Which group in the periodic table is known to form 2-coordinate complexes?

Group 11 elements, which include copper, silver, and gold, are well-known for their ability to form 2-coordinate complexes. This tendency stems from their electronic configuration and the involvement of their d-orbitals in bonding. The d-orbitals can engage in back-donation, allowing these metals to form stable complexes with ligands that can donate two pairs of electrons.

For example, copper(I) can engage in coordination with ligands that effectively occupy only two binding sites, leading to the formation of linear complexes. The geometrical arrangements can often accommodate ligands such as phosphines or other suitable bidentate ligands that only require two coordination positions.

In contrast, the other groups mentioned generally do not preferentially form 2-coordinate complexes to the same extent. Group 12 elements, such as zinc and cadmium, typically form tetrahedral or octahedral complexes. Group 13 elements, like aluminum, often engage in larger coordination numbers due to their higher tendency to form stable complexes with various ligands. Group 14 elements, such as silicon and germanium, also favor higher coordination numbers in their complexes, leading to tetrahedral arrangements. Therefore, Group 11 distinctly stands out for the formation of 2-coordinate complexes due