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coordination complex were noted by Thabet and co-workers in 1972, who
highlighted the rapid (within minutes) complexation of anhydrous cobalt(
II
)
chloride by manual grinding with phosphines, phosphine and arsine oxides,
as well as organic ligands like dimethylglyoxime.
7
Possibly the first report
1
of
a mechanochemical synthesis of a coordination polymer is the transfor-
mation of the pre-synthesized 1D polymer of zinc bromide and pyrazine,
ZnBr
2
(pyrazine), into a 2D square grid framework ZnBr
2
(pyrazine)
2
by
grinding with extra pyrazine.
61
A bridging ligand that is often used for
mechanosyntheses of coordination polymers is bipy. For example, neat
grinding of zinc chloride and bipy readily yields the 2D coordination poly-
mer Zn(bipy)Cl
2
, which, interestingly, adopts only one out of three known
polymorphic forms of the coordination polymer.
47,62
In contrast, the
analogous cobalt-based polymer Co(bipy)Cl
2
was not obtainable by neat
grinding of anhydrous CoCl
2
and bipy. Instead, this polymer could be syn-
thesized either by a ligand exchange reaction of CoCl
2
6H
2
O and bipy,
suggesting that the water produced by desolvation of the reagents plays a
role in mechanochemical reactivity (Figure 7.4a), or by LAG reaction of CoCl
2
and bipy. Another example of a ligand addition leading to a coordination
polymer by grinding was presented by Pichon and James,
43
who utilized neat
grinding of copper(
II
) acetylacetonate or hexafluoroacetylacetonate with bipy
to construct 1D polymers held together by long axial Cu-N bonds
(Figure 7.4b).
Reactions
20
of metal chlorides and cnge have already been noted as il-
lustrations of excellent control of reaction stoichiometry arising from
mechanochemical synthesis. These reactions, however, can also serve to il-
lustrate how the mechanosynthesis of coordination polymers can be
Figure 7.4 Examples of the mechanochemical synthesis of coordination polymers
by ligand addition reactions: (a) illustration of the difference in mechano-
chemical reactivity of bipy towards anhydrous CoCl
2
and CoCl
2
6H
2
O
47
and (b) the synthesis of a 1D coordination polymer from copper(
II
)
acetylacetonate and bipy.
43
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