Molecular structure and spectroscopic properties of new neodymium complex with 3-bromo-2-chloro-6-picolinic N-oxide showing the ligand-to-metal energy transfer

Article abstract of DOI:10.1016/j.molstruc.2020.128967

A new neodymium [Nd(BCPN)₃(NO₃)₃(H₂O)₂] complex with 3-bromo-2-chloro-6-picolinic N-oxide was synthesized and characterized by means of spectroscopic studies and DFT quantum chemical calculations. The IR, Raman, electron UV-VIS and emission spectra measurements were performed. The femtosecond excitation was used to establish an excited energy level depopulation mechanism. The influence of the halo-groups position on the structural and optical properties of the studied compound was discussed. Ligand-to-metal energy transfer in the studied neodymium complex was analysed.

Full text of DOI:10.1016/j.molstruc.2020.128967

Journal Pre-proof
Molecular structure and spectroscopic properties of new neodymium
complex with 3-bromo-2-chloro-6-picolinic N-oxide showing the
ligand-to-metal energy transfer
Lucyna Macalik , Maria Wandas , Wojciech Sasiadek ,
Î
Jadwiga Lorenc , Rados law Lisiecki , Jerzy Hanuza
PII:
S0022-2860(20)31291-6
DOI:
Reference:
https://doi.org/10.1016/j.molstruc.2020.128967
MOLSTR 128967
To appear in:
Journal of Molecular Structure
Received date:
Revised date:
Accepted date:
23 April 2020
23 July 2020
23 July 2020
Please cite this article as: Lucyna Macalik , Maria Wandas , Wojciech Sasiadek , Jadwiga Lorenc ,
Î
Rados law Lisiecki , Jerzy Hanuza , Molecular structure and spectroscopic properties of new
neodymium complex with 3-bromo-2-chloro-6-picolinic N-oxide showing the ligand-to-metal energy
transfer, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/j.molstruc.2020.128967
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Highlights:
 A new neodymium complex with 3-bromo-2-chloro-6-picolinic N-oxide was synthesized
 Oxygen of N-oxide group, nitrate anions and water units form NdO3O’3O”2 polyhedron
 The determined lifetime of 4F3/2 level is 1.3 s
 Bromo-chloro-derivatives of picoline N-oxides participate in the energy transfer
 Femtosecond laser pulses were used for excitation of ligand-to-metal energy transfer

Molecular structure and spectroscopic properties of new neodymium complex with 3-bromo-
2-chloro-6-picolinic N-oxide showing the ligand-to-metal energy transfer
Lucyna Macalik1,*, Maria Wandas2, Wojciech Sąsiadek2, Jadwiga Lorenc2, Radosław Lisiecki1,
Jerzy Hanuza1
1 Institute of Low Temperature and Structure Research, 2 Okólna str., 50-422 Wrocław, Poland
2 Department of Bioorganic Chemistry, Institute of Chemistry and Food Technology, Faculty of
Production Engineering, Wrocław University of Economics and Business, 118/120 Komandorska
str., 53-345 Wrocław, Poland
* Corresponding author: L.Macalik@intibs.pl
A new neodymium [Nd(BCPN)3(NO3)3(H2O)2] complex with 3-bromo-2-chloro-6-picolinic N-
oxide was synthesized and characterized by means of spectroscopic studies and DFT quantum
chemical calculations. The IR, Raman, electron UV-VIS and emission spectra measurements were
performed. The femtosecond excitation was used to establish an excited energy level depopulation
mechanism. The influence of the halo-groups position on the structural and optical properties of the
studied compound was discussed. Ligand-to-metal energy transfer in the studied neodymium
complex was analysed.
Keywords: Nd(III) complex; Picolinic N-oxide; Molecular structure; Femtosecond laser excitation;
DFT calculations; Ligand-to-metal energy transfer
1. Introduction
Pyridine derivatives form a class of compounds widely used in solving various biological,
pharmaceutical and medical problems. These applications depend on the type and number of
substituents in the pyridine ring and the properties of reagents attached to these units. For example,
halopyridines are a source of fungicidal and insecticidal products used in industry. They are also
applied to generate antihistamines and antiarrythymics for pharmaceutical purposes [1]. Pyridine-N-
oxides constitute a specific wide group of compounds that in spite of years of research still can be
used in new applications. Their amino- and nitro-derivatives are employed as an organic part of

ionic salts, hybrid materials, ferroelectrics and optically non-linear products [2,3]. Bioactivity of
such compounds was utilized in production of antibiotics, cancerostatics, mutagenic agents,
anticonsulvants and fungistatic drugs [4-11]. The applications of the pyridine derivatives as the
ligands binding the lanthanide ions initiated a new direction of their use as light emitting systems.
The pyridine N-oxide derivatives seem to play an important role in these applications due to their
strong absorption and effective radiative transfer from the ligand to the lanthanide ion [12-14]. They
can act as antenna media [15-17]. Their energy transfer efficiency depends on the energy gap
between the electron states of the organic ligand and electronic levels of Ln3+ ion. Moreover,
quenching processes of the surroundings should be considered in this process. Understanding of
these effects in pyridine N-oxide complexes is necessary to improve the overall luminescence yield
of similar systems.
To better understanding phenomena connected with the molecular interactions, some
computational strategies and training sets have been tested. Matrix isolation studies provided results
for isolated molecules in order to obtain necessary reference data for the spectra studies of
molecular interactions predict properties of larger biomolecules [18]. Introduction in the Gaussian
code of an effective algorithm based on finite difference evaluations of third and semi diagonal
fourth derivatives [19] paved the route for a more systematic investigation of larger molecules [20,
21]. Some papers reported results showing that this model is very useful for semi rigid molecules
and that a remarkable accuracy is obtained at the B3LYP level with medium size basis sets [22, 23].
The efficiency, scaling, and ease of use of the computational approach paves the route for reliable
interpretations of IR and Raman spectra of more complex molecules and unstable species.
The present paper presents the results of spectroscopic studies on a new neodymium(III)
complex with 3-bromo-2-chloro-6-picolinic N-oxide. We characterized its vibrational and electron
properties recording the IR, Raman, optical absorption and emission spectra. Quantum chemical
DFT calculations were performed to assign the measured bands to the respective energy transitions.
Femtosecond laser pulses were used for excitation of the ligand-to-metal energy transfer in the
studied complex.

2. Experimental
2.1. Synthesis and chemical analysis
3-bromo-2-chloro-6-picolinic N-oxide, used as the ligand complexing the neodymium ion,
was synthesized according to the method described previously [24]. Commercially available 2-
chloro-3-nitropicoline (17.2 g) dissolved in 150 mL of ethanol was added to a solution of 40 mL 80
% hydrazine hydrate in 60 mL of ethanol with Raney nickel catalyst. The reaction mixture was
heated to 70 ºC for 10 min and left for half an hour at room temperature. After filtering off nickel,
the solvent was removed on a rotary evaporator under reduced pressure. Then 100 mL of water was
added and the mixture was extracted with ether. The extract was dried with anhydrous magnesium
sulphate, ether was removed and the residue was re-crystallized from benzene + petroleum ether.
The obtained 2-chloro-3-amino-picoline (4.3 g) was added to freshly prepared solution of CuBr (20
gr CuSO4, 15 g KBr, 50 mL H2O, 4 g NaHSO3). This mixture was cooled down to 5 ºC, treated
with small portions of saturated NaNO2 solution, heated to 50 ºC and kept at this temperature for 10
min. Next, this mixture was alkalized with 50 % KOH and distilled with water steam. The product
of distillation was extracted with the ether and the obtained in this way extract was dried with
anhydrous sodium sulphate. The ether removed and the residue was used in N-oxidation reaction.
The neodymium complex was obtained by dissolving 99.99% Nd(NO3)3 and 3-Br-2-Cl-6-
picolinic N-oxide (BCPN) in 10 mL of water in the 1 : 3 molecular ratios. This reaction mixture
was heated at 90 ºC briefly stirring until a clear solution was obtained. Irradiation of the solution
with a quartz lamp for 5 min led to precipitation of a grey-blue crystalline product. It was filtered,
washed with ethanol and dried in vacuum. The product formula was obtained by elemental
chemical analysis which gave the following content: experimental – C = 21.04 %, H = 1.75 %, N =
8.01 %, Br = 22.88 % and Cl = 9.95 %. Such a composition corresponds to the formula:
[Nd(C6H5BrClNO)3(NO3)3(H2O)2] for which the calculated values are as follows: C = 20.92 %,, H
= 1.85 %, N = 8.13 %, Br = 23.19 % and Cl = 10.29 %. The melting point determined for the ligand
was 116 ºC and for the complex - 184 ºC.
According to the chemical data the composition of the studied neodymium complex was
established. Its structure was confirmed by the quantum chemical calculations performed for the 3-

bromo-2-chloro-6-picolinic N-oxide ligand and its neodymium complex. The results of these
calculations are presented in the part 2.5. The molecular structure of the studied neodymium
complex is shown in Fig. 1.
The complete set of the atomic coordinates for the studied neodymium complex is given in
supplementary materials. Fig. S1 shows the simplified structure of Nd(BCPN)3(NO3)3(H2O)2]
complex. Table S1 present atomic coordinates of 3-bromo-2-chloro-6-picolinic N-oxide and Table
S2 - atomic coordinates of the Nd(BCPN)3(NO3)3(H2O)2 complex.
Fig. 1. Molecular structure of the studied Nd(BCPN)3(NO3)3(H2O)2 complex.
2.2. Infrared and Raman studies
IR spectra were measured using a Nicolet iS50 FT-IR (Thermo Scientific) spectrometer
equipped with an Automated Beamsplitter exchange system (iS50 ABX containing DLaTGS KBr
detector and DLaTGS Solid Substrate detector for mid-IR and far-IR regions, respectively), a built-
in all-reflective diamond ATR module (iS50 ATR), Thermo Scientific Polaris™ and HeNe laser as
an IR radiation source. Polycrystalline IR spectra were collected in the 4000 - 100 cm-1 range.
Samples were prepared in the form of KBr pellets and Nujol suspension in the mid- and far-IR
ranges, respectively. The advanced ATR correction software a part of OMNICTM 6.2 program
attached to a Thermo Scientific NicoletTM FT-IR spectrometer was used in the studies of
polycrystalline samples. Spectral resolution of 4 cm-1 was applied in the measurements. Raman
spectra in the 4000 – 80 cm-1 range were measured in back scattering geometry with a FT Bruker

110/S spectrometer. The resolution was 2.0 cm-1. The YAG:Nd (excitation wavelength 1064 nm)
laser was used as an excitation source.
2.3. Electron absorption spectra
Room temperature electron absorption spectra were measured in the 200 – 1500 nm spectral
range using a Cary-Varian 5E UV-VIS-near-IR spectrophotometer. In the case of a weak signal of
the spectrum, the spectrophotometer was switched to measurements in the diffuse reflectance mode.
Diffuse reflectance spectra were recorded with a Praying Mantis diffuse reflectance accessories. In
these measurements the base line was first recorded for Al2O3 powder, and next this line was
subtracted from those obtained for particular powder sample spectra.
2.4. Emission spectra measurements
Decay profiles and emission spectra were recorded with a grating spectrograph (Princeton
Instr. Model Acton 2500i) coupled to a streak camera (Hamamatsu Model C5680). For excitation a
femtosecond laser (Coherent Model ‘‘Libra’’) was used. The laser delivers a train of 89 fs pulses at
a wavelength of 800 nm and a pulse energy of 1 mJ, with repetition rates regulated up to 1 kHz. To
attain light pulses at different wavelengths the laser was coupled to an optical parametric amplifier
(Light Conversion Model OPerA) that can operate in the range 230 – 2800 nm.
2.5. Quantum chemical calculations
The geometry optimization of the studied 3-bromo-2-chloro-6-picolinic N-oxide ligand was
performed using Gaussian 03 program package [25] starting from the X-ray geometry and applying
the B3LYP approach [26-28] with the 6-311++G(d,p) basis set [26-30]. Its molecular structure and
used atomic numbering is presented in Figure 2. Tables 1 and 2 list the selected geometrical
parameters calculated for the free ligand and the complex, respectively.

Fig. 2. Molecular structure of the 3-bromo-2-chloro-6-picolinic N-oxide ligand with atomic
numbering.
Table 1. Selected geometrical parameters for the 3-bromo-2-chloro-6-methyl-N-pyridine-oxide
molecule.
Bond distance
[Å]
Bond angle
[º]
C1-C2
C1-Cl1
C1-N1
C2-C3
C2-Br1
C3-C4
C3-H1
C4-C5
C4-H2
C5-C6
C5-N1
C6-H3
C6-H4
C6-H5
N1-O1
1.39
1.71
1.38
1.39
1.90
1.39
1.08
1.38
1.08
1.49
1.38
1.09
1.09
1.09
1.28
C2-C1-Cl1
C2-C1-N1
C1-C2-C3
C1-C2-Br1
Cl1-C1-N1
C1-N1-C5
C1-N1-O1
C3-C2-Br1
C2-C3-C4
C2-C3-H1
C4-C3-H1
C3-C4-C5
C3-C4-H2
C5-C4-H2
C4-C5-C6
C4-C5-N1
C6-C5-N1
C5-C6-H3
C5-C6-H4
C5-C6-H5
C5-N1-O1
H3-C6-H4
H3-C6-H5
H4-C6-H5
124.0
120.6
120.2
120.7
115.4
119.7
120.7
119.0
118.3
120.4
121.3
121.7
120.1
118.2
125.0
119.4
115.6
110.6
110.1
110.6
119.6
109.7
106.1
109.7
Table 2. Selected geometrical parameters for the [Nd(BCPN)3(NO3)3(H2O)2] complex (see Fig. S1).
Bond distance
[Å]
Bond angle
L1-Nd-L2
[º]
Nd-L1 (L2 and L3)
2.30
81.6

Nd-ONO2
Nd-OH2
2.30
2.30
1.35
1.36
1.35
1.36
1.37
1.36
1.36
L2-Nd-L3
L1-Nd-L3
169.8
106.6
105.7
73.5
98.0
179.0
97.6
74.3
108.0
61.7
(L1) N-O
(L2) N-O
(L3) N-O
O2N-O’N
O2N-O’’N
O2N-O’’’N
O=NO2Nd
L1-Nd-O’NO2 (and O’’NO2)
L2-Nd-O’NO2 (and O’’NO2)
L3-Nd-O’NO2 (and O’’NO2)
L1-Nd-O’’’NO2
L2-Nd-O’’’NO2
L3-Nd –O’’’NO2
L1-Nd-O’H2
L2-Nd-O’H2
L3-Nd-O’H2
L1-Nd-O’’H2
119.6
60.2
L2-Nd-O’’H2
L3-Nd-O’’H2
117.3
63.8
O2NO’-Nd-O’H2
O2NO’-Nd-O’’H2
O2NO’-Nd-O’’NO2
O2NO’-Nd-O’’’NO2
H2O’’-Nd-O’H2
117.5
72.2
177.5
74.3
167.5
The IR and Raman spectra measured for the neodymium complex indicate that the
intermolecular interactions between the components of the unit cell are weak (see Fig. S2). The
small number of the observed bands than predicted theoretically suggests the lack of the factor
group splitting in the experimental spectra. Therefore, the calculations were performed for the
monomeric molecule. The scaling factors were used to correct the evaluated wavenumbers for
vibrational anharmonicity and deficiencies inherent to the used computational level. The ChemCraft
program was used for visualization of the vectoring graphics of the normal modes [31]. In the
Potential Energy Distribution (PED) procedure the BALGA program was used [32]. The mean
square deviation [33] between the experimental and calculated unscaled wavenumbers was used for
calculation of the scaling factor for the ligand. For the Raman spectra 0.96 scaling factor was used
for the range 3500 – 2500 cm-1 and 0.98 for the range 2499 – 80 cm-1 of the spectra. The theoretical
Raman intensities were calculated using the ChemCraft computer program [31].
3. Results and discussion
3.1. Vibrational spectra
Infrared (from 1700 cm-1) and Raman (from 3200 cm-1) spectra of the studied neodymium
complex are shown in Figures 3 and 4, respectively. They are compared to the spectra of the ligand

used for neodymium(III) complexation. The assignment of the observed bands to the respective
normal modes is proposed in Table 3. It was based on the quantum chemical calculations performed
in this work and compared to the results of our previous studies performed for other pyridine N-
oxide compounds [34-36].
Fig. 3. MIR and FIR spectra of the studied ligand and its neodymium complex.

Fig. 4. Raman spectra of the studied ligand and its neodymium complex.
Table 3. The observed IR and Raman and calculated wavenumbers (in cm-1) using B3LYP/6-
311++G(2d,2p) wavenumbers with PEDs values and their assignment to the respective
normal modes based on the PED calculations.
No
Calculated Experimental data of BCPN
Experimental data of Nd- Assignment of the
wave-
complex
normal modes
numbers
IR
RS
IR
RS
3376 w
3266 w
3116 w
3107 w
3090 sh
3064 w
3049 sh
3031sh
-
(H2O)
1
3131
-
-
-
(C-H)P
3102 w
3092 sh
3069 w
3042 s
-
3104 sh
3090 w
3071 m
3048 w
-
3094 vw
2
3
3107
3040
-
-
-
(C-H)P
as(CH3)
4
5
3001
2956
2997 w
-
2998 w
-
2988 sh
2978 m
-
2928 s
-
-
-
as(CH3)
s(CH3)
combinations
-
-
2961w
2912w
2878 vw
2845 vw
2774 vw
2736 vw
-
1606 m
1600 m
1533 w
1486 s
1473 sh
1461 sh
1444 s
1416 m
-
1385 m
-
1358 s
1288 w
-
1272 vw
1243 vs
-
1215 s
-
2962m
2914m
2877 w
2824 vw
2803 vw
2737 w
-
1605 m
1570 vw
1533 w
1489 vw
1471 vw
1457 vw
1441 w
1418 w
1398 vw
1384 m
-
1361 w
1290 vw
-
1273 vw
1239 vw
-
1217 m
1208 sh
1148 vw
1126 w
1088 m
1040 vw
-
2926 vw
-
-
2774 vw
2760 vw
1648 w
1606 vw
-
1548 vw
1493 m
1474 sh
1460 vs
1445 s
1425 sh
–
1384 w
1365 m
1358 sh
1295 vs
1283sh
1274 vs
1242 sh
1231 s
1216 sh
1208 s
1148 w
1132 m
1091 w
1030 sh
1031 m
1026 sh
-
-
(H2O)
(P) + 13 δ(CH)
6
1615
1607 vs
-
1550 vw
1489 w
1468 vw
7
8
9
1538
1472
1457
(P) + 17 δ(CH)
as(CH3)
(P) + 29 δ(CH)
10
11
1448
1413
1447 vw
1425 vw
-
1384 vw
1375 vw
1364 sh
-
as(CH3)
s(CH3)
42 ()+22 δas(CH3)+
17 δ(CH)+ 15 ν(NO)
as(NO3) - 3(E)
(P) + 13(CH)P
() + 17 (CH)P
12
13
1354
1308
-
-
14
15
1234
1211
1234 s
-
1214 w
-
1150 vw
1131 vw
1093 w
1033 sh
1036 m
-
(P)+ 33 ν(C-CH3)
+ 19 (CH)P
(NO) + 18 ()
16
17
18
1156
1144
1053
1160 vw
1126 m
1087 m
1041 m
-
(P) + 41 δ(CH)
(CH3) + 41 δ()
(CH)P + 31 δ()
s(NO3) - 1(A1)
-
-

19
20
1016
944
988 m
941 w
933 vw
916 vw
896 w
882 m
-
990 vw
941 vw
-
916 vw
896 w
-
-
993 m
938 vw
-
990 vw
930 vw
-
-
-
-
-
849 vw
-
776 s
-
(CH3) + 23 δ()
(CH)P
21
22
910
879
906 sh
898 sh
889 m
861 vw
845 w
833 vw
816 m
801 sh
779 w
734 w
696 w
670 vw
644 w
600 sh
588 m
560 m
490 w
463 vw
450 w
352 w
(P) + 25 (CH3)+
16 γ(CH)
(-CH3)+ 33 (P)
+ 11 (CH)P +
s(NO3) - 2(A2)
-
-
-
-
23
800
800 m
775 w
-
800 vw
776 vs
-
(NO) + 38 γ(CH)
+ 13 γ()
-
-
-
735 vw
-
-
643 w
-
582 vw
579 vw
490 vw
465 vw
-
as(NO3) - 4(E)
24
25
26
717
667
621
698 w
667vw
641 w
619 vw
580 m
573 m
493 w
456 m
-
699 vw
665 vw
643 m
-
578 m
572 sh
492 w
458 vw
-
(P) + 38 γ(NO)
(P)+ 15 δ(C-CH3)
(P) + 22 (CH3)
+ 10 (C-CH3)
(P) + 29 γ(NO)
(P) + 19 γ(NO)
(-Cl) + 36 (
(-Br) + 32 () +
12 δ(C-CH3)
(-Cl) + 38 (C-
CH3) + 17 (NO)
(NO) + 25 γ(P) +
20 (r)
γ(C-CH3)+ 30 (P)
(NdO8)
44Clr)
+ 21 (P) + 15 (NO)
(-Br) + 26 () +
23 (-Cl)
27
28
29
30
584
562
504
449
31
32
33
34
35
36
352
322
293
267
244
200
340 w
345 w
357 vw
305 vw
312 w
315 sh
305 sh
289 vw
-
264 vw
290 s
-
264 vw
290 vw
273 m
260 sh
291 m
280 sh
265 vw
235 w
227 w
221 sh
-
202 w
-
-
211 w
204 w
-
217 w
203 w
162 m
145 w
135 sh
-
217 sh
-
τ(CH3)
174 m
150 vw
141 w
112 m
63 s
(NdO8)
(-Br)+ 22 (-Cl)
37
163
154 vw
142 w
38
39
115
86
-
-
110 m
96 sh
71 (P) + 26(CH3)
(P) + 20 γ(CBr)
-
ν, stretching; δ, in plane bending; γ, out of plane bending; ρ, rocking; ω, wagging; τ, torsion.
The vibrational spectra of the studied BCPN ligand and its Nd(BCPN)3(NO3)3(H2O)2
complex should be analyzed taking into account the structural units constituting these compounds.
Pyridine ring, methyl and N-oxide groups as well as chlorine and bromide atoms build the ligand
molecule but nitrate anions, water units and europium coordination polyhedron additionally appear
in the complex. Their presence should be separately taken into account in the analysis of the IR and
Raman spectra.

The assignment of pyridine ring vibrations in the studied compound is relatively easy due to
the strong correlation with the spectra of free pyridine [37-42]. The following wavenumbers
observed in the spectra are assigned to the pyridine ring modes: (CH)p: 3064 – 3116 cm-1; (p):
1600 – 1607, 1533 – 1550, 1460 – 1474 cm-1, (CH)p + δ(p): 1358 – 1364, 1272 – 1295, 1231 –
1243 cm-1;(p): 1148 – 1160 cm-1; (CH)p: 1090 – 1093, 1033 – 1041, 930 – 941 cm-1; (p) +
(CH)p: 889 – 906 cm-1; (p): 670 – 699, 600 – 644, 578 – 588, 560 – 579, 289 – 291, 260 – 265
cm-1. These bands fit well the literature data.
The methyl groups vibrations are described by three fundamental (CH3) bands
corresponding to one symmetric and two asymmetric vibrations. They are usually observed in the
range between 2900 and 3000 cm-1 [35-36, 42]. In the present work these vibrations were located at
the following wavenumbers: as(CH3): 2978 – 3049 cm-1, s(CH3): 2926 – 2928 cm-1, as(CH3):
1486 – 1493, 1441 – 1447 cm-1; s(CH3): 1384 – 1425 cm-1; (CH3): 1126 – 1132, 988 – 993 cm-1;
(-CH3): 861 – 889 cm-1 and (CH3): 202 – 217 cm-1.
The BPCN ligands act as monodendate units bonded to the neodymium ion through the
oxygen of the N–O group. The characteristic vibrations of this chromophore are observed in the
ranges: 1208 – 1217 cm-1 for stretching, 775 – 816 cm-1 for in-plane and 305 – 315 cm-1 for out-of-
plane bending modes.
The vibrations of the C-Cl bond of the BPCN ligand contribute into several bands from the
150 – 700 cm-1 range. In the IR and Raman spectra of the ligand and complex these vibrations are
observed in the following ranges: the in-plane stretching (C-Cl) vibration at 490 – 493 cm-1, in-
plane bending (C-Cl) vibration at 340 – 357 cm-1 and the out-of plane bending (C-Cl) vibration
at 135 – 154 cm-1. These wavenumbers fit well the calculated values (Table 3) and the literature
data [43-47].
The assignment of C–Br stretching and bending vibrations was accomplished on the basis of
the calculated PED data and comparison with similar molecules [48-51]. In the IR and Raman
spectra of the studied 5-bromo-2-nitropyridine ligand and its neodymium complex the C–Br
stretching vibration coupled with ring deformation is observed in the range 450 – 465 cm-1 and the

bending vibration in the range 227 – 235 cm-1. The C–Br out-of-plane bending vibration was
assigned to the bands in the range 135 – 154 cm-1.
The vibrational characteristics of nitrate anion is well known [52]. All reported in literature
vibrations are observed in the spectra of Nd((BCPN)3(NO3)3(H2O)2 complex. They appear in the
vibrational spectra at the following wavenumbers: as(NO3) - 3(E): 1365 – 1375 cm-1; s(NO3) -
1(A1): 1026 – 1036 cm-1; s(NO3) - 2(A2): 833 – 849 cm-1 and as(NO3) - 4(E): 734 – 735 cm-1.
Since the coordination of this ion in the complex changes its symmetry from D3 to C2v, all these
vibrations become both IR and Raman active, all the respective bands have their counterparts in
these spectra.
The presence of two water units in the neodymium complex is clearly confirmed by the IR
spectra. The broad bands centered at 3376 and 3266 cm-1 originate from the stretching (H2O)
vibrations and the band at 1648 cm-1 corresponds to the bending modes.
New spectral contours can be isolated when the spectra of the ligand and complex are
compared. They are observed in the IR spectra as medium intensity broad band at 273 cm-1
[ν(NdO8)] and another bands at 162 and 135 cm-1 [δ(NdO8)]. In the Raman spectra, they are
observed at 280, 174 and 141 cm-1 being significantly less intense. They correspond to the
stretching and bending vibrations of the NdO3O’3O”2 polyhedron formed by three oxygen atoms of
the N-oxide group, three oxygen atoms of the nitrate anions and two oxygen atoms of the water
units.
It should be noted that both IR and Raman spectra confirm the structure of the neodymium
complex formed by coordination of three 3-bromo-2-chloro-6-picolinic N-oxide ligands, three
nitrate anions and two water units.
3.2. Optical absorption spectra
Two -electron units compose the structure of the studied compound: pyridine ring and N-
oxide group. The later unit can act as both an electron-donor and electron-acceptor in relation to the
pyridine ring. The chlorine and bromine atoms situated at the 2 and 3 positions to the N-oxide
group, are the typical electron-donor substituents. The room temperature electronic absorption

spectra of the ligand and studied neodymium complex are presented in Figure 5. They are
dominated by ligand transitions displayed as strong bands in the 200 – 350 nm range. This spectral
band contains three clearly resolved components located at 203, 231 and 280 nm. They correspond
to electron transitions inside the pyridine ring as well as between the NO-chromophore and the
pyridine. They should be assigned to the  - * transitions between the singlet states of the ligand.
On the low energy slope of these bands, weaker bands are visible at 328 and 339 nm for the ligand
and 338 nm for the complex. They should be described as n - * transitions of the ligand. These
bands include all the singlet and triplet levels of the ligand. The calculated singlet electron levels,
oscillator strengths, orbital configuration and electron transitions of 3-bromo-2-chloro-6-methyl-N-
pyridine N-oxide molecule are listed in Table 4.
Fig. 5. The UV-ViS absorption spectra of the studied ligand and its neodymium complex.
Magnified parts of the chosen ranges are shown in insets.
Table 4. Calculated singlet electron level, oscillator strength, orbital configuration and electron
transition of the 3-bromo-2-chloro-6-methyl-N-pyridine-oxide molecule.
Electron
level
Oscillator
strength
Orbital
configuration* transition
Electron
ΔE (nm) ΔE (cm-1)
1
2
298.1
296.5
33546
33727
0.0000
0.0155
52 →55
πCC→ π*CC
53 →55
54 →55
54 →56
nO→ π*CC
πCC→ π*CC
πCC→ π*CC
3
279.1
35829
0.0000
54 →57
πCC→ π*CC

4
261.9
38182
0.0870
53 →56
54 →55
54 →56
nO→ π*CC
πCC→ π*CC
πCC→ π*CC
5
6
7
250.2
243.1
239.1
39968
41135
41824
0.0000
0.0003
0.2745
52 →56
53 →57
πCC→ π*CC
nO→ π*CC
50 →55
53 →55
54 →56
πCC→ π*CC
nO→ π*CC
πCC→ π*CC
8
9
230.4
229.3
43403
43611
0.0057
0.0055
54 →58
πCC→ π*CC
52 →57
53 →56
πCC→ π*CC
nO→ π*CC
10
216.9
46104
0.0002
51 →55
n→ π*CC
* The numbering of the orbital configurations was taken from the Gaussian program – their electron
structure can be derived from the GaussView program.
The HOMO and LUMO molecular orbitals for the 3-bromo-2-chloro-6-methyl-N-pyridine-
oxide molecule are shown in Fig. 6 indicating the distribution of electron density over the ligand.
The theoretical HOMO  LUMO energy gap equals to 41,824 cm-1, i.e. at  = 239.1 nm (Table 4).
Such a picture suggests that in the HOMO  LUMO excitation the low electron pair of the oxygen
atom of the NO group is transferred to * antibonding orbitals of the pyridine ring (53 → 55
transition in Table 4 and Figure 6).
Fig. 6. The calculated HOMO and LUMO molecular orbitals for the 3-bromo-2-chloro-6-methyl-N-
pyridine-oxide molecule.

Calculated energies of triplet states of the BPCN molecule were located at the following
wavelengths (wavenumbers): 523.6 nm (19,099 cm-1), 341.9 (29,248), 324.8 (30,788), 308.4
(32,425), 293.2 (34,106), 285.3 ( 35,051), 264.1 (37,864), 254.0 (39,370), 239.4 (41,771) and 231.7
(43,159). The oscillator strengths of these transitions equal to zero.
In the visible and near infrared region the absorption spectrum of the neodymium complex
shows weak bands that can originate from the absorption transitions of the Nd3+ ion [53]. Some
bands in the UV region corresponding to the f-f forbidden transitions lie at 306 nm (32,679 cm-1) -
4I9/2 → 2H9/2, 327 nm (30,581 cm-1) - 4I9/2 → 2I13/2, 4D7/2, 2L17/2 and 341 nm (29,325 cm-1) - 4I9/2
→
4D3/2, 4D5/2, 2I11/2, 4D1/2, 2L15/2. The same weak bands also appear in the yellow-red and near infrared
region and correspond to the transitions from the 4I9/2 ground state to 4G5/2, 2G7/2 at 575 nm (17,391
cm-1), 581 nm (17,212 cm-1) and 587 nm (17,036 cm-1); to 4F7/2, 4S3/2 at 734 nm (13,624 cm-1), 741
nm (13,495 cm-1) and 744 nm (13,441 cm-1).
3.3. Emission spectra
The samples were excited by means of the laser at 266 nm. This excitation line is consistent
with the energies of the singlet and triplet ligand levels. It was found that a broadband ligand
emission is observed at 414 nm. Figure 7 presents the emission spectra of the ligand and the studied
neodymium complex. The emission band presenting the ligand luminescence appears in the wide
range 350 – 800 nm and 350 – 600 in the spectrum of complex. The decay times of the
luminescence were determined for the ligand and the complex. The former was excited at 266 nm
and recorded value 0.30 ns proves that it originates from the S1 → S0 transition inside the ligand. It
is the order characteristic for the transition between the singlet states.

Fig. 7. The luminescence spectra of the ligand and its neodymium complex under 266 nm
excitation.
Fig. 8. The luminescence spectra of the neodymium complex under excitation at 803 nm.
The emission spectrum of neodymium complex recorded at room temperature in the 350 –
1100 nm spectral range under excitation at 266 nm consists of series bands corresponding to the
4
4
4
transitions from the metastable F3/2 level of Nd3+ ion to the terminal I9/2 and I11/2 levels as
assigned in Figure 7. The neodymium ions in the materials under study appear to be Nd3+ i.e. the
following electronic configuration 4f3 and 4I9/2 ground state are considered. In accordance with Nd3+
energy level diagram the observed emission bands were assigned to appropriate electronic f–f
4
transitions from F3/2 luminescent level to the lower-lying excited states. The emission spectra are
4
recorded at room temperature, hence the transitions from two crystal field components of F3/2
multiplet to crystal field sublevels of 4IJ manifolds occur. The luminescent 4F3/2 neodymium level is

separated from lower-energy multiplets ca 5500 cm-1 and consequently, the contribution of
adequate radiative transitions can be quite efficient in the investigated material. It can be seen that
the emission band related to the 4F3/2 → 4I11/2 transition and located at 1059 nm is the most intensive
and contains one prominent maximum with the shoulder at 1072 nm. On the other hand, the
emission band in the 850 - 950 nm range related to the 4F3/2 → 4I9/2 transition is complex and broad.
It consists of four clear visible components with maximum at 870, 874, 882 and 903 nm,
respectively. The line at 532 nm is due to Nd:YAG laser. Two very weak bands are also observed in
the emission spectrum. They could be ascribed to the following transitions: 2H11/2 → 4I9/2 at 614 nm
and 2H9/2, 4F5/2 → 4I9/2 at 805, 825 nm. The third emission band with maximum at 1330 cm-1 of the
4
4
Nd3+ ion originates from the F3/2 → I13/2 transition and it is observable under 803 nm excitation
(Figure 8). The decay curve of luminescence excited at 803 nm is shown in Figure 9. The
determined lifetime of 4F3/2 level is 1.3 s.
Fig. 9. The decay curve of luminescence from the 4F3/2 level.
On the basis of the recorded emission spectra, the mechanism of the energy transfer in the
studied materials could be proposed and presented in Figure 10. Upon irradiation, the organic
ligands absorb ultraviolet radiation to the excited singlet state (S1← S0) which is radiatively
deactivated through fluorescence or by fast non-radiative intersystem crossing (ISC) from the
4
excited S1 state to the T1 triplet state and next to the F3/2 level of Nd3+ ion. For the most efficient
energy transfer to neodymium ion the triplet state should be located 2000 to 3500 cm−1 above the

emitting level of the lanthanide ion. For the studied complexes this energy level gap is fulfilled.
This mechanism is consistent with those proposed in [54-56].
Fig. 10. The proposed ligand – Nd3+ ion path of the energy migration in the Nd-complex.
4. Conclusions
The studied in the present work [Nd(BCPN)3(NO3)3(H2O)2] complex formed with BCPN
ligand (3-bromo-2-chloro-6-picolinic N-oxide) appears in the molecular form containing the
NdO3O’3O”2 polyhedron formed by three oxygen atoms of the N-oxide group, three oxygen atoms
of the nitrate anions and two oxygen atoms of the water units. The vibrational spectra confirm the
statements derived from the results of the chemical analysis. The complexation of the ligand to Nd3+
ion occurs through the three N-oxide groups, three nitrate anions and two water units.
The DFT calculation shows that the BCPN belongs to the ligands whose triplet states lie
above the emitting neodymium levels. This configuration facilitates the energy transfer between the
ligand and the neodymium ions.
Two decay times were determined from the femtosecond luminescence studies. The decay
time 0.30 ns originates from the S1 → S0 transition inside the ligand – it is the order characteristic

for the transition between the singlet states. The decay time 1.3 s corresponds to the emission from
the 4F3/2 level excited state of the neodymium.
Bromo-chloro-derivatives of picoline N-oxides due to their complexation properties of the
lanthanide ions and convenient distribution of their singlet and triplet states constitute a prospective
group of ligands participating in the effective ligand-to-metal energy transfer process.
Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
Conflict of interest:
There are no conflicts of interest to declare.
Acknowledgement: This research work was supported by the National Science Centre, Poland
under the project No. 2014/15/B/ST5/04730.
References
1.
S. Shimizu, N. Watanabe, T. Kataoka, T. Shoji, N. Abe, S. Morishita, H. Ichimura,
Pyridine and Pyridine Derivatives, Ullmann’s Encyclopedia of Industrial Chemistry.
(2000) doi:10.1002/14356007.a22_399.
2.
3.
R. Jakubas, Z. Ciunik, G. Bator, Ferroelectric properties of [4-NH2C5H4NH][SbCl4], Phys.
Rev. B 67 (2003) 024103 (1-6).
A.P. Jeyakumari, S. Manivannan, S. Dhanuskodi, Spectral and optical studies of 2-amino-
5-nitropyridinium dihydrogen phosphate: A semiorganic nonlinear optical material,
Spectrochim. Acta A 67 (2007) 83-86.
4.
M. Inuzuka, H. Miyano, M. Tomoeda, Specific action of 4-nitropyridine 1-oxide on
Escherichia coli K-12 Pro+ strains leading to the isolation of proline – requiring mutants:
isolation and characterization of Pro- mutants, Antimicrob. Agents Chemother. 10 (1976)
325-332.
5.
6.
7.
T.K. Ha, Ab initio SCF and CI study of the electronic spectrum of pyridine N-oxide,
Theoret. Chim. Acta (Berl), 43 (1977) 337-349.
G.V. Kulkarni, A. Ray, Molecular orbital studies on some 4-substituted pyridine N-oxides
and 4-nitroquinoline N-oxide, J. Mol. Struct. 71 (1981) 253-262.
Von E. Ochiai, Aromatic Amine Oxides, Elsevier, Amsterdam 1967.

8.
9.
N. Haginoya, S. Kobayashi, S. Komoriya, T. Yoshino, T. Nagata, Y. Hirokawa, T.
Nagahara, Design, synthesis, and biological activity of non-amidine factor Xa inhibitors
containing pyridine N-oxide and 2-carbamoylthiazole units, Bioorg. Med. Chem. 12 (2004)
5579-5586.
S. Marchais-Oberwinkler, B. Nowicki, V.W. Pike, C. Halldin, J. Sandell, Y-H. Chou, B.
Gulyas, L.T. Brennum, L. Farde, H.V. Wikstrӧm, N-Oxide analogs of WAY-100635: new
high affinity 5-HT1A receptor antagonists, Bioorg. Med. Chem. 13 (2005) 883-893.
10. J. Balzarini, M. Stevens, E. De Clercq, D. Schols, C. Pannecouque, Pyridine N-oxide
derivatives: unusual anti-HIV compounds with multiple mechanisms of antiviral action, J.
Antimicrob. Chemother. 55 (2005) 135-138.
11. J. Balzarini, E. Keyaerts, L. Vijgen, F. Vandermeer, M. Stevens, E. De Clercq, H.
Egbering, M. Van Ranst, Pyridine N-oxide derivatives are inhibitory to the human SARS
and feline infectious peritonitis coronavirus in cell culture, J. Anrimicrob. Chemother. 57
(2006) 472-481.
12. K. Binnemans, Lanthanide-based luminescent hybrid materials, Chem. Rev. 109 (2009)
4283-4374.
13. N. Sabbatini, M. Guardigli, J.-M. Lehn, Luminescent lanthanide complexes as
photochemical supramolecular devices, Coord. Chem. Rev. 123 (1993) 201-228.
14. G.F. de Sá, O.L. Malta, C. de Mello Donegá, A.M. Simas, R.L. Longo, P.A. Santa-Cruz,
E.F. da Silva, Jr., Spectroscopic properties and design of highly luminescent lanthanide
coordination complexes, Coord. Chem. Rev. 196 (2000) 165-195.
15. Y.W. Yip, H. Wen, W.T. Wong, P.A. Tanner, K.L. Wong, Increased antenna effect of the
lanthanide complexes by control of a number of terdentate N-donor pyridine ligands,
Inorg. Chem, 51 (2012) 7013-7015.
16. N. Sabbatini, M. Guardigli, I. Manet, R. Ungaro, A. Casnati, R. Ziessel, G. Ulrich, Z.
Asfari, J.M. Lehn, Lanthanide complexes of encapsulating ligands: Luminescent devices at
the molecular level, Pure Appl. Chem. 67 (1995) 135-140.
17. S.I. Weissman, Intramolecular Energy Transfer. The Fluorescence of Complexes of
Europium, J. Chem. Phys. 10 (1942) 214-217.
18. H. Rostkowska, K. Szczepaniak, M. . Nowak, J. Leszczynski, K. KuBulat, W.B. Person,
Tautomerism and Infrared Spectra of Thiouracils. Matrix Isolation and ab Initio Studies, J.
Am. Chem. Soc. 112 (1990) 2147-2160.
19. O. Christiansen, Møller–Plesset perturbation theory for vibrational wave functions, J.
Chem. Phys. 119 (2003) 5773-5781.
20. V. Barone, Vibrational spectra of large molecules by density functional computations
beyond the harmonic approximation: the case of pyrrole and furan, Chem. Phys. Letters
383 (2004) 528–532.

21. C. Adamo, T. Le Bahers, M. Savarese, L. Wilbraham, G. García, R. Fukuda, M. Ehara, N.
Rega, I. Ciofini, Exploring excited states using Time Dependent Density Functional
Theory and density-based indexes, Coordin. Chem. Revs 304–305 (2015) 166–178.
22. V. Barone, G. Festa, A. Grandi, N. Rega, N. Sanna, Accurate vibrational spectra of large
molecules by density functional computations beyond the harmonic approximation: the
case of uracil and 2-thiouracil, Chem. Phys. Letters 388 (2004) 279–283.
23. P. Goszczycki, K. Stadnicka, M.Z. Brela, J. Grolik, K. Ostrowska, Synthesis, crystal
structures, and optical properties of the π-π interacting pyrrolo[2,3-b]quinoxaline
derivatives containing 2-thienyl substituent, J. Mol. Structure 1146 (2017) 337-346.
24. H. Ciurla, A. Puszko, Synthesis of dihalopicoline N-oxides and their 4-nitro-derivatives,
Khim. Geterocikl. Soed. 10 (1996) 1366-1971.
25. M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, Jr
J.A. Montgomery, T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J.
Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P.
Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O.
Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui,
A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I.
Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A.
Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C.
Gonzalez, J.A. Pople, Gaussian 03, Revision A.1, Gaussian, Inc., Pittsburgh PA, 2003.
26. A.D. Becke, Density-functional thermochemistry. IV. A new dynamical correlation
functional and implications for exact-exchange mixing, J. Chem. Phys. 104 (1996) 1040-
1046.
27. C. Lee, W. Yang, R.G. Parr, Development of the Colle-Salvetti correlation-energy formula
into a functional of the electron density, Phys. Rev. B 37 (1988) 785-789.
28. R.G. Parr, W. Yang, Density Functional Theory of Atoms and Molecules, Oxford Univ.
Press, New York, 1989.
29. A.D. McLean, G.S. Chandler, Contracted Gaussian basis sets for molecular calculations. I.
Second row atoms, Z=11-18, J. Chem. Phys. 72 (1980) 5639-5648.
30. R. Krishnan, J.S. Binkley, R. Seeger, J.A. Pople, Self-consistent molecular orbital
methods. XX. A basis set for correlated wave functions, J. Chem. Phys. 72 (1980) 650-
654.
31. G.A. Andrienko, ChemCraft Molecular Visualization Program, version 1.8 (Build 486).

32. M.J. Nowak, L. Lapinski, BALGA computer program for PED calculations (H.
Rostkowska, L. Lapinski, M.J. Nowak, Analysis of the normal modes of molecules with
D3h symmetry. Infrared spectra of monomeric s-triazine and cyanuric acid, Vibr. Spectrosc.
49 (2009) 43-51).
33. M.A. Palafox, V.K. Rastogi, Quantum chemical predictions of the vibrational spectra of
polyatomic molecules. The uracil molecule and two derivatives, Spectrochim. Acta A 58
(2002) 411-440.
34. P. Godlewska, L. Macalik, J. Lorenc, R. Lisiecki, W. Ryba-Romanowski, J. Hanuza, S.M.
Kaczmarek, H. Fuks, G. Leniec, Optical and magnetic properties of neodymium(III) six-
coordinate complexes of 2,6-lutidine N-oxide derivatives, J. Solid State Chem. 276 (2019)
294-301.
35. I. Bryndal, J. Lorenc, L. Macalik, J. Michalski, W. Sąsiadek, T. Lis, J. Hanuza, Crystal
structure, vibrational and optic properties of 2-N-methylamino-3-methylpyridine N-oxide -
Its X-ray and spectroscopic studies as well as DFT quantum chemical calculations, J. Mol.
Struct. 1195 (2019) 208-219.
36. J. Lorenc, J. Hanuza, J. Janczak, Structural and vibrational study of 3- or 5-methyl
substituted 2-N-ethylamino-4-nitropyridine N-oxides, Vibr. Spectrosc. 59 (2012) 59-70.
37. F. Partal Urena, M. Fernández Gómez, J.J. López Gonzáles, E. Martinez Torres, A new
insight into the vibrational analysis of pyridine, Spectrochim. Acta A 59 (2003) 2815-
2839.
38. K.B. Wilberg, V.A. Walters, K.N. Wong, S.D. Colson, Azines: vibrational force field and
intensities for pyridine, J. Phys. Chem. 88 (1984) 6067-6075.
39. G. Socrates, Infrared and Raman Characteristic Group Frequencies and references therein,
3rd ed., J. Wiley and Sons. Ltd., 2004.
40. G. Varsányi, S. Szöke, Vibrational spectra of benzene derivatives, Akademiai Kiado,
Budapest, 1969.
41. D. Lin-Vien, N.B. Colthup, W.G. Fateley, J.G. Grasselli, The Handbook of Infrared and
Raman Characteristic Frequencies of Organic Molecules, Academic Press: Boston, 1991.
42. I. López Tocón, M.S. Woolley, J.C. Otero, J.I. Marcos, Vibrational spectrum of 3-methyl
and 4-methylpyridine, J. Mol. Struct., 470 (1998) 241-246.
43. G. Varsányi, Assignments for Vibrational Spectra of Seven Hundred Benzene Derivatives,
vols. 1–2, Adam Hilger, 1974.
44. W. Zierkiewicz, D. Michalska, Th. Zeegers-Huyskens, Molecular structures and infrared
spectra of p-chlorophenol and p-bromophenol. Theoretical and experimental studies, J.
Phys. Chem. A 104 (2000) 11685-11692.

45. N. Sundaraganesan, B. Dominic Joshua, M. Rajamoorthy, C.H. Gangadhar, FT-IR, FT-
Raman spectra and ab- initio DFT vibrational analysis of 2-chloro-5-aminopyridine, Indian
J. Pure Appl. Phys. 45 (2007) 969-978.
46. V. Pouchaname, R. Madivanane, A. Tinabaye, K.B. Santhi, Vibrational spectroscopy
(FTIR and FTRaman) investigation using DFT analysis on the structure of 2-chloro-5-
nitropyridine, Sciencia Acta Xaveriana 2 (2011) 83-100.
47. P. Boopalachandran, H.L. Sheu, J. Laane, Vibrational spectra, structure, and theoretical
calculations of 2-chloro- and 3-chloropyridine and 2-bromo- and 3-bromopyridine, J. Mol.
Struct. 1023 (2012) 61-67.
48. E.F. Mooney, The infra-red spectra of chloro- and bromobenzene derivatives—II.
Nitrobenzenes, Spectrochim. Acta 20 (1964) 1021-1032; The infrared spectra of chloro-
and bromobenzene derivatives—I: Anisoles and phenetoles, Spectrochim. Acta 19 (1963)
877-887.
49. J.H.S. Green, W. Kynaston, H.M. Paisley, Vibrational spectra of monosubstituted
pyridines, Spectrochim. Acata 19 (1963) 549-564.
50. S. Sivakumar, G. Raja, M.E. Rajasaravanan, Studies on structures, vibrational frequencies
of 3-amino-2-bromo pyridine based on density functional theory calculations, Vibr.
Spectrosc. 38A (2011) 4574-4578.
51. M. Karabacak, M. Cinar, S. Ermec, M. Kurt, Experimental vibrational spectra (Raman,
infrared) and DFT calculations on monomeric and dimeric structures of 2- and 6-
bromonicotinic acid, J. Raman. Spectrosc. 41 (2010) 98-105.
52. K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, John Wiley &
Sons Inc., New York-London, 1963, pp. 90-95.
53. W.T. Carnall, P.R. Fields, K. Rajnak, Spectral intensities of the trivalent lanthanides and
actinides in solution. II. Pm3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+ and Ho3+, J. Chem. Phys. 49
(1968) 4412-4423.
54. J.C. Bünnzli, Benefiting from the unique properties of lanthanide ions, Acc. Chem. Res. 39
(2006) 53-61.
55. E. Huskowska, I. Turowska–Tyrk, J. Legendziewicz, J.P. Riehl, The structure and
spectroscopy of lanthanide(III) complexes with 2,2’-bipyridine-1,1’-dioxide in solution
and in the solid state: effects of ionic size and solvent on photophysics, ligand structure and
coordination, New J. Chem. 26 (2002) 1461-1467.
56. P. Gawryszewska, V.M. Amirkhanov, V.A. Trush, D. Kulesza, J. Legendziewicz, The
ligand-to-metal energy transfer and the role of Lewis base ligands and silver plasmons in
emission of new type of lanthanide phosphors, J. Luminesc. 170 (2016) 340-347.

Figure Caption
Fig. 1. Molecular structure of the studied Nd(BCPN)3(NO3)3(H2O)2 complex.
Fig. 2. Molecular structure of the 3-bromo-2-chloro-6-picolinic N-oxide ligand with atomic
numbering.
Fig. 3. MIR and FIR spectra of the studied ligand and its neodymium complex.
Fig. 4. Raman spectra of the studied ligand and its neodymium complex.
Fig. 5. The UV-ViS absorption spectra of the studied ligand and its neodymium complex.
Magnified parts of the chosen ranges are shown in insets.
Fig. 6. The calculated HOMO and LUMO molecular orbitals for the 3-bromo-2-chloro-6-methyl-N-
pyridine-oxide molecule.
Fig. 7. The luminescence spectra of the ligand and its neodymium complex under 266 nm
excitation.
Fig. 8. The luminescence spectra of the neodymium complex under excitation at 803 nm.
Fig. 9. The decay curve of luminescence from the 4F3/2 level.
Fig. 10. The proposed ligand – Nd3+ ion path of the energy migration in the Nd-complex.
Table Caption
Table 1. Selected geometrical parameters for the 3-bromo-2-chloro-6-methyl-N-pyridine-oxide
molecule.
Table 2. Selected geometrical parameters for the [Nd(BCPN)3(NO3)3(H2O)2] complex (see Fig. S1).
Table 3. The observed IR and Raman and calculated wavenumbers (in cm-1) using B3LYP/6-
311++G(2d,2p) wavenumbers with PEDs values and their assignment to the respective
normal modes based on the PED calculations.
Table 4. Calculated singlet electron level, oscillator strength, orbital configuration and electron
transition of the 3-bromo-2-chloro-6-methyl-N-pyridine-oxide molecule.

GRAPHICAL Abstract