Maximal occupation by bases of π-hole bands surrounding linear molecules.

Linear molecules such as CO contain a positive π-hole ring that surrounds C on the molecule's equator. Quantum calculations examine the question as to how many bases can simultaneously bind to this ring. Linear molecules examined are TO , where T = C, Si, Ge, Sn; bases are NCH and NH . CO engages in the weakest of the tetrel bonds, and can bind up to three NCH and two NH . Unlike σ-hole tetrel bonds, Si forms the strongest tetrel bonds, with interaction energies as high as 43 kcal/mol with NH . But like GeO , SiO can sustain only two bases in its equatorial ring. The π-hole ring of SnO can engage in up to four tetrel bonds with either NCH or NH , even though these bonds are weaker than those with GeO or SiO . As all of these complexes cast TO in the role of multiple electron acceptor, the resulting negative cooperativity makes each successive bond weaker than its predecessor as bases are added, as well as reducing the magnitude of the central molecule's π-hole.