A New Three-dimensional Lanthanide Framework Constructed by Oxalate and 3, 5-pyridinedicarboxylate
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A New Three-dimensional Lanthanide Framework Constructed by Oxalate and 3,5-pyridinedicarboxylate Michael A. Lawandy, Long Pan, Xiaoying Huang and Jing Li* Department of Chemistry, Rutgers University, Camden NJ 08102 Tan Yuen and C. L. Lin Department of Physics, Temple University, Philadelphia, PA 19122 ABSTRACT Hydrothermal reactions of rare-earth metal acetates and nitrates with oxalic acid (H2C2O4) and 3,5-pyridinedicarboxylic acid (H2pddc) in triethylamine/water solutions have yielded five isostructural polymers with the general formula: [Ln(pddc)(C2O4)1/2(H2O)2]⋅H2O. [Ln = La(1), Pr(2), Nd(3), Eu(4) and Er(5)]. These compounds crystallize in monoclinic crystal system, space group P21/n, Z = 4, with only slight variations in their unit cell parameters: 1 a = 7.747(2), b = 9.954(2), c = 15.134(3) Å, β = 98.64(3)o, V = 1153.8(4) Å3; 2 a = 7.707(2), b = 9.895(2), c = 15.006(3) Å, β = 98.54(3)o, V = 1131.7(4) Å3; 3 a = 7.688(2), b = 9.897(2), c = 14.955(3) Å, β = 98.43(3)o, V = 112 5.6(4) Å3; 4 a = 7.638(2) , b = 9.842(2) , c = 14.809(3) Å, β = 98.42(3)o, V = 1101.2(4) Å3; 5 a = 7.573(2) , b = 9.761(2) Å, c = 14.630(3) Å, β = 98.10(3)o, V = 1070.7(4) Å3. The structure of these compounds is composed of 2D Ln(pddc) layers that are interconnected by chelating oxalate. Within the layer, each rare-earth metal forms a monodentate bond with each of the four pddc groups. The metal centers in the neighboring layers are bridged through µ4-oxalate, resulting in a three-dimensional framework. The remaining two sites around the eight-coordinate Ln are occupied by water molecules. Compounds 2, 3, and 5 exhibit paramagnetic behavior and 1 is diamagnetic. They are thermally stable up to 250°C. INTRODUCTION The demand for new materials with practical applications has promoted research in the design and synthesis of functional coordination polymers that possess attractive properties, such as zeolite-like characteristics, catalytic activity, magnetism and non-linear optical behavior [1, 2]. Suitable choices of metals and ligands based on their coordination habits and geometric preferences often produce novel structures with interesting and specific properties. Recently, others and we have investigated a number of systems involving multi-ligands, for example, magnetically active systems containing transition metals and oxalate/4,4'-bipyrdrine [3, 4]. Rare earth metals are attractive as metal centers for construction of magnetically interesting coordination polymers that also exhibit other interesting and advantageous properties, such as high dimensionality, optical activity, and thermal stability. In this study, we report a novel threedimensional framework built upon lanthanide metals and two ligands, oxalate and 3,5pyridinedicarboxylate. EXPERIMENTAL DETAILS Chemicals and Reagents. All chemicals were used as purchased without purification. La(O2CCH3)3⋅1.5H2O (99.9%), Pr(NO3)3⋅6H2O (99.9%), Nd(NO3)3⋅6H2O (99.9%,), Eu(NO3)3⋅6H2O (99.9%), Er(NO3)3⋅xH2O (99.9%), oxalic acid (H2C2O4⋅2H2O, 97%), Et3N GG6.12.1
(99+%) were purchased from Al
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