aValues in parentheses are for the highest-resolution shell. bRmerge =Σ|(I -< I > )|/σ(I), where I is the observed intensity. cRwork = Σhkl||Fo| - |Fc||/ Σhkl|Fo|, calculated from working data set. dRfree is calculated from 5.0% of data randomly chosen and not included in refinement.