From Isolated Dimers to an Ordered Antiferromagnetic Ground State in Cation Radical Salts of Cp2Mo(dmit) with Small Anions (Br-, BF-4)

The structural and magnetic properties of two 1:1 salts of the open-shell d1 organometallic radical cation Cp2Mo(dmit)+· (dmit2for 2-thioxo -1,3-dithiole-4,5-dithiolate) with BF-4 and Br- are described and analyzed. The two structures differ not only from each other but also from those reported for the three isostructural PF-6, AsF-6, SbF-6 salts with an unfolded MoS2C2 metallacycle. In [Cp2Mo(dmit)][BF4], the MoS2C2 metallacycle is folded by 23.21(5)° along the S–S hinge and the cations are associated into inversion-centered dimers weakly interacting with each others as reflected by the magnetic susceptibility measurements. In [Cp2Mo(dmit)][Br], the MoS2C2 metallacycle is folded by 30.45(4)° and the Br- anion is involved in C–H··· Br hydrogen bonds. The cations interact antiferromagnetically, giving rise to a three-dimensional set of HOMO–HOMO intermolecular interactions and confirmed by the stabilization of an antiferromagnetic ground state below TNéel=4.5 K.