poldahafen 2, by quoting the depository number CSD 5 1 119, the names of the authors, and the journal citation. 161 Magnetic measurements: The molar susceptibilities of 1 and 2 were measured on powdered samples in the temperature region 93-293 K Because of its unique thermal behavior, liquid sulfur has been the subject of numerous physicochemical and theoretical investigations. As a rule, it is assumed that, below the polymerization temperature (159"C), the melt essentially consists of S, molecules. However, we have already previously shown by means of vibrational spectra"] that rings other than S, (mainly S,, S6, and S, with n > 8) are present at all temperatures in liquid sulfur, and that these-in comparison with S8-are considerably more reactive species and strongly influence the properties of the melt[21.The separation of sulfur homocycles by means of highpressure liquid chromatography (HPLC)[31 now enables a much more accurate quantitative analysis. Using this technique, we have now found that, after establishment of the equilibrium at constant temperature (23 samples, 13 temperatures) and then quenched in liquid nitrogen, accurately weighed at 20 "C (4.1-7.2g), and immediately extracted quantitatively with ca. 200 mL CS2[41. After filtration and dilution to a prescribed volume, the solution was analyzed quantitatively by HPLC. The insoluble residue (polymeric sulfur, S,) was washed with CS,, dried, and weighed.In the chroma tog ram^'^^, the areas A of 18 S, ring-molecules (n = 6-23) could be measured by electronic integration. For the calibration, at least ten solutions of different concentration c of each of the pure compounds were measured in the case of S6, S,, s8, Sl0, S12, and SZ0. The calibration curve was linear (c = aA) with a correlation coefficient better than 0.9999 over the range 5-500 bg S/mL CS2. Since the slope a is proportional to the number of S atoms in the molecule (except in the case of S7), the calibrations could be calculated for the remaining molecules.Representative analytical values at 13 different temperatures are listed in Table 1. As expected[61, the concentrations of the S, rings ( n f 8 ) pass through a maximum at 159°C: besides 3% S,, only 83.4% S, is present. The missing "rest" of the 100% assay is ascribed to soluble s,, molecules (n > 23) and analytical errors (maximally 3"/0). Molecules with n < 6 were not detectable.After S8 and S,, the most frequently occurring molecules in the melt are S6, S9, and Si2. The relevant reaction enthalpies AH(1) of Equation (1) can be calculated from the temperature-dependence of the concentrations of the molecules listed in Table 1. From the linear regressions in the temperature range 116-159 "C the values shown in Table 2 are obtained.Assuming an equally strong intermolecular interaction (per atom) for all molecules in the melt (zero enthalpy of mixing), the mean bond energies (m.B.E.) in the sulfur rings shown in Figure 1 can be calculated from the AH( I)
