X-ray data collection and refinement statistics.

aRmerge = ΣhΣj |Ih,j−h|/ΣhΣj|Ih,j|, where Ih,j is the jth observation of reflection h. bRwork = Σh||Foh|−|Fch||/Σh|Foh|, where Foh and Fch are the observed and calculated structure factor amplitudes respectively for the reflection h. cRfree is equivalent to Rwork for a 5% subset of reflections not used in the refinement. Numbers in parentheses refer to the outer resolution shell.