Isolation and Characterization of [MnFe(CO)₁₀]⁺: The Missing Link in the 3 <i>d</i> Dimetal Decacarbonyl Series

The heterodinuclear dimetal decacarbonyl cation [MnFe(CO)₁₀]⁺ has been synthesized by combining the metalloradical [Fe(CO)₅]^+⋅ with half an equivalent of Mn₂(CO)₁₀. The complex was subsequently isolated and characterized using single-crystal X-Ray Diffraction (scXRD), as well as IR, Raman, NMR and Mössbauer spectroscopy. Experimental results, complemented by DFT calculations of the relaxed force constants and an analysis of the electron density, reveal that the interaction between the two {M(CO)₅} fragments in [MnFe(CO)₁₀]⁺ is in between a covalent and a dative bond, representing a borderline case between the 2x17 VE and the 16+18 VE electron counting. Additionally, the known isoelectronic anion [CrMn(CO)₁₀]^- was prepared as its [PPN]⁺ salt and characterized for the first time by scXRD. These finding complete the series of structurally characterized isoelectronic dimetal decacarbonyls, spanning from [Cr₂(CO)₁₀]^2- to [Fe₂(CO)₁₀]²⁺, the characteristics of all of which are compared based on experiment and theory.