Determination of complex structures by combined neutron and synchrotron X-ray powder diffraction

Abstract

THE feasibility of determining crystal structures from powder diffraction data has improved substantially during the past decade. Early work using laboratory X-ray data1,2 has been followed by studies that take advantage of the higher resolution provided by synchrotron X-ray3 and neutron4 diffraction instrumentation. Other advances have been made in the computational aspects of the problem5,6. Nevertheless, there has remained a disparity between the complexity of structures that can be solved, ab initio, from powder data, and those that can in principle be refined by the Rietveld profile method7. For example, refinements with up to 34 atoms8 and 132 positional parameters9 have been reported, but the most complex unknown structure to be solved from powder data contains only 17 atoms in the asymmetric unit cell10. Here we describe the solution and refinement of Ga2(HPO3)3.4H2O, a novel framework structure with 29 atoms in the asymmetric unit cell and 117 structural parameters, by the combined use of synchrotron X-ray and neutron powder diffraction. Exploiting the complementary nature of these techniques further extends the power of powder diffraction for structure determination.