A recent investigation led by Dr. Frank Tambornino at Philipps-University of Marburg has now shone a spotlight on this elusive molecule. Tambornino and his colleagues set out to investigate what happens when thiocarbonyl dithiocyanate is synthesised in the lab.

Interestingly, they discovered that the atoms within the molecule they synthesised are not in a stable arrangement. In its stable form, the molecule’s arms – which consist of a nitrogen atom, carbon atom and sulphur atom – are connected to the molecule’s central carbon atom via each arm’s nitrogen atom. However, in the team’s molecule, these arms are back-to-front – connected through their sulphur atoms.

The team used computer models to figure out why this was the case. They discovered that it’s all about the path that the reaction takes. During its synthesis, thiocarbonyl dithiocyanate forms quickly through a low-energy shortcut, locking in this less stable form before it has a chance to rearrange into a more stable state.

Additionally, the team’s thiocarbonyl dithiocyanate molecule consistently adopts a highly unusual shape in its solid form. Most molecules of this type settle into a so-called ‘syn-syn’ arrangement – where both of the molecule’s arms point outwards. But this one was an exception, forming a ‘syn-anti’ shape, with one arm pointed inward and one flipped outward.

Tambornino and his colleagues were surprised by this finding, because this ‘syn-anti’ form usually isn’t a stable shape for the molecule. In fact, other arrangements should be lower in energy and therefore much more likely to form. However, here a combination of so-called ‘steric repulsion’ and electronic effects make this ‘syn-anti’ shape lowest in energy.

The researchers then conducted further experiments – modifying the synthesis conditions in an attempt to create a more stable version of the molecule. This led to the discovery of a related molecule called chlorothiocarbonyl thiocyanate. Tambornino’s team also experimented with safer and more efficient ways of producing these molecules, by replacing toxic solvents with safer alternatives.

They then decided to test how thiocarbonyl dithiocyanate reacts with other substances. When they added alcohol, they synthesised a molecule called thioimidodicarbonic diethyl ester that had never been made before. This molecule, in turn, turned out to be useful for capturing metal atoms. For instance, it was able to lock around a nickel atom to form a neat square.

The team’s study opens the door to creating new types of ligands – molecules that can grip metal atoms in precise ways – which could be useful for environmental remediation, and in designing catalysts or sensors. Tambornino and his collaborators show that by revisiting forgotten corners of chemistry, we can discover new tools for future innovations.