Two new lanthanide-nitronyl nitroxide complexes: Magnetic and fluorescence properties

Article abstract of DOI:10.1016/j.poly.2018.09.035

Two new lanthanide complexes of nitronyl nitroxide radical have been synthesized and characterized on the structure, magnetism and fluorescence: [Ln(hfac)₃(NITPh-(OCH₃)₂)₂](Ln = (Tb(1),Dy(2)), (NITPh-(OCH₃)₂ = 2-(3′,4′-dimethoxy-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide); hfac = hexafluoroacetylacetonate). Two complexes crystallize in monoclinic space group C2/c, which have similar mononuclear structures. The central metal ion is eight coordinated by six oxygen atoms from three hfac molecules and two oxygen atoms from two nitronyl nitroxide radicals. The varying temperature magnetic susceptibility indicates that there are weak antiferromagnetic interaction between metal ions and nitronyl nitroxide radicals in complexes 1 (zJ′ = ?0.145 cm^?1) and 2 (zJ′ = ?0.140 cm^?1). Ac magnetic susceptibility studies exhibit no single-molecule magnet behavior in complexes 1 and 2. In addition, the fluorescence properties of 1 show that it is an excellent fluorescent probe of recognizing Cr₂O₇^2? anion. Because of the linear relationship at low concentration and detection limit reached 1 × 10^?7 M, it can be used as a luminescence-based sensor for quantitative analysis.

Full text of DOI:10.1016/j.poly.2018.09.035

Accepted Manuscript
Two new lanthanide-nitronyl nitroxide complexes: magnetic and fluorescence
properties
Pei-Pei Sun, Shuai-Liang Yang, Chen-Xi Zhang, Qing-Lun Wang
PII:
S0277-5387(18)30587-4
https://doi.org/10.1016/j.poly.2018.09.035
POLY 13434
DOI:
Reference:
Polyhedron
To appear in:
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Accepted Date:
25 May 2018
15 September 2018
Please cite this article as: P-P. Sun, S-L. Yang, C-X. Zhang, Q-L. Wang, Two new lanthanide-nitronyl nitroxide
complexes: magnetic and fluorescence properties, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.
2018.09.035
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Two new lanthanide-nitronyl nitroxide complexes: magnetic and
fluorescence properties
Pei-Pei Sun a, Shuai-Liang Yang b, Chen-Xi Zhang ab*and Qing-Lun Wang cd
aCollege of Chemical Engineering and Materials Science, Tianjin University of Science and
Technology, Tianjin 300457, P. R. China
bKey Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai
University, Tianjin 300071, P. R. China
cCollege of Chemistry, Nankai University, Tianjin 300071, P. R. China
ABSTRACT
Two new lanthanide complexes of nitronyl nitroxide radical have been synthesized and
characterized on the structure, magnetism and fluorescence: [Ln(hfac)3(NITPh-
(OCH3)2)2](Ln=(Tb(1),Dy(2)),
(NITPh-(OCH3)2=2-(3′,4′-dimethoxy-phenyl)-4,4,5,5-
tetramethyl-imidazoline-1-oxyl-3-oxide)； hfac=hexafluoroacetylacetonate). Two complexes
crystallize in monoclinic space group C2/c, which have similar mononuclear structures. The
central metal ion is eight coordinated by six oxygen atoms from three hfac molecules and two
oxygen atoms from two nitronyl nitroxide radicals. The varying temperature magnetic
susceptibility indicates that there are weak antiferromagnetic interaction between metal ions
and nitronyl nitroxide radicals in complexes 1 (zJ′ = -0.145 cm−1) and 2 (zJ′ = -0.140 cm−1).
Ac magnetic susceptibility studies exhibit no single-molecule magnet behavior in complexes
1 and 2. In addition, the fluorescence properties of 1 show that it is an excellent fluorescent
2-
probe of recognizing Cr2O7 anion. Because of the linear relationship at low concentration
and detection limit reached 1×10-7 M, it can be used as a luminescence-based sensor for
quantitative analysis.
Keywords: Nitronyl nitroxide; Lanthanides; Magnetic properties; Luminescence properties
1. Introduction
In recent years, the unique structure and properties of nitronyl nitroxide radical have attracted
many researchers due to their advantages such as good chemical stability, versatility, easy to
modify[1-2]. The metal-radical method has been proved to be one of the most effective methods for
synthesizing molecular-based magnetic materials[3-4]. Based on the electronic arrangement rule,
the 4f electron orbit of lanthanide ions is effective shielded by the outer-shell electrons.
Furthermore, lanthanide ions have large anisotropic magnetic moments, the energy barrier value
increase obviously, therefore magnetic characteristics of lanthanide ions are difficult to be
analyzed[5]. To explore the magnetic properties of lanthanide-radical complexes, different types of
lanthanide complexes with nitronyl nitroxide radicals were synthesized[6]. Tb(III) and Dy(III) ions
have large magnetic anisotropies and become an ideal choice for constructing SMMs and SCMs[7-
8], especially since the first 4f–2p SMM [Dy(hfac)3NITpPy] was reported[9]. Hence, we decided
to use Tb and Dy ions combined with new nitronyl nitroxide radicals to obtain single-
molecule magnets.
Lanthanide metal with light physical characteristics of photochemical stability, long
fluorescence lifetime, emission wavelength and large Stokes shift, can avoid the

Corresponding author. Email: zcx@tust.edu.cn

interference of stray light and fluorescence system itself, thus greatly increases the
sensitivity of the sensor[10]. Therefore, lanthanide metal complexes have been widely used
for the sensation of biological anions, metal ions, and oxides[11]
.
In order to detect the new lanthanide-radical magnetic coupling systems and to better
understand the properties of 4f-2p magnetic interactions, two mononuclear lanthanide-radical
complexes ([Ln(hfac)3(NITPh-(OCH3)2)2] (Ln=Tb(1),Dy(2)) were synthesized successfully
by using a new nitronyl nitroxide radical (NITPh-(OCH3)2=2-(3′,4′-dimethoxy-phenyl)-
4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) (Scheme 1). Their crystal structures and
magnetic properties were described in this paper. Meanwhile, the luminescence
characteristics of complex 1 show the characteristic emission peaks of Tb(III) ions and the
2-
ability to recognize Cr2O7 . Therefore, complex 1 can be used as a luminescence-based
2-
sensor for the quantitative and sensitive detection of Cr2O7 .
O
N
O
N
O
O
Scheme 1. Structure of the NITPh-(OCH3)2
2. Experimental
2.1. General
All of the reagents and solvents are of analytical grade without purification.
[13]
Ln(hfac)3·2H2O (Ln=Tb(1),Dy(2))[12] and NITPh-(OCH3)2 were synthesized according
to known methods. C, H and N were analyzed on a Model 240 Perkin-Elmer elemental
analyzer. Complexes 1 and 2 were measured using a WGH-30A double beam infrared
spectrophotometer with KBr tablets in the 4000-400cm-1 range. The PXRD was recorded
on the Shimadzu Labx XRD-6100 diffractometer using the Cu target tube and the graphite
monochromator, and operated under the 40kV and 30.0mA. The intensity data were
continuously scanned from 5° to 50° degrees in 2θ/θ mode, with the step length of 0.02°
and the scan speed of 5° min-1. MPMS-7 SQUID magnetometer recorded magnetic data.
The diamagnetic corrections were carried out by the Pascal′s constants for all the atoms[14]
.
Luminescence characteristics were recorded on F-280FL spectrophotometer. UV-vis
spectral data were recorded by TU-1901. The infrared absorption peak and UV-vis spectral
data of complexes 1 and 2 are listed in Table S1-S2.
2.2. Synthesis of NITPh-(OCH3)2
2.2 g of 3,4-dimethoxybenzaldehyde was added to 3.1 g of 2,3-dimethyl butane-2,3-
hydroxylamine[13], and the reaction was stirred magnetically for 24 hours at room
temperature. A precipitate formed, the mixture was suction filtered, washed several times
with anhydrous ethanol, and dried in a vacuum oven at 40 °C for 12 hours to crush the
white product into a powder. Then, 2.1 g powder was added to 63 mL of dichloromethane,
then 3.0 g of a saturated solution of sodium periodate was added, magnetically stirred at
room temperature, the mixture turned from white to dark blue. The reaction was carried out

for one hour. After concentrating and purifying, the filtrate volatilize in at room
temperature and dark blue crystals were obtained. The yield was 58%.
2.3. Synthesis of [Ln(hfac)3(NITPh-(OCH3)2)2](Ln=Tb(1),Dy(2))
21 mg (0.025 mmol) of Tb(hfac)3·2H2O was added in 15 mL of N-heptane. The mixture
was magnetically stirred and refluxed at 110°C for 2 hours, cooled to 80°C, and then a
solution of NITPh-(OCH3)2 dissolved in 3 mL of CH2Cl2 was added. After refluxing for 30
min, the mixture was cooled and filtered, the filtrate was placed in a beaker, tardily
volatilize at about 4°C. Dark blue rhombohedral crystals suitable for X-ray diffraction
analysis were obtained after several days. Anal.Calcd(1) for C45H45TbF18N4O14
(Yield:41%): C, 39.50%, H, 3.29%, N, 4.10%; found: C, 39.37%, H, 3.48%, N, 4.18%. IR
(KBr, cm-1): 3494 (m), 2957(w), 3023(w), 1385(m), 1374(s), 1322(s), 1212(s).
The preparation of complex 2 is the same procedure as that of complex 1, but using
Dy(hfac)3·2H2O instead of Tb(hfac)3·2H2O. Anal.Calcd(2) for C45H45DyF18N4O14 (Yield:
39 %)：C, 39.41%, H, 3.28%, N, 4.09%; found: C, 38.97%, H, 3.31%, N, 4.23%. IR (KBr,
cm-1): 3502(m), 2931(w), 3101(w), 1330(m), 1362(s), 1294(s), 1217(s).
2.4. Crystal structure determination
The crystal structures data of complexes 1 and 2 were determined using a Bruker
SMART type 1000 X-ray diffractometer, using Mo Kα radiation (λ = 0.7107 Å)
monochromatized by a graphite monochromator at 113K. The diffraction points were
collected by ω-ψ scan method, the non-hydrogen atomic coordinates were solved by direct
method, and the coordinates and anisotropic thermal parameters were corrected by the least
square method. Hydrogen atoms were generated theoretically at the specific atoms and
refined isotropically with fixed thermal factors[15]. All computations and corrections were
implemented using the SHELXTL (olex 2) package[16]. The crystallographic data of the
obtained complexes are shown in Table 1.
Table 1．Crystal structure data and processing parameters for complexes 1-2.
Complexes
1
2
Empirical formula
C45H45TbF18N4O14
1366.77
113(2)
C45H45DyF18N4O14
1370.35
113(2)
Formula weight
T/ K
Color
Dark blue
monoclinic
C2/c
Dark blue
monoclinic
C2/c
Crystal system
Space group
a(Å)
20.911(10)
11.500(6)
22.945(12)
90.00
20.9451(4)
11.5010(3)
23.0265(4)
90.00
b(Å)
c(Å)
α (º)
β (º)
91.334(17)
90.00
91.4300(18)
90.00
γ (º)
Z
4
4
Volume (Å3)
5516(5)
1.646
5545.1(2)
1.628
Calculated density(mg/m3)
Absorption coefficient (mm-1)
F(000)
1.407
1.411
2728
2732

θ range for data collection (º)
Reflections
3.233 to 27.588
32875 / 15732
[R(int) = 0.0107]
1.067
3.208 to 27.421
32678 / 11827
[R(int) = 0.0268]
1.053
collected/unique
Goodness-of-fit on F2
R1[I＞2σ(I)]
0.0287
0.0323
wR2[I＞2σ(I)]
0.0967
0.1897
R1 (all data)
0.0643
0.0559
wR2 (all data)
0.1429
0.2013
2.5. The process of fluorescence study
The luminescent characteristics of complex 1 were studied in aqueous solution at room
temperature. For sensing of anions, 4 mg of the powder sample of complex 1 was
2-
-
2-
dispersed in 8 ml of salt solution KyX (X = Cl-, SO4 , Br-, NO3 , I-, and Cr2O7 , y = 1 or 2,
1 mM) and sonicated to form a suspension for fluorescence studies at room temperature.
(slit = 10 nm, PMT voltage = 950 V, scan rate = 1200 nm / min)
3. Results and discussion
3.1. Description of the crystal structures
Single-crystal X-ray diffraction analysis showed that complexes 1 and 2 crystallize in
monoclinic C2/c space group. They have similar mononuclear tri-spin structures (Figs. 1
and S1). The coordination polyhedron of complexes 1 and 2 can be described as a twisted
dodecahedron with triangular faces[17]. The crystal structure of complex 1 is described as
an example. The Tb(III) ion is eight coordinated by six oxygen comes from three hfac,
with the Tb-Ohfac bond length is in the range of 2.332(1)-2.409(1) Å, which is similar to
other Tb-nitroxide radicals complexes previously reported[18-19]. Another two oxygen
atoms come form two NITPh-(OCH3)2 with the Tb-ORad bond of 2.331(1) Å. The
uncoordinated N-O bond length (1.271(2) Å) is shorter than the coordinated N-O bond
length (1.307(2) Å). The bond angle of the ORad-Tb-ORad is 142.030(4)º . The dihedral
angle formed by five atoms on the O-N-C-N-O moieties of the nitronyl nitroxide radicals
and benzene ring is 25.227(60)º. The selected bond lengths and angles of complex 1 are
shown in Table S3.
Fig. 1. The molecular structure
of complex 1 (Hydrogen atoms and
fluorine atoms are not shown
for the sake of clarity)
For complex 2, due to
the substitution of the
crystal parameters, bond
slightly different. The
the lanthanide contraction,
central ions causes the
angles and bond lengths
bond length of Dy-Ohfac is
2.398(1) Å, which is similar
between
2.328(1)-
to the data reported in
the literature[18-21]
.
The
bond length of Dy-ORad is 2.325(1) Å. The uncoordinated N-O bond length (1.278(0) Å)
is also shorter than the coordinated N-O bond length (1.305(0) Å). The major bond lengths
and angles of complex 2 are shown in Table S4.
There are three types of hydrogen bonds in complex 1, which are C3-H13B…F6 (2.502
(2) Å ), C14-H14A…O2 (2.598 (2) Å), and C15-H15B…O3 (2.514 (2) Å) (Fig. S2). The
C3-H13B…F6 combines adjacent molecules into one-dimensional chains. The one-

dimensional chains are connected by C14-H14A…O2 to form a two-dimensional planar
structure and then through C15-H15B…O3 further form a three-dimensional
supramolecular network structure. There are two types of hydrogen bonds in complex 2,
which are C1-H1A…F4 (2.52 (2) Å) and C12-H12C…O4 (2.55 (2) Å). In Fig. S3, it can
be seen that due to the hydrogen bonding, complex 2 formed a 3D supermolecular network
structure. The lengths and angles of the intermolecular hydrogen bonds of complexes 1 and
2 are listed in Table S5.
3.2. Powder X-ray Diffraction
In order to determine whether the crystal structure really represents bulk material，the
X-ray powder diffraction patterns of complexes 1 and 2 are shown in Fig. S4 and S5. The
PXRD patterns are consistent with the results of a single crystal data simulation, reflecting
the purity of the synthesized bulk material.
3.3. Magnetic property for complexes 1 and 2
Temperature-dependent magnetic susceptibility tests for complexes 1 and 2 were done
under the conditions of an applied magnetic field of 1000 Oe and a temperature range of 2-
300 K. The temperature dependence of χM and χMT are shown in Figs. 2 and 3. The χMT
value of complex 1 at room temperature is 12.64 cm3 K mol-1, which is slightly higher than
the theoretical value 12.56 cm3 K mol-1 for uncoupled single Tb(III) ion (7F6, S=3, L=3, g
= 3/2, C=11.82 cm3 K mol-1) plus two radicals (S = 1/2). With the temperature decreasing,
the χMT value slightly increase from 300 - 80 K and then decreases sharply at low
temperature, reaching the minimum value of 4.09 cm3 K mol-1 at 2 K. This phenomenon
may be due to the weak antiferromagnetism between Tb(III) ion and nitronyl nitroxide
radicals and the depopulation of Ln(III) Stark energy level caused by crystal field
disturbance. For complex 2, at room temperature, the magnetic moment χMT value is about
14.99 cm3 K mol-1, which is resemblance to the theoretical value 14.92 cm3 K mol-1 for
uncoupled single Dy(III) ion (6H15/2, S=5/2, L=5, g = 4/3, C=14.17cm3 K mol-1) plus two
radicals (S = 1/2, 0.375 cm3 K mol-1). Upon cooling, the
reached the minimum value of 6.01 cm3 K mol-1 at 2 K.
χMT value decreases steadily and

Fig. 2. Temperature dependence of
χ
M (bottom) and
χ
MT (top) of complex 1 at 1000 Oe.
Fig. 3. Temperature dependence of
M (bottom) and
MT (top) of complex 2 at 1000 Oe.
Due to the large anisotropy of Ln(III) (Ln=Tb, Dy), it is difficult to apply a strict
magnetic interaction theory to this tri-spin system. Therefore, in order to roughly estimate
the magnetic interactions in the tri-spin molecule, we used the approximate model for
complexes 1 and 2 with equation (1)-(3) in SI [22-23]. The
χTb and χDy can be described by the
formula equation (4) and (5) in SI, respectively.
The best fitting parameters are g = 1.50, Δ = -0.56 cm−1, zJ′ = -0.145 cm−1 for complex 1
and g = 1.36, Δ = -4.67×10-2 cm−1, zJ′ = -0.14 cm−1 for complex 2. The negative zJ′ values
are indicative of the antiferromagnetic interactions between paramagnetic species in
complexes 1 and 2[24-25]
.
The magnetic interactions and corresponding distances of these complexes are listed in
Table 2. By comparison, it can be found that similar complexes have zJ′ values within a

certain range. With the bond length of ORad-Tb(III) decrease, the magnetic interaction turn
to strong, thus, the value of zJ′ increase. However, Dy complexes do not play this rule, this
maybe due to the fitting model ignoring some magnetic effect.
Table 2．The magnetic interactions and corresponding distances reported of complexes 1-2 in the
literatures.
Complexes
ORad-Tb(III) (Å)
Δ(cm-1)
zJ′(cm-1)
ref
[Tb(hfac)3(NITPh-3-Br-4-OMe)2]
[Tb(hfac)3(NITPh-Pa)2][a]
Tb(hfac)3(NITPh-(OCH3)2)2
Complexes
2.355
-0.190
-0.120
-0.565
Δ(cm-1)
-0.090
-0.070
-0.145
zJ′(cm-1)
18
2.333 and 2.335
2.331
19
this work
ref
ORad-Dy(III) (Å)
[Dy(hfac)3(NITPh-3-Br-4-OMe)2]
2.362
-0.050
+0.070
-0.0538
-0.080
-0.0133
-0.140
18
[b]
Dy(hfac)3(NITPhSCF3)2
2.310 and 2.329
2.316 and 2.322
2.303 and 2.345
2.325
-0.0101
-0.070
19
[Dy(hfac)3(NITPh-Pa)2]
{Dy(hfac)3[NITPhp-OCH2CH=CH2]2}[c]
20
-0.0005
-0.0468
21
Dy (hfac)3(NITPh-(OCH3)2)2
this work
[a]NITPh-Pa=2-(3′,4′-dioxylmethylene-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide；
[b]NITPhSCF3 = 2-(4-trifluoromethylthiophenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide；
[c]NITPhp-OCH2CH=CH2=2-(4′-Alloxylphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide.
The results of alternating current susceptibility of complexes 1 and 2 show that there are
no non-zero out-of-phase signal, indicating that there is no slow magnetic relaxation[26]
Therefore, complexes 1 and 2 have no single molecule magnet behavior. This may be
resulted from the fact that a small energy barrier cannot prevent the reversal of spins[27-28]
.
.
The test charts are shown in Figs. S6 and S7, respectively. (test conditions: 0 DC field, 961
Hz, 3.0 Oe AC electric field, temperature: 2-12 K.)
3.4. Luminescence Properties of complex 1
The luminescent properties of complex 1 were measured at room temperature.
Considering that complex 1 has excellent stability in aqueous systems, a series of
fluorescence experiments were performed in aqueous solution (Fig. S4). The peak at 312
nm is a π→π* transition absorption peak caused by the conjugated double bond on the
benzene ring, while the absorption peak at 219 nm is attributed to the π→π* transition
absorption band generated by the conjugated group of the ONCNO fragment. The
fluorescence spectrum also shows the characteristic emission peak of Tb(III) ions at 336
nm excitation (Fig. S8). The luminescence peaks centered around at 360, 548.5, 94, and
46.5 nm can be belong to the transitions of 5D4 →7FJ (J = 3, 4, 5 and 6 ) of complex 1 (Fig.
4). Among these emission peaks, 5D4 →7F5 caused by the electron dipole transition has the
strongest emission at 548.5 nm[29-30]
.

Fig. 4. Emission spectrum in aqueous solution.
Furthermore,in order to study the effect of different anions on the fluorescence intensity
of complex 1, the prepared crystal sample of complex 1 was grinded and dispersed in a salt
2-
-
2-
solutions of KyX (X= Cl-, SO4 , Br-, NO3 , I-, and Cr2O7 ), y = 1 or 2), and finally a
2-
suspension was formed by an ultrasonic method. It is clear that the Cr2O7 anion has a
pronounced fluorescence quenching effect on the complex 1, while other anions have little
effect on the fluorescence intensity (Fig. 5). To test the selectivity of complex 1,
interference experiment was performed (Fig. S9). The Cr2O72- anion added to other anionic
solution, the fluorescence intensity decreased immediately, then we could observe the
2-
2-[31-38]
quenching of Cr2O7 to achieve the detection of Cr2O7
in water. With the increases
2-
of Cr2O7 concentration, the intensity of luminescence gradually decreases (Fig. 6). In
addition, the quenching effect can be analyzed by the Stern-Volmer equation: I0/I = 1 +
Ksv[A], in which Ksv is quenching constant (M-1), I0 and I are the fluorescence intensities of
complex 1 before and after the addition of anions, [A] is the molar concentration of anions
(mM), respectively[39]
.

Fig. 5. Luminescence intensity of the transition (548.5nm) of complex 1 in different anions salt solution
(1mM). I and I0 denote the fluorescence intensity of complex 1 in anions solutionand water, respectively.
2-
Fig. 6. Emission spectra of complex 1 with different concentration of Cr2O7 aqueoussolution (from 0 to
10-3 M).
2-
The Stern-Volmer quenching curve for Cr2O7 anion display linear at low
concentrations (from 10-7 to 10-4 M) (Fig. 7), with a correlation coefficient of 0.982,
however the Stern-Volmer quenching curve off-linear at high concentrations. This
phenomenon illustrates the quenching of static and dynamic processes. The value of Ksv is
approximated as 2.10 × 104 M-1. According a ratio of 3δ/k, further detailed analysis
2-
showed that the detection limit was 10-7 M of Cr2O7 anion[40]. Compared with the MOFs
listed in Table S6, the detection limit is very low, which means that it is very promising in
2-
the selective and sensitive test for Cr2O7 .
Fig. 7. The Stern-Volmer plot of I0/I versus the concentration of Cr2O72- for complex 1 at low concentration
(from 10-7 to 10-4 M).

2-
In order to further analyze the possible quenching mechanism of Cr2O7 anion[41]. The
UV excitation spectrum of the Tb complex overlap strongly with the absorption spectrum
of the Cr2O72- anion, while other anions have almost no overlap with this wavelength range
(Fig. S10). Therefore, the aqueous solution containing Cr2O72- anion can forcefully absorb
the energy of the excitation wavelength, reducing the energy transfer efficiency from the
nitronyl nitroxide radical to the Tb(III) ion, eventually leading to the quenching of
luminescence[42]
.
4. Conclusions
To sum up, we successfully obtained two mononuclear tri-spin crystals
([Ln(hfac)3(NITPh-(OCH3)2)2] (Ln(III)=Tb(1), Dy(2)) by using 3,4-dimethoxyphenyl
nitronyl nitroxide radical. The variable temperature magnetic susceptibility of complexes 1
and 2 indicates that there are antiferromagnetic interactions between the Ln(III) ions and
radicals in complexes 1 and 2. Ac magnetic studies of complexes 1 and 2 did not show
frequency dependence, indicating that these two complexes may not exhibit SMM
behavior. Besides, the fluorescence spectrum of the complex 1 showed the characteristic
2-
emission peak of the Tb(III) ion and had the ability to identify the Cr2O7 anion. Because
of the lower detection limit (1×10-7 M) and almost linear at low concentration, complex 1
2-
may potentially sensitive detection of Cr2O7 anion and serve as a luminescence-based
sensor for quantitative analysis.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Nos.
21371104, 20771081, 21101096, and 21471084) and Laboratory Innovation Fund (30003)
of Tianjin University of Science and Technology.
Appendix A. Supplementary data
CCDC 1830531(1), 1830532(2) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.ac.uk/data_ request/cif.
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Graphical Abstract
In complexes 1 and 2, isolated mononuclear molecules connect each other through intermolecular
hydrogen bonds to form 3D supermolecular framework. Quantitative estimate of the magnetic
interaction parameters between paramagnetic species in complexes 1 and 2, The result indicates
that there are weak antiferromagnetic interaction between metal ions and nitronyl nitroxide
2-
radicals. The study of luminescence properties show that complex 1 may potentially detect Cr2O7
anions sensitively and as a luminescence-based sensor for quantitative analysis, due to the lower
detection limit (1 × 10 −7 M) and almost linear at low concentrations.
Graphical abstract synopsis
1. In complexes 1 and 2, isolated mononuclear molecules connect each other through
intermolecular hydrogen bonds to form 3D supermolecular framework.
2. Quantitative estimate of the magnetic interaction parameters between paramagnetic species in
complexes 1 and 2, The result indicates that there are weak antiferromagnetic interaction
between metal ions and nitronyl nitroxide radicals
2-
3. The study of luminescence properties show that complex 1 may potentially detect Cr2O7
anions sensitively and as a luminescence-based sensor for quantitative analysis, due to the
lower detection limit (1 × 10 −7 M) and almost linear at low concentrations.