Chemistry Reference
In-Depth Information
Powder Diffraction Crystallography
of Molecular Solids
Kenneth D.M. Harris
Abstract Many important crystalline solids cannot be prepared as single crystals of
suitable size and quality for structural characterization by conventional single-
crystal X-ray diffraction techniques and can instead be prepared only as microcrys-
talline powders. However, recent advances in techniques for determining crystal
structures directly from
powder
X-ray diffraction data have created a unique oppor-
tunity for establishing structural properties of such materials. This chapter surveys
the applications of powder X-ray diffraction across various aspects of structural and
materials chemistry, focusing mainly on the opportunities that have emerged in
recent years for carrying out complete crystal structure determination from powder
X-ray diffraction data and giving particular emphasis to the case of molecular crystal
structures. The current scope and future potential of powder X-ray diffraction as a
strategy for crystal structure determination are discussed, and examples of
applications across several disciplines of materials chemistry are presented.
Keywords Powder diffraction
Molecular solids
Organic crystals
Crystal
structure
Direct space
Structure solution
Structure determination
Contents
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
2
Structure Determination from Powder XRD Data ......................................... 136
2.1 Relationship Between a Crystal Structure and Its Diffraction Pattern . . . . . . . . . . . . . 136
2.2 How to Compare Experimental and Calculated Powder XRD Patterns . . . ......... 138
2.3 Overview of the Structure Determination Process . . ................................ 139
2.4 Unit Cell Determination (Indexing) .................................................. 140
2.5 Preparing the Intensity Data for Structure Solution: Profile Fitting ................ 140
2.6 Structure Solution . . ................................................................... 142
2.7 Structure Refinement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
