Supramolecular
assembly utilizing simultaneous formation of three
pnictogen bonds around a single antimony vertex was explored via X-ray
crystallography, solution NMR, and computational chemistry. An arylethynyl
(AE) ligand was designed to complement the three electrophilic regions
around the Sb compound. Though solution studies reveal large binding
constants for individual pyridyl units with the Sb donor, the rigidity
and prearrangement of the AE acceptor proved necessary to achieve
simultaneous binding of three acceptors to the Sb-centered pnictogen-bond
donor. Calculations and X-ray structures suggest that negative cooperativity
upon sequential binding of three acceptors to a Sb center limits the
utility of triple-pnictogen bonding pyridyl acceptors. These limitations
can be negated, however, when positive cooperativity is designed into
a complementary acceptor ligand.
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