Polymorphism of the dinuclear Co(III)–Schiff base complex [Co(2)(o-van-en)(3)]·4CH(3)CN (o-van-en is a salen-type ligand)

Reactions of Co(OH)(2) with the Schiff base bis­(2-hy­droxy-3-meth­oxy­benzyl­idene)ethyl­enedi­amine, denoted H(2)(o-van-en), under different conditions yielded the previously reported complex aqua­[bis­(3-meth­oxy-2-oxido­benzyl­idene)ethyl­enedi­amine]­cobalt(II), [Co(C(18)H(18)N(2)O(4))(H(2)O)], 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, [Co(2)(C(18)H(18)N(2)O(4))(3)]·4CH(3)CN, 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 [Co(2)(o-van-en)(3)] complex mol­ecules, in which each Co(III) atom is coordinated by one tetra­dentate dianionic o-van-en ligand in an uncommon bent fashion. The pseudo-­octa­hedral coordination of the Co(III) 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 [Co(2)(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.