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Aminoguanidinium(1+) pentafluorozirconate: multiple redetermination and comparisons
C R Ross1, M R Bauer, R M Nielson
1Department of Structural Biology, St. Jude Children's Research Hospital, 332 North Lauderdale Street, Memphis, TN 38105-2794, USA.
Acta Crystallographica. Section B, Structural Science
|September 27, 2002
Summary
Structural analysis of CN(4)H(7)ZrF(5) revealed significant underestimations in atomic coordinate and unit-cell parameter uncertainties. Radiation-induced changes likely caused these variations, impacting crystal structure determination.
Area of Science:
- Inorganic Chemistry
- Crystallography
- Materials Science
Background:
- Previous structural determination of CN(4)H(7)ZrF(5) by Bukvetskii et al. required independent redetermination.
- Analysis of four crystal structures revealed discrepancies suggesting non-normal distribution of data.
Purpose of the Study:
- To independently redetermine the crystal structure of CN(4)H(7)ZrF(5).
- To investigate the causes of structural variations and underestimations in uncertainty calculations.
Main Methods:
- X-ray diffraction measurements on three different crystals.
- Normal probability analysis of atomic coordinates and unit-cell parameters.
- Analysis of reflection intensities and axial lengths.
Main Results:
- Joint standard uncertainties for atomic coordinates (e.g., x(Zr)) were underestimated by up to 16.5 times.
- Unit-cell parameters (e.g., b axis) showed underestimations of uncertainty by up to 83.0 times.
- Observed variations are consistent with radiation-induced structural changes, not a normal distribution.
Conclusions:
- The study highlights significant underestimation of uncertainties in crystallographic data due to radiation damage.
- The CN(4)H(7)(+1) cation is planar, with the NH(2) group's plane normal to the cation.
- Chains of distorted ZrF(7) pentagonal bipyramids linked by N-H...F bonds were identified.