Dioxouranium complexes with pentadentate s-triazine Schiff base ligands: Synthesis, crystal structure and optical properties

Article abstract of DOI:10.1016/j.poly.2016.01.014

Using the reactions of 2,4-dihydrazino-(R)-s-triazine (R – methoxy (DHMT)) with salicylaldehyde and o-vanillin ligands 2,4-Bis(2-hydroxybenzylidenehydrazino)-6-methoxy-s-triazin (L1) and 2,4-Bis(2-hydroxy-3-methoxybenzylidenehydrazino)-6-methoxy-s-triazin (L2) were obtained. Using the reaction of 2,4-dihydrazino-(R)-s-triazine (R – amino (DHAT)) with o-vanillin ligand 2,4-Bis(2-hydroxy-3-methoxybenzylidenehydrazino)-6-amino-s-triazine (L3) was obtained. By the reactions of the prepared ligands, derivatives of hydrazo-s-triazine, with uranyl acetate or nitrate, three new complexes were prepared. X-ray diffraction shows that the UO₂²⁺ion is in a pentagonal bipyramidal coordination environment. Two oxygen atoms of the UO₂²⁺ion occupy the axial positions and three atoms of nitrogen and two atoms of oxygen construct the equatorial plane. The uranyl(VI) complexes were characterized by single-crystal X-ray diffraction, UV–vis, fluorescence and IR spectroscopy. Thermal stabilities of the complexes were investigated using thermogravimetric analysis.

Full text of DOI:10.1016/j.poly.2016.01.014

Accepted Manuscript
Dioxouranium complexes with pentadentate s-triazine Schiff base ligands: syn-
thesis, crystal structure and optical properties
Lubomír Pavelek, Vít Ladányi, Marek Nečas, Silvie Vallová, Kamil Wichterle
PII:
S0277-5387(16)00018-8
DOI:
http://dx.doi.org/10.1016/j.poly.2016.01.014
POLY 11776
Reference:
Polyhedron
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Accepted Date:
3 November 2015
9 January 2016
Please cite this article as: L. Pavelek, V. Ladányi, M. Nečas, S. Vallová, K. Wichterle, Dioxouranium complexes
with pentadentate s-triazine Schiff base ligands: synthesis, crystal structure and optical properties, Polyhedron
(2016), doi: http://dx.doi.org/10.1016/j.poly.2016.01.014
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Dioxouranium complexes with pentadentate s-triazine Schiff
base ligands: synthesis, crystal structure and optical
properties
Lubomír Pavelek a,*, Vít Ladányi b,c, Marek Nečas b,d, Silvie Vallová a, Kamil Wichterle a
a
Department of Chemistry, Faculty of Metallurgy and Materials Engineering, VŠB-Technical
University of Ostrava, 17. listopadu 15, Ostrava-Poruba CZ-70833, Czech Republic
b
Department of Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno
CZ-61137, Czech Republic
c
RECETOX, Faculty of Science, Masaryk University, Kamenice 5, 62500 Brno CZ-62500,
Czech Republic
d
CEITEC – Central European Institute of Technology, Masaryk University, Kamenice 5, 625 00
Brno-Bohunice CZ-62500, Czech Republic
* Corresponding author. Tel.: +420 704735413; E-mail address: lubomir.pavelek@vsb.cz
Abstract: Using the reactions of 2,4-dihydrazino-(R)-s-triazine (R – methoxy (DHMT)) with
salicylaldehyde and o-vanillin ligands 2,4-Bis(2-hydroxybenzylidenehydrazino)-6-methoxy-s-
triazin (L1) and 2,4-Bis(2-hydroxy-3-methoxybenzylidenehydrazino)-6-methoxy-s-triazin (L2)
were obtained. Using the reaction of 2,4-dihydrazino-(R)-s-triazine (R – amino (DHAT)) with o-
vanillin ligand 2,4-Bis(2-hydroxy-3-methoxybenzylidenehydrazino)-6-amino-s-triazine (L3) was
obtained. By the reactions of the prepared ligands, derivatives of hydrazo- s-triazine, with uranyl
acetate or nitrate, four new complexes were prepared. X-ray diffraction shows that the UO22+ ion
2+
is in a pentagonal bipyramidal coordination environment. Two oxygen atoms of the UO2 ion
occupy the axial positions and three atoms of nitrogen and two atoms of oxygen construct the
equatorial plane. The uranyl(VI) complexes were characterized by single-crystal X-ray diffraction,
UV-vis, fluorescence and IR spectroscopy. Thermal stabilities of the complexes were investigated
using thermogravimetric analysis.
Keywords: Uranyl(VI), Complexes, Triazine ligands, X-ray structure, Optical properties
1. Introduction
The chemical compound 1,3,5-triazine, (C3N3H3), also known as s-triazine, is a symmetric six-
membered N-heterocyclic aromatic ring consisting of alternating carbon and nitrogen atoms.
Chlorinated derivative of s-1,3,5-triazine called cyanuric chloride (C3N3Cl3) and its derivatives are
currently intensively studied heterocyclic compounds with interesting biological qualities for
pharmaceutical industry, mainly antifungal, antibacterial, antimalaric and antineoplastic [1-6]. In

2
addition to the applications of s-1,3,5-triazine derivatives, their usage in rubber-making or textile
industry is extremely important as well [7]. Nitrogen-rich derivatives have potential to be used as
energetic explosives [8].
By simple substitution of chlorine atoms in cyanuric chloride, using controlled conditions
(temperature) and different nucleophiles, various 2,4,6-mono, di- and trisubstituted, symmetrical
and non-symmetrical derivatives bearing different substituents can be prepared [9-11]. Cyanuric
chloride has temperature-dependent differential reactivity for displacement of chlorides with
nucleophiles during SNAr as shown in reaction Scheme 1 [12, 13].
Please insert Scheme 1 here
Cyanuric chloride reacts efficiently with hydrazine hydrate to give mono-, di- or tri- substituted
hydrazo- derivatives [14]. Several prepared and well explored hydrazo- s-triazines derivatives
already exist. s-Triazine derivatives are of considerable current interest in coordination chemistry
and supramolecular chemistry [15]. 2,4,6-trisubstituted-triazine derivatives proved their great
potential in field of material chemistry, both for their π-interaction abilities and for their aptitude
to be involved in intricate H-bond networks [16, 17].
Ramírez et al. published a study on the complexation of two bis-tridentate triazine ligands with
large metal ions Hg(II) and Pb(II) [18, 19]. A new triazine-based ligand with threefold symmetry
gave five heptacoordinate complexes in reaction with Mn(II) [20]. By the reaction of 2,4,6-tris(2-
isopropylidene-1-yl)hydrazono-1,3,5-triazine with Zn(II) salt, a mononuclear complex with a
trigonal bipyramidal geometry around the Zn(II) was prepared [21]. Tei and coworkers published
the preparation of powdered Eu(III) and Gd(III) complexes by the reaction with triazine-
dihydrazino-tetracetate polydentate ligands [22].
The coordination chemistry of uranium has experienced increasing attention over recent years
[23-25]. Uranium element in oxidation state VI typically forms a particularly stable uranyl(VI) ion
2+
(UO2 ) [26, 27]. Some uranyl(VI) complexes are based on structural motifs of 2,6-
diacetylpyridine derivatives. These complexes exhibit pentagonal bipyramidal or hexagonal
bipyramidal coordination spheres [28-30].
This study reports a preparation of three chelating ligands from the reaction of s-triazine as a
common base with salicylaldehyde and o-vanillin as demonstrated in Scheme 2. By the reaction of
these ligands with uranyl salts (acetate and nitrate), three complexes of uranyl(VI) featuring
pentagonal bipyramidal UO22+ metal ions were prepared.
2. Experimental
2.1. Reagents and techniques
The chemicals used in this experiment were commercially available reagents and were used
without further purification. UO2(OCOCH3)2·2H2O (Lachema), UO2(NO3)2·6H2O (Lachema),
N,N-Dimethylformamide (Sigma-Aldrich, 98%), cyanuric chloride (Aldrich, 99%), hydrazine
hydrate (Sigma-Aldrich, 50-60%), sodium bicarbonate (Sigma-Aldrich), methanol (Sigma-

3
Aldrich, anhydrous, 99.8%), tetrahydrofuran (Sigma-Aldrich, anhydrous, 99.9%), ammonia
solution (Sigma-Aldrich, 28%), acetone (Sigma-Aldrich) and deionized water were used to
synthesized the complexes.
FT-IR spectra were recorded using ATR technique by ALPHA FT-IR spectrometer (Bruker) in
the 4000 – 400 cm-1 region. The reported FT-IR signal intensities were defined as w = weak, m =
medium and s = strong. Elemental analysis (C, H and N) were performed using Elementar Vario
EL III. Single-crystals were collected on a Rigaku MicroMax-007 HF rotating anode four-circle
diffractometer with Mo-Kα radiation. The temperature during data collection was 120(2) K. The
structures were solved by direct methods and refined using the full-matrix least-squares method on
F2 with anisotropic thermal parameters for all nonhydrogen atoms (ShelXTL) [31, 32]. A
summary of the crystallographic data and structure refinement parameters is given in Table 3. The
molecular graphics as well as additional structural calculations were drawn and interpreted using
Diamond, ver. 3.2 (http://www.crystalimpact.com/diamond/Default.htm).
UV-vis absorption spectra of ligands and complexes were recorded using a Shimadzu UV-1602
spectrophotometer or GBC Scientific Equipment Cintra 2020 spectrophotometer in 1-cm quartz
cuvette. The fluorescence emission spectra were performed on a FLS 920 fluorescence
spectrometer (Edinburgh instruments) equipped with a 450 W Xe lamp and PMT detector with a
double grating monochromator for both the excitation and the emission. The measurements were
performed in 1-cm fluorescence cuvettes in front face-geometry arrangement.
The thermogravimetric analyses of the complex 1 was performed using simultaneous TG-DTA
apparatus Netzsch STA 409 EP equipped with a high-sensitive analytical balance for measuring
the mass change of the sample as a function of temperature or time (TG curves). The sample
carrier system contains the type S thermocouples (Pt10%Rh-Pt) to measure the temperature and
the temperature difference (DTA curves). Thermal analyses of the complexes 2 and 3 (TG/DSC)
were done on a Netzsch STA 449C Jupiter apparatus. Samples (1-10 mg in weight) were heated
up to 1000 °C in the crucibles (α-Al2O3) in a dynamic atmosphere of a dry air (flow rate of 100
cm3 min-1; complex 1) or a synthetic air (flow rate of 70 cm3 min-1; complexes 2 and 3) at a
heating rate of 10 °C min-1.
X-ray diffraction (XRD) patterns were recorded on a Bruker AXS D8 Advance X-ray
diffractometer with silicon strip detector LynxEye. The diffractometer operated at: radiation
CoKα, 40 kV and 40 mA, step mode with steps 0.014o 2θ and time 1s on steps. For the
calculations of the lattice parameters and the size of the coherent diffraction domain the Rietveld
method was used (Bruker Diffrac Topas program, version 4.2).
2.2. Synthesis of ligands L1, L2 and L3
The synthetic pathways to obtain intermediate and final compounds are shown in Scheme 2.
Stage 1: Cyanuric chloride (13.0 g, 70 mmol) was added into a solution of sodium bicarbonate
(6.5 g, 77 mmol) in methanol (100 ml) at 10 ºC and the resulting suspension was stirred for 1 h at
room temperature. Solid white product was removed by filtration. Dry product was recrystallized
in hot hexane to give 2,4-dichloro-6-methoxy-s-triazine (DCMT). DCAT (2,4-dichloro-6-amino-

4
s-triazine) was prepared by using a similar procedure: cyanuric chloride (13.0 g, 70 mmol) was
dissolved in acetone (30 mL) at 0 ºC and poured into 35 mL of iced-water to form a very fine
suspension. The resulting suspension was stirred for 15 min at 0 ºC and then ammonium
hydroxide solution (13.6 g, 28%, 108 mmol) was being gradually added. The mixture was stirred
at 0 ºC for 30 min and room temperature for 30 min. White solid was filtered, washed with water
(2x 100 mL) and dried to obtain pure DCAT.
Stage 2: DCMT (10.05 g, 55.56 mmol) or DCAT (9.2 g, 55.56 mmol) was suspended in
tetrahydrofuran (200 ml) and stirred vigorously for 10 min. One portion of hydrazine hydrate
(11.5 g, 0.227 mol) was added at room temperature and stirred for 1 h. After that, the mixture was
refluxed for additional 12 h. The solution was cooled at room temperature. Cold distilled water
was added into solutions and the precipitated products were collected by filtration and dried to
obtain pure DHMT (2,4-Dihydrazino-6-methoxy-s-triazine) and DHAT (2,4-Dihydrazino-6-
amino-s-triazin) powders.
Stage 3: A reaction sequence according to Scheme 2 for L1 and L2: DHMT (1.37 g, 8 mmol)
was dissolved in 200 mL of anhydrous tetrahydrofuran and then added in one step salicylaldehyde
(L1) (1.95 mL, 16 mmol) or o-vanillin (L2) (2.43 g, 16 mmol). The solution was heated under
reflux over the night. After cooling the solutions to room temperature, the crude products were
obtained as a white (L1) and yellow powders (L2). Ligand L3 was prepared by a similar
procedure: DHAT (1.25 g, 8 mmol) was dissolved in 200 mL of anhydrous tetrahydrofuran and
then o-vanillin (L1) (1.95 ml, 16 mmol) was added to produce ultrafine powders.
For L1 (white powder): Yield: 31%. Elemental analysis (calcd) for C18H17N7O3 (379.37): C,
56.99; H, 4.52; N, 25.84%. Found: C, 56.78; H, 4.61; N, 25.69%. IR (ATR, ν/cm-1): ν = 3568 (w);
2914 (w); 1618 (s); 1574 (s); 1516 (s); 1479 (s); 1366 (s); 1268 (m); 1156 (m); 951 (w); 799 (m);
742 (s).
For L2 (yellow powder): Yield: 32%. Elemental analysis (calcd) for C20H21N7O5 (439.42): C,
54.67; H, 4.82; N, 22.31%. Found: C, 54.53; H, 4.71; N, 22.19%. IR (ATR, ν/cm-1): ν = 3542 (w);
2933 (w); 1621 (s); 1578 (s); 1516 (s); 1461 (m); 1371 (s); 1269 (m); 1172 (m); 952 (w); 804 (m);
748 (s).
For L3 (yellow powder): Yield: 38%. Anal. Calcd. for C19H20N8O4 (424.41): C, 53.77; H, 4.75;
N, 26.40%. Found: C, 53.62; H, 4.89; N, 26.28%. IR (ATR, ν/cm-1): ν = 3484 (w); 3268 (w);
3177 (w); 2978 (w); 1566 (s); 1471 (m); 1422 (s); 1246 (s); 1077 (w); 725 (w).
Please insert Scheme 2 here
2.3. Synthesis of complex [UO2(L1)]·2(DMF) (1)
Caution: Uranium salts were used during the procedure of these experiments, which entailed
radioactive hazards associated with uranium salts. Uranium is a toxic metal so care had to be taken
during the manipulation.
A suspension of L1 (379.4 mg; 1 mmol) in DMF (30 mL) and UO2(OCOCH3)2·2H2O (424 mg;
1 mmol) was treated with Et3N (1.51 mL; 1.5 mmol). The final solution was stirred for 1 h and

5
subsequently filtered. The dark red filtrate was left to evaporate slowly, giving dark red crystals
suitable for X-ray diffraction analysis, formed after three weeks. The crystals were filtered off,
washed with a little diethyl ether and stored under vacuum. Yield: 23%. Elemental analysis (calcd)
for C24H29N9O7U (793.59) (1): C, 36.32; H, 3.68; N, 15.89%. Found: C, 36.19; H, 3.81; N,
15.34%. IR (ATR, ν/cm-1): ν = 3141 (w); 2956 (w); 1651 (s); 1602 (m); 1537 (s); 1461 (m); 1385
(w); 1357 (m); 1092 (w); 889 (s); 797 (m); 752 (m); 662 (w).
2.4. Synthesis of complex [UO2(L2)]·2(DMF) (2)
The synthesis of 2 was performed in the same way as the preparation of 1, using ligand L2
(439.4 mg; 1 mmol). Dark red plate crystals in 20% yield. Elemental analysis (calcd) for
C26H33N9O9U (853.64) (2): C, 36.58; H, 3.90; N, 14.77%. Found: C, 36.42; H, 3.77; N, 14.61%.
IR (ATR, ν/cm-1): ν = 3451 (w); 2933 (w); 2833 (w); 1654 (s); 1531 (s); 1455 (m); 1384 (s); 1248
(m); 1215 (w); 1082 (m); 889 (s); 744 (w); 726 (w); 663 (w).
2.5. Synthesis of complex [UO2(L3)]·2(DMF) (3)
A suspension of L3 (424.4 mg; 1 mmol) in DMF (30 mL) and UO2(NO3)2 ·6H2O (502 mg; 1
mmol) was treated with Et3N (1.51 mL; 1.5 mmol). The resulting solution was stirred for 1 h and
subsequently filtered. The dark red filtrate was left to evaporate slowly, giving dark red pillar
crystals suitable for X-ray diffraction analysis, formed after three weeks. The crystals were filtered
off, washed with a little diethyl ether and stored under vacuum. Yield: 30%. Elemental analysis
(calcd) for: C25H32N10O8U (838.64) (3): C, 35.81; H, 3.85; N, 16.70%. Found: C, 35.55; H, 3.98;
N, 16.60%. IR (ATR, ν/cm-1): ν = 3420 (w); 3341 (m); 3250 (w); 2927 (w); 1651 (s); 1614 (s);
1508 (m); 1437 (s); 1247 (m); 1081 (m); 890 (s); 745 (m).
3. Results and discussion
3.1. IR spectra
The infrared spectra of the three complexes 1-3 were recorded in the region 4000-500 cm-1 (Fig.
S1-S3 in ESI). The vibrational spectrum is one of the most effective methods to characterize the
U=O bonding in uranyl complexes. This study shows that the ligands are well suited to form stable
complexes with dioxouranium(VI) units. In the spectra of [UO2(L1)]·2(DMF) (1),
[UO2(L2)]·2(DMF) (2) and [UO2(L3)]·2(DMF) (3), the presence of the UO22+ unit is confirmed by
a strong band at 890 cm-1 (Table 1) [33]. After coordination, the various vibrations of U-O are
assigned to bands occurring at 550-520 cm-1 and U-N are assigned to weak bands occurring at
420-410 cm-1, respectively, which confirms the involvement of the oxygen and nitrogen atoms in
the coordination sphere of uranyl(VI) [34]. The characteristic C=N stretching of triazine ring in
L1, L2 and L3 appears as a strong signal in the range of 1580-1560 cm-1. Weak absorption bands
in the region 3200-2900 cm-1 are typical of NH stretching vibrations in hydrazine side chain and a
series of absorption bands in the range 1270-1150 cm-1 are typical of the C-O-C bonds [35]. The
absorption bands around 3450-3250 cm-1 in complex 3 are assigned to antisymmetric and

6
symmetric stretching vibrations of the NH2 group [36]. The shift in N-N positions in the spectra is
indicative of bonding of the hydrazine nitrogen to uranyl(VI) (Table 1) [37].
Please insert Table 1 here
3.2. UV-vis and luminescence properties
Solutions of the ligands and complexes for absorption and fluorescence spectra were prepared
in DMF. The calculation of molar absorption coefficients of the ligands and complexes is
presented in Table 2. The L1 ligand has two strong absorption bands at 302 nm, 342 nm and a
weak absorption band with maximum around 375–405 nm (Fig. 1). The L2 ligand has one strong
absorption band with maximum at 318 nm and a weak absorption band with maximum around
392–410 nm. The hump in 360–366 nm region is caused by changing the lamp in a
spectrophotometer. The L3 ligand has one strong absorption band with maximum at 314 nm. The
absorption maxima of the uranyl complexes are found at 321 nm (1), 320 nm (2) and 311 nm (3).
All the three uranyl complexes have weaker absorption properties than the respective ligands and
their spectra are bathochromically shifted by long tail up to 600 nm.
Please insert Table 2 here
Please insert Figure 1 here
Fluorescence spectra of ligands and complexes were measured upon the excitation wavelength
around their absorption maximum. Presented spectra were collected from three repetitions.
All fluorescence spectra have uniform shape with one broad band and one maximum (Fig. S4
in ESI). Spectra of ligands L2 and L3 and all uranyl(VI) complexes 1–3 have the emission
maximum around 415 nm (L2: 414 nm, L3: 414.5 nm, 1: 416 nm, 2: 416.5 nm, 3: 415 nm). The
emission maximum of the ligand L1 (Fig. 2) is from these values slightly bathochromically shifted
to 429 nm (ca. 14 nm shift). The emission intensity of the uranyl(VI) complexes decreases steeply
towards longer wavelengths to the emission maximum, unlike in the case of ligands L2 and L3.
Please insert Figure 2 here
Fluorescence emission spectra of uranyl(VI) complexes are very similar to emission spectra of
ligands which indicates that emission especially comes from the ligands, not from uranyl(VI)
cation. We assume that uranyl(VI) central ion specifically affected ligand fluorophores by
coordination that causes characteristic shape and emission maximum of the complexes.
3.3. X-ray structure of complexes 1, 2 and 3.
In all the present compounds, UO2 units are perpendicularly embedded in approximate
pentagonal formations (Fig. 3) of donor atoms, giving overall seven-coordinate uranium atoms

7
(Fig. 4). The uranium atom and the five donor atoms of the ligand fit in least-squares planes with
r.m.s. deviations ranging from 0.0324 Å in 1 to 0.1165 Å in 3. The deviations from planarity are
further developed in the ligand frameworks, being particularly pronounced in 2 and 3. The planes
of aromatic rings C1 to C6 and C12 to C17 are progressively deflected from the aforementioned
least-squares planes through the uranium and the donor atoms (Fig. 5). All methoxy groups are
essentially in-plane with the attached aromatic rings, giving rise to torsion angles not larger than
4.8(5) °.
Selected bond lengths and angles are listed in Table 4. The present structures are best compared
with
related
uranyl
complexes
derived
from
2,6-diacetylpyridine-bis(4-
methoxybenzoylhydrazone) (x1), 2,6-diacetylpyridine-bis(N4-phenylsemicarbazone) (x2) and 2,6-
diacetylpyridine(benzoylhydrazone)-(N4-phenylsemicarbazone) (x3) [38, 39]. While the N-U-N
bond angles in 1 to 3 are very similar to related angles in x1 to x3, the O-U-N angles are
significantly wider as a result of larger bite distances of donor atoms attached to aromatic rings in
1 to 3. Accordingly, the O-U-O angles in 1 to 3 are narrower, while still larger than in sterically
less confined environments in seven-coordinate uranium complexes with a tridentate and two
monodentate ligands [40, 41]. All the 1 to 3 crystallize with two molecules of DMF per formula
unit. In spite of the presence of DMF which is often found to complete coordination polyhedra of
uranyl complexes with salen-type ligands [42-44], interactions between DMF and the uranium
atoms in 1 to 3 were not observed. Obviously, the narrow O-U-O angles prevent an increase of the
uranium coordination number to eight that is observed for the related complex x2 in the presence
of DMSO.
Although coordinate bonds were not observed between DMF molecules and the uranium atoms,
N-H…O hydrogen bonds connect all the NH moieties of the ligands with the DMF molecules.
While in 2 and 3 this results in [UO2(L2)]·2(DMF) and [UO2(L3)]·2(DMF) units, respectively,
due to a simple 1:1 N-H…O bonding pattern, in 1 supramolecular dimers are formed through 1:2
N-H…O bonds, as shown in Figure 6. The N…O donor-to-acceptor distances in these hydrogen
bonds range from 2.691(6) to 3.065(6) Å. The presence of NH2 moiety in 3 leads to the formation
of a group of N-H…O interactions between neighboring [UO2(L3)] molecules, with N…O donor-
to-acceptor distances ranging from 2.966(3) to 3.147(3) Å. A linear hydrogen-bonded chain is thus
formed which extends along the crystallographic c-direction (Fig. 7).
Please insert Figure 3 here
Please insert Figure 4, 5, 6, 7 here
Please insert Table 3 here

Please insert Table 4 here

3.4. Thermal analyses
TG and DTA/DSC experiments show that the complexes 1 and 2 follow similar decomposition
pathways. The first weight losses up to 200 °C correspond to the evaporation of DMF. The thermal
degradation proceeds in two stages in temperature range 300-600 °C (Figs. S5(1)-S6(2) in ESI),
starting with a precipitous mass decrease accompanied by strong exothermic effects with a maximum
at 380 °C for 1 and 351 and 422 °C for 2, respectively. The following decomposition proceeds over a
broader temperature range between 400 and 600 °C.
Please insert Figure 8 here
Please insert Table 5 here
The TG curve of 3 again shows the loss of DMF up to 230 °C and subsequent decomposition of the
organic part of the complex. In opposite to 1 and 2, the thermal degradation of 3 is initiated by a
gradual mass decrease over a broad temperature range up to 500 °C, followed by a sudden weight drop
accompanied by a strong exothermic effect with a maximum at 550 °C. As suggested by a shoulder
peak near the exothermic maximum, the step consists of at least two reaction processes. Powder XRD
measurement done on the residue left after the thermal decomposition of 3 confirmed the U3O8 phase
(Fig. S7 in ESI). The thermal analysis data are summarized in Table 5 including theoretical weight
losses calculated for the transformation of the complexes to U3O8.
4. Conclusions
This work has presented the preparation of three novel pentadentate triazine-based ligands and their
mononuclear UVIO2 complexes, which were characterized by X-ray crystallography and IR, UV-vis,
fluorescence spectroscopy and TG/DTA/DSC. The ligands are bound to the UVIO2 units using one of
the triazine N atoms and two chelate arms, giving overall five-coordinate uranyl cations. Higher metal
coordination numbers resulting from the saturation of the coordination sphere by DMF were not
achieved due to small O-U-O angles. The DMF molecules interact with the NH units of the ligands by
hydrogen bonding and a supramolecular 1D chain is allowed through N-H···O hydrogen bonding in
the presence of the ligand with NH2 moiety.
The prepared ligands L1-L3 confirm the usefulness of novel pentadentate triazine-based derivatives
as excellent in-plane chelating ligands, which are easily derivatized and can be considered as
interesting alternatives to salen ligands.
Acknowledgments
This work was supported by the Ministry of Education of the Czech Republic (SP2014/43) and
European Regional Development Fund (CZ.1.05/1.1.00/02.0068). The X-ray part of the work was

10
carried out with the support of X-ray Diffraction and Bio-SAXS Core Facility of CEITEC. The authors
thank Michal Babiak (Masaryk University) for helpful comments concerning X-ray analysis, Zdeněk
Moravec for TG/DSC measurements (Masaryk University), Gabriela Ondrušková and Ján Krausko
(Masaryk University) for luminescent measurements.
Appendix A. Supplementary Data
X-ray crystallographic files in CIF format have been deposited at the Cambridge Crystallographic
Data Center, CCDC Nos. 1060125, 1060126 and 1432228. This material is available free of charge on
the Internet at via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated with this article can be found, in the
online version.

11
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13
Figure captions
Scheme 1. Differential reactivity of cyanuric chloride with R-NH2, R1-NH2, R2-NH2 = N nucleophiles.
Scheme 2. Reagents and conditions: (a) NH3 (aq), CH3COCH3, 0 ºC, 1 h; (b) CH3OH, NaHCO3, 10 ºC,
1 h; (c) N2H4·H2O, THF, reflux 12 h; (d) CH3OH, reflux 24 h.
Fig. 1. The molar absorption coefficients spectra of ligands L1–L3, complexes 1–3.
Fig. 2. Fluorescence emission spectra of ligand L1 and complex 1. Concentration and excitation
wavelength of L1: c = 5.5 · 10-4 M, λexc = 300 nm, 1: c = 6.3 · 10-5 M, λexc = 321 nm.
Fig. 3. Coordination polyhedron of the uranium atom in 1.
Fig. 4. The structure of 1 showing the atom labeling scheme. Thermal ellipsoids are drawn at the 50%
probability level.
Fig. 5. Conformations of 1, 2 and 3 (from top). Angles of aromatic ring planes to equatorial
coordination planes (see text) are 8.3/7.8° (1), 26.1/7.9° (2), and 28.6/28.7° (3).
Fig. 6. Hydrogen bonding pattern in 1.
Fig. 7. Linear polymers of 3 resulting from multiple N-H…O hydrogen bonds.
Fig. 8. TG and DSC curves for 3.

14
Scheme 1.

15
Scheme 2.

16
Fig. 1.

17
Fig. 2.

18
Fig. 3.

19
Fig. 4.

20
Fig. 5.

21
Fig. 6.

22
Fig. 7.

23
Fig. 8.

24
Table 1 Selected infrared spectral data of ligands L1, L2, L3 and complexes 1, 2 and 3 (ν/cm-1).
Ligand/
complex
Triazine bands
Selected Type
of stretching
ν
asymU-
O
ν
symU-O
U-O
U-N
(phenolic)
L1
1
1573 (C=N)
1651, 1602, 1537, 1461
1578 (C=N)
1038-952 (N-N);
1032-969 (N-N)
1048-942 (N-N)
1055-959
-
-
-
-
409
-
889
-
860
-
520
-
L2
2
1645, 1599, 1527, 1459
1566 (C=N)
890
-
863
-
518
-
414
-
L3
3
1020-940 (N-N)
1032-969 (N-N);
3338 (NH2)
1651, 1614, 1551, 1508
890
858
521
412

25
Table 2
Absorption properties of ligands L1–L3 and complexes 1–3.
λmax, nm, (ε, mol-1 dm3 cm-1)
293 (33600), 302 (38800), 332 (36500), 342 (37400), 375 (4900),
405 (3500)
L1
308 (25000), 321 (25800), 361 (25200)
318 (43700), 344 (21500), 392 (3400), 410 (3100)
320 (28000), 366 (19700)
1
L2
2
315 (39600), 340 (21200)
L3
3
311 (32600), 371 (16200)
Concentration of L1 c = 1.5 · 10-5 M, 1 c = 3.5 · 10-5 M, L2 c = 1.4 · 10-5 M, 2 c = 4.9 · 10-5 M, L3
c = 4.5 · 10-5 M, 3 c = 2.7 · 10-5 M.

26
Table 3
X-ray structure data collection and refinement parameters for complex [UO2(L1)]·2(DMF) (1),
[UO2(L2)]·2(DMF) (2), [UO2(L3)]·2(DMF) (3).
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C24H29N9O7U
793.59
C26H33N9O9U
853.64
C25H32N10O8U
838.64
monoclinic
P21/c
monoclinic
P21/c
orthorhombic
P212121
13.8612(6)
22.7398(8)
8.9752(4)
90
8.338(4)
26.555(3)
13.767(2)
90
12.58820(10)
13.89550(10)
17.5978(2)
90
b (Å)
c (Å)
α (°)
β (°)
102.849(4)
90
90.36(2)
90
90
γ (°)
90
V (Å3)
2758.2(2)
4
3048.2(16)
4
3078.20(5)
4
Z
Dcalcd. (g·cm-3)
1.911
1.860
1.810
F(000)
1536
1664
1632
µ(mm-1)
5.946
5.392
5.336
Measured/unique reflections
Data/restraints/parameters
R1/wR2 [I >2σ(I)]
R1/wR2 [all data]
GooF
15012/5045
5045/6/375
0.0337/0.0751
0.0382/0.0785
1.038
17135/5562
5562/0/413
0.0481/0.0942
0.0634/0.1013
1.169
18424/5623
5623/0/397
0.0151/0.0386
0.0153/0.0387
1.088
∆ρmax /∆ρmin (e. Å-3)
2.680/-1.256
3.491/-1.155
0.961/-0.391

Table 4
Selected bond lengths [Å] and angles [°] for [UO2(L1)]·2(DMF) (1), [UO2(L2)]·2(DMF) (2), [UO2(L3)]·2(DMF) (3) and related compounds
[UO2(x1)], [UO2(x2)(DMSO)] and [UO2(x3)].
[UO2(x1)]a
[UO2(x2)(DMSO)]b
[UO2(x3)]b
1
2
3
U1–O1
1.772(3)
1.770(3)
2.210(4)
2.216(3)
2.613(4)
2.610(4)
2.495(4)
174.07(16)
94.89(13)
69.62(13)
69.89(13)
62.75(13)
62.90(13)
1.776(5)
1.775(5)
2.223(5)
2.205(5)
2.596(6)
2.608(6)
2.499(6)
175.8(2)
96.46(18)
69.84(19)
69.73(18)
61.92(19)
62.52(19)
1.7791(19)
1.7803(19)
2.235(2)
2.225(2)
2.597(2)
2.576(2)
2.503(2)
176.54(8)
96.43(8)
69.97(7)
70.11(8)
62.31(8)
62.11(8)
1.77(1)
1.77(1)
2.32(1)
2.30(1)
2.47(1)
2.49(1)
2.52(1)
178.8(5)
106.8(5)
63.5(5)
63.3(4)
63.3(4)
63.3(4)
1.752(5)
1.763(5)
2.360(5)
2.368(5)
2.559(6)
2.583(6)
2.610(6)
1.70(2)
1.726(1)
2.30(1)
2.33(1)
2.53(2)
2.55(2)
2.54(2)
U1–O2
U1–O3
U1–O4
U1–N1
U1–N6
U1–N7
O1–U1–O2
O3–U1–O4
O3–U1–N1
O4–U1–N6
N1–U1–N7
N6–U1–N7
113.7(2)
61.5(2)
61.3(2)
61.6(2)
61.1(2)
109.9(6)
62.7(5)
63.7(6)
61.2(5)
62.4(6)
X-ray diffraction data collected at 295 Ka and 293 Kb.

Table 5
Thermal analysis data for complexes 1 – 3.
Mass loss I
Residual
massfound
c/calcd d (%)
34.5/35.4
Mass loss IIb
(%)
Complex
Step I (°C)
found/calcd a
Endo I (°C)
Step IIb (°C)
Exo IIb (°C)
∆mtot(%)
(%)
1
2
130-170
124-153
18.8/18.4
16.0/17.1
150
140
350-415
330-387
387-443
529-600
34.0
27.6
14.6
32.6
380
351
422
550
65.5
66.8
33.3/32.9
3
142-235
17.2/17.4
160
66.15
33.5/33.5
a Mass loss calculated for two molecules of DMF.
b Values given for prominent exothermic event(s).
c Values given for t = 650 °C
dResidual mass calculated for U3O8 established by XRD (Fig. S7).

Graphical abstract – pictogram
Three new mononuclear uranyl complexes have been synthesized using three new Schiff-base
ligands based on s-triazine derivative. Crystal structures show pentagonal bipyramidal geometry
around uranium atom with the 3-aza and 2-oxo coordinating sites of the ligand.