Molecules We Have Recently Met

Brief summaries are given of work on the vibrational spectra of the following compounds. (1) N(SiH₃)₃. A Raman study of the ¹⁴N⁻¹⁵N isotopic shift of the totally symmetric NSi₃ stretching mode confirms that the heavy atom skeleton is planar in the gas phase. In condensed phases it is slightly distorted from D_3h in some undetermined manner. (2) Si(NCO)₄, Ge(NCO)₄, and Ge(Na)₄. Each of these molecules has some Raman bands with depolarization ratios between 0 and 0.75, showing that the molecules are not tetrahedral. (3) Cyclopropenone-d₀ and -d₂. A good assignment of the fundamentals has been made, and the forms of the normal modes calculated. The bands at 1483 cm⁻¹ (d₀) and 1409 cm⁻¹ (d₂) are nearly pure =C stretches, making them the lowest such modes known. (4, 5) Tetramethylenecyclobutane and its perchloro derivative. The former is planar (D_4h); the latter is not. (6) F₂C=C=C=CF₂. This is planar (D_2d). (7) B₄Cl₄. This has an unusual B₄ tetrahedral cage. A reliable set of assignments has been made and force constants determined. (8) Trithiadiborolanes. The B₂S₃ ring is planar.