Structural and spectroscopic studies of halocuprate(I) and haloargentate(I) complexes [M2XnX′4-n]2-

The complexes [Cu2Br4](2-), [Cu2Br4](2-), [Cu2I2Br2](2-), [Cu2I3CI](2-), [Ag2Cl4](2) - have been characterized as their isomorphous bis(triphenylphosphoranylidene)ammonium ([Ph3PNPPh3](+) = PNP+) salts by single crystal structural determinations. All anions show the centrosymmetric doubly halogen-bridged forms [XM(mu-X)(2)MX](2-) with three-coordinate metal atoms that have been observed in [M2X4]2- complexes with other large organic cations. In [Cu2I2Br2](2-) the iodide ligands occupy the bridging positions and the bromide the terminal positions, while in [Cu2I3Cl](2-), obtained in an attempt to prepare [Cu2I2Cl2](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 [Ag2Cl4](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 [Ag2Cl4](2-) complexes with organic cations. The v(MX) bands have been assigned in the far-IR spectra, and confirm previous observations regarding the unexpectedly simple IR spectra of [Cu2X4](2-) complexes.