Coordination pyramid inversion, angular cluster core and homochiral single-stranded helix formation in polynuclear Mn(II) assemblies supported by bicompartmental salen type ligand based on o-xylylenediamine platform

Abstract

Despite the rich history, salen-type compartmental ligands still attract considerable attention due to the wide potential applications of their complexes. By varying the flexibility of the spacer group, connecting two NO-chelating salicylideneamine moieties, and adjusting the type of anchored additional binding sites or co-ligands used, one can achieve the formation of 3d-metal clusters with the desired nuclearity In this work we report on the synthesis of two new binuclear {Mn ^II ₂ } (1-Mn ₂ Cl ₃ and 1-Mn ₂ Cl ₂ ) and one angular (pseudo-linear) trinuclear {Mn ^II ₃ } (1 ₂ -Mn ₃ Cl ₂ ) clusters, supported exclusively by o-xylylenediamine Schiff base derivative, bearing o-methoxy substituted salicylideneamine units and acting as bicompartmental ligand. The structure of all prepared compounds was established by SCXRD, revealing the role of o-xylylenediamine platform on the diversity of coordination motifs, displayed by studied coordination compounds. For the first time, in the case of {Mn^II₂} clusters, displaying similar coordination motif, it was established that Mn atom, accommodated within the N₂O₂ coordination pocket, can adopt two different orientations of the MnN₂O₂Cl coordination pyramid relative to o-xylylene spacer group. Additionally, the H-bonding, electrostatic and CH/π interactions between anionic 1-Mn ₂ Cl ₃ cluster and NHEt ₃ cation species produces the formation of helices, stacked in homochiral crystal wit polar chiral P4 ₁ space group, which is firstly reported for complexes, based on salen-type ligands. Finally, the formation of trinuclear complex 1 ₂ -Mn ₃ Cl ₂ , exhibiting the unusual angular motif of the cluster core, stabilized by ligand structure and intramolecular CH/π-bonding, is observed.