Novel compounds of 4-amino-1,2,4-triazole with dicarboxylic acids - crystal structures, vibrational spectra and non-linear optical properties

Article abstract of DOI:10.1016/j.molstruc.2007.03.007

Three novel 4-amino-1,2,4-triazole compounds with oxalic, succinic and adipic acids have been prepared and X-ray structural analysis has been carried out. The organic salt 4-amino-1,2,4-triazol-1-ium hydrogen oxalate crystallizes in the monoclinic space group P2₁, a = 3.7280(2), b = 18.349(1), c = 4.9680(4) ?, β = 101.134(5)°, V = 333.44(4) ?³, Z = 2, R = 0.0284 for 1328 observed reflections. The crystal structure consists of periodically alternating layers (parallel to a axis) formed by chains of hydrogen oxalate anions connected by strong O-H?O hydrogen bonds. The layers are interconnected by 4-amino-1,2,4-triazol-1-ium cations via N-H?O hydrogen bonds. The addition compound 4-amino-1,2,4-triazole-succinic acid (1:1) crystallizes in the monoclinic space group P2₁/c, a = 11.8130(5), b = 5.0690(3), c = 16.5280(5) ?, β = 117.285(3)°, V = 879.58(7) ?³, Z = 4, R = 0.0352 for 1701 observed reflections. The crystal structure is formed by zig-zag chains (parallel to b axis) of 4-amino-1,2,4-triazole molecules, connected by N-H?N hydrogen bonds, and isolated molecules of succinic acid which interconnect these chains by O-H?N and N-H?O hydrogen bonds. The addition compound 4-amino-1,2,4-triazole-adipic acid (2:1) crystallizes in the monoclinic space group P2₁/c, a = 6.3610(3), b = 8.0580(2), c = 14.8750(5) ?, β = 104.072(2)°, V = 739.57(5) ?³, Z = 2, R = 0.0487 for 1793 observed reflections. The crystal structure consists of pairs of parallel linear chains (mediated by N-H?N hydrogen bonds) of 4-amino-1,2,4-triazole molecules that are interconnected by isolated adipic acid molecules via O-H?N and N-H?O hydrogen bonds. Neighbouring chains, which are parallel to a axis, do not exhibit any H-bond contact between each other. The FTIR and FT Raman spectra of all three compounds were recorded, calculated and discussed. Quantitative measurements of second harmonic generation of powdered 4-amino-1,2,4-triazol-1-ium hydrogen oxalate at 800 nm were performed and a relative efficiency of 38% (compared to KDP) was observed.

Full text of DOI:10.1016/j.molstruc.2007.03.007

Available online at www.sciencedirect.com
Journal of Molecular Structure 873 (2008) 46–60
www.elsevier.com/locate/molstruc
Novel compounds of 4-amino-1,2,4-triazole with dicarboxylic acids –
crystal structures, vibrational spectra and non-linear optical properties
a,
a
a
b
a
*
´
ˇ
ˇ
ˇ
ˇ
Irena Matulkova , Ivan Nemec , Karel Teubner , Petr Nemec , Zdenek Micka
a
Charles University in Prague, Faculty of Science, Department of Inorganic Chemistry, Hlavova 8, 128 40 Prague 2, Czech Republic
b
Charles University in Prague, Faculty of Mathematics and Physics, Department of Chemical Physics and Optics, Ke Karlovu 3,
121 16 Prague 2, Czech Republic
Received 1 December 2006; received in revised form 28 February 2007; accepted 3 March 2007
Available online 12 March 2007
Abstract
Three novel 4-amino-1,2,4-triazole compounds with oxalic, succinic and adipic acids have been prepared and X-ray structural analysis
has been carried out. The organic salt 4-amino-1,2,4-triazol-1-ium hydrogen oxalate crystallizes in the monoclinic space group P21,
3
˚
˚
a = 3.7280(2), b = 18.349(1), c = 4.9680(4) A, b = 101.134(5)ꢀ, V = 333.44(4) A , Z = 2, R = 0.0284 for 1328 observed reflections. The
crystal structure consists of periodically alternating layers (parallel to a axis) formed by chains of hydrogen oxalate anions connected
by strong O–Hꢀ ꢀ ꢀO hydrogen bonds. The layers are interconnected by 4-amino-1,2,4-triazol-1-ium cations via N–Hꢀ ꢀ ꢀO hydrogen bonds.
The addition compound 4-amino-1,2,4-triazole–succinic acid (1:1) crystallizes in the monoclinic space group P21/c, a = 11.8130(5),
3
˚
˚
b = 5.0690(3), c = 16.5280(5) A, b = 117.285(3)ꢀ, V = 879.58(7) A , Z = 4, R = 0.0352 for 1701 observed reflections. The crystal struc-
ture is formed by zig-zag chains (parallel to b axis) of 4-amino-1,2,4-triazole molecules, connected by N–Hꢀ ꢀ ꢀN hydrogen bonds, and
isolated molecules of succinic acid which interconnect these chains by O–Hꢀ ꢀ ꢀN and N–Hꢀ ꢀ ꢀO hydrogen bonds.
The addition compound 4-amino-1,2,4-triazole–adipic acid (2:1) crystallizes in the monoclinic space group P21/c, a = 6.3610(3),
3
˚
˚
b = 8.0580(2), c = 14.8750(5) A, b = 104.072(2)ꢀ, V = 739.57(5) A , Z = 2, R = 0.0487 for 1793 observed reflections. The crystal struc-
ture consists of pairs of parallel linear chains (mediated by N–Hꢀ ꢀ ꢀN hydrogen bonds) of 4-amino-1,2,4-triazole molecules that are inter-
connected by isolated adipic acid molecules via O–Hꢀ ꢀ ꢀN and N–Hꢀ ꢀ ꢀO hydrogen bonds. Neighbouring chains, which are parallel to a
axis, do not exhibit any H-bond contact between each other.
The FTIR and FT Raman spectra of all three compounds were recorded, calculated and discussed.
Quantitative measurements of second harmonic generation of powdered 4-amino-1,2,4-triazol-1-ium hydrogen oxalate at 800 nm
were performed and a relative efficiency of 38% (compared to KDP) was observed.
ꢁ 2007 Elsevier B.V. All rights reserved.
Keywords: 4-Amino-1,2,4-triazole; 4-Amino-1,2,4-triazol-1-ium chloride; 4-Amino-1,2,4-triazol-1-ium hydrogen oxalate; 4-Amino-1,2,4-triazole–succinic
acid (1:1); 4-Amino-1,2,4-triazole–adipic acid (2:1); Crystal structure; Vibrational spectra; HF; B3LYP; MP2; Second harmonic generation
1. Introduction
act as a bridge between metal centres and mediate exchange
coupling. Spin crossover compounds with iron(II) [2,6] can
act as an example. The another application of triazole
ligand lies in medical research – complex with Pt(II) [7]
exhibit antitumor activity (human cancer) similar to cis-
platin. Triazole derivatives are also used in the synthesis
of antibiotics, fungicides, herbicides, plant growth hor-
mone regulators [8], and potentially good corrosion inhib-
itors [9,10].
The utilisation of the 1,2,4-triazole moiety as a part of
ligand system in metal complexes has gained considerable
attention in recent years [1–5]. The 1,2,4-triazole system
is also of magnetochemical interest because it is able to
*
Corresponding author. Tel.: +420 221 951 245; fax: +420 221 951 253.
´
E-mail address: irena.mat@atlas.cz (I. Matulkova).
0022-2860/$ - see front matter ꢁ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.03.007

I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
47
Materials based on triazole compounds with dicarbox-
ylic acids exhibit many important properties. The two car-
boxylic groups can form linear structures by hydrogen
bonds [11] and these assemblies (for example with unsatu-
rated dicarboxylic acid) can be used for charge transfer
[12]. On the other hand, a molecule of saturated dicarbox-
ylic acid can form an inert spacer between two triazole
rings. Such materials can be used in optical research as
molecular switches [13]. From the point of view of prepara-
tion of non-linear optical (NLO) crystals, these materials
combine highly polarisable cations or molecules (i.e. carri-
ers of non-linear properties) with hydrogen-bonding
organic acids providing thermal and structural stability.
This concept based on encapsulation of organic cations
between chains or layers of organic or inorganic anions
for building of acentric crystalline NLO materials was suc-
cessfully applied for example in the case of 2-amino-5-
nitropyridinium salts [14–16]. Another example of such a
material based on the related 3-amino-1,2,4-triazole moiety
consists in 3-amino-1,2,4-triazolinium(1+) hydrogen L-tar-
trate, which was studied [17] as a promising novel com-
pound for second harmonic generation (SHG).
Hydrogen bonding is generally one of the most effective
and popular tools for the design of crystal structures. The
role of several types of hydrogen bonds in crystal engineer-
ing of NLO materials was widely discussed and explained
[18–23]. Furthermore, hydrogen bonding in these com-
pounds has a notable energetic contribution to the total lat-
tice energy [24] and also contributes to the second-order
NLO tensor coefficient (dijk) of the crystals [25,26].
Only a few papers concerning vibrational spectroscopic
studies of triazoles and their compounds have been pub-
lished yet [1,17,27,28]. Although detailed examination of
vibrational spectra is important not only from the stand-
point of characterization of promising new NLO materials
but also with regard to the vibrational contribution to
molecular hyperpolarizabilities in these materials [29–32].
This work is part of our project focused on preparation
and study of new materials (based on hydrogen-bonded salts
of organic cations) for SHG and deals with the systems capa-
ble of forming a variety of intermolecular hydrogen bonds
based on 4-amino-1,2,4-triazole compounds with dicarbox-
ylic acids. The crystal structures, vibrational spectra and
optical properties of three new compounds: 4-amino-1,2,4-
Table 1
Basic crystallographic data, data collection and refinement parameters for 4-atox, 4-atsuc and 4-atadip
Identification code
4-atox
4-atsuc
4-atadip
Empirical formula
Formula weight
Temperature (K)
C4H6N4O4
174.13
150(2)
3.7280(2)
18.349(1)
4.9680(4)
101.134(5)
333.44(4)
2
1.734
Monoclinic
P21
0.155
180
C6H10N4O4
202.18
150(2)
11.8130(5)
5.0690(3)
16.5280(5)
117.285(3)
879.58(7)
4
1.527
Monoclinic
P21/c
0.129
424
C10H18N8O4
314.32
293(2)
6.3610(3)
8.0580(2)
14.8750(5)
104.072(2)
739.57(5)
2
1.411
Monoclinic
P21/c
0.112
332
˚
a (A)
˚
b (A)
˚
c (A)
b (ꢀ)
3
˚
Volume (A )
Z
Calculated density (Mg/m3)
Crystal system
Space group
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm)
Diffractometer and radiation
Scan technique
0.20 · 0.18 · 0.15
0.43 · 0.40 · 0.38
0.45 · 0.40 · 0.38
˚
Nonius Kappa CCD, Mo k = 0.71073 A
x and w scans to fill the Ewald sphere
Completeness to h
Range of h, k and 1
27.46, 91.7%
27.48, 99.5%
ꢁ15 fi 15, ꢁ6 fi 4, ꢁ21 fi 20
2.77–27.48
7255/2011 (0.0260)
1701
27.47, 98.9%
ꢁ4 fi 4, ꢁ23 fi 23, ꢁ6 fi 6
ꢁ8 fi 8, ꢁ10 fi 10, ꢁ19 fi 19
h Range for data collection (ꢀ)
Reflection collected/unique (Rint
No. of observed reflection
Criterion for observed reflection
Absorption correction
Function minimized
4.74–27.46
2.82–27.47
)
4240/1344 (0.0280)
1328
11290/1695 (0.0360)
1695
I > 2r(I)
None
2
RwðF 2o ꢁ F 2c Þ
Parameters refined
125
143
112
R, wR [I > 2r(I)]
R, wR (all data)
Value of S
Max. and min. heights in final Dp map (eA
Weighting scheme
0.0284, 0.0749
0.0289, 0.0753
1.093
0.207 and ꢁ0.158
0.0352, 0.0849
0.0447, 0.0923
1.044
0.0487, 0.1258
0.0640, 0.1380
1.040
0.423 and ꢁ0.397
ꢁ3
˚
)
0.252 and ꢁ0.249
w ¼ ½r2ðF 2oÞ þ ðaPÞ þ bPꢂꢁ1
2
P ¼ ðF 20 þ 2F 2c Þ=3
a = 0.0432
b = 0.0609
a = 0.0432
a = 0.0936
b = 0.2015
b = 0.0609
Sources of atomic scattering factors
Programs used
SHELXL97 [36]
SHELXL97 [36], PLATON [49], SIR97 [35]

48
I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
triazol-1-ium hydrogen oxalate (4-atox) salt and adducts of
4-amino-1,2,4-triazole with succinic acid (4-atsuc) and adi-
pic acid (4-atadip) are presented and discussed.
2. Experimental
4-Amino-1,2,4-triazole (4-at) was prepared and puri-
fied by a slightly modified procedure described previously
in the literature [33,34]: 6 ml (0.14 mol) of formic acid
(90%, Lachema) and 11.5 ml (0.23 mol) of hydrazine
monohydrate (99%, Fluka) were very carefully mixed
under cooling in a water ice bath. The flask was
equipped with a Liebig distillation condenser and heated
(over 1 h) in a sand bath to a temperature of 200 5 ꢀC
(measured in the sand bath). The excess of hydrazine and
water was distilled off slowly. The distillation started
when the temperature in the sand bath reached 195 ꢀC
and the mixture was heated for additional four hours
after the end of the distillation. After standing overnight,
the reaction mixture was heated to 200 ꢀC under reduced
pressure (water vacuum pump) for two hours to remove
the residues of water and hydrazine. After cooling, the
colourless melt solidified. The solid product was dis-
solved in 14.5 ml of ethanol and the same volume of
diethyl ether and left to crystallise in a refrigerator.
The reaction yield was 3.0 g (51%) of white needles,
m.p. 354–355 K. The purity of the prepared compound
Fig. 1. Atom numbering of 4-atox. Dashed lines indicate hydrogen bonds.
a
400 MHz Varian Unity spectrometer: 1H NMR
(DMSO, ref. DMSO d 2.5 ppm) d 6.2 (2H, d), 8.4 (2H,
d). 13C NMR (DMSO, ref. DMSO d 39.5 ppm) d 143.6
(s). The product was also characterised by its FTIR spec-
trum, which was compared to the literature [1,27].
Crystals of 4-atox, 4-atsuc and 4-atadip were prepared
from equimolar mixtures of aqueous 4-at solution with
an aqueous solution of oxalic acid dihydrate (purum, Lac-
hema) or methanolic solutions of succinic acid (p.a., Lache-
ma) or adipic acid (purum, Lachema), respectively. The
colourless solutions obtained were kept in a desiccator over
sulphuric acid at room temperature. The colourless crystals
prepared by slow spontaneous crystallisation were filtered
off, washed with methanol and dried in a desiccator over
1
was checked by H and 13C NMR spectra recorded on
Table 3
Table 2
Selected bond lengths (A) and angles (ꢀ) for 4-atsuc
˚
Selected bond lengths (A) and angles (ꢀ) for 4-atox
Bond/angle
Value
Angle
Value
Bond/angle
Value
Angle
Value
N(1)–N(6)
N(1)–C(2)
N(1)–C(5)
N(4)–C(5)
N(3)–N(4)
C(2)–N(3)
C(7)–O(12)
C(7)–O(11)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
C(10)–O(14)
C(10)–O(13)
N(1)–N(6)–H(6A)
N(1)–N(6)–H(6B)
H(6A)–N(6)–H(6B)
C(2)–N(1)–C(5)
Hydrogen bonds
1.409(2)
1.347(2)
1.356(2)
1.309(2)
1.388(2)
1.307(2)
1.214(2)
1.326(2)
1.504(2)
1.522(2)
1.503(2)
1.217(2)
1.321(2)
110(1)
C(2)–N(1)–N(6)
C(5)–N(1)–N(6)
C(5)–N(4)–N(3)
C(2)–N(3)–N(4)
N(4)–C(5)–N(1)
N(3)–C(2)–N(1)
O(12)–C(7)–O(11)
O(12)–C(7)–C(8)
O(11)–C(7)–C(8)
C(7)–C(8)–C(9)
C(10)–C(9)–C(8)
O(14)–C(10)–O(13)
O(14)–C(10)–C(9)
O(13)–C(10)–C(9)
C(7)–O(11)–H(11)
C(10)–O(13)–H(13)
123.8(1)
129.9(1)
107.5(1)
107.0(1)
109.3(1)
110.0(1)
119.7(1)
123.2(1)
117.1(1)
112.3(1)
113.5(1)
123.1(1)
123.8(1)
113.0(1)
113(1)
N(1)–C(2)
N(1)–C(5)
N(1)–N(6)
C(2)–N(3)
N(3)–N(4)
N(4)–C(5)
C(7)–O(9)
C(7)–O(10)
C(7)–C(8)
C(8)–O(12)
C(8)–O(11)
C(2)–N(1)–C(5)
C(2)–N(1)–N(6)
C(5)–N(1)–N(6)
N(3)–C(2)–N(1)
Hydrogen bonds
1.336(2)
1.362(2)
1.414(2)
1.311(2)
1.366(2)
1.309(2)
1.239(2)
1.266(2)
1.545(2)
1.211(2)
1.309(2)
106.8(1)
124.4(1)
128.6(1)
106.7(1)
C(2)–N(3)–N(4)
C(2)–N(3)–H(3)
N(4)–N(3)–H(3)
C(5)–N(4)–N(3)
N(4)–C(5)–N(1)
N(1)–N(6)–H(6A)
N(1)–N(6)–H(6B)
H(6A)–N(6)–H(6B)
O(9)–C(7)–O(10)
O(9)–C(7)–C(8)
O(10)–C(7)–C(8)
O(12)–C(8)–O(11)
O(12)–C(8)–C(7)
O(11)–C(8)–C(7)
C(8)–O(11)–H(11)
111.8(1)
123(2)
125(2)
103.8(2)
110.9(1)
107(2)
107(2)
115(2)
127.0(2)
118.8(1)
114.2(1)
125.9(2)
120.8(1)
113.3(1)
111(2)
106(1)
111(2)
106.2(1)
109(1)
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
<(DHA)
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
<(DHA)
N(3)–H(3)ꢀ ꢀ ꢀO(10)
N(3)–H(3)ꢀ ꢀ ꢀO(12)
N(6)–H(6A)ꢀ ꢀ ꢀO(9)
N(6)–H(6A)ꢀ ꢀ ꢀO(11)i
N(6)–H(6B)ꢀ ꢀ ꢀO(9)ii
O(11)–H(11)ꢀ ꢀ ꢀO(10)iii
1.01(3)
1.01(3)
0.88(3)
0.88(3)
0.82(2)
0.84(3)
1.72(3)
2.40(3)
2.21(3)
2.35(2)
2.23(3)
1.69(3)
2.711(2)
2.951(2)
3.031(2)
3.012(2)
2.921(2)
2.531(2)
167(3)
113(2)
154(2)
132(2)
143(2)
178(3)
N(6)–H(6A)ꢀ ꢀ ꢀO(12)i
N(6)–H(6A)ꢀ ꢀ ꢀO(14)i
N(6)–H(6B)ꢀ ꢀ ꢀN(6)ii
O(11)–H(11)ꢀ ꢀ ꢀN(3)iii
O(13)–H(13)ꢀ ꢀ ꢀN(4)iv
0.90(2)
0.90(2)
0.93(2)
0.94(2)
0.96(2)
2.43(2)
2.22(2)
2.28(2)
1.76(2)
1.71(2)
2.848(2)
3.053(2)
3.173(2)
2.689(1)
2.666(2)
109(1)
154(2)
161(2)
169(2)
171(2)
Note. Symmetry transformations used to generate equivalent atoms: (i)
ꢁx + 1, y ꢁ 1/2, ꢁz + 1; (ii) ꢁx + 1, y ꢁ 1/2, ꢁz + 2; (iii) x ꢁ 1, y, z ꢁ 1.
Abbreviations. A, acceptor; D, donor.
Note. Symmetry transformations used to generate equivalent atoms: (i)
ꢁx + 1, y ꢁ 1/2, ꢁz + 3/2; (ii) ꢁx + 1, y + 1/2, ꢁz + 3/2; (iii) ꢁx + 2, ꢁy,
ꢁz + 2; (iv) x, ꢁy + 1/2, z ꢁ 1/2. Abbreviations. A, acceptor; D, donor.

I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
49
Table 4
Selected bond lengths (A) and angles (ꢀ) for 4-atadip
Bond/angle
Value
Angle
Value
N(1)–C(2)
N(1)–C(5)
N(1)–N(6)
C(2)–N(3)
N(3)–N(4)
N(4)–C(5)
C(7)–C(7)i
1.345(2)
1.347(2)
1.408(2)
1.302(2)
1.386(2)
1.303(2)
1.511(3)
1.512(3)
1.497(2)
1.208(2)
1.305(2)
105.5(2)
129.9(2)
124.6(2)
N(3)–C(2)–N(1)
C(2)–N(3)–N(4)
C(5)–N(4)–N(3)
N(4)–C(5)–N(1)
N(1)–N(6)–H(6A)
N(1)–N(6)–H(6B)
H(6A)–N(6)–H(6B)
C(7)–C(7)–C(8)
C(9)–C(8)–C(7)
O(10)–C(9)–O(11)
O(10)–C(9)–C(8)
O(11)–C(9)–C(8)
C(9)–O(11)–H(11)
110.0(2)
107.6(2)
106.2(2)
110.7(2)
104(2)
111(2)
107(2)
C(7)–C(8)
C(8)–C(9)
113.2(2)
114.0(2)
121.6(2)
124.0(2)
114.3(2)
109(2)
C(9)–O(10)
C(9)–O(11)
C(2)–N(1)–C(5)
C(2)–N(1)–N(6)
C(5)–N(1)–N(6)
Hydrogen bonds
Fig. 3. Atom numbering of 4-atsuc. Dashed lines indicate hydrogen
bonds.
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
2.07(3)
2.40(3)
1.63(4)
d(Dꢀ ꢀ ꢀA)
2.940(2)
3.025(2)
2.669(2)
<(DHA)
N(6)–H(6A)ꢀ ꢀ ꢀO(10)ii
N(6)–H(6B)ꢀ ꢀ ꢀN(4)iii
O(11)–H(11)ꢀ ꢀ ꢀN(3)iii
0.91(2)
0.95(3)
1.04(4)
160(2)
123(2)
175(3)
strained to ride on their parent atoms, with Uiso(H) = 1.5
Ueq(C). Hydrogens attached to oxygen and nitrogen atoms
were localized on difference Fourier maps and refined iso-
tropically. The basic crystallographic data, measurement
and refinement details are summarized in Table 1.
Crystallographic data for 4-atox, 4-atsuc and 4-atadip
have been deposited with the Cambridge Crystallographic
Data Center as supplementary publications CCDC
252739, CCDC 252738 and CCDC 259835, respectively.
Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge
CG21, EZ, UK (fax: +44 1223 336 033; e-mail: deposit@
ccdc.cam.ac.uk).
Note. Symmetry transformations used to generate equivalent atoms: (i)
ꢁx + 2, ꢁy + l, ꢁz + l; (ii) ꢁx + l, y ꢁ l/2, ꢁz + l/2; (iii) x ꢁ l, y, z.
Abbreviations. A, acceptor; D, donor.
KOH (average dimensions of crystals were 0.5 · 1.0 · 6.0,
0.5 · 1.0 · 1.5 and 1.0 · 1.5 · 4.0 mm for 4-atox, 4-atsuc
and 4-atadip, respectively).
Collection of X-ray data of 4-atox, 4-atsuc and 4-atadip
was performed on a Nonius Kappa CCD diffractometer
(MoKa radiation, graphite monochromator). The temper-
ature of the crystal was controlled by an Oxford Cryosys-
tems liquid nitrogen Cryostream Cooler. The phase
problem was solved by direct methods (SIR-92 [35]) and
the non-hydrogen atoms were refined anisotropically,
using the full-matrix least-squares procedure (SHELXL-97
[36]). Hydrogen atoms attached to carbon atoms were
calculated in a geometrically idealized position with
The infrared spectra were recorded by nujol and fluorol-
ube mull techniques on a Nicolet Magna 760 FTIR spec-
trometer with 2 cmꢁ1 resolution (4 cmꢁ1 resolution in
FAR IR region) and Happ-Genzel apodization in the 85–
4000 cmꢁ1 region.
The Raman spectra of polycrystalline samples were
recorded on a Nicolet Magna 760 FTIR spectrometer
˚
˚
Csp3 ꢁ H ¼ 0:97 A and Csp2 ꢁ H ¼ 0:93 A, and con-
Fig. 2. Packing scheme of 4-atox (projection to xy plane). Dashed lines indicate hydrogen bonds.

50
I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
Fig. 4. Packing scheme of 4-atsuc (projection to xz plane). Dashed lines indicate hydrogen bonds.
Fig. 6. Atom numbering in 4-atadip. Dashed lines indicate hydrogen
bonds.
Fig. 5. The arrangement of 4-at units: (a) Zig-zag arrangement in 4-atsuc
structure; (b) The arrangement in 4-atadip structure. Dashed lines indicate
hydrogen bonds.
and Raman intensities using the same basis set. The calcu-
lated geometry and frequencies scaled with precomputed
vibrational scaling factors [39] were compared to the
experimental values.
The UV–Vis–NIR spectrum of 4-atox single crystal was
recorded in the 190–1100 nm range using a Unicam UV
300 spectrometer.
equipped with Nicolet Nexus FT Raman module (2 cmꢁ1
resolution, Happ-Genzel apodization, 1064 nm Nd:YVO4
laser excitation, 450 mW power at the sample) in the
100–3700 cmꢁ1 region.
The quantum chemical calculations were performed by
applying closed-shell restricted Hartree–Fock (HF), Den-
sity Functional Theory (B3LYP) and Møller–Plesset per-
turbation (MP2) methods with the 6-31G and 6-311G
basis sets. The calculations and visualisation of the
results were carried out with the Gaussian 98W [37]
and GaussView [38] program packages. The geometry
optimisations, also yielding the molecular energies, were
followed by frequency calculations together with IR
The measurements of SHG at 800 nm were performed
with 90 fs laser pulses generated at an 82 MHz repetition
rate by a Ti:sapphire laser (Tsunami, Spectra Physics).
For quantitative determination of the SHG efficiency, the
intensity of the back-scattered laser light at 400 nm gener-
ated in the sample was measured by a grating spectrograph
with diode array (InstaSpec II, Oriel) and the signal was
compared with that generated in KDP (i.e. KH2PO4).
The experiment was performed using a powdered sample

I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
51
Fig. 7. Packing scheme of 4-atadip (projection to yz plane). Dashed lines indicate hydrogen bonds.
˚
(75–150 lm particle size) loaded into 5 mm glass cells using
a vibrator and the measurements were repeated on different
areas of the same sample (the results were averaged). This
experimental procedure minimises the signal fluctuations
induced by sample packing.
C7–O9 (1.239(2) A) bonds compared to the C8–O12
˚
(1.211(2) A) bond is in accordance with more intensive
participation of the O10 and O9 atoms in the hydrogen
bond system. Especially oxygen O10 participates in the
two strongest hydrogen bonds of the O–Hꢀ ꢀ ꢀO and N–
Hꢀ ꢀ ꢀO type.
3. Results and discussion
The addition compound 4-atsuc crystallizes in the
monoclinic system with the space group P21/c. Bond
lengths and angles including those of the hydrogen bonds
are listed in Table 3 and the atom numbering is depicted
in Fig. 3. The crystal structure is formed by zig-zag
chains (parallel to b axis) of 4-amino-1,2,4-triazole mole-
cules, connected by N–Hꢀ ꢀ ꢀN hydrogen bonds, and iso-
lated molecules of succinic acid, which interconnect
these chains by strong O–Hꢀ ꢀ ꢀN (2.666(2) and
3.1. Crystal structures
The crystals of 4-atox belong in monoclinic system
(space group P21). The bond lengths and angles including
those of hydrogen bonds are listed in Table 2. The atom
numbering is depicted in Fig. 1. The crystal structure con-
sists of periodically alternating layers (parallel to a axis)
formed by chains of hydrogen oxalate anions connected
˚
2.689(1) A) and medium to weak N–Hꢀ ꢀ ꢀO hydrogen
˚
by O–Hꢀ ꢀ ꢀO hydrogen bonds with lengths of 2.531(2) A.
bonds (see Fig. 4).
The layers are interconnected by 4-amino-1,2,4-triazol-1-
ium cations via N–Hꢀ ꢀ ꢀO hydrogen bonds. These hydrogen
bonds consist of a linear (two-center) H-bond (N6ꢀ ꢀ ꢀO9i
The amine group of the base participates in the N–
Hꢀ ꢀ ꢀN hydrogen bonds (i.e. N6–H6Bꢀ ꢀ ꢀN6ii with the
˚
length of 3.173(2) A) forming the chains (see Fig. 5a) and
˚
distance equal to 2.921(2) A) and two pairs of bifurcated
also in bifurcated bonds of N–Hꢀ ꢀ ꢀO type connecting the
(three-center) H-bonds, connecting the nitrogen atom N3
with oxygens O10 and O12 by the H3 atom (2.711(2) and
N6 atom with oxygens O12 and O14 by H6A atom
˚
(2.848(2) and 3.053(2) A, respectively).
The protonised carboxylic groups of succinic acid attain
two different values for C–O (1.214(2) and 1.217(2) A) and
˚
2.951(2) A, respectively) and amine group nitrogen N6 with
˚
oxygens O9 and O11 by H6A atom (3.031(2) and
˚
˚
3.012(2) A, respectively).
C–O(H) (1.326(2) and 1.321(2) A) bond lengths.
The formation of 4-amino-1,2,4-triazol-1-ium cation by
protonation of the N3 atom results in minimal changes in
the triazole ring geometry. Only slight shortening of the
N1–C2 and N3–N4 distances compared to uncharged mole-
cules were observed in the 4-atsuc and 4-atadip structures (see
Tables 2–4). The cation rings are mutually oriented in paral-
lel with no H-bonds interaction between them (see Fig. 2).
The lengths of the C–O bonds correspond with the
existence of the hydrogen oxalate anion in the crystal
The 4-atadip addition compound, which crystallizes in
a 2:1 (base to acid) ratio, belongs in the monoclinic sys-
tem (space group P21/c). Bond lengths and angles includ-
ing those of the hydrogen bonds are listed in Table 4.
The atom numbering is depicted in Fig. 6. The crystal
structure consists of pairs of parallel linear chains (med-
iated by N–Hꢀ ꢀ ꢀN hydrogen bonds – see Fig. 5b) of 4-
amino-1,2,4-triazole molecules that are interconnected
by isolated adipic acid molecules via strong O–Hꢀ ꢀ ꢀN
and medium N–Hꢀ ꢀ ꢀO hydrogen bonds (see Fig. 7) with
˚
structure. Elongation of the C7–O10 (1.266(2) A) and

52
I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
˚
lengths of 2.669(2) and 2.940(2) A, respectively. Neigh-
bouring chains, which are parallel to the a axis, do not
exhibit any H-bond contact between each other. The
˚
N–Hꢀ ꢀ ꢀN hydrogen bonds with a length of 3.025(2) A
connect nitrogen atom N6 of amine group with triazole
ring atom N4. Different crystal packing (compared to
4-atsuc) is mainly induced by the enhanced steric require-
ments of adipic acid.
As in the case of 4-atsuc, the protonised carboxylic
groups of adipic acid exhibit two different values for the
˚
˚
C–O (1.208(2) A) and C–O(H) (1.305(2) A) bond lengths.
3.2. Geometric optimisation and calculation of vibrational
frequencies
In order to assign the vibrational manifestations of 4-
amino-1,2,4-triazole and 4-amino-1,2,4-triazol-1-ium spe-
cies, computational geometry optimisation followed by
vibrational frequencies calculation were performed. The
selection of functionals (HF, MP2, B3LYP) and basis sets
(6-31G and 6-311G) in principle results from the previous
paper [27] dealing with triazoles.
The results obtained from geometry calculations are
compared with the X-ray structure determination in Tables
5 and 6. According to this comparison, the best results were
obtained for the HF method with the 6-311G basis set for
both calculated species. In the HF method, the value of the
bond lengths fluctuate around the values obtained from the
crystal data. Application of the MP2 and B3LYP methods
leads to systematic overestimation of the bond lengths
except for the value for the N1–N6 bond in the case of
the B3LYP methods. The values of the inter-atomic angles
fluctuate slightly around the values obtained in the crystal
structure determinations.
Tables 7 and 8 contain the calculated and experimental
values of the fundamental frequencies of the 4-amino-1,2,4-
triazole molecule and the 4-amino-1,2,4-triazol-1-ium cat-
ion, respectively. The intensities of the calculated IR and
Raman bands are presented on a relative scale from 0 to
100. The proposed assignment of the vibrational bands is
based on visualisation of the atom motions in the Gauss-
View [38] program. The best match with experimental
records was again observed for the HF/6-311G method.
The largest differences between the calculated and recorded
peak positions were observed for the stretching N–H vibra-
tions because the formation of hydrogen bonds was not
reflected in the calculations.
3.3. Vibrational spectra
The FTIR and FT Raman spectra of 4-atox, 4-atsuc and
4-atadip recorded at room temperature are depicted in
Figs. 8–10, respectively. The assignment of the observed
bands is based on ab initio calculations (HF/6-311G) of
4-at and 4-at(1+) vibrational spectra and previous papers
concerning 4-amino-1,2,4-triazole [1] and carboxylic acids
[40–43].

I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
53
Table 6
Comparison of the results of X-ray structure determination and computational geometry optimisation for 4-amino-l,2,4-triazol-l-ium cation (4-at(l+))
X-ray structure determination for 4-atox
Geometry optimisation
B3LYP/6-311G
˚
HF/6-311G
MP2/6-311G
˚
˚
˚
Bond
(A)
Angle
(ꢀ)
Bond (A)
Angle (ꢀ)
Bond (A)
Angle (ꢀ)
Bond (A)
Angle (ꢀ)
N(1)–C(2)
N(1)–C(5)
N(1)–N(6)
N(3)–N(4)
N(3)–H(3)
N(4)–C(5)
N(6)–H(6A)
N(6)–H(6B)
C(2)–N(3)
1.336(2)
1.362(2)
1.414(2)
1.366(2)
1.01(3)
1.309(2)
0.88(3)
0.82(2)
N(1)–N(6)–H(6A)
N(1)–N(6)–H(6B)
N(3)–C(2)–N(1)
N(4)–N(3)–H(3)
N(4)–C(5)–N(1)
C(2)–N(1)–C(5)
C(2)–N(1)–N(6)
C(2)–N(3)–N(4)
C(2)–N(3)–H(3)
C(5)–N(1)–N(6)
C(5)–N(4)–N(3)
H(6A)–N(6)–H(6B)
106(2)
107(2)
1.355
1.390
1.390
1.390
1.000
1.310
1.000
1.000
1.320
115.00
115.00
105.84
118.69
110.70
107.08
123.21
112.45
128.84
129.69
103.87
118.23
1.330
1.380
1.370
1.370
0.990
1.280
0.990
0.990
1.300
114.42
114.39
106.26
119.32
109.98
107.26
123.42
111.71
128.94
129.32
104.75
117.56
1.360
1.390
1.400
1.400
1.010
1.340
1.010
1.010
1.340
112.94
112.95
105.59
118.53
110.35
108.04
122.06
112.66
128.79
129.90
103.33
116.56
106.7(1)
125(2)
110.9(1)
106.8(1)
124.4(1)
112(1)
1.311(2)
123(2)
128.6(1)
103.8(2)
115(2)
3.3.1. Vibrational spectra of 4-atox
um(1+) cation in the 4-atox structure is the very strong
Raman band of mixed mring, mN–NH2, dNH and dCH
vibrations at 1405 cmꢁ1 (1408 cmꢁ1 in the IR spectrum).
The medium intense bands located in the 1075–1030 cmꢁ1
region, which were assigned to the mixed mring, dCH and
dNH vibrations, are similarly significant. For the assign-
ment of the rest of the 4-at (1+) vibrational bands, see
Table 9.
The strong bands in the 3300–2200 cmꢁ1 region in the
IR spectrum correspond to the stretching vibrations of
the N–H groups connected to the N–Hꢀ ꢀ ꢀO hydrogen
˚
bonds with lengths of 3.031–2.711 A. The band attributed
to the out-of-plane bending mode cN–H(ꢀ ꢀ ꢀO) is located
at 972 cmꢁ1 in the infrared spectrum. The broad, medium
intensity bands in the 2100–1850 cmꢁ1 region in the IR
spectrum (assigned to the O–H stretching vibrations)
reflect the presence of the short O–Hꢀ ꢀ ꢀO hydrogen bond
3.3.2. Vibrational spectra of 4-atsuc and 4-atadip
˚
with a length of 2.531 A. The recorded positions of the
The structured, strong to medium-intensity bands in the
IR spectra and weak bands in the Raman spectra in the
3400–2900 cmꢁ1 region of the both compounds are associ-
ated (according to [44,45]) with the stretching vibrations of
the N–H bonds, which participate in the hydrogen bonds
bands of the N–H and O–H stretching vibrations are in
agreement with the correlation curves [44,45] for the N–
Hꢀ ꢀ ꢀO and O–Hꢀ ꢀ ꢀO hydrogen bonds, which were found
in 4-atox crystal structure.
˚
The band of the stretching C@O vibration, which is
characteristic for the presence of the protonised carbox-
ylic group in the crystal structure, were recorded at
1717 cmꢁ1 (IR spectrum) and 1723 cmꢁ1 (Raman spec-
trum). The strong to medium-intensity bands of the anti-
symmetric (overlapping with triazole vibrations) and
symmetric stretching vibrations of carboxylate COOꢁ
group were observed in the IR spectrum at 1590 and
1428 cmꢁ1, respectively. Other significant manifestations
of the hydrogen oxalate anion are the strong IR-active
bands of the mixed dCOH, mC–O and mCC vibrations at
1266 and 1232 cmꢁ1 or the bands of the mixed mCC,
dCOO and dCOH vibrations at 913, 901 cmꢁ1 (IR) and
890 cmꢁ1 (Raman). The bands of the dCOO vibrations
at 713 cmꢁ1 (IR) or 710 cmꢁ1 (Raman) and xCOO vibra-
tions at 486 cmꢁ1 (IR) or 491 cmꢁ1 (Raman) are also
characteristic.
of N–Hꢀ ꢀ ꢀN (with the lengths of 3.025 and 3.173 A) or
˚
N–Hꢀ ꢀ ꢀO (with lengths of 3.053 and 2.848 A) types.
The manifestations of strong O–Hꢀ ꢀ ꢀN hydrogen
˚
bonds with the lengths of 2.666 and 2.689 A (4-atsuc) or
˚
2.669 A (4-atadip) are very interesting. The corresponding
IR bands (according to H-bonds lengths) of the stretching
O–H vibrations are located in the 2900–2200 cmꢁ1 region.
In any case, broad, weak to medium-intensity bands with
maxima at 1865 cmꢁ1 (4-atsuc) and 1930 cmꢁ1 (4-atadip)
can be interpreted as the result of Fermi interaction of
O–H stretching vibration with the overtones of bending
modes. For example, similar bands were also observed
in the IR spectra of the complexes formed by pyrazoles
[46]. Bands that can be assigned to out-of-plane cO–
H(ꢀ ꢀ ꢀN) bending modes were recorded in the 850–
1010 cmꢁ1 region in the IR spectra of both addition
compounds.
The bands assigned to the triazole C–H group stretching
vibrations were observed at 3148 and 3112 cmꢁ1 in the
Raman spectrum and at 3156 cmꢁ1 in the IR spectrum.
The strong band at 1656 cmꢁ1 recorded in the IR spectrum
is attributed to the deformation vibration of the NH2
group attached to the triazole ring. The most characteristic
band related to the existence of 4-amino-1,2,4-triazolini-
The stretching modes of the CH2 groups of dicarboxylic
acids were recorded in the 2950–2860 cmꢁ1 region. The
more complicated structure of these bands observed in
the case of 4-atadip is in accordance with the higher num-
ber of CH2 groups in the molecule of adipic acid. The
bands of characteristic mC@O stretching modes of carbox-
ylic groups, which are very intensive in the IR spectra, are

Table 7
Calculated (scaled) and measured fundamental frequencies (cmꢁ1) of 4-at molecule
B3LYP
MP2
HF
Measured 4-amino-1,2,4-triazole
6-31G
S.F.a
0.962
IR/
Raman
intensities
6-311G
S.F.a
0.966
IR/
Raman
intensities
6-31G
S.F.a
0.957
IR/
Raman
intensities
6-311G
S.F.a
0.950
IR/
Raman
intensities
6-31G
S.F.a
0.903
IR/
Raman
intensities
6-311G
S.F.a
0.904
IR/
Raman
intensities
Assignment
IR
Raman
230
305
386
491
615
0/1
15/4
3/2
100/3
14/0
232
301
384
561
617
0/0
20/3
3/2
100/2
19/0
220
291
370
470
588
0/1
38/5
6/6
26/0
51/7
220
286
365
533
587
0/1
31/4
5/2
24/0
2/0
241
352
397
564
643
0/1
14/5
2/2
100/4
22/1
235
343
393
635
640
0/1
23/3
4/1
30/1
100/1
cC–N–NH2
sNH2
dC–N–NH2
crg
xNH2, mN–
NH2, drg
crg, sNH2
xNH2, drg
cCH
258 w
353 wb 394 w
417 m
405 w
620 s
629 w
656
680
798
826
0/0
3/6
2/1
9/0
658
685
789
819
0/0
11/7
2/1
628
651
764
791
1/0
100/5
6/2
625
651
750
778
25/7
1/1
21/0
100/4
688
699
890
919
0/1
6/7
1/1
7/1
687
709
864
892
0/1
37/7
1/0
680 m
852 s
889 s
880 s
939 s
679 vs
851 w
13/0
14/5
12/1
cCH
880 w
940 w
830
0/7
845
1/8
794
22/1
803
3/6
922
1/10
949
1/3
drg, mrg,
dCH
908
0/2
14/4
7/4
0/5
911
1/2
20/4
8/6
1/4
869
985
1107
1122
2/3
865
976
1098
1110
2/3
949
0/3
19/5
3/7
5/5
955
2/11
32/5
1/7
mrg, dCH
mrg, dCH
dCH
dCH, mN–
NH2 mrg
mrg, drg,
dCH, dNH2
957 s
961 s
1029
1157
1172
1027
1155
1169
19/4
26/6
1/4
20/5
19/10
1/3
1045
1205
1210
1039
1198
1209
1070 s
1186 s
1205 s
1074 s
1189 s
1208 s
9/6
1243
0/1
1243
0/2
1189
7/2
1181
5/3
1276
0/3
1280
0/3
1292 m
1321 s
1321 w
1244
1348
0/2
0/12
1265
1342
0/3
1/14
1191
1290
0/3
0/8
1202
1275
0/4
0/8
1280
1413
0/2
0/16
1298
1410
1/4
7/21
qNH2
1346 m 1345 m
1382 m 1378 s
mrg, mN–
NH2, dCH
mrg, dCH
mrg, mN–
NH2, dCH,
dNH2
1406
1452
2/1
6/4
1400
1455
3/1
8/4
1346
1389
1/4
16/2
1330
1382
0/3
13/2
1493
1530
5/0
16/9
1479
1530
5/0
27/8
1452 s
1518 s
1449 w
1517 m
1652
3196
3214
3426
3558
7/12
0/40
0/67
2/100
6/47
1671
3170
3190
3404
3532
11/11
0/41
1/69
1/100
6/45
1581
3058
3076
3279
3405
17/12
0/48
1/73
5/100
13/48
1587
3012
3030
3233
3355
17/11
0/50
0/76
2/100
9/46
1679
3162
3181
3432
3563
10/9
0/44
0/75
4/100
11/49
1694
3127
3147
3401
3524
16/9
0/44
1/75
3/100
10/49
dNH2
mCH
mCH
mNH2
mNH2
1625 m 1629 w
3101 m 3108 s
3122 m 3124 s
3200–3330
ꢀ
Note. Abbreviations and symbols: m, stretching; d, deformation or in-plane bending; c, out-of-plane bending; x, wagging; s, torsion; q, rocking; rg, ring.
a
Precomputed vibrational scaling factor [39].

Table 8
Calculated (scaled) and measured fundamental frequencies (cmꢁ1) of 4-at(l+) cation
B3LYP
MP2
HF
Measured 4-amino-1,2.4-triazol-1-ium
chloride
6-31G
S.F.a
0.962
IR/
Raman
intensities
6-311G
S.F.a
0.966
IR/
Raman
intensities
6-31G
S.F.a
0.957
IR/
Raman
intensities
6-311G
S.F.a
0.950
IR/
Raman
intensities
6-31G
S.F.a
0.903
IR/
Raman
intensities
6-311G
S.F.a
0.904
IR/
Raman
intensities
Assignment
IR
Raman
247
273
374
13/3
2/2
70/1
251
273
389
10/1
6/2
11/1
236
261
358
3/1
19/5
4/2
239
260
370
2/1
22/3
4/2
273
351
402
1/1
11/4
4/1
264
345
400
1/1
17/53
4/12
cC–N–NH2
sNH2
dC–N–NH2
290 m
283 w
334 w
412 m
428 m
443 m
569 w
624 s
665 m
678 m
838 m
883 m
932 s
430
627
652
695
790
863
894
89/4
17/0
7/0
3/7
71/1
8/1
465
629
652
695
789
855
900
100/3
13/0
5/0
5/8
59/0
6/0
412
600
624
665
756
826
855
76/6
16/0
4/0
38/6
52/1
27/1
1/0
441
597
619
661
750
813
855
63/5
19/0
0/0
48/6
61/0
22/0
1/0
519
648
669
705
843
924
941
100/5
12/1
15/1
7/7
53/1
6/4
574
639
665
708
812
915
936
100/4
18/0
12/1
17/8
64/0
4/1
xNH2
crg, cCH
575 w
627 w
663 w
680 s
crg, cCH, cNH
xNH2, mrg, dCH
cNH, cCH
cCH
mrg, drg, dNH,
dCH
890 w
933 w
7/3
0/0
3/1
7/3
903
958
1027
1133
1187
1243
0/0
2/4
7/9
4/5
2/2
0/1
903
966
1025
1134
1187
1246
6/3
3/5
8/10
4/5
2/3
2/7
864
917
983
1084
1136
1190
3/4
0/5
7/9
6/7
3/3
4/3
858
918
974
1077
1128
1184
5/3
1/7
7/12
6/8
4/5
4/3
990
4/5
0/0
7/9
3/4
2/3
1/13
996
0/0
cCH, cNH, drg
mrg, dCH
mrg, dCH, dNH
mrg, cCH, dNH
cCH, mrg
1027
1045
1159
1216
1280
1004
1041
1157
1217
1281
12/6
7/11
3/4
3/4
2/14
1027 s
1033 s
1077 s
1157 m
1209 m
1314 m
1078 m
1165 w
1206 m
1311 m
mrg, drg, dCH,
dNH
1247
1339
2/6
4/8
1265
1340
0/2
3/8
1193
1281
0/2
4/21
1202
1273
0/3
3/23
1288
1372
0/2
3/5
1302
1372
0/3
4/5
qNH2
1327 m
1360 m
1334 m
1361 m
mrg, mN–NH2,
dNH, dCH
mrg, mN–NH2,
dNH, dCH
mrg, dNH, dCH,
mN–NH2
mrg, dNH2, dNH,
dCH
dNH2
mCH
mCH
mNH2
mNH2
mNH
1386
1471
1513
3/20
8/5
1380
1471
1515
2/21
8/5
1327
1408
1448
5/5
1311
1397
1439
5/4
1464
1527
1584
1/22
19/8
8/4
1456
1518
1581
3/27
2/7
1408 m
1521 m
1556 w
1637 m
1411 vs
1523 w
1553 w
15/3
4/4
17/4
3/3
13/2
9/2
2/4
1645
3212
3220
3446
3511
3591
a
17/7
33/20
6/79
35/100
100/64
36/43
1661
3186
3195
3421
3519
3564
16/7
23/23
5/76
22/100
79/64
23/42
1574
3074
3081
3298
3360
3437
17/8
31/17
4/90
26/100
100/63
29/46
1578
3027
3035
3250
3343
3386
20/8
29/22
5/85
23/100
100/65
27/43
1677
3163
3177
3422
3509
3567
17/8
19/34
6/75
22/100
82/62
29/46
1688
3131
3145
3398
3518
3536
22/8
20/34
6/72
19/99
94/65
26/45
1644 w
3114 sh
3134 m
3210 w
3130 s
3195 s
)
Precomputed vibrational scaling factor [39].

56
I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
Fig. 8. FTIR (compiled from nujol and fluorolube mulls) and FT Raman spectra of 4-atox.
Fig. 9. FTIR (compiled from nujol and fluorolube mulls) and FT Raman spectra of 4-atsuc.
Fig. 10. FTIR (compiled from nujol and fluorolube mulls) and FT Raman spectra of 4-atadip.

I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
57
Table 9
Table 9 (continued)
FTIR and FT Raman spectra of 4-atox
IR (cmꢁ1
)
Raman (cmꢁ1
)
Assignment
IR (cmꢁ1
)
Raman (cmꢁ1
)
Assignment
134 w
99 w
3280 m
3224 w
3177 m
3156 m
3122 s
3278 w
3224 w
3181 w
3148 m
mN–H(ꢀ ꢀ ꢀO)
Note. Abbreviations and symbols: vs, very strong; s, strong; m, medium;
w, weak; b, broad; sh, shoulder; rg, ring; m, stretching; d, deformation or
in-plane bending; c, out-of-plane bending; q, rocking; x, wagging; twi,
twisting; s, torsion; subscript s, symmetric; subscript as, antisymmetric.
mCH
mN–H(ꢀ ꢀ ꢀO)
3112 m
mCH
3077 m
mN–H(ꢀ ꢀ ꢀO)
3027 w
2993 w
2938 w
2828 w
Table 10
FTIR and FT Raman spectra of 4-atsuc
IR (cmꢁ1
)
Raman (cmꢁ1
)
Assignment
2660 mb
2525 mb
2430 mb
1982 mb
1942 mb
1717 s
1694 m
1656 s
1590 sb
1565 s
3298 m
3149 s
3099 s
3047 m
3007 mb
3297 w
3147 vs
3096 m
3045 w
3004 w
2950 m
2936 s
mN–H(ꢀ ꢀ ꢀO), mN–H(ꢀ ꢀ ꢀN)
mCH
mO–H(ꢀ ꢀ ꢀO)
mN–H(ꢀ ꢀ ꢀO)
mCH2
1723 m
1690 w
mC@O
?
dNH2
2940 m
2890 mb
2830 mb
2730 mb
2595 mb
2515 mb
1865 wb
1786 w
masCOOꢁ
mO–H(ꢀ ꢀ ꢀN)
mrg, dNH2, dNH, dCH
2817 w
2570 w
1561 s
1560 w
1550 s
1521 s
1523 m
1478 w
1441 w
mrg, dNH2, dNH, dCH, mN–NH2
mC–O, dCOH, mCC
1470 m
1455 m
1428 m
1408 s
1368 m
1343 m
1336 sh
1316 sh
?
msCOOꢁ
mrg, mN–NH2, dNH, dCH
1699 s
1699 m
1661 w
1541 w
1532 w
1463 w
mC@O
dNH2
1405 vs
1380 w
1664 m
1541 sh
1531 m
mrg, mN–NH2, dCH, dNH2
qNH2
1337 w
1308 w
1287 s
1274 w
mrg, dCH
dCH2
mrg, drg, dCH, dNH
dCOH, mC–O
dCOH, mC–O, mCC
dCOH, mC–O, mCC
cCH, mrg
1430 sh
1416 m
1383 m
1349 sh
1335 m
1310 s
1419 m
1382 vs
1349 m
1331 m
1266 s
1232 s
1204 sh
mrg, mN–NH2, dCH
qNH2
mrg, drg, dCH, dNH2
mC–O, xCH2, mCC, qCOO
twi CH2
1200 s
1175 m
1154 w
1123 m
1076 m
1044 m
1031 m
dCOH, mC–O, mCC
mrg, cCH, dNH
?
mrg, dCH, dNH
mrg, dCH
1159 m
1284 w
1223 m
1193 m
1219 m
1194 s
1186 s
1169 s
1082 s
dCH, mN–NH2, mrg
dCOH, xCH2, dCH
1083 m
1037 m
twi CH2
mCC, dCCC
mrg, dCH
972 m
cN–H(ꢀ ꢀ ꢀO)
1085 w
1075 m
1059 m
996 s
959 w
935 s
954 w
937 m
?
930 sh
913 s
901 s
850 w
713 s
681 m
mrg, drg, dNH, dCH
mCC, dCOO, dCOH
mCC, dCOO, dCOH, cCH
cNH, cCH
dCOO
xNH2, mrg, dCH
crg, cCH, cNH
1057 m
995 m
961 m
890 s
848 w
710 m
681 m
669 w
663 w
639 w
627 w
560 w
491 s
mCC, dCCC
899 m
890 sh
853 m
797 w
679 w
628 m
623 s
cCH, mCC, mC–O
893 w
678 vs
cCH, cO–H(ꢀ ꢀ ꢀN)
qCH2, cCOO, twi CH2
xNH2, drg
658 w
?
628 s
556 w
486 s
451 m
442 m
410 w
351 m
325 m
crg, cCH
xNH2
xCOO
dC–N–NH2
qCOO, mC–O
626 w
565 w
xNH2, mN–NH2, drg
cCOO, qCH2, cCOH
?
540 w
437 w
407 m
270 w
146 s
dC–N–NH2
sNH2, dC–O, mCC
cC–N–NH2
dCCC, dC–O
twi CC, qCH2
External modes
415 w
dCOO
sNH2
qCOO
387 w
277 w
202 w
150 w
127 w
113 w
81 w
307 w
205 s
188 vs
147 vs
cC–N–NH2
External modes
187 s
152 w

58
I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
located at 1699 cmꢁ1 (4-atsuc) and 1693 cmꢁ1 (4-atadip). If
the positions of this vibration recorded in the IR spectra of
all three compounds (1717 cmꢁ1 in 4-atox) are compared, a
red shift with increasing chain length of the acid is
observed. This trend is in agreement with earlier studies
[40] concerning saturated n-aliphatic acids. Other signifi-
cant bands connected with the presence of carboxylic
groups are the strong bands in the IR spectra at 1310,
1194 and 1186 cmꢁ1 (4-atsuc) or 1283, 1202 and
1193 cmꢁ1 (4-atadip), which are associated especially with
the mC–O, dCOH and xCH2 mixed vibrations. The stretch-
ing mCC vibrations of the skeleton of dicarboxylic acids are
the predominant vibrational motion linked with the strong
Raman bands recorded at 935 and 910 cmꢁ1 in the spectra
of 4-atsuc and 4-atadip, respectively. For the assignment of
the rest of the vibrational manifestations of succinic and
adipic acids in studied addition compounds, see Tables
10 and 11, respectively.
The bands assigned to the stretching C–H vibrations of
triazole ring were observed in the 3180–3070 cmꢁ1 region.
Contrary to our expectations and the results of vibrational
spectra calculations, only one band of the mCH vibration
was recorded in the case of 4-atadip. This observation is
even more interesting in regard of the presence of two 4-
amino-1,2,4-triazole molecules in the asymmetric unit of
4-atadip. Medium intensity bands corresponding to the
deformation vibration of the NH2 group, attached to the
triazole ring, were observed at approx. 1660 and
1620 cmꢁ1 in the spectra of 4-atsuc and 4-atadip, respec-
tively. The blue shift of this vibration in the case of 4-atsuc
compared to 4-atadip is connected with more intensive par-
ticipation of the NH2 group in the system of N–Hꢀ ꢀ ꢀO and
N–Hꢀ ꢀ ꢀN hydrogen bonds in the crystal structure of 4-
atsuc. The most characteristic bands of the 4-amino-
1,2,4-triazole molecule are located at approx. 1530, 1385,
1075, 680 and 625 cmꢁ1 in the spectra of both addition
compounds. For their particular assignment see Tables 10
and 11.
Table 11
FTIR and FT Raman spectra of 4-atadip
IR (cmꢁ1
)
Raman (cmꢁ1
)
Assignment
3335 s
3335 w
3273 w
3208 w
3129 s
3045 w
2935 m
2915 vs
2867 m
2818 w
mN–H(ꢀ ꢀ ꢀO), mN–H(ꢀ ꢀ ꢀN)
3268 m
3209 m
3127 s
mCH
3043 m
2945 m
2925 m
2873 m
2820 m
2792 m
2725 m
2676 m
2644 m
2545 mb
2513 m
2490 m
1930 mb
1809 m
1693 s
mN–H(ꢀ ꢀ ꢀO), mO–H(ꢀ ꢀ ꢀN)
mCH2
mO–H(ꢀ ꢀ ꢀN)
2740 w
2660 w
2570 w
2500 w
?
1689 m
1618 m
1525 m
1470 w
1443 m
1422 s
1411 w
1392 m
1379 s
mC@O
dNH2
1621 m
1529 m
1463 m
1439 m
mrg, mN–NH2, dCH, dNH2
dCH2, mrg, dCH
xCH2
1416 s
1390 sh
1375 s
mrg, mN–NH2, dCH
1367 s
1343 sh
1314 sh
1283 s
1342 m
1305 w
1272 w
1242 w
1223 w
qNH2
twi CH2
xCH2, dCOH, mC–O
xCH2, dCOH, mC–O
twi CH2, qCH2
xCH2, dCOH, mC–O, dCH,
mN–NH2, mrg
mrg, dCH, mCC, dCCC
mCC
cO–H(ꢀ ꢀ ꢀN)
1202 s
1193 s
1077 m
1036 m
1010 m
992 m
957 m
930 m
913 w
899 m
880 s
862 w
734 w
687 w
679 w
668 w
627 s
1197 s
1080 s
1052 m
992 m
957 w
mrg, dCH
drg, mrg, dCH, qCH2, cCOO
mCC, mC–O
cCH
910 s
3.4. Second harmonic generation
876 w
qCH2
Non-centrosymmetric crystals of 4-atox (monoclinic
space group P21) are optically transparent down to
300 nm (see Fig. 11) and thermally stable up to the melt-
ing point at 454 K. Quantitative measurements of the
SHG efficiency were carried out at 800 nm by the modi-
fied powder technique developed by Kurtz and Perry
[47]. The relative efficiency of powdered 4-atox was
observed as equal to 38% compared to KDP. The
observed intensity dependence of SHG is depicted on
Fig. 12.
687 s
681 s
xNH2, drg, qCOO, dCCC
xNH2, drg
qCOO
xNH2, mN–NH2, drg
dC–O , mCC, dCCC
dC–N–NH2
667 w
628 w
507 w
415 w
393 w
385 w
499 w
415 w
396 m
378 w
353 m
sNH2
295 w
264 m
209 w
?
269 w
cC–N–NH2
External modes
Discussed crystals of 4-atox can serve as another exam-
ple of NLO material based on encapsulation of highly
polarisable organic cations carrying NLO properties
between the layers of hydrogen bonding organic anions.
182 w
143 w
121 w
130 vs

I. Matulkova´ et al. / Journal of Molecular Structure 873 (2008) 46–60
59
acid molecules via O–Hꢀ ꢀ ꢀN and N–Hꢀ ꢀ ꢀO hydrogen
bonds. Neighbouring chains do not exhibit any H-bond
contact between each other. Different protonisation of
dicarboxylic acids in 4-atox, 4-atsuc and 4-atadip com-
pounds can be easily explained by the values of the dis-
sociation constants at 298 K [48]. Oxalic acid is a much
stronger acid (pK1 = 1.23, pK2 = 4.19), forming the
hydrogen oxalate of 4-at(1+), than succinic (pK1 = 4.22,
pK2 = 5.70) and adipic (pK1 = 4.44, pK2 = 5.44) acids,
forming addition compounds with 4-at under similar
conditions.
The FTIR and FT Raman spectra of all three com-
pounds were recorded and their interpretation is based
on quantum chemical calculations of the isolated 4-
amino-1,2,4-triazole molecule and its monocation.
The observed SHG efficiency (38% compared to KDP)
together with optical transparency and thermal stability
indicate the possibility of utilisation of 4-atox crystals as
a novel NLO material.
Fig. 11. UV–Vis–NIR spectrum of 4-atox single crystal plate.
Acknowledgements
This work was financially supported by the Grant
Agency of Charles University in Prague (Grant No. 337/
2005/B-Ch) and is part of the long term Research Plan of
the Ministry of Education of the Czech Republic No.
MSM0021620857.
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