Single crystals of CoSr5(AsF6)12·8HF were obtained as one of the products after the crystallization of 3KF/CoF2/SrF2 mixture in the presence of AsF5 in anhydrous HF. The CoSr5(AsF6)12·8HF is monoclinic, C/2c (No.15), with a = 26.773(5) , b = 10.087(2) , c = 21.141...