A theoretical study on the structure, formation and nature of EE and C–E bonds (E¼Si, Ge, Sn) in catenated compounds of the group 14 elements including disila-, digerma- and distannacyclobutene ring formed from the reaction of 1-thiacyclohept-4-yne and E(NR)2SiR2 molecules [E¼Si, Ge, Sn, R¼t-Bu, H, F, Cl, Br] in 1:2 mole ratio has been investigated at the M06/def2-TZVPP level of theory. The results showed that the formation energy of the products of the reaction above with Si(NBr)2SiBr2 and Sn(NF)2SiF2 reactants has greatest and the smallest value, respectively. In agreement with the values of formation energies, both the calculated Wiberg bond indices (WBI) for EE and CE bonds and (BCP) of EE bond in the products of two above reactants have largest and smallest values, respectively. The nature of EE bond in the products was also studied with atoms in molecules (AIM) and natural bond orbital (NBO) analyses. The data con¯rmed that the EE bond is partly covalent. In addition, the nature of CE bond was investigated with energy decomposition analysis (EDA) and it was shown that the covalent contribution is in the range 4853% depending on the types of E atom and corresponding substituents.
