  Single crystal X-ray diffraction studies were performed for the Sb-doped
112-type iron-based superconductor Ca1-xLaxFeAs2 with the superconducting
transition temperature Tc of 47 K. Doped Sb preferably substituted not for
As(1) in the FeAs layers but for As(2) in the layers of As zigzag chains.
Structural reasons for Tc enhancement by Sb doping were discussed.
