Synthesis, Characterization and Crystal Structure of [Tetra-μ3-iodotetrakis{1'-(diphenylphosphino)ferrocenecarboxylic Acid-P}tetracopper(I)]-Acetic Acid (1 : 2)

The title compound was prepared by the reaction of 1'-(diphenylphosphino)ferrocenecarboxylic acid with copper(I) iodide in acetic acid. It has the tetrameric structure of the heterocubane type and all four monomeric units are crystallographically independent. The central Cu4I4 core is severely distorted from the Oh symmetry as a consequence of disparate radii of the atoms; however, this does not lead to transformation of the core into a stepped arrangement, the feature otherwise common for similar tetrameric structures. The ligand behaves as a monodentate phosphine and completes the approximately tetrahedral coordination polyhedron around copper(I). The carboxyl groups remain undissociated and uncoordinated but participate in intermolecular hydrogen bonding. Two carboxyl groups link the molecules of the tetramer into a zig-zag chain; the remaining two are bonded to molecules of solvating acetic acid which act as spacers between the chains. As expected, the geometry of the flexible ligand is remarkably influenced by the hydrogen bonding, the main conformation changes taking place at the P-C bonds and in the mutual arrangement of the cyclopentadienyl rings.