Mean Amplitudes of Vibration of F3ClO

As a continuation of our studies devoted to the vibrational and bond properties of molecules and ions containing interhalogen or halogen-oxygen bonds we have now performed an analysis of the bond characteristics of chlorine trifluoride oxide (chlorosyl trifluoride, F3ClO), through a calculation of its mean amplitudes of vibration from spectroscopic data. The interesting F3ClO molecule has been obtained by either direct fluorination of Cl2O, NaClO2 or ClONO2 or by glow discharge of F2 in the presence of solid Cl2O [1]. Its vibrational (IR and Raman) spectra are consistent with a trigonal bipyramidal structure around the chlorine atom (Cs-symmetry) containing the oxygen atom, one fluorine atom and a lone pair in the equatorial plane and the other two fluorine atoms in axial positions [2]. The mean amplitudes of vibration were calculated by the method of the characteristic vibrations of Müller et al. [3] (cf. also [4, 5]). The necessary vibrational frequencies were taken from the paper of Christe and Curtis [2] and the following geometric parameters were used: d (Cl–O) = 1.42 Å, d (Cl–F (eq)) = 1.62 Å, < OClF (eq) = 120° and < F (ax) Cl (F (ax) = 180° [2]. The results of the calculations, in the temperature range between 0 and 1000 K are shown in Table 1. As it can be seen, the Cl–O bond is particularly strong, as reflected by the relatively low mean amplitude values and its weak temperature dependence. On the other hand, and as expected for a multiple halogenoxygen bond, this linkage shows a very characteristic mean amplitude of vibration. It is comparable with values calculated, at 298 K, for other chlorine (V) species, for example 0.0358 Å in ClF4O – [6], 0.0360 Å in ClO2F [7] and 0.0366 Å in ClO2F2 – [8], and is even slightly lower than in the ClO3 – anion (0.040 Å) [4]. Interestingly, this bond also presents a very high force constant (9.37 mdyn/Å) [2]. The values calculated for the Cl–F bonds reflect a slightly different behaviour of these two geometrically different interhalogen bonds. The equatorial Cl–F bond is somewhat stronger than the two axial ones, as reflected by its lower mean amplitude value and weaker temperature dependence. This finding is in agreement with the respective force constants (3.16 mdyn/Å for the Cl–F (eq) bond and 2.34 mdyn/Å for the Cl–F (ax) bonds[2]). The force constant for the axial bonds is identical with that previously calculated for ClF2 – [9]. Consequently, this linkage also shows a similar mean amplitude in both species, although the overall bond strength is slightly lower in the anion (mean amplitude of vibration of the Cl–F bond in ClF2 – is 0.0595 Å at 298.16 K [10], probably due to the lower oxidation state of chlorine and the presence of the negative charge. On the other hand, the two sets of Cl–F amplitude values show that these bonds are slightly stronger than in ClO2F2 – (0.0622 Å at 298 K) [8] and in ClF4O –