Eduard Zintl

Eduard Zintl ( born January 21, 1898 in Weiden in der Oberpfalz, † January 17, 1941 in Darmstadt ) was a German chemist, after the chemical classes of Zintl phases and Zintl ions are named as well as the Zintl border between 3 and 4th main group of the periodic table of elements.


Schooling and studies

His school days spent Eduard Zintl in pastures and Bayreuth. After he had moved with his family to Munich, he was 18 years old the Abitur examination. At this time, just the first World War was raging in Europe, the young Edward was called up for military service. His chemistry studies at the Bavarian Academy of Sciences, he was thus able to accommodate only 21 years old. But that did not prevent him to start an unparalleled academic career. Already in the first semesters, he fell through above-average grades on - Otto Hönigschmid, head of the German atomic weight laboratory, became aware of him: he made ​​him the famulus ( student assistants ) and asked him his private laboratory available where Eduard Zintl on the provisions of important atomic weights ( bromine, antimony, silver, gold, ... ) involved. He even received a special permit: he could begin his dissertation before he his second association exam (equivalent to the diploma examination ) had filed.

PhD and Habilitation

Eduard Zintl his doctorate in 1923, at the age of 25 years with the work " revision of the atomic weight of bromine by complete synthesis of silver bromide ." As a private assistant in the nuclear laboratory, he was responsible for his doctoral degree graduate students of Otto Hönigschmid (including Günther Rienäcker and Joseph Goubeau ) and devoted himself to the hitherto neglected potentiometric titration, a quantitative analysis method. In this field, he was soon to luminary.

In addition, he authored a textbook entitled " Introduction to the study of inorganic chemistry ." The preface of the comprehensive good 360 pages work begins with a sentence that was typical of his style of teaching and would accompany him through his life: "Modern Inorganic Chemistry is applied physical chemistry ." Inspired by recent studies by Charles August Kraus, found the deep blue solutions of metals in liquid ammonia his ever increasing interest. Already in Munich, he began with their closer exploration. In 1925, two years after his graduation, Eduard Zintl habilitation in chemistry. At the time in Munich " Atomic Lab " at Otto Hönigschmid he always looked back with joy. He used a very warm relationship with his doctor father, whose favorite pupil he was, and who had referred to him as " the most outstanding and versatile head in the field of contemporary inorganic chemistry." The work in the nuclear laboratory earned him luck in his private life. He learned here Margarethe Steinheil know and love, which was awarded his doctorate at the same institution. The two married in 1924.

1928-1933: Professor at the University of Freiburg

Eduard Zintl remained at the Munich Academy as curator until 1928 he followed a call as associate professor at the Albert -Ludwigs- University of Freiburg. Here he became head of the department of inorganic chemical laboratory. Space and funds were not exactly generous, but Eduard Zintl conducted with great experiment his lab and went full on in his work. He and his graduate students to have lived virtually in the laboratory.

A little distracted by events outside the research, Eduard Zintl developed a subject with which his name should remain connected even after his death for ever: the area of the intermetallic phases ( ie, the connections between two or more metals ) - more precisely, the later named after him Zintl ions and Zintl phases. His first, still quite short paper on this topic published in 1929: " Salt-like compounds of sodium and its transition to intermetallic phases ". 1931 was followed by more detailed reports on its work with lead, tin, and many other elements in liquid ammonia. The Liebig Medal was awarded by the Association of German Chemists for the investigation of intermetallic phases him later ( 1938). Zintls ambition to overcome any difficulties in the synthesis of chemicals was remarkable. So he and his colleagues developed methods to investigate air-sensitive substances using X-ray diffractometry. Now in his lab also air- unstable compounds such as alkali metal hydrides which could be taken and described in more detail under the microscope.

In his lectures at the University of Freiburg Zintl mediated less specific peculiarities of the individual chemical substances, but was primarily an overview of the basics that were necessary in order to better understand the content of the textbooks. Because " he did not want to read what was read " ( in an obituary of Eduard Zintl after his death ). This interest in exploring, formulating and mediation of laws is indicative of Zintls entire life's work.

Since 1933: Professor at the Technical University of Darmstadt

A reputation as a full professor at the Technical University of Darmstadt reached the chemist in 1933. On 1 October this year, he appeared there to the position as head of the Institute of Inorganic Chemistry. Already in 1923 he had expressed in his textbook, Modern Inorganic Chemistry was applied physical chemistry; this view he could clarify for all now: Zintl taught at the Technical University of Darmstadt, a physico-chemical department and gave the united institute the name " Institute of Inorganic and Physical Chemistry ".

But gradually became clear to all that this institution is simply too little space was available, as new chemical apparatus were in the meantime been developed, which were indispensable for the laboratory work, but some took to space. A new building was needed - Zintl organized a spacious, modernly equipped building in close proximity to the old building. The foundation stone was laid on October 1, 1937. But not only the classroom, but also the curriculum for students of chemistry in Darmstadt modernized Zintl. He established a new course of study, in which a basic training followed by advanced training. This concept was later adopted in a thorough reform of the Chemistry program at all universities and colleges from the Reich Education Ministry.

Unlike many university professors who devoted themselves solely to the research at their institutes, Zintl also cooperated with the chemical industry. He was an employee of I.G. Farben This collaboration emerged, inter alia, new research on oxo - compounds and oxides. However, despite this influence on the part of the industry got its work in research and teaching is not the character of a research purpose: Zintl remained faithful to the basic research. 1938 on the Reich Labor Conference of the German chemists in Bayreuth, he summed up his views of research as follows:

" We drive [ ... ] in science policies in the long run, and we strive through basic research a comprehensive theory, because it brings us closer to the ultimate goal of all sciences. It is to predict new. [ ... ] But this is all basic research ultimately for the purpose of research in the long run. "

Besides, he still led the editors of the Journal of the Royal Astronomical Society.

Zintl, this important and ingenious chemist, could be 43 years of age not complete: he died on 17 January 1941, a serious illness and was able to move into the new, not live to see him with planned institute. The new building Zintl was awarded in honor of the name " Eduard- Zintl - Institute for Inorganic and Physical Chemistry " In his commemoration on January 21, 1942.

Polyanions and the Zintl border

Reports of A. Joannis in the 90s of the 19th century, according formed in the reaction of lead with sodium in liquid ammonia intense green colored solutions. Eduard Zintl interested in the chemistry that was behind this reaction. He used the methods of potentiometric titration and the electrolytic transfer, in which he was expert to investigate this phenomenon. And he succeeded. For he showed the first that the colored solutions, which had already added a long time to ponder the scientists, possessed polar character. In other words, they contain charged particles.

Eduard Zintl came to the conclusion that it is in this type of particles acted to polyanions, ie by more atoms of the same element that had annealed and as dressing had negative charge. The counter-ion was enveloped by the solvent molecules alkali metal cation. In the described reaction of lead with sodium in liquid ammonia, thus forming a polyanionic salt of composition [ Na ( NH3) x] 4 [ Pb9 ] 4 -. Polyanions disintegrated, however, as soon as it is completely removed the solvent.

That halogens ( fluorine, chlorine, bromine, iodine) and chalcogens (oxygen, sulfur, selenium and tellurium), able to form anions, has been known for some time. But Eduard Zintl had now demonstrated that even elements further to the left in the periodic table ( such as lead ) were capable. He had the following investigations are polyanions of other elements by - and indeed of tin, antimony and bismuth.

However, there were elements that never arose in their reaction with sodium in liquid ammonia polyanions - and these were the elements that are more than four main groups stand in front of the noble gases in the periodic table (eg, indium, thallium, mercury). Here is always formed only insoluble compounds that shaped typical alloy structures. These were the same products that were obtained by the fusion of the pure metals. Thus Zintl difference between Anionenbildnern and non - Anionenbildnern, ie elements to four main groups are one in front of the noble gases and are capable of forming anions or polyanions, and elements further to the left in the periodic table that does not have this property. This boundary between the third and fourth main group was referred to in an obituary of Eduard Zintl of Fritz Laves as Zintl border or Zintl line. Today it is still known by that name, even if it is now seen as less generally valid and useful than previously thought. ( For in the meantime also polyanions of indium could be produced -. Although not in liquid ammonia, but in reactions without solvents at much higher temperatures )

Such polyanions of the heavier metals, that were previously known only in liquid ammonia were later designated in honor of its discoverer as Zintl ions.

Intermetallic phases

In the reaction of elements of main group 3 (e.g., thallium ) with sodium in liquid ammonia was no Zintl Eduard polyanions. Instead, he got an alloy- like system. In this intermetallic compound (ie, the connection between the two metals sodium and thallium ), he had a new, unknown building by: NaTl the structure. The special feature is that the atoms of the two elements ( thallium and sodium) are another each independently arranged like the carbon atoms in diamond.

He realized for the first time, the principle behind the construction of many intermetallic phases: the anions form a structure corresponding to that which is also assumes an element having the same number of valence electrons. In this case, the forms formally singly negatively charged thallium (with four valence electrons ), a structure that forms of carbon ( in the fourth main group, ie, also with four valence electrons! ) Due to the same valence as well. This law is now known as classical Zintl concept, it was later extended by Wilhelm Klemm and E. Busmann.

Inspired by these new results, Eduard Zintl systematically investigated many other compounds of metals with each other. Fritz Laves then led in the aforementioned obituary of Eduard Zintl the term Zintl phases. He was so successful an umbrella term for the many intermetallic compounds, the Zintl had described found.

Nowadays, the term Zintl phase thinks intermetallic phases with strong ionic bonds, ie substances in which the nature of the bond represents a transitional form between metal and ionic bonding. These are the alkali metal and alkaline earth metal compounds with metals or semi-metals of the third to fifth main group, so components with a relatively high electronegativity. The prototype of the Zintl phases is NaTl still. Since Zintl phases are constructed ionic, their enthalpies of formation are similar to those of typical salts due to the additional lattice energies. They have salt- like brittleness and melting points are higher than those of the metal components. In addition, they dissolve in contrast to alloys good in coordinating solvents such as liquid ammonia.