Trends in the Bond Multiplicity of Cr₂, Cr₃, and Cr₂M (M = Zn, Ni, Fe, Mn) Complexes Extracted from...

Extended metal atom chains constitute an interesting class of molecules from both theoretical and applied points of view. In the chromium-based series Cr₂M(dpa)₄X₂ (with M = Zn, Ni, Fe, Mn, Cr), the direct metal-metal interactions span a wide range of possibilities and so do their associated properties. The multiplicity and symmetry components of the metal-metal bond are herein analyzed via the effective bond order (EBO) concept using complete active space self-consistent field wave functions and compared with similar bimetallic Cr₂L₄X₂ systems. The bond multiplicity follows a trend dominated by the Cr-Cr distance which, in turn, depends on the nature of the axial ligand (X). Cr₂M compounds present asymmetric structures with virtually no interaction between the Cr₂ unit and M, whereas fully symmetric structures with delocalized bonding among the three metals are also possible in Cr₃ complexes. In such cases, a strategy that involves localization of the molecular orbitals into each Cr-Cr pair is applied to quantify the contribution of each pair to the overall metal-metal bond multiplicity.