Hr. Karfunkel et al., CRYSTAL PACKING CALCULATIONS AND RIETVELD REFINEMENT IN ELUCIDATING THE CRYSTAL-STRUCTURES OF 2 MODIFICATIONS OF 4-AMIDINOINDANONE GUANYLHYDRAZONE, Acta crystallographica. Section B, Structural science, 52, 1996, pp. 555-561
The crystal structures of two modifications (termed A and B) of 4-amid
inoindanone guanylhydrazone (AIGH), 2-(4-amidino-1-indanylideneamino)g
uanidine, have been determined. Modification B, for which single cryst
als were available, has been treated in the usual manner. The determin
ation of modification A, for which no single crystals were available,
was made on the basis of the X-ray powder pattern and ab initio packin
g calculations. It has been shown that it is possible to determine in
a routine manner the crystal structure of a polar and moderately flexi
ble molecule, which can be specified as several tautomeric forms, usin
g a combination of high-precision computational chemistry and Rietveld
refinement. The resulting R factor was ca 10%. Although the resolutio
n of the powder diagram allowed for indexing, it is shown that the str
ucture determination is also possible without indexing the powder diag
ram. The presented structure determination should be understood as an
example of a new and generalized use of the Rietveld refinement where
the two main problems, indexing of the powder pattern and making an in
itial structure guess, could be bypassed.