Polynuclear complexes of vanadium(IV) and lithium with branched triazine-based Schiff base ligands

Article abstract of DOI:10.1080/00958972.2020.1807016

Four dendrimeric hexa- or nona-dentate Schiff base ligands based on triazine structure and several lithium and vanadium(IV) complexes with these ligands were synthesized and characterized by elemental analysis, ¹H NMR and IR spectra. The synthe

Full text of DOI:10.1080/00958972.2020.1807016

Journal of Coordination Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Polynuclear complexes of vanadium(IV) and
lithium with branched triazine-based Schiff base
ligands
Anna Jurowska , Maciej Hodorowicz & Janusz Szklarzewicz
To cite this article: Anna Jurowska , Maciej Hodorowicz & Janusz Szklarzewicz
(2020) Polynuclear complexes of vanadium(IV) and lithium with branched triazine-
based Schiff base ligands, Journal of Coordination Chemistry, 73:14, 2069-2084, DOI:
10.1080/00958972.2020.1807016
To link to this article: https://doi.org/10.1080/00958972.2020.1807016
View supplementary material
Published online: 24 Aug 2020.
Submit your article to this journal
Article views: 17
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gcoo20

JOURNAL OF COORDINATION CHEMISTRY
2020, VOL. 73, NO. 14, 2069–2084
https://doi.org/10.1080/00958972.2020.1807016
Polynuclear complexes of vanadium(IV) and lithium with
branched triazine-based Schiff base ligands
Anna Jurowska, Maciej Hodorowicz and Janusz Szklarzewicz
ꢀ
Faculty of Chemistry, Jagiellonian University, Krakow, Poland
ABSTRACT
ARTICLE HISTORY
Received 15 April 2020
Accepted 16 July 2020
Four dendrimeric hexa- or nona-dentate Schiff base ligands based
on triazine structure and several lithium and vanadium(IV) com-
plexes with these ligands were synthesized and characterized by
1
KEYWORDS
elemental analysis, H NMR and IR spectra. The synthetic methods
Triazine; Schiff base;
vanadium; lithium;
spectroscopy
are described, and we paid special attention to the need to use a
co-ligand (in case of vanadium complexes) to prevent the cre-
ation of polynuclear systems. All complexes belong to a small
group of compounds with dendrimeric Schiff base ligands.
1. Introduction
Control of structures using supramolecular interactions is an area of great interest in
chemistry and biochemistry as well as in crystal engineering [1, 2]. Crystal engineering
CONTACT Janusz Szklarzewicz
Jagiellonian University, Gronostajowa 2, 30-387 Krakow, Poland
Szklarze@Chemia.uj.edu.pl, Janusz.szklarzewicz@uj.edu.pl
Faculty of Chemistry,
ꢀ
Supplemental data for this article is available online at https://doi.org/10.1080/00958972.2020.1807016.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2070
A. JUROWSKA ET AL.
and supramolecular synthetic methodology require knowledge of the strength and dir-
ectional characteristics of the intermolecular forces. Part of supramolecular chemistry
concentrates on dendrimers which are monodispersed, highly branched molecules ter-
minated with multiple functional groups. Their structures lead to several interesting
properties, including good solubility and low viscosity [3, 4]. Many dendritic architec-
tures have been described, including polyamines [5], polyphenylene [6], triazine-con-
taining dendrimers [7, 8], polyamidoamines [9], carbosilanes [10] and polynuclear
metal complexes [11].
1,3,5-Triazine-containing compounds are powerful chelating agents and have been
used for preparation of metal complexes [12] and liquid crystals [13]. S-triazine deriva-
tives have proven their great potential in supramolecular chemistry [14]. Recently tria-
zines have found extensive use as reagents in the conversion of functional groups
[15]. Stepwise selective substitution of cyanuric chloride is utilized in the preparation
of triazine-based dendrimers [16]. The systematic replacement of chlorine atoms under
appropriate temperature improves the utility of this inexpensive and readily available
compound for the preparation of mono-, di- and tri-substituted S-triazines [17, 18] and
offers access to a number of useful molecules, from medicinal chemistry to advanced
materials [19, 20]. Despite the possibility to obtain mono- and di-substituted triazines
we concentrated only on tri-substituted products due to the problems with substitu-
tion of the remaining chlorine atoms by NH2 group of hydrazides in the next step of
the synthesis. Most literature data relate to the properties and applications of triazine
derivatives, but the number of papers with formation of complexes based on triazine
is very limited.
In the present paper we describe the synthesis of four dendrimeric Schiff base
ligands based on triazine which were used in synthesis of lithium and vanadium com-
plexes. The composition of ligands and complexes was determined based on elemen-
1
tal analysis, IR and H NMR spectra.
2. Experimental
2.1. Materials and methods
In syntheses the 2,4,6-trichloro-1,3,5-triazine, 4-hydroxybenzaldehyde, 4-hydroxyaceto-
phenone, sodium hydroxide, 4-pyridinecarboxylic acid hydrazide, 3-pyridinecarboxylic
acid hydrazide, 2-pyridinecarboxylic acid hydrazide, 3-hydroxy-2-naphthoic acid hydra-
zide, acetone, THF, [VO(acac)2], metallic lithium and NaOH were used. All chemicals
were of analytical grade (Aldrich) and were used as supplied. Microanalysis of carbon,
hydrogen and nitrogen were performed using an Elementar Vario MICRO Cube elem-
ental analyzer. Magnetic susceptibility measurements were performed on
a
SHERWOOD SCIENTIFIC magnetic susceptibility balance. Solid samples for IR spectros-
1
copy were recorded on a Nicolet iS5 FT-IR spectrophotometer. H NMR spectra were
measured on a Bruker AVANCE III 600 MHz Instrument in DMSO-d6. Thermogravimetric
measurements were performed on
a
TGA/SDTA 851e Mettler Toledo
Microthermogavimeter at scan speed 10 ꢀ/min from 25 to 600 ꢀC under argon. The
vanadium content in complexes was determined using spectrometric determination of
vanadium peroxides, the calibration curve was made using NH4VO3. The electronic

JOURNAL OF COORDINATION CHEMISTRY
2071
absorption spectra in UV-Vis range were recorded on a Shimadzu UV-3600 UV-Vis-NIR
spectrophotometer equipped with a CPS-240 temperature controller.
2.2. Synthetic procedures
2.2.1. Synthesis of 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine (1) [N3C3(-OC6H4-p-CHO)3]
2,4,6-tris(4-formylphenoxy)-1,3,5-triazine (1) was synthesized according to general lit-
erature method [21]. To 2,4,6-trichloro-1,3,5-triazine (0.012 mol, 2.30 g) in 20 mL of
acetone, 4-hydroxybenzaldehyde (0.036 mol, 4.43 g), dissolved in 20 mL of acetone was
added. The reaction mixture was stirred and held in an ice bath (0–5 ꢀC) as long as
the NaOH (0.037 mol, 1.51 g), dissolved in 15 mL of water, was added. The mixture was
stirred at room temperature for 120 minutes and then heated at 70 ꢀC in an oil bath
for 180 minutes. The white precipitate was filtered off, washed with water and air
dried. Yield: 85%. Anal. Calc. for C24H15N3O6: C, 65.31; H, 3.43; N, 9.52%. Found: C,
64.37; H, 3.38; N, 9.57%. IR (ATR, cmꢁ1): 1698 (C ¼ O), 1567 (C ¼ Ntriazine), 1162 (C–O),
842 (C–Ntriazine).
2.2.2. Synthesis of 2,4,6-tris(4-acetylphenoxy)-1,3,5-triazine (2) [N3C3(-OC6H4-
p-CH3O)3]
2,4,6-tris(4-acetylphenoxy)-1,3,5-triazine (2) was synthesized similarly to 1. To 2,4,6-tri-
chloro-1,3,5-triazine (0.012 mol, 2.30 g) in 20 mL of acetone, 4-hydroxyacetophenone
(0.036 mol, 5.03 g), dissolved in 20 mL of acetone, was added. The reaction mixture
was stirred and held in an ice bath (0–5 ꢀC) as long as the NaOH (0.037 mol, 1.53 g),
dissolved in 15 mL of water, was added. The mixture was stirred at room temperature
for 120 minutes and then heated at 70 ꢀC in an oil bath for 180 minutes. The white
precipitate was filtered off, washed with water and air dried. Yield: 90%. Anal. Calc. for
C27H21N3O6: C, 67.07; H, 4.39; N, 8.69%. Found: C, 66.90; H, 4.68; N, 8.63%. IR (ATR,
cmꢁ1): 1688 (C ¼ O), 1566 (C ¼ Ntriazine), 1169 (C–O), 848 (C–Ntriazine).
2.2.3. Synthesis of triazine-based Schiff base ligands (3a-d)
2,4,6-tris(4-formylphenoxy)-1,3,5-triazine (1) (0.221 g, 0.5 mmol) was added to a solution
of 4-pyridinecarboxylic acid hydrazide (0.208 g, 1.5 mmol) in THF (70 mL). The colorless
solution was heated under reflux for 19 h. The solvent was then removed by evapor-
ation under reduced pressure. The residue (3a) was filtered off, washed with the hot
THF and dried in air at room temperature. The same procedure was performed for 3b-
d. As hydrazide components the 3-pyridinecarboxylic acid hydrazide (3b), 2-pyridine-
carboxylic acid hydrazide (3c) or 3-hydroxy-2-naphthoic acid hydrazide (3d) were used.
The scheme of the syntheses is presented in Figure 1.
For 3a - yield: 78%. Anal. Calc. for C42H38N12O10: C, 57.93; H, 4.40; N, 19.30%.
Found: C, 57.26; H, 4.025; N, 18.73%. IR (ATR, cmꢁ1): 3219 (N–H), 1660 (C ¼ O), 1608
1
(C ¼ Nimine), 1572 (C ¼ Ntriazine), 1361 (C–O–Ar). H NMR (DMSO-d6, 25 ꢀC) (d: ppm): 7.36
(d, 2H, Ar–H), 7.81 (d, 2H, Ar–H), 7.81 (d, 4H, Ar–H), 8.49 (s, 1H, N ¼ CH), 8.76 (d, 2H,
Ar–H), 12.08 (s, 1H, N–H).
For 3b – yield: 74%. Anal. Calc. for C42H34N12O8: C, 60.43; H, 4.11; N, 20.13%. Found:
C, 60.19; H, 4.165; N, 19.69%. IR (ATR, cmꢁ1): 3223 (N–H), 1659 (C ¼ O), 1607

2072
A. JUROWSKA ET AL.
Figure 1. Scheme of the dendrimer Schiff base ligands (3a-3d) syntheses.
1
(C ¼ Nimine), 1570 (C ¼ Ntriazine), 1369 (C–O–Ar). H NMR (DMSO-d6, 25 ꢀC) (d: ppm): 7.36
(d, 2H, Ar–H), 7.56 (t, 1H, Ar–H), 7.80 (d, 2H, Ar–H), 8.25 (d, 1H, Ar–H), 8.48 (s, 1H,
N ¼ CH), 8.75 (d, 1H, Ar–H), 9.06 (s, 1H, Ar–H), 12.03 (s, 1H, N–H).
For 3c - yield: 76%. Anal. Calc. for C42H34N12O8: C, 60.43; H, 4.11; N, 20.13%. Found:
C, 60.87; H, 4.01; N, 19.90%. IR (ATR, cmꢁ1): 3289 (N–H), 1682 (C ¼ O), 1610 (C ¼ Nimine),
1572 (C ¼ Ntriazine), 1360 (C–O–Ar).
For 3d - yield: 82%. Anal. Calc. for C57H41N9O10: C, 67.66; H, 4.08; N, 12.46%. Found:
C, 67.72; H, 4.04; N, 12.22%. IR (ATR, cmꢁ1): 3057 (O–H), 1668 (C ¼ O), 1611 (C ¼ Nimine),
1
1582 (C ¼ Ntriazine), 1371 (C–O–Ar). H NMR (DMSO-d6, 25 ꢀC) (d: ppm): 7.30–7.85 (d,
Ar–H), 8.50 (s, 1H, N ¼ CH), 11.28 (s, 1H, O–H), 11.99 (s, 1H, N–H).
2.2.4. Synthesis of [Li3(3d)(H2O)6]ꢂ4H2O (4)
0.40 M MeOLi solution was prepared by dissolving 70 mg of lithium in 25 mL of metha-
nol. To 10 mg (10 mmol) of 3d, a MeOLi solution was added until a clear solution was
formed (ca. 0.158 mL, 63.2 lmol). After a few hours, the resulting precipitate was fil-
tered off, rinsed with a small amount of methanol and then air dried. Anal. Calc. for
C57H56Li3N9O19: C, 57.44; H, 4.74; N, 10.58%. Found: C, 57.34; H, 4.19; N, 10.02%.
2.2.5. Synthesis of [VO(OMe)(3d)2/3]n (5) and [fVO(EtO)(phen)g3] (3d) (6)
[VO(acac)2] was used in a molar ratio to the ligand of 3:1. All reactions were performed
under argon to prevent oxidation of vanadium(IV) to vanadium(V). The synthesis of
the vanadium(IV) complex with 3d was carried out in two different ways. In method

JOURNAL OF COORDINATION CHEMISTRY
2073
A, 3d ligand was used and the reaction was performed in methanol. The second
method (B) was carried out by in situ ligand formation, the individual components (1
and 3-hydroxy-2-naphthoic acid hydrazide) in a molar ratio of 1:3 were dissolved in
ethanol. In method B additionally 1,10-phenanthroline was added at the end of the
reaction to precipitate the product by saturation of coordination sphere of vanadium.
A. To 0.0987 g (0.1 mmol) of the 3d ligand, dissolved in 30 mL of methanol, 0.0795 g
(0.3 mmol) of [VO(acac)2] was added. The mixture was refluxed under argon for
90 minutes. The resulting gray-green amorphous precipitate was filtered and rinsed
with a small amount of methanol. The solid was then air dried and 0.0723 g of 5
was obtained.
B. To 0.256 g (0.5 mmol) of 1, 30 mL of ethanol and 0.303 g (1.5 mmol) of 3-hydroxy-2-
naphthoic hydrazide were added. The mixture was refluxed under argon for 30 minutes.
0.398 g (1.5 mmol) of [VO(acac)2] was then added to the yellow solution and heated for
10 minutes. Then 0.270 g (1.5 mmol) of 1,10-phenanthroline was added to the brown
solution, followed by filtration of the brown fine-crystalline precipitate, rinsing with a
small amount of ethanol and air dried giving 0.496 g of 6. Anal. Calc. for C99H75N15O15V3:
C, 63.67; H, 4.05; N, 11.25; V, 8.20%. Found: C, 63.53; H, 3.97; N, 10.95; V, 8.50%.
2.2.6. Synthesis of [fVO(acac)g3(tkh)] (7)
The Schiff base ligand (tkh) derived from 2 and 3-hydroxy-2-naphthoic acid hydrazide
was prepared in situ. To 0.251 g (0.5 mmol) of 2, 30 mL of methanol and 0.307 g
(1.5 mmol) of 3-hydroxy-2-naphthoic acid hydrazide were added. The mixture was
refluxed under argon for 30 minutes. 0.387 g (1.5 mmol) [VO(acac)2] was added to the
clear yellow solution and the resulting fine crystalline brown precipitate was filtered
off and rinsed with a small amount of methanol. 0.473 g of 7 was obtained. Anal. Calc.
for C75H63N9O18V3: C, 58.83; H, 4.15; N, 8.23; V, 10.00%. Found: C, 58.61; H, 4.32; N,
8.37; V, 9.64%.
2.2.7. Synthesis of [fVO(EtO)(phen)g3(tkh)]ꢂ4H2O (8)
To 0.256 g (0.5 mmol) of 2, 30 mL of ethanol and 0.303 g (1.5 mmol) of 3-hydroxy-2-
naphthoic hydrazide were added. The mixture was refluxed under argon for
30 minutes. 0.398 g (1.5 mmol) of [VO(acac)2] was then added to the clear yellow solu-
tion and the resulting brown solution was heated for a further 30 minutes. Then
0.270 g (1.5 mmol) of 1,10-phenanthroline was added, and the resulting red fine crys-
talline precipitate was filtered off and rinsed with a small amount of ethanol. 0.549 g
of product was obtained. Anal. Calc. for C102H89N15O19V3: C, 61.82; H, 4.53; N, 10.60; V,
7.73%. Found: C, 61.56; H, 4.37; N, 10.17; V, 7.42%.
2.2.8. Synthesis of [VO(acanh2)(OEt)] (9)
Complex 7 (0.2 g) was dissolved in ethanol and refluxed 15 minutes. After 2 days the
formed crystals were filtered off, washed with a small amount of ethanol and air dried.
Anal. Found: C, 54.83; H, 4.86; N, 7.10%. Calculated for C18H19N2O5V: C, 54.81, H, 4.92,
N, 7.13%.

2074
A. JUROWSKA ET AL.
3. Results and discussion
3.1. General remarks to the syntheses
As 1 and 2 were obtained according to methods described in the literature, only pur-
ity of the products was checked by elemental analyses and infrared spectra, which
were found to be consistent with the literature data [21, 22]. In our research we
planned to receive the asymmetrical systems in which only one or two chlorine atoms
in cyanuric chloride were substituted. However, the resulting products were unstable,
and we observed a change in their color, even if the products were stored at ꢁ20 ꢀC.
All three chlorine atoms in 2,4,6-trichloro-1,3,5-triazine have been substituted on 4-
hydroxybenzaldehyde or 4-hydroxyacetophenone for 1 and 2, respectively, and the
obtained ligands were used in the synthesis of complexes and more extensive poly-
nuclear systems.
Ligand 1 contains three aldehyde groups. Due to large steric hindrances, triazine
nitrogens and oxygens are hardly available as donors for d-electron metals. The oxy-
gens of the aldehyde groups may be coordinated to the metallic center, however, in
synthesis of the Schiff bases they are converted to nitrogens with the separation of
water molecules. Thus, it can be considered that in 3a-3d, the core originated from 1
does not have donor atoms available for coordination and all donor atoms must come
from amine or hydrazide components of the Schiff base. In syntheses of 3a-3d,
selected aromatic hydrazides possessing two donor atoms in positions enabling forma-
tion of a five-membered ring after coordination of the metal ion have been used.
Additionally, a third donor was introduced - nitrogen in the pyridine ring, by using
such hydrazides as pyridine-4-carbohydrazide, pyridine-3-carbohydrazide and pyridine-
2-carbohydrazide. The presence of a nitrogen in the aromatic ring increases the hydro-
philic properties of the ligand, compared to those with benzene ring, this increase in
solubility of ligands in polar solvents is crucial for complex formation. Another aspect
is the position of the nitrogen in the pyridine ring of selected hydrazides. In the case
of pyridine-2-carbohydrazide (a substituent in the ortho position), there is an add-
itional possibility of coordinating the nitrogen of the pyridine ring with the oxygen of
the carbonyl moiety (also a five-membered ring after coordination of the metal ion). It
is therefore possible to obtain more complicated structures, on the other hand, these
may cause problems with the formation of mixtures in which the metal will be coordi-
nated once to the carbonyl oxygen and to the imine nitrogen, and once to the car-
bonyl oxygen and to the pyridine nitrogen. Therefore, it was decided to obtain
ligands in which the pyridine nitrogen would be in the meta and para position (pyri-
dine-3-carbohydrazide and pyridine-4-carbohydrazide were used). Then, the resulting
complexes with such ligands could be compared with the complex with a ligand in
which the amine component is pyridine-2-carbohydrazide. It should also be mentioned
that in the case of meta and para positions, it is also possible to coordinate to the
nitrogen of the pyridine ring due to the flexibility of the obtained ligands. The ligand
with the pyridine nitrogen in the para position may coordinate as a single-binding lig-
and (with lower power), however, in this case no competition between the metal ions
appears. Complexes with 3a and 3b can serve as metaloligands in formation of more
complicated polymeric structures. Due to geometry of 3a-3d only two donor atoms

JOURNAL OF COORDINATION CHEMISTRY
2075
(from six available) can coordinate to one metal center, so ligands 3a-3d can bind
three metal centers in total.
Initially, syntheses of 1 and pyridine-carbohydrazide ligands were carried out as
Schiff base syntheses - the components, in a suitable molar ratio, were dissolved in
ethanol and refluxed for 60 minutes. Using this synthetic procedure, one of the sub-
strates (usually 1) was obtained as a result of the reaction, which was confirmed by
the infrared spectra and elemental analysis. It was decided to perform the synthesis
using a literature method, in which the authors received similar type of ligands based
on 1 and para-substituted aromatic hydrazides [23]. THF was used to dissolve the
Schiff base components and the synthesis was carried out in an oil bath at 70 ꢀC for
18 h. The resulting 3a-d ligands are amorphous, yellow solids, stable in solid state and
almost insoluble in water and most organic solvents except DMSO (excluding 3c).
Only 3d dissolves relatively well in MeOH and EtOH. The characterization of ligands
was made using methods such as elemental analysis, infrared spectroscopy and 1H
1
NMR. The results of H NMR are summarized in section 2.2.3 and the spectra are pre-
sented in Supplementary Material. For 3c due to the problems with solubility the
structure was proposed based on elemental analysis and comparison of IR spectra of
all three pyridine-carbohydrazide Schiff base ligands. Due to the insignificant solubility
of 3a-3c only 3d was used for the synthesis of complexes with metals such as lithium
and vanadium(IV).
3.2. Characteristics of 4
Complex 4, [Li3(3d)(H2O)6]ꢂ4H2O, is a light yellow amorphous solid. It is poorly soluble
in water and in selected organic solvents such as ethanol, methanol, acetonitrile and
acetone. In Figure 2 the proposed structure is presented, omitting four waters
of hydration.
In 4, the lithium coordination sphere is composed of a bidentate 3d ligand with
oxygen donor carbonyl and hydroxyl moieties, as well as two water ligands and thus
the coordination number is four. The branched Schiff base ligand coordinates one lith-
ium in each arm, resulting in a multi-core complex compound.
The infrared spectrum in the 550–4000 cmꢁ1 range for 4 (Figure 3) was compared
to the spectrum of 3d. Figure 3 presents the spectra with a cutoff between 1800 and
2500 cmꢁ1 due to the lack of bands in this region.
Significant changes are observed in the spectrum of 4 relative to that of 3d which
can be attributed for the formation of a lithium salt of 3d. These changes include
intensity and band position changes. The bands located at 1298 and 1322 cmꢁ1, attrib-
uted to the oscillation of the OH group, disappeared on coordination to lithium.
Similar changes are observed in the 2800–3500 cmꢁ1 region. In addition, the shift of
the band from 1668 cmꢁ1 to 1634 cmꢁ1 associated with the oscillation of the carbonyl
moiety is observed. These changes, as well as changes in all other band positions and
intensities indicate bidentate coordination of 3d to lithium. The estimated stoichiom-
etry Li:3d (3:1), changes in the IR spectra in OH and C ¼ O region and relatively small
changes in the C ¼ N and NH bands support the formula of 4 presented in Figure 2.
The infrared spectrum confirms the presence of water molecules (bands at

2076
A. JUROWSKA ET AL.
Figure 2. The structure of 4; waters of hydration are omitted for clarity.
Figure 3. IR (with ATR correction) spectra for 3d (black, solid line) and 4 (red, dashed line).

JOURNAL OF COORDINATION CHEMISTRY
2077
Figure 4. Scheme of the monomer unit of 5.
Figure 5. The structure of 6.
700–890 cmꢁ1, 1260–1410 cmꢁ1, 1640 cmꢁ1 and the broad bands at 2750–3750 cmꢁ1);
it is however difficult to attribute these bands directly to water of hydration or water
as aqua ligands. This is probably caused by the fact that the interactions of aqua
ligands with lithium are relatively weak and overlaps with those of water of hydration
resulting in band broadening.

2078
A. JUROWSKA ET AL.
Figure 6. IR spectra of 3d (black, solid line), 5 (red, dotted line) and 6 (blue, dashed line).
3.3. Characteristics of 5 and 6
Reaction of [VO(acac)2] with 3d results in ligand coordination, but in methanol as solv-
ent fast precipitation of gray-green, amorphous product is observed. Its composition
indicates that vanadium is coordinated to two 3d ligands, resulting in a polymeric
structure presented in a simplified manner in Figure 4. The product is almost insoluble
in water and in organic solvents.
To avoid formation of 5, ethanol was used as a solvent and 3d was synthesized in situ;
phen (as a co-ligand) was used to precipitate 6 and to prevent further coordination of 3d.
Fine crystalline, brown precipitate of 6, with formula presented in Figure 5, was isolated.
The isolated salt, in contrast to 5, shows good solubility in organic solvents; only in water
poor solubility is observed. Despite many attempts to recrystallize isolated compounds,
large enough single crystals, suitable for X-ray structural analysis, were not obtained.
Longer period of crystallization results in slow formation of 5 and release of phen.
Both complexes were stable as solids. The vanadium is six coordinate with oxido,
methoxy (5) or ethoxy (6), bidentate 3d (5 and 6) and phen (6) ligands. When phen
was not used as a co-ligand, the coordination sphere of vanadium is filled with a
second 3d ligand. This results in formation of polymeric compound, thus 5 is almost
insoluble. Presence of phen during synthesis results in its coordination and formation
of monomeric 6. The synthetic procedure may also indicate that polymeric 5 is less
stable and its heating in the presence of phen should convert it into 6.
The IR spectra of 5 and 6 were compared with the spectrum of 3d (Figure 6). In
the spectrum of 5, an intense band at 990 cmꢁ1 is observed, which is related to the
V ¼ O moiety. For 3d, the vibrations associated with the carbonyl group (1668 cmꢁ1),
the imine bond (1611 cmꢁ1) and the hydroxyl group (3057 cmꢁ1) are observed. In the
spectrum of 5, the bands related to the carbonyl and imine moieties were changed
(the carbonyl group shifted to 1659 cmꢁ1 and the imine band shifted to 1638 cmꢁ1),

JOURNAL OF COORDINATION CHEMISTRY
2079
Figure 7. The structure of 7.
which is connected with coordination of vanadium to the carbonyl oxygen. Based on
the infrared spectrum, it can be concluded that the resulting compound is a polymer
in which the vanadium coordination sphere can be saturated by another 3d ligand.
The structure of this compound is indicated by the presence of the one intense band
at 990 cmꢁ1. In a similar system, [VO(acac)2] band at 995 cmꢁ1 was also attributed to
V ¼ O vibration [24]. This supports proposed structure of 5 in which only oxygen
donors are present around vanadium. The polymeric structure of 5 was confirmed also
by magnetic measurements based on which the molar weight can be estimated on
783 80 per one vanadium d1 center. A gram susceptibility value for 5 is
1.62 ꢃ 10ꢁ6 cm3ꢂgꢁ1. Assuming the vanadium magnetic moment at 1.73 mB, the molar
mass of the compound per vanadium of 778 g is obtained. This corresponds to the
coordination of not one, but two ligand molecules to one vanadium ion, which gives
a total 2/3 mole of ligand per one mole of vanadium, as schematically shown in
Figure 4. With the compound structure assumed in the figure, vanadium is also coordi-
nated with oxo ligand, and for filling the charge and coordination number with
methoxy group, which gives a molar mass of 778 gꢂmolꢁ1
.
In the spectrum of 6, a band located at 961 cmꢁ1 characteristic for V ¼ O is
observed. In addition, there is a band related to the mC¼N vibration at 1622 cmꢁ1, a
band at 2600–3500 cmꢁ1 characteristic for the vibration of the hydroxyl group present
in the hydrazide fragment, as well as the band originating from the vibration of the
carbonyl group of hydrazide (1637 cmꢁ1). The intense band at 1365 cmꢁ1 is derived

2080
A. JUROWSKA ET AL.
Figure 8. The structure of 8; waters of hydration are omitted for clarity.
from the vibration of the C–O–Ar moiety present in the resulting Schiff base ligand.
There is also observed a band attributed to the C ¼ Ntriazine (1582 cmꢁ1). In general,
spectra of 5 and 6 are similar. The main differences relate to the presence of bands
derived from the phen ligand at 744 cmꢁ1, 1438 cmꢁ1 and 1505 cmꢁ1, as observed in
other complexes with phen ligand [25].
The TG analysis (Supplementary Material) indicates that above 300 ꢀC decompos-
ition of the Schiff base ligand is observed. The EtO ligands at 250 ꢀC are released first
(Dmexp ¼ 7.62%, Dmcalc ¼ 7.40%).
3.4. Characteristics of 7 and 8
The in situ formed ligand based on 2 and 3-hydroxy-2-naphthoic acid hydrazide react
with [VO(acac)2] yielding 7 as a stable, fine-crystalline brown precipitate. When phen
was added, before isolation of 7, the acacꢁ ligand in 7 is substituted with phen, result-
ing in formation of 8 as a stable, red, finely crystalline precipitate. Structures of 7 and
8 are presented in Figures 7 and 8, respectively.
In each arm of 7 and 8 the Schiff base ligand coordinates by oxygen of the car-
bonyl group and oxygen of the deprotonated hydroxyl group, and the coordination
sphere is filled additionally with oxido (7 and 8), acacꢁ (7), ethoxy (8) and phen
(8) ligands.

JOURNAL OF COORDINATION CHEMISTRY
2081
Figure 9. IR spectra of 2 (black, solid line), 3-hydroxy-2-naphthoic acid hydrazide (red, dashed line)
and 7 (blue, dotted line).
The complexes form very fine crystals that we were unable to measure single crys-
tal X-ray structures. 7 is unstable in ethanolic solution and decomposes to a new crys-
talline product (9), whose single crystal X-ray was identical with that described in
literature as a product of reaction of [VO(acac)2] and 3-hydroxy-2-naphthoic acid
hydrazide [26]. The decomposition of 7 after recrystallization indicates that the Schiff
base imine bond is not very stable and acetylacetone ligand from [VO(acac)2] can
exchange the triazine part. In this process we also observed a simple vanadium oxida-
tion from V(IV) to V(V).
The IR spectra of 7 and 8 are presented in Figures 9 and 10, respectively. For com-
parison, the spectra of 2 and 3-hydroxy-2-naphthoic acid hydrazide are also included.
Figure 11 summarizes the spectra of 7 and 8.
The presented spectra indicate formation of a vanadium(IV) complex with a Schiff
base ligand based on 2 and 3-hydroxy-2-naphthoic acid hydrazide. In the spectrum of
the product (blue line) a band located at 958 cmꢁ1 (for 7) and 959 cmꢁ1 (for 8) charac-
teristic for the V ¼ O group appears. Bands associated with vibration of the C–O–Ar
group (1362 cmꢁ1 for 7 and 1373 cmꢁ1 for 8), the vibration of the C ¼ O bond origi-
nating from the hydrazide ligand fragment (1681 cmꢁ1 for 7 and 1683 cmꢁ1 for 8), as
well as the vibration originating from the formed imine bond C ¼ N (1638 cmꢁ1 for 7
and 1626 cmꢁ1 for 8) in a Schiff base ligand are observed. There is also a band located
at 1568 cmꢁ1 (for 7) and 1584 cmꢁ1 for 8, which can be assigned to the C ¼ Ntriazine
linkage, confirming the presence of a triazine ring in the resulting compounds. In
spectra of 7 and 8 there is no band at 1688 cmꢁ1 (C ¼ O), which is observed in the
spectrum of 2, indicating condensation of all three carbonyl groups by 3-hydroxy-2-
naphthoic acid hydrazide. The change in the spectra of the resulting complexes above
3000 cmꢁ1, relative to the spectrum of 3-hydroxy-2-naphthoic acid hydrazide, indicates

2082
A. JUROWSKA ET AL.
Figure 10. IR spectra of 2 (black, solid line), 3-hydroxy-2-naphthoic acid hydrazide (red, dashed
line) and 8 (blue, dotted line).
Figure 11. Comparison of the IR spectra of 7 (black, solid line) and 8 (red, dashed line).
participation of the hydroxyl group in the formation of the vanadium coordination
sphere - the disappearance of the band characteristic for the OH group. The spectra of
7 and 8 are similar, which is related to the coordination of the same Schiff base ligand
(tkh), whose vibrations dominated the spectra of 7 and 8. Only the changes connected
with different ligands, bands at 1266 cmꢁ1, 1435 cmꢁ1 and 1503 cmꢁ1 (for acac- ligand
in 7) and 724 cmꢁ1, 1426 cmꢁ1 and 1506 cmꢁ1 (for phen ligand in 8), are observed.

JOURNAL OF COORDINATION CHEMISTRY
2083
The TG measurements for 7 and 8 indicate that complexes are moisture sensitive
and similarly, to previous study, the Schiff base ligand decomposes [27]. For 8 water
molecules are released at 200 ꢀC (Table S1 in Supplementary Material), assigned to
2.5 H2O (Dmexp ¼ 2.11%, Dmobl ¼ 2.27%). The elemental analysis results give the for-
mula with 4 H2O, however it was measured directly after complex isolation, while the
TG measurements are much later. As seen in TG for 6-8, the constant mass loss is
observed starting from room temperature, for 8, it means that only the water, which
remained after this time, could be determined by TG measurements. As the water is
not strongly bonded, this is a common problem for such materials of por-
ous structure.
4. Conclusion
Six symmetrical branched ligands based on triazine structure were synthesized and
characterized. 2,4,6-Trichloro-1,3,5-triazine, used in syntheses, gives the opportunity to
obtain asymmetrical systems in which only one or two chlorine atoms would be sub-
stituted. Despite the literature descriptions, we have found that with 4-hydroxybenzal-
dehyde the resulting unsymmetrical compounds were not stable. Decomposition
processes were observed, along with a change in their color, even if the products
were stored at ꢁ20 ꢀC. It was necessary to substitute all chlorine atoms. We also
proved that choosing the right solvent in synthesis is important, as well as selection
of the Schiff base components that will increase the solubility of the resulting dendri-
meric ligands based on triazine. Initially, ligand 1 was used as an aldehyde component
and pyridine carbohydrazides as amine components due to the presence of at least
two donors and a nitrogen in the pyridine ring, which increases the solubility of the
entire ligand molecule. As a result, pyridine-based dendrimeric ligands (3a-3c) had
poor solubility, therefore 3-hydroxy-2-naphthoic acid hydrazide was chosen, in which
the presence of the hydroxyl group increased the solubility of the branched ligand
and it was possible to use 3d in the synthesis of complexes.
Five complexes were isolated and characterized both in one- and in multi-stage
reactions. The type of solvent was very important for the synthesis of vanadium(IV)
complexes with 3d and tkh ligands. Syntheses carried out in methanol did not require
the use of additional ligands as precipitation of the fine crystalline product occurred
when [VO(acac)2] was added. In ethanol, formation of polymeric compound was
observed, the coordination sphere is occupied by another arm of 3d ligand from
another molecule forming a polymeric structure. To prevent polymer formation 1,10-
phenanthroline was used to saturate the coordination sphere and precipitation of
monomer was observed. In the case of the tkh ligand, the monomeric compounds
were formed, whether phenanthroline was used or not.
Disclosure statement
No potential conflict of interest was reported by the author(s).

2084
A. JUROWSKA ET AL.
ORCID
Janusz Szklarzewicz
http://orcid.org/0000-0001-9747-9238
References
[1] J.M. Lehn. Angew. Chem. Int. Ed. Engl., 27, 89 (1988); J.M. Lehn. Proc. Natl. Acad. Sci., 99,
4763 (2002).
[2] A.D. Burrows, C.-W. Chan, M.M. Chowdhry, J.E. McGrady, D.M.P. Mingos. Chem. Soc. Rev.,
24, 329 (1995); M.D. Hollingsworth. Science, 295, 2410 (2002); B. Moulton, M.J. Zaworotko.
Chem. Rev., 101, 1629 (2001); G.R. Desiraju. Chem. Commun., 1475 (1997); G.R. Desiraju.
Acc. Chem. Res., 35, 565 (2002); G. Desiraju. Nature, 412, 397 (2001).
[3] J.M.J. Frechet, D.A. Tomalia. Dendrimers and Other Dendritic Polymers, Wiley, New York
(2001).
[4] D.A. Tomalia, A.M. Naylor, W.A. Goddard. Angew. Chem. Int. Ed. Engl., 29, 138 (1990).
[5] R. Sharma, I. Zhang, T.C. Shiao, G.M. Pavan, D. Maysinge, R. Roy. Nanoscale, 8, 5106
(2016).
€
[6] B.A.G. Hammer, K. Mullen. J. Nanopart. Res., 20, 262 (2018).
[7] S. Vembu, S. Pazhamalai, M. Gopalakrishnan. Med. Chem. Res., 25, 1916 (2016).
[8] J. Lim, E.E. Simanek. Adv. Drug Deliv. Rev., 64, 826 (2012).
[9] Y. Tsuchido, Y. Sakai, K. Aimu, T. Hashimoto, K. Akiyoshi, T. Hayashita. New J. Chem., 39,
2620 (2015).
[10] D.Y. Son. Chem. Commun. (Camb.), 49, 10209 (2013).
[11] S. Serroni, A. Juris, M. Venturi, S. Campagna, I.R. Resino, G. Denti, A. Credi, V. Balzani. J.
Mater. Chem., 7, 1227 (1997).
[12] P. Gamez, P. de Hoog, M. Lutz, A.L. Spek, J. Reedijk. J. Reedijk. Inorg. Chim. Acta, 351, 319
(2003).
[13] B. Feringan, P. Romero, J.L. Serrano, R. Gimenez, T. Sierra. Chemistry, 21, 8859 (2015).
[14] T.J. Mooibroek, P. Gamez. Inorg. Chim. Acta, 360, 381 (2007).
[15] G. Blotny. Tetrahedron, 62, 9507 (2006).
[16] D. Gajjar, R. Patel, H. Patel, P.M. Patel. Int. J. Pharm. Pharm. Sci., 6, 357 (2014).
[17] D. Bartholomew, In Comprehensive Heterocyclic Chemistry II, A.J. Boulton (Ed.), Vol. 6, pp.
575–636, Pergamon, Oxford (1996).
[18] D.L. Comins, S. O’Connor, In Advances in Heterocyclic Chemistry, A.R. Katritzky (Ed.), Vol.
44, p. 243, Academic Press, New York (1988).
[19] E.M. Smolin, L. Rapoport (Eds.), Chemistry of Heterocyclic Compounds: s-Triazines and
Derivatives, Vol. 13, Wiley, Hoboken, USA (2008).
[20] G. Giacomelli, A. Porcheddu, In Comprehensive Heterocyclic Chemistry III, K. Turnbull (Ed.),
Vol. 9, pp. 197–290, Elsevier Science & Technology, Oxford (2008).
[21] F.J. Allan, G.G. Allan. Recl. Trav. Chim. Pays-Bas., 78, 375 (2010).
[22] F.G. Khan, M.V. Yadav, A.D. Sagar. Indo Am. J. Pharm. Res., 4, 5099 (2014).
[23] S.S. Machakanur, B.R. Patil, D.S. Badiger, R.P. Bakale, K.B. Gudasi, S.W.A. Bligh. J. Mol.
Struct., 1011, 121 (2012).
[24] R.N. Nenashev, N.E. Mordvinova, V.P. Zlomanov, V.L. Kuznetsov. Inorg. Mater., 51, 891
(2015).
[25] A.A. Schilt, R.C. Taylor. J. Inorg. Nucl. Chem., 9, 211 (1959).
ꢀ
[26] P. Paciorek, J. Szklarzewicz, A. Jasinska, B. Trzewik, W. Nitek, M. Hodorowicz. Polyhedron,
87, 226 (2015).
[27] J. Szklarzewicz, A. Jurowska, D. Matoga, K. Kruczała, G. Kazek, B. Mordyl, J. Sapa, M.
_
Papiez. Polyhedron, 185, 114589(2020).