Dual-Emission from a Single-Phase Eu–Ag Metal–Organic Framework: An Alternative Way to Get White-Light Phosphor

A new bifunctional NTB (tris­(benzimidazol-2-ylmethyl)­amine)-type ligand incorporating coordination discriminable tripodal benzimidazolyl and monodentate pyridyl groups, tris­((pyridin-3-ylmethyl)­benzoimidazol-2-ylmethyl)­amine (3-TPyMNTB), has been prepared to assemble 4d–4f heterometallic three-dimensional metal–organic frameworks (MOFs) in a stepwise route: (1) direct reaction of 3-TPyMNTB with Ln­(ClO₄)₃ affords monomeric complexes [Eu­(3-TPyMNTB)₂]­(ClO₄)₃·2.5MeCN (<b>1</b>-<b>Eu</b>) and [Gd­(3-TPyMNTB)₂]­(ClO₄)₃·2MeCN·2CHCl₃ (<b>1</b>-<b>Gd</b>), and (2) assembly of the precursors <b>1</b>-<b>Eu</b> and <b>1-</b><b>Gd</b> with AgClO₄ gives rise to infinite MOFs [EuAg₃(3-TPyMNTB)₂(H₂O)­(MeCN)]­(ClO₄)₆·4MeCN (<b>2</b>-<b>Eu</b>-<b>Ag</b>) and [GdAg₃(3-TPyMNTB)₂(H₂O)­(MeCN)]­(ClO₄)₆·4MeCN (<b>2</b>-<b>Gd</b>-<b>Ag</b>), respectively. In monomer <b>1</b>-<b>Eu</b>, the ligand shows an antenna effect to transfer absorbed energy to Eu³⁺ center to emit characteristic red luminescence, while in 4d–4f heterometallic MOF <b>2</b>-<b>Eu</b>-<b>Ag</b>, the ligand centered emission is resensitized by Ag⁺ ions to generate dual emissions, coming up with the direct white-light emission from a single crystal. The detailed photoluminescent study has been carried out in both solid state and solution to elucidate the emission nature