First-row transition metal complexes of ENENES ligands: the ability of the thioether donor to impact the coordination chemistry

The reactions of two variants of ENENES ligands, E(CH2)(2) NH(CH)(2)SR, where E = 4-morpholinyl, R = Ph (a), Bn (b) with MCl2 (M = Mn, Fe, Co, Ni and Cu) in coordinating solvents (MeCN, EtOH) affords isolable complexes, whose magnetic susceptibility measurements suggest paramagnetism and a high-spin formulation. X-Ray diffraction studies of available crystals show that the ligand coordinates to the metal in either a bidentate kappa(2)[N, N'] or tridentate kappa(3) [N, N', S] fashion, depending on the nature of ligand and/or identity of the metal atom. In the case of a less basic SPh moiety, a bidentate coordination mode was identified for harder metals (Mn, Fe), whereas a tridentate coordination mode was identified in the case of a more basic SBn moiety with softer metals (Ni, Cu). In the intermediate case of Co, ligands a and b coordinate via. kappa(2)[N, N'] and. kappa(2)[N, N', S] coordination modes, which can be conveniently predicted by DFT calculations. For the softest metal (Cu), ligand a coordinates in a kappa(3)[N, N', S] fashion.