Ligands bonded to metal ion or through-metal interacting ligands? Analysis of unusual bonds formation in the (BDTA)(2)[Co(mnt)(2)] material

The cohesion in the material (BDTA)(2)[Co(mnt)(2)] (1) is analyzed in the light of experimental data and ab initio calculations (BDTA = 1,3,2-benzodithiazolyl, and mnt(2-) = maleonitrildithiolate). It is demonstrated that the duality of the thiazyl radical BDTA as cation and ligand stems from the competition between the Co(II) ion-sulfur-rich part of the ligand interactions (i.e. sigma-type interactions), and the equatorial ligand mnt(2-)-benzyl moiety contacts (i.e. pi-pi interactions). The molecular changes observed between the low-temperature and high-temperature regimes are interpreted on the basis of multireference CASSCF wavefunction and subsequent CASPT2 calculations using an original Lewis-like picture. The Jahn-Teller-like distortion is accompanied by an unusual electronic redistribution affecting the sigma-type and pi-pi interactions, leading to short (2.65 angstrom) and long (3.48 angstrom) Co-BDTA distances in good agreement with X-ray data. Due to its intrinsic architecture and radical character, the BDTA ligand is simultaneously involved in weak metal-ligand and ligand-ligand bonds. Such lability in bond formations is of prime importance in bistable materials preparation. The role traditionally attached to the metal center in transition metal complexes is reconsidered in systems such as 1, where significant charge transfers are quantified between the low and high temperature phases.