Cage-size effects on the encapsulation of P2 by fullerenes

The classic pnictogen dichotomy stands for the great contrast between triply bonding very stable N-2 molecules and its heavier congeners, which appear as dimers or oligomers. A banner example involves phosphorus as it occurs in nature as P-4 instead of P-2, given its weak pi-bonds or strong sigma-bonds. The P-2 synthetic value has brought Lewis bases and metal coordination stabilization strategies. Herein, we discuss the unrealized encapsulation alternative using the well-known fullerenes' capability to form endohedral and stabilize otherwise unstable molecules. We chose the most stable fullerene structures from C-n (n = 50, 60, 70, 80) and experimentally relevant from C-n (n = 90 and 100) to computationally study the thermodynamics and the geometrical consequences of encapsulating P-2 inside the fullerene cages. Given the size differences between P-2 and P-4, we show that the fullerenes C-70-C-100 are suitable cages to side exclude P-4 and host only one molecule of P-2 with an intact triple bond. The thermodynamic analysis indicates that the process is favorable, overcoming the dimerization energy. Additionally, we have evaluated the host-guest interaction to explain the origins of their stability using energy decomposition analysis.

Automated summary

The classic dichotomy between nitrogen and its heavier congeners is discussed in the context of encapsulation of phosphorus compounds in fullerene cages. Computational studies show that fullerene structures C-70 to C-100 can encapsulate P-2 molecules with intact triple bonds, excluding P-4. Thermodynamic analysis confirms the favorable nature of the encapsulation process.