Cyclobutadiene complexed with Li atom and the effects of substituting by F atom in LiC 4H 4

Abstract

The 12 structures of the LiC 4H 4− n F n ( n=0–4) complexes with all real frequencies are got at the MP2/6-311++G** level. These complexes are all charge-separated species Li +(C 4H 4− n F n ) − with large interaction energies (−2.13 to −5.34 eV) at the CCSD(T)/6-311++G** level. Different from benzene ring which acts as an electron donor in Li·C 6H 6, the cyclic C 4H 4− n F n ( n=0–4) are electron acceptors. Interestingly, in the LiC 4H 4 complex, the subunit C 4H 4 presents an out-of-plane ‘roof’ structure ( C 2 v ), which differs from the planar rhombus or rectangular structure of C 4 H 4 − , and also differs from the square structure ( D 4 h ) of C 4 H 4 2 − in the LiC 4H 4Li complex. The complex in LiC 4H 4− n F n ( n=1–4) has low symmetry ( C s or C 1) due to F substituent(s). The LiC 4H 4− n F n complexes with F(2) substituent exhibit different structural characteristics from those without F(2) substituent. Thus the 11 F-substituted complexes plus LiC 4H 4 are clearly divided into A (without F(2)) and B (with F(2)) two groups. The electron correlation contributions are obviously different between the complexes in group A and those in group B for interaction energies and vertical ionization energies (VIE).