... SHELXS97 University of Göttingen, Germany.] ) and refined on F 2 with all data using SHELXL97 (Sheldrick, 1997b [Sheldrick, GM (1997b). ... A weighting scheme based upon P = [F o 2 + 2F c 2 ]/3 was employed in order to reduce statistical bias (Wilson, 1976 [Wilson ... Acta Cryst. ...