Double-stranded helical lanthanide(III) supramolecular networks with rigid diimine ligands: Synthesis, structure, and physical properties

Two lanthanide coordination complexes [Nd(NO3)3(CH3OH)2(4,4′-bipy)2] (1) (4,4′-bipy=4,4′-bipyridine) and [4,4′-Hbipy][La(NO3)4(H2O)2(4,4′-bipy)] (2), with a salt of cationic diprotonated 4,4′-bipy, [2(4,4′-H2bipy)][4(NO3)] (3), have been identified and isolated from a methanol solution of Ln(NO3)3·6H2O, 4,4′-bipyridine and pyrazine in 1:2:1 ratio. Their structures have been determined by single-crystal X-ray diffraction analyses, which reveal that 1 has an interesting three-dimensional supramolecular architecture containing 21 double-stranded helical chains through hydrogen bonding and π–π interactions, while 2 and 3 have well defined infinite chiral 3D open networks that undergo self-interpenetration. The electrospray ionization mass spectra (ESI-MS) indicate that the covalent complex has higher stability than the electrostatic bonding one. ESI-MS/MS of these ions reveal that the Ln–O bond forms a stronger coordinated bonding than that of Ln–N system and the nitrate anion remains bound to the lanthanide centers after complete dissociation in methanol solution.

Graphical abstractTwo lanthanide 3D supramolecular complexes have been identified and isolated from a methanol solution of Ln(NO3)3·6H2O, 4,4′-bipyridine and pyrazine in a 1:2:1 ratio. The structural diversities show that the nature of the products is evidently sensitive to the presence of a trace amount of acid and different radii of Ln3+.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Two novel lanthanide complexes containing 4,4′-bipyridine have been identified. ► Structures were determined by X-ray diffraction, ESI-MS and IR spectra. ► Luminescence and TGA were investigated. ► MS/MS reveal that the Ln−O bond is more stable than the Ln–N one.