Structural and spectral characterization of the compounds nGly·ZnCl2·mH2O (n = 1,2,3; m = 0,2)

Article abstract of DOI:10.1016/j.molstruc.2008.07.012

The coordination behaviour of Zn²⁺ ions in chloride-glycine aqueous solutions and the formation of different complexes were discussed to predict the crystallization of compounds. The crystal structures of three compounds, Gly·ZnCl₂,

Full text of DOI:10.1016/j.molstruc.2008.07.012

Journal of Molecular Structure 918 (2009) 55–63
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structural and spectral characterization of the compounds
nGlyꢀZnCl ꢀmH O (n = 1,2,3; m = 0,2)
2
2
a,
b
b
b
a
c
*
S. Tepavitcharova , D. Havlí cˇ ek , I. N eˇ mec , P. Vojtíšek , D. Rabadjieva , J. Plocek
a
Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bontchev Str., Bl. 11, 1113 Sofia, Bulgaria
b
Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Albertov 2030, 128 40 Prague 2, Czech Republic
c
ˇ
Institute of Inorganic Chemistry of the ASCR, v. v. i., 250 68 Re zˇ u Prahy, Czech Republic
a r t i c l e i n f o
a b s t r a c t
The coordination behaviour of Zn2+ ions in chloride-glycine aqueous solutions and the formation of dif-
ferent complexes were discussed to predict the crystallization of compounds. The crystal structures of
Article history:
Received 18 May 2008
Received in revised form 14 July 2008
Accepted 15 July 2008
Available online 22 July 2008
three compounds, GlyꢀZnCl
determined. The data showed the building units of the crystal structures of compounds 2GlyꢀZnCl
monoclinic crystal system, space group C2/c) and 3GlyꢀZnCl
Pna2 ) to be discrete distorted electroneutral tetrahedra [Zn(Gly)
ions (trans or cis), and isolated H O molecules or Gly zwitterions. Infinite chains of [Zn(Gly)2/2Cl
2
, 2GlyꢀZnCl
2
ꢀ2H
2
O and 3GlyꢀZnCl2, crystallizing from the above solutions were
2 2
ꢀ2H O
(
2
(orthorhombic crystal system, space group
Cl ], only differing in the position of Cl
2 2
ꢁ
1
Keywords:
2
2
] tetra-
GlyꢀZnCl
2
hedra build the crystal structure of the compound GlyꢀZnCl
2 1
(monoclinic crystal system, space group P2 ),
2
GlyꢀZnCl
GlyꢀZnCl
2
ꢀ2H
2
O
ꢁ
thus forming a coordination polymer. The Cl ions are in cis-position and Gly zwitterions are bidentately
coordinated to two neighbouring Zn2 ions, contrary to the monodentate coordination in the previous
two structures. The FTIR and FT Raman spectra of all three compounds were recorded and discussed.
Their thermal behaviour was also studied, the similarities and differences were explained by the struc-
tural features.
3
2
+
Crystal structure
Vibrational spectra
Thermal behaviour
Ó 2008 Elsevier B.V. All rights reserved.
1
. Introduction
2. Experimental
Glycin (Gly,
ent inorganic compounds. Some of them, e.g. triglycine sulphate
TGS) [1], triglycine selenate (TGSe) [2], GlyꢀAgNO [3] and
nGlyꢀMeX ꢀ2H O (Me = Mn, Co; X = Cl, Br; n = 1,2) [4–6] are known
to have ferroelectric properties, or, e.g. 2GlyꢀMnCl ꢀ2H O [7], a high
ꢀ2H O was
a
-aminoacetic acid) forms complexes with differ-
Three compounds, GlyꢀZnCl
2
, 2GlyꢀZnCl
2
ꢀ2H
2
O and 3GlyꢀZnCl
2
,
were obtained from aqueous solutions of Gly and ZnCl
2
by the
(
3
method of isothermal evaporation of the solvent. The molar ratios
were 1:3, 1:1 and 3:1, respectively. The preparative temperature
2
2
o
o
2
2
for the first compound was 50 C and for the others 25 C. Analyt-
ical reagents were used. The anhydrous compound GlyꢀZnCl
hydrated easily while the other two compounds, 2GlyꢀZnCl ꢀ2H
and 3Gly.ZnCl , were stable under standard conditions. The com-
position of the solid phases was confirmed by chemical analyses.
biological activity. Recently the compound 2GlyꢀZnCl
2
2
2
proved to have a potential to regulate the activities of antioxidant
enzymes as well as essential trace elements during fasciolosis in
rats [8,9] and during parasitoses in chicks [10].
2
2
O
2
2
+
The purpose of this paper is to elucidate the coordination
Titrimetric methods (complexometric for Zn ions and neutraliza-
tion analysis in the presence of formaldehyde for Gly [12]) were
applied. The accuracy of the analysis was about 0.1–0.2%. The
water content in the crystal phases was determined gravimetri-
cally and by TG analysis. The N,O-deuterated compounds were pre-
pared by repeated recrystallization of natural compounds from
O (99%) in a desiccator over KOH.
The X-ray data collection was carried out on an Enraf-Nonius
CAD4-MACH III four circle diffractometer (MoKa radiation, graph-
ite monochromator). The intensity was corrected for the Lorentz-
polarization factor. The positions of non-hydrogen atoms were
determined using direct methods (SIR-92) [13], and the hydrogen
atoms were localized on differential Fourier maps. The thermal
parameters were refined anisotropically for the non-hydrogen
2
+
behavior of Zn in chloride-glycine aqueous solutions and to char-
2+
acterize the crystallizing compounds. Zn is a biologically active
trace element whose deficiency is likely to affect a number of
different enzyme systems. The literature data on zinc-glycine com-
pounds are very limited and concern only the system Gly–ZnCl
O [11]. In this paper, crystal structures, vibrational spectra and
the results of TG-DTA measurements on three compounds,
GlyꢀZnCl , 2GlyꢀZnCl ꢀ2H O and 3GlyꢀZnCl , crystallizing from the
above system, are presented and discussed.
2
–
H
2
D
2
2
2
2
2
*
Corresponding author. Tel.: +359 2 979 39 26; fax: +359 2 870 50 24.
E-mail address: stepav@svr.igic.bas.bg (S. Tepavitcharova).
0
022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.07.012

5
6
S. Tepavitcharova et al. / Journal of Molecular Structure 918 (2009) 55–63
atoms and isotropically for the hydrogen atoms. Refinement of
coordinates and thermal parameters was carried out by the least
squares method using the SHELXL 97 program [14]. Crystallo-
groups, or by both simultaneously, the first one being more
2
+
probable. Due to the low energy of the Zn -Cl bond and the
2
+
ꢁ
2
high energy of the Zn -H O bond, only the participation of Cl
graphic data for Gly.ZnCl
deposited with the Cambridge Crystallographic Data Center as sup-
plementary publications CCDC 685696, CCDC 685697 and CCDC
2
, 2Gly.ZnCl
2
ꢀ2H
2
O and 3GlyꢀZnCl
2
were
ions in the formation of zinc complexes is probable. Formation
of tetrahedral zinc-glycine, zinc-chloride and mixed zinc-chlo-
ride-glycine
complexes
[Zn(Gly)Cl
3
],
[Zn(Gly)
2
2
Cl ]
and
6
85698, respectively. Copies of the data can be obtained free of
[Zn(Gly) Cl] is possible in the saturated solutions, but the mixed
3
charge on application to CCDC, 12 Union Road, Cambridge CG21,
EZ, UK (fax: +44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk).
The infrared spectra were recorded by DRIFTS and nujol or flu-
orolube mull (KBr and AgCl windows) techniques on a Nicolet
complexes are predominating. Depending on the conditions
(composition of the solution and temperature) the equilibrium
is shifted towards different ratios of these complexes. The com-
2 2
plexes [Zn(Gly) Cl ] are of a high stability on account of the geo-
ꢁ1
Magna 760 FTIR spectrometer with 2 cm resolution and Happ-
metrical factors. The salt crystallization depends on the
sufficiently high thermodynamic activity in the solution of the
complexes characteristic of its crystal structure and the stability
of this crystal structure.
ꢁ1
Genzel apodization in the 400–4000 cm region.
The Raman spectra of polycrystalline samples were recorded on
a Nicolet Magna 760 FTIR spectrometer equipped with Nicolet
ꢁ1
Nexus FT Raman module (2 cm resolution, Happ-Genzel apodi-
zation, 1064 nm Nd:YVO laser excitation, 300 mW power at the
4
3.1. Crystal structures
ꢁ1
sample) in the 100–3700 cm region.
TG-DTA measurements were carried out on Simultaneous Ther-
mal Analysis Netzsch STA 409, QMG 420. Measurements were
done in synthetic air–atmosphere flowing at a rate of 75 ml/min.
The crystal structures of the compounds 2GlyꢀZnCl
3GlyꢀZnCl have been found to be analogous. Their building units
are discrete distorted electroneutral tetrahedra [Zn(Gly) Cl ] and
isolated H O molecules (Fig. 1) or Gly zwitterions (Fig. 2). The tet-
rahedra in both structures differ in the position of Cl ions only:
trans for 2GlyꢀZnCl ꢀ2H O and cis for 3GlyꢀZnCl2. The Gly zwitteri-
ons are monodentately coordinated to the Zn ion by one oxygen
atom from the carboxyl group. The compound 2GlyꢀZnCl ꢀ2H
crystallizes in the monoclinic crystal system, space group C2/c
in the orthorhombic crystal system,
. All relevant crystallographic data are listed in
2
ꢀ2H
2
O and
2
2
2
Analysis range was 20–750 °C, heating rate, 10 °C/min, and Al
2
O
3
2
ꢁ
was the reference. Sample weight was about 50 mg.
2
2
2
+
3
. Results and discussion
The crystallization from solutions is determined by the avail-
2
2
O
and the compound 3GlyꢀZnCl
2
able complexes which can be incorporated into the crystal struc-
space group Pna2
1
ture without being changed. In the zinc chloride-glycine aqueous
ꢁ
Table 1.
solutions under consideration Cl ions, H
2
O molecules and Gly
Infinite chains of [Zn(Gly)2/2Cl
2
] tetrahedra build the crystal
zwitterions compete for being involved in the coordination shell
2
+
structure of the GlyꢀZnCl
2
compound, thus forming a coordination
polymer (Fig. 3). Contrary to the previous two structures, in this
compound the glycine zwitterions are bidentately coordinated to
of Zn ions, thus forming complexes. The formation of zinc
2+
complexes is connected with appropriate Zn -ligand bond ener-
gies. The coordination of Gly zwitterions occurs easily and may
be achieved by means of oxygen atoms from the carboxyl groups
2
+
two neighbouring Zn ions by the two oxygen atoms from their
ꢁ
carboxyl groups. The Cl ions are in cis-position, similarly to the
(
monodentate or bidentate) or a nitrogen atom from the amino
Fig. 1. Crystal structure of 2GlyꢀZnCl
2
ꢀ2H
2
O with the atom numbering scheme and anisotropic displacement ellipsoids.

S. Tepavitcharova et al. / Journal of Molecular Structure 918 (2009) 55–63
57
Fig. 2. Crystal structure of 3GlyꢀZnCl
2
with the atom numbering scheme and anisotropic displacement ellipsoids.
Table 1
Basic crystallographic data, data collection, and refinement parameters of 2GlyꢀZnCl
2
ꢀ2H
2
O, 3GlyꢀZnCl
2
and GlyꢀZnCl
2
2
2
GlyꢀZnCl ꢀ2H
2
O
3GlyꢀZnCl
2
GlyꢀZnCl
2
CCDC No.
685697
685698
685696
Empirical formula
Formula weight
Temperature
C
4
H
14
N
2
O
6
Cl Zn
2
C
6
H
15
N
3
O
6
Cl
2
Zn
C
2
H
5
Cl
2 2
NO Zn
322.44
293(2)K
0.71073
361.48
293(2)K
0.71073
211.36
293(2) K
0.71073
Wavelength
Crystal system, space
group
Monoclinic, C2/c
Orthorhombic, Pna2
1
Monoclinic, P2
1
Unit cell dimensions
a = 14.4311(6) Å
b = 6.9116(3) Å
b = 126.170(3)°
c = 14.1803(5) Å
a
c
= 90°
= 90°
a = 15.247(2) Å = 90°
b = 11.2090(10) Å
b = 90°
a
a = 4.7330(1) Å;
b = 10.8650(3) Å;
b = 95.978(2)°
a
= 90°
= 90°
c = 15.5530(10) Å
2658.7(5) Å3
c
= 90°
c = 6.2050(2) Å;
c
3
3
Volume
1141.79(8) Å
317.351(15) Å
3
3
3
Z, Calculated density
Absorption coefficient
F(000)
4, 1.876 g/cm
8, 1.807 g/cm
2, 2.212 g/cm
ꢁ
1
ꢁ1
ꢁ1
2.629 mm
656
2.272 mm
4.617 mm
1472
208
Crystal size
h Range for data
collection
0.3 ꢂ 0.3 ꢂ 0.2 mm
0.2 ꢂ 0.3 ꢂ 0.4 mm
0.5 ꢂ 0.4 ꢂ 0.4 mm
3.19–24.97°
2.24–24.97°
3.75–27.50°
Index ranges
Reflections collected/
unique
h(ꢁ17;13), k(0;8), l(ꢁ11;16)
1357/1005 [R(int) = 0.0662]
h(0;18), k(0;13), l(0;18)
2428/2428
h(ꢁ6;5), k(ꢁ14;13), l(ꢁ8;8)
4808/1429 [R(int) = 0.0661]
Completeness to h
Refinement method
Data/restraints/
parameters
h = 24.97° 93.7%
Full-matrix least-squares on F
1005/0/98
h = 24.97° 90.9%
h = 27.50° 99.6%
2
Full-matrix least-squares on F2
Full-matrix least-squares on F2
1429/1/94
2428/0/446
Goodness-of-fit on F2
Final R indices
Reflections observed
R indices (all data)
Largest diff. peak and
hole
1.158
1.071
1.071
R
1
= 0.0286, wR
986
= 0.0290, wR
2
= 0.0668
= 0.0670
R
1
= 0.0218, wR
2222
= 0.0276, wR
2
2
= 0.0549
= 0.0577
R
1
= 0.0356, wR
1426
1
R = 0.0356, wR
2
2
= 0.0906
= 0.0906
R
1
2
R
1
0.580 and ꢁ0.807
0.792 and ꢁ0.243
0.551 and ꢁ0.712
Weighting scheme
w = [r
2(F
0
2
) + (0.0438P) + 0.6101P]
2
ꢁ1
w = [
r
2(F 2
]/3
0
) + (0.0377P)2 + 0.8087P] P = [F 2
ꢁ1
0
w = [
+ 2F ]/3
c
r
2(F 2) + (0.0586P)2 + 0.2685P] P = [F 2
0
ꢁ1
0
2
2
2
2
P = [F
0
+ 2F
c
]/3
+ 2F
c
compound 3GlyꢀZnCl2. The compound crystallizes in monoclinic
crystal system, space group P2 (Table 1).
The bond distances and angles for the three structures are given
in Table 2. They are not significantly different.
(Table 3). Week hydrogen bonds of O–HꢀꢀꢀO, N–HꢀꢀꢀO and N–HꢀꢀꢀCl
O (Table 3). Finally, hydrogen
1
type are typical for 2GlyꢀZnCl
ꢀ2H
2 2
bonds of N–HꢀꢀꢀO and N–HꢀꢀꢀCl type are present in 3GlyꢀZnCl
2
crys-
tal structure (Table 3).
The hydrogen bond network for the compound GlyꢀZnCl
2
is lim-
According to Pauling [15], the least stable of the three structures
is that of GlyꢀZnCl (third Pauling rule). On this basis we assumed
ited only to the bonds of N–HꢀꢀꢀCl type connecting different chains
2

5
8
S. Tepavitcharova et al. / Journal of Molecular Structure 918 (2009) 55–63
2
Fig. 3. Crystal structure of GlyꢀZnCl with the atom numbering scheme and anisotropic displacement ellipsoids.
Table 2
Selected bond lengths (Å) and angles (°)
3
GlyꢀZnCl (mol. 1)
2
3Gly. ZnCl
2
(mol. 2)
2GlyꢀZnCl
2
.2H
2
O (instead O(3) read O(1a), instead Cl(2) read Cl(1a))
2
GlyꢀZnCl (instead O(3) read O(2))
2
+
Geometry of coordinated shell of Zn
Zn–O(1)
Zn–O(3)
Zn–Cl(1)
Zn–Cl(2)
O(1)–Zn–O(3)
O(1)–Zn–Cl(1)
O(1)–Zn–Cl(2)
O(3)–Zn–Cl(1)
O(3)–Zn–Cl(2)
Cl(1)–Zn–Cl(2)
1.967(3)
1.999(3)
2.238(1)
2.274(1)
102.7(1)
119.3(1)
112.4(1)
111.3(1)
101.5(1)
108.19(5)
1.979(3)
2.013(3)
2.225(2)
2.267(1)
103.5(1)
121.2(1)
109.8(1)
110.1(1)
101.6(1)
108.82(6)
1.981(1)
1.981(1)
1.982(3)
1.991(3)
2.238(1)
2.246(1)
101.89(13)
118.98(10)
112.79(10)
106.18(12)
105.88(12)
109.77(4)
2.2346(5)
2.2346(5)
97.84(9)
118.80(5)
107.62(4)
118.80(5)
107.62(4)
106.70(3)
3
GlyꢀZnCl
2
(mol. 1)
3GlyꢀZnCl
2
(mol. 2)
2GlyꢀZnCl
2
.2H
2
O
GlyꢀZnCl
2
Coordinated molecules Gly
Zn–O(2)–C(1)
Zn–O(1)–C(1)
C(1)–O(1)
C(1)–O(2)
C(1)–C(2)
–
–
–
137.65(26)
115.98(28)
1.259(5)
1.242(5)
1.507(5)
112.2(3)
1.286(5)
1.222(6)
1.497(7)
1.491(7)
124.9(4)
112.7(3)
1.269(5)
1.225(5)
1.506(7)
1.466(7)
125.4(4)
120.6(1)
1.265(3)
1.240(3)
1.513(3)
1.471(3)
126.4(2)
C(2)–N(1)
O(1)–C(1)–O(2)
1.464(7)
123.58(36)
3
GlyꢀZnCl
2
(mol. 8)
3GlyꢀZnCl
2
(mol. 9)
Non-coordinated molecule Gly (for 3GlyꢀZnCl
2
only)
C(1)–O(1)
1.262(6)
1.256(6)
1.506(8)
1.472(6)
125.0(6)
1.263(6)
1.245(6)
1.524(8)
1.478(7)
127.1(5)
C(1)–O(2)
C(1)–C(2)
C(2)–N(1)
O(1)–C(1)–O(2)
3
GlyꢀZnCl
2
(mol. 1)
3GlyꢀZnCl
2
(mol. 2)
Coordinated molecule Gly (for 3GlyꢀZnCl
2
only)
Zn–O(3)–C(3)
113.0(3)
1.278 (6)
1.222(6)
1.512(7)
1.457(7)
125.8(4)
115.1(3)
1.276(5)
1.236(6)
1.520(6)
1.466(6)
125.6(4)
C(3)–O(3)
C(3)–O(4)
C(3)–C(4)
O(4)–N(2)
O(3)–C(3)–O(4)
and proved the compound GlyꢀZnCl
2
to crystallize at high temper-
respectively. The assignment of the observed bands (Tables 4–6) is
based on recent papers [16,17] concerningvibrational spectra of gly-
o
atures (50 C). The compounds 2GlyꢀZnCl
ꢀ2H
2 2
O and 3GlyꢀZnCl
2
have to crystallize easily even at low temperatures. Contrary to
cine and our previous paper [18] focused on glycine adducts. The
+
Balkunova et al. [11], we have proved the existence of the com-
assignment of deformation vibrations of the NH
3
group was con-
o
pound 3GlyꢀZnCl
2
even at 25 C.
firmed by recording and analysis of spectra of N,O-deuterated ana-
logues. Vibrational manifestations connected with formation of
2
+
3.2. Vibrational spectra
tetrahedral Zn complexes (i.e. mZn–Cl and mZn–O vibrations) were
assigned according to papers [19,20] dealing with zinc complexes.
And finally, assignment of the bands corresponding to the O–H and
N–H stretching vibrations are in agreement with the curves
The FTIR and FT Raman spectra of GlyꢀZnCl
2
, 2GlyꢀZnCl
2
ꢀ2H
2
O and
3
GlyꢀZnCl recorded at room temperature are depicted in Figs. 4–6,
2

S. Tepavitcharova et al. / Journal of Molecular Structure 918 (2009) 55–63
59
Table 3
Hydrogen bonds in the compounds 2GlyꢀZnCl
2
ꢀ2H
2
O, 3GlyꢀZnCl
d(HꢀꢀꢀA)
Hydrogen bonds with HꢀꢀꢀA < r(A) + 2.000 Å and <DHA >110°
2
and GlyꢀZnCl
2
D–H
d(D–H)
<DHA
d(DꢀꢀꢀA)
A
2
GlyꢀZnCl ꢀ2H
2
2
O
N1–H11
N1–H11
N1–H12
N1–H13
O9–H91
O9–H92
0.82(4)
0.82(4)
0.80(3)
0.87(4)
0.85(4)
0.70(5)
2.46(3)
2.65(3)
2.10(3)
2.01(4)
2.05(4)
2.22(5)
145(4)
124(4)
166(3)
176(3)
171(5)
173(4)
3.174(3)
3.180(3)
2.887(3)
2.876(3)
2.884(3)
2.918(3)
O2 [ꢁxꢁ1/2, ꢁy+1/2, ꢁz]
Cl [xꢁ1/2, y+1/2, z]
O9 [ꢁxꢁ1/2, ꢁy+3/2, ꢁz]
O9 [x, ꢁy+1, z+1/2]
O2
O2 [ꢁx, ꢁy+1, ꢁz]
3GlyꢀZnCl
2
N11–H111
N11–H113
N12–H121
N12–H122
N12–H123
N12–H123
N21–H211
N21–H212
N21–H213
N21–H213
N22–H221
N22–H222
N81–H811
N81–H812
N81–H813
N91–H911
N91–H911
N91–H912
N91–H913
0.84(5)
0.76(5)
0.82(5)
0.79(8)
0.94(7)
0.94(7)
1.32(6)
0.76(6)
0.77(6)
0.77(6)
1.05(9)
0.78(8)
0.76(6)
1.04(7)
0.76(6)
0.88(6)
0.88(6)
1.02(6)
0.87(5)
1.99(5)
2.22(5)
2.13(5)
2.67(8)
2.17(6)
2.64(8)
1.51(6)
2.23(7)
2.51(6)
2.78(5)
1.77(9)
2.26(8)
2.12(6)
1.75(8)
2.19(5)
2.07(6)
2.72(6)
1.96(7)
1.90(5)
160(5)
165(5)
155(4)
176(6)
135(5)
116(5)
154(5)
170(5)
156(5)
122(6)
167(6)
167(6)
149(5)
168(5)
161(5)
138(5)
131(5)
152(8)
174(4)
2.796(6)
2.965(6)
2.891(6)
3.464(5)
2.915(6)
3.166(5)
2.755(6)
2.978(6)
3.233(6)
3.264(5)
2.796(6)
3.032(6)
2.797(6)
2.782(6)
2.923(6)
2.781(6)
3.361(3)
2.898(5)
2.767(5)
O92 [x, yꢁ1, z]
O13 [x+1/2, ꢁyꢁ1/2, z]
O81 [ꢁxꢁ1/2, yꢁ1/2, z+1/2]
Cl22 [xꢁ1/2, ꢁyꢁ1/2, z]
O91 [xꢁ1/2, ꢁyꢁ1/2, z]
Cl21 [xꢁ1/2, ꢁyꢁ1/2, z]
O82 [x, y+1, z]
O23 [xꢁ1/2, ꢁy+1/2, z]
O14 [x, y+1, z]
Cl11 [x, y+1, z]
O92 [ꢁx+1, ꢁy+1, zꢁ1/2]
O81 [x+1/2, ꢁy+1/2, z]
O12 [xꢁ1/2, ꢁyꢁ1/2, z]
O91 [ꢁx, ꢁy, zꢁ1/2]
O24 [xꢁ1/2, ꢁy+1/2, z]
O22 [x+1/2, ꢁy+1/2, z]
Cl21 [x+1/2, ꢁy+1/2, z]
O14 [x+1/2, ꢁyꢁ1/2, z]
O82 [ꢁx+1/2, y+1/2, z+1/2]
GlyꢀZnCl
2
N1–H1A
N1–H1A
N1–H1B
0.89(9)
0.89(9)
0.97(10)
2.56(9)
2.79(9)
2.43(10)
131(7)
141(7)
140(8)
3.215(5)
3.532(6)
3.232(5)
Cl2 [ꢁx, y+1/2, ꢁz]
Cl1 [x, y, zꢁ1]
Cl2 [ꢁx+1, y+1/2, ꢁz]
FTIR
FT Raman
4000
3500
3000
2500
2000
1500
1000
500
0
-
1
Wavenumber [cm ]
Fig. 4. FTIR (compiled from nujol and fluorolube mulls) and FT Raman spectra of GlyꢀZnCl
2
.
[
21,22] correlating the position of vibrational bands with the length
Unequal coordination of glycine zwitterions in studied crystal
structures is reflected in changes of positions of COO stretching
ꢁ
of the appropriate hydrogen bonds found in the crystal structure.
As it was expected, the overall character of the spectra of all
three compounds is generally similar. The main differences can
be observed in N–H or O–H groups stretching region due to differ-
ent hydrogen bonding schemes (see Table 3). For the IR spectra of
vibrations bands. In the case of GlyꢀZnCl
2
(bidentate coordination
of glycine) distance between the bands of symmetric and antisym-
metric stretching vibrations is much higher compared to spectra of
2GlyꢀZnCl
2
2 2
ꢀ2H O and 3GlyꢀZnCl (monodentate coordination of
2
GlyꢀZnCl ꢀ2H
2 2
O and 3GlyꢀZnCl
2
is also typical the presence of sev-
glycine).
ꢁ
1
eral bands in 1900–2700 cm region, which are characteristic for
overtones and combination vibrations.
The changes in positions and intensities of bands in the IR spectra
+
corresponding to NH
3
deformation vibrations (which are sensitive

6
0
S. Tepavitcharova et al. / Journal of Molecular Structure 918 (2009) 55–63
FTIR
FT Raman
4000
3500
3000
2500
2000
1500
1000
500
0
-
1
Wavenumber [cm ]
Fig. 5. FTIR (compiled from nujol and fluorolube mulls) and FT Raman spectra of 2GlyꢀZnCl
2
ꢀ2H
2
O.
FTIR
FT Raman
4000
3500
3000
2500
2000
1500
1000
500
0
-
1
Wavenumber [cm ]
Fig. 6. FTIR (compiled from nujol and fluorolube mulls) and FT Raman spectra of 3GlyꢀZnCl
2
.
todeuteration)inthe1480–1600 cmꢁ1 regioncanbecorrelatedwith
different hydrogen bonding in crystals of all three compounds.
Generally, we can conclude that recorded vibrational spectra of
studied compounds are fully in accord with their refined crystal
structures. The minor differences in position and splitting of gly-
cine vibrational bands can be also explained by increasing number
of structurally independent glycine zwitterions in asymmetric
The decomposition scheme only of the crystal hydrate
O slightly differs from those of the anhydrous com-
2GlyꢀZnCl
2
ꢀ2H
2
pounds. Two-steps dehydration was registered – the first step with
o
a temperature maximum at 104 C when 3/2 molecules of the crys-
o
tal water eliminate and the second one at 138 C when ½ mole-
cules of the crystal water eliminate, respectively.
The second thermal process for 2Gly.ZnCl
2
.2H
2
O and the first
is
units of GlyꢀZnCl
2
, 2GlyꢀZnCl
2
ꢀ2H
2
O and 3GlyꢀZnCl
2
, respectively.
one for the anhydrous compounds GlyꢀZnCl
2
and 3GlyꢀZnCl
2
the glycine melting which runs together with compounds decom-
o
3.3. Thermal behaviour
position. The highest melting temperature (229 C) was registered
for GlyꢀZnCl
tion of glycine zwitterions to Zn exists. For 3GlyꢀZnCl
2GlyꢀZnCl ꢀ2H O with a monodentate coordination of glycine in
their structures the melting temperatures are practically equal –
2
, in whose structure more stable bidentate coordina-
2
+
The thermal behaviour of the compounds GlyꢀZnCl
2
,
2
and
2
GlyꢀZnCl ꢀ2H O and 3GlyꢀZnCl shows a significant similarity (Ta-
2
2
2
2
2
ble 7 and [11]) which follows from their crystal structures.

S. Tepavitcharova et al. / Journal of Molecular Structure 918 (2009) 55–63
61
Table 4
FTIR and FT Raman spectra of GlyꢀZnCl
2
FT Raman (cm 1
ꢁ
)
FTIR (cm
ꢁ1
)
Assignment
FT Raman (cm
ꢁ1
)
FTIR (cm
ꢁ1
)
Assignment
1
1
2
2
3
3
5
54s
65s
Lattice modes
1452s
1460sh
1470sh
1478s
1563s
1589s
1600s
1642s
1736w
2541w
2685w
d
s
NH +
d CH
3
q
CCN
1454m
1471sh
1481s
1563m
1580w
1599w
2
10m
59m
02vs
90m
11s
Lattice modes
d
d
s 3
NH +
+
m
Zn–Cl
CCN
COO
as NH
3
q
q
m
x
c
ꢁ
ꢁ
511m
58w
587m
m
as COO
5
Zn–O
ꢁ
5
87w
COO
?
6
6
20wb
82m
N–H(ꢀꢀꢀX)
ꢁ
d COO
2686w
2799w
2901w
7
8
08w
86w
709m
885m
m
q
s
CCN
CH
2901m
2936m
2976m
3012m
3023m
3100sh
3133s
3187s
3230sh
3489m
9
01m
2
9
1
1
1
1
1
1
19s
919m
2973s
3014m
m
m
s
CH
2
031s
086m
101m
308s
348s
412s
1031m
1087m
1101w
1309s
1348s
1410s
m
q
as CCN
NH
3
as CH
2
+
3098w
3130w
3190w
3235w
m
N–H(ꢀꢀꢀX)
x
s
CH
CH
COO
d CH
2
2
ꢁ
m
s
1
441s
2
Note. Abbreviations and symbols: vs, very strong; s, strong; m, medium; w, weak; b, broad; sh, shoulder;
m
, stretching; d, deformation or in-plane bending; c, out-of-plane
bending; q, rocking; x, wagging; s, twisting; s, symmetric; as, antisymmetric; atom X = O, Cl.
Table 5
FTIR and FT Raman spectra of 2GlyꢀZnCl
2 2
.2H O
FT Raman (cm 1
ꢁ
)
FTIR (cm
ꢁ1
)
Assignment
FT Raman (cm
ꢁ1
)
FTIR (cm
ꢁ1
)
Assignment
ꢁ
1
1
1
2
3
4
5
30m
60s
76s
34m
08s
Lattice modes
1636s
mas COO
d H O
2
?
q
CCN
1653sh
1974w
2036w
2176w
2228w
2280w
2432w
2520m
2553m
2645m
2737m
2826m
2909s
Lattice modes
m
Zn–Cl
CCN
COO
02w
00m
403m
502m
q
q
m
ꢁ
5
55m
Zn–O
ꢁ
5
7
96w
10w
603m
708s
x
COO
ꢁ
d COO ,
CCN
CH
c N–H(...X)
9
04s
m
s
9
1
1
1
1
1
1
11s
917m
q
2
041s
120m
144m
313m
339s
405sh
1044m
1124m
1140m
1310m
1343s
1397s
m
q
as CCN
NH
3
+
2958 s
3017 m
3070w
3197w
2958s
3000sb
3016s
m
m
m
m
s
CH
N–H(ꢀꢀꢀO)
as CH
N–H(ꢀꢀꢀO)
2
x
s
CH
CH
COO
2
2
2
ꢁ
m
s
3045sb
1
411s
1
1
430m
442s
d CH
2
3140sh
3197s
3370s
1444s
481m
1519s
+
1
d
d
s 3
NH
1
1
519m
582m
3340w
3435w
m
m
N–H(ꢀꢀꢀX),
O–H(ꢀꢀꢀO)
m O–H(ꢀꢀꢀO)
+
as NH
3
1
603s
3449s
1
611m
1615sh
o
2
19 and 215 C, respectively. The glycine decomposition and oxi-
the compound GlyꢀZnCl
oxidation of the rests of organics with maximum around
511 °C and simultaneous ZnCl evaporation with maximums
around 562, 594 and 634 C and end at 690 °C (near ZnCl
boiling point). For the compound 3GlyꢀZnCl decomposition
and burning of organic parts is finished around the tempera-
2
it is observable decomposition and
dation of air atmosphere is inhomogeneous process and takes place
in several steps – for 2GlyꢀZnCl ꢀ2H O the maximums are at 260
melting); the most significant steps
are at 290 C (induced by ZnCl melting) and
they are at 244 and 291 C (induced
melting), respectively. The end of the process decomposi-
2
2
2
o
o
and 294 C (induced by ZnCl
2
2
o
for GlyꢀZnCl
2
2
2
o
o
3
17 C; and for 3GlyꢀZnCl
2
by ZnCl
2
ture 582 °C. With rising of temperature the ZnCl
and all effects are over at 720 °C. For 2GlyꢀZnCl .2H
vable ZnCl
and end at 705 °C.
In conclusion, the lower thermal stability possesses
2GlyꢀZnCl
2
evaporates,
tion and oxidation depends on the glycine content in the three
compounds. The highest temperature (582 C) was registered for
GlyꢀZnCl and the lowest, (462 C), for GlyꢀZnCl
The process of ZnCl
small temperature differences for the three compounds. For
2
2
O is obser-
o
2
evaporation with maximums around 541 °C, 567 °C
o
3
2
2
.
2
melting is practically similar, with
a
o
2
ꢀ2H
2
O (up to 78 C) in comparison with the anhydrous

6
2
S. Tepavitcharova et al. / Journal of Molecular Structure 918 (2009) 55–63
Table 6
FTIR and FT Raman spectra of 3GlyꢀZnCl
2
FT Raman (cm 1
ꢁ
)
FTIR (cm
ꢁ1
)
Assignment
CCN
lattice modes
FT Raman (cm
ꢁ1
)
FTIR (cm
ꢁ1
)
Assignment
1
2
2
2
3
3
4
5
5
5
6
6
8
9
9
9
55s
q
1334m
1409s
1417sh
1335sh
1412s
1419s
s
m
CH
COO
2
ꢁ
02m
61m
79s
s
m
Zn–Cl
CCN
1426sh
07m
62w
90w
14w
62w
90m
74w
88w
87m
01s
1440m
1446sh
1486w
1495w
1561w
1583m
d CH
2
q
q
1447s
ꢁ
NH +
as NH +
490w
514m
561m
595m
674w
688w
887m
896m
919s
COO
d
d
s
3
1499s
1562s
m
x
Zn–O
3
ꢁ
COO
ꢁ
d COO
CCN,
CH
1602s
ꢁ
1615w
1631w
1646w
m
as COO
m
s
c
N–H(ꢀꢀꢀX)
1643s
1944wb
2435m
2531m
2615s
2694s
2810s
2877s
12s
30w
q
2
,
c
N–H(ꢀꢀꢀX)
?
929m
9
34m
1031m
035m
1
031m
mas CCN
2620w
1
+
1
1
1
1
1
1
1
099w
113m
126m
135m
301m
316s
1099m
1112m
1127m
1136m
1300s
q
NH
3
m
m
N–H(ꢀꢀꢀO)
2880w
2950sh
2960s
2975sh
3009s
s
CH
2
2960s
x
CH
2
1318s
1325s
3009s
3180sb
m
m
as CH
2
N–H(ꢀꢀꢀX)
321s
s
CH
2
3175w
Table 7
TG-DTA data interpretation of GlyꢀZnCl
2
, 3GlyꢀZnCl
2
, and 2GlyꢀZnCl
2
2
ꢀ2H O in (°C)
Compound Phase transition/effect description
Data from DTA and TG
max (oC)
T
D
T
Dm, %
Calc.
Exp.
GlyꢀZnCl
2
GlyꢀZnCl
Glycine – melting
Glycine – decomposition
2
? Gly" + ZnCl
2
229
290, 317
290
229–462
462–690
ꢁ35.5
ꢁ64.5
ꢁ32.1
ꢁ61.7
ZnCl
ZnCl
2
– melting
2
"
511, 562, 594, 634
3
2
GlyꢀZnCl
2
3GlyꢀZnCl
2
? 3Gly" + ZnCl
2
Glycine – melting
219
244, 291
291
Glycine – decomposition
219–582
582–720
ꢁ62.3
ꢁ37.7
ꢁ63.2
ꢁ33.1
ZnCl
ZnCl
2
– melting
2
"
630
GlyꢀZnCl
2
ꢀ2H
2
O
2GlyꢀZnCl
Step I ? ꢁ1.5H
Step II ? ꢁ0.5H
2
ꢀ2H
2
O ? 2GlyꢀZnCl
2
2
2
+ H O"
O
104
138
78–120
120–194
ꢁ8.4
ꢁ2.8
ꢁ8.7
ꢁ2.5
2
O
2
GlyꢀZnCl
2
? 2 Gly" + ZnCl
2
Glycine – melting
215
Glycine – decomposition
260, 294
294
541, 567
217–501
501–705
ꢁ46.5
ꢁ42.3
ꢁ47.1
ꢁ40.0
ZnCl
ZnCl
2
– melting
"
2
o
compounds GlyꢀZnCl
2
which is stable up to 229 C and 3GlyꢀZnCl
2
–
Pna2
1
). Infinite chains of [Zn(Gly)2/2Cl
2
] tetrahedra form GlyꢀZnCl
2
o
up to 219 C.
(monoclinic crystal system, space group P2
1
).
Vibrational spectra of all three compounds were recorded, ana-
lyzed and assigned. The overall character of the spectra is in accord
with refined crystal structures.
The close thermal behaviour found for the three compounds is
also in accordance with their structural similarity.
4
. Conclusion
The coordination behaviour of Zn2+ ions in aqueous chloride-
glycine solutions and the formation of mixed zinc complexes are
responsible for the salt crystallization. The mixed complexes
Acknowledgements
[
2 2
Zn(Gly) Cl ] have been predicted to be predominating in these
solutions and to be characteristic of the crystal structures of the
crystallizing compounds. The crystal structures of the obtained
The study was carried out with the financial support of the
Bulgarian Academy of Sciences and the Academy of Sciences of
the Czech Republic and is part of a long term Research Plan of
the Ministry of Education of the Czech Republic No.
MSM0021620857.
compounds GlyꢀZnCl
2
, 2GlyꢀZnCl
2
ꢀ2H
2
O and 3GlyꢀZnCl
2
have been
Cl ] are the main building
solved. The discrete tetrahedra [Zn(Gly)
2
2
units for 2GlyꢀZnCl
2
ꢀ2H
2
O (monoclinic crystal system, space group
(orthorhombic crystal system, space group
C2/c) and for 3GlyꢀZnCl
2

S. Tepavitcharova et al. / Journal of Molecular Structure 918 (2009) 55–63
63
[
10] V. Koinarski, M. Gabrashanska, N. Georgieva, P. Petkov, Bull. Veterinary
Institute in Pulawy 50 (2006) 1.
References
[
[
11] L.N. Balkunova, M.K. Kidinov, Zh. Neorg. Khim. 27 (1982) 1040.
12] D.A. Skoog, D.M. West, Fundamentals of Analytical Chemistry, vol. 1, Mir,
Moscow, 1979. p. 258 (in Russian).
13] A. Altomare, M.C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi,
G. Polidori, J. Appl. Cryst. 27 (1994) 435.
14] G.M. Sheldrick, SHELXL-97” Program for Crystal Structure Refinement from
Diffraction Data, University of Göttingen, Göttingen, 1997.
15] L. Pauling, Die Natur der chemischen Bindung, Verlag Chemie, Weinheim,
[
[
1] R. Pepinsky, Y. Okaya, D. Eastman, T. Mitsui, Phys. Rev. 107 (1957) 1538.
2] M.E. Lines, A.M. Glass, Principles and Application of Ferroelectrics and Related
Materials, Mir, Moscow, 1981. p. 137, 360, 695 (in Russian).
3] J.K. Mohana Rao, M.A. Viswamitra, Acta Crystallogr. B28 (1972) 1484.
4] C. Balarew, V. Spasov, S. Tepavitcharova, Ferroelectrics 158 (1994) 157.
5] R. Mrozek, Z. Rz a˛ czy n´ ska, M. Sikorska-Iwan, T. Głowiak, J. Chem. Crystallogr. 29
[
[
[
[
[
[
(
7) (1999) 803.
[
[
6] R. Mrozek, Z. Rz a˛ czy n´ ska, M. Sikorska-Iwan, J. Therm. Anal. Cal. 63 (2001) 839.
7] M. Gabrashanska, S. Tepavitcharova, C. Balarew, M.M. Galvez-Morros, P.
Arambarri, J. Helminthol. 73 (1999) 313.
8] M. Gabrashanska, S. Tepavitcharova, Y. Manga-Gonzalez, S. Ermidou-Pollet, Y.
Mizinska-Boevska, B. Miñambres-Rodríguez, M. Anisimova, in: Proc. 3rd
International Symposium FESTEM, Santiago de Compostela, Spain, 16–19
May, 2007..
1962.
[
[
[
[
[
[
[
16] J. Baran, H. Ratajczak, Vibr. Spectrosc. 43 (2007) 125.
17] A. Matei, N. Drichko, B. Gompf, M. Dressel, Chem. Phys. 316 (2005) 61.
18] I. N eˇ mec, I. Císa rˇ ová, Z. Mi cˇ ka, J. Solid State Chem. 140 (1998) 71.
19] M. Oussaïd, P. Becker, C. Carabatos-Nédelec, Phys. Stat. Sol. (b) 207 (1998) 499.
20] M. Oussaïd, P. Becker, C. Carabatos-Nédelec, Phys. Stat. Sol. (b) 222 (2000) 553.
21] A. Lautié, F. Froment, A. Novak, Spectrosc. Lett. 9 (1976) 289.
22] A. Novak, Struct. Bonding 18 (1973) 177.
[
[
9] M. Gabrashanska, M.Y. Manga-Gonzalez, S. Ermidou-Pollet, M. Anisimova, S.
Tepavitcharova, Trace Elem. Electroly. 25 (2008), in press..