[PPh(4)](2)[MoSe4] and [PPh(4)](2)[WSe4] react with 2 equiv of CuCN in CH3CN to afford [PPh(4)](2)[(NC)Cu(mu-Se)(2)Mo(mu-Se)(2)Cu(CN)]. CH3CN (1) and [PPh(4)](2)[(NC)Cu(mu-Se)(2)W(mu-Se)(2)Cu(CN)].CH3CN (2), respectively. Compounds 1 and 2 are isostructural. Compound 1 crystallizes in the triclinic space group C-i(1)-P1 $($) over bar$$ with two formula units in a cell of dimensions a = 13.208(3) Angstrom, b = 14.254(3) Angstrom, c = 14.573(3) Angstrom, alpha = 72.47(3)degrees, beta = 74.09(3)degrees, and gamma = 79.12(3)degrees at 113 K. Full anisotropic refinement of the structure on F-o(2) led to a value of R(F) = 0.028 for those 7546 data having F-o(2) > 2 sigma(F-o(2)). The [(NC)Cu(mu-Se)(2)Mo(mu-Se)(2)Cu(CN)](2-) anion of 1 comprises two CuCN fragments ligating the opposite edges of a tetrahedral [MoSe4](2-) moiety; the Cu-Mo-Cu angle is 179.13(2)degrees. Compounds 1 and 2 display an IR band at 2250 cm(-1), which may be assigned to a CN stretching mode of the CH3CN solvate. Such a solvate molecule was found in the crystal structure of 1. The Se-77 NMR spectra show a resonance at 1195 ppm for 1 and 920 ppm for 2. Addition of excess PMe(2)Ph to solutions of 1 and 2 results in the formation of [PPh(4)](2)[(NC)Cu(mu-Se)(2)MoSe2] (3) and [PPh(4)](2)[(NC)Cu(mu-Se)(2)WSe2] (4), respectively. Compounds 3 and 4 are isostructural. Compound 3 crystallizes in the monoclinic space group C-2h(6)-C2/c with four formula units in a cell of dimensions a = 11.254(2) Angstrom, b = 20.153(4) Angstrom, c = 20.191(4) Angstrom, and beta = 91.74(3)degrees at 113 K. Full anisotropic refinement of the structure on F-o(2) led to a value of R(F) = 0.055 for those 3588 reflections having F-o(2) > 2 sigma(F-o(2)). The [(NC)Cu(mu-Se)(2)MoSe2](2-) anion of 3, which has a crystallographically imposed 2-fold axis, comprises a CuCN fragment ligated across an edge of the tetrahedral [MoSe4](2-) moiety. The Se-77 NMR spectra show resonances at 1030 and 1820 ppm for compound 3 and at 782 and 1383 ppm for compound 4. The remaining NMR, IR, and electronic spectroscopic data of the four title compounds are also consistent with their solid-state structures.