A first copper chloride selenate was obtained upon attempted preparation of a selenate analog of chlorothionite. The new compound is monoclinic, P21/c, a = 7.1833(5) Å, b = 11.7784(8) Å, c = 8.2419(6) Å, β = 91.083(2)°, V = 697.20(8) Å3, R1 = 0.033. KCu(SeO4)Cl(H2O)2 has no structural analogs and adds to the small family of transition metal selenate halides. The CuO3(H2O)2Cl strongly distorted octahedra share common O-O edges thus forming dimeric units with a Cu-Cu distance of 3.49 Å. Dimeric units and SeO4 tetrahedra in KCu(SeO4)Cl(H2O)2 share common O atoms to produce unique [Cu(SeO4)Cl(H2O)2]- chains. We discuss further perspectives of the selenate halide family and expected differences in crystal chemistry of sulfate and selenate halides.