Ball-milling Mechanochemical Synthesis of Coordination Bonds: Discrete Units, Polymers and Porous Materials - Ball Milling Towards Green Synthesis: Applications, Projects, Challenges - page 170

isonicotinate MOF Cu(ina) 2 . 45 The porous framework was obtained quanti-
tatively by neat milling, with the byproducts water and acetic acid most likely
included in its pores (Figure 7.8a). The same synthetic strategy was used to
construct the industrially relevant framework HKUST-1 (pore diameter ca.
9 Å) by neat grinding of copper( II ) acetate with trimesic acid. 76 As noted
previously, application of the LAG and ILAG techniques enabled the facile
and rapid, topologically specific transformation of zinc oxide into micro-
porous pillared MOFs based on zinc fumarate or terephthalate sheets. 36,52,53
Mechanochemistry was also applied for the synthesis of ZIFs directly from
a metal oxide. 54 Whereas grinding ZnO with solid imidazole is of very
limited scope for making ZIFs, advanced techniques such as LAG or ILAG
enable rapid and quantitative synthesis of a variety of close-packed and open
ZIFs, including the commercially highly relevant ZIF-8. The grinding liquid
and salt catalysts in ILAG can both enhance the reactivity of ZnO and imi-
dazole ligands, as well as exert control over the final product topology. This
is illustrated in Figure 7.8b in the case of ZIFs based on 2-ethylimidazole,
where different choices of the ionic additive and the grinding liquid enabled
the selective formation of zeolite rho (RHO), analcime (ANA) and b-quartz
(qtz) frameworks. 54 Mechanosynthesis of ZIFs proceeds through a stepwise
mechanism in which the most porous structures are formed first and sub-
sequently transform into close-packed structures via intermediate

Figure 7.8 (a) The first reported mechanochemical synthesis of a porous MOF, by

neat grinding of copper( II ) acetate hydrate with isonicotinic acid
(Hina). 45 Acetic acid and water produced in the reaction become in-
cluded in the open MOF product and can be removed by thermal
treatment. (b) Interconversion of porous and non-porous ZIFs in the
ILAG mechanochemical reaction of ZnO with 2-ethylimidazole. 54