The reactions of laser-ablated C, Si, Ge, Sn, and Pb atoms with BF3 have been studied using matrix isolation Fourier transform infrared (FTIR) spectroscopy and density functional theoretical (DFT) calculations. All atoms generate the inserted complex F2B-MF, which were trapped in inert gas and identified by the isotopic substitutions and DFT frequency calculations. DFT and CCSD(T) calculations show that triplet F2B-CF is the most stable isomer with two singly occupied molecular orbitals, while singlet F2B-MF (M= Si, Ge, Sn and Pb) molecules possess a near right angle B-M-F moiety with lone pair electrons on the M atom. The bonding difference between C and other group 14 atoms is mainly caused by relativistic effect, which is that, for heavier metal atom valences, s and p orbitals have a lower tendency to form hybrid orbitals.