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Materi PengayaanPolimer Koordinasi

Coordination Polymers; Design, Analysis and Application

Stuart R. Batten, Suzanne M. Neville and David R. Turner

�� Coordination polymers Coordination polymers are infinite repeating are infinite repeating structures of bridging structures of bridging ligandsligands connecting metal ions, connecting metal ions, which may occur as onewhich may occur as one--, two, two--, or three, or three--dimensional networks.dimensional networks.

1D Coordination Polymer

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2D Coordination Polymer

3D Coordination Polymer

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�� The development of coordination polymer research was The development of coordination polymer research was reinforced by the growth of two other closely related reinforced by the growth of two other closely related areas: areas: crystal engineering crystal engineering and and supramolecularsupramolecular chemistry chemistry (particularly (particularly metallosupramolecularmetallosupramolecular chemistry).chemistry).

�� Crystal engineering involves the design and synthesis of Crystal engineering involves the design and synthesis of solidsolid--state structures; state structures; crystal engineering is not the crystal engineering is not the same as crystal structure prediction.same as crystal structure prediction.

�� SupramolecularSupramolecular chemistry is chemistry is the chemistry of the the chemistry of the intermolecular bond, covering the structures and intermolecular bond, covering the structures and functions of the entities formed by the association of functions of the entities formed by the association of two or more chemical species.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 lanthanoidmetals.

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.

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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.S

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Regarding the charge balance of the whole structure, the positively charged metal ions can be balanced by either anionic ligands or non-coordinated 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.

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Synthetic TechniquesSynthetic Techniques

�� coordination polymers are coordination polymers are insoluble insoluble once synthesized (a once synthesized (a property which is advantageous for other aspects) and so property which is advantageous for other aspects) and so rere--crystallization is not an optioncrystallization is not an option..

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).

Properties and ApplicationsProperties and Applications

Ordered solids such as coordination polymers are Ordered solids such as coordination polymers are able to show interesting features such as:able to show interesting features such as:

��Magnetism (longMagnetism (long--range ordering, spinrange ordering, spin--crossover, crossover, conductivity)conductivity)

��Porosity (gas storage, ion and guest exchange), etc. Porosity (gas storage, ion and guest exchange), etc.

��NonNon--linear optical activity, linear optical activity,

��Heterogeneous catalysis, Heterogeneous catalysis,

��Luminescence,Luminescence,

��Reactive networks, Reactive networks, chiralchiral networks, etcnetworks, etc

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Porous materialsPorous materials

A prime example of a porous A prime example of a porous coordination polymer, coordination polymer, developed by developed by YaghiYaghi, et al., is , et al., is [Zn[Zn44O(BDC)O(BDC)33].8DMF.C].8DMF.C66HH55Cl, Cl, known as known as MOFMOF--55, where BDC is , where BDC is 1,41,4--benzenedicarboxylate.benzenedicarboxylate.

This and related materials were This and related materials were reported as having very high reported as having very high methane storage methane storage capacities capacities that are significantly better that are significantly better than than zeoliteszeolites, with pore sizes , with pore sizes up to 28.8Å. up to 28.8Å.