Antenna- and Metal-Triggered Luminescence in Dense 1,3-Benzodinitrile Metal-Organic Frameworks ∞3[LnCl3(1,3-Ph(CN)2)], Ln = Eu, Tb

Luminescent homoleptic dense 1,3-benzodinitrile MOFs (metalorganic frameworks) of Eu3+ and Tb3+ were prepared from the anhydrous chlorides LnCl(3) (Ln = Eu, Tb) and a melt of the linker ligand 1,3-benzodinitrile [1,3-Ph(CN)(2)=C6H4(CN)(2)]. The 1,3-benzodinitrile ligands act as chemical scissors and cut down the LnCl3 structure to 2D sheets of trigonal Cl ion prisms around the rare earth ions and interlinks these nets to form a 3D framework structure of the formula (3)(infinity)[LnCl(3)(1,3-Ph(CN)(2))]. Both compounds exhibit photoluminescence of the trivalent rare earth ions although they are fully concentrated (100?% luminescence centres), and are the sole examples in which a dinitrile linker is utilized as an antenna for rare earth luminescence subsequent to a transfer of the energy from an excited ligand state to an excited 4f state of the rare earth ion. The antenna effect is most efficient for the terbium-containing framework, whereas the europium spectrum also exhibits metal 4f4f excitation. The emission can be attributed to 4f4f transitions of Eu3+ and Tb3+, which give a red emission for europium (intra 4f(6) (D0 -> F40)-D-5-F-7) and a green emission for terbium (intra 4f(8) (D4 -> F06)-D-5-F-7). For Eu3+ a rather uncommon case was observed, in which the 5D4?7F4 transition shows the highest intensity because of a strong ligand-polarizability- and temperature-dependent dynamic coupling (DC) effect. It is known that luminescence as an intrinsic property of the framework can be triggered in such MOFs by different excitation routes and that both the organic and the inorganic parts are essential for the functionality of these hybrid materials.