Supramolecular networks of Mn(III)–Schiff base complexes assembled by nitrate counterions: X-ray crystal structures of 1D chains and 2D networks

A series of Mn(III) nitrate complexes have been synthesized from dianionic hexadentate Schiff bases obtained by condensation of 3-methoxy-2-hydroxybenzaldehyde with different diamines. The complexes have been characterised by elemental analysis, ESI mass spectrometry, IR and 1H NMR spectroscopy. Magnetic studies and molar conductivity measurements were also performed. Complexes [MnL1(H2O)2]2·2NO3·2CH3OH (1), [MnL2(H2O)2]2·2NO3·2CH3OH (2) and [MnL5(H2O)2]2·2NO3·6H2O (5) were crystallographically characterised. The X-ray structures show an octahedral geometry around the metal with the Schiff base in the equatorial plane acting as tetradentate and water or methanol molecules in the axial positions. The octahedron entities are linked in pairs by μ-aquo bridges between neighbouring axial water molecules and also by π–π stacking interactions, establishing dimeric and polymeric structures. Nitrate anions are accommodated in the cavities of the framework and form hydrogen bonds with the aqua ligands and the methanol or crystal water, leading to infinite supramolecular aggregates of the complexes. Comparison of chloride, perchlorate and nitrate complexes indicate that the nature of the anions is the key factor directing the structural topologies.

Graphical abstractCounterions with different coordination abilities or modes can play a key role in crystal engineering and reveals that an anion-template effect can take place in the coordination-driven self-assembly.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Anion control of the self-assembly of manganese(III)–Schiff base complexes. ► 1D and 2D supramolecular structures of manganese(III) complexes. ► Study of the magnetic interactions between neighbouring manganese(III) ions. ► Nitrate counterions induce 1D chain of manganese complexes.