Mononuclear lanthanide complexes with tetradentate bis(phosphorylamino)-substituted 1,8-naphthyridine ligand: Synthesis and structural studies

The complexes of 2,7-bis(diphenylphosphorylamino)-1,8-naphthyridine (L) with lanthanide nitrates Ln(NO3)3 (Ln = Nd, Lu) were investigated to elucidate the coordination ability of a novel type of potentially tetradentate ligands – bis(phosphorylamino) substituted naphthyridines. Mononuclear complexes of 1:1 and 1:2 composition, namely, [Nd(L)(NO3)3] (1a), [Nd(L)(NO3)3]·H2O (1b), [Lu(L)(NO3)2(H2O)](NO3) (2), [Nd(L)2(NO3)2(H2O)](NO3) (3), [Lu(L)2(NO3)(H2O)](NO3)2·0.75CH3CN·H2O (4a) and [Lu(L)2(NO3)(H2O)](NO3)2 (4b) were synthesized and studied by IR, Raman, and 31P NMR spectroscopy in solid state and in solution. Structures of the complexes 1b and 4a were determined by X-ray diffraction. According to X-ray crystallography, vibrational spectroscopy and C, H, N, P elemental analysis data in solid 1:1 complexes one neutral molecule of L serves most likely as O,O,N,N-tetradentate ligand while in the 1:2 complexes only one ligand molecule coordinates in the same O,O,N,N-tetradentate fashion, and the second one serves as O-monodentate one. In solution the coordination mode of the ligand is preserved in all complexes.

Graphical abstractNew O,O,N,N-tetradentate phosphoryl-containing ligand based on 1,8-naphthyridine forms 1:1 and 1:2 mononuclear complexes with Ln(NO3)3 (Ln = Nd, Lu). Their structures in solid state and solution were examined by IR, Raman, 31P NMR spectroscopy, and X-ray diffraction. Role of H-bonding in complex structure formation is under discussion.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Lanthanide complexes of new phosphoryl-containing 1,8-naphthyridine were obtained. ► Structures were elucidated by IR, Raman, 31P NMR spectroscopy and X-ray diffraction. ► Solid state and solution structures of complexes were studied. ► H-bonding in free ligand and complex structures is revealed.