Isolation of a trigonal bipyramidal Mn(II) diradical complex with an intermediate spin state ($S$ = 3/2)

Isolation of Mn(ii) complexes featuring an intermediate spin state (S$_{Mn}$2+ = 3/2) is quite rare. Previous studies have only speculated on the existence of such species in systems such as paddle-wheel-type tris(cyclopentadienyl)manganese(ii) and tris(allyl)manganese(ii) anions, which are proposed to exhibit mixed S$_{Mn}$2+ = 3/2 and S$_{Mn}$2+ = 5/2 states based on theoretical investigations. Herein, we report on the isolation and structural characterisation of an unprecedented Mn(ii)-bis(dithiolene-radical) complex (1), in which the Mn(ii) centre adopts a distorted trigonal bipyramidal coordination geometry and possesses an intermediate spin state (S$_{Mn}$2+ = 3/2). Magnetic susceptibility and EPR studies revealed that the Mn(ii) centre, coordinated by an S$_5$ donor set, is antiferromagnetically coupled to two unpaired electrons on the chelating ligands. Complex 1 has been further characterised by XPS, IR, UV-Vis, and Raman spectroscopy. The redox property of 1 was investigated using cyclic voltammetry measurements. 1$^−$ was generated in THF solution via the reduction of 1 with KC$_8$.