Solvent dependent nuclearity of manganese complexes with a polydentate hydrazone-based ligand and thiocyanate anions

The reaction of Mn(II) chloride with the 2-benzoylpyridyl-(2-picolyl)-hydrazone ligand (HL) and thiocyanate anions in different solvent systems affords mono- [Mn(HL)2(SCN)2] (1), di- [Mn2(HL)2(SCN)4] (2) and a tetra-nuclear complex [Mn4(L)4(SCN)4].2(CH3CN) (3) with concomitant different coordination modes of the ligands. Remarkably, the nuclearity of the complexes only depends on the solvent used, ethanol for 1, n-propanol for 2 and acetonitrile for 3. The complexes have been characterized by elemental analysis, IR spectroscopy technique and the molecular structures determined by single crystal X-ray analysis. In 1 and 2 the ligands are present in its neutral form, while they are deprotonated in 3, but more significantly in all structures a different denticity of ligands was detected: in complex 1 one molecule is tridentate coordinated though the N,N,O donor set, the other bidentate through N,O; in 2 the ligands is of N,N,O-tridentate; finally in 3 each ligand, acting as N,N,O,N-tetradentate species, bridges two metals to form a tetranuclear assembly. The crystal structures have been described using the Hirshfeld surface analysis. Finally, we have studied the ability of the thiocynato ligand to participate in H-bonding and C–H/π interactions by means of DFT calculations (B3LYP/6-31+G∗∗).