The series of anhydrous lanthanide chlorides LnCl 3 , Ln ¼ Pr-Tb, and 4,4 0 -bipyridine (bipy) constitute (1-8), 0 # x, y # 0.5. The series of MOFs exhibits the opportunity of tuning the emission colour in-between green and red. Depending on the atomic ratio Gd:Eu:Tb, the yellow region was covered for the first time for an oxygen/carboxylate-free MOF system. In addition to a ligand to metal energy transfer (LMET) from the lowest ligand-centered triplet state of 4,4 0 -bipyridine, a metal to metal energy transfer (MMET) between 4f-levels from Tb 3+ to Eu 3+ is as well vital for the emission colour. However, no involvement of Gd 3+ in energy transfers is observed rendering it a suitable host lattice ion and connectivity centre for diluting the other two rare earth ions in the solid state. The materials retain their luminescence during activation of the MOFs for microporosity.

By solvent free syntheses of the rare earth trichlorides LnCl(3), Ln = Pr, Nd, Sm, Eu, Tb with melts of 4,4'-bipyridine two-dimensional frameworks of the formula (2)(infinity)[Ln(2)Cl(6)(4,4'-bipy)(3)] x 2(4,4'-bipy) are obtained, with 4,4'-bipy = C(10)H(8)N(2), 4,4'-bipyridine. 4,4'-Bipyridine acts both as a linker ligand as well as a template and populates all cavities in the structures. The template can be evaporated at temperatures >200 degrees C giving a new high temperature compound with a yet unknown structure. Further heating results in the release of the remaining linking equivalents of the ligand and reformation of LnCl(3). Thus the reaction can be run in cycles if the evaporated ligand is collected. Luminescence in the visible range without quenching by concentration is observed for the lanthanides Eu and Tb, which is identified for Eu(III) with the transitions (5)D(0)-->(7)F(J) and (5)D(4)-->(7)F(J) for Tb(III). The hybrid character of the material is reflected by the additional strong antenna effect of the ligand: main excitation is observed via the 4,4'-bipyridine linkers followed by an energy transfer to the metal centres. It is remarkable that both the template containing MOFs as well as the new high temperature compounds exhibit luminescence properties.

The three-dimensional frameworks infinity(3)[LnCl3(1,4-Ph(CN)2)] of the lanthanides Ln = Sm (1), Gd (2), Tb (3), and infinity(3)[Ln2Cl6(1,4-Ph(CN)2)] for the group 3 metal Y (4) were obtained as single crystalline materials by the reaction of the anhydrous chlorides of the referring rare earth elements with a melt of 1,4-benzodinitrile. No additional solvents were used for the reactions. The dinitrile ligand is strongly coordinating and substitutes parts of the chlorine coordination. The Ln halide structures are reduced to two-dimensional networks, whereas coordination of both nitrile functions to the metal ions renders bridging in the third direction accessible. This enables formation of new metal organic framework (MOF) structure types with the large 1,4-benzodinitrile spacers interlinking infinity (2)[LnCl3] planes. In comparison to 1,4-Ph(CN)2 the mono functional benzonitrile ligand does not constitute framework structures, which is underlined by comparison with a reaction of yttrium chloride with PhCN resulting in the molecular complex [Y2Cl6(PhCN)6] (5) with end-on coordination PhCN ligands. The coordination spheres of the rare earth ions consist of double capped (infinity(3)[LnCl3(1,4-Ph(CN)2)] (1-3)) as well as single capped trigonal prisms (infinity(3)[Ln2Cl6(1,4-Ph(CN)2)] (4)) of chloride ions and N[triple bond]C groups while 5 displays edge sharing pentagonal bipyramids as coordination polyhedra. Sm (1), Gd (2), and Tb (3) exhibit isotypic framework structures with intercrossing dinitrile ligands. The group 3 metal Y (4) gives a framework with a coplanar arrangement of ligands and a lower ligand content. The largest cavities within the MOF structures of 1-4 have diameters of 3.9-8.0 A. All compounds were identified by single crystal X-ray analysis. Mid IR, Far IR, and Raman spectroscopy, microanalyses and simultaneous Differential Thermal Analysis-Thermogravimetry (DTA/TG) were also carried out to characterize the products. Crystal data for infinity(3)[LnCl3(1,4-Ph(CN)2)] (1-3): Pnma, T = 170(2) K; Sm (1): a = 7.172(1) A, b = 22.209(3) A, c = 6.375(1) A, V = 1015.4(3) A(3), R1 for F(o) > 4sigma(F(o)) = 0.032, wR2 = 0.079. Gd (2): a = 7.116(1) A, b = 22.147(4) A, c = 6.345(1) A, V = 1000.0(3) A(3), R1 for F(o) > 4sigma(F(o)) = 0.033, wR2 = 0.085. Tb (3): a = 7.090(2) A, b = 22.140(4) A, c = 6.325(2) A, V = 992.8(3) A(3), R1 for F(o) > 4sigma(F(o)) = 0.025, wR2 = 0.061. Crystal data for infinity (3)[Y2Cl6(1,4-Ph(CN)2)] (4): P1, T = 170(2) K; a = 6.653(2) A, b = 6.799(2) A, c = 9.484(2) A, V = 397.9(2) A(3), R1 for F(o) > 4sigma(F(o)) = 0.027, wR2 = 0.069. Crystal data for [Y2Cl6(PhCN)6] (5): P2(1)/c, T = 170(2) K; a = 9.767 (2) A, b = 12.304(3) A, c = 19.110(4) A, V = 2294.8(8) A(3), R1 for F(o) > 4sigma(F(o)) = 0.041, wR2 = 0.092.

Keywords: Metal-organic frameworks / Luminescence / Lanthanides / Antenna effect Luminescent homoleptic dense 1,3-benzodinitrile MOFs (metal-organic frameworks) of Eu 3+ and Tb 3+ 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 =C 6 H 4 -(CN) 2 ]. The 1,3-benzodinitrile ligands act as chemical scissors and cut down the LnCl 3 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 ϱ 3 [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 [a]

Construction of the framework structure {}^3_\infty[La2Cl6(bipy)5]·4bipy (1), bipy = 4,4′‐bipyridine, C10H8N2, is achieved by reaction of the anhydrous halide LaCl3 with molten 4,4′‐bipyridine. Five equivalents of bipyridine are used for the framework construction linking LaCl3 units to give an extended, three‐dimensional MOF. Furthermore, four additional equivalents of bipyridine per LaCl3 unit are incorporated within the crystalline MOF, which is thereby completely filled with bipy molecules. This compound formation results in the extraordinary high uptake of nine equivalents of bipyridine per equivalent of the formula and a volume increase of eight times the volume of LaCl3. Further heating of the MOFs results in a stepwise release of all nine equivalents of bipyridine and reformation of the anhydrous chloride at 425 °C. Formation and disassembly can be run in cycles and are reversible. Thus two interesting yet opposing aspects are the reversible construction and disassembly of the MOF framework.