Differential Binding of Tetrel-Bonding Bipodal Receptors to Monatomic and Polyatomic Anions

Previous work has demonstrated that a bidentate receptor containing a pair of Sn atoms can engage in very strong interactions with halide ions via tetrel bonds. The question that is addressed here concerns the possibility that a receptor of this type might be designed that would preferentially bind a polyatomic over a monatomic anion since the former might better span the distance between the two Sn atoms. The binding of Cl^- was thus compared to that of HCOO^-, HSO₄^-, and H₂PO₄^- with a wide variety of bidentate receptors. A pair of SnFH₂ groups, as strong tetrel-binding agents, were first added to a phenyl ring in ortho, meta, and para arrangements. These same groups were also added in 1,3 and 1,4 positions of an aliphatic cyclohexyl ring. The tetrel-bonding groups were placed at the termini of (-C≡C-)_n (n = 1,2) extending arms so as to further separate the two Sn atoms. Finally, the Sn atoms were incorporated directly into an eight-membered ring, rather than as appendages. The ordering of the binding energetics follows the HCO₂^- > Cl^- > H₂PO₄^- > HSO₄^- general pattern, with some variations in selected systems. The tetrel bonding is strong enough that in most cases, it engenders internal deformations within the receptors that allow them to engage in bidentate bonding, even for the monatomic chloride, which mutes any effects of a long Sn···Sn distance within the receptor.