ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
A single crystal magnetic resonance study of C4Cd, [(C4H9NH3)2Cd]Cl4, specifically deuterated at a variety of positions is reported. This class of compound forms bilayered structures and C4Cd itself undergoes at least three phase transitions over the temperature range studied, 120 to 350 K. The experimental results yield a detailed picture of the variation of molecular ordering in the butyl chain with temperature and structural phase and bear substantial resemblance to 2H NMR results reported for lipid membranes. In the high and intermediate phases, complete order tensors are determined in the bilayer frame which are compared (unsuccessfully) with the disordered high temperature x-ray structure of the isomorphous manganese analog, C4Mn. On the time scale of 10−5 s, the butyl chain is nearly stationary at 120 K where it is found to occupy the expected all-trans configuration which runs parallel to the bilayer normal. At temperatures between the intermediate phase and 120 K, a mosaic structure is observed in which the C–D bonds occupy for long times ((approximately-greater-than)10−3 s) a distribution of orientations. A qualitative model for the high and intermediate phases based on gauche–trans isomerization is presented. To explain the measured order tensors, we assume that (a) gauche–trans isomerization is coupled to molecular reorientation and (b) the configurations are distorted from ideal diamond lattice configurations so as to make molecular packing more compact. It is suggested that in the mosaic structure, configurations containing gauche sequences remain populated but the isomerization rate is dramatically slowed. © 1996 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.472151
