He earned his PhD in 1923, at the age of 25, with a thesis on the molar mass of bromine. He stayed with
Otto Hönigschmid's group, where he was involved in the supervision of PhD students, for example
Josef Goubeau and
Günther Rienäcker. From 1928 till 1933 he was professor of inorganic chemistry at the
University of Freiburg. During this period he studied the structure of
complex anions formed by metals in a solution of
sodium in
ammonia. [Na(NH3)x]+4[Pb9]4− is one of the examples he discovered. Working in an atomic weight laboratory as a student assistant had provided him a lot of experience with chemical elements and how they react with each other. He noted that the atomic volume contraction between these compounds were formed and it could indicate cation formation.
Work at Darmstadt In 1933 he moved to a position at the
Technische Universität Darmstadt, where a new building for inorganic and physical chemistry was planned and built. The research on complex anions led him to the discovery of the
Zintl phases. The structure of Zintl phases were ionic, and the structure of the anion (aka Zintl ion) could result an electronic state. His study focused on intermetallic compounds and how the electron could be transferred from a more electropositive metal. In the Zintl phase, the structure of the
Zintl ion (polyanion) should be similar to an isoelectronic element. For example, in Na2Tl, the polyanion is tetrahedral (Tl4)8−, similar to the phosphorus molecule P4. ==Further reading==