Polymorphism of the dinuclear CoIII-Schiff base complex [Co2(o-van-en)3]·4CH3CN (o-van-en is a salen-type ligand).

Reactions of Co(OH)2 with the Schiff base bis(2-hydroxy-3-methoxybenzylidene)ethylenediamine, denoted H2(o-van-en), under different conditions yielded the previously reported complex aqua[bis(3-methoxy-2-oxidobenzylidene)ethylenediamine]cobalt(II), [Co(C18H18N2O4)(H2O)], 1, under anaerobic conditions and two polymorphs of [μ-bis(3-methoxy-2-oxidobenzylidene)ethylenediamine]bis{[bis(3-methoxy-2-oxidobenzylidene)ethylenediamine]cobalt(III)} acetonitrile tetrasolvate, [Co2(C18H18N2O4)3]·4CH3CN, i.e. monoclinic 2 and triclinic 3, in the presence of air. Both novel polymorphs were chemically and spectroscopically characterized. Their crystal structures are built up of centrosymmetric dinuclear [Co2(o-van-en)3] complex molecules, in which each CoIII atom is coordinated by one tetradentate dianionic o-van-en ligand in an uncommon bent fashion. The pseudo-octahedral coordination of the CoIII atom is completed by one phenolate O and one amidic N atom of the same arm of the bridging o-van-en ligand. In addition, the asymmetric units of both polymorphs contain two acetonitrile solvent molecules. The polymorphs differ in the packing orders of the dinuclear [Co2(o-van-en)3] complex molecules, i.e. alternating ABABAB in 2 and AAA in 3. In addition, differences in the conformations, the positions of the acetonitrile solvent molecules and the pattern of intermolecular interactions were observed. Hirshfeld surface analysis permits a qualitative inspection of the differences in the intermolecular space in the two polymorphs. A knowledge-based study employing Full Interaction Maps was used to elucidate possible reasons for the polymorphism.