Flash Communication: Strong Antiferromagnetic Coupling in a Cr(I) Dimer Supported by a Bulky Imidazolin-2-iminato Ligand

Chemical reduction of the previously reported Cr­(II) chloride dimer supported by a bulky imidazolin-2-iminato ligand, [Cr­(μ2-NImDipp)­(Cl)]2, affords the Cr­(I) dimer [Cr­(μ2-NImDipp)]2 (1) in moderate crystalline yield (NImDipp = 1,3-bis­(2,6-diiso­propyl­phenyl)­imidazolin-2-iminato, Dipp = 2,6-diisopropylphenyl). Single-crystal X-ray diffractometry analysis of 1 reveals a Cr2N2 diamond core structure by two bridging iminato ligands and a strong η6 interaction between the Cr­(I) ion and one of the flanking Dipp group. A salient feature in 1 is the long Cr···Cr distances of 2.7274(5) and 2.6548(4) Å. Complex 1 is diamagnetic in solution at 300 K, suggesting that the Cr­(I) ions have a strong antiferromagnetic interaction. Both unrestricted and broken symmetry density functional theory calculations indicate that 1 has two low-spin (S = 1/2) Cr­(I) ions with a very large antiferromagnetic exchange coupling constant (J), resulting in a diamagnetic ground state at 300 K.