Data collection and refinement statistics.

1Statistics for data from the highest-resolution shell are shown in parentheses. 2 R sym =( ΣΣ | I hkl −〈I〉 | ) /( Σ I hkl ) , where the average intensity <I> is taken overall symmetry equivalent measurements and Ihkl is the measured intensity for any given reflection. 3 R work =( Σ | | Fo | −k| Fc | | ) /( Σ | Fo | ) , where Fo and Fc are the observed and calculated structure factor amplitudes, respectively. 4Rfree was calculated for R factor using only an unrefined subset of reflections data (5%). Data collection and refinement statistics.