Mapping the geometry of metal three-coordination using crystal structure data:: Reaction pathway for ligand addition to linear HgII species

Symmetry-modified principal-component analysis has been used to visualise the geometrical distortions of three-coordinate metal centres observed in crystal structures retrieved from the Cambridge Structural Database. It is shown that compounds of Cu, Ag, Hg, Zn, and An dominate the dataset, and exhibit distortions away from the trigonal planar archetype towards a) T-shaped and b) Y-shaped geometries. A small number of compounds, principally of Cu and Ag, also show distortions towards trigonal pyramidal geometries. The interconversions from Y-shaped geometries, through the trigonal planar form to T-shaped geometries are clearly mapped by the PC analysis. For Hg-II complexes, it is possible to interpret the transition from T-shaped geometries to the trigonal planar form in terms of a reaction pathway for ligand addition to linear L-1-Hg-II-L-2 species.