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Solving complex open‐framework structures from X‐ray powder diffraction by direct‐space methods using composite building units
Author(s) -
Inge A. Ken,
Fahlquist Henrik,
Willhammar Tom,
Huang Yining,
McCusker Lynne B.,
Zou Xiaodong
Publication year - 2013
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889813013101
Subject(s) - crystallography , crystal structure , space (punctuation) , powder diffraction , infrared spectroscopy , diffraction , unit (ring theory) , space group , chemistry , cluster (spacecraft) , materials science , x ray crystallography , physics , mathematics , optics , computer science , programming language , mathematics education , organic chemistry , operating system
The crystal structure of a novel open‐framework gallogermanate, SU‐66 {|(C 6 H 18 N 2 ) 18 (H 2 O) 32 |[Ga 4.8 Ge 87.2 O 208 ]}, has been solved from laboratory X‐ray powder diffraction (XPD) data by using a direct‐space structure solution algorithm and local structural information obtained from infrared (IR) spectroscopy. IR studies on 18 known germanates revealed that the bands in their IR spectra were characteristic of the different composite building units (CBUs) present in the structures. By comparing the bands corresponding to Ge—O vibrations in the IR spectra of SU‐66 with those of the 18 known structures with different CBUs, the CBU of SU‐66 could be identified empirically as the Ge 10 (O,OH) 27 cluster (Ge 10 ). The unit cell and space group (extinction symbol P ‐‐ a ; a = 14.963, b = 31.593, c = 18.759 Å) were determined initially from the XPD pattern and then confirmed by selected‐area electron diffraction. The structure of SU‐66 was solved from the XPD data using parallel tempering as implemented in FOX [Favre‐Nicolin & Černý (2002). J. Appl. Cryst. 35 , 734–743] by assuming P 2 1 ma symmetry and two Ge 10 clusters in the asymmetric unit. Rietveld refinement of the resulting structure using synchrotron XPD data showed the framework structure to be correct and the space group to be Pmma . The framework has extra‐large (26‐ring) one‐dimensional channels and a very low framework density of 10.1 Ge/Ga atoms per 1000 Å 3 . SU‐66, with 55 framework atoms in the asymmetric unit, is one of the more complicated framework structures solved from XPD data. Indeed, 98% of the reflections were overlapping in the XPD pattern used for structure solution. Tests on other open‐framework germanates (SU‐62, SU‐65, SU‐74, PKU‐12 and ITQ‐37) for which the XPD data, unit cell, space group and IR spectra were available proved to be equally successful. In a more complex case (SU‐72) the combination of FOX and powder charge flipping was required for structure solution.