Materi Pengayaan Polimer Koordinasi

Transcription

1 Materi Pengayaan Polimer Koordinasi Coordination Polymers; Design, Analysis and Application Stuart R. Batten, Suzanne M. Neville and David R. Turner Coordination polymers are infinite repeating structures of bridging ligandsconnecting metal ions, which may occur as one-, two-, or three- dimensional networks. 1D Coordination Polymer 1

2 2D Coordination Polymer 3D Coordination Polymer 2

3 The development of coordination polymer research was reinforced by the growth of two other closely related areas: crystal engineering and supramolecularchemistry chemistry (particularly metallosupramolecular chemistry). Crystal engineering involves the design and synthesis of solid-state state structures; crystal engineering is not the same as crystal structure prediction. Supramolecularchemistry chemistry is the chemistry of the intermolecular bond, covering the structures and functions of the entities formed by the association of two or more chemical species. There are several important aspects that should be considered in the construction of coordination polymers. These are: the geometry of the metal ion, the size and shape of the bridging ligands, the charge balance of the whole structure. In general, although it depends on the type of the ligand, transition metals have more predictable coordination geometries than the lanthanoid metals. Geometry of Metal Ions Transition metals demonstrate a large range of accessible properties of both a geometric and electronic nature. It is also often easier to make coordination polymers in a predictable fashion with these metals. In particular, coordination polymers generally focused on the first row transition metals are now common, possibly due to their low cost, abundance and ease of chemistry. There are two reasons for incorporating transition metals into coordination polymers, and both of these ways often apply together in the one material. The first use is as building blocks, to direct a certain framework topology. The other use is for their electronic properties, such as magnetism or redox potential. prananto@ub.ac.id 3

4 Size and Shape of Bridging Ligand As important as the metal ions, the size and shape of the bridging ligand can also affect the size and the geometry of the polymer. The shorter the spacer or ligand used (i.e. cyanide, halides), the smaller the cavities or channels will be, when used alone. However, by combining short spacers with larger ones (i.e. dicyanamide (dca, N(CN)2-), tricyanomethanide (tcm, C(CN)3-), with polypyridine or polyaromatic based ligands), a more open structure is possible. Furthermore, ligands with more complex geometries may generate more complex networks. The geometry of the new structure is frequently a reflection of the geometry of the ligands involved. Charge balance of whole structure Regarding the charge balance of the whole structure, the positively charged metal ions can be balanced by either anionic ligands or noncoordinated anions, such as BF4-, PF6-, etc. which commonly fill the voids in the crystalline lattice. The structure obtained can often be templated by the shapes and the sizes of the anions. Furthermore, the size and shape of the cation can play a significant role in the network, in the use of counter-anions. prananto@ub.ac.id 4

5 Synthetic Techniques Self-assembly is a thermodynamically controlled process with the most stable product forming under the specific conditions that are used. Subtle changes in the reaction conditions, e.g., temperature, pressure, or solvents, can yield vastly different products as is often displayed in the synthesis of aluminosilicate networks (i.e., zeolites). coordination polymers are insoluble once synthesized (a property which is advantageous for other aspects) and so re- crystallization is not an option. Properties and Applications Ordered solids such as coordination polymers are able to show interesting features such as: Magnetism (long-range ordering, spin-crossover, conductivity) Porosity (gas storage, ion and guest exchange), etc. Non-linear optical activity, Heterogeneous catalysis, Luminescence, Reactive networks, chiral networks, etc prananto@ub.ac.id 5

6 Porous materials A prime example of a porous coordination polymer, developed by Yaghi, et al., is [Zn 4 O(BDC) 3 ].8DMF.C 6 H 5 Cl, known as MOF-5, where BDC is 1,4-benzenedicarboxylate. This and related materials were reported as having very high methane storage capacities that are significantly better than zeolites, with pore sizes up to 28.8Å. prananto@ub.ac.id 6