Past exam of the chemistry course of the year 1 of the natural sciences course of the University of Cambridge / 2024 / Paper 1 / 6 / b

The Hg–S interaction is expected to be stronger than Hg–N by the hard and soft acids and bases argument. $\mathrm{H}{\mathrm{g}}^{2+}$ is a soft, readily polarizable Lewis acid. The sulfur end of thiocyanate is a softer and more polarizable donor than its nitrogen end, so it better matches mercury's electronic response and covalent bonding preference.

Nitrogen being more electronegative does not by itself make it the preferred donor to a soft metal. Charge concentration and polarizability are distinct properties. The extended solid can still contain Hg–N contacts that complete the bridging network; the prediction concerns their relative bonding preference, not the absence of N coordination.^[ref]