Structure of Phase III and Polymorphism of (CH3)3CBr

Philippe Négrier (1) , Maria Barrio (2) , Jose Luis Tamarit (2) , Nestor Veglio (2) , Denise Mondieig (1)

1 CPMOH - Centre de physique moléculaire optique et hertzienne
2 ETSEIB - Departament de Fisica i Enginyeria Nuclear [UPC, Barcelone]

The polymorphism of 2-bromo-2-methyl-propane ((CH3)3CBr) has been investigated by both thermal and X-ray powder diffraction experiments. The long time unknown structure of the low-temperature phase III has been determined by X-ray powder diffraction as orthorhombic Pmn21, with lattice parameters a = 19.1350(4) A ° , b = 5.7378(1) A ° , and c = 10.9626(2) A ° at 180 K, Z = 8 and with an asymmetric unit containing one molecule in a general position and two additional molecules placed in a mirror (Z0 =1þ1/2þ1/2). The phase transitions between the different phases have been characterized at normal pressure as well as at high pressures (up to 300 MPa). From the p-T slopes of the two-phase coexistence lines and density measurements as a function of pressure, the volume variations at the transition points have been obtained and compared with those obtained by means of X-ray powder diffraction at normal pressure. The packing as well as the anisotropy of the intermolecular interactions have been analyzed by means of the thermal-expansion tensor and compared with tert-butyl ((CH3)3CX, X = Cl, CN) related compounds.

Domaines: Cristallographie

Philippe Négrier, Maria Barrio, Jose Luis Tamarit, Nestor Veglio, Denise Mondieig. Structure of Phase III and Polymorphism of (CH3)3CBr. Crystal Growth & Design, 2010, 10 (6), pp.2793-2800. ⟨10.1021/cg100425g⟩. ⟨hal-00495006⟩