Protonated 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine and its Fe(II) bischelates: Syntheses and molecular structures

Compounds of the molecular formulae, [LH3](NO3)3 (1), [Fe(LH)2](PF6)4·5H2O (2), [Fe(L)2][Fe(L)(LH)](PF6)5·H2O (3), [Fe(L)2][Fe(L)(LH)](BF4)5·2H2O (4) and [Fe(L)2](Cr2O7)·6H2O (5) have been synthesized using 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine (L). The molecular structures of all the compounds were determined. The Fe(II) complexes are high spin in nature at room temperature and upon cooling a gradual spin-transition is observed. Among 1–5, hydrogen-bonding, π···π, and anion···π interactions as well as water tetramer and pentamer are present in the molecular packing.

Graphical abstractThe tri-protonated salt and iron(II) bischelates of L containing di-protonated, mono-protonated as well as non-protonated ligands were synthesized, structurally characterized.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► 4′-(2-Pyridyl)-2,2′:6′,2″-terpyridine was isolated as its tri-protonated salt. ► Iron(II) bischelates of 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine have been synthesized with different counter ions. ► The uncoordinated 4′-(2-pyridyl) moiety in iron(II) bischelate show two levels of protonation.