Synthesis, characterization, structural and theoretical analysis of a series of electron deficient, monomeric thallium iron carbonylate isostructural and isolobal to diiron nonacarbonyl

Extended Hückel and density functional calculations on the isoelectronic [Fe2(CO)6(μ-CO)3−n{μ-TlFe(CO)4}n]n− (n=0–3) series show that the nature of the Fe⋯Fe interaction is quite similar within the series, despite of the different observed internuclear separations. An orbital explanation is provided to explain why these compounds are diamagnetic despite of the absence of a real FeFe bond. In the cases of n=1–3, the formation of dimers allows the release of the electron deficiency on Tl centers through donation from an iron lone pair, leaving almost unchanged bonding within the associated monomers. The stability of the dimers with respect to dissociation appears to be limited by the destabilizing ionic interaction between the negatively charged monomers.