Carboxylate Groups in a 90° Arrangement: 1,3-Allenedicarboxylic Acid and Its Alkali Metal and Thallium(I) Coordination Compounds

Article abstract of DOI:10.1002/ejic.201900520

With its two carboxylate functions arranged in an 90° angle, 1,3-allenedicarboxylic acid (point group C₁) possesses a symmetry distinguished from all other dicarboxylic acids which are generally utilized as linker compounds in coordination polymers or MOFs. Crystal structures of coordination compounds with the 1,3-allenedicarboxylate dianion are reported herein for the first time. The diacid was converted with metal carbonates M₂CO₃ to furnish the crystalline lithium, sodium, rubidium, cesium and thallium(I) compounds. In the solid state, their structures differ significantly. Common motif is the dianion, which is linked by the cations to columns, layers or strands. The sodium compound exhibits an unusual structural feature: One of the three crystallographically different sodium ions coordinates to four instead of six oxygen atoms with seesaw geometry, i.e. two equatorial positions of an octahedral coordination are unoccupied. Thus, an almost linear (179°) O-Na-O unit holds two ancillary oxygen atoms with perpendicular geometry (angles 94° and 95°).

Full text of DOI:10.1002/ejic.201900520

A Journal of
Accepted Article
Title: Carboxylate groups in a 90° arrangement: 1,3-Allenedicarboxylic
Acid and its Alkali Metal and Thallium(I) Coordination
Compounds
Authors: Christoph Kahrs, Marc Schmidtmann, Mathias Wickleder, and
Jens Christoffers
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201900520
Link to VoR: http://dx.doi.org/10.1002/ejic.201900520

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
Carboxylate groups in a 90° arrangement: 1,3-Allenedicarboxylic
Acid and its Alkali Metal and Thallium(I) Coordination Compounds
Christoph Kahrs,[a] Marc Schmidtmann,[a] Mathias S. Wickleder,[b] Jens Christoffers*[a]
[a] M.Sc. C. Kahrs, Dr. M. Schmidtmann, Prof. Dr. J. Christoffers, Institut für Chemie,
Carl von Ossietzky Universität Oldenburg, 26111 Oldenburg, Germany. Fax:
+49(0)441 798 3873. Email: jens.christoffers@uol.de. Homepage:
www.christoffers.chemie.uni-oldenburg.de
[b] Prof. Dr. M. S. Wickleder, Department für Chemie, Universität zu Köln, 50939
Köln, Germany
Graphical Abstract
H
O
OM
•
MO
O
H
M = Li, Na, Rb, Cs, Tl
Key Topic: Coordination polymers. With a torsion angle of 90°, the allene
dicarboxylate is a structurally unique dianion; in the crystal structure of its sodium
compound, the cation has unprecedented "seesaw" coordination geometry.
Abstract: With its two carboxylate functions arranged in an 90° angle, 1,3-
allenedicarboxylic acid (point group C1) possesses a symmetry distinguished from all
other dicarboxylic acids which are generally utilized as linker compounds in
coordination polymers or MOFs. Crystal structures of coordination compounds with
the 1,3-allenedicarboxylate dianion are reported herein for the first time. The diacid
was converted with metal carbonates M2CO3 to furnish the crystalline lithium,
sodium, rubidium, cesium and thallium(I) compounds. In the solid state, their
structures differ significantly. Common motif is the dianion, which is linked by the
cations to columns, layers or strands. The sodium compound exhibits an unusual
structural feature: One of the three crystallographically different sodium ions
coordinates to four instead of six oxygen atoms with seesaw geometry, i.e. two
equatorial positions of an octahedral coordination are unoccupied. Thus, an almost
1
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
linear (179°) O-Na-O unit holds two ancillary oxygen atoms with perpendicular
geometry (angles 94° and 95°).
Keywords: Alkali metals, Thallium compounds, Carboxylic acid, Allene, Crystal
structure
Introduction
The majority of metal organic frameworks and coordination polymers utilize aromatic
oligocarboxylic acids as linker moieties.[1] The flexible accessibility of various structu-
ral subtypes with different symmetries, which is based on a rich and well developed
synthetic organic chemistry targeting benzene carboxylic acids, is clearly the key ad-
vantage of this compound class. The use of olefinic carboxylic acids, such as maleic
(1)[2] and fumaric acid (2),[3] is much less precedented in the literature (Figure 1). The
stereoisomeric compounds 1 and 2 are planar and possess both a mirror plane within
their carbon skeleton (point groups C2v and C2h, respectively). In contrast, 1,3-allene-
dicarboxylic acid (3) is, due to the linear, sp-hybridized central carbon atom, not pla-
nar, therefore chiral (point group C1). Both carboxylic groups are arranged in a 90° di-
hedral angle. Interestingly, to the best of our knowledge no crystallographic data of
coordination compounds of diacid 3 have been reported so far. An exception is a
dimolybdenum complex containing additional amidate ligands.[4] We therefore
considered compound 3 as a promising linker unit for coordination polymers.
Actually, we started our investigations with the solid state structures of alkali metal
compounds of diacid 3 including the compound of thallium(I). These compounds
should be useful starting materials for the preparation of coordination polymers or
even metal-organic frameworks. Especially, the Tl(I) compound should be very useful
for metathesis reactions with metal halides. We favor the thallium variant over the
usually used silver(I) compounds because Ag+ is readily reduced in the presence of
unsaturated organic species.
O
OH
O
O
O
OH
OH
•
HO
HO
HO
O
O
1
2
3
Figure 1. Maleic (1) and fumaric acid (2) and 1,3-allenedicarboxylic acid (3).
2
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
Results and Discussion
The literature-known gram-scale preparation of racemic compound 3 required two
synthetic steps and started with dimethyl acetone dicarboxylate (4). Conversion with
PCl5 gave respective vinylchloride first, which was subsequently submitted to ester
hydrolysis with hydrochloric acid to furnish the intermediate product 5 (30%) as a
mixture of (E)- and (Z)-isomers after recrystallization (Scheme 1).[5] Elimination with
soda lye proceeded straightforward to give the diacid 3 after acidification with sulfuric
acid requiring no further purification (93% yield).[6] Aqueous solutions of compound 3
were treated with stoichiometric amounts of respective metal carbonates M2CO3,
upon gas evolution is observed. Evaporation of the resulting mixtures under ambient
conditions over three days gave the respective compounds 6a–6e as colorless
crystalline solids containing single crystals suitable for X-ray structure analysis. With
exception of the cesium compound 6d, the compounds were obtained as hydrates. In
case of K2CO3, the respective compound of diacid 3 could only be obtained as an
amorphous solid.
(a)
Cl
O
MeO2C
CO2Me
HO2C
CO2H
30%
5
4
(b) 93%
(c)
HO2C
•
CO2H
MO2C
•
CO2M
6a (M = Li),
3
6b (M = Na),
6c (M = Rb),
6d (M = Cs),
6e (M = Tl).
Scheme 1. Preparation of 1,3-allenedicarboxylic acid (pentadienedioic acid, "glutinic
acid", 3) and its compounds 6a–6e; reagents and conditions: (a) 1. 1.06 equiv. PCl5,
40°C, 40 min, 2. HCl–H2O, 100°C, 5 h; (b) 3.05 equiv. NaOH–H2O, 23°C, 4 d; (c)
M2CO3, water, 23°C, cryst. over 3 d.
The compounds 6a–6e obtained from the acid 3 are colorless crystalline materials
and have the compositions Li2[C3H2(CO2)2] · 2 H2O (6a), Na2[C3H2(CO2)2] · 3.5 H2O
(6b), Rb2[C3H2(CO2)2] · H2O (6c), Cs2[C3H2(CO2)2] (6d), and Tl2[C3H2(CO2)2] · 0.5
3
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
H2O (6e) (Table 1).[7] All compounds exhibit the allene dicarboxylate dianion
[C3H2(CO2)2]2– (Figure 2). The distances observed in the anion differ only slightly bet-
ween the different compounds (Table 3). The distances C–O are typical for the car-
boxylate moiety, i.e. about 1.25 Å, while the distances between the carbon atoms are
indicative for double bonds C=C (1.31 Å) and single bonds C–C (1.51 Å). According
to the cumulative double bonds the torsion angle C1-C2-C4-C5 of the anion should
have a value of 90°. Even if this is essentially true, the differences of this angle are
significant between the compounds. For the compounds of the alkali metals there
seems to be a dependence on the radius of the cation. Thus, the torsion angle
increases in the row Li, Na, Rb, Cs with values of 86.4° (Li), 93.7° (Na), 99.4° (Rb),
99.0° and 102.1° (Cs). Interestingly, for the Tl compound the torsion angle shows
values of 84.9° and 99.0° within the same crystal structure.
Figure 2. The allene dicarboxylate dianion [C3H2(CO2)2]2–. The distances are given in
Å as found in the crystal structure of Rb2[C3H2(CO2)2] · H2O (6c). The distances are
essentially the same in all investigated compounds.
The crystal structures of the new compounds 6a–6e are quite different. In the non-
centrosymmetric Li2[C3H2(CO2)2] · 2 H2O (space group Cc, compound 6a) the
[C3H2(CO2)2]2– anions and the Li+ cations are arranged into layers (Figure 3). The
cations are in tetrahedral coordination of oxygen atoms with distances Li–O between
1.92 and 2.02 Å (Table 2). The oxygen atoms belong to carboxylate groups of the
anion and to one of the two crystallographically different H2O molecules. Two [LiO4]
tetrahedra are linked via a common edge and the formed [Li2O6] entities are further
connected by a common vertex. The layers are stacked in [010] direction of the unit
cell. The second H2O molecule resides between these layers. One of the two water
molecules, represented by oxygen atom O5, is linked to two neighbouring H2O
molecules (O6). The water molecule involving O6 forms two hydrogen bonds to
oxygen acceptor atoms being part of the allene dicarboxylate anion. With respect to
the donor acceptor distances and the angles D-H···A all hydrogen bonds are
4
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
medium strong hydrogen bonds (Table 4).[8] It is noteworthy to mention that these
hydrogen bonds take care for the connectivity of the above mentioned layers of the
structure.
Figure 3. Layer structure of Li2[C3H2(CO2)2] · 2 H2O (6a). The right part of the figure
shows a view on top of one of the layers (color code: Li red, O blue, C grey). The
oxygen atoms of the H2O molecules are drawn with light blue color, the oxygen
atoms from the anion are dark blue.
The structure of Na2[C3H2(CO2)2] · 3.5 H2O (6b) consists of strands formed by the
linkage of the [C3H2(CO2)2]2– dianions by the sodium ions Na1 and Na2 (Figure 4,
right). These strands are linked by further sodium ions (Na3) to layers which are sta-
cked in the [010] direction of the unit cell. The cations Na2 and Na3 are coordinated
octahedrally by oxygen atoms which originate from carboxylate groups and H2O mo-
lecules, respectively. The distances Na–O for these cations show typical values
around 2.4 Å (Table 2). Interestingly, the coordination of Na1 is very special. This
cation is surrounded by four oxygen atoms with quite short distances of about 2.3 Å.
Two coordination sites (assuming preferred octahedral coordination) of the Na1 ion
remain unoccupied, which results in an almost linear O5-Na1-O5' arrangement and
perpendicular O2-Na1-O5 and O2-Na1-O2' angles (Figure 5). The next nearest
neighbors are the carbon atoms C3 and C4 of the anion with distances Na–C already
above 3.3 Å. Between these carbon atoms of the anion a double bond is formed.
There are no further contacts to oxygen atom below 4.5 Å. To the best of our
knowledge this type of coordination for an alkali metal ion is very unique. The layers
in the crystal structure are held together by hydrogen bonds involving both, the Na-
coordinated water molecules and non-bonded water molecules between the layers.
In compound 6b three of the water molecules (with the oxygen atoms O5, O6, and
5
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
O7) are bonded to Na+ ions. The fourth water molecule (O8) is situated on a special
site (4d) in the crystal structure and not attached to a cation. All of the water
molecules display medium strong to weak hydrogen bonds as can be deduced from
the parameters given in Table 4. The special situation of a bifurcated hydrogen bond
is found for the hydrogen atom H7B. This means that is has two acceptor atoms (O8
and O3) leading to long donor-acceptor-distances and small angles within the bridge.
However, this special situation is well described in literature.[9, 10]
Figure 4. Crystal structure of Na2[C3H2(CO2)2] · 3.5 H2O (6b). The anions are connec-
ted to strands by Na1 and Na2 ions (right). The strands are further linked by Na3 ions
to sheets (left). The coordination of the Na1 ion is unique because the coordination
sphere is completed by carbon atoms at distances of about 3.3 Å (emphasized by
green lines) (color code: Na red, O blue, C grey).
Figure 5. Sodium ion with unusual "seesaw" coordination geometry in the crystal
structure of compound 6b. Distances Na1–O2 2.318(1) Å, Na1–O5 2.304(1) Å,
angles O5-Na1-O5' 176°, O2-Na1-O2' 94°, O2-Na1-O5 95° (color code: Na red, O
blue, H colorless).
In the crystal structure of Rb2[C3H2(CO2)2] · H2O (6c) the dicarboxylate anions and
one half of the Rb+ ions (Rb2) are arranged to layers which extend in the (010) plane
6
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
(Figure 6). These layers are connected by the Rb1 ions to double layers which are
stacked in the [010] direction of the unit cell. The layers are linked by bonds between
the Rb2 ion of one layer and carboxylate oxygen atoms of adjacent layers. The cry-
stallographically different Rb+ ions are in sevenfold (Rb1) and sixfold (Rb2) coordina-
tion of oxygen atoms with typical distances Rb–O between 2.76 and 3.08 Å (Table 2).
The H2O molecule in the crystal structure is bonded via the oxygen atom O5 to the
Rb+ ion. Two medium strong hydrogen bonds are formed by the hydrogen atoms of
the water molecule with O3 atoms as acceptors (Table 4).
Figure 6. Crystal structure of Rb2[C3H2(CO2)2] · H2O (6c). The anions and the Rb2
ions are arranged to layers which are connected further by Rb1 ions to double layers
(color code: Rb red, O blue, C grey).
Cs2[C3H2(CO2)2] (6d) is the only compound in the row that contains no crystal water.
The structure (Figure 7) contains two crystallographically different anions which show
essentially the same bond lengths and angles. The unit cell of the compound shows
a slightly pseudo-hexagonal metric (a ≈ c, β ≈ 120°). The dicarboxylate dianions are
stacked in a hexagonal packing fashion (…ABAB…) and the Cs+ ions are located
between the anion layers. They are coordinated by seven and six oxygen atoms, re-
spectively, and the distances Cs–O are found between 3.07 to 3.31 Å (Table 2). It is
noteworthy to mention that some of the Cs+ ions show a slight disorder over two posi-
tions.
7
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
Figure 7. Crystal structure of Cs2[C3H2(CO2)2] (6d). The anions are stacked in a
…ABAB… fashion (right) in the pseudo-hexagonal unit cell (left) (color code: Cs red,
O blue, C grey).
The most complex structure under investigation is that of Tl2[C3H2(CO2)2] · 0.5 H2O
(6e). The structure contains two crystallographically different dicarboxylate dianions
(Figure 8). They show very similar bond lengths but the torsion angle C1-C2-C4-C5
differs remarkably between the anions. For one ion it is small as 84.9°, while the
other anions display an angle of 99°. In the crystal structure the anions run in co-
lumns along the [010] direction and the four crystallographically different Tl+ ions are
located within and between these columns. The distances Tl–O are strongly influ-
enced by the lone pair of the cation. Thus, there are shorter bonds between 2.5 and
2.9 Å and longer bonds with distances between 3.3 and 3.8 Å (Table 2). If the longer
bonds are taken into account the coordination numbers for the thallium atoms are 6
(Tl1 and Tl4), 9 (Tl2) and 10 (Tl3). In the structure of compound 6e the H2O molecule
(O9) is bridging two thallium cations. The oxygen atom is the donor for two hydrogen
bridges involving oxygen atoms of the anion (O2 and O4) (Table 4).
8
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
Figure 8. Crystal structure of Tl2[C3H2(CO2)2] · 0.5 H2O (6e). The columns of anions
along the [010] direction are emphasized by the blue circle (color code: Tl red, O
blue, C grey). The oxygen atoms of the H2O molecules are drawn with light blue
color, the oxygen atoms from the anion dark blue. The oxygen coordination of the
four Tl+ ions is given separately. Short bonds (<3.0 Å) art drawn as grey lines, long
bonds (>3.3 Å) are shown as broken dark yellow lines.
9
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
Table 1. Crystallographic Data for Li2[C3H2(CO2)2] · 2 H2O (6a), Na2[C3H2(CO2)2] · 3.5 H2O (6b), Rb2[C3H2(CO2)2] · H2O (6c),
Cs2[C3H2(CO2)2] (6d), and Tl2[C3H2(CO2)2] · 0.5 H2O (6e); λ = 0.71073 Å in all cases.
6a
6b
6c
6d
6e
Formula
M / g mol–1
a / Å
C5H6Li2O6
175.98
7.5486(11)
12.657(2)
8.275(1)
105.510(5)
761.9(2)
4
C5H9Na2O7.5
235.10
6.277(2)
18.982(7)
16.252(6)
90
C5H4O5Rb2
315.02
C5H2Cs2O4
391.89
C5H3O4.5Tl2
543.81
10.6262(3)
4.2056(1)
20.3785(6)
104.518(1)
881.63(4)
4
14.6707(6)
8.9344(4)
13.5756(5)
117.574(2)
0.8290(2)
8
23.7834(8)
6.4563(2)
20.9353(7)
105.225(2)
1.5637(5)
16
b / Å
c / Å
β / °
V / Å3
1936(1)
8
Z
space group
T / K
Cc (no. 9)
130
Pnna (no. 52)
130
P21/c (no. 14)
100
P21/c (no. 14)
130
C2/c (no. 15)
100
Dcalc / g cm–3
μ / mm–1
R1 [FO > 2σ(FO)][a]
wR2 [FO > 2σ(FO)][b] 0.0719
R1 (all data)[a]
1.534
1.613
2.373
3.301
4.658
13.7
22.3
110.81
92.05
414.47
0.0290
0.0453
0.1249
0.0590
0.1328
1904689
0.0142
0.0259
0.0202
0.0352
0.0551
0.0456
0.0315
0.0734
1904688
0.0176
0.0259
0.0256
wR2 (all data)[b]
CCDC number[7]
0.0360
0.0561
0.0471
1904690
1904691
1904692
2
2 2 ½
[a] R1 is defined as ∑║Fo│–│Fc║ / ∑│Fo│ for I > 2σ(I); [b] wR2 is defined as {∑w(Fo – Fc2)2 / ∑w(Fo ) } .
10
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
Table 2. Metal-oxygen bond lengths (in Å) compounds in 6a, 6b, 6c, 6d, and 6e.
Compound 6a
Li1–O3
Compound 6d
Cs1–O2
Cs1–O6
Cs1–O4
Cs1–O4
Cs1–O1
Cs1–O2
Cs1–O5
Cs1–O3
Cs2–O3
Cs2–O2
Cs2–O6
Cs2–O8
Cs2–O4
Cs2–O1
Cs2–O2
Cs3–O7
Cs3–O3
Cs3–O5
Cs3–O8
Cs3–O1
Cs3–O7
Cs3–O6
Cs3–O5
Cs4–O4
Cs4–O7
Cs4–O8
Cs4–O5
Cs4–O6
Cs4–O3
Cs4–O7
Compound 6c
Rb1–O1
Rb1–O1
1.918(2)
1.922(2)
1.979(2)
1.990(2)
1.906(2)
1.927(2)
1.986(2)
2.025(2)
3.069(3)
3.161(3)
3.261(3)
3.267(3)
3.267(3)
3.277(3)
3.319(3)
3.495(3)
3.080(3)
3.095(3)
3.126(3)
3.158(3)
3.191(3)
3.191(3)
3.388(3)
3.068(3)
3.096(3)
3.200(3)
3.260(4)
3.312(3)
3.400(3)
3.425(3)
3.444(3)
3.097(3)
3.097(4)
3.121(4)
3.151(3)
3.160(3)
3.225(3)
3.364(4)
Li1–O4
Li1–O1
Li1–O5
Li2–O1
Li2–O2
Li2–O3
Li2–O5
Compound 6b
Na1–O5
Na1–O2
Na2–O5
Na2–O2
Na2–O2
Na3–O4
Na3–O6
Na3–O7
Na3–O4
Na3–O7
Na3–O6
Compound 6e
Tl1–O6
2.304(1) (2x)
2.318(1) (2x)
2.394(1) (2x)
2.436(1) (2x)
2.437(1) (2x)
2.304(1)
2.374(1)
2.381(1)
2.383(1)
2.431(1)
2.533(1)
2.574(2)
2.600(3)
2.608(3)
3.164(4)
2.736(3)
2.800(3)
2.888(2)
2.908(3)
3.037(4)
2.778(3)
2.797(3)
2.835(3)
Tl1–O2
Tl1–O2
Tl1–O9
Tl2–O8
Tl2–O6
Tl2–O7
Tl2–O1
Tl2–O9
Tl3–O8
Tl3–O3
2.7596(6)
2.9145(6)
Tl3–O4
11
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
Tl3–O8
Tl3–O6
Tl3–O5
Tl4–O5
Tl4–O7
Tl4–O5
Tl4–O7
Tl4–O1
2.845(3)
Rb1–O5
Rb1–O3
Rb1–O1
Rb1–O5
Rb1–O2
Rb2–O2
Rb2–O2
Rb2–O4
Rb2–O4
Rb2–O4
Rb2–O5
2.9711(7)
2.903(3)
2.987(2)
2.755(2)
2.801(3)
2.873(2)
2.937(2)
2.946(3)
2.9786(6)
3.0193(7)
3.0268(7)
3.0878(7)
2.8168(6)
2.8189(6)
2.8569(6)
2.9000(6)
2.9218(6)
2.9503(7)
Table 3. Bond lengths (in Å) and the torsion angles for the [C3H2(CO2)2]2– dianions in
Li2[C3H2(CO2)2] · 2 H2O (6a), Na2[C3H2(CO2)2] · 3.5 H2O (6b), Rb2[C3H2(CO2)2] · H2O
(6c), Cs2[C3H2(CO2)2] (6d), and Tl2[C3H2(CO2)2] · 0.5 H2O (6e).
6a
6b
6c
6d
6e
C1–C2
1.506(1)
1.506(2)
1.511(1)
1.501(5)
1.498(5)
1.506(4)
1.502(4)
C2–C3
1.309(2)
1.308(1)
1.502(2)
1.256(1)
1.260(1)
1.259(1)
1.257(1)
86.4°
1.305(2)
1.313(2)
1.501(2)
1.256(2)
1.266(2)
1.265(2)
1.259(2)
93.7°
1.312(1)
1.310(1)
1.509(1)
1.2531(9)
1.2605(9)
1.2636(9)
1.2555(9)
99.4°
1.309(5)
1.329(6)
1.303(5)
1.310(4)
C3–C4
1.311(5)
1.321(6)
1.317(5)
1.310(4)
C4–C5
1.508(5)
1.519(6)
1.499(5)
1.500(4)
C1–O1
C1–O2
C5–O3
C5–O4
C1-C2-C4-C5
1.258(5)
1.262(5)
1.257(4)
1.257(4)
1.265(5)
1.273(5)
1.275(4)
1.262(4)
1.245(5)
1.243(5)
1.253(4)
1.264(4)
1.257(5)
1.256(5)
1.263(4)
1.264(4)
102.1°
99.0°
99.0°
84.9°
12
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
Table 4. Bonding parameters (distances in Å and angles D-H···A) of the hydrogen
bonds in compounds 6a, 6b, 6c, and 6e.
D-H···A[a]
D–H
H···A
D–A
D-H···A
Compound 6a
O5–H5A···O6
O5–H5B···O6
O6–H6A···O2
O6–H6B···O4
Compound 6b
O5–H5A···O1
O5–H5B···O3
O6–H6A···O3
O6–H6B···O4
O7–H7A···O1
O7–H7B···O8
O7–H7B···O3
O8–H8···O3
0.80(3)
0.77(2)
0.77(3)
0.80(3)
1.93(3)
2.11(2)
1.94(3)
1.94(3)
2.725(1)
2.868(1)
2.706(1)
2.728(1)
172(3)
170(2)
171(3)
170(3)
0.87(2)
0.82(3)
0.95(3)
0.83(4)
0.90(3)
0.74(2)
0.74(2)
0.96(2)
1.87(2)
1.96(3)
1.89(3)
2.11(4)
1.76(3)
2.54(1)
2.53(2)
2.11(3)
2.713(2)
2.763(2)
2.811(2)
2.933(2)
2.668(2)
3.218(1)
3.130(1)
2.885(2)
164(2)
169(2)
163(3)
171(3)
178(2)
152(2)
139(2)
137(3)
Compound 6c
O5–H5A···O3
O5–H5B···O3
Compound 6e
O9–H9A···O3
O9–H9B···O4
0.84(2)
0.85(2)
1.99(2)
1.91(2)
2.8048(9)
2.7514(9)
164(2)
170(1)
0.77(7)
0.84(6)
1.95(7)
2.02(6)
2.707(4)
2.827(6)
168(7)
159(5)
[a] D: donor atom; A: acceptor atom.
Conclusion
On the hunt for new coordination polymers we aim at the utilization of novel linker
compounds with unique properties. The application of 1,3-allenedicarboxylic acid (3)
as linker unit is so far unprecedented, although this compound features an outstan-
ding structural property, namely the 90° torsion angle between the two carboxylate
units. Therefore, we have prepared alkali metal (Li, Na, Rb and Cs) as well as the
thallium(I) compounds 6a–6e by converting the respective metal carbonates with
diacid 3 in aqueous solution. The structure of the dianion [C3H2(CO2)2]2– is more or
less the same in all five crystalline materials. However, the crystal structures of the
13
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
compounds differ significantly. In the lithium compound 6a the dianions and the tetra-
hedrally coordinated lithium cations are arranged into layers, while two [LiO4] tetrahe-
dra are linked by a common edge. The sodium compound 6b shows the most signifi-
cant structural feature of this investigation: From three crystallographically indepen-
dent Na ions, Na1 and Na2 form strands with the dianion. These strands were further
connected by the third Na3. The cations Na2 and Na3 are coordinated octahedrally
by oxygen atoms which originate from carboxylate groups and H2O molecules, re-
spectively. Remarkably, the coordination of Na1 is very special. This cation is coordi-
nated by only four oxygen atoms with a "seesaw" arrangement, i.e. two cis-coordi-
nation sites of an octahedron are unoccupied. At these positions the nearest neigh-
bors are carbon atoms with a distance of more than 3.3 Å; no further oxygen atoms
are found closer than 4.5 Å to this Na1 ion. The rubidium and cesium compounds 6c
and 6d also form layered structures, with the cations Rb+ and Cs+ coordinated by six
and seven oxygen atoms. The thallium(I) compound 6e forms the most complex
structure with four crystallographically different cations located within and between
columns of two crystallographically different dianions.
Experimental Section
1
General: H and 13C NMR spectra were recorded on Bruker Avance DRX 500 and
300 instruments. Multiplicities of carbon signals were determined with DEPT experi-
ments. MS and HRMS spectra of products were obtained with a Waters Q-TOF Pre-
mier (ESI, neg. mode) spectrometer. IR spectra were recorded on a Bruker Tensor
27 spectrometer equipped with a diamond ATR unit. Single crystal X-ray data of 6a–
6e were measured on a Bruker AXS diffractometer (Mo-Kα radiation, λ = 0.71073 Å,
Kappa 4-circle goniometer, Apex II CCD detector). For compounds 6a and 6b emπri-
cal absorption corrections using equivalent reflections, and for compounds 6c, 6d
and 6e numerical absorption corrections were performed with the program
SADABS;[12] the structures were solved with the program SHELXS[11] and refined with
SHELXL[13] using the OLEX2[14] GUI. All starting materials were commercially
available.
3-Chloro-2-pentenedioic acid (5).[5] Phosphorus pentachloride (6.33 g, 30.4 mmol)
was slowly added to dimethyl 1,3-acetone dicarboxylate (4) (5.00 g, 28.7 mmol) and
14
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
the resulting solution was heated to 40°C for 40 min. Subsequently, the mixture was
cooled (ice-water bath) and then poured onto ice (20 g) and the resulting mixture was
stirred for another 30 min at 23°C. The aqueous layer was extracted with CH2Cl2 (3 x
50 mL). The combined organic layers were dried (MgSO4) and evaporated after filtra-
tion. The residual red oil was suspended in half-concentrated hydrochloric acid (20
mL) and the mixture was heated to reflux for 5 h. The resulting solution was extracted
with MTBE (3 x 50 mL). The combined organic layers were dried (MgSO4) and eva-
porated after filtration. The crude product was purified by recrystallization from ben-
zene (30 mL) to yield the title compound 5 (1.41 g, 8.57 mmol, 30%) as a colorless
1
solid (mp 129°C, ref.[5] mp 112–115°C). According to H NMR spectroscopy, the
material consists of two stereoisomers (ratio 3:1), however, (E)- and (Z)-configura-
1
tions could not be assigned. H NMR (300 MHz, acetone-d6), major isomer: δ = 3.61
(s, 2 H), 6.39 (s, 1 H) ppm, minor isomer: δ = 4.14 (s, 2 H), 6.30 (s, 1 H) ppm. The
signals of the acidic protons are not observed. The spectroscopic data are in accor-
dance with the literature.[5] C5H5ClO4 (164.54 g/mol).
Pentadienedioic acid (3).[6] Aqueous NaOH (2 mol/L, 13.1 mL, 26.1 mmol) was
added to a solution of chloro compound 5 (1.41 g, 8.57 mmol) in water (5 mL) and
the resulting solution was stirred at 23°C for 4 d. The mixture was acidified with sulfu-
ric acid (2 mol/L, 10 mL). The aqueous layer was extracted with MTBE (6 x 30 mL).
The combined organic layers were dried (MgSO4) and evaporated after filtration to
yield the title compound 3 (1.02 g, 7.99 mmol, 93%) as a colorless solid (dec. 155°C).
1H NMR (500 MHz, acetone-d6): δ = 6.14 (s, 2 H), 9.82 (br s, 2 H) ppm. 13C{1H} NMR
(125 MHz, acetone-d6): δ = 92.25 (2 CH), 164.60 (2 C), 220.80 (C) ppm. IR (ATR):
nu(tilde) = 3029 (w), 2889 (w), 2616 (w), 2516 (w), 1960 (m), 1671 (s), 1259 (vs), 876
–
(s), 826 (s), 688 (s) cm–1. HRMS (ESI, neg. mode): calcd 127.0037 (for C5H3O4 );
found 127.0027 [M – H+]. C5H4O4 (128.08 g/mol).
General procedure (GP): M2CO3 (1.0 equiv.) was added to a solution of 1,3-allene
dicarboxylic acid (3, 1.0 equiv.) in water (13 L/mol). The solution was stirred for 5 min
and transferred into a crystallizing dish. After slow evaporation of the solvent over a
three days under ambient conditions, colorless crystals were obtained.
Lithium 1,3-allenedicarboxylate dihydrate (6a). According to the GP, Li2CO3 (29 mg, 0.39
mmol) and diacid 3 (50 mg, 0.39 mmol) were converted to furnish compound 6a as a
15
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
colorless solid (mp >225°C). IR (ATR): nu(tilde) = 3215 (m), 3096 (m), 1959 (m), 1578 (s),
1368 (s), 830 (s), 735 (s) cm–1. Elemental analysis calcd. (%) for Li2(C5H2O4) ∙ 2 H2O (175.98
g/mol): C 34.13, H 3.44; found: C 34.10 H 3.48.
Sodium 1,3-allenedicarboxylate-3.5-hydrate (6b). According to the GP, Na2CO3 (41 mg,
0.39 mmol) and diacid 3 (50 mg, 0.39 mmol) were converted to furnish compound 6b as a
colorless solid (mp 104–105°C). IR (ATR): nu(tilde) = 3313 (w), 3010 (w), 1955 (m), 1562 (s),
1345 (s), 619 (s) cm–1. Elemental analysis calcd. (%) for Na2(C5H2O4) ∙ 3.5 H2O (235.10
g/mol): C 25.54, H 3.86; found: C 25.40 H 3.63.
Rubidium 1,3-allenedicarboxylate monohydrate (6c). According to the GP, Rb2CO3 (90
mg, 0.39 mmol) and diacid 3 (50 mg, 0.39 mmol) were converted to furnish compound 6c as
a colorless solid (mp >225°C). IR (ATR): nu(tilde) = 3443 (w), 3180 (w), 1945 (m), 1566 (s),
1330 (s) cm–1. Elemental analysis calcd. (%) for Rb2(C5H2O4) ∙ H2O (315.02 g/mol): C 19.06
H 1.28; found: C 19.11 H 1.08.
Cesium 1,3-allenedicarboxylate (6d). According to the GP, Cs2CO3 (127 mg, 0.39 mmol)
and diacid 3 (50 mg, 0.39 mmol) were converted to furnish compound 6d as a colorless solid
(mp >225°C). IR (ATR): nu(tilde) = 3389 (w), 2989 (m), 1936 (m), 1567 (s), 1313 (s), 1225
(s), 921 (s), 849 (s), 716 (s) cm–1. Elemental analysis calcd. (%) for Cs2(C5H2O4) (391.89
g/mol): C 15.32 H 0.51; found: C 15.21 H 0.44.
Thallium(I) 1,3-allenedicarboxylate hemihydrate (6e). Due to the pronounced toxicity of
thallium compounds, the following operation as well as further handling of the product were
performed with appropriate safety precautions. According to the GP, Tl2CO3 (183 mg, 0.39
mmol) and diacid 3 (50 mg, 0.39 mmol) were converted to furnish compound 6e as a
colorless solid (dec 124°C). IR (ATR): nu(tilde) = 3215 (w), 2986 (w), 1935 (m), 1518 (s),
1301 (s), 713 (s) cm–1. Elemental analysis calcd. (%) for Tl2(C5H2O4) ∙ 0.5 H2O (543.81
g/mol): C 11.04 H 0.56; found: C 10.35 H 0.33.
Acknowledgement
Financial support from the Deutsche Forschungsgemeinschaft is gratefully
acknowledged. MTBE was obtained as a generous gift from Evonik Industries, Marl,
Germany.
16
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
[1] Reviews: a) J. D. Evans, B. Garai, H. Reinsch, W. Li, S. Dissegna, V. Bon, I.
Senkovska, R. A. Fischer, S. Kaskel, C. Janiak, N. Stock, D. Volkmer, Coord.
Chem Rev. 2019, 380, 378–418; b) L. Jiao, Y. Wang, H.-L. Jiang, Q. Xu, Adv.
Mater. 2018, 30, 1703663; c) W. Xu, K. B. Thapa, Q. Ju, Z. Fang, W. Huang,
Coord. Chem. Rev. 2018, 373, 199–232; d) W. Lu, Z. Wei, Z.-C. Gu, T.-F. Liu,
J. Park, J. Park, J. Tian, M. Zhang, Q. Zhang, T. Gentle III, M. Bosch, H.-C.
Zhou, Chem. Soc. Rev. 2014, 43, 5561–5593; e) H. Furukawa, K. E. Cordova,
M. O'Keeffe, O. M. Yaghi, Science 2013, 341, 1230444; f) C. Wang, D. Liu, W.
Lin, J. Am. Chem. Soc. 2013, 135, 13222–13234; g) V.-R. Lee, J. Kim, W.-S.
Ahn, Korean J. Chem. Eng. 2013, 30, 1667–1680; h) T. R. Cook, Y.-R. Zheng,
P. J. Stang, Chem. Rev. 2013, 113, 734–777; i) F. A. A. Paz, J. Klinowski, S. M.
F. Vilela, J. P. C. Tome, J. A. S. Cavaleiro, J. Rocha, Chem. Soc. Rev. 2012,
41, 1088–1110.
[2] a) S. Sharma, M. Yawer, M. Kariem, H. N. Sheikh, Monatsh. Chem. 2016, 147,
349–357; b) G. A. Farnum, D. P. Martin, L. K. Sposato, R. M. Supkowski, R. L.
LaDuca, Inorg. Chim. Acta 2010, 363, 250–256; c) F. Bonhomme, T. M. Alam,
A. J. Celestian, D. R. Tallant, T. J. Boyle, B. R. Cherry, R. G. Tissot, M. A.
Rodriguez, J. B. Parise, M. Nyman, Inorg. Chem. 2005, 44, 7394–7402; d) Z.
Shi, L. Zhang, S. Gao, G. Yang, J. Hua, L. Gao, S. Feng, Inorg. Chem. 2000,
39, 1990–1993.
[3] a) F. Ke, C. Peng, T. Zhang, M. Zhang, C. Zhou, H. Cai, J. Zhu, X. Wan, Sci.
Rep. 2018, 8, 939; b) S. Karmakar, J. Dechnik, C. Janiak, S. De, J. Hazard.
Mater. 2016, 303, 10–20; c) E. Alvarez, N. Guillou, C. Martineau, B. Bueken, B.
Van de Voorde, C. Le Guillouzer, P. Fabry, F. Nouar, F. Taulelle, D. de Vos, J.-
S. Chang, K. H. Cho, N. Ramsahye, T. Devic, M. Daturi, G. Maurin, C. Serre,
Angew. Chem. Int. Ed. 2015, 54, 3664–3668; Angew. Chem. 2015, 127, 3735–
3739; d) F. Jeremias, D. Fröhlich, C. Janiak, S. K. Henninger, RSC Adv. 2014,
4, 24073–24082; e) H. Furukawa, F. Gandara, Y.-B. Zhang, J. Jiang, W. L.
Queen, M. R. Hudson, O. M. Yaghi, J. Am. Chem. Soc. 2014, 136, 4369–4381;
f) G. Wißmann, A. Schaate, S. Lilienthal, I. Bremer, A. M. Schneider, P.
Behrens, Micropor. Mesopor. Mater. 2012, 152, 64–70.
[4] a) F. A. Cotton, J. P. Donahue, C. A. Murillo, J. Am. Chem. Soc. 2003, 125,
5436–5450; b) F. A. Cotton, J. P. Donahue, C. A. Murillo, R. Yu, Inorg. Chim.
Acta 2005, 358, 1373–1376.
17
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900520
European Journal of Inorganic Chemistry
[5] K. Afarinkia, M. J. Bearpark, A. Ndibwami, J. Org. Chem. 2003, 68, 7158–7166.
[6] J. M. van der Zanden, Recl. Trav. Chim. Pays-Bas 1935, 54, 289–293.
[7] The crystallographic data for compounds 6a–6e were deposited under CCDC-
1904688 (6a), CCDC-1904689 (6b), CCDC-1904690 (6c), CCDC-1904691 (6d)
and CCDC-1904692 (6e). These data can be obtained free of charge via
www.ccdc.cam.ac.uk, or by emailing data_request@ccdc.cam.ac.uk, or by con-
tacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cam-
bridge CB2 1EZ, UK; fax: +44 1223 336033.
[8] G. A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford University Press,
1997.
[9]
G. Chiari, G. Ferraris, Acta Cryst. 1982, B38, 2331–2341.
[10] H. D. Lutz, Structure and Bonding 1988, 69, 97–125.
[11] L. Krause, R. Herbst-Irmer, G. M. Sheldrick, D. Stalke, J. Appl. Cryst. 2015, 48,
3–10.
[12] G. M. Sheldrick, Acta Cryst. 2008, A64, 112–122.
[13] G. M. Sheldrick, Acta Cryst. 2015, C71, 3–8.
[14] D. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H. Puschmann, J.
Appl. Cryst. 2009, 42, 339–341.
18
This article is protected by copyright. All rights reserved.