Molecular structure and conformational composition of decamethyl-n-tetrasilane, Si4Me10, by gas electron diffraction and density functional theory calculations

Density functional theory calculations on n-Si4Me10 at the B3PW91/6-311G* level indicate six minima on the potential-energy surface corresponding to two anti conformers with φ(SiSiSiSi) dihedral angles of ±160°, two gauche conformers with φ=±57°, and two orthogonal conformers with φ=±92°. The relative energies of the three conformers were calculated to be 0.0 (anti), 2.9 (gauche) and 3.0 kJ mol−1 (orthogonal). Least-squares refinements on gas electron diffraction data recorded at room temperature yielded the mole fractions χ(anti)=0.51(6), χ(gauche)=0.32(8) and χ(ortho)=0.17(14). The data thus confirm the presence of the anti and gauche conformers, while the presence of the ortho is probable but not certain. The main bond distances and valence angles of the most prevalent (anti) conformer are (calc./exp.): Si(1)Si(2)=237.1/235.0(6) ppm; Si(2)Si(3)=237.4/235.4(6) ppm; Si(1)C=189.5/189.3(2) ppm; Si(2)C=190.3/190.1(2) ppm; Si(1)Si(2)Si(3)=112.5/112.4(5)°.