Completing the series of Group VI heterotrimetallic M2Cr(dpa)4Cl2 (M2 = Cr2, Mo2, MoW and W2) compounds and investigating their metal–metal interactions using density functional theory

• Preparation of Mo2Cr(dpa)4Cl2 and W2Cr(dpa)4Cl2 with short metal–metal distances.
• Magnetic susceptibility indicates S = 2 states for the compounds.
• Calculations reveal a 3c/3e partial bond between the M2 unit and Cr.
• TDDFT indicates a δ → δ∗ transition with M2-to-Cr charge transfer character.

Metalation of the quadruply bonded Mo2(dpa)4 and W2(dpa)4 (dpa = 2,2′-dipyridylamido) compounds with CrCl2 results in the formation of the new heterotrimetallic complexes Mo2Cr(dpa)4Cl2 (1) and W2Cr(dpa)4Cl2 (2). X-ray crystal structures of 1 and 2 reveal short Mo2⋯Cr and W2⋯Cr distances of 2.69 and 2.65 Å, respectively. Electronic absorption spectra and electrochemical data for 1 and 2 are presented. Variable temperature magnetic susceptibility measurements establish the electronic spin states of 1 and 2, which are S = 2. Molecular orbital analysis by density functional theory (DFT) calculations reveals a 3-center/3-electron sigma bonding configuration leading to a partial sigma type interaction between the M2 quadruply bonded unit and Cr in 1 and 2. Time-dependent DFT provides support for the assignment of the lowest energy feature in the electronic absorption spectra of 1 and 2 as a δ → δ∗ transition with M2-to-Cr charge transfer character.

The new heterotrimetallic complexes Mo2Cr(dpa)4Cl2 (1) and W2Cr(dpa)4Cl2 (2) are described, having short Mo2⋯Cr and W2⋯Cr distances of 2.69 and 2.65 Å, respectively, and electronic spin states of S = 2. Molecular orbital analysis by density functional theory (DFT) calculations reveals a 3-center/3-electron sigma bonding configuration leading to a partial sigma type interaction between the M2 quadruply bonded unit and Cr in 1 and 2. Time-dependent DFT provides support for the assignment of the lowest energy feature in the electronic absorption spectra of 1 and 2 as a δ → δ∗ transition with M2-to-Cr charge transfer character.Figure optionsDownload as PowerPoint slide