Polymorphism of crystalline poly(hydroxymethyl) compounds. V. Xhyphen;ray diffraction investigation of crystalline and plastic 2hyphen;bromohyphen;2hyphen;nitrohyphen;1,3hyphen;propanediol

摘要

Between room temperature and its melting point (401 K), BrNO2C(CH2OH)2exhibits one phase transition, at 367 K, to form an orientationally disordered crystalline (ODIC) phase I. The ordered form phase II is monoclinicCc,a=8.020(3),b=9.659(2),c=8.965(2) Aring;, bgr;=91.00(1)deg;,Z=4,Dx=1.913 g/cm3, andDm=1.845 g/cm3. A total of 596 independent reflections were refined using leasthyphen;squares techniques to a final agreement factor of 0.031. The structure can be described in terms of a threehyphen;dimensional hydrogenhyphen;bonded network of interconnected, parallel chains, with the molecular centers of the four molecules in the unit cell in an approximate tetrahedral arrangement reminiscent of a facehyphen;centered unit cell. Yet, the ODIC phase I is bodyhyphen;centered cubic lsqb;a=7.11(6) Aring;,Z=2rsqb;. The relationship between the fcc and bcc structures is reviewed in terms of the phase IIndash;phase I transition.