1. 1) G. M. Sheldrick: Acta Cryst. C71, 3 (2015).
2. 2) Rigaku Corporation: CrystalStructure ver. 4.1 (2014).
3. 3) Bruker AXS Inc.: APEX2 ver. 2014.5-0 (2014).
4. 4) http://shelx.uni-ac.gwdg.de/SHELX/
5. G. M. Sheldrick: User guide to crystal structure refinement with SHELXL.