Polymorphism of crystalline poly(hydroxymethyl) compounds. III. The structures of crystalline and plastic tris(hydroxymethyl)aminomethane

Abstract

Between 5 °K and its m.p. (446.0 °K), tris, H2NC(CH2OH)3, exhibits one phase transition, at 407.3 °K, to form the orientationally disordered (plastic) phase I. The ordered form, phase II, is orthorhombic, Pn21a, a=8.844(1) Å, b=7.794(1) Å, c=8.795 (1) Å, Z=4, Dx=1.327 g/cm3, and Dm=1.320 g/cm3. The crystal structure can be described in terms of layers of molecules approximately normal to the c axis, with strong intralayer hydrogen bonding and weak interlayer hydrogen bonding. The crystal structure of phase II was studied using x-ray diffraction at 144, 295, 297, 348, 382, and 395 °K. Full-matrix least-squares refinement of single-crystal diffractometer data resulted in R values between 2–4% for all but the highest-temperature data sets. Although the integrity of the structure is maintained throughout this temperature range, subtle effects are noted that indicate the increased thermal motion as phase I is approached. Phase I is body-centered-cubic, Im3m, with a=6.876(6) Å at 423 °K, Z=2, and Dx=1.237 g/cm3. A comparison of the two structures and the experimental investigation of a single sample in both phases indicate that the mechanism of the phase transition involves a realignment of the molecules within the the layers and a lessening of the interlayer distance. The formation of a bcc lattice in phase I, rather than a fcc lattice as was found in the other members of this series, has been tentatively interpreted in terms of the ellipsoidal shape of the tris molecule.

Molecular Interactions and Packing in Molecular Alloys between Nonisomorphous Plastic Phases

“…7. Table 6 reports the been the subject of many studies (13,(21)(22)(23)(24)(25)(26)(37)(38)(39), particularly with vibrational techniques (14,39) in order to ac-molecular volumes and K values for the analyzed and some related systems. In spite of the low K values for count for the differences between CH 2 OH and NH 2 interactions.…”

“…(ii) the disappearance of the reflections corresponding to the orthorhombic lattice and the appearance of reflections found to be body centered cubic (space group Im3m with As a consequence of the above patterns some relevant Z ϭ 2) by means of a single crystal study (13). The lattice characteristics of the binary phase diagram can be inferred.…”

“…methyl)aminomethane, are tetrahedral molecules whose low temperature solid forms are governed by strong interSimple organic compounds with molecules of almost actions due to hydrogen bonds (12)(13)(14). globular shape possess molecular reorientational freedom This study must be also located in a more general framewithin a certain range of temperatures.…”

Temperature-Dependent Structure–Energy Changes in Crystals of Compounds with Poly(hydroxymethyl) Grouping

“…For that, compounds of RC(CH 2 OH) 3 type were chosen, where R = NO 2 , NH 2 , CH 2 OH. The structures of the compounds were obtained earlier (4)(5)(6).…”

Structure and Properties of [(CH2OH)3CNH3]H2AsO4

“…Tris(hydroxymethyl)aminomethane, (CH 2 OH) 3 CN H 2 , abbreviated as Tris, is commonly known as buffering agent, and its crystalline form at room temperature is noncentrosymmetric, space group Pn2 1 a [1,2]. The pseudo-globular Tris-molecule forms numerous salts, which being also noncentrosymmetric, are topics of interest due to their potential use in nonlinear optics and signal processing.…”