Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

4B2/2005G146

Structural analysis of water-soluble citrates and peroxocitrates complexes
available only in the powder crystalline form
V. PETRYKIN*1, K. TOMITA1, M. KAKIHANA1, E.R. de CAMARGO2, H. SAWA3,4.
1
IMRAM, Tohoku Univ., Katahira 2-1-1, Aoba-ku, Sendai 980-8577 Japan
2
Institute of Chemistry, Unicamp, CP-6154, Campinas, 13083-970, Brazil
3
Photon Factory, High Energy Research Organization, Oho, Tsukuba, Ibaraki 305-0801, Japan
4Dept. of Materials Structure Science, Graduate Univ. for Advanced Studies, 305-0801, Japan
Introduction
Development of convenient, non-toxic d-transition
metals’ compounds useful as precursors for solutionbased synthesis of inorganic materials is an exciting
challenge in materials chemistry. We achieved a
considerable progress in the synthesis and structuralcharacterizations of water-soluble titanium (IV)compounds [1-3]. For those complexes single crystals
could be obtained and used for structure solution by
conventional approach. Meanwhile a series of titanium,tantalum and cobalt compounds could be obtained only inthe form of crystalline powder. At the same time
resolution of the conventional powder X-ray
diffractometer and the intensities of the patterns did notallow choice of the space group and structure solution.
In this work, we attempted to collect high-resolution
powderpatterns
forthreenewcomplexes
Sr[Ti(C6H4O7)O2]·2H2O, Ba[Ti(C6H4O7)O2]·2H2O andH4[Co(C6H5O7)2] using BL-4B2 powder diffraction facility
and use the data for structure solution.
Experiment
Powder diffraction data were collected at room
temperature in the flat plate geometry using Multi
Detector System at BL-4B2 beam station for three metalcomplexes: H4[Co(C6H5O7)2], Sr[Ti(C6H4O7)O2]·2H2O,Ba[Ti(C6H4O7)O2]·2H2O. The wavelength was 1.20525Å.
To find optimal resolution, intensity and sample exposure
time to the X-ray beam several data sets were collected inOOO
the 2θ range from -5 till 154.98 using ∆2θ=0.005-0.01
and sampling time of 2-8s/step. The intensities ofreflections were extracted by LeBail procedure in theRIETICA program and used in structure solution program
EXPO [4]. Direct method was used and the structure wasexpanded using Fourier technique.
Results
Due to the instrument design, data should be collectedOO
in the whole 2θ range from -5 till 154.98 . However theOintensities of reflections decline rapidly at 2θ>60 and
can not be used. The indexing of the diffraction patternsof peroxo-citrato complexes M[Ti(C6H4O7)O2]·2H2O(where M = Sr and Ba) failed. In addition, samples
changed their color from light-orange into pale yellow,
which indicates that peroxo group is decomposed due to138

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the exposure to the X-ray beam. Probably low
temperature data collection should be attempted.
Diffraction pattern of cobalt citrate complex
H4[Co(C6H5O7)2] could be indexed as orthorhombic latticewith a=5.9122(2)Å, b=10.4129(3)Å, c=13.44282(15)Å
and reflection conditions corresponding to P212121 (no.
19) space group. The intensities of first 830 reflections
were extracted by LeBail procedure with final
Rwp=9.57%. They were used for structure solution.
Cobalt and four oxygen atoms were located by direct
method. After the refinement cycle, two more oxygen
atoms were found in the nearest coordination of cobalt.
Co has slightly distorted octahedral environment with CoO distance of 1.950-2.197Å. The shortest Co-Co distanceof 3.689Å suggests that two cobalt ions should becoordinated by one citric acid molecule in the bi-dentate
manner. Examination of difference Fourier map gave
three more carbon atoms that allows a construction ofpartial structure in Fig. 1. Fig. 1 shows that Co atoms
coordinated by citric acid are arranged into stripes along aaxis, and probably such stripes are kept together byhydrogen bonds between protonated groups of citric acids.
Unfortunately, further expansion of the structure by
Fourier technique is difficult. However, this framework
can be used for structure expansion by molecularmechanics optimization. This work is currently under way.

Fig. 1. Part of the Co-citrate crystal structure, solved
ab initio using powder diffraction data.
References[1] M. Kakihana et al., Inorg. Chem. 40, 891 (2001)[2] M. Kakihana et al., Inorg. Chem. 43, 4546, (2004)[3] K. Tomita et al., Angew. Chem. 45, 2378 (2006)[4] A. Altomare et al., J. Appl. Cryst. 32, 339, (1998)* valery@tagen.tohoku.ac.jp