Ball-milling Mechanochemical Synthesis of Coordination Bonds: Discrete Units, Polymers and Porous Materials - Ball Milling Towards Green Synthesis: Applications, Projects, Challenges - page 169

hydrogen bonding, thus demonstrating a one-pot mechanochemical process
that combines three levels of molecular self-assembly (Figure 7.7b). A more
complex system, involving five distinct reactants, was demonstrated by Chow
et al. who milled magnesium oxide, salicylic acid, 15-crown-5, acetonitrile
and water all at once to obtain an acetonitrile inclusion compound of a
complex salt involving a simple mononuclear metal-organic cation and a
trinuclear metal-organic anion. 75 This one-pot reaction demonstrated how
mechanochemical acid-base neutralization can be coupled to the formation
of coordination bonds, hydrogen bonds and molecular inclusion.
That the mechanochemical syntheses of coordination bonds and covalent
bonds can be combined in a one-pot reaction was first shown by Ferguson
and co-workers, who explored the synthesis of the discrete mononuclear
complex of zinc with the popular bis(salicylidene)ethylenediamine (H 2 salen)
ligand (Figure 7.7c,d). 76 One-pot milling of zinc oxide, salicylaldehyde and
ethylenediamine quantitatively yielded the expected complex in a process
that combined acid-base neutralization with the formation of covalent and
coordination bonds. In addition to this three-component one-pot mechano-
chemical reaction, the same complex could readily be obtained by a con-
secutive (also known as telescopic) two-step reaction strategy in which the
ligand was first mechanochemically synthesized from salicylaldehyde and
ethylenediamine, followed by the addition of zinc oxide and further milling.
The consecutive reaction strategy was also applicable for the preparation of
analogous complexes of nickel( II ) and copper( II ), by replacing zinc oxide in
the second milling step with either nickel( II ) acetate tetrahydrate or copper( II )
acetate monohydrate, respectively. 76 A systematic exploration of multi-
component sequential and one-pot reactions based on mutually orthogonal
chemical reactions was recently described by Hern ´ ndez and co-workers,
who targeted organometallic complexes of rhenium( I ) based on the Re(CO) 3
fragment relevant for catalysis and design of model radiopharmaceuticals. 77
A judicious choice of oxidative addition and ligand exchange reactions
allowed the mechanochemical one-pot synthesis of a complex organo-
metallic fluoride complex from altogether five components, using the metal
carbonyl as the simplest and most readily accessible metal precursor. 77
7.6 Functional Metal-Organic Materials
This section highlights selected examples that illustrate the use of
mechanosynthesis for making functional and, in some cases, commercially
relevant metal-organic materials, specifically microporous MOFs, pharma-
ceuticals and luminescent materials.
7.6.1 Microporous Metal-Organic Frameworks
The possibility of forming a porous materials by mechanochemistry was first
demonstrated 1 in the acid-base reaction of copper( II ) acetate monohydrate
and isonicotinic acid (Hina), which provided the open copper( II )