Structural and Spectroscopic Studies of Halocuprate(I) and Haloargentate(I) Complexes [M 2 X n X′ 4− n ] 2−

The complexes [Cu 2 Br 4 ] 2− , [Cu 2 I 4 ] 2− , [Cu 2 I 2 Br 2 ] 2− , [Cu 2 I 3 Cl] 2− , [Ag 2 Cl 4 ] 2− have been characterized as their isomorphous bis(triphenylphosphoranylidene)ammonium ([Ph 3 PNPPh 3 ] + = PNP + ) salts by single crystal structural determinations. All anions show the centrosymmetric doubly halogen‐bridged forms [XM(μ‐X) 2 MX] 2− with three‐coordinate metal atoms that have been observed in [M 2 X 4 ] 2− complexes with other large organic cations. In [Cu 2 I 2 Br 2 ] 2− the iodide ligands occupy the bridging positions and the bromide the terminal positions, while in [Cu 2 I 3 Cl] 2− , obtained in an attempt to prepare [Cu 2 I 2 Cl 2 ] 2− , two of the iodide ligands occupy the bridging positions with the third iodide and the chloride ligand occupying two statistically disordered terminal positions. In [Ag 2 Cl 4 ] 2− the distortion from ideal trigonal coordination of the metal atom is greater than in the copper complexes, but less than in other previously reported [Ag 2 Cl 4 ] 2− complexes with organic cations. The ν(MX) bands have been assigned in the far‐IR spectra, and confirm previous observations regarding the unexpectedly simple IR spectra of [Cu 2 X 4 ] 2− complexes.