Syntheses, structures and properties of 5-azotetrazolyl salicylic acid and its dilanthanide complexes

Article abstract of DOI:10.1039/c4dt00278d

Two hydrated 5-azotetrazolyl salicylic acid (H₃ASA) of [(H ₃ASA)·H₂O] (1) and [(H₃ASA) ·4H₂O] (2) and five H₃ASA based dinuclear Ln ³⁺ complexes of {[Ln₂(H_1.5ASA) ₄(H₂O)₈]·6H₂O} [Ln = Dy (3), Tb(4)], {[Gd₂(H_1.5ASA)₄ (H₂O) ₈]·5H₂O} (5), {[Sm₂(H _1.5ASA)₄(H₂O)₈]·6H ₂O} (6) and {[Eu₄(H_1.5ASA)₈(H ₂O)₁₈]·10H₂O} (7) have been synthesized and characterized by single crystal X-ray diffraction analysis. In 1 and 2, the neutral H₃ASA molecules show a trans-enol-E isomer but display two different dihedral angles. Complexes 3-7 exhibit three types of dinuclear structures in which the anionic ligands show two trans-enol-E/Z isomers. The photochromic and photoluminescent properties of 1, 3-7 and the magnetic properties for 3-7 were investigated. the Partner Organisations 2014.

Full text of DOI:10.1039/c4dt00278d

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Syntheses, structures and properties of
5-azotetrazolyl salicylic acid and its dilanthanide
complexes†
Cite this: Dalton Trans., 2014, 43,
9090
Wen-Bin Chen,a Zhi-Xin Li,a Xin-Wei Yu,a Meng Yang,a Yan-Xuan Qiu,a Wen Dong*a
and Ya-Qiu Sun*b
Two hydrated 5-azotetrazolyl salicylic acid (H3ASA) of [(H3ASA)·H2O] (1) and [(H3ASA)·4H2O] (2) and five
H3ASA based dinuclear Ln3+ complexes of {[Ln2(H1.5ASA)4(H2O)8]·6H2O} [Ln
= Dy (3), Tb(4)],
{[Gd2(H1.5ASA)4 (H2O)8]·5H2O} (5), {[Sm2(H1.5ASA)4(H2O)8]·6H2O} (6) and {[Eu4(H1.5ASA)8(H2O)18]·10H2O}
(7) have been synthesized and characterized by single crystal X-ray diffraction analysis. In 1 and 2, the
neutral H3ASA molecules show a trans-enol-E isomer but display two different dihedral angles. Com-
plexes 3–7 exhibit three types of dinuclear structures in which the anionic ligands show two trans-enol-
E/Z isomers. The photochromic and photoluminescent properties of 1, 3–7 and the magnetic properties
for 3–7 were investigated.
Received 25th January 2014,
Accepted 15th March 2014
DOI: 10.1039/c4dt00278d
www.rsc.org/dalton
nescent and magnetic materials.2 Currently, it is a particular
challenge to assemble novel lanthanide complexes with
Introduction
In the past few decades, a great deal of research has been different functional properties.3 An efficient approach for the
carried out on lanthanide complex-based inorganic–organic generation of hybrids is to assemble appropriate organic
hybrid materials due to their multifunctional, versatile and ligands into lanthanide ion systems by coordinating bonding
modulated properties.1 It is believed that these types of hybrid interactions. Because different ligands can control the struc-
materials can not only preserve or even improve the respective tures and properties of the target molecules by different co-
features of the components but also produce new properties ordinating and bridging modes, choosing the right ligands is
depending on the synergy between the organic ligands and in- particularly important for the synthetic strategy. Triazole, tetra-
organic lanthanide ions. Because of the intrinsic abundant zole and salicylic acid have been proven to be desirable ligands
photoluminescent and magnetic properties of lanthanide due to their multicoordinating atoms and their own functional
ions, inorganic–organic hybrid lanthanide complexes can properties.4 Meanwhile, azo conjugated aromatic compounds
exhibit potential applications in the development of new lumi- are also desirable types of ligands because the azo linker is
known to be an efficient electronic bridge, which prompts the
creation of extended-conjugated systems, and such types of
aSchool of Chemistry and Chemical Engineering, Guangzhou Key Laboratory for
compounds can show a potential trans to cis photoisomeriza-
tion property.5 Very recently, the pronounced bathochromic
Environmentally Functional Materials and Technology, Guangzhou University,
Guangzhou, 510006, China. E-mail: dw320@aliyun.com
bDepartment of Chemistry, Tianjin Normal University, Tianjin, 300383, China.
absorption and photochromism of 1,1′-azobis-1,2,3-triazole,
1,1′-azobis-tetrazole and 5,5′-azotetrazolate based complexes
E-mail: hxxysyq@mal.tjnu.edu.cn
†Electronic supplementary information (ESI) available: The atomic labeling dia-
were reported.6 The H3ASA, which contains azo, salicylic acid
grams of 4–7; 3D supramolecular structures of 1–7; photoisomerization of 1; the
and tetrazole moieties, should be one of the especially desir-
able candidates because it can dissociate mono-, di- and tri-
temperature-dependent changes of UV-vis absorption spectra of aqueous solu-
tions of 1; TD-DFT calculations for the absorption spectra of the alkaline
valent anions, and each anion can not only give multiple co-
aqueous solution of 1; the color changes of 4–7 before and after 365 nm UV
ordinating and bridging modes, but also exhibit different trans/
irradiation; luminescent spectra of 1 and 5–7; X-ray powder diffraction patterns
cis-enol/keto-Z/E isomers based on the photoisomerization
reactions (Scheme 1). To the best of our knowledge, up to now
there has not yet been a report concerning the structures,
photochromic, photoluminescent and magnetic properties of
well-defined single crystals of the H3ASA based Ln3+ metallic
complexes.7 Here, seven novel H3ASA based compounds (1–7)
for 3–7; the plots of χMT versus T for 4–7; M versus H plots in the field range
0–40 000 (70 000) Oe for 3–5; M versus H/T plots in the field range 0–70 000 Oe
for 4; temperature-dependence of the in-phase (χ′) and out-of-phase (χ″) of ac
susceptibility of 3 at 250–1500 Hz; the 1/χM versus T plot in the range from 300 to
2 K for 5 and CIF files. CCDC 922441 for 1, 946733 for 2, 922442 for 3, 922443
for 4, 922444 for 5, 922445 for 6, 922446 for 7. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c4dt00278d
9090 | Dalton Trans., 2014, 43, 9090–9097
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composition analysis was performed with the Hisnfeld
method using the program Multiwfn 2.5.8
Syntheses of [(H3ATSA)·H2O] (1) and [(H3ASA)·4H2O] (2)
Scheme 1 The photoisomerization reaction of the ASA3− anion.
5-Azotetrazolyl salicylic acid was synthesized according to the
method reported in ref. 9: 5-amino-1H-tetrazole (2.06 g,
0.02 mol) was dissolved in 50 mL of distilled water, 3 mL of
concentrated hydrochloric acid was added. The reaction solu-
tion was stirred, cooled and kept at −5 to 0 °C in an ice bath
(ice and sodium chloride) and diazotized by the slow addition
of a solution of sodium nitrite (0.02 mol, 1.38 g) in water
(20 mL), followed by stirring for 30 min at −5 to 0 °C. Then a
solution of salicylic acid (0.02 mol, 2.76 g) in ethanol (20 mL)
was slowly added to the solution of the diazonium salt at
0–5 °C. The resulting mixture was stirred for 12 h and then the
yellow precipitate was filtered and washed with water (yield:
73.2%). The yellow crystals of 1 and red crystals of 2 were
obtained after recrystallization in acid solution with a pH of
about 5. FT-IR (KBr, cm−1): 3241m, 1659s, 1494s, 1445s, 1186s,
760m, 696m for 1. Anal. Calcd for 1 of C8H8N6O4 (%): C, 38.07;
H, 3.17; N, 33.31. Found(%): C, 38.11; H, 3.26; N, 33.35. FT-IR
(KBr, cm−1): 3456m, 3236s, 1661s, 1483s, 1444s, 1294s, 1156s,
891s, 756s, 695s, 533m for 2. Anal. Calcd for 2 of C8H14N6O7
(%): C, 31.35; H, 4.57; N, 27.43. Found(%): C, 31.25; H, 4.78;
N, 27.38.
were synthesized and their crystal structures, photochromism,
photoluminescence and magnetism were investigated and
discussed.
Experimental
Materials and physical measurements
All commercial reagents and solvents were used without
further purification unless otherwise stated. IR spectra were
recorded as pressed KBr pellets on a Bruker Tensor 27 spectro-
photometer. Elemental analyses were carried out using a
Perkin-Elmer analyzer model 240. UV-vis absorption spectra of
1 in aqueous solution were collected on a U-1800 Ultraviolet-
Visible Spectrophotometer. The solid-state diffuse reflectance
spectra were measured on a Hitachi UV-2501PC spectrophoto-
meter equipped with an integrating sphere attachment and
against a BaSO4 plate as the standard. Luminescence spectra
were recorded with an F-4500 fluorescence spectrophotometer.
Fluorescent imaging experiments for solid samples were con-
ducted with a Nikon 55i Fluorescent Microscope. The mag-
netic measurements of the sample of 3–7 were carried out
using a SQUID magnetometer in the temperature range of
2–300 K at a constant magnetic field (1000 Oe). Ac data were
collected in the range 2–5.5 K with an applied alternating field
of 3.5 Oe at different frequencies in the range 0–1500 Hz.
Syntheses of 3–6
10 mL aqueous solution of MCl3·6H2O (0.01 mmol) was added
to a solution of 5-azotetrazolyl salicylic acid (0.0504 g,
0.2 mmol) in 10 mL of water and 10 mL of ethanol and stirred
for 5 min, then a drop of dilute NH3·H2O (2 mol L−1) was
added to adjust the pH to about 5. The resulting mixture was
filtered and block crystals were obtained by slow evaporation
of the filtrate after several days, which were then washed with
ethanol to give a 36.5% yield of 3 (based on Dy3+), 28.9% yield
of 4 (based on Tb3+), 28.5% yield of 5 (based on Gd3+) and
33.2% yield of 6 (based on Sm3+). Anal. Calcd for 3 of
C32H46N24O26Dy2 (%): C, 25.47; H, 3.05; N, 22.28. Found(%): C,
25.49; H, 3.09; N, 22.32. FT-IR (KBr, cm−1): 3196m, 1627m,
1580s, 1443s, 1175m, 837w, 683m, 563w. Anal. Calcd for 4 of
C32H46N24O26Tb2 (%): C, 25.59; H, 3.07; N, 22.39. Found(%): C,
25.63; H, 3.13; N, 22.45. FT-IR (KBr, cm−1): 3306m, 1635m,
1558s, 1391s, 1246m, 1149m, 756m, 671m. Anal. Calcd for 5 of
C32H42N24O26Gd2 (%): C, 25.71; H, 2.81; N, 22.50. Found(%):
C, 25.76; H, 2.84; N, 22.56. FT-IR (KBr, cm−1): 3234m, 1628m,
1582s, 1387s, 1170m, 844w, 681m, 561w. Anal. Calcd for 6 of
C32H46N24O26Sm2 (%): C, 25.88; H, 3.10; N, 22.65. Found(%):
C, 25.60; H, 3.21; N, 22.69. FT-IR (KBr, cm−1): 3151s, 1623m,
1593s, 1441s, 1173m, 840w, 684m.
X-Ray crystallography and data collection
The crystals were filtered from the solution and immediately
coated with hydrocarbon oil on the microscope slide. Suitable
crystals were mounted on glass fibers with silicone grease and
placed in a Bruker Smart APEX(II) area detector using graphite
monochromated Mo-Kα radiation (λ = 0.71073 Å) at 173(2)/
298(2) K. The structures were solved by direct methods and
successive Fourier difference syntheses (SHELXS-97) and
refined by full-matrix least-squares procedure on F2 with aniso-
tropic thermal parameters for all non-hydrogen atoms
(SHELXL-97). Hydrogen atoms in the azotetrazolyl were added
by electron density peak and other hydrogen atoms including
water hydrogen atoms were added theoretically and were
riding on their parent atoms. CCDC 922441 for 1, 946733 for
2, 922442 for 3, 922443 for 4, 922444 for 5, 922445 for 6,
922446 for 7.†
Syntheses of 7
Quantum calculations
10 mL aqueous solution of EuCl3·6H2O (0.0366 g, 0.01 mmol)
All the quantum-chemical calculations were performed with was added to a solution of 5-azotetrazolyl salicylic acid
the Gaussian 09 suite using the time dependent density func- (0.0756 g, 0.3 mmol) in 10 mL of water and 10 mL of ethanol
tional theory (TD-DFT) method at the B3LYP/6-31+G(d,p) level and stirred for 5 min and a drop of dilute NH3·H2O (2 mol L−1
)
based on the crystal structures obtained in this work. Orbital was added to adjust the pH to about 5. The resulting mixture
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was filtered and block crystals were obtained by slow evapor-
ation of the filtrate after several days and washed with ethanol.
Yield: 31.6% (based on Eu3+). Anal. Calcd for
7 of
C64H92N48O52Eu4 (%): C, 25.83; H, 3.09; N, 22.60. Found(%): C,
25.86; H, 3.21; N, 22.65. FT-IR (KBr, cm−1): 3396m, 3225m,
1627m, 1580s, 1441s, 1170s, 837m, 681m, 561m.
Results and discussion
Crystal structures of 1–7
Table 1 gives the crystallographic data for compounds 1–7. The
atomic labeling diagrams for 1 and 2 are shown in Fig. 1a,b,
respectively. The crystals of 1 and 2 are yellow and red, respecti-
vely. 1 and 2 show two different space groups in which each
unit cell contains a fundamental H3ASA molecule and two
different lattice water molecules. In 1 and 2, the neutral H3ASA
molecules show a trans-enol-E isomer with the bond length for
C2–O3 (phenol) being 1.354(3) Å for 1 and 1.341(4) Å for 2.
The dihedral angles between the tetrazole and phenyl ring of
H3ASA are 0.62° in 1 and 39.1° in 2, which display a coplanar
and very twisted structure, respectively. The yellow colour of 1
and red of 2 should originate from the differences in dihedral
angles. The O–H⋯O and O–H⋯N hydrogen bonding and π–π
stacking interactions between the tetrazole and phenyl rings
are responsible for the stabilization of the 3D supramolecular
structure (Fig. S2, ESI†). The atomic labeling diagram of 3 is
depicted in Fig. 1c and the atomic labeling diagrams of 4–7
are shown in Fig. S3 ESI.† Complexes 3 and 4 are isostructural
molecules in which each Dy3+ or Tb3+ ion coordinates to four
carboxylate oxygen atoms from three ligands and four water
molecules to give an eight-coordinated square antiprism. In
complex 5, each Gd3+ ion shows a square antiprism environ-
ment surrounded by eight oxygen atoms from four carboxylate
oxygen atoms of three ligands and four water molecules. Each
Sm3+ ion shows a distorted tricapped trigonal prismatic
environment surrounded by nine oxygen atoms from four
carboxylate oxygen atoms of three ligands and five water mole-
cules in complex 6. However, there are two μ2 bridging water
molecules in 6 (Fig. S3c, ESI†). In 7, there are two different
coordinating environments for Eu3+ ions in which an Eu3+ ion
shows an eight-coordinated environment that is similar to the
Dy3+ ion in 3 and another Eu3+ ion is nine-coordinated with a
tricapped trigonal prismatic structure. In 3–7, the H2ASA− and
HASA2− anions show trans-enol-E and trans-enol-Z isomers,
respectively. The H2ASA− anion acts as a chelate ligand with
two carboxylate oxygen atoms coordinating to a Ln3+ ion and
each HASA2− anion acts as a μ2 bridging ligand with two carb-
oxylate oxygen atoms linking two Ln3+ ions to give a dinuclear
complex. The Ln3+⋯Ln3+ distances are 4.88, 4.85, 5.13, 4.23
and 4.93(5.32) Å for 3–7, respectively. The H2ASA− and HASA2−
anionic ligands are approximately coplanar because the di-
hedral angles between the tetrazole and phenyl ring are 1.30
and 7.62° for 3, 1.53 and 7.88° for 4, 1.35 and 3.62° for 5,
10.30 and 11.20° for 6, and 1.93 and 5.32° for 7. In complexes
3–7, the π–π staking between the tetrazole and phenyl aromatic
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2 mol L−3 NaOH aqueous solution, the solutions show two
clearly intense absorption peaks at 260 and 355 nm
accompanied by a decrease in intensity and an unresolved
weak shoulder peak around 430 nm. When the pH increases
from 10.21 to 11.64, an added new red-shifted maximum
absorption peak around 445 nm appears with an increase in
intensity. When the pH increases from 11.64–13.10, the solu-
tion exhibits two maximum absorption peaks around 276 and
445 nm and a weak shoulder peak around 410 nm. The
absorption peaks for the aqueous solution of 1 at a pH scale of
4.55–13.10 should originate from the intrinsic chromophoric
salicylic and tetrazolate π or azo n electronic excitation of the
trans-enol isomers of H3ASA or its anions. Fig. 2b gives the
photochromic properties for the alkaline aqueous solution of
1 with a concentration of 5 × 10−5 mol dm−3 and a pH of 11.64
under 365 nm UV light irradiation at room temperature. Upon
irradiation of the aqueous solution for 5 minutes with 365 nm
UV light, two absorption peaks around 276 and 445 nm
decrease in intensity and two new absorption peaks at around
260 and 355 nm are noted, also four regions with three iso-
sbestic points at 270, 297 and 375 nm can be distinguished.
When the UV light irradiation continuously increases for
25 minutes, the absorption intensity at the 355 nm peak
largely increases. When the time of UV light irradiation
increases for 60 minutes, the original two absorption peaks at
276 and 445 nm become unresolved. The phenomenon of the
maximum absorption peak transfer from 445 to 355 nm
should originate from the trans-enol to cis-enol photoisomeri-
zation reaction of the ASA3− anion (Scheme 1).6c Moreover, the
photochromism of the aqueous solution of 1 is in accordance
with the first-order kinetics (Fig. S5, ESI†), and the photochro-
Fig. 1 The atomic labeling diagrams: (a) for 1, (b) for 2, (c) for 3. All H
atoms and lattice water molecules have been omitted for clarity.
rings and the two O–H⋯O and O–H⋯N hydrogen bonding
interactions link the complex units and lattice water molecules
to give a 3D supramolecular packing structure (Fig. S4, ESI†).
The pH-dependent UV-vis spectra and photochromism of
aqueous solution of 1
Fig. 2a gives the pH-dependent UV-vis spectra of the aqueous
solution of 1 with a concentration of 5 × 10−5 mol dm−3. The
pH of the aqueous solution of 1 (5 × 10−5 mol dm−3) is 4.55.
When the pH increases from 4.55 to 10.21 by titration with
mism rate constant is about 2.824 × 10−2 min−1 6a
The temp-
.
erature-dependent changes of the UV-vis absorption spectra of
the alkaline aqueous solutions of 1 with a concentration of
5 × 10−5 mol dm−3 and pH of 11.64 in the temperature range
of 32–100 °C are given in Fig. S6, ESI.† When the temperature
of the aqueous solutions of 1 increases from 32 to 100 °C, the
three absorption peaks around 280, 400 and 445 nm decrease
in intensity and two new absorption peaks at around 260 and
355 nm are noted, also four regions with three isosbestic
points at 270, 297 and 375 nm could be distinguished. The
thermochromic properties of the aqueous solutions of 1 are
very similar to the characteristics of photochromism and
should also be assigned to the trans-enol to cis-enol isomeric
reaction of the ASA3− anion. For the TD-DFT calculations of
the absorption peaks of the alkaline aqueous solution of 1 and
the photoisomerization reaction see the ESI (Fig. S7, ESI†).
The photochromic properties of crystal powder samples of 1
and 3
Fig. 3 gives the color changes and the corresponding diffuse
reflectance spectra of the crystal powder samples of 1 and 3
after 365 nm UV light irradiation at room temperature. From
the diagrams, the two crystal powder samples change to dark
brown from the original bright yellow for 1 and orange for 3
after irradiation for 30 min. Before light irradiation, the crystal
Fig. 2 (a) The pH-dependent UV-vis spectral changes of the aqueous
solutions of 1. (b) The UV-vis spectral changes of 1 in alkaline aqueous
solution with a pH of 11.64 under 365 nm UV irradiation.
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Fig. 4 (a) The emission spectra of 1. (b) Excitation and emission spectra
of 3 and 4. Inset is the photoluminescent image of the solid sample of 1,
3, 4 taken with a fluorescent microscope.
Fig. 3 (a), (b) The color and corresponding diffuse reflectance spectra
of the crystal powder samples of 1 and 3 before and after 365 nm UV
light irradiation, respectively.
peaks of the Tb3+ ion around 491, 543, 584 and 620 nm, which
correspond to the 5D4–7F6, 5D4–7F5, 5D4–7F4, 5D4–7F3 tran-
sitions, respectively. The two solid samples of 3 and 4 display
yellow-green images and green images when observed by a
fluorescent microscope under UV light excitation, respectively
(Fig. 4b, insert). However, the solid samples of 5–7 only display
two fluorescent emissive peaks, around 460 and 540 nm, that
come from the anionic ligands, with the characteristic
fluorescent emissive peaks of Sm3+ and Eu3+ ions not being
observed (Fig. S9, ESI†). Based on the above photoluminescent
spectra of 1, 3–7, a selective antenna effect of the H3ASA ligand
for inducing Dy3+ and Tb3+ ion photoluminescence was found.
powder samples of 1 and 3 display two distinguishable absorp-
tion peaks centered around 330 nm and 450 nm. After light
irradiation, the samples show an a new red shift peak at
around 600 nm. The absorption peak around 330 nm and
450 nm can be attributed to the intrinsic π electronic tran-
sitions from the chromophoric tetrazolate, azo and salicylic
groups. The larger red shift peak around 600 nm may be attrib-
uted to the keto isomer from the photoisomeric reaction.10
The crystal powder samples of 4–7 show similar photochromic
properties to 3 (Fig. S8, ESI†).
Luminescence of the solid samples of 1, 3–7
Magnetic properties of 3–7
The photoluminescent spectra of the solid samples of 1, 3–7 In order to probe the magnetic behaviour of 3–7, the tempera-
are depicted in Fig. 4 and Fig. S9, ESI.† Under 340 nm UV light ture dependence of the magnetic susceptibilities of 3–7 have
excitation, the solid phase of 1 exhibits a maximum emissive been measured for microcrystalline samples over the tempera-
peak around 460 nm and a shoulder peak around 370 nm ture range 2–300 K under an applied direct current (dc) mag-
(Fig. 4a). The solid sample of 1 shows a blue image when netic field of 1000 Oe. The plots of χMT versus T for 3–7, where
observed by a fluorescent microscope under UV light excitation χM is the molar magnetic susceptibility, are shown in Fig. 5
(Fig. 4a, insert). Both solid samples of 3 and 4 exhibit Dy3+ and and Fig. S10, ESI.† As shown in Fig. 5a, the observed χMT value
Tb3+ ionic characteristic fluorescent emissive peaks under for 3 at 300 K is 28.87 cm3 K mol−1, which is in agreement
340 nm UV light excitation, respectively (Fig. 4b). 3 exhibits the with the theoretical value of 28.34 cm3 K mol−1 for two non-
480 and 571 nm characteristic emissive peaks of the Dy3+ ion, interacting Dy3+ ions (6H15/2, S = 5/2, L = 5, g = 4/3, χT =
and the 457 and 529 nm characteristic peaks of the H2ASA− 14.17 cm3 K mol−1). Upon decreasing the temperature, χMT
and HASA2− anionic ligands. The 480 and 571 nm peaks gradually decreases to reach 23.40 cm3 K mol−1 at 4.5 K. The
4
4
should correspond to the F9/2–6H15/2, F9/2–6H13/2 transitions, decreasing values of χMT is most likely due to depopulation of
respectively. The 457 and 529 nm maximum emissive peaks the Stark sublevels in Dy3+ systems. Finally, below 4.5 K a
should originate from the π electronic radiative relaxation of sharp increase can be observed and the χMT reaches a
the anionic ligands. 4 displays four characteristic emissive maximum value of 25.60 cm3 K mol−1 at 2 K. Such an increase
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barriers and relaxation times were approximated using a
method recently employed by Bartolome et al.13 based on the
following equation:
ꢀ
ꢁ
χ′′
χ′
ln
¼ lnðωτÞ þ Ea=kBT
The calculated energy barrier of 3 was found to be 3.75 K
whereas the relaxation time is 5.76 × 10−5 s (Fig. S13, ESI†).
This behavior is consistent with the behavior of a single mole-
cule magnet and the values of the energy barrier and relax-
ation time are comparable with that observed in other Dy(III)-
based SMMs.12,14
The plot χMT versus T for 4 is depicted in Fig. S10, ESI.† The
χMT value of 24.09 cm3 K mol−1 at 300 K is in good agreement
with the expected value of 23.63 cm3 K mol−1 for two non-
interacting Tb3+ ions (7F6, S = 3, L = 3, g = 3/2). Upon cooling to
12 K, the χMT of the product gradually decreases to 21.47 cm3
K mol−1, which is most likely due to the depopulation of the
Stark sublevels in the Tb3+ systems. Then the χMT of the
product increases to 27.85 cm3 K mol−1 at 2 K, which is prob-
ably due to the presence of an intramolecular ferromagnetic
interaction between the Tb3+ ions. The M versus H plots for 4
in the field range 0–70 000 Oe below 8 K are shown in Fig. S14,
ESI.† The magnetization measurement for 4 also shows a rela-
tively rapid increase below 10 kOe and a slow linear increase
without complete saturation up to 70 kOe. The maximum mag-
netization of 11.5μB at 70 kOe at 2.5 K is lower than the
expected saturation value for two non-interacting Tb3+ ions
[gJ × J = 3/2 × 6 = 9μB per Tb3+]. The M versus H/T plots for 4
shows no superimposition on a single master curve (Fig. S15,
ESI†), which suggests the presence of low-lying excited states
or/and significant magnetic anisotropy. The magnetic suscep-
tibility studies of 5–7 were plotted as χMT versus T in Fig. S9,
ESI.† The observed χMT values at 300 K are 12.27, 0.19 and
6.78 cm3 K mol−1 for 5–7, respectively. The theoretical calcu-
lated χMT values for two non-interacting Gd3+ (8S7/2, S = 7/2, L =
0, g = 2) ions are 15.76 cm3 K mol−1. Upon decreasing the
Fig. 5 (a) The plot of χMT versus T for 3 in the magnetic field of 1000
Oe at 2–300 K. Insert is the plot of M versus H/T in the field range
0–40 000 Oe; (b) (c) frequency-dependence of the in-phase (χ’) and
out-of-phase (χ’’) of ac susceptibility of 3 at 2 K–3.5 K.
can be attributed to intramolecular ferromagnetic interactions
between the Dy3+ ions.11,12 The magnetization (M) of 3 that
was collected from a zero dc field to 40 kOe below 8 K is
shown in Fig. S11, ESI.† The magnetization of 3 shows a rela-
tively rapid increase below 10 kOe and a slow linear increase
without complete saturation up to 40 kOe. The magnetization
reaches a maximum value of 13.5μB at 2.5 K and 40 kOe. This
value is lower than the expected saturation value for two non-
interacting Dy3+ ions [gJ × J = 4/3 × 15/2 = 10μB per Dy3+], which
is likely due to crystal-field effects and the low-lying excited
states. The M versus H/T plot is given in the insert of Fig. 5a.
The lack of a superimposition on a single master curve as
expected for an isotropic system with a well-defined ground
state and the lower magnetization values for 3 suggests the
presence of low-lying excited states or/and significant magnetic
anisotropy.11 The alternating current (ac) magnetic suscepti-
bility for 3 was performed in a zero-dc field as a function of
the ac frequency between 0.1 and 1500 Hz in the temperature
range 2–3.5 K (Fig. 5b,c). The in-phase (χ′) and out-of-phase
(χ″) signals show obvious frequency dependence at low temp-
erature, but no peak was observed (Fig. S12, ESI†). The energy
temperature, χMT gradually decreases to reach 9.06 cm3
K
mol−1 at 2 K, which indicates antiferromagnetic interactions
between Gd3+ ions. The 1/χM versus T plot in the range from
300 to 2 K obeys the Curie–Weiss law (χM = C/(T − θ)) with a
Weiss constant θ of −7.13 K (Fig. S16, ESI†). The negative
Weiss constant further confirms an intramolecular antiferro-
magnetic interaction between adjacent Gd3+ ions. The field
dependence of the magnetisation below 8 K reveals a relatively
rapid increase of the magnetisation below 10 kOe and then a
very slow linear increase without complete saturation up to
70 kOe (Fig. S17, ESI†). The maximum magnetization of 7.83μB
at 70 kOe is lower than the expected saturation value for two
non-interacting Gd3+ ions [gJ × J = 2 × 7/2 = 7μB per Gd3+]. For
6, the theoretical calculated χMT values for two non-interacting
Sm3+ (6H5/2, S = 5/2, L = 5, g = 2/7) ions are 0.18 cm3 K mol−1
,
which is in agreement with the observed value. However, the
magnetic properties of the Eu3+ ions in 7 are difficult to inter-
pret even at room temperature due to the presence of
thermally populated excited states.
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Conclusions
In summary, a novel organic functional ligand of H3ASA with
two hydrated crystals that are yellow (1) and red (2) in color,
and its five lanthanide complexes (3–7) were synthesized and
reported for the first time. The solids of 1, 3–7 display photo-
chromic properties and the trans-enol to cis-enol transition for
the ASA3− anion is demonstrated by TD-DFT calculations. The
photoluminescence of the solids of 1, 3–7 were reported and a
selective antenna effect of the H3ASA ligand for inducing Dy3+
and Tb3+ ionic photoluminescence was found. The magnetic
properties of 3–7 were investigated and the SMM behavior of 3
was demonstrated. This work demonstrates that H3ASA based
lanthanide complexes show photochromic, photoluminescent
and magnetic properties and are promising novel functional
materials that may be suitable for applications in optical and
magnetic devices.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (no. 21271052), the Science and Technol-
ogy Program Foundation of Guangzhou (no. 2013J4100016)
and the Program Foundation of the second batch of inno-
vation teams of Guangzhou Bureau of Education (13C04).
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