand-field-theory to a kind of complementarity principle between knowledge and understanding. After that I shall collect some personal facts, which may be useful for those who are interested in the phenomena of the genesis of science. All other people in the audience I beg to excuse this short introductory chapter of my talk. At the end I want to say something about my personal relation to ligand-field-theory. . Alfred Werner (Ref. 5) in his Nobel-Lecture from 1914 has been very cautious with statements about the nature and the action of chemical forces in complex compounds. In his famous book from 1905 he had tr.eated complex chemistry. from a purely phenomenologicál point of view.