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liquid gave a mixture of two compounds with compositions CuI(dpn)
0.5
and
Cu
4
I
4
(dpn)
2
(CH
2
Cl
2
)
0.5
. The crystal structure of luminescent CuI(dpn)
0.5
was established from separately grown single crystals, and revealed the
presence of 1D polymeric (CuI)
N
chains composed of edge-fused planar and
butterfly-shaped Cu
2
I
2
. The detailed structure of Cu
4
I
4
(dpn)
2
(CH
2
Cl
2
)
0.5
is
not known but its redshifted (ca. 575 nm) luminescence is most likely the
result of a Cu
4
I
4
core found in the isostructural Cu
4
I
4
(dpn)
2
obtained by
thermal desolvation of Cu
4
I
4
(dpn)
2
(CH
2
Cl
2
)
0.5
.
95
Consequently, mechano-
chemistry and associated control over reaction stoichiometry could be ap-
plied to explore, with the aid of structural characterization from XRPD data,
the diversity of metal-organic subunits applicable for making fluorescent
materials.
The, so far, only application of mechanochemistry for the synthesis of a
commercially relevant luminescent material was reported by Ma and co-
workers who described the synthesis of the important and archetypal OLED
material (8-hydroxoquinolinate)
3
aluminium (Alq
3
) directly from basic alu-
minium acetate and the organic ligand 8-hydroxyquinoline (Figure 7.11b).
11
Besides being a pioneering (and successful) effort in the solvent-free
manufacture of a commercial OLED material, this work also recognized the
presence of an intermediate phase, characterized via structure solution from
X-ray powder diffraction data, as a previously unknown acetic acid solvate of
Alq
3
, Alq
3
AcOH (Figure 7.11b). Importantly, the solvate Alq
3
AcOH is also
luminescent, demonstrating the ability to discover and characterize novel
potentially functional materials by a combination of mechanosynthesis and
structure determination using X-ray powder diffraction. The authors also
highlighted the ability to manufacture in facile fashion the OLED material
Alq
3
on a scale of at least 50 g and, if high purity of the product is necessary,
perform direct sublimation from the reaction mixture, in that way achieving
an entirely solvent-free access to a technologically important metal-organic
material.
11
7.7 New Properties and Synthetic Opportunities
arising from Mechanochemical Synthesis of
Metal-Organic Materials
7.7.1 Structural Dynamics under Mechanochemical
Conditions
A recently reported effect in MOF chemistry, which might become of con-
siderable importance, is the highly dynamic nature of the frameworks
under conditions of liquid-assisted grinding. For example, grinding of ZnO
and terephthalic acid with water, DMF or methanol yields 1D, 2D or 3D
forms of the zinc terephthalate polymer, respectively (Figure 7.12a).
52,71,95
Different forms were almost completely interconvertible by brief grinding
with a suitable liquid and such fluxional behavior also permitted the
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