Angewandte
Chemie
DOI: 10.1002/anie.201409834
Mechanochemistry
Direct In Situ Investigation of Milling Reactions Using Combined
X-ray Diffraction and Raman Spectroscopy**
Lisa Batzdorf, Franziska Fischer, Manuel Wilke, Klaus-Jꢀrgen Wenzel, and
Franziska Emmerling*
Abstract: The combination of two analytical methods includ-
ing time-resolved in situ X-ray diffraction (XRD) and Raman
spectroscopy provides a new opportunity for a detailed analysis
of the key mechanisms of milling reactions. To prove the
general applicability of our setup, we investigated the mecha-
nochemical synthesis of four archetypical model compounds,
ranging from 3D frameworks through layered structures to
organic molecular compounds. The reaction mechanism for
each model compound could be elucidated. The results clearly
show the unique advantage of the combination of XRD and
Raman spectroscopy because of the different information
content and dynamic range of both individual methods. The
specific combination allows to study milling processes com-
prehensively on the level of the molecular and crystalline
structures and thus obtaining reliable data for mechanistic
studies.
immediate advantages: 1) an integral information on the
composition of the crystalline material, its transitions, and
crystallite size together with 2) information on the molecular
level of either crystalline, nanocrystalline, amorphous, liquid,
or volatile phases. When studying milling reactions under
realistic conditions, it is even more appropriate to rely on two
methods in order to exclude measurement artifacts. Conse-
quently, the combination of these methods in one experiment
presented here allows to observe simultaneously the complete
formation process on the molecular and crystalline level. The
formation of the MOFs ZIF-8 (1) and (H2Im)[Bi(1,4-bdc)2]
(2), the metal phosphonate CoPhPO3*H2O (3), and the 1:1
cocrystal theophylline:benzoic acid (TP:BA) (4) were ana-
lyzed under realistic milling conditions to examine the
applicability of the setup.
Figure 1a shows the setup including the ball mill, a Per-
spex grinding jar, the Raman probe head, and the optical path
with CCD detector for XRD. The experiments were per-
formed at frequencies between 30 to 50 Hz covering reaction
times of 15 or 30 minutes. Raman spectra and XRD patterns
Over the past decade, mechanochemistry has attracted
significant interest as a fast and effective method for
obtaining pure compounds.[1] The method is a promising
alternative synthesis strategy for inorganic, metal–organic,
and organic compounds.[1a,2] Despite the wide application of
mechanochemistry the mechanisms of milling reactions are
not fully understood. Typically, mechanistic information is
derived from ex situ experiments which include an interrup-
tion of the synthesis for sample drawing.[3] Air-sensitive or fast
converting intermediates and fast phase changes cannot be
detected under these conditions. In addition, products result-
ing from an interrupted synthesis might differ from those
obtained in a continuous synthesis.[1b,4] So far, the inability to
monitor these reactions directly in situ precludes detailed
mechanistic studies.
Pioneering in situ investigations of milling processes using
either Raman spectroscopy or synchrotron X-ray diffraction
have been reported recently.[5] To access complete and
comprehensive information on the reaction mechanisms,
there is a necessity to combine XRD and Raman spectros-
copy in one experiment. This combination has the following
Figure 1. a) Schematic diagram of the experimental setup for collecting
Raman spectra and XRD powder patterns during the mechanochemical
synthesis. Raman spectra and XRD patterns were typically collected
every 30 s. The vibration ball mill is used with 10 mL Perspex grinding
jars and two 10 mm stainless steel grinding balls. During the measure-
ments the grinding jar oscillates around the position of measurement.
b–e) View of the crystal structures of the investigated metal–organic
frameworks ZIF-8 (Zn(MeIm)2 (MeIm=2-methylimidazolate)) 1 and
(H2Im)[Bi(1,4 bdc)2] (Im=imidazole, bdc=benzenedicarboxylate) 2,
the metal phosphonate cobalt(II) phenylphosphonate monohydrate
CoPhPO3*H2O (Ph=phenyl) 3, and the cocrystal theophylline:benzoic
acid (1:1) 4.
[*] M. Sc. L. Batzdorf,[+] Dipl.-Chem. F. Fischer,[+]
Dipl.-Chem. M. Wilke,[+] Dipl.-Ing. K.-J. Wenzel, Dr. F. Emmerling
BAM Federal Institute for Materials Research and Testing
Richard-Willstꢀtter-Str. 11, 12489 Berlin (Germany)
E-mail: franziska.emmerling@bam.de
[+] These authors contributed equally to this work.
[**] We gratefully acknowledge financial support by the DFG through
SPP 1415 (grant number Em198/5-2).
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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