Page 185 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Encyclopedia of Physical Science and Technology en012i-947 July 26, 2001 11:11

Polymers, Inorganic and Organometallic 693

of the metallophthalocyanine dihydroxide. Similar poly-
mers with S, Se, and Te as bridging atoms are known
and are soluble in strong acids. Moreover, they have fa-
vorable dynamic–mechanical properties comparable to
®
polyamides (e.g., Kevlar ). If doped with iodine, shish
kebab polymers exhibit potentially useful magnetic, elec-
tronic and optical behavior.
2. The molecular photonic wire composed of a zinc–
porphyrin chain with a boron dipyrromethane group at one
end and a free base prophyrin at the other end (Fig. 38).
This oligomer is photochromic and absorbs blue-green
light at boron and emits red light at the uncomplexed site.
Such macromolecules have potential as molecular wires
in molecular devices.

A general method of preparing coordination polymers
involves the reaction of the free metal, metal salt, or
FIGURE 37 Metallophthalocyanine (shish kebab) polymers.
metal complex with a polydentate ligand. For example,
the reaction of nickel acetate with bis(1,2-dioxime) gives
a polymer with tetracoordination of the ligand nitrogen
IV. INORGANIC POLYMERS
WITH TRANSITION METALS atoms with nickel (Eq. 29). Metal-containing polymers
with two or more different atoms of the ligand bonded to
the metal are also possible (Eq. 30).
A. Transition Metal Coordination Polymers

There are numerous examples of inorganic polymers with R C CCH 3
transition elements. These polymers have the metal as O N N O
CH 3 C C R C CCH 3
an integral part of or pendant to the polymer backbone. Ni(O 2 CCH 3 ) 2 CH 3 CO 2 H H Ni H
HON NOH HON NOH
Generally the metal is attached to a ligand (L) by one O N N O
or more σ-coordinate covalent bonds (M ← L) through CH 3 C C
heteroatoms such as O, N, P, or S on L. The polymer
arises by connecting metal units through the ligands. (29)
Examples of coordinating ligands are polydentate chelat-
ing compounds such as porphyrins, phthalocyanines,
phosphinates, β-diketones, dioximes, Schiff bases, and HO OH 2HX O O
MX 2 M
crown ethers. Several coordination polymers with differ- :N N: :N N:
ent ligands are shown in Fig. 36.
Two interesting cases are worth noting:
(30)

1. The poly(metallophthalocyanine) (shish kebab) To date, owing to their low solubility, aggregation to
polymers in which M = Si, Ge, Sn, or Ni. These poly- give intractable solids, and difficulty in processing, there
mers are made up of planar phthalocyanine units with are relatively few commercial applications for coordina-
the N atoms tetracoordinated to M. The macrocycles tion polymers. Some materials have found promise as non-
are stacked one dimensionally through metalloxy bonds linear optical materials, electrical conductors, photosensi-
(Fig. 37). The materials are prepared by dehydration tive coatings and films, and bioactive releasing agents. For

FIGURE 38 Zinc-porphyrin (photonic wire) polymer.