Alfred Werner and the Nobel Prize in Chemistry

Alfred Werner, a distinguished Swiss chemist and professor at the University of Zurich, was awarded the 1913 Nobel Prize in Chemistry for his groundbreaking work on coordination compounds and their structure. His theory laid the foundation for modern coordination chemistry, a field that studies the interactions between metal ions and their surrounding ligands.

Werner's Experimental Methodology

Werner conducted his research through the preparation and isolation of various complex compounds by the action of ammonia on cobalt chloride, a transition metal. Through meticulous experimentation, he was able to deduce the nature of the interactions between these metal ions and their ligands, thereby pioneering the understanding of coordination chemistry.

Theoretical Contributions

Werner's theory, proposed in the early 20th century, introduced a clear distinction between primary and secondary valencies in coordination compounds, which significantly advanced the field.

Primary and Secondary Valencies

Werner postulated that a central metal atom or ion in a complex exhibits two types of valencies: primary and secondary. Primary valencies are ionisable and correspond to the oxidation state of the central metal ion, while secondary valencies, represented by thick lines, correspond to the coordination number, which is satisfied by ligands such as negative ions or neutral molecules.

Examples and Applications

Consider the complex [CoClNH35]Cl2. This compound ionises in solution to produce a total of three ions: two chloride ions outside the square bracket and one complex ion inside. Here, one chloride ion is fulfilling both primary and secondary valencies, stabilising the complex without ionising.

Directional and Non-Directional Valencies

The secondary valencies are directional, meaning they arrange the ligands in space around the central metal ion. In contrast, primary valencies are non-directional. The geometry of the complex is determined by the arrangement of the ligands in space with the central metal ion as the center.

Implications and Modern Notation

Based on Werner's theory, we can derive various structures for coordination complexes like CoCl3.nNH3. The square bracket notation is a modern technique where the central metal ion is enclosed in square brackets, and the ionisable atoms or groups are written outside. Ligands attached to the central metal atom can be anions, cations, or neutral molecules.

Conclusion

The contributions of Alfred Werner to coordination chemistry have been monumental, providing foundational knowledge that continues to guide research and innovation in this field. His theories on primary and secondary valencies have not only explained the structures of coordination compounds but also paved the way for further advancements in materials science and pharmaceuticals.