The thermodynamic stability of P 8 , A CBS‐Q study

The thermodynamic stabilities of P 2 , P 4 , and three P 8 cage structure were investigated through high‐precision CBS‐Q calculations. The CBS‐Q values for the bond energy of P 2 (ΔE o : +115.7 kcal mol −1 ) and the formation of P 4 from P 2 (Δ E o :‐56.6 kcal mol −1 ) were in excellent agreement with the experimental values (E o : +117 and ‐56.4 kcal mol −1 respectively). Among the P 8 cages, the cubane structure was the least stable (Δ E o +37 kcal vs. 2×P 4 ). The most stable P 8 isomer adopts a cuneane structure resembling S 4 N 4 , and is more stable than white phosphorus at T = 0 K (Δ E o −3.3 kcal mol −1 ), but still unstable under standard conditions for entropic reasons (Δ G o of +8.1 kcal mol −1 vs. 2×P 4 ). The CBS‐Q energies represent significant revisions (6–20 kcal mol −1 ) of previous computational predictions obtained by high‐level single method calculations. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:453–457, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20119