The Effect of Terminal Ligands on the Dimensionality and Topology of Metal Dicarboxylate Coordination Structures
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The Effect of Terminal Ligands on the Dimensionality and Topology of Metal Dicarboxylate Coordination Structures
Long Pan, Nancy Ching, Xiaoying Huang, Jeongyong Lee, Jing Li* Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ 08854 Tan Yuen, C. L. Lin, and Jason Zan Department of Physics, Temple University, Philadelphia, PA 19122
ABSTRACT Solvothermal/hydrothermal reactions of 4,4′-biphenyldicarboxylic acid (H2bpdc) and cobalt (II) salt with pyridine derivative ligands such as 3-methylpyridine (3-pic), 4-methylpyridine (4-pic), as well as a longer terminal ligand 4-benzylpyridine (4-bzpy) generated four new extended structures: 1D zigzag polymer chain 1 crystallized in C2/c with a formula [Co(bpdc)(3-pic)2]·(3pic); 1D helical chain compound 2 crystallized in P41 with a formula [Co(bpdc)(4-pic)2], 2D non-interpenetrating network 3 crystallized in P2221 with a formula [Co(bpdc)(4-pic)2]·(4pic)0.5·H2O, and 2D non-interpenetrating network 4 crystallized in P2/c, formulated as [Co(bpdc)(bzpy)2]. Our studies show that terminal ligands play an important role in affecting the dimensionality and topology of the structures formed. Magnetic susceptibility and isothermal magnetization results revealed an antiferromagnetic ground state for 3 with a transition temperature T = 4.7 K, and paramagnetic behavior at high temperature range for 1 and 2. INTRODUCTION The construction of new types of extended coordination polymers has made important progress since last decade. However, most of the structures reported so far deal with only one type of ligands, either a dicarboxylate acid or an exo- pyridine analogue. There are fewer examples of metals simultaneously bound to both carboxylate groups and exo-bidentate ligands. A promising route to design structures with ligand tenability is to incorporate multiple ligands having various coordination groups. Such structures composed of two or more different ligands will likely undergo a structure transformation when exposed to a suitable solvent containing either a harder or a softer electron donating atom. Applying this strategy, we have previously succeeded in designing and constructing a number of structures with recyclability, for example, »PMs. [1,2] Undoubtedly, incorporation of multidentate dicarboxylate and monodentate (terminal) exoligands to the metal organic coordination structures offers an excellent means for designing and building new extended coordination polymers with structural transformation properties. These structures can be modified systematically by changing their terminal ligands, allowing them to acquire various architectures and topologies. A number of these structures are promising for specific applications. In the sections that follow, we describe the synthesis and structure characterization of four new cobalt containing crystal structures based on this strategy, and discuss their interesting magnetic properties. EXPERIMENT SECTION Chemicals and reagents:
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All chemicals were used as received without further pur
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