Liquid Crystalline Zinc Chloride

  • PDF / 2,035,139 Bytes
  • 6 Pages / 417.6 x 639 pts Page_size
  • 11 Downloads / 221 Views

DOWNLOAD

REPORT


that it should be possible to create a new family of metallomesogens in which small amounts of anisotropic organic templates could template structure in inorganic fluids. RESULTS and DISCUSSION Halozeotype Melts and Glasses: We have recently described the preparation of halozeotype materials based on the analogy between SiO 2 and ZnC12.4 Like zinc chloride itself, 5 the copper zinc chloride halozeotype materials can readily be supercooled to a glass by cooling at a rate greater than 50°C/min. Interestingly, cross-polarized optical microscopic analysis of certain glassy droplets of [H2NMe 2][CuZnsCI1 2], CZX-3, shows remarkable birefringence that completely extinguishes light every 900 upon rotation of the sample between the cross polarizers, indicating a coherent molecular organization in the droplet. Similar birefringence is not observed for the glass of CZX-1, [CuZnsCl12], in which the [HNMe 3]+ cation templates the Sodalite-type structure, because of its isotropic cubic symmetry. However, neutron scattering studies of CZX-1, using the deuterated template [DN(CD 3)3]+, provide strong evidence for the templated organization of intermediate range order of the metal halide framework in both the glass and molten states. The plot of S(Q) vs. Q for viterous CZX-1 is shown in Figure 1a. (Similar scattering data is obtained up to greater than 500 above the melting point.) Two prepeaks (the first and second sharp diffraction peaks) indicative of intermediate range order are observed at Q = 0.77A' and 1.18A-1. This result is in notable contrast to the single prepeak at 1.0 A' observed for non-templated ZnC12 .5 The low-Q scattering features exhibit remarkable correspondence to the Bragg reflections of the crystalline structure as seen by 243 Mat. Res. Soc. Symp. Proc. Vol. 559 01999 Materials Research Society

the superposition of the calculated powder diffraction pattern and the neutron scattering data presented in Figure la. The two prepeaks in this S(Q) vs. Q plot correspond exactly to the (110) and the (200) diffraction planes of crystalline CZX-1. Upon devitrification of the sample at about 70'C the remainder of the Bragg peaks are observed to grow in. Particularly notable is the (211) reflection which is absent in the glass but grows in at 1.45A-' in the devitrified

sample.

a)

neutron scattering of glass

2

It is further

4

Q(A')

X-ray diffraction 8

6

interesting to recognize that the b) diffraction planes from the X-ray crystal structure that coincide with the prepeaks of glassy CZX-1 also correspond to a distance which is exactly the diameter of the 6-rings and 4-rings, respectively, which make up the: 3-cages of the sodalite framework. The latter also corresponds to the plane spacing for the combination of a 6-ring/4-ring/6R(A) ring pattern that is the size of half of the P3-cage. By contrast the (211) Figure 1. a) S(Q) vs. Q plot of the Neutron planes, which are present in the Scattering from [DN(CD 3)3]CuZn 5 Cll 2, and the X-ray crystalline phase but absent from powder diffraction pattern. b) Plot of t

Data Loading...