Structures and dynamic behaviors of tetra-hydridodimetallenes, M2H4, (M= Si, Ge, Sn): A DFT study and NBO analysis

B3LYP/6-31G**, B3LYP/3-21G*, B3LYP/LANL2DZ* and B3LYP/LANL2DZ** based density functional theory (DFT) methods were used to investigate the ground state structures and configurational properties of ethane (1), and tetra-hydridodimetallenes, M2H4, [M= Si (2: disilene), Ge (3: digermene) and Sri (4: distannene)]. All used methods show that the ground state structure of compound 1 is planar (D-2h symmetry), while the ground state structure of compounds 2-4 is trans bent (with C-2h symmetry). The barrier heights of the atom inversion process (C-2h -> C-2h' involving a plane symmetrical transition state structure with D2h symmetry) are decreased from compounds 2 to 4. Al so: the obtained results indicate that the barrier heights of MM-bond rotation (D-2h -> D-2h', involving a perpendicular transition state structure with D-2d symmetry) are decreased from compounds 2 to 4. Based on the B3LYP/6-31G**, B3LYP/3-21G*, B3LYP/LANL2DZ* and B3LYP/LANL2DZ** optimized ground state geometries, the NBO analysis of donor-acceptor (bond-antibond) interactions revealed that the stabilization energies associated with the electronic delocalization from OM-H bonding orbital to pi*(M=M) anti-bonding orbital (sigma(M-H) ->pi*(M=M)), increase from compounds 1 to 4. Also, the donor-acceptor interactions, as obtained from NBO analysis, showed that the pi(M=M) -> sigma*(M-H) resonance energy increase from compound 1 to 4. Further, the results showed that the energy-gaps between pi(M=M) bonding and pi*(M=M) antibonding orbitals decrease from compounds 1 to 4. These facts could fairly explain the decrease of occupancies of sigma(M-H) and pi(M=M) bonding orbitals and the increase of occupancies of pi*(M=M) antibonding orbitals from compounds 1 to 4. Effectively, NBO results revealed that the n values in the mean hybrid orbitals ((sp(n)) over bar) decrease from compound 1 to 4. NBO analysis sp(35.37), sp(7.88), sp(3. 77) and sp(3.36), respectively. These facts could explain increase the increase of the pyramidalization at the M atoms (trans bending) from compound 1 to 4.