Room-Temperature FTIR Spectra of the Cyclic S4 (H2O)4 Cluster in Crystalline Li2(H2O)4(B12F12): Observation of B and E ν(OH) Bands and Coupling of Strong O-H•••O and Weak O-H•••F Vibrations

Room-temperature-attenuated total reflection-Fourier transform infrared (FTIR) spectra of the structurally characterized crystalline lithium salt Li-2(H2O)(4)(B12F12), which contains a cyclic S-4 symmetry (H2O)(4) cluster, and several partially or completely deuterated isotopologs, suggest the following conclusions: (i) B and E normal modes gave rise to two distinguishable nu(OHbound) bands, separated by 42 cm(-1), two distinguishable nu(OHfree) bands, separated by 13 cm(-1), and two distinguishable delta(HOH) bands, separated by 19 cm(-1), in the FTIR spectrum of Li-2(H2O)(4)(B12F12); (ii) B and E normal modes gave rise to two distinguishable nu(ODbound) bands separated by 20 cm(-1) in the FTIR spectrum of Li-2(H2O)(4)(B12F12); (iii) coupling between nu(OHbound) and nu(OH free ) normal modes or between nu(ODbound) and nu(ODfree) normal modes is weak, but finite, and resulted in shifts of 4-10 cm(-1) for the respective bands in the spectra of Li-2(H2O)(4)(B12F12) vs Li-2(HOD)(D2O)(3)(B12F12) or in the spectra of Li-2(D2O)(4)(B12F12) vs Li-2(HOD)(H2O)(3)(B12F12); and (iv) a delta(DOD) band for an S-4 (D2O)(4) cluster, at ca. 1202 cm(-1), was observed for the first time. In addition, FTIR spectra of the lithium salt containing cyclic [(HOD)(H2O)(3)] or [(HOD)(D2O)(3)] clusters are the first examples in which bands that are unambiguously assigned to both HO-D center dot center dot center dot O and DO-H center dot center dot center dot O hydrogen bonds in the same sample have been observed for a water tetramer.