Studies on the relative stabilities of Mn(II) and Mn(III) in complexes with N4O2 donor environments: crystal structures of [Mn(pybzhz)2] and [Mn(Ophsal)(imzH)2] ClO4 (pybzhz = N-(benzoyl)-N′-(picolinylidene) hydrazine, Ophsal = N,N′-o-phenylenebis(salicyl

Manganese(II) complexes of four aroyl hydrazone ligands were prepared and characterized by different physicochemical techniques. The complexes are of the type Mn(L)2, where L stands for the deprotonated hydrazone ligand. One of the compounds, Mn(pybzhz)2, was also characterized by single crystal structure determination. In all these complexes, the Mn(II) is in an N4O2 donor environment and the Mn(II) center cannot be oxidized either chemically or electrochemically. However, when another ligand Ophsal is used to give the compound [Mn(Ophsal)(imzH)2]ClO4, which was also characterized by X-ray crystal structure determination, manganese can easily avail the +3 oxidation state. The relative stabilities of the +2 and +3 oxidation states of manganese were analyzed and it was concluded that the extent of distortion from the perfect octahedral geometry is the main controlling factor in these cases.