Prof. Felix Tuczek - Coordination chemistry, the molecular chemistry of transition metals

Coordination chemistry is a part of inorganic chemistry. It deals with coordination compounds (“complexes”) which consist of a neutral (or charged) central atom (usually a transition metal) and a set of ligands. The number of ligands which are coordinated to the central atom varies from 2 to about 9. For each coordination number (CN) typical coordination polyhedra are formed. The most frequent CN is 6, being associated with an octahedral geometry, but also many complexes with CN 4 (tetrahedral or square-planar) and 8 (cubic or tetragonal-antiprismatic geometry) exist. Due to their open-shell character with usually several unpaired electrons transition-metal (and, equally, rare-earth) complexes often have interesting magnetic and optical properties as well as unique reactivities.

Coordination compounds with ligands like water, ammonia or cyanide are denoted as „Werner-type complexes“ after Alfred Werner, who was a professor of chemistry at the University of Zürich. With an article published in 1893 in Zeitschrift für Anorganische Chemie he laid the conceptual foundations of coordination chemistry.¹ In order to prove his coordination theory Werner and his coworkers in the following years synthesized a large number of complex compounds, providing the theoretical basis for complex chemistry which is still valid today. In 1913 Werner was awarded the Nobel Prize for Chemistry "in recognition of his work on the linkage of atoms in molecules by which he has thrown new light on earlier investigations and opened up new fields of research especially in inorganic chemistry".²

Since the early days of Alfred Werner transition-metal complexes have developed to an important class of compounds which are employed in catalysis, in medicine, in analytical chemistry, as dyes or pigments and in many other areas. A modern branch of coordination chemistry is bioinorganic chemistry which deals with the role of metal centers in biology. Metalloproteins are involved in many key processes in living systems such as the transport or the metabolism of small molecules, energy transfer, redox reactions or the formation and degradation of proteins and nucleic acids. Bioinorganic chemistry aims at reproducing these processes with simple model complexes and this way understand the often complicated functions of their biological counterparts in more detail. Examples of this approach comprise the activation of dioxygen in the enzyme tyrosinase^3,4 or the conversion of dinitrogen to ammonia by the enzyme nitrogenase.^5,6