Synthesis and crystal structure of two zinc-containing complexes of triethanolamine

Article abstract of DOI:10.1016/j.poly.2017.04.022

Two new zinc-containing complexes [Zn₂(TEA)(C₆H₅COO)₃] (1) and ([Zn(TEA)(H₂O)₂]SO₄)·H₂O (2) were synthesized and characterized by IR spectroscopy, elemental analysis, DSC and TG analysis. Their structure was determined by single-crystal X-ray diffraction. In the binuclear, mixed-ligand [Zn₂(TEA)(C₆H₅COO)₃] complex, one zinc atom is six-coordinated by nitrogen and three oxygen atoms of tetradentate triethanolamine (TEA) and two oxygen atoms of two different benzoate ligands, forming the distorted octahedron of the ZnNO5 type. The second zinc atom is five-coordinated, forming the distorted trigonal bipyramid. Two zinc atoms are bridged by two carboxylate groups of two benzoate ligands and one oxygen atom of the deprotonated hydroxyethyl group of TEA. Cationic complex 2 consists of [Zn(TEA)(H₂O)₂]²⁺ cations and SO₄^2? anions. The coordination polyhedron around the zinc atom corresponds to a distorted octahedron (ZnNO5 type). The TEA ligand is tetradentately coordinated to the cation, forming three chelate rings. The coordination sphere of the Zn cation is completed by two aqua ligands.

Full text of DOI:10.1016/j.poly.2017.04.022

Accepted Manuscript
Synthesis and crystal structure of two zinc-containing complexes of triethanol-
amine
Y. Kondratenko, V. Fundamensky, I. Ignatyev, A.A. Zolotarev, T. Kochina,
V.L. Ugolkov
PII:
S0277-5387(17)30291-7
DOI:
http://dx.doi.org/10.1016/j.poly.2017.04.022
POLY 12600
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
21 December 2016
18 April 2017
Please cite this article as: Y. Kondratenko, V. Fundamensky, I. Ignatyev, A.A. Zolotarev, T. Kochina, V.L. Ugolkov,
Synthesis and crystal structure of two zinc-containing complexes of triethanolamine, Polyhedron (2017), doi: http://
dx.doi.org/10.1016/j.poly.2017.04.022
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SYNTHESIS AND CRYSTAL STRUCTURE OF TWO ZINC-CONTAINING
COMPLEXES OF TRIETHANOLAMINE
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Y. Kondratenko1, V. Fundamensky1,2, I. Ignatyev3, A.A. Zolotarev4, T. Kochina1,3, V.L.
Ugolkov1
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1 Grebenshchikov Institute of Silicate Chemistry RAS, nab. Makarova, 2, St. Petersburg, 199034
Russia
2St. Petersburg Stt. Inst. Technol., Moskovskii pr. 26, St. Petersburg, Russia
3 Department of radiochemistry, Institute of Chemistry, St. Petersburg State University, 7/9
University emb., St. Petersburg 199034, Russia.
4 Department of Crystallography, Institute of Earth Sciences, St. Petersburg State University,
University Emb., 7/9, 199034 St. Petersburg, Russia
*Corresponding author. Tel.:+78123284802, e-mail: kondratencko.iulia@yandex.ru
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Keywords: zinc complexes; triethanolamine; N,O donor ligands; synthesis; X-ray structure;
thermal behavior.
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Abstract
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Two
new
zinc-containing
complexes
[Zn2(TEA)(C6H5COO)3]
(1)
and
([Zn(TEA)(H2O)2]SO4)·H2O (2) were synthesized and characterized by IR spectroscopy,
elemental analysis, DSC and TG analysis. Their structure was determined by single-crystal X-
ray diffraction. In the binuclear, mixed-ligand [Zn2(TEA)(C6H5COO)3] complex, one zinc atom
is six-coordinated by nitrogen and three oxygen atoms of tetradentate triethanolamine (TEA) and
two oxygen atoms of two different benzoate ligands, forming the distorted octahedron of the
ZnNO5 type. The second zinc atom is five-coordinated, forming the distorted trigonal bipyramid.
Two zinc atoms are bridged by two carboxylate groups of two benzoate ligands and one oxygen
atom of the deprotonated hydroxyethyl group of TEA. Cationic complex 2 consists of
[Zn(TEA)(H2O)2]2+ cations and SO42- anions. The coordination polyhedron around the zinc atom
corresponds to a distorted octahedron (ZnNO5 type). The TEA ligand is tetradentately
coordinated to the cation, forming three chelate rings. The coordination sphere of the Zn cation is
completed by two aqua ligands.
Introduction
The interaction of the triethanolamine (TEA), polydentate N,O-donor ligand, with metal salts
leads to the formation of complexes of different structure. There are cationic mononuclear
complexes, in which metal atoms are usually coordinated by two TEA ligands. The TEA ligand
generally acts as tri(N,O,O’)-, tetra(N,O,O’,O’’)dentate ligand or at the same time as tri- and
tetradentate ligand (fig. 1). This structure was found for complexes TEA with Ni2+ (X=SO4 [1],
X=С6H4(COO)2-1,4 [2], X=C7H4NO3S [3], X=C4O4 [4], X=Cl [5], X=CH3COO [6]), Co2+
(X=C6H4(OCH2COO)2-1,4 [7], X=C7H4NO3S [8], Zn2+ (X= C7H4NO3S [9]), Cu2+ (X= C4O4
[10]) salts (figure 1a); with Cd2+ (X=C7H4NO3S [11], X=C4O4 [12], Hg2+ (X= C7H4NO3S [11])
and Mn2+ (X= C7H4NO3S [13]) salts (figure 1 b); and with Pb2+ (X= NO3 [14]), Cd2+ (X= NO3
[15]), Sr2+ (X= Cl [16], X=2,4-(NO2)2C6H3O [17]), Yb2+ (X= ClO4 [18]) salts (figure 1c). Due to
the chelate cyclic structure of a cation, these complexes can be considered as metallated
alkanolammonium ionic liquids. Earlier, we have reported the synthesis, structure and properties
of protic alkanolammonium ionic liquids based on triethanolammonium salts of biologically
active carbonic acids [19, 20].

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Figure 1. Structure of cationic mononuclear complexes of TEA with metal salts MX2 (M=Cu,
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Zn, Co, etc., X - anion of protic acid)
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The interaction of TEA with metal salts can leads to the formation (neutral or cationic)
mono- bi- and polynuclear mixed-ligand complexes. In the mononuclear mixed-ligand
complexes metal atoms are coordinated by N, O atoms of TEA and atoms of other ligands
(solvents or anions). TEA usually acts as a tetradentate ligand using all donor sites. Structure of
neutral mononuclear complexes presented in fig. 2a was determined for complexes Cd(II) and
Zn(II) with TEA and p-nitrobenzoic acid [21], Cu(II) with TEA and malonic acid [22], orotic
acid [23] and chloride ligand [24]. Structure of cationic mononuclear mixed-ligand complexes
(figure 2b) was found for Cu(II)-containing complexes with TEA and aqua ligands (Z=SO4)
[25]; imidazole and aqua ligands (Z=(ClO4)(C10H8O6)0.5) [26]; and a picrate (PIC) ligand
(Z=(PIC)(H2O)) [27].
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Figure 2. Structure of a) neutral mononuclear mixed-ligand complexes of TEA (X, Y –two
atoms of bidentate ligand or two different monodentate ligands; Z – monodentate ligand (or only
X and Y ligands)); b) cationic mononuclear mixed-ligand complexes of TEA (X, Y –two atoms
of bidentate ligand or two different monodentate ligands; Z- counterion)
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In some cases, TEA can lose one or more of their ethanolic hydrogens being as
triethanolaminate anions, which also behave as ligands similar to TEA [28]. The deprotonation
of TEA often leads to the formation of bi - or polynuclear complexes in which deprotonated
ethanolic oxygen atoms act as bridging ligands. The fragment of the polynuclear complex
structure in which deprotonated branch of TEA couples two metal atoms are presented in figure
3. Polynuclear Cu(II)-containing complexes of deprotonated TEA were prepared by Ozarowski
et al [29], Escovar et al [30], Atria et al [31], Karabach et al [32, 33] and etc.
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Figure 3. Fragment of the polynuclear complex structure (M=Cu, Zn, etc., X,Y,Z - any ligands
(molecules of solvent, anions of acids, etc.)
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Complexes of TEA with metal salts possess catalytic activity and can be used as selective
catalysts for the peroxidative oxidation of alkanes under mild conditions [34, 35], as efficient
catalysts for the hydroxylation of aryl iodides and bromides in water [36], and for selective
oxidation of alkylarenes to phenyl ketones under mild reaction conditions [37]; and as catalysts
of electrochemical reduction of oxygen [38].
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Preliminary pharmacological studies have revealed that transition metal complexes of
TEA protect animals from ethanol and carbon monoxide poisoning [39, 40], and possess
pronounced immune-modulating and antiproliferative properties [41]. The complex of TEA with
zinc 2-methylphenoxyacetate increases the activity of tritophanyl-tRNA-synthesase enzyme by
1.5 times. This exerts the antiangiogenic and antiatherogenic action [42].
In this work, the interaction of TEA with zinc salts was investigated with the purpose of
obtaining new potentially biologically active compounds. A special attention is paid to the study
of the single crystal X-ray structure of complexes and their thermal behavior.
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16 2. Experimental and Theoretical Details
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IR spectra were recorded by the Nicolet 8700 (Thermo Scientific) FTIR spectrometer. Pellets for
studying IR spectra of compounds were produced by pressing in KBr. Elemental analysis was
performed on Elemental analyzer Euro EA3028-NT for the simultaneous determination of C, H,
N. TG and DSC measurements were performed using simultaneous thermal analysis NETZSCH
STA 429 CD with a platinum-rhodium of sample holder of type "TG + DSC" and the possibility
of detecting degradation products. A quadrupole mass spectrometer QMS 403 C (NETZSCH)
was used for analysis of decomposition products that allow to analyze the products of thermal
decomposition in the range from 1 to 121 nuclear-charging units. The measurements were made
in the temperature range from 40 to 650-690 °C under an air (the air flow was 50 cm3 per
minute) using a heating rate of 10 ºC/min. 10 mg ( 0.01 mg) pellets of complexes 1 and 2 were
pressed for analysis.
2.1. The single crystal X-ray diffraction experiment
The single crystal X-ray diffraction experiment of complexes 1 and 2 was performed on Agilent
Technologies Xcalibur Eos diffractometer at 100 K using monochromated MoKα radiation.
Experimental details are shown in Table 1. Structure 1 has been solved by the direct methods and
refined by means of the SHELX program [43] incorporated in the OLEX2 program package
[44]. The carbon-bound H atoms were placed in calculated positions and were included in the
refinement in the ‘riding’ model approximation, with Uiso(H) set to 1.2Ueq(C) and C-H 0.97 Å
for the CH2 groups, Uiso(H) set to 1.5Ueq(C) and C-H 0.96 Å for the CH3 groups and Uiso(H) set
to 1.2Ueq(C) and C-H 0.93 Å for the CH groups. All H atoms bonded to O atoms were located in
a difference Fourier map and refinement isotropic mode.
Empirical absorption correction was applied in CrysAlisPro [45] program complex using
spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.
The structure 2 has been solved and refined by SIR 2014 software [46]. Hydrogen atoms were
determined similar to structure 1.
Supplementary crystallographic data for this paper have been deposited at Cambridge
Crystallographic Data Centre (CCDC 1522775 and 1522777) and can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif.
Table 1. Experimental details
Complex 1
Crystal data
C27H29NO9Zn2
Complex 2
Chemical formula
C6H21NO10SZn

Mr
642.25
Monoclinic, P21/n
100
364.66
Monoclinic, P21/c
100
Crystal system, space group
Temperature (K)
a, b, c (Ǻ)
10.0373 (6),
7.4350 (4),
15.1571 (9),
12.6502 (8)
103.504 (6)
1386.17 (14)
4
14.7208 (10),
18.9814 (13)
99.298 (6)
β (°)
V (Å3)
2767.8 (3)
Z
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Radiation type
MoKα (λ = 0.71073 Å)
1.79
MoKα (λ = 0.71073 Å)
1.97
µ (mm-1)
Crystal size (mm)
0.25 × 0.18 × 0.12
Data collection
Xcalibur, Eos diffractometer
Multi-scan
0.26 × 0.21 × 0.15
Diffractometer
Absorption correction
Tmin, Tmax
Xcalibur, Eos diffractometer
Multi-scan
0.840, 1.000
24838, 6245, 5330
0.664, 1.000
10003, 3926, 3465
No. of measured, independent
and observed [I>2σ(I)]
reflections
Rint
θmin, θmax
0.035
2.767, 27.499
Refinement
0.030, 0.068, 1.05
6245
0.029
2.820, 30.930
R[F2> 2σ(F2)], wR(F2), S
No. of reflections
No. of parameters
No. of restraints
0.039, 0.059, 0.86
3465
172
0
358
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H-atom treatment
mixed
0.43, −0.35
mixed
1.18, −0.69
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∆ρmax, ∆ρmin (eǺ− )
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2.2. Synthesis
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1) Synthesis of the [Zn2(TEA)(C6H5COO)3] complex (1). The methanol solution of TEA (5.5
mmol, 0.82 g) was slowly added to the insoluble in methanol zinc benzoate (5.5 mmol, 1.70 g).
The resulting reaction mixture was stirred during 3 h at 60–65 °C. The dissolution of zinc
benzoate and precipitation of the formed complex was observed during the reaction. The
precipitate was filtered off, and resulting solution was left for crystallization. After 1 day,
colorless crystals were formed, and crystals for X-ray diffraction analysis was selected. The yield
of complex 1 was 65 %. Elemental analysis calculated for C27H29NO9Zn2, %: С 50.49; H 4.55; N
2.18, found, %: С 50.13; H 4.48; N 2.21.
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Zinc benzoate (1a) was prepared by dropping the aqueous solution of sodium benzoate
(17 mmol, 2.44 g) to the aqueous solution of zinc chloride (8.5 mmol, 1.16 g) at stirring and
heating (60-70 °C). The powder of zinc benzoate was precipitated from solution almost
immediately. Precipitate was filtered off, washed with water and dried in the opened air. The
yield of zinc benzoate was 70%.
2) Synthesis of ([Zn(TEA)(H2O)2]SO4)·H2O complex (2). The methanol solution of TEA (4
mmol, 0.60 g) was slowly added to the solution of citric acid (4 mmol, 0.84 g) and zinc sulfate
(ZnSO4·7H2O, 4 mmol, 1.15 g) dissolved in water-methanol mixture. The resulting reaction
mixture was stirred during 3 h at 60–65 °C. After the completion of the reaction, the final
slightly cloudy solution was left for 4 days, and colorless crystals suitable for single crystal X-
ray diffraction were formed. The yield of complex 2 was 62 %. Elemental analysis calculated for
C6H21NO10SZn, %: С 19.76; H 5.80; N 3.84, found, %: С 19.21; H 5.35; N 3.76.

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Complex of the ([Zn(TEA)(H2O)2]SO4)·H2O composition have also been obtained by the
interaction of triethanolamine (5.5 mmol, 0.82 g) with zinc sulfate (ZnSO4·7H2O, 5.5 mmol,
1.57 g) in the water. The resulting reaction mixture was stirred during 2 h at 60–65 °C. During
the reaction a precipitate was observed. After the completion of the reaction, the precipitate was
filtered off, washed with water and dried in the open air. The elemental composition of the
reaction product coincide with the complex composition 2, that is ([Zn(TEA)(H2O)2]SO4)·H2O.
The yield of product was 80%.
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2.3. Computational methods
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Structures of the Zn2(TEA)(C6H5COO)3 molecule and the [Zn(TEA)(H2O)2]+SO4 ion pair was
optimized by using the B3LYP [47, 48] hybrid density functional method. Basis set were the
standard 6-31G(d) set [49] and the Dunning correlation-consistent aug-cc-pVDZ set [50, 51].
Vibrational spectra were calculated at the same levels of theory which were used for obtaining
equilibrium geometries. All these methods and basis sets were used as implemented in the
Gaussian09 program [52].
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3. Results and discussion
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Complex 1. The [Zn2(TEA)(C6H5COO)3] complex (1) was prepared by the interaction of
TEA with zinc benzoate, 1a (the molar ratio 1:1). Zinc benzoate, according to single crystal X-
ray diffraction data, possesses a linear polymeric structure. Each zinc atom is in a distorted
tetrahedral environment, coordinated by four oxygen atoms from four different benzoate ligands.
All benzoate ligands are coordinated to zinc atoms in a bidentate mode. One oxygen atom of the
carboxylate anion is coordinated to one zinc atom and the other oxygen atom to the another zinc
atom [53].
The interaction of polymeric zinc benzoate with TEA leads to the formation of binuclear
complex 1, in which the coordination environment of both zinc atoms changes and the
coordination number of one of them increases to six. The obtaining of the complex 1 is
accompanied by a TEA dissociation to the triethanolaminate-anion [OCH2CH2N(CH2CH2OH)2]-
formation. The coordinating ability of the triethanolaminate-anion is maximal, realizing a
tetradentate coordination by using all N and O atoms. The geometry of deprotonated TEA is
close to the geometry of triethanolammonium cation [N+H(CH2CH2OH)3], formed by a proton
transfer from the protic acid to the TEA molecule [20, 21]. In 1, the distances between N and O
atoms TEA range from 2.727(2) Å to 2.820(2) Å and are close to the corresponding distances in
the cations of triethanolammonium salts, N+H(CH2CH2OH)3·X- [20, 21]. It should be noted that
distance between nitrogen and deprotonated oxygen atom (O4) is slightly higher than the N···O
distances in the other two hydroxyethyl branches of TEA (2.820(2) Ǻ against 2.727(2) and
2.769(2) Ǻ).
The Zn1 atom is six-coordinated by nitrogen (N10) and three oxygen atoms of the
tetradentate deprotonated TEA (O4, O6 and O8) and two oxygen atoms (O1 and O2) of two
different benzoate-ligands. The coordination polyhedron of the Zn1 atom is a distorted
octahedron of the ZnNO5 type, in which the Zn1-O bond lengths are in the range 2.0049(14) -
2.2151(15), the Zn1-N10 bond length is 2.1496(17) Å (table 2). At almost equal distances of Zn-
O and Zn-N, the O1-Zn1-N10 angle is 170.48(6) ° that leads to the distortion of an octahedron.
The Zn2 atom is coordinated by one oxygen atom of deprotonated hydroxyethyl group of
TEA (O4), two oxygen atoms of one benzoate-ligand (O3 and O9) and two oxygen atoms of two
different benzoate-ligands (O7 and O5).
The distance between the Zn2 atom and the O3, O4, O5 and O7 oxygen atoms is equal to
1.9769(15) Å, 1.9818(14) Å, 1.9921(14) Å and 1.9478(15) Å, respectively, whereas the distance
between Zn2 and O9 atoms is significantly higher, 2.561(2) Å. The Addison parameter value for
Zn2 is 0.833. The inclusion in the coordination of the fifth oxygen atom (O9) leads to a distorted

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trigonal-bipyramidal coordination of the Zn2 atom. The angle between axial atoms, O9-Zn2-O4,
is equal to 165.15(6) °. Probably, the geometry of the central atom corresponds to sp3d
hybridized Zn2 atom. sp3d hybridization state of zinc atom was found in tetrasodium
nitrilotrimethylenetriphosphonatozincate tridecahydrate [54]. The sp3d hybridization of the
silicon atom in silatrane, that has the same distorted trigonal-bipyramidal geometry, was
confirmed by quantum chemical calculations [55].
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Thus, two zinc atoms (Zn1 and Zn2) are bridged by the deprotanated oxygen atom of
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TEA and by two carboxylate groups of two benzoate ligands.
The Zn1-Zn2 distance is
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3.1850(5) Ǻ. Two zinc atoms demonstrate different coordination numbers - five (for Zn2) and
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six (for Zn1).
The neighbouring molecules of 1 are linked by relatively weak intermolecular hydrogen
bonds between two OH groups of TEA and oxygen atoms of benzoate ligand as well as by the
deprotonated oxygen atom of TEA of the other molecule (O6-H6···O9 and O8-H8···O4, table 3
and figure 5), thus forming the infinite two-dimensional network.
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Figure 4. The scheme of the complex 1 synthesis and its molecular structure with the atom-
numbering scheme according to single crystal X-ray diffraction
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Figure 5. Crystal structure of complex 1, viewed along the b axis. Dashed lines indicate the
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intermolecular hydrogen bonding.

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The vibrational spectrum of the Zn2(TEA)(C6H5COO)3 calculated at the equilibrium
geometry obtained at the B3LYP/6-31G(d) level of theory (Fig. 6) was used for the assignment
of the IR spectrum (Fig.1S). Equilibrium bond distances of the central fragment of the molecule
are compared with experimental data at Fig. 6.
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Figure 6. Equilibrium bond lengths (B3LYP/6-31(d), Å) of the central fragment of 1 compared
to the corresponding experimental bond lengths (black and green colors correspond to the
experimental and calculated bond distances, respectively)
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This comparison shows that theoretically predicted bond lengths are in a fair agreement
with experimental ones. One exception concerns one Zn2-O9 bond length. In the experimental
X-ray structure it equals 2.561(2) Å (Table 2), while equilibrium distance is 2.277 Å (Fig. 6).
This discrepancy is due to the fact that the weak Zn2-O9 bond is substantially perturbed by the
hydrogen bond O6-H6•••O9 (Table 3). This interaction is not included in our theoretical model.
For the adjacent Zn2-O8 bond this discrepancy is not observed. This effect is not taken into
account in the model of the isolated Zn2(TEA)(C6H5COO)3 complex.
Band at 3220 cm-1 emerge from stretching vibrations of OH bonds bound to oxygen
atoms of neighboring molecules (O6-H6···09 and O8-H8···O4) with O···O interatomic
distances of 2.647(2) Å and 2.628(2) Å lengths. Bands centered at 3030 cm-1 belong to CH
stretchings of phenyl groups and those below are methylene group stretchings. Bands in the
1610–1100 cm-1 and 1030-650 cm-1 ranges are the superposition of C-O stretchings as well as
methylene and phenyl group deformations. The 1060 cm-1 band should be assigned to C-O
stretching modes due to its high intensity.
Complex 2. With the purpose of obtaining new zinc-containing complexes with TEA and
biologically active carboxylic acid we investigated the interaction of TEA with the inorganic
Zn2+ salt and citric acid. However, as a result of this reaction the water-insoluble complex of
[Zn(TEA)(H2O)2]SO4·H2O composition was isolated from the reaction medium.
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The asymmetric unit of 2 consists of the mononuclear [Zn(TEA)(H2O)2]2+ cation, one sulfate
anion and one lattice water molecule. The last two species form the outer sphere of the complex.
The Zn(1) atom is coordinated by nitrogen (N1) and three oxygen (O1, O6 and O9) atoms of the

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tetradentate TEA ligand and two oxygen (O3 and O7) atoms of two water molecules (Fig. 7).
The coordination polyhedron of the zinc atom is a highly distorted octahedron ZnNO5, in which
Zn-O bond lengths and O-Zn-N bond angles are in the range of 1.998(2) - 2.168(3) Ǻ, 80.05(8) -
95.72(8) °, respectively. The Zn-N bond length is 2.119(2) Ǻ, and the O3-Zn1-N1 bond angle is
172.03(8) °. In contrast to the binuclear complex 1, TEA retains all its hydroxyl protons in the
mononuclear cationic complex 2.
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Oxygen atoms of the sulfate anion form hydrogen bonds with OH groups of two different
coordinated water molecules (O3···O5, 2.680(3) Å and O7···O4, 2.726(3) Å) and one OH-group
of TEA (O9···O8, 2.710(3) Å) of one cation and OH-groups of TEA (O1···O2, 2.670(3) Å and
O6···O8, 2.726(3) Å) and coordinated water (O3···O2, 2.640(2) Å) of two neighboring cations.
These interactions along with hydrogen bonds between cations and lattice water molecules
(O7···O10, 2.664(4) Å) as well as between lattice water molecules and sulfate anions (O10···O5,
2.786(3) Å and O10···O4, 2.739(4) Å) link species forming the crystal network (Fig. 8, Table 3).
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Figure 7. View of the structure of complex 2, showing the atom-labelling scheme.
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Figure 8. Crystal structure of complex 2, viewed along the a axis. Dashed lines indicate the
intermolecular hydrogen bonding.
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In the model of the [Zn(TEA)(H2O)2]+ SO4 ion pair only three cation-anion hydrogen bonds are
taken into account. The equilibrium structure of this model optimized at the B3LYP/aug-cc-
pVDZ level of theory is presented in Fig. 9.
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Theoretical Zn-O bond lengths are in a fair agreement with X-ray values despite the fact that
lattice interactions of the [Zn(TEA)(H2O)2]+ ion with similar cations, lattice water and sulfate
anions are not included in the model calculation. The only exclusion is the Zn1-O6 bond length
(experimental – 2.168(3) Å , theoretical 2.475 Å) the oxygen atom of which is involved in the
hydrogen bonding with a sulfate-anion (Table 3).
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16
17
18
19
20
The IR spectrum of 2 (Fig. 2S) in the 4000-3000 cm-1 frequency range is characterized by two
bands centered at 3350 and 3150 cm-1. They obviously stem from hydrogen bonded stretching
vibrations of the [Zn(TEA)(H2O)2]+ cation hydroxyl groups belonging either to Zn coordinated
water molecules or TEA hydroxyl groups. Hydrogen bonds in which these hydroxyl groups are
involved are of two types: one is characterized by O-H···O bond lengths lying in the 2.64-2.68 Å
range, the other in the 2.71-2.79 Å range. Two bands in the 4000-3000 cm-1 frequency range may
be assigned to these two types of H- bonded hydroxyls. Below methylene stretching bands are
situated. Bands in the 1700-1600 cm-1 frequency range belong to bending vibrations of
coordinated water molecules and those below them to stretching and bending vibrations of the
TEA skeleton.
21
22
23
24
25
Figure 9. Equilibrium Zn-O and hydrogen bond lengths (Å) optimized at the B3LYP/aug-cc-
-
pVDZ level of theory of the [Zn(TEA)(H2O)2]+SO4 ion pair compared to the corresponding
experimental bond lengths of 2 (black and green colors correspond to the experimental and
calculated bond distances, respectively)
26
Table 2. Selected bond lengths and angles for 1 and 2 complexes
Bond
d, Ǻ
Bond
d, Ǻ
1
Zn1-O1
Zn1-O2
2.0049(14)
2.1201(15)
Zn2-O3
Zn2-O4
1.9769(15)
1.9818(14)

Zn1-O4
Zn1-O6
Zn1-O8
Zn1-N10
2.1031(14)
2.2151(15)
2.1429(15)
2.1496(17)
Zn2-O5
Zm2-O7
Zn2-O9
1.9921(14)
1.9478(15)
2.561(2)
2
1
Zn1-N1
Zn1-O1
Zn1-O3
Angle
2.119(2)
2.103(2)
1.998(2)
ω, deg
Zn1-O6
Zn1-O7
Zn1-O9
Angle
2.168(3)
2.092(3)
2.153(2)
ω, deg
O1-Zn1-O2
O1-Zn1-O4
O1-Zn1-O6
O1-Zn1-O8
O1-Zn1-N10
O2-Zn1-O6
O2-Zn1-O8
O2-Zn1-N10
O3-Zn2-O7
O3-Zn2-O9
O4-Zn2-O5
O4-Zn2-O7
O4-Zn2-O9
92.55(6)
97.72(6)
102.10(6)
90.14(6)
170.48(6)
82.15(6)
167.65(6)
96.76(6)
114.79(6)
56.32(6)
97.02(6)
108.92(6)
165.15(6)
O4-Zn1-O2
O4-Zn1-O6
O4-Zn1-O8
O4-Zn1-N10
O8-Zn1-O6
O8-Zn1-N10
N10-Zn1-O6
O3-Zn2-O4
O3-Zn2-O5
O5-Zn2-O7
O5-Zn2-O9
O7-Zn2-O9
97.41(6)
160.18(5)
94.16(6)
83.07(6)
85.50(6)
80.34(6)
77.33(6)
109.72(6)
115.05(6)
109.80(6)
86.01(6)
83.44(6)
2
O1-Zn1-N1
O1-Zn1-O3
O1-Zn1-O6
O1-Zn1-O7
O1-Zn1-O9
O3-Zn1-N1
O3-Zn1-O6
O3-Zn1-O7
80.93(8)
101.31(8)
93.93(8)
85.40(8)
158.61(8)
172.03(8)
92.13(7)
92.10(8)
O3-Zn1-O9
O6-Zn1-N1
O6-Zn1-O7
O6-Zn1-O9
O7-Zn1-N1
O7-Zn1-O9
O9-Zn1-N1
98.86(7)
80.05(8)
175.76(8)
92.36(8)
95.72(8)
86.82(8)
80.06(8)
1
2
Table 3. Geometric parameters of the hydrogen bonds in the 1 and 2.
D-H···A
D-H (Ǻ)
H···A (Ǻ)
D···A (Ǻ)
Angle D-H···A,
deg
1
0.87
0.85
1.80
1.78
2
2.647(2)
2.628(2)
167.3
177.2
O6-H6···O9
O8-H8···O4
O1-H···O2
O6-H···O8
O9-H···O8
O3-HA···O5
O3-HB···O2
O7-HA···O10
O7-HB···O4
O10-HA···O5
O10-HB···O4
0.85
0.97
0.84
0.84
0.99
0.96
0.96
0.80
0.85
1.85
1.76
1.88
1.84
1.68
2.85
1.77
2.00
1.90
2.670(3)
2.726(3)
2.710(3)
2.680(3)
2.640(2)
2.664(4)
2.726(3)
2.786(3)
2.739(4)
159.4
170.2
172.3
174.5
163.5
69.3
171.0
169.5
168.4
3

1
2
TG and DSC study of 1 and 2.
The results of the complex thermal analysis of 1 revealed that the destruction proceeds in five
stages (figure 3S). In the 60 - 120°C range the weight loss of 0.86% was observed that is due to
the loss of adsorbed water from the surface of the sample. This is confirmed by the gradual
increase of 18 mass content in gaseous decomposition products. In the range from 154 to 194 °C
the melting of the sample occurred, as evidenced by a symmetrical endothermic effect with a
maximum at 179°C. It can be noted, that after melting the decomposition of complex 1 is
accelerated. After 280°C the active decomposition of 1 is started, which is accompanied by the
liberation of water and carbon dioxide (18 and 44 mass). In the range from 383 to 450°C, the
loss is amounted to 27.38%, accompanied by a strong exothermic effect with three maxima at
403, 413 and 426 °C on DSC curve. In this interval there is an active liberation of water, carbon
dioxide, and benzene (peaks on the curves of 18, 44, 78 and 51 masses). At heating above 559
°C, no significant effects are observed, the decomposition terminates with the formation of solid
residue, that is zinc oxide (26.75 %) at 650 °C.
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
The thermal decomposition of complex 2 (figure 4S) also proceeds in several stages. In the 63 -
112°C range, the process is characterized by the maximum rate of decomposition (DTG curve) at
83°C with a 3.08% mass loss, and the first peak appears on the curve of 18 mass, that is, water is
liberated. In this interval, a small endothermic effect with a maximum at 83°C may be observed
on the DSC curve. In the 93 - 121°C range, the endothermic effect with a maximum at 112 °C is
associated with the melting effect of the sample, after which the rate of decomposition is
increased. The solid residue (26.87 %) is formed at 660 °C, as in the case of complex 1, that is
associated with the zinc oxide formation.
23
24
25
26
27
28
Comparison of the decomposition dynamics of complexes 1 and 2 shows that for sample 2 the
decomposition starts earlier at the beginning of melting (about 112°C), which is accompanied by
water evaporation (loss of coordinated and lattice water). The carbon dioxide liberation starts at
211°C. For sample 1, the decomposition starts after melting at 179 °C. Here, very weak water
evaporation also occurs, and after 280°C the main decomposition of the sample starts that is
accompanied by the water and carbon dioxide liberation.
29
30
Conclusions
31
32
33
34
35
36
37
38
39
40
41
42
Two new mono- and binuclear Zn(II)-containing complexes were obtained by the direct
interaction of TEA with corresponding Zn(II) salts and characterized by IR spectroscopy and
elemental analysis, as well as by complex thermal analysis. In the binuclear complex
[Zn2(TEA)(C6H5COO)3] (1), two zinc atoms have different coordination environments: the first
zinc atom is hexacoordinated with distorted octahedral geometry and the second zinc is
pentacoordinated with distorted trigonal-bipyramidal geometry. The formation of the complex 1
is accompanied by the TEA dissociation. The infinite two-dimensional network of 1 is formed by
[Zn2(TEA)(C6H5COO)3] molecules connected by intermolecular hydrogen bonds. The
comparison of the X-ray structure of 1 with the equilibrium B3LYP/6-31G(d) geometry of the
molecule shows that the absence of these hydrogen bonds in the theoretical model only slightly
affects its structure. In the mononuclear cationic complex, [Zn(TEA)(H2O)2]SO4·H2O,
coordination number of zinc is six with a highly distorted octahedral geometry. Two solvent

1
2
3
4
5
6
(water) molecules are present in the coordination polyhedron of zinc. The crystal structure of 2 is
formed by the [Zn(TEA)(H2O)2]+ cations linked by sulfate anions and water molecules outside
the coordination sphere of zinc. Thermal studies of both complexes reveal that the binuclear
complex 1 is significantly more stable than the cationic mononuclear complex 2. The
endothermic melting peaks of 1 and 2 in the DSC curve were found at 179 °C and 112 °C,
respectively.
7
Acknowledgements
8
9
Scientific researchers were performed at the “Centre for Optical and Laser Materials Research”,
“Chemical Analysis and Materials Research Centre”, “Centre for X-ray Diffraction Studies” and
“Termogravimetric and Calorimetric Research Centre” of Research park of St. Petersburg State
University.
10
11
12
13
The work was supported by the Grant of FASIE (No 10280GU (16.06.2016).

1
2
3
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7
Two new mono- and binuclear complexes were obtained by the direct interaction of triethanolamine
with corresponding Zn(II) salts. Their X-ray single crystal structure was determined and they were
characterized by IR spectroscopy and elemental analysis, as well as by DSC and TG analysis.
8
9

1