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

Abstract

<jats:title>Abstract</jats:title><jats:p>The complexes [Cu<jats:sub>2</jats:sub>Br<jats:sub>4</jats:sub>]<jats:sup>2−</jats:sup>, [Cu<jats:sub>2</jats:sub>I<jats:sub>4</jats:sub>]<jats:sup>2−</jats:sup>, [Cu<jats:sub>2</jats:sub>I<jats:sub>2</jats:sub>Br<jats:sub>2</jats:sub>]<jats:sup>2−</jats:sup>, [Cu<jats:sub>2</jats:sub>I<jats:sub>3</jats:sub>Cl]<jats:sup>2−</jats:sup>, [Ag<jats:sub>2</jats:sub>Cl<jats:sub>4</jats:sub>]<jats:sup>2−</jats:sup> have been characterized as their isomorphous bis(triphenylphosphoranylidene)ammonium ([Ph<jats:sub>3</jats:sub>PNPPh<jats:sub>3</jats:sub>]<jats:sup>+</jats:sup> = PNP<jats:sup>+</jats:sup>) salts by single crystal structural determinations. All anions show the centrosymmetric doubly halogen‐bridged forms [XM(μ‐X)<jats:sub>2</jats:sub>MX]<jats:sup>2−</jats:sup> with three‐coordinate metal atoms that have been observed in [M<jats:sub>2</jats:sub>X<jats:sub>4</jats:sub>]<jats:sup>2−</jats:sup> complexes with other large organic cations. In [Cu<jats:sub>2</jats:sub>I<jats:sub>2</jats:sub>Br<jats:sub>2</jats:sub>]<jats:sup>2−</jats:sup> the iodide ligands occupy the bridging positions and the bromide the terminal positions, while in [Cu<jats:sub>2</jats:sub>I<jats:sub>3</jats:sub>Cl]<jats:sup>2−</jats:sup>, obtained in an attempt to prepare [Cu<jats:sub>2</jats:sub>I<jats:sub>2</jats:sub>Cl<jats:sub>2</jats:sub>]<jats:sup>2−</jats:sup>, 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<jats:sub>2</jats:sub>Cl<jats:sub>4</jats:sub>]<jats:sup>2−</jats:sup> 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<jats:sub>2</jats:sub>Cl<jats:sub>4</jats:sub>]<jats:sup>2−</jats:sup> 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<jats:sub>2</jats:sub>X<jats:sub>4</jats:sub>]<jats:sup>2−</jats:sup> complexes.</jats:p>