The molecular structure and the puckering potential function of silacyclobutane as determined by gas electron diffraction and relaxation constraints from ab initio calculations

Abstract

Gas electron diffraction is applied to determine the geometric parameters of the silacyclobutane molecule using a dynamic model where the ring puckering was treated as a large amplitude motion. The structural parameters and the parameters of the potential function were refined taking into account the relaxation of the molecular geometry estimated from ab initio calculations at the MP2/6-311+G(d, p) level of theory. The potential function has been described as V( ϕ) = V 0[( ϕ/ ϕ e) 2 − 1] 2 with the following parameters V 0 = 0.82 ± 0.60 kcal/mol and ϕ e = 33.5 ± 2.7°, where ϕ is a puckering angle of the ring. The geometric parameters at the minimum V( ϕ) ( r a in Å, ∠ α in degrees and uncertainties given as three times the standard deviations including a scale error) are: r(Si–H ax) = 1.467(96), r(Si–H eq) = 1.468(96), r(Si–C) = 1.885(2), r(C–C) = 1.571(3), r(C–H) = 1.100(3), ∠CSiC = 77.2(9), ∠HSiH = 108.3, ∠SiCH eq = 123.5(16), ∠SiCH ax = 111.9(16), ∠CC 5H eq = 118.4(24), ∠CC 5H ax = 112.3(24), ∠HC 3H = 107.7, ∠ δ(HSiH) = 6.6, ∠ δ(HC 3H) = 7.0, where the tilts δ, ∠HSiH, and ∠HC 3H are estimated from ab initio constraints. The structural parameters are compared with those obtained for related compounds.