Constrained Rietveld refinement of [beta-H-1(1)] decadeuteriodopamine deuteriobromide using powder neutron diffraction data

The room-temperature crystal structure of [beta-H-1(1)]decadeuteriodopamine deuteriobromide has been refined using pulsed neutron diffraction data collected from a powder sample. A Rietveld refinement involving 93 structural parameters converged to give a chi(2) of 1.99 for the fit, with 5366 observations and 111 basic variables. The agreement factors R(wp) = 2.47%, R(p) = 2.74%, R(I) = 5.70% and R(E) = 1.75% indicate an excellent fit to the data. Slack chemical constraints were used in the refinement to impose prior chemical sense on the final structure. The dopamine cation is extensively hydrogen bonded to bromide ions, and the hydrogen-bond geometries are well defined.