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MAD techniques applied to powder data: The method of the joint probability distribution functions

Carmelo Giacovazzo 1,3Angela Altomare 1Maria Cristina Burla 2Gaetano Campi 1Cuocci Corrado 1Benny Danilo Belviso 1Fabia Gozzo 4Moliterni Anna Grazia 1Giampiero Polidori 2Rizzi Rosanna 1

1. CNR-Istituto di Cristallografia (IC), via Amendola 122/O, Bari 70126, Italy
2. Università di Perugia, Dip. di Scienze dellla Terra, Perugia 06100, Italy
3. Università di Bari, Dip. Geomineralogico, Bari 70125, Italy
4. Swiss Light Source, Paul Scherrer Institute, Villigen PSI 5232, Switzerland


The method of joint probability distribution functions has been applied to powder data to find the anomalous scatterer substructure. The method needs two wavelength data: the conclusive formulas provide estimates of the substructure structure factors, from which the anomalous scatterer positions should be found by Patterson or Direct Methods. The theory has been applied to two compounds. The crystal structure of the first, trans-dichlorido-diacetate-ammine-(1-adamantylamine) Pt(IV), C14 H26 N2 O4 Cl2 Pt was unknown: we used Pt as anomalous scatterer. The crystal structure of the second, Iron(II) phthalocyanine bis (pyridine), C32 H16 N8 Fe (C5 H5 N)2, was known: we used Fe as anomalous scatterer. Both the two substructures were correctly located.
The method of joint probability distribution of structure factors has been re-formulated to  phase the full structure reflections, given the substructure. The phases  so obtained resulted carefully estimated, thus leading to the solution of the (unsolved)  first test structure and to confirm the solved one.


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Related papers

Presentation: Oral at 11th European Powder Diffraction Conference, Microsymposium 11, by Carmelo Giacovazzo
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-04-29 15:42
Revised:   2009-06-07 00:48