Construction of various supramolecules by π-π interactions: Self-assembly of nickel(II) macrocyclic complexes containing pyridine pendant arms with bidentate ligands

The supramolecular compounds, [Ni(C₂₀H₃₂N₈(en)] (ClO₄)₂ · 2 H₂O (1), [Ni(C₂₀H₃₂N₈) (isonicotinate)₂] (2), and [Ni(C₂₀H₃₂N₈)(BQDC)] · 3 H₂O (3), have been constructed by the self-assembly of a nickel(II) macrocyclic complex containing pyridyl pendant rings, [Ni(C₂₀H₃₂N₈)] (ClO₄)₂ · 2 H₂O, with ethylenediamine (hereafter noted en), isonicotinic acid, and potassium 2,2′-biquinoline-4,4′-dicarboxylate, (K₂BQDC · 3 H₂O), respectively, in MeCN/H₂O. The X-ray crystal structure of 1 indicates that one en coordinates a nickel(II) macrocyclic complex to form a folded macrocyclic complex, which ends up with a stacking dimer via C-H···π and offset face-to-face π - π interactions between the pyridine pendant groups. The X-ray crystal structure of 2 indicates that two isonicotinate ions coordinate a nickel(II) macrocyclic complex at the axial positions and the pyridine groups of the coordinated isonicotinates are involved in offset face-to-face π-π interactions, which gives rise to a 1D chain. The 1D chains are linked together via the offset face-to-face π-π interactions between the pyridine groups of the macrocycle to generate a 2D network. The X-ray crystal structure of 3 indicates that each BQDC^2- ion coordinates two nickel(II) macrocyclic complexes and each nickel(II) macrocyclic unit binds two BQDC^2- ions at the axial positions to form a 1D chain. The 1D chains experience the intramolecular hydrogen bonding as well as the interchain offset face-to-face π-π interactions between the pyridyl pendant rings of the macrocycle and the BQDC^2- ions, which gives rise to a 2D sheet, Between the 2D sheets herringbone π-π interactions exist, which results in a 3D framework.