The First Dinitrile Frameworks of the Rare Earth Elements: ∞3[LnCl3(1,4-Ph(CN)2)] and ∞3[Ln2Cl6(1,4-Ph(CN)2)], Ln = Sm, Gd, Tb, Y; Access to Novel Metal-Organic Frameworks by Solvent Free Synthesis in Molten 1,4-Benzodinitrile

The three-dimensional frameworks (3)(infinity)[LnCl(3)(1,4-Ph(CN)(2))] of the lanthanides Ln = Sm (1), Gd (2), Tb (3), and (3)(infinity)(Ln(2)Cl(6)(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 (2)(infinity)[LnCl(3)] 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 ((3)(infinity)[LnCl(3)(1,4-Ph(CN)(2))] (1-3)) as well as single capped trigonal prisms ((3)(infinity)[Ln(2)Cl(6)(1,4-Ph(CN)(2))] (4)) of chloride ions and N 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 (3)(infinity)[LnCl(3)(1,4Ph(CN)(2))] (1-3): Pnma, T = 170(2) K; Sm (1): a = 7.172(1) angstrom, b = 22.209(3) angstrom, c = 6.375(1) angstrom, V = 1015.4(3) angstrom(3), R-1 for F-o > 4 sigma(F-o)) = 0.032, wR(2) = 0.079. Gd (2): a = 7.116(1) angstrom, b = 22.147(4) angstrom, c = 6.345(1) angstrom, V = 1000.0(3) angstrom(3), R-1 for F-o > 4 sigma(F-o) = 0.033, wR(2) = 0.085. Tb (3): a = 7.090(2) angstrom, b = 22.140(4) angstrom, c = 6.325(2) angstrom, V = 992.8(3) angstrom(3), R-1 for F-o > 4a(F-o) = 0.025, wR(2) = 0.061. Crystal data for (3)(infinity)[Y2Cl6(1,4-Ph(CN)(2))] (4): P (1) over bar, T = 170(2) K; a = 6.653(2) angstrom, b = 6.799(2) angstrom, c = 9.484(2) angstrom, V = 397.9(2) angstrom(3), R-1 for F-o > 4 (F-o) = 0.027, wR(2) = 0.069. Crystal data for [Y2Cl6(PhCN)(6)] (5): P2(1)/c, T = 170(2) K; a = 9.767 (2) angstrom, b = 12.304(3) angstrom, c 19.110(4) angstrom, V = 2294.8(8) angstrom(3), R-1 for F-o > 4 sigma(F-o) = 0.041, wR(2) = 0.092.