Hydrogen bonding has long-dominated in the field of molecular recognition. The high polarity of the element-hydrogen bond leads to strong intramolecular interactions. Heavy p-block elements, when bonded to electronegative elements can have similar or greater bond polarities which lead to equally strong intramolecular interactions. These secondary bonding interactions were recognized as important structure directing features in solid state structures as early as 1968 in seminal works by Bent, Hassel and Alcock. The presence of these interactions involving bromine or iodine was observed even earlier and the topological similarity to hydrogen bonds led to Dumas coining the term <i>halogen bond</i> specifically for this subset of secondary interactions in 1978. While significant progress has been made with halogen bonds, progress towards predictable molecular recognition and self-assembly using the secondary interactions involving the chalcogens (+2 or +4) or pnictogens (+3) has lagged behind despite their ability to form multiple and stronger interactions.<br/>We have use DFT to aid in the design of several antimony(III) systems that are predicted to recognize either neutral or anionic species in a predictable manner. Synthetic studies have validated these predictions. Compounds containing one antimony with three polar bonds have been used to self-assembly helical columns when steric hindrance is minimized or self-assembled bilayers when longer alkyl chains are incorporated (Fig. 1). These bilayers are inverted with respect to typical phospholipid bilayers, having the lipid-like tails pointing out. The ability to bind anions can be engineered by tethering two antimony(III) centers together in the same molecule (Fig. 2). Solution studies have been used to validate the anion binding and models have been developed for the different species that are present in equilibrium in solution. These systems both demonstrate ways in which the secondary bonding interactions of antimony(III) can be utilized in the field of molecular recognition and self-assembly.

Controlling molecular recognition and self-assembly with pnictogen(III) secondary bonding interactions in the solid and solution states

255th National Meeting (2018)

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