Ab Initio Study of Nonadditivity Effects: Spin-Spin Coupling Constants for Tetrafluoroethene in Ternary pi Complexes
C2F4 coupling constants have been evaluated at EOM-CCSD/(qzp,qz2p) in binary complexes with electron donors X (X = HLi, Cl−, CN−) and with the electron acceptor FH, and in ternary complexes FH:C2F4:X in which X and FH are located on opposite faces of the C2F4 π cloud. The electron donors X and the electron acceptor FH have opposite effects on 1J(C−C), 1J(C−F), 2J(C−F), and 3J(F−F) in binary complexes. Effects of X and FH on a particular coupling constant in a ternary complex are additive if the change in the coupling constant in this complex relative to C2F4 is within 1 Hz of the sum of the changes in the corresponding binary complexes. This is the case for 1J(C−F). Both positive and negative nonadditivities are computed for the remaining coupling constants. Although the values of most coupling constants lie between the values for FH:C2F4 and C2F4:X, that is not the case for 2J(C−F), and the effect of FH is enhanced by the presence of X. Moreover, values of 3J(F−F) trans and cis for FH:C2F4:X when X is Cl− or CN− bonded through C are within 1 Hz of the values for the corresponding binary complex C2F4:X. Significant differences can be found between the relative contributions of the PSO, FC, and SD terms to total J and to the nonadditivities of J in ternary complexes FH:C2F4:X.