Azulene?1?carboxylate - A new azulene-based building block for coordination polymers

Article abstract of DOI:10.1016/j.inoche.2018.11.021

For the first time, the easily accessible azulene?1?carboxylate anion has been employed as building block for the construction of crystalline coordination polymers. Neutralization of azulene?1?carboxylic acid (3) with NaOH in aqueous solution provided the dark purple sodium salt C₁₀H₇CO₂Na·H₂O (4) in 85% isolated yield. Single-crystal X-ray diffraction of 4 revealed a supramolecular layer structure in the crystalline state. Subsequent treatment of 4 with 1 equiv. of Me₃SnCl afforded a rare organotin derivative of azulene, namely polymeric [C₁₀H₇CO₂SnMe₃]_n (5) as purple crystals (82% yield).

Full text of DOI:10.1016/j.inoche.2018.11.021

Inorganic Chemistry Communications 99 (2019) 176–179
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Short communication
Azulene‑1‑carboxylate - A new azulene-based building block for
☆
coordination polymers
⁎
Sascha Danzmann, Phil Liebing, Felix Engelhardt, Liane Hilfert, Frank T. Edelmann
Chemisches Institut der Otto-von-Guericke-Universität Magdeburg, 39106 Magdeburg, Germany
G R A P H I C A L A B S T R A C T
New crystalline coordination polymers have been constructed using for the first time the azulene‑1‑carboxylate anion as building block.
A R T I C L E I N F O
A B S T R A C T
Keywords:
For the first time, the easily accessible azulene‑1‑carboxylate anion has been employed as building block for the
Azulene
construction of crystalline coordination polymers. Neutralization of azulene‑1‑carboxylic acid (3) with NaOH in
Azulene‑1‑carboxylate
Organotin compounds
X-ray structure
aqueous solution provided the dark purple sodium salt C10
H
7
CO
2
Na·H O (4) in 85% isolated yield. Single-crystal
2
X-ray diffraction of 4 revealed a supramolecular layer structure in the crystalline state. Subsequent treatment of
with equiv. of Me SnCl afforded rare organotin derivative of azulene, namely polymeric
CO SnMe (5) as purple crystals (82% yield).
4
1
3
a
Coordination polymer
[
C
10
H
7
2
]
3 n
Azulene (C10
H
8
, 1, cf. Scheme 1) has fascinated chemists for
coordination polymers [12], as well as a number of π-π-bonded
dimers [13–16].
many decades due to its unusual electronic properties as well as its
unique royal-blue color [1,2]. Potential practical applications of
azulene and derivatives thereof include advanced electrochromic
materials [3,4], optoelectronics [5,6], liquid crystal displays [7],
and the manufacture of cosmetics [8]. There are only limited stu-
dies on polymeric or supramolecular assemblies based on azulene.
Prominent examples are e.g. supramolecular complexes of calix[4]
azulenes [9–11], azulene-based spacers in one-dimensional
We report here the first-time use of the readily accessible azule-
ne‑1‑carboxylate anion in the synthesis of crystalline coordination
polymers, including a rare example of an azulene organotin derivative
[17,18]. The synthetic protocol leading to the title compounds is out-
lined in Scheme 1. Treatment of the parent azulene 1 [19] with tri-
fluoroacetic anhydride (TFAA) in dichloromethane solution according
to a published procedure [20] afforded 1‑trifluoroacetylazulene 2 in
☆
Dedicated to Professor Dieter Kaufmann on the occasion of his 70th birthday.
⁎
Corresponding author.
E-mail address: frank.edelmann@ovgu.de (F.T. Edelmann).
https://doi.org/10.1016/j.inoche.2018.11.021
Received 26 October 2018; Accepted 23 November 2018
Available online 24 November 2018
1387-7003/ © 2018 Elsevier B.V. All rights reserved.

S. Danzmann et al.
Inorganic Chemistry Communications 99 (2019) 176–179
Scheme 1. Bottom-up synthesis of the title compounds 4 and 5 (TFAA = trifluoroacetic anhydride) starting from azulene (1) [21,22].
Fig. 1. Single-crystals (a) and asymmetric unit
of 4 in the crystal (b). Displacement ellipsoids
drawn at the 50% probability level, symmetry-
equivalent atoms are semi-transparent. Selected
bond lengths [pm] and angles [°]: Na-O
1
2
57.9(1), Na-O1′ 230.7(1), Na-O
1
″
238.3(1),
Na-O
2
233.4(1), Na-O
-Na-O
-Na-O
″-Na-O
′-Na-O
-Na-O
3
229.3(1),
O
1
-Na-O
′-Na-O
′-Na-O
-Na-O
″-Na-O
1
′
8
1
1
1
1
9.93(4),
O
1
1
″
85.64(4),
53.41(3),
104.18(4),
O
1
1
″
09.63(4),
27.27(4),
48.96(4),
14.80(4), O
O
1
2
O
1
1
2
3
3
O
1
2
3
O
O
1
103.48(4),
O
1
2
3
97.34(4), C11-O
1
127.2(2),
C11-O
2
126.9(2), C1-C11 147.9(2), O
1
-C11-O
2
1
21.6(1).
Fig. 2. a,b. Polymeric ladder structure of 4 in the crystal (a); Association of the ladders to supramolecular layers by C
2
1(4)-type OeH⋯O hydrogen bonds. The
hydrogen-bonded O⋯O distances are 276.3(2) and 283.6(2) pm, and the H⋯O separations are estimated at 182(2) and 192(2) pm.
high yield. Hydrolysis using aqueous NaOH followed by acidification
azulene‑1‑carboxylates were formed, but only in the case of sodium the
provided the starting material azulene‑1‑carboxylic acid (3, also named
reaction product C10
H
7
CO
2
Na could be isolated as a dark purple,
1
‑azuloic acid) as a lavender, microcrystalline solid [20]. Surprisingly,
crystalline hydrate C10
H
7
CO
2
Na·H O (4) in 85% yield [21]. Especially
2
no well-defined simple alkali metal salts have been reported in the
previous literature. We found that such salts are easily accessible by
neutralization of 3 with alkali metal hydroxides (MOH, M = Li–Cs) in
aqueous solutions. In all cases, dark purple solutions of the alkali metal
in the case of M = Rb and Cs, all crystallization attempts led to for-
mation of insoluble decomposition products. Finally, a novel organotin
derivative of 3 could be prepared by treatment of sodium salt 4 with 1
equiv. of trimethyltin chloride in aqueous solution affording a purple
177

S. Danzmann et al.
Inorganic Chemistry Communications 99 (2019) 176–179
both 2 and 3, the molecules are further aggregated to chain-like as-
semblies by π-π-stacking interactions between parallel-oriented azu-
lenyl moieties. The closest C···C separations are 340.8(2) pm (2) and
3
35.1(2) pm (3).
The main goal of the present study was to utilize the azule-
ne‑1‑carboxylate anion as a new building block for crystalline co-
ordination polymers. This was achieved by structurally characterizing
the new compounds 4 and 5 which both exhibit remarkable macro-
molecular structures in the crystalline state. Well-formed, dark purple,
needle-like single-crystals of 4 (cf. Fig. 1a) were grown by slow eva-
poration of an aqueous solution. Fig. 1b depicts the asymmetric unit in
the crystal structure of 4.
The carboxylate moiety adopts a μ -bridging κO,O′:κO:κO co-
3
ordination, and the sodium atom displays an irregular penta-co-
ordination which is completed by one H O ligand. The interconnection
of sodium atoms by azulene‑1‑carboxylate ligands results in a ladder-
like polymeric structure, being composed of edge-shared Na rings
2
O
2 2
(
Fig. 2, a). This arrangement might be supported by π-π-stacking in-
Fig. 3. Asymmetric unit of compound 5 in the crystal. Displacement ellipsoids
teractions between the parallel-arranged azulene backbones. However,
drawn at the 50% probability level, symmetry-equivalent atoms are semi-
the closest C⋯C contact between neighbored azulen‑1‑yl groups is
transparent. Selected bond lengths [pm] and angles [°]: Sn-O
1
218.5(1), Sn-O
-Sn-O
2
2
′
′
3
50.8(2) pm and therefore considerably larger than the values observed
2
1
1
1
32.2(1), Sn-C12 211.4(2), Sn-C13 211.9(2), Sn-C14 211.7(2),
O
1
for 2 and 3. The polymeric ladders in 4 are further interconnected by
72.87(5), C12-Sn-C13 119.81(8), C12-Sn-C14 124.22(9), C13-Sn-C14
15.56(9), Sn-O
1
-C11 128.4(1), Sn″-O
2
2
-C11 142.4(1), C11-O
1
127.3(2), C11-O
2
OeH⋯O hydrogen bonds between H O ligands and one of the car-
2
25.0(2), C1-C11 147.1(2), O
1
-C11-O
122.4(2).
boxylate oxygens (O2), displaying a chain-like pattern which can be
1
described by the graph set C
2
(4) [24]. The result is a supramolecular
layer structure with the azulene backbones situated at the surface
precipitate in 82% isolated yield, which could be identified as poly-
(Fig. 2, b).
meric [C10
H
7
CO
2
SnMe
3
]
n
(5) (cf. Scheme 1).
Purple, needle-like single crystals of the organotin derivative 5 were
obtained by slow cooling a saturated solution in acetone to r.t. Despite
the preparation in aqueous solution, the compound does not contain
coordinated water molecules or water of crystallization. The co-
ordination of the carboxylate group is simpler than in the sodium de-
rivative 4, being a μ-bridging κO:κO′ mode (Fig. 3). The tin atom dis-
plays a typical trigonal-bipyramidal coordination, with two carboxylate
oxygen atoms occupying the axial positions. Consequently, the mole-
cular structure of 5 is a polymeric chain composed of alternating tri-
methyltin and azulene‑1‑carboxylate building blocks (Fig. 4). Supra-
molecular interactions between the chains have not been observed, and
the azulene‑1‑yl groups are not properly oriented for efficient π-π
stacking.
The new compounds 4 and 5 were fully characterized in a
straightforward manner through their IR and NMR spectra as well as
1
13
elemental analyses. The H and C NMR of both compounds were
readily interpretable and in good agreement with the expected for-
mulation. In the IR spectrum of 4, bands attributable to the carbonyl
−1
group were observed at 1576 (νas C]O) and 1537 (ν C]O) cm . The
s
high purity of the organotin derivative 5 was indicated by a single re-
1
19
sonance (δ = 58.2 ppm) in the
Sn NMR spectrum.
The molecular and crystal structures of 2–5 have all been de-
termined by single-crystal X-ray diffraction [23]. Surprisingly, the
crystal structures of the long-known 1‑trifluoroacetylazulene (2) and
azulene‑1‑carboxylic acid (3) had not been determined before. Dark
red, needle-like single-crystals of 2 and 3 were obtained by slow eva-
poration of saturated solutions in acetone. The crystal structure of 2
contains monomeric molecules, while in 3 hydrogen-bonded dimers
In summarizing the results reported here, we successfully estab-
lished the readily accessible azulene‑1‑carboxylate anion as a new
building block for crystalline coordination polymers. The dark-purple
comprising a central eight-membered ring with two OeH⋯O hydrogen
sodium salt C10
H
7
CO
2
Na·H O (4) features a supramolecular layer
2
2
bonds (graph set R
2
(8) [24]) are present (cf. Figs. S2–S7 in the SI). In
structure in the crystalline state, containing polymeric ladders which
Fig. 4. Polymeric chain structure of 5 in the crystalline state (coordination polyhedra around the tin atoms highlighted in purple). (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of this article.)
178

S. Danzmann et al.
Inorganic Chemistry Communications 99 (2019) 176–179
are linked by OeH⋯O hydrogen bonds. Treatment of 4 with 1 equiv. of
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2
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179