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Table 6 Energetic properties of the hydrogen bonds As shown in Table 4 ?, the hydrogen bonds in these hydrates may be classified according to the donor and acceptor species, which of itself reveals interesting trends in the ways these structures are organized with increasing hydration state. Notably, the interstitial water molecules that occur once the cation is ��saturated�� serve more often than not to bridge between the cationic and anionic polyhedra instead of forming hydrogen bonds with other interstitial water molecules. Categorization of the hydrogen-bond energies in Table 6 ? according to the types listed in Table 4 ? shows that the weakest hydrogen bonds (mean = 32.4?��?3.3?kJ?mol?1) are those between Mg-coordinated waters and sulfate O atoms. The hydrogen bonds donated by free interstitial waters to the sulfate O atoms are similarly weak, 32.9?��?2.5?kJ?mol?1. On the other hand, hydrogen bonds formed between water molecules are significantly stronger; Bleomycin molecular weight those between Mg-coordinated water and interstitial water have a mean energy of 39.0?��?2.3?kJ?mol?1 and the single hydrogen bond between two interstitial waters has an energy of 36.7?kJ?mol?1. The exception, again, is the H9B?Ow6 bond; whilst this is not quite the weakest hydrogen bond in the structure it is much the weakest (by ??25%) of the water�Cwater hydrogen bonds. 3.3. The Raman spectrum ? MgSeO4��9H2O crystallizes in the centrosymmetric space group P21/c having a primitive cell with C 2h point-group symmetry and four formula units per unit cell; all ions and molecules are located on sites of C 1 symmetry. Based on a consideration of the normal vibrational modes Duvelisib cost of the ionic polyhedra and the neutral water molecules, we have carried out a factor group analysis by the correlation method to determine the symmetry species of all Raman-active modes. Allowing for the modes corresponding to translation of the entire crystal, we find that there are 198 normal PRDX4 modes summarized as ��opt(Raman) = 99?Ag + 99B 1g. The majority of these vibrations are associated with the water molecules, grouped into three distinct portions of the spectrum (Fig. 11 ?). The highest frequency modes, observed between ??3100�C3600?cm?1, correspond with the O��H symmetric and asymmetric stretch, ��1 and ��3, respectively. At higher temperatures, the asymmetric potential well in which the H atoms are oscillating leads to thermal broadening of the peaks, although it is nonetheless possible to identify five discrete Lorentzian contributions to the high-frequency feature. When the temperature is reduced to 78?K, however, the peaks sharpen substantially, making it possible to clearly identify at least seven individual bands (Fig. 12 ?). Figure 11 Raman spectrum of MgSeO4��9H2O at 259 and 78?K, measured on the (0?1?1) face of a single crystal. Pertinent groups of vibrational modes contributing to the observed features are labelled.