Abstract The structures of Cu(NH 3) 4(CuBr 2) 2 and Cu(NH 3) 4(CuCl 2) 2 · H 2O were determined by X-ray single-crystal analysis. Both compounds belong to space group I4/mmm, and there are two formula weight units per unit cell. The structures were solved by Patterson sections, Fourier and difference-Fourier analyses, and refined by block-diagonal least squares. Each copper(II) ion lies in the plane of four nitrogen atoms. The copper(I) ions are tetrahedrally coordinated to four halide ions. The tetrahedra are joined on edges and extend as infinite chains along the c axis. There are eight equally spaced halide ions about copper(II) at a distance of 4·2 Å which is much greater than those normally associated with copper(II) halide covalent bonds. The visible spectra of these compounds can be explained in terms of crystal field splittings of the d orbitals while that of the iodide complex  may also be due to charge transfer transitions which involve both the cupricammine plane and cuprous iodide chains.