Single Crystal XRD Pattern Obtained From Magnetically Aligned Powder

Department of Applied Chemistry, Tokyo Metropolitan University* National Institute for Materials Science**
â—‹Tsunehisa Kimura* Fumiko Kimura** Masashi Yoshino*

There are two major routes to reach the structure determination of a crystal by diffraction methods: a single-crystal analysis and a powder pattern analysis. Each of them has the advantages and disadvantages. For example, the former cannot be applied to some compounds that do not crystallize to sizes large enough suitable for this analysis. The latter is a powerful means because of its wide applicability to any powder samples, but special cares should be paid, for example, to the overlapping of peaks, etc.
In the present paper, we propose the third route that would cover the disadvantages encountered by the single-crystal and powder methods. We used the magnetic alignment of crystallites to convert powder to a pseudo-single crystal. Crystals belonging to the biaxial crystal system (orthorhombic, monoclinic, triclinic) have three different diamagnetic susceptibility axes, i.e., the easy and hard magnetization axes and the intermediate one. We have developed a new technique by which the easy and hard axes are simultaneously aligned with respect to the laboratory coordinates.[1]
For the demonstration purpose, we used pulverized L-alanine crystallites (orthorhombic).[2] The powder was suspended in a UV curable resin precursor and subjected to a dynamic elliptic magnetic field to achieve 3-D alignment, followed by solidification of the resin. The obtained pseudo-single crystal exhibited the XRD pattern close to that of the original single crystal.
[1] T. Kimura, M. Yoshino, Langmuir, 21, 4805-4808 (2005).
[2] T. Kimura, F. Kimura, M. Yoshino, Langmuir, 22, 3464-3466 (2006).