Lanthanide Complexation of 2,6-Bis(5,6-dipyridyl-1,2,4-triazinyl)pyridine - Solvent- and Lanthanide-Ion-Controlled Ligand Coordination Mode and Denticity

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2,6-Bis(5,6-dipyridyl-1,2,4-triazinyl)pyridine (PyBTP) is an interesting ligand owing to the possible variation of its coordination sites and denticity in complexation. Therefore, solution and solid-phase lanthanide complexations were studied with PyBTP in two solvents, viz., acetonitrile and methanol, through various spectroscopic and single-crystal X-ray diffraction techniques. The results from all of these studies consistently showed the interesting observation of solvent-dependent changes to the ligand coordination mode and denticity, which are reported for the first time for trivalent lanthanide (Ln3+) complexes. The ligand coordination is affected by the size of the lanthanide ion. This observation can provide clues for the development of intra-lanthanide and lanthanide-actinide separation methods through the exploitation of the variable complexing behaviour of a particular ligand. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.