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The vibrational spectrum of B4Cl4

1976; Pergamon Press; Volume: 32; Issue: 1 Linguagem: Inglês

10.1016/0584-8539(76)80058-x

1873-3824

Fred R. Brown, Foil A. Miller, C. Sourisseau,

Solid-state spectroscopy and crystallography

Infrared and Raman spectra of solid B4Cl4 have been measured from 35 to 3500 cm−1. Raman depolarization measurements were made on a CCl4, solution, and two i.r. bands were obtained for the vapor. The i.r. spectrum is surprisingly sparse; only one band was found below 925 cm−1. The spectra can be understood very well on the assumption of aTd structure in which the boron atoms form a tetrahedral cage, with the BCl bonds directed away from the center of the tetrahedron. In the crystal the symmetry is known to be distorted very slightly toD2d, and the Raman spectra show splittings compatible with this. The eight fundamentals forTd symmetry have been assigned as follows (solid state frequencies):a1: 1302, 358;e: 692, 117;f1: [343] (inferred);f2: 978, 514, 110 cm−1. They are believed to be reliable, except that 110 and 117 may be interchanged. A normal coordinate calculation has been made. It shows that the twoa1 modes are almost completely mixed. The most interesting force constants arekr(BCl) = 4.08 andkR(BB) = 2.3 ± 0.1 mdyn/A˚. The former is in the normal range, but the latter is quite low by analogy to some related compounds. This reflects the electron-deficient nature of the molecule.