X-ray crystallography. X-ray crystallographic data were collected on an Oxford Diffraction Gemini CCD diffractometer with Mo-Kα radiation (0.71073 Å) operating within the range 2 < 2θ < 50°. The sample was cooled to 190 K with an Oxford Cryosystems Desktop Cooler. Data reduction and empirical absorption corrections were performed using CrysAlisPro (Rigaku Oxford Diffraction, Yarnton, Oxfordshire, UK). The structure was solved by Direct Methods and refined with SHELX  and all of the calculations and refinements were carried out by WinGX package . All non-H atoms were refined aniostropically. The thermal ellipsoid plot was produced with ORTEP  and the unit cell diagram was drawn with PLATON . Crystallographic data including structure factors in CIF format have been deposited with the Cambridge Crystallographic Data Centre (CCDC 1569026).