Abstract
Chalcogen bonds are noncovalent interactions and are increasingly coming into focus
for the design of complex structures in research areas such as crystal engineering,
molecular recognition and catalysis. Conceptionally, chalcogen bonds can be considered
as interaction between one σ-hole and one Lewis base center. Herein, we analyze the interaction between bidentate chelating
ligands having two nucleophilic centers with one single σ-hole of a chalcogenazole (two-lone-pair/one-σ-hole interactions). Referring
to this, we show by quantum chemical calculations and X-ray studies that three bond
types are possible: in the first case, a chalcogen bond is formed between the σ-hole
and only one of the Lewis base centers. In the second case, a strong bond is formed
by one nucleophilic center; the second center provides only a small amount of additional
stabilization. In the third case, two equivalent bonds to the σ-hole are formed by
both Lewis base centers. According to the calculations, the bifurcated bonds are stronger
than simple chalcogen bonds and lead to a more rigid molecular arrangement in the
complex.
Key words
bifurcated bonds - chelate ligands - chalcogen bonding - DFT calculations - σ-hole