Synthesis, Structural Characterization, and DFT Investigations of [MxM'5-xFe4(CO)16]3- (M, M' = Cu, Ag, Au; M ≠ M') 2-D Molecular Alloy Clusters.

Miscellaneous 2-D molecular alloy clusters of the type [MxM'5-xFe4(CO)16]3- (M, M' = Cu, Ag, Au; M ≠ M') have been prepared through the reactions of [Cu3Fe3(CO)12]3-, [Ag4Fe4(CO)16]4- or [M5Fe4(CO)16]3- (M = Cu, Ag) with M'(I) salts (M' = Cu, Ag, Au). Their formation involves a combination of oxidation, condensation, and substitution reactions. The total structures of several [MxM'5-xFe4(CO)16]3- clusters with different compositions have been determined by means of single crystal X-ray diffraction (SC-XRD) and their nature in solution elucidated by electron spray ionization mass spectrometry (ESI-MS) and IR and UV-visible spectroscopy. Substitutional and compositional disorder is present in the solid state structures, and ESI-MS analyses point out that mixtures of isostructural clusters differing by a few M/M' coinage metals are present. SC-XRD studies indicate some site preferences of the coinage metals within the metal cores of these clusters, with Au preferentially in corner sites and Cu in the central site. DFT studies give theoretical support to the experimental structural evidence. The site preference is mainly dictated by the strength of the Fe-M bonds that decreases in the order Fe-Au > Fe-Ag > Fe-Cu, and the preferred structure is the one that maximizes the number of stronger Fe-M interactions. Overall, the molecular nature of these clusters allows their structures to be fully revealed with atomic precision, resulting in the elucidation of the bonding parameters that determine the distribution of the different metals within their metal cores.