Structural, spectral and thermal properties of 2-(2-pyridylamino)pyridinium trihydrogen pyromellitate

Article abstract of DOI:10.2298/JSC130706115P

The title compound, (Hdipya)(H₃pyr), where Hdipya is protonated 2,2'-dipyridilamine and H₃pyr is the monoanion of pyromellitic acid (H₄pyr), was obtained from a reaction mixture containing Zn(II) ions, dipya, Na₄pyr (in the mole ratio 2:2:1) and HNO₃. The products (micro- and single-crystalline) were characterized by X-ray structure determination, FT-IR spectroscopy and TG/DSC analysis. The most striking structural feature of (Hdipya)(H₃pyr) are short inter- and extremely short intramolecular hydrogen bonds. These bonds mutually connect cations and anions making thin layers parallel to the crystallographic (223) plane. In addition, quite unusual, linear proton-bound polymeric {H(H₂pyr) ^-}_n were identified in the structure. The results of crystal structure determination are compared with FT-IR and TG/DSC data. The low position of the ν_as(COO) vibration at 1660 cm^-1 is in accordance with strong hydrogen bonding. This value could be used as a measure of the C=O bond order, which was calculated to be 1.81.

Full text of DOI:10.2298/JSC130706115P

J. Serb. Chem. Soc. 79 (6) 637–648 (2014)
JSCS–4614
UDC 547.585+547.855.1+547.233:
548.7:543.42–74:547.415
Original scientific paper
Structural, spectral and thermal properties of
2-(2-pyridylamino)pyridinium trihydrogen pyromellitate
1
#
*
1#
2#
DEJAN POLETI , JELENA ROGAN , LIDIJA RADOVANOVIĆ
and MARKO RODIĆ3#
1Department of General and Inorganic Chemistry, Faculty of Technology and Metallurgy,
University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia, 2Innovation Center, Faculty
of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade,
Serbia and 3Faculty of Sciences, University of Novi Sad, Trg Dositeja Obradovića 3,
21000 Novi Sad, Serbia
(Received 7 June, revised 24 October, accepted 25 October 2013)
Abstract: The title compound, (Hdipya)(H3pyr), where Hdipya is protonated
2,2′-dipyridilamine and H3pyr is the monoanion of pyromellitic acid (H4pyr),
was obtained from a reaction mixture containing Zn(II) ions, dipya, Na4pyr (in
the mole ratio 2:2:1) and HNO3. The products (micro- and single-crystalline)
were characterized by X-ray structure determination, FT-IR spectroscopy and
TG/DSC analysis. The most striking structural feature of (Hdipya)(H3pyr) are
short inter- and extremely short intramolecular hydrogen bonds. These bonds
mutually connect cations and anions making thin layers parallel to the crys-
tallographic (223) plane. In addition, quite unusual, linear proton-bound poly-
meric {H(H2pyr)-}n were identified in the structure. The results of crystal struc-
ture determination are compared with FT-IR and TG/DSC data. The low posi-
tion of the νas(COO) vibration at 1660 cm-1 is in accordance with strong hyd-
rogen bonding. This value could be used as a measure of the C=O bond order,
which was calculated to be 1.81.
Keywords: pyromellitic acid; 2,2′-dipyridylamine; crystal structure; FT-IR
spectra; TG/DSC analysis.
INTRODUCTION
Pyromellitic or 1,2,4,5-benzenetetracarboxylic acid (H pyr), one of 12 ben-
4
zenepolycarboxylic acids, is used in the production of polyesters and polyamides.
4–
Anions of H pyr, in particular pyr , are well-known as very prospective ligands
4
in coordination chemistry due to the presence of eight O atoms as potential
1
ligating sites that can coordinate up to ten metal centers. The crystal structure of
*Corresponding author. E-mail: dejan@tmf.bg.ac.rs
# Serbian Chemical Society member.
doi: 10.2298/JSC130706115P
637
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638
POLETI et al.
2
H pyr was published in 1971, and earliest transition metal (TM) complexes with
4
3
the tetra-anion of H pyr were published just after that. The first structurally
characterized complexes were described at the beginning of the 1990s. Later,
4
4
during structural studies of TM complexes, it was shown that the tetra-anion
4–
5
pyr usually acts as a centrosymmetric bridging ligand and can build discrete,
6
7
8
chain, layered, or framework structures. A survey of the Cambridge Structural
Database, CSD, showed that the partially deprotonated forms: Hpyr , H pyr
and H pyr are, as a rule, not coordinated.
9
3–
2–
2
–
3
Binary and ternary TM complexes with anions of aromatic polycarboxylic
10
acids have been studied for a long time. In line with this subject, attempts were
4–
made to prepare mixed ligand Mn(II) and Zn(II) complexes with pyr and 2,2′-
-dipyridylamine (dipya) as an N,N′ ligand. Surprisingly, the title compound con-
taining only potential ligands was obtained instead. Such compounds can be clas-
sified into two major groups, as co-crystals (adducts) or organic salts (proton-
11
transfer complexes), but between them there are so-called “disordered solid
12,13
forms”,
where hydrogen atoms are not undoubtedly located or they are dis-
ordered. Although such compounds are much less frequent in comparison with
single-component organics or the corresponding complexes, the number of stu-
died examples permanently increases since their possible importance for pharma-
14,15
ceutical chemistry was recognized.
Even ferroelectric properties were found
16
in some compounds. Therefore, it seemed worthwhile to study the obtained
compound in detail.
9
In the CSD there is a very limited number of structurally characterized
compounds concerning molecule of H pyr or its partially deprotonated ions.
4
There are, however, several similar organic salts: (Hpy)(H pyr), where py is
3
13
17
2–
pyridine, (NMe )(H pyr), a series of H pyr salts with different pyridinium
4
3
2
19
18
derivatives, (cytosinium) (H pyr)·H O, and (Hbipy) (H pyr)(H pyr), where
2
2
2
2
2
4
20
bipy is 2,2′-bipyridine, which was characterized structurally and by FT-IR and
21
NMR spectroscopy.
On the other hand, dipya is well known as a chelating ligand. A search of the
9
CSD revealed some 170 compounds containing dipya. Most of them were TM
complexes, and there were no examples of uncoordinated dipya in its neutral
form. At the same time, there were only eight compounds containing protonated
dipya, which can be present as monoprotonated 2-(2-pyridylamino)pyridinium,
Hdipya, or diprotonated 2,2′-iminodipyridinium(2+), H dipya. Such protonated
2
forms are not coordinated, and in five out of eight cases tetrahalidometalates,
2–
9
[MX ] (M = Co, Cu or Hg; X = Cl or Br), were present as counter ions.
4
Herein, crystal structure of the title compound, (Hdipya)(H pyr), together
3
with its FT-IR spectral and thermal properties are described and correlated with
each other.
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2-(2-PYRIDYLAMINO)PYRIDINIUM TRIHYDROGEN PYROMELLITATE
639
EXPERIMENTAL
The starting reagents pyromellitic acid (> 95 %), 2,2′-dipyridylamine (98 %), Mn(II)
nitrate solution, 45–50 % in dilute nitric acid (all Sigma–Aldrich) and Zn(NO)3·6H2O (p.a.
Kemika, Zagreb) were used without any purifications.
Preparation of the microcrystalline product. Into 100 cm3 of an aqueous solution con-
taining 0.74 g (2.5 mmol) of Zn(NO3)2·6H2O, first 5 cm3 of HNO3 solution (c = 1 mol dm-3),
then 0.43 g of dipya (2.5 mmol) dissolved in 10 cm3 of an EtOH/H2O mixture (3:1 volume
ratio) was added. The pH value of this mixture was 2. Then, 50 cm3 of an aqueous solution of
Na4pyr (0.32 g; 1.25 mmol) was slowly added under stirring. The final pH value was 4. After
standing for 24 h, the obtained precipitate was filtered and rinsed with H2O, EtOH and Et2O.
Yield: 84.6 %; Anal. Calcd. for C20H15N3O8: C, 56.48; H, 3.55; N, 9.88 %. Found: C, 56.27,
H, 3.62, N, 9.91 %; FT-IR (KBr, cm-1): 3470 (bw), 3117 (m), 3097 (m), 3061 (m), 3024 (m),
2993 (m), 2920 (w), 1715 (m), 1660 (s), 1604 (s), 1562 (s), 1451 (s), 1311 (w), 1292 (w), 1270
(w), 1250 (w), 1170 (m), 1151 (m), 1005 (m), 955 (m), 901 (m), 771 (s), 748 (s), 594 (m), 559
(w), 532 (m). The compound was soluble in DMSO but insoluble in H2O and EtOH.
A similar procedure using Mn(II) instead of Zn(II) ions resulted in a white microcrys-
talline powder in a comparable yield (78.9 %). As revealed by elemental analysis and FT-IR
spectroscopy, this product was identical to the product obtained in the presence of Zn(II) ions.
Preparation of single-crystals. Into 50 cm3 of an aqueous suspension containing 0.25 g
(1 mmol) of H4pyr was added 0.17 g of dipya (1 mmol) dissolved in 5 cm3 of EtOH. Then, 50
cm3 of an aqueous solution containing 0.30 g (1 mmol) of Zn(NO3)2·6H2O was added drop-
wise under continuous stirring. The mixture was gently heated at 50 °C for 3 h, filtered to
remove a small quantity of unreacted H4pyr, and left standing under ambient conditions. The
first crystals appeared after 24 h, but single-crystals of appropriate size were collected after 10
days.
Characterization. The FT-IR spectra were recorded on a Bomem MB-100 (Hartmann
Braun) spectrophotometer (4000–600 cm-1 region) using KBr pellets. The thermal properties
of the compound were examined from room temperature up to 380 °C using an SDT Q600
TGA/DSC instrument (TA Instruments) in a dry nitrogen atmosphere (flow rate: 100 cm3 min-1)
at a heating rate of 20 °C min-1. The sample mass was 8.14 mg.
Room temperature (22 °C) single-crystal X-ray diffraction data were collected on an
Oxford Gemini S diffractometer equipped with CCD detector, using monochromatized Cu Kα
radiation (λ = 1.5418 Å). A multi-scan correction for absorption was applied. The structure
was solved by direct methods (SIR97)22 and refined on F2 by full-matrix least-squares using
the programs SHELXL9723 and WinGX.24 All non-hydrogen atoms were refined anisotro-
pically. The positions of the C- and N2-bonded H atoms were calculated geometrically and
refined by the riding model with Uiso = 1.2U(C,N). H atoms from OH groups were found in
ΔF maps and refined with the Uiso = 1.5U(O) constraint. The Hdipya cation was disordered
over a centre of symmetry with congener atoms having 0.5 site occupancies; the individual
pyridyl groups were refined using the FLAT constraint with equal displacement parameters
for the corresponding A and B atoms. Attempts to determine the H atom that protonates dipya
were unsuccessful, very likely because this atom was spread over four positions (N1A, N1B
and their centrosymmetric counterparts, see Fig. 1. Selected crystal data and refinement
results are listed in Table I. CCDC 948070 contains supplementary crystallographic data for
this paper. This data can be obtained free of charge at http://www.ccdc.cam.ac.uk/cgi-
-bin/catreq.cgi.
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640
POLETI et al.
Fig. 1. Molecular structure of (Hdipya)(H3pyr) with atomic numbering scheme. Displacement
ellipsoids are drawn at the 50 % probability level. Disordered Hdipya ions are marked by
different shades of gray. Symmetry codes: (i) 1 – x, 1 – y, 1 – z; (ii) 1 – x, 1 – y, –z;
(iii) 1 + x, 1 + y, –z.
TABLE I. Crystal data and structure refinement for (Hdipya)(H3pyr)
Empirical formula
M / g mol-1
Crystal system
Space group
a, b, c / Å
C20H15N3O8
425.35
Triclinic
P1
3.8268(2), 9.2726(6), 13.3494(8)
α, β, γ / º
74.761(6), 81.845(5), 82.935(6)
V / Å3
450.59(5)
Z
1
ρc / g cm-3
μ / mm-1
1.568
1.056
F(000)
220
Crystal dimensions, mm
0.09×0.10×0.31
θ
max / °
72.12
Range of h, k, l
–4 ≤ h ≤ 3, –11 ≤ k ≤ 11, –16 ≤ l ≤ 16
Reflections collected
Independent reflections
Completeness, %
Data/restraints/parameters
(Δ/σ)max
7605
1770 (Rint = 0.0361)
99.6
1770/6/169
0.001
S
1.116
R indices (I > 2σ (I))
R indices (all data)
Δρmax, Δρmin (both in e Å-3)
R1 = 0.0533, wR2 = 0.1282
R1 = 0.0631, wR2 = 0.1341
0.150, –0.205
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2-(2-PYRIDYLAMINO)PYRIDINIUM TRIHYDROGEN PYROMELLITATE
641
RESULTS AND DISCUSSION
Synthesis
As described in the Experimental, the title compound was obtained during
attempts to synthesize ternary Zn(II)–dipya-pyr complexes or their Mn(II) anal-
ogues. This demonstrates the difficulties in the preparation of such complexes, in
9
25
spite of being known. A similar experience was already published by Ha,
when (Hdipya) [MnCl ] was obtained instead of the expected Mn(II)–dipya
2
4
complex, and it was not reported previously for Zn(II) complexes. Such behavior
can be partly explained by an increase on the thermodynamic stability of the
26
protonated dipya in respect to the neutral molecule, but since dipya complexes
of many TMs are known, the specific role of Zn(II)/Mn(II) ions and the pH of the
reaction mixture should not be neglected.
Crystal structure
In the structure of (Hdipya)(H pyr), both the Hdipya and H pyr ions are
3
3
positioned around the symmetry centre, and only half of each species belongs to
the asymmetric unit (Fig. 1). Besides, Hdipya is disordered over a centre of sym-
metry with equal allocation of both entities. A comparable disorder was found in
26
some organostannates, and in the analogous (Hdipya)(Hpht), where Hpht is the
27
hydrogen phthalate ion. One of pyridyl N atoms has to be protonated, but it
was not possible to locate the corresponding H atom. Both N atoms from the
pyridyl rings could be protonated because N1A···O1 and N1B···O1 distances are
3.018(7) and 3.121(5) Å, respectively, i.e., they could form hydrogen bonds.
Therefore, the H atom is very likely spread over four possible positions.
The whole Hdipya is practically perfectly planar with a negligible dihedral
angle between the mean-planes of the two pyridyl rings. In three known dipya
polymorphs and five crystallographically different dipya molecules, this angle
28
varied between about 4 and 40°. A very similar variety of angles was also
10
found in some TMs–dipya complexes. The planarity of Hdipya might be
explained by symmetry constraints or by extended delocalization of the π elec-
trons. However, the influence of intramolecular (intra-H) and intermolecular
29
(inter-H) hydrogen bonds could also be important. According to Haddad et al.,
weak intra-H bonding is also possible between the protonated and unprotonated
N atom from adjacent pyridyl rings (Fig. 1, atoms N1A and N1B). As usual, pyri-
dyl rings are less regular than benzene rings.
At first sight, the H pyr ion (Fig. 1) is fully protonated, i.e., it should be
3
described as a neutral H pyr molecule, not as a monoanion. However, the H2
4
atom is in special position (site symmetry: 1 ) and with a 0.5 site occupancy
factor. The geometry data for the H pyr anion are listed in Table II. While the
3
C–C bond distances are as expected, the angles, in particular C1–C2–C3 and
C2–C3–C5, strongly deviate from the values found in H pyr·2H O (max.
4
2
30
121.7°). This is the consequence of the stress caused by the presence of the
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642
POLETI et al.
…
intra-H bond O2–H1 O3 and the formation of seven-membered, S(7), pseudo-
-rings. In respect to the aromatic ring, the C–COO groups are inclined in the
opposite sides, with the corresponding angles of 13.3° for the C2C1O1O2 group
and 73.6° for the C3C5O3O4 group. This intra-H bond is extremely short and
clearly asymmetrical (Table III, Fig. 1). Very similar geometries were already
13,18–20
31,32
found in H pyr and H pyr anions.
and in some Hpht complexes.
2
3
TABLE II. Bond distances and angles in H3pyr ion (For O–H bond distances, see Table III)
Bond distance, Å
O1–C1
O3–C5
C1–C2
C2–C4
C3–C5
1.202(4)
1.225(3)
1.527(3)
1.391(3)
1.513(3)
O2–C1
O4–C5
C2–C3
C3–C4
1.297(3)
1.251(3)
1.406(3)
1.391(3)
Bond angle, °
O1–C1–O2
O2–C1–C2
C1–C2–C4
C2–C3–C4
C4–C3–C5
C2–C4–H4
O3–C5–O4
O4–C5–C3
121.2(3)
119.9(2)
113.0(2)
118.0(2)
115.2(2)
117.9(2)
122.2(3)
115.8(2)
O1–C1–C2
C1–C2–C3
C3–C2–C4
C2–C3–C5
C2–C4–C3
C3–C4–H4
O3–C5–C3
118.9(2)
129.2(2)
117.8(2)
126.8(2)
124.2(2)
117.9(2)
121.9(2)
TABLE III. Geometry of hydrogen bonds in (Hdipya)(H3pyr); Symmetry codes: (iv) –x, –y + 2,
–z + 1; (v) x – 1, y, z
D–H···A
d(D–H) / Å
d(H···A) / Å
Angle (DHA) / °
d(D···A) / Å
O2–H1···O3
1.11(4)
1.24a
0.86
1.34(4)
1.24a
1.87
167(3)
180a
165
2.435(3)
2.477(2)
2.706(4)
O4–H2···O4iv
N2–H2A···O1v
a
Atom H2 is in a special position and its coordinates were fixed during refinement
…
iv
Another, inter-H bond O4–H2 O4 ((iv) –x, –y + 2, –z + 1) is symmetrical
and also very short, but a little longer than the intra-H bond (Table III). In com-
…
27
parison to typical O O distances found in related Hpht compounds, the intra-H
bond is slightly longer, whereas inter-H bond is shorter than expected. This shows
how strong the inter-H bond is in this case. Being that the inter-H bond is sym-
metrical, H pyr could also be viewed as a polymeric proton-bound trihydrogen
3
–
pyromellitate anion, {H(H pyr) } (Fig. 2). Again, there is great similarity with
Hpht compounds, in which proton-bound anions are also found.
difference is that {H(H pyr) } is polymeric, while [H(Hpht) ] ions are only dime-
2
n
33–35
The main
–
–
2
n
2
ric. This is because H pyr could be considered as developed from H pht by
4
2
mirroring two COOH groups in the ortho-position to another pair of COOH
–
2–
groups. Thus, only H pyr and H pyr can make polymeric proton-bound anions,
3
2
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2-(2-PYRIDYLAMINO)PYRIDINIUM TRIHYDROGEN PYROMELLITATE
643
–
36
while Hpht is restricted to dimeric forms. To the best of our knowledge, a
similar polyanion was found only in (NMe )(H pyr), described by Rodriguez-
4
3
17
Cuamatzi et al. However, those chains were of a zig–zag type, while here the
presented chains are linear (Fig. 2) and so could be regarded as unprecedented.
Fig. 2. Motif of hydrogen bonds (thin dark lines) in the (223) crystallographic plane. Color
codes for atoms: H – white, C – light gray, N – dark gray and O – black.
In the structure, there is another hydrogen bond between the amine N2 atom
and O1 (Fig. 1, Table III). Since all hydrogen bonds are concentrated in one plane,
thin layers approximately parallel to the crystallographic (223) plane are formed
–
(Fig. 2). The {H(H pyr) } and Hdipya ions are assembled in alternating rows
2
n
making a non-rectangular grid. The layers are stacked together by short parallel-
-displaced π–π interactions. For example, all distances between the plane of one
benzene ring and benzene C atoms from the nearest layer are 3.490(5) Å. Anal-
19
17
ogous layers also exist in (cytosinium) (H pyr)·H O, and in (NMe )(H pyr).
2
2
2
4
3
Spectral and thermal properties
A sequence of weak and sometimes broad IR bands between 3500 and 3200
–1
21
cm is indicative for numerous hydrogen bonds. According to the literature,
–1
even weak and very broad bands centered at 2900, 2430 and 1900 cm could also
be ascribed to strong hydrogen bonding. In some cases, they could be extremely
strong and broad. Bands between about 3120 and 2990 cm are characteristic
for stretching N–H and C–H vibrations in secondary amines and aromatic rings.
37
–1
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644
POLETI et al.
–1
It seems that the stretching N–H band was shifted from 3244 cm in dipya to
–1
3117 or 3097 cm in (Hdipya)(H pyr), suggesting stronger hydrogen bonding.
3
In the “fingerprint” region, there are bands of different origin typical for
substituted benzene rings and secondary amines; they agree with the bands in the
individual components. Especially characteristic for dipya is a prominent doublet
–1
due to N–H out of plane bending at 771 and 748 cm . Both vibrations were
–1
slightly shifted with respect to pure dipya (768 and 735 cm ) and very likely
38
overlap with the corresponding C–H vibrations.
–1
The most interesting part of the FT-IR spectrum is the 1720–1250 cm
region (Fig. 3), where many strong bands are expected: asymmetrical and sym-
metrical stretching vibrations of COOH and the corresponding COO groups, C–C
and C–N stretching vibrations of aromatic rings and N–H bending in a secondary
39
aromatic amine. (Asymmetrical ν (COOH) vibrations, characteristic for orga-
as
nic acids, are often labelled ν(C=O) and called carbonyl, due to the presence of
37
double C=O bond). Consistent to the literature, ν (COOH) and ν (COOH)
as
s
–1
frequencies for H pyr are at 1710 and 1266 (as doublet at 1278 and 1255) cm ,
4
–1
respectively, and the present experimental data agree within ±5 cm with these
values. These bands are broad and usually the most intense in the spectrum.
38
Surprisingly, the corresponding bands in the FT-IR spectrum of (Hdipya)(H pyr)
3
–1
are medium to weak, but one additional very prominent band at 1660 cm
appeared. At first sight, this band could be attributed to the secondary amine
–1
N–H bending group frequency, which is located at 1604 cm in dipya. However,
such high wavenumbers are observed only in the case of coordinated dipya and
10
–1
the band is typically very sharp. Therefore, the band at 1660 cm should be
ascribed to the ν (COOH) or carbonyl C=O vibrations. Such a low position of
as
38
ν (COOH) is not expected, and, together with no unambiguous identification
as
of ν (COOH) vibrations, has to be correlated to the extremely short and strong
s
20,21
hydrogen bonds involving all O atoms from H pyr. In (Hbipy) (H pyr)(H pyr),
3
2
2
4
just the opposite behavior was observed, ν (COOH) is shifted to the higher
as
–1
wavenumbers (1726 cm ), which was explained by the absence of hydrogen bonds.
In the tetrathiafulvalene–p-chloranil (TTF–CA) complex, which is a widely
40
studied charge-transfer organic compound, the position of C=O vibrations was
used to determine the degree of charge transfer from TTF to CA. In other words,
ν (COOH)/ν(C=O) could be related to the C=O bond order. For H pyr ν (COOH)
as
4
as
–1 39
was at 1710 cm , and this corresponds to a bond order of 2. In alkali metal
salts, the COOH groups are ionized and, due to delocalization of the electrons in
COO groups, the bond order should be 1.5. The available data for the two alkali
39
–1
metal salts K pyr and Na pyr (this study) give an identical value, 1580 cm
4
4
for ν (COO). From these values, it is easy to calculate the C=O bond order in
as
(Hdipya)(H pyr), which was 1.81. By analogy to the “degree of charge transfer”
3
41
this quantity could be used to measure the “degree of proton transfer”, and
should be correlated to the geometry of hydrogen bonding in (Hdipya)(H pyr).
3
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2-(2-PYRIDYLAMINO)PYRIDINIUM TRIHYDROGEN PYROMELLITATE
645
However, the observed geometry of H pyr ions (Table II) does not enable a
3
simple explanation of the calculated value. For O1–C1 and O2–C1 pair, bond
distances can be judged as normal when compared to the H pyr and common
4
2
COOH values. Nevertheless, O3–C5 bond is longer than expected and O4–C5
bond distance corresponds to the typical values found in ionized COO groups.
9
This could be a possible cause for the low value of ν (COOH), although an
as
extensive coupling of vibrational modes should also be kept in mind.
Fig. 3. FT-IR spectrum (KBr pellets) of (Hdipya)(H3pyr).
As shown in Fig. 4, the decomposition of (Hdipya)(H pyr) began at 237 °C
3
(onset temperature) and ended at about 325 °C with a total mass loss. No melting
Fig. 4. TG/DSC curves of (Hdipya)(H3pyr) under a dynamic N2 atmosphere at a heating
rate of 20 °C min-1 (exotherm up).
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646
POLETI et al.
was observed and the decomposition started around the boiling point of dipya
(222 °C), suggesting that this molecule escaped first. Although the TG curve
decreased rapidly, the shape of the DSC curve indicated that the disintegration
occurred in at least three, probably four, highly overlapped steps, which could
not be resolved. The total molar decomposition enthalpy was relatively high,
o
–1
Δ
H
= 461.2 kJ mol . In comparison to TM complexes with dipya and some
dec
m
10
polycarboxylate ligands,
the initial decomposition temperature of
(Hdipya)(H pyr) was lower, very likely owing to the absence of coordinative
3
bonds. In analogous systems (py) (H tpht), where H tpht is terephthalic acid,
2
2
2
and (py) (H tms), where H tms is trimesic acid, the total degradation was found
3
3
3
13
to be at 339 and 366 °C, respectively. There, however, loss of py molecules
started just above room temperature, although the boiling point of py is 115 °C.
CONCLUSIONS
A new organic salt (Hdipya)(H pyr) was prepared unpredictably during
3
efforts to obtain ternary Zn(II) or Mn(II) complexes with dipya and pyr ligands.
26
Besides the higher stability of Hdipya with respect to dipya, the presence of
2+
2+
Zn or Mn ions, as well as a starting mixture pH value of 4 most likely
affected the reaction mechanism and the formation of (Hdipya)(H pyr). The
3
compound consisted of disordered Hdipya cations and H pyr anions connected
3
by hydrogen bonds. There were short inter- and extremely short intra-H bonds. In
this way, thin layers parallel to the (223) plane were formed. Due to the very
strong and symmetrical inter-H bond, the H pyr anions could furthermore be
3
–
regarded as polymeric {H(H pyr) } anions. The position and shape of the cha-
2
n
racteristic bands revealed by FT-IR spectroscopy undoubtedly confirmed the
structural findings in (Hdipya)(H pyr), and the value of ν (COO) vibration was
3
as
used for measuring the “degree of proton transfer”, which was calculated to be
1.81. The TG/DSC analysis proved that (Hdipya)(H pyr) decomposed in several
3
–1
overlapping steps and a total molar decomposition enthalpy of 461.2 kJ mol
was calculated.
SUPPORTING INFORMATION
Crystallographic data can be obtained free of charge at http://www.ccdc.cam.ac.uk/cgi-
-bin/catreq.cgi.
Acknowledgement. This study was financially supported by the Ministry of Education,
Science and Technological Development of the Republic of Serbia (Grant No. 45007).
Available on line at www.shd.org.rs/JSCS/
_________________________________________________________________________________________________________________________
(CC) 2014 SCS. All rights reserved.

2-(2-PYRIDYLAMINO)PYRIDINIUM TRIHYDROGEN PYROMELLITATE
647
И З В О Д
СТРУКТУРНА, СПЕКТРАЛНА И ТЕРМИЧКА СВОЈСТВА
2-(2-ПИРИДИЛАМИНО)ПИРИДИНИJУМ-ТРИХИДРОГЕНПИРОМЕЛИТАТА
ДЕЈАН ПОЛЕТИ1, ЈЕЛЕНА РОГАН1, ЛИДИЈА РАДОВАНОВИЋ2 и МАРКО РОДИЋ3
1
Катедра за општу и неорганску хемију, Технолошко–металуршки факултет,Универзитет у
2
Београду, Карнегијева 4, 11000 Београд, Иновациони центар Технолошко–металуршког факултета,
3
Универзитет у Београду, Карнегијева 4, 11000 Београд и Природно–математички факултет,
Универзитет у Новом Саду, Трг Доситеја Обрадовића 3, 21000 Нови Сад
Описано једињење, (Hdipya)(H3pyr), где је Hdipya протоновани 2,2′-дипиридил-
амин, а H3pyr моноанјон пиромелитне киселине (H4pyr), добијено је из реакционе
смеше која је садржала Zn(II) јоне, dipya, Na4pyr (молски однос 2:2:1) и HNO3. Произ-
води (микро- и монокристални) окарактерисани су рендгенском структурном анализом,
FT-IR спектроскопијом и TG/DSC анализом. Врло необично структурно својство
(Hdipya)(H3pyr) јесте присуство кратких интер- и екстремно кратких интрамолекулских
водоничних веза, које међусобно повезују катјоне и анјоне градећи танке слојеве пара-
лелне кристалографској равни (223). Такође, у структури су нађени до сада веома ретки,
линеарни полимерни анјони {H(H2pyr)-}n настали повезивањем преко протона. Резул-
тати рендгенске структурне анализе упоређени су са подацима добијеним FT-IR спек-
троскопијом и ТG/DSC анализом. Ниска фреквенција νas(COO) вибрације на 1660 cm-1
у
сагласности је са постојањем јаких водоничних веза. Ова вредност искоришћена је за одре-
ђивање реда C=O везе (“степена преноса протона”) и израчунато је да он износи 1,81.
(Примљено 7. јуна, ревидирано 24. октобра, прихваћено 25. октобра 2013)
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