Study on the Structure, Thermodynamic property, and Fluorescence of Pyridin-2-ylmethyl-tert-butylamine Dimethyl aluminum complex

Article abstract of DOI:10.1002/zaac.202000478

Pyridin-2-ylmethyl-tert-butylamine dimethyl aluminum complex with a planar five-membered ring was synthesized and characterized by elemental analysis, UV-Vis spectra, TG/DSC, ¹H NMR, and ¹³C NMR. Through single-crystal diffraction, it is proved that the structure of the alkyl aluminum complex is a planar five-membered ring. By comparison the crystal data of 11 kinds of five-membered ring dialkyl aluminum complexes, we found that the planar five-membered ring dialkyl aluminum is formed when there is at least one unequal sp² hybrid nitrogen in the ligand. TG/DSC study of the compound′s thermodynamic properties showed the thermal decomposition temperature of complex 7 was determined to be 210 °C. The rigid plane structure of the product was proved by fluorescence analysis. When the excitation wavelength was 380 nm, the emission wavelength was 478 nm.

Full text of DOI:10.1002/zaac.202000478

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.202000478
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Study on the Structure, Thermodynamic property, and
Fluorescence of Pyridin-2-ylmethyl-tert-butylamine
Dimethyl aluminum complex
Ruiyuan Liu,[a] Shuyan Yang,[a] and Yuqiang Ding*[a]
Pyridin-2-ylmethyl-tert-butylamine dimethyl aluminum complex
is formed when there is at least one unequal sp2 hybrid
with
a
planar five-membered ring was synthesized and
nitrogen in the ligand. TG/DSC study of the compound’s
thermodynamic properties showed the thermal decomposition
1
characterized by elemental analysis, UV-Vis spectra, TG/DSC, H
NMR, and 13C NMR. Through single-crystal diffraction, it is
proved that the structure of the alkyl aluminum complex is a
planar five-membered ring. By comparison the crystal data of
11 kinds of five-membered ring dialkyl aluminum complexes,
we found that the planar five-membered ring dialkyl aluminum
°
temperature of complex 7 was determined to be 210 C. The
rigid plane structure of the product was proved by fluorescence
analysis. When the excitation wavelength was 380 nm, the
emission wavelength was 478 nm.
Introduction
nitrogen ligand five-membered ring dialkyl aluminum complex
containing β-hydrogen has not been reported.
Bidentate nitrogen ligand complexes have
a
widespread
Pyridin-2-ylmethyl-substituted amine is a ligand similar to
α-aminoaldimine, which is partially replaced by pyridine. This
ligand retains β-hydrogen relative to α-aminoaldimine. The
complexes of nickel, cobalt, and copper with pyridin-2-ylmeth-
yl-substituted amine have been used in ethylene polymer-
ization and optical properties.[11] Bidentate nitrogen ligand five-
membered ring dialkyl aluminum complexes have been exten-
sively studied. However, few studies have been reported on the
alkyl aluminum complexes based on pyridin-2-ylmethyl-substi-
tuted amine. Only two studies have investigated similar
structures, including 5,6,7-trihydroquinolyl and quinolin-8-
amine derivatives.[12] Previous studies did not consider β-hydro-
gen. Therefore, we have prepared the pyridin-2-ylmethyl-tert-
butylamine dimethyl aluminum complex, obtained the crystal
structure, and studied the optical properties and thermodynam-
ics. To study the formation conditions of planar bidentate
nitrogen ligand five-membered ring dialkyl aluminum complex,
we further analyzed the structural characteristics of several
kinds of five-membered ring dialkyl aluminum complexes from
the inner ring angle and intra-ring bond length and the effects
of different N-donor on the configuration of the corresponding
five-membered rings complexes.
application in the fields of catalysis,[1] atomic layer deposition
and chemical vapor deposition precursors,[2,3] and organometal-
lic chemistry.[4] Four-membered rings, five-membered rings, and
six-membered rings are common ring-forming forms of biden-
tate nitrogen ligand complex chelates.[5] The five-membered
ring configuration has a planar configuration and a non-planar
configuration. More and more attention has been paid to the β-
hydrogen elimination of non-planar five-membered ring config-
urations such as pyrrole and indole-functionalized secondary
amines complexes[6] and the redox conversion of planar five-
membered ring α-diimine.[7]
Aluminum is a heavy main group metal.[8] The major metal
complexes can also exhibit transition metal compounds’
properties under specific ligands’ action with the development
of organometallic chemistry.[9] Research on bidentate nitrogen
ligand five-membered ring dialkyl aluminum complexes has
been widely reported in recent years. For example, α-diimine
and 8-Anilide-5,6,7-trihydroquinoline dialkyl aluminum com-
plexes are used as highly active catalysts in the ring-opening
polymerization cyclic esters;[12,19] α-diimine and 2-imino pyridine
dialkyl aluminum are used to study redox ligands.[10] The
properties of planar five-membered ring dialkyl aluminum
complexes are valuable to study. However, a planar bidentate
Results and Discussion
As seen in Scheme 1, the reaction of AlMe3 with one equiv. of
tBuHNCH2 (ο-C6H5N) in hexane at À 30 C afforded dimethyl
[a] R. Liu, S. Yang, Prof. Y. Ding
°
The Key Laboratory of synthetic and biological colloids, Ministry of
Education, School of Chemical and Material Engineering, Jiangnan
University, Wuxi 214122, Jiangsu Province, China
Fax: 86-510-85917763
aluminum complex (Scheme 1) in high yield. Compound 7 was
obtained as solid in good yield and purified through crystal-
°
lization at À 30 C in n-hexane after extraction of ether-removed
residue. Both elemental and NMR spectra of complex 7 were
consistent with the proposed monomeric structure, implying
the formation and purity. When the ligand‘s substituent is
E-mail: yding@jiangnan.edu.cn
Supporting information for this article is available on the WWW
under https://doi.org/10.1002/zaac.202000478
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Table 1. Selected Bond Lengths (Å) and Angles (deg) (Summary
of Data CCDC 1538588).
Al1À N1
1.98
1.838
1.964
1.345
1.448
1.446
0.97
121.30 (11)
84.76 (14)
113.0 (3)
115.9 (3)
115.3 (3)
C6À C5
C4À H4
C1À H1
C1À C2
C7À C8
C7À C9A
1.479
0.929
0.93
1.364
1.551
1.496
Al1À N2
Al1À C10
N1À C5
N2À C6
N2À C7
C6À H6A
N2À Al1À C10
N2À Al1À N2
C5À N1À Al1
C6À N2À Al1
N1À C5À C6
C10À Al1À C10A
C10À Al1À N1
C7À N2À C6
109.30 (2)
107.53 (12)
116.5 (3)
Scheme 1. Synthesis of Pyridin-2-ylmethyl-tert-butylamine and Pyr-
idin-2-ylmethyl-tert-butylamine dimethyl aluminum complex.
N2À C6À C5
111.0 (3)
isopropyl or n-propyl, the oily product is obtained, but it can
not be separated, purified, and characterized. The products with
substituent TMS can be distilled to obtain reliable products
with low melting-point, but after exposure, the products quickly
change from colorless solid to purple oily liquid, and the peak
shape is disorderly detected by nuclear magnetic hydrogen
spectroscopy. It is judged that the Pyridin-2-ylmethyl-substi-
tuted amine dimethyl aluminum complex is sensitive to light,
and only a tert-butyl product is obtained. The crystal data and
crystallographic data of Compound7 are shown in Figure 1,
Table 1 and Table 5. The sum of the inner angles of the five-
°
membered ring C5À C6À N2À Al1À N1 is 540 , which is a plane.
Eleven five-membered ring dialkyl aluminum complexes in
Scheme 2 and Scheme 3are used as the five-membered ring
structure‘s research objects. According to the degree of
saturation in the ring, compounds 1 and 2 are ethylenediamine
derivative dimethyl aluminum, and there is no double bond in
the ring. The ring of the compound (3, 4a–b, 5a–c, 6, 7, and 9a–
c) contains an unsaturated bond, the unsaturated bonds are
introduced by imine, pyridine, pyrrole, benzene ring, and
cyclohexene; α-diimine and 2- iminopyridine are redox ligands.
Radical anionic and derived anionic are redox states of ligands
in compounds (10a, 11a) and compounds (10b, 11b).[20,21]
Scheme 2. Selected five-membered ring dialkyl aluminum com-
plexes (1–9a).
As shown in Table 2, the sum of the inner ring angles of
°
°
compounds 1 and 2 is 517–519 (<540 ), a non-planar
Scheme 3. Selected five-membered ring dialkyl aluminum com-
plexes (9b–11b).
structure. Ethylenediamine derivatives (saturated structure)
react with alkyl aluminum to form non-planar five-membered
ring dialkyl aluminum complexes. The sum of the inner angles
of the ring of the compounds (8, 10a, 10b, 11a, and 11b) is
Figure 1. Molecular structure of Pyridin-2-ylmethyl-tert-butylamine
dimethyl aluminum complex in the crystal.
°
540 , which is a plane structure. Redox ligands (α-diimine and
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Table 2. Selected Bond Angles (deg).
N2À AlÀ N1
AlÀ N2À C2
C1À C2À N2
C2À C1À N1
C1À N1À Al
�
1
2
3
4a
86.77–86.85
87.13
85.62
100.34–100.83
99.52
109.83
111.0
109.75–109.76
110.34
115.98
115.4
107.18–108.40
107.49
115.13
115.8
113.52–114.16
115.24
101.62
~517.5
519.6
528.2
84.2
112.6
539.0
4b
5a–5c
85.9
84.84–85.58
113.3
119.5
114.7
106.0
114.32
112.80
113.50
113.0
115.3
116.99–116.42
111.17
114.99
539.4
~533.0
107.63
103.04
109.90
115.9
109.08
107.38
115.9
111.0
113.1
107.4–108.52
115.73
115.1
115.13
115.21
117.66
115.21
115.4
115.3
113.1
117.4–117.7
116.5
112.4
115.16
111.93
6
7
8
85.18
84.76
83.30
84.01–84.68
85.28
83.64
84.31
83.88
539.9
540.0
540.0
540.0
540.0
540.0
540.0
540.0
115.3
9a–9c
10a
10b
11a
11b
113.6–113.80
110.37
113.86
111.27
111.98
114.01
116.87
2-imino pyridine) react with alkyl aluminum to form planar five-
membered ring dialkyl aluminum complexes. Unlike dialkyl
aluminum complexes with saturated structure and redox
ligands, the sum of compound‘s (3–7 and 9a–c) five-membered
coordination bonds formed by pyridine and imine with
aluminum center can form a planar structure. Imine nitrogen
and pyridine nitrogen are non-isotropic sp2 hybrids, while
pyrrole nitrogen is isotropic sp2 hybridizing. When the
NÀ CÀ CÀ N ligand containing unequal sp2 hybrid nitrogen reacts
with alkyl aluminum, it tends to form a planar five-membered
ring dialkyl aluminum complex. The sum of the combined
NÀ AlÀ N angles and the ring‘s inner angles has a similar rule: the
higher the structure‘s conjugate degree, the sharper the angle.
As shown in Table 3, the NÀ CÀ CÀ N bond length of the
planar five-membered ring (7–11) is shorter than that of the
NÀ CÀ CÀ N of the non-planar five-membered ring (1,2,5a–c).
Because of the introduction of benzene (3, 6) and cyclohexene
(4a, b), the bond length of C1À C2 is considerably shortened
(1.348–1.434 Å), which makes the bond length of NÀ CÀ CÀ N
relatively shorter, so it is not suitable to participate in the
comparison. Because of the NÀ CÀ CÀ N bond length‘s contrac-
tion, under a similar bond length of AlÀ N, the NÀ AlÀ N angle is
sharper than that of the saturated structure. The coordination
bond (AlÀ N2) length (2.003–2.049 Å) of the non-planar five-
membered ring dialkyl aluminum complex (1–3, 4b,5a–c) is
°
interior angles is 528–540 . The presence of unsaturated bonds
in the ring makes the dialkyl aluminum complex closer to
forming a planar five-membered ring. A five-membered ring
dimethyl aluminum complex with an unsaturated bond has
both planar and non-planar results. 1,2-diamino benzenes
dimethyl aluminum (3), imino-amide dialkyl aluminum, and
Mono-anionic pyrrolyl dimethyl aluminum (5a–c) are non-planar
five-membered rings. Quinolin-8-amine derivatives dimethyl
aluminum (6), α-diimine dimethyl aluminum (alkylation product,
9a–c), and pyridin-2-ylmethyl-tert-butylamine dimethyl alumi-
num (7) are planar five-membered rings. Compound 4a, b has a
structure similar to that of the compound 9a–c, has a five-
membered ring close to the plane (the sum of the ring‘s inner
°
angles is 539 ). When the unsaturated bond is opposite to the
center of aluminum (3), it tends to form a non-planar five-
membered ring. When pyrrole nitrogen is bonded with
aluminum, it cannot form a planar structure. However, the
Table 3. Selected Bond Lengths (Å).
Al1À N1
Al1À N2
C1À C2
C1À N1
C2À N2
�
(N1À C1À C2À N2)
1
2
1.865–1.876
1.836
2.016–2.043
2.049
1.519–1.524
1.520
1.465–1.467
1.455
1.489–1.495
1.501
4.473–4.486
4.476
3
4a
1.865
1.897
2.023
1.968
1.411
1.434
1.378
1.344
1.477
1.333
4.266
4.111
4b
5a–5c
6
1.856
1.878–1.888
1.880
2.045
2.003–2.027
1.985
1.348
1.494–1.500
1.418
1.494
1.372–1.382
1.385
1.395
1.499–1.502
1.382
4.237
4.365–4.384
4.185
7
1.838
1.980
1.479
1.448
1.345
4.272
8
1.915
1.839–1.845
1.914
1.874
1.906
1.915
1.984–1.988
1.935
1.956
1.963
1.496
1.502–1.518
1.391
1.485
1.430
1.337
1.286–1.295
1.375
1.381
1.386
1.337
1.467–1.477
1.390
1.295
1.383
4.170
4.255–4.290
4.156
4.161
4.199
9a–9c
10a
10b
11a
11b
1.871
1.988
1.492
1.379
1.360
4.231
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greater than 2.0 Å; the coordination bond (AlÀ N2) length
8.405 Å). The planar five-membered ring is contractible relative
to the non-planar five-membered ring structure.
(1.915–1.988 Å) of the planar five-membered ring dialkyl
aluminum complex (6–11) is less than 2.000 Å. The bond
lengths of the two types of aluminum-nitrogen bonds in the
compound (8, 10a, 11a) are the most similar because the
ligand‘s redox state is radical-anionic. When the compound is
converted from radical-anionic to derived anionic, the bond
length of AlÀ N1 of compound decreases, and the bond length
of AlÀ N2 of compound increases. The bond lengths of the two
aluminum-nitrogen bonds of α-diimine and 2-iminopyridine
derived anionic dialkyl aluminum complex (10b, 11b) are close
to compound 6. The AlÀ N bond length of the compound (7,
9a–c) is similar, and the AlÀ N1 bond length is shorter than that
of the compound (10b, 11b). The sum of intra-ring bond lengths
of planar five-membered rings (<8.1 Å). The sum of intra-ring
bond lengths of non-planar five-membered rings (8.246–
As shown in Table 4, the average AlÀ C length of alkyl
aluminum is between 1.950–1.984 Å. The compound‘s average
AlÀ C bond length (10a, 11a) is longer than the compound (10b,
11b). The change of the state of redox ligand affects the length
of AlÀ C bonds. Under non-redox ligands’ action, the range of
bond length of five-membered ring dialkyl aluminum com-
plexes is small (1.950–1.969 Å). Planar five-membered rings or
non-planar five-membered rings have little influence on the
length of AlÀ C.
It is worth noting that 7 is a planar five-membered ring
dialkyl aluminum complex containing β-H, compared with a
non-planar five-membered ring dialkyl aluminum complexes
(1,2, 5a–c) containing βÀ H. The bond length of CÀ H of 7 is
0.97 Å, while CÀ H of five-membered ring dialkyl aluminum
complexes (1,2, 5a–c) is 0.99 Å.
Ethylenediamine dialkyl aluminum complexes have low
thermal stability, and thermal decomposition ocurs around
Table 4. Selected AlÀ C Lengths (Å).
[3a]
°
150 C, commonly used as the precursor of chemical vapor
AlÀ C
AlÀ C
deposition. A non-planar five-membered ring structure may
lead to thermal decomposition of ethylenediamine dialkyl
aluminum complexes at elevated temperatures. Compared with
ethylenediamine dimethyl aluminum complex, compound 7 is a
planar five-membered ring dimethyl aluminum complex with
βÀ H. If the plane structure has better thermal stability under a
similar structure, it can provide a new idea for chemical vapor
deposition and atomic layer deposition precursors.
1
2
1.966
1.970
7
8
1.964
1.969
1.963–1.969
1.981
1.961
1.984
1.969
3
4a
1.962
1.965
9a–9c
10a
10b
11a
11b
4b
5a–5c
6
1.966
1.950–1.959
1.962
TGA evaluated compound 7 under the Ar atmosphere‘s
°
thermal properties at a heating rate of 10 C/min from 30 to
Table 5. Crystallographic data and refinement details for com-
pound 7.
°
800 C. As shown in Figure 2, it can be noticed that the weight
loss curve is divided into two stages of weight loss curve, and
Compound
7
°
the weight loss rate changes obviously near 210 C, which can
Formula
Mw
Color
Crystal system
Space group
a/Å
C12H21AlN2
220.29
colorless
Monoclinic
P 21/m
7.9104 (15)
7.5465 (14)
12.127 (2)
90
107.824 (4)
90
689.2 (2)
2
1.062
0.122
240
be inferred to be the thermal decomposition point of the
product. After taking out the thermogravimetric crucible, it is
found that the bottom of the crucible has a black metallic
luster, but there is no apparent reaction in hydrochloric acid,
b/Å
c/Å
α/o
β/o
γ/o
V/Å3
Z
Dc/gcmÀ 3
μ/mmÀ 1
F (000)
Crystal size/mm
2θ range/o
Index range
0.36×0.25×0.14
2.327–22.174
À 10%h%10
À 9%k%9
À 15%l %13
6135
No.of reflns
collected No. of indep. reflns. (Rint)
R, wR2 (I>2σ (I))
1715 (0.0497)
0.0653, 0.1870
0.1073, 0.2154
1.061
1715/15/93
0.518, À 0.537
R, wR2 (all data)
Figure 2. Thermogravimetric analysis (TGA) and Differential Scan-
ning Calorimeter (DSC) of Pyridin-2-ylmethyl-tert-butylamine
dimethyl aluminum complex at atmospheric pressure and 60 mL/
Goodness of fit, F 2
Data/restraints/params.
Largest diff. peak, hole/e Å3
min Ar purge gas at a 10 C/min heating rate.
°
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and the decomposition product may be a mixture of carbon,
nitrogen, and aluminum. The structure‘s thermal decomposition
°
temperature is about 210 C, higher than that of ethylenedi-
amine methyl aluminum.[3a]
°
The TG curve‘s inflection point appears at about 210 C, and
similar to the DSC curve, there is also an upward trend of the
DSC curve at this position, corresponding to the exothermic
process of thermal decomposition. It shows that compound 7
°
presents evaporation before 210 C and endothermic decom-
°
position after this 210 C.
Vapor pressure-temperature plot was obtained to under-
stand better TGA analysis‘s thermal properties, which is
according to the Langmuir and Antoine equation‘s theoretical
basis, choosing benzoic acid as a standard.[22] As shown in
Figure 3, compound 7 can provide sufficient vapor pressure
Figure 4. UV-Vis spectra and Fluorescence spectra of Pyridin-2-
ylmethyl-tert-butylamine dimethyl aluminum complex dissolved in
hexane.
°
under below 200 C. From the above thermal studies, it is clear
that compound 7 was appropriate for CVD precursors. Com-
bined with the thermogravimetric curve and saturated vapor
pressure curve, compound 7 can produce enough vapor
°
pressure in the range of 100–200 C, and the thermal decom-
°
position temperature is above 210 C. The volatilization process Conclusions
and thermal decomposition process are carried out separately,
so compound 7 has a potential application prospect in chemical
vapor deposition and atomic layer deposition.
Compared with 11 five-membered ring dimethyl aluminum
complexes with different configurations, the ligands forming
planar five-membered rings contain at least one unequivalent
sp2 hybrid nitrogen (imine, pyridine). Compared with ethyl-
enediamine dimethyl aluminum, the thermal decomposition
temperature of the planar methyl aluminum complex formed
As shown in Figure 4, the maximum absorption wavelength
of compound 7 is 380 nm, and the emission wavelength is
478 nm (Under the emission wavelength of 480 nm, the
maximum excitation wavelength is 374 nm). The ligand has
only one pyridine ring, the ligand does not have fluorescence
properties, and the rigid plane structure formed by coordina-
tion with alkyl aluminum has fluorescence properties. The
complexes’ fluorescence properties also show that the
NÀ CÀ CÀ NÀ Al five-membered rings of alkyl aluminum com-
plexes are in the same plane, consistent with the crystal data.
°
by the introduction of pyridine is increased to 210 C. Pyridin-2-
ylmethyl-tert-butylamine dimethyl aluminum complex can be
used as both atomic layer deposition precursors and chemical
vapor deposition precursors due to the increase of decom-
position
temperature.
Pyridin-2-ylmethyl-tert-butylamine
dimethyl aluminum complex has fluorescence properties (ex-
citation wavelength 380 nm, emission wavelength 478 nm, cyan
light), consistent with the single crystal‘s rigid plane results.
Experimental Section
General Considerations: All reactions were performed under a dry
nitrogen atmosphere using standard Schlenk techniques. Hexane
dried over Na/benzophenone ketyl and distilled before use.
Complexes L1 were synthesized according to the previous
literature. 1H and 13C NMR spectra were recorded on Bruker AVANCE
III HD 400 MHz spectrometer, and the chemical shifts were
internally referenced by the residual solvent signals relative to
°
tetramethylsilane. All NMR spectra have been determined at 25 C.
X-ray data were collected with Bruker D8 Venture. The TG curve
was obtained with an STA 449 F3 analyzer at atmospheric pressure
°
and 60 mL/min Ar purge gas at a 10 C/min heating rate. From 30
°
to 800 C. Photoluminescence spectra were recorded on CARY
Eclipse.
Experimental Details
tBuHNCH2 (ο-C6H5N) (L): tBuHNCH2 (ο-C6H5N) A 30 mL solution of
ethanol that contained 2-pyridine carboxaldehyde (2.40 mL,
25 mmol) and t-butylamine (2.65 mL, 25 mmol) was stirred with the
Figure 3. Vapor pressure-temperature curves for Pyridin-2-ylmethyl-
tert-butylamine dimethyl aluminum complex.
°
presence of 4 Å activated molecular sieves at 20 C for 24 h. Added
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excess NaBH4 (1.00 g, 26 mmol) to the reaction solution. The
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°
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under reduced pressure, the residue was distilled to give a yellow
1
liquid product in 60%. H NMR (400 MHz, CDCl3): 8.51 (d, 1H, Py H),
7.61 (m, 1H, Py H), 7.30 (d, 1H, Py-H), 7.11 (m, 1H, Py H), 3.86 (s, 2H,
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°
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°
a yellow crystal. M.P.: 28.8–34.5 C, Anal. (calcd, %): C 63.4 (63.2), H
10.2 (10.2). N 13.5 (13.5); H NMR (400 MHz, C6D6) δ 7.38 (m, 1H, Py
1
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H), 6.72 (m, 1H, Py H), 6.44 (m, 1H, Py H), 6.27 (m, 1H, Py H), 4.08 (br,
2H, Py-CH2N), 1.39 (s, 9H, NC (CH3)3), À 0.53 (s, 6H, AlMe2); 13C NMR
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Py), 122.6 (s, Py), 52.0 (s,PyÀ CH2N), 51.3 (s, C (CH3)3), 31.3 (s, C
(CH3)3), À 5.8 (s, AlMe2).
Supporting Information:
CCDC 1538588 contains the supplementary crystallographic
data for 7. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (+44) 1223–336-033; or e-mail: deposit@ccdc.-
1
cam.ac.uk. The H NMR, 13C NMR spectra of compound 7, and
crystallographic data are available from the supporting informa-
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Acknowledgments
We thank the financial support from the Postgraduate Research
& Practice Innovation Program of Jiangsu Provence (KYCX18–
1807).
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· methyl aluminum
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complex · structure · thermodynamic properties · planar five-
membered ring
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Manuscript received: December 26, 2020
Revised manuscript received: February 21, 2021
Accepted manuscript online: March 11, 2021
Z. Anorg. Allg. Chem. 2021, 1096–1101
www.zaac.wiley-vch.de 1101
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