On the existence of collective interactions

Recently, Sowlati-Hashjin et al.1 have used the exchange-correlation interaction collectivity index (ICIXC; ICIXC  [0,1]) to conclude that the nature of the Li–C chemical bond in LiCF3 differs significantly from that in LiCPh3 (Ph = phenyl). Whereas the Li–C bond of LiCF3 is classified as a conventional two-center two-electron bond (ICIXC = 0.910, ICIXC > 0.9 and close to 1), that of LiCPh3 is categorized as a collective bond (ICIXC = 0.393). The authors claim that collective bonds take place in systems composed of MAR3 (M = metal; A = C, B or Al; R = substituent) when M forms a stronger bond with the substituents R than with the central atom A. They claim the M–A interaction is either destabilizing or weakly stabilizing, whilst the 1,3-M···R interactions are strongly stabilizing, but their method does not provide a causal mechanism that would demonstrate the correctness of this interpretation of the ICIXC index. Here, we prove the opposite, namely, that the Li–CPh3 bond is not reinforced or provided by collective interactions, but that it is weakened by 1,3-M•••R contacts, which reduce the bond overlap.