STRUCTURES OF 2 BINARY N-ALKANE SOLID-SOLUTIONS

From X-ray diffractometer single-crystal data, the structures of two binary n-alkane phases have been determined. (I) beta-C24H50, C26H54, beta-tetracosane-hexacosane, mole fraction of C24H50 0.77, hence effective molecular weight 345.39, space group Bb2(1)m (No. 36), a = 4.992 (1), b = 7.503 (3), c = 67.448 (8) angstrom, Z = 4, D(x) = 0.91 g cm-3, 201 significant reflections out of 588, R = 0.11 and wR = 0.09. The structural motif gives an n-alkane backbone 27 carbons long with C-atom sites well resolved on the F map. The outer three C-atom sites at each end of the motif have occupancies less than unity. (II) beta0-C20H42, C22H46, beta0-icosane-docosane, mole fraction of C20H42 0.72, hence effective molecular weight 290.41, space group Fmmm, a = 5.020 (1), b = 7.711 (4), c = 58.6 (2) angstrom, Z = 4, D(x) = 0.85 g cm-3, 36 significant reflections out of 302, R = 0.16 and wR = 0.12. The F map showed no resolved C-atom peaks, probably due to high thermal disorder.