50 Years of Chemistry in Opole
Crystalline structures of salts of oxalic acid and
aliphatic amines
Błażej DZIUK, Krzysztof EJSMONT*, Jacek ZALESKI – Faculty of Chemistry, Opole University,
Opole, Poland
Please cite as: CHEMIK 2014, 68, 4, 391–395
Introduction
Oxalic acid is the first representative of aliphatic dicarboxylic
acids in homologous series. It is well soluble in water, from which
it crystallizes forming dihydrate crystals. Due to its reactivity and its
ability to form crystals, excessive concentration of oxalic acid in the
organism might be a reason of microelements deficiency and may
result in nephrolithiasis.
Designing new materials of set structure and properties is currently
a very important research area in material engineering. It is based on
i.a. potential ability to form hydrogen bonds between molecules/ions
forming the crystal [1].
Carboxylic acid molecules, both in protonated and anionic form
might interact in crystals via strong hydrogen bonds, generating dimeric
forms, or as in case of dicarboxylic acids – linear chains. Hydrogen bonds
in such systems are classified as strong, therefore carboxylic acids are
often used as “building blocks” in construction supramolecular crystal
networks based on hydrogen bonds [2].
(Fig. 2c, monoclinic system, space group P21/n) strong hydrogen
bonds O-H...O are also present between mononegative oxalic
anions forming in this manner flat chain parallel to the Y direction
of crystalline network. The hydrogen bonds O-H...O, N-H...O and
C-H...O between ethyldimethylammonium cations, water molecules
and mononegative oxalic anions form in the crystals channels of
dimensions 5.073(5) and 3.267(4)Å, parallel to Y axis[11].
(a) Description
Oxalic acid molecule, as well as its anionic forms, has four oxygen
atoms/ions that are at the same time potential donors and acceptors of
strong hydrogen bonds. Therefore, it is ideal component for designing
crystalline networks stabilized with strong hydrogen bonds.
In this area of material engineering also aromatic multi carboxylic
acids are used. And so, for instance, pyromellitic acid having four
carboxylic groups have potential ability to create both two- and threedimensional hydrogen bond networks in crystals [3].
The crystalline networks of carboxylic acids and amine salts
additionally contains hydrogen bonds, where nitrogen atom might
play role of both, donor and acceptor. The crystals of such salts were
subject of many studies using among other X-ray diffractometry.
This studies have shown that mononegative oxalic anions may occur
in crystals as isolated ions or form both flat and twisted chains.
Additionally mononegative ions might form cyclic eight-member
dimers [4÷6]. Binegative oxalic anions might also exist in isolated
form forming linear flat chains and linear chains containing anions
arranged perpendicularly to each other (Fig.1) [7, 8].
The example of crystalline network where isolated binegative
oxalic anion is present may be structure of salt formed with tertbutylamine. In monoclinic crystals (space group C2/m) of this compound
each oxalic acid anion is surrounded by two tert-butyloammonium
cations, forming strong hydrogen bonds of type N–H...O (Fig. 2a) [9].
Crystalline structure of ethylammonium oxalate (Fig. 2b, moncolinic
system, group C2/c) contains ethylammonium cations, mononegative
oxalic anions and water molecules Strong hydrogen bonds
O-H...O between mononegative oxalic anions cause formation
of chain parallel to Y axis of crystal network. The hydrogen bonds
O-H...O and N-H...O between ethylammonium cations, water
molecules and mononegative oxalic anions form in the crystals
channels of dimensions 7.1909(6) and 3.078(4)Å, parallel to Y
axis[10]. In the crystalline structure of ethyldimethylammonium oxalate
Corresponding author:
Krzysztof EJSMONT– Sc.D., e-mail: [email protected]
394 •
(b)
(c) (d)
(e)
(f)
Fig 1. Various motives of oxalic anions present in crystals of amine
salts: (a) single anion; (b) linear flat chain of monoanions; (c) anion
cyclic dimers; (d) mixed; flat chain of mononegative anions; (e) chain
of mononegative ions twisted in relation to each other; (f) chain of
binegative anions arranged perpendicularly to each other.
(a) (b)
(c) (d)
Fig. 2. Arrangement of molecules in oxalate crystals
(a) tert-butylammonium [9]; (b) ethylammonium [10];
c) ethyledimethylammonium [11]; (d) diehtylammonium [12]
nr 4/2014 • tom 68
Table 1
Geometrical characteristics of hydrogen bonds of type O–H...O for
different arrangements of anions in crystals – experimental and
calculated using quantum- mechanical methods
O–H [Å] H…O [Å] O…O [Å] O–H…O [°] References
Motif type
Cyclic dimer
(Fig. 1c)
Linear, flat chain
of monoanions
(Fig. 1b)
Crystal
0.820
1.875
2.618
149.98
[5]
MP2
0.983
2.059
2.880
139.67
Crystal
0.963
1.605
2.563
172.40
[5]
Average
of CSD
database
0.906
1.652
2.552
173.13
[16]
MP2
1.207
1.207
2.414
180.00
Mixed, flat chain of
mononegative anions
(Fig. 1d)
Crystal
0.896
1.623
2.514
171.81
[6]
Chain of mononegative anions twisted
in relation to each
other (Fig. 1e)
Crystal
0.900
1.690
2.588
176.60
[8]
Chain of binegative
anions arranged
perpendicularly to
each other
(Fig. 1f)
Crystal
0.850
2.200
2.919
143.00
[7]
Additionally for linear flat chain of monoanions, that occurs most
often in crystals of oxalic acid and aliphatic amines, average values of
geometrical characteristics O–H..O were calculated, based on data
from database Cambridge Structural Database (CSD) [16]. Quantum
mechanical calculations have shown that among five structural motives
formed in solid by isolated oxalic anions only two can exist: cyclic dimer
and linear flat monoanion chain. Based on geometrical data presented
in Table 1 one might conclude that the distance between anions forming
isolated dimer is a little longer than for crystal. For isolated linear flat
chains of monoanions the hydrogen bond O–H...O connecting anions
becomes linear and hydrogen atom becomes placed exactly in the
middle between donor and acceptor.
The CSD database [16] has almost 70 structures of salts of oxalic
acid with aliphatic amines. In such structures isolated binegative
oxalic anion occurs most often (approx. 35%), while slightly smaller
amount (approx. 30%) might be found in linear chains formed from
mononegative anions. Other anions form much smaller part – isolated
mononegative anions (approx. 15%) and linear chains of binegative
anions (approx. 5%). The anions in form of dimers and mixed linear
chains are the smallest group from groups found in CSD.
Summary
The crystalline structures of salts of oxalic acid and aliphatic amines
present rich variety of arrangements and packing of ions present in
the network. Mononegative anions might form cyclic dimers or
nr 4/2014 • tom 68
arrange in linear chains of nature resembling stepwise structure, as
well as mixed chains. For binegative anions one can distinguish linear
flat chains and linear chains containing anions arranged parallel to each
other. Additionally, both types of anions might be isolated. In such
crystals many types of strong hydrogen bonds occur, mainly of types
O–H…O and N–H...O.
Acknowledgements
The Authors would like to thanks the Wroclaw Centre for Networking and
Supercomputing allowing them to perform quantum mechanical calculations.
Literature
1. Desiraju R., Acc. Chem. Res. 2002, 35, 565–573.
2. Rodrigez-Caumatzi P., Arillo-Flores O.I., Bernal-Uruchutru M.I., Höpfl H.:
Cryst. Grow. Des. 2005, 5, 167–175.
3. Ejsmont, K., Zaleski, J.: Acta. Cryst. 2006, E62, o2672-o2674.
4. MacDonald J.C., Doeewstein C.P., Pilley M.M.: Cryst. Grow. Des., 2001,
1, 29–38.
5. Vaidhyanathan R., Natarajan S., Rao C.N.R.: J. Mol. Struct. 2002, 608, 123–133.
6. Ali A.J., Athimoolam S., Bahadur S.A: Acta. Cryst. 2012, E68, o416.
7. Braga D., Chelazzi L., Ciabatti I., Grepioni F.: New J. Chem. 2013, 37, 97–104.
8. Larsen I.K., Acta. Cryst. 1985, C41, 749-752.
9. Ejsmont K., Zaleski J.: Acta. Cryst. 2006, E62, o2512–2513.
10. Ejsmont K., Zaleski J.: Acta. Cryst. 2006, E62, o3879-o3880.
11. Ejsmont K.: Acta. Cryst. 2006, E62, o5852-o5854.
12. Ejsmont K.: Acta. Cryst. 2007, E63, o107-o109.
13. Vaidhyanathan R., Natarajan S., Rao C.N.R.: J. Chem. Soc., Dalton Trans.
2001, 699–706.
14. Gaussian 09, Revision D.01, Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.;
Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.;
Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian,
H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara,
M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda,
Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.;
Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov,
V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J.
C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.;
Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski,
J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador,
P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.; Foresman, J. B.;
Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian, Inc., Wallingford CT, 2009.
15. Møller C., Plesset M.: Phys. Rev. 1934, 46, 618–622.
16. Allen F. H.: Acta. Cryst. 2002, 10, 380–388.
Błażej DZIUK, is a student of 2nd year of second degree studies of the
Faculty of Chemistry of the Opole University (field of studies: Biological
Chemistry). Scientific interests: supramolecular chemistry, crystal networks of
salts of multi carboxylic acids with aliphatic amines.
* Krzysztof EJSMONT – Sc.D., is a graduate of the Faculty of Physics,
Mathematics and Chemistry of the State Higher Pedagogical College (1992).
He obtained his Ph.D. degree from the Institute of Low Temperature and
Structure Research, Polish Academy of Science in Wroclaw (1999). After
obtaining a doctorate, he earned habilitation at the Faculty of Chemistry of the
University of Lodz (2013). Currently he works at the Faculty of Chemistry, Opole
University. Scientific interests: structural chemistry, π-electron delocalization
and aromaticity of cyclic systems. He is the author of 61 articles in journals from
ISI Master Journal List.
e-mail: [email protected]; phone: +48 77 452 71 06
Professor Jacek Zaleski – (Ph.D. Eng.) was a graduate of the Faculty of
Chemistry of the Wroclaw University of Technology (1987). He obtained
Ph.D. degree in 1990 and habilitation in 1996 from the Faculty of Chemistry
of the University of Wroclaw. The title of full professor was conferred on
him in 2002. Scientific interests: studies of structures and phase transitions of
halogeno-antimoniates (III) and bismuthates (III); design and analysis of crystalline
networks of multi carboxylic acids and amines based on hydrogen bonds, analysis
of electron density distribution of organic and inorganic derivatives. He died on
27 December 2008.
• 395
50 Years of Chemistry in Opole
In the crystal of diethylammonium oxalate linear chains are also
present – they connect mononegative oxalic anions via hydrogen
bonds of type O-H...O (Fig. 2d, monoclinic system, group P2/c). Due
to the small distance of O...O equal to 2.452(1)Å the hydrogen atom
in this interaction is placed equidistantly from donor and acceptor.
Perpendicular to these chains are diethylammonium cations arranged
in chains forming strong three-center hydrogen bonds N-H...O [12].
Two mononegative oxalic anions might form mentioned earlier eightmember cyclic rings (Fig.1c). In this structure next to two strong
hydrogen bonds of type O-H...O forming dimer, are also hydrogen
bonds of type N-H...O formed between dimer and amine [13].
Table 1 shows geometrical characteristics of hydrogen bonds of
type O-H...O present in different motives formed by the oxalic anions in
crystals. These data is compared with geometrical data obtained using
quantum mechanical calculations using software Gaussian09 [14] with
MP2 method [15] in basis set 6–31G++(2d,2p).