The polymorphism of 1-heptadecanol (C 17 H 35 OH), 1-octadecanol (C 18 H 37 OH), 1-nonadecanol (C 19 H 39 OH), and 1-eicosanol (C 20 H 41 OH) has been studied by X-ray powder diffraction, differential scanning calorimetry (DSC), Raman scattering, and infrared spectroscopy (IR). At room-temperature two monoclinic forms, and γ, are observed. For the n-alkanols with an even number of carbons the stable form is γ, whereas is the stable form for the n-alkanols with an odd number of carbons. On heating, these phases transform to a monoclinic, rotator form R' IV at a few degrees below the melting point. A metastable form is obtained by quenching from the melt for 1-octadecanol and 1-eicosanol, which is isostructural with the -phase of the odd alkanols. Cell parameters, temperatures, and enthalpies of the transitions are reported.

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OH with Dn ¼ 2, and C 16 OH-C 20 OH with Dn ¼ 4. The phase that melts is either the monoclinic R 0 IV (C2/m, Z ¼ 4) or the hexagonal R 0 II (R3m, Z ¼ 6) rotator form. One of the most important issues in the melting of these systems is that when the two original compounds of the system are isostructural, the phase diagram does not always show total miscibility. In the systems studied here, only the C 15 OH-C 16 OH, C 18 OH-C 19 OH and C 19 OH-C 20 OH systems show total miscibility. In the other systems in which the two original compounds are isostructural, miscibility is partial, as in the systems where the two original compounds are not isostructural. In this family, as in other families of mixed crystals, there is an excess enthalpy-entropy compensation. This compensation has a temperature dimension, and is called the compensation temperature (y) of the family and/or subfamily. In the case of the R 0 II and R 0 IV rotator forms of the n-alkanols family its value is 362 K. This value is in line with the trend show by a large group of organic and inorganic mixed crystalline materials.

Hirshfeld surfaces and two-dimensional fingerprint plots are used to visualize and analyze intermolecular interactions in six new phosphoramidate structures, [2,6-F2-C6H3C(O)NH]P(O)[X]2 {X = N(C2H5)2 (1), [X]2 = NHCH2C(CH3)2CH2NH and with one CH3OH solvated molecule (2)}, [C6H5O]2P(O)Y [Y = NC4H8O (3), NHC6H4(3-Br) (4)] and [Z]2P(O)OP(O)[Z]2 [Z = N(CH3)(CH2C6H5) (5), NHC6H4(4-CH3) (6)]. Study of the short intermolecular contacts in structures (1)-(6) by Hirshfeld surfaces demonstrate that the O atom of P=O is a better H-atom acceptor than the O atom of C=O for (1) and (2), and also relative to the O atom of the C6H5O group for (3) and (4), and relative to the bridge O atom of the P(O)OP(O) segment for (5) and (6). The results confirm that the crystal packing is related to the kind of substituent linked to the P atom. Compounds (1), (2), (4) and (6), with characteristic N-H···O hydrogen bonds, show a pair of intense spikes (including the intermolecular H···O contacts) in the fingerprint plots, summarizing the major features of each structure in the related two-dimensional plot. For (3) and (5), without any N-H unit, the two short spikes are observed for (3) but are absent for (5). The upper d(e) and d(i) values (distances to the Hirshfeld surfaces for the nearest atoms outside and inside) in the fingerprint plots are more compact in (3) than in (4), and in (5) than in (6), reflecting the more efficient packing in (3) and (5). The tertiary N atoms of (3) and (5) do not take part in any intermolecular contacts involving H atoms. Moreover, structures (3)-(6) show greater contribution from C···H contacts relative to O···H contacts. Finally, Hirshfeld surfaces and fingerprint plots are employed for a comparison of the two independent molecules in the asymmetric unit of (1) and also, for a comparison of (6), in the orthorhombic crystal system, with the previously reported monoclinic polymorph (Pourayoubi, Fadaei et al., 2012).