Family of dumbbell Ni4Ln2 (Ln = Pr, Sm, Eu, Gd, Tb, Ho, Er) complexes: Syntheses, structures, luminescent and magnetic properties

Article abstract of DOI:10.1039/c3dt32935f

The synthesis and characterization of a family of heterometallic Ni ₄Ln₂ complexes (Ln = Pr(1), Sm(2), Eu(3), Gd(4), Tb(5), Ho(6) and Er(7)) of the formula [Ni₂LnL¹L ²(OH)(H₂O)]₂ are reported, where H ₄L¹ is 3,3′-(1E,1′E)-(2,2′-(2- aminoethylazanediyl)bis(ethane-2,1-diyl)bis(azan-1-yl-1-ylidene)) bis(methan-1-yl-1-ylidene)bis(2-hydroxybenzoic acid) and H₂L ² is 3-formyl-2-hydroxybenzoic acid. The molecular structures of 1-7 were determined by single-crystal X-ray diffraction and reveal that they are isostructural. In all of these compounds, the six metal ions are held together to form a novel Ni₄Ln₂O₁₀ core and exhibit a relatively rare dumbbell-type structure. In these compounds, the Ni ions are in slightly distorted square-pyramidal or octahedral environments. An all-oxygen coordination environment (8O) is present around the central lanthanide ion, which is present in a distorted square antiprismatic geometry. The Ln-Ln and Ln-O_avg bond distances in 1-7 show a gradual reduction proceeding from 1 to 7, in accordance with the lanthanide contraction. The luminescent properties of all the compounds have been studied. The magnetic susceptibility analysis demonstrate antiferromagnetic interactions within complex 4.

Full text of DOI:10.1039/c3dt32935f

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Family of dumbbell Ni4Ln2 (Ln = Pr, Sm, Eu, Gd, Tb, Ho, Er) complexes:
syntheses, structures, luminescent and magnetic properties
Baolin Liu,a,b Qingxia Liu,a Hongping Xiao,*c Wu Zhanga and Ruojie Tao*a
Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X
5
DOI: 10.1039/b000000x
The synthesis and characterization of a family of heterometallic Ni4Ln2 complexes (Ln = Pr(1), Sm(2),
Eu(3), Gd(4), Tb(5), Ho(6) and Er(7)) of formula [Ni2LnL1 L2(OH)(H2O)]2 are reported, where H4L1 is
3,3'ꢀ(1E,1'E)ꢀ(2,2'ꢀ(2ꢀaminoethylazanediyl)bis(ethaneꢀ2,1ꢀdiyl)bis(azanꢀ1ꢀylꢀ1ꢀylidene))bis(methanꢀ1ꢀylꢀ
1ꢀylidene)bis(2ꢀhydroxybenzoic acid), H2L2 is 3ꢀformylꢀ2ꢀhydroxybenzoic acid. The molecular structures
10 of 1ꢀ7 were determined by singleꢀcrystal Xꢀray diffraction and reveal that they are isostructural. In all of
these compounds, the six metal ions are held together to form novel Ni4Ln2O10 core, exhibit a relatively
rare dumbbellꢀtype structure. In these compounds, the Ni ions are in slightly distorted squareꢀpyramidal
or octahedral environments. An allꢀoxygen coordination environment (8O) is present around the central
lanthanide ion, which is present in a distorted square antiprismatic geometry. The LnꢀLn and LnꢀOavg
15 bond distances in 1-7 show a gradual reduction proceeding from 1 to 7 in accordance with lanthanide
contraction. The luminescent properties of all compounds have been studied. The magnetic susceptibility
analysis demonstrate antiferromagnetic interaction within complex 4.
squareꢀplanar Ni(II) ions were obtained.18 To avoid this, we have
Introduction
designed a new tripodal Schiffꢀbase ligand (H6L = 3, 3', 3''ꢀ(1E,
50 1'E, 1''E)ꢀ(2, 2', 2''ꢀnitrilotris(ethaneꢀ2,1ꢀdiyl) tris(azanꢀ1ꢀylꢀ1ꢀ
ylidene))tris(methanꢀ1ꢀylꢀ1ꢀylidene)tris(2ꢀhydroxybenzoic acid),
(H6L), was used in this study to build 3dꢀ4f heterometallic
coordination polymers. The main novelty of this work is that one
imine bond in the ligand H6L is degraded into NH2 group, giving
55 the new ligand H4L1 (Scheme 1). It is the first example from
hydrated Ni(II) salt promoting partial hydrolysis of the Schiff
base ligand.
The chemistry of heterometallic 3dꢀ4f complexes have attracted
20 considerable attention due to their structural diversity,1 and
versatile applications in magnetic,2 luminescent,3 adsorptive,4 and
electrical materials.5 Among all the heteronuclear edifice, most
are about the CuꢀLn systems,6 which contain oneꢀdimensional
chains,6a twoꢀdimensional layers6b and threeꢀdimensional
25 networks6c, while a few with NiꢀLn,7 FeꢀLn,8 CoꢀLn,9 ZnꢀLn10,
MnꢀLn11 and CrꢀLn12 systems are reported. We have recently
joined ongoing efforts in this area and have initially focused
primarily on NiꢀLn species. We were interested to discover
whether NiꢀLn combinations could be optimized to take
30 advantage of the second order orbital angular momentum of NiII
ions,13 which means that they also can provide large negative
zero field splitting parameters. It is worth noting that there are
Herein, we reported the syntheses, crystal structures,
luminescent properties and magnetic properties of
seven
as
60 dumbbell
coordination
clusters
formulated
[Ni2LnL1L2(OH)(H2O)]2 [Ln = Pr(1), Sm(2), Eu(3), Gd(4), Tb(5),
Ho(6) and Er(7)].
only
a few reports centered on the synthesis of NiꢀLn
HO
HOOC
N
N
OH
COOH
N
N
heterometallic single molecule magnets (SMMs).14
35
To facilitate the formation of 3dꢀ4f clusters, many researchers
have employed polydentate chelating ligands, such as Schiff
bases,15 Nꢀsubstituted diethanolamines,16 and tripodal ligands.17
All the ligands are appealing for mixedꢀmetal systems because
the chemical characteristics of the polydentate (N and O atoms)
HO
HOOC
H6L
40 can fulfill the coordination affinities to 3d and 4f metal ions for N
and O atoms. Such polydentate ligands have led to the discovery
of many interesting 3dꢀ4f clusters, some of which display SMM
behaviour. It is noteworthy that syntheses of NiꢀLn based SMMs
remain relatively scarce. These NiꢀLn complexes have been less
45 studied than the CuꢀLn examples, probably because there is no
strict control over the coordination geometry of the 3d metal ion.
Indeed in some cases NiꢀLn complexes containing diamagnetic
-
Ni2+
NO3
HO
HOOC
N
N
OH
COOH
O
OH
N
COOH
+
H2N
H4L1
H2L2
Scheme 1 Proposed process for the formation of H4L1
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corrections were made with Pascal’s constants for all atoms.
Experimental Section
Preparation of ligand H6L.
General
The ligand H6L was prepared by refluxing a solution of 3ꢀformylꢀ
20 2ꢀhydroxybenzoic acid (4.98 g, 30 mmol), trisꢀ(2ꢀ
aminoethyl)amine (1.46 g, 10 mmol) in ethanol (50 mL) during 3
h. After cooling to room temperature, yellow precipitate were
obtained, which were filtered off, washed with cool ethanol, and
diethylether and airꢀdried. Yield, 5.13 g, 87%. Anal. Calcd (%)
25 for C30H30N4O9: C, 61.02; H, 5.08; N, 9.49. Found: C, 60.68; H,
4.98; N, 9.39. 1H NMR (DMSOꢀd6, δ, ppm): 3.00 (6 H, t, 3 CH2),
3.82 (6 H, t, 3 CH2), 6.51 (3 H, t, 3 CH), 7.42 (3 H, dd, 3 CH),
7.95 (3 H, dd, 3 CH), 8.66 (3 H, br s, 3 CH), 10.33 (3 H, s, 3
OH),12.84 (3 H, br s, 3 COOH). IR(KBr, cmꢀ1 ): 3430(b), 1694(s),
30 1658(s), 1600(s), 1530(s), 1470(s), 1320(s), 1240(s), 1180(m),
1150(s), 1070(s), 1010(w), 893(s), 858(m), 752(s), 739(m),
602(m), 550(s), 528(w), 471(m).
All chemicals and solvents were in analytical grade and used as
commercially available. 3ꢀformylꢀ2ꢀhydroxybenzoic acid was
prepared by the literature method.19 Elemental analyses for C, H
and N were carried out on a PerkinꢀElmer 2400II analyzer. The
infrared spectra were recorded on an Avaterꢀ360 spectrometer
5
1
using KBr pellets in a range of 400~4000 cmꢀ1. H NMR spectra
was recorded on Bruker ACꢀ400 spectrometer. The UVꢀvis
10 spectra were recorded on a UVꢀ550 spectrometer in a range of
400~800 nm. The fluorescence spectra were measured on a Fꢀ
7000 Fluorometer. Thermogravimetric analysis was carried out
on an TGA/SDTA851e analyzer in a nitrogen atmosphere, and
the complexes were heated to 1000℃ at a heating rate of 10℃
15 minꢀ1. Magnetic measurement was carried out on polycrystalline
samples with a MPMSꢀ7SQUID magnetometer. Diamagnetic
Table 1 Crystallographic Data and Refinement for 1-4
1
2
3
C60H74N8Ni4O33Eu2
1974.03
4
C60H74N8Ni4O32Gd2
1968.61
Formula
C60H73N8Ni4O32.5Pr2
1942.93
C60H75N8Ni4O32.5Sm2
1963.82
Formula weight
Crystal system
Monoclinic
Monoclinic
Monoclinic
Monoclinic
a/Å
b/Å
c/Å
α/°
12.770(4)
18.183(6)
15.616(5)
90.00
12.7048(6)
18.1777(9)
15.5866(8)
90.00
12.703(3)
18.339(5)
15.578(4)
90.00
12.6620(10)
18.1513(14)
15.5428(12)
90.00
β/°
γ/°
100.262(5)
90.00
3568(2)
296(2)
99.9870(10)
90.00
3545.1(3)
296(2)
98.101(4)
90.00
3592.9(16)
296(2)
99.7790(10)
90.00
3520.3(5)
296(2)
Volume/Å3
T/K
Space group
Z
P21/n
1
1.809
1958
P21/n
1
1.840
1974
P21/n
2
1.675
1804
P21/n
2
1.857
1972
Dcalcd (g cmꢀ3)
F(000)
Rint
0.0679
0.0436
0.0449
0.0361
R1/wR2 [I >2σ(I)]
R1/wR2(all data)
GOF on F2
0.0514 /0.1070
0.0904/0.1175
0.971
0.0341/0.0794
0.0519/0.0856
1.026
0.0383/0.1074
0.0471/0.1123
1.069
0.0306/0.0666
0.0479/0.0710
1.011
35 Table 2 Crystallographic Data and Refinement for 5-7
5
6
7
Formula
Formula weight
Crystal system
a/Å
b/Å
c/Å
C60H74N8Ni4O32Tb2
C61H74N8Ni4O32Ho2
C60H73N8Ni4O31.5Er2
1971.95
Monoclinic
12.6435(13)
18.3018(19)
15.4157(16)
90.00
1995.98
Monoclinic
12.636(4)
18.317(5)
15.566(5)
90.00
1979.63
Monoclinic
12.596(2)
18.121(3)
15.466(3)
90.00
α/°
β/°
γ/°
96.424(2)
90.00
3544.8(6)
296(2)
98.222(5)
90.00
3565.8(18)
296(2)
99.104(3)
90.00
3485.7(11)
296(2)
Volume/Å3
T/K
Space group
Z
P21/n
2
1.848
1976
P21/n
2
1.859
1996
P21/n
1
1.886
1978
Dcalcd (g cmꢀ3)
F(000)
Rint
0.0429
0.0441
0.0540
R1/wR2 [I >2σ(I)]
R1/wR2(all data)
GOF on F2
0.0378/0.1043
0.0513/0.1102
1.058
0.0313/0.0727
0.0454/0.0770
1.010
0.0369/0.0824
0.0619/0.0890
0.993
experimental procedure, as described for complex 1. Using the
40 appropriate salt yielded the desired complexes.
Complexes
[Ni2PrL1L2(OH)(H2O)]2·8H2O (1). A water solution of NaOH
All complexes 1ꢀ7 were prepared and isolated through the same
2
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(0.24 g, 6 mmol) was added to the Schiffꢀbase H6L ligand (0.590
g, 1 mmol) dissolved in 10 mL of water. The reaction mixture 60 reflection, and determining lattice parameters, SAINT20a for
SMART20a was used for collecting frames of data, indexing
was stirred for 5 min. Then, a solution of Ni(OAc)2ꢁ4H2O (0.25 g,
1 mmol) and Pr(NO3)3ꢁ6H2O (0.427 g, 1 mmol) in methanol (30
mL) was added dropwise, and the mixture was kept stirring for
another 2 h at room temperature. The resulting pale green
integration of the intensity of reflections and scaling, SADABS20b
for absorption correction, and SHELXTL20c,d for space group and
structure determination and leastꢀsquares refinements on F2. The
hydrogen atom positions were calculated theoretically and
5
solution was filtered and allowed to stand at room temperature. 65 included in the final cycles of refinement in a riding model along
Green block single crystals, suitable for Xꢀray diffraction
analysis, were formed after 1 month. Yield: 0.44 g, 45% (based
with attached carbon atoms.
10 on the nickel salt). Anal. Calcd (%) for C60H73N8Ni4O32.5Pr2: C,
37.09; H, 3.79; N, 5.77. Found: C, 36.82; H, 3.54; N, 5.59.
IR(KBr, cmꢀ1): 3430(b), 1640(s), 1600(s), 1556(s), 1440(s),
1410(s), 1310(s), 1230(s), 1190(m), 1150(m), 1140(m), 1080(s),
1039(w), 966(s), 874(s), 831(m), 804(m), 760(s), 669(s), 633(m).
Results and Discussion
IR and UV-vis spectra of complexes
In the IR spectra of ligand H6L, the band at 1694 cmꢀ1 can be
70 ascribed to the stretching vibration of the ν(COOH) vibration
band, the broad band at 3430 cmꢀ1 can be assigned to the ν(OH)
band21 and the absorption band at 1658 cmꢀ1 corresponds to the
stretching vibration of the C=N(imine) band.22 In the title
complexes, the COOꢀ asymmetrical vibration band of νas(COO)
15
[Ni2SmL1L2(OH)(H2O)]2·8.5H2O (2). Yield: 0.44 g, 45%
(based on the nickel salt). Anal. Calcd (%) for
C60H75N8Ni4O32.5Sm2: C, 36.70; H, 3.85; N, 5.71. Found: C,
36.48; H, 3.61; N, 5.56. IR(KBr, cmꢀ1): 3428(b), 1642(s),
1600(s), 1553(s), 1440(s), 1417(s), 1310(s), 1230(s), 1190(m), 75 exhibits one intense absorption band around 1560 cmꢀ1, which
20 1150(m), 1140(m), 1080(s), 1038(w), 966(s), 874(s), 831(m),
806(m), 766(s), 669(s), 633(m).
may be attributed to νas(COO) band of the monodentate
coordination carboxyl group; while the other intense absorption
band around 1410 cmꢀ1 may be assigned to νs(COO), the
symmetrical vibration band of monodentate coordination
[Ni2EuL1L2(OH)(H2O)]2·9H2O (3). Yield: 0.47 g, 48% (based
on the nickel salt). Anal. Calcd (%) for C60H74N8Ni4O33Eu2: C,
36.51; H, 3.78; N, 5.68. Found: C, 36.39; H, 3.57; N, 5.52. 80 carboxyl group.23 The differences between antisymmetric and
25 IR(KBr, cmꢀ1): 3412(b), 1627(s), 1592(s), 1558(s), 1442(s),
1409(s), 1301(s), 1234(s), 1201(m), 1177(m), 1157(m), 1082(s),
1041(w), 976(s), 879(s), 831(m), 806(m), 763(s), 669(s), 625(m).
[Ni2GdL1L2(OH)(H2O)]2·8H2O (4). Yield: 0.42 g, 43% (based
symmetric stretching bands indicate that the carboxylate group
coordinated to the metal ions in a bridging fashion. The absence
of a characteristic absorption band in the range of 1700 cmꢀ1
indicates the complete deprotonation of the ligands and
on the nickel salt). Anal. Calcd (%) for C60H74N8Ni4O32Gd2: C, 85 coordination to metal ions. The C=N(imine) band shifts to lower
30 36.61; H, 3.79; N, 5.69. Found: C, 36.44; H, 3.59; N, 5.54.
IR(KBr, cmꢀ1): 3430(b), 1640(s), 1600(s), 1562(s), 1450(s),
1410(s), 1311(s), 1233(s), 1197(m), 1168(m), 1146(m), 1082(s),
1032(w), 966(s), 876(s), 831(m), 798(m), 764(s), 671(s), 633(m).
frequency about 10 cmꢀ1 in the title complexes.
UVꢀvis spectra were recorded for all of the complexes in
CH3OH (5.0 × 10ꢀ4 mol Lꢀ1) (Fig. S1). In the visible region, all of
the complexes 1ꢀ7 show an absorption peak range from 547 to
[Ni2TbL1L2(OH)(H2O)]2·8H2O (5). Yield: 0.56 g, 57% (based 90 594nm, which can be assigned to the spinꢀallowed dꢀd transition
3A2gꢀ3T2g range from. This can also be seen from the molar
absorption coefficient (ε/Lꢁmolꢀ1ꢁcmꢀ1), 94.4(1), 109(2), 117.2(3),
153.2(4), 41.4(5), 276(6), 80.8(7). The similarity of the optical
spectrum for all of the complexes is indicative of the invariance
95 of the coordination environment around Ni centers in these
complexes.
24
35 on the nickel salt). Anal. Calcd (%) for C60H74N8Ni4O32Tb2: C,
36.55; H, 3.78; N, 5.68. Found: C, 36.32; H, 3.57; N, 5.51.
IR(KBr, cmꢀ1): 3426(b), 1641(s), 1600(s), 1556(s), 1452(s),
1408(s), 1309(s), 1232(s), 1198(m), 1169(m), 1148(m), 1081(s),
1031(w), 966(s), 874(s), 829(m), 800(m), 766(s), 669(s), 634(m).
40
[Ni2HoL1L2(OH)(H2O)]2·7H2O·CH3OH (6). Yield: 0.44 g,
44% (based on the nickel salt). Anal. Calcd (%) for
C61H74N8Ni4O32Ho2: C, 36.71; H, 3.74; N, 5.61. Found: C, 36.56;
H, 3.52; N, 5.49. IR(KBr, cmꢀ1): 3427(b), 1640(s), 1600(s),
1562(s), 1455(s), 1415(s), 1310(s), 1233(s), 1199(m), 1160(m),
Crystal Structures of 1-7
The reaction of rareꢀearth nitrate salts and nickel acetate with H6L
in a mixture of water and methanol in a 1:3 molar ratio, in the
100 presence of NaOH, leads to the formation of hexanuclear
heterometallic Ni4Ln2 clusters 1-7 in about 45% yield. The result
reveals that one imine bond in the ligand H6L is degraded into
NH2 group, giving the new ligand H4L1 like Zn2+, Cu2+ and Cd2+
reported in the literature,25 the Ni2+ catalyzed partial degradation
105 of imineꢀphenol ligand takes place as reported here. According to
the idea proposed earlier by J. Parr and coꢀworkers,25 a proposed
process for the formation of H4L1 was suggested in Scheme 1.
Coordination and so deprotonation of one arm of the ligand H6L
45 1146(m), 1080(s), 1032(w), 968(s), 877(s), 831(m), 808(m),
766(s), 673(s), 634(m).
[Ni2ErL1L2(OH)(H2O)]2·7.5H2O (7). Yield: 0.51 g, 52%
(based on the nickel salt). Anal. Calcd (%) for
C60H73N8Ni4O31.5Er2: C, 36.40; H, 3.72; N, 5.66. Found: C, 36.23;
50 H, 3.51; N, 5.53. IR(KBr, cmꢀ1): 3425(b), 1641(s), 1600(s),
1553(s), 1453(s), 1412(s), 1317(s), 1236(s), 1200(m), 1167(m),
1148(m), 1079(s), 1033(w), 968(s), 876(s), 831(m), 810(m),
760(s), 673(s), 636(m).
to Ni2+ possibly forms small quantities of H3O+NO3 in situ,
110 which catalyses the hydrolysis of the remaining unbound 3ꢀ
carboxylsalicylidene arms back to amine groups, then bind to the
metal centre.
ꢀ
X-ray Crystallography
55 The crystal data and the cell parameters for 1-7 are given in Table
1 and 2. The crystal data for 1-7 have been collected on a Bruker
SMART APEX CCD diffractometer with
monochromatized Mo Kα radiation (λ = 0.71073 Å). The program
graphite
Singleꢀcrystal Xꢀray diffraction analyses reveal that
compounds 1ꢀ7 are isomorphous, crystallizing in the monoclinic
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space group P21/n; the structure of 4 will be described as
representative of the whole series. The crystal structure consists
of entities [Ni2GdL1L2(OH)(H2O)]2 and water molecules of
crystallization. A perspective view of the hexanuclear portion is
depicted in Fig. 1. Selected bond parameters of 1ꢀ7 are
summarized in Table 1 and 2. The complex core can be described
as two Ni2GdO4 subunits held together by two carboxyl groups
(Fig. 2). Each Ni2GdO4 subunit comprises two Ni ions and one
Gd ion, in which the three metallic ions are connected to each
5
10 other by means of three phenoxo groups and one hydroxyl group.
In addition, three phenoxo group adopt a doubly bridged mode,
and each connects one Ni ion and one Gd ion. Meanwhile, the
hydroxyl group just adopts a triply bridged mode linking two Ni
ions and one Gd ion.
15
Fig. 1 Compound [Ni2GdL(OH)(H2O)]2 (4); hydrogen atoms and solvent
molecules omitted for clarity.
Table 3 Selected Bond Distances for 1-7
1
2
3
4
5
6
7
Ni1ꢀN
Ni1ꢀO
2.178(6)
2.022(7)
1.956(6)
2.052a
2.036(5)
1.986(5)
2.011a
2.166(3)
2.019(3)
1.954(3)
2.0463a
2.039(2)
1.982(3)
2.0105a
2.165(5)
2.039(6)
1.970(5)
2.058a
2.057(4)
1.994(4)
2.0255a
2.166(3)
2.026(3)
1.960(3)
2.0506a
2.036(2)
1.979(2)
2.0075a
2.158(5)
2.038(6)
1.966(5)
2.054a
2.035(4)
1.981(4)
2.008a
2.171(3)
2.032(3)
1.972(3)
2.0583a
2.045(3)
1.981(2)
2.013a
2.167(3)
2.015(3)
1.957(3)
2.0463a
2.035(2)
1.968(2)
2.0015a
Ni2ꢀN
Ni2ꢀO
2.015(6)
2.022(4)
2.040(5)
2.042(5)
2.055(5)
2.059(5)
2.0436a
2.021(3)
2.010(3)
2.031(2)
2.046(2)
2.053(3)
2.064(3)
2.0408a
2.026(5)
2.022(4)
2.030(4)
2.053(4)
2.054(4)
2.090(4)
2.0498a
2.025(3)
2.052(3)
2.007(2)
2.028(2)
2.047(2)
2.068(2)
2.0404a
2.029(6)
2.006(4)
2.045(4)
2.091(5)
2.036(4)
2.050(4)
2.0456a
2.022(3)
2.005(3)
2.028(2)
2.046(2)
2.054(3)
2.087(3)
2.0428a
2.027(3)
1.993(2)
2.018(2)
2.038(2)
2.051(2)
2.092(2)
2.0384a
LnꢀO
2.481(4)
2.395(5)
2.450(4)
2.480(4)
2.357(5)
2.372(5)
2.435(4)
2.491(4)
2.4326a
2.440(2)
2.357(2)
2.415(2)
2.433(2)
2.329(3)
2.346(3)
2.392(2)
2.440(2)
2.394a
2.439(3)
2.428(3)
2.412(3)
2.342(3)
2.331(4)
2.391(3)
2.363(4)
2.438(3)
2.393a
2.410(2)
2.332(2)
2.389(2)
2.407(2)
2.308(3)
2.335(2)
2.375(2)
2.413(2)
2.3711a
2.406(4)
2.387(4)
2.310(4)
2.390(4)
2.292(4)
2.320(4)
2.403(4)
2.367(4)
2.3593a
2.393(2)
2.303(2)
2.374(3)
2.375(2)
2.271(3)
2.308(3)
2.344(2)
2.383(2)
2.3438a
2.377(2)
2.294(2)
2.348(2)
2.353(2)
2.261(2)
2.287(2)
2.337(2)
2.365(2)
2.3277a
Ni1ꢀLn
Ni2ꢀLn
Ni1ꢀNi2
LnꢀLn
3.5375(13)
3.1902(12)
3.4444(15)
4.0483(11)
3.5001(6)
3.1617(5)
3.4343(8)
3.9862(4)
3.5057(11)
3.1672(10)
3.4447(13)
3.9788(7)
3.4783(5)
3.1449(5)
3.4221(6)
3.9511(4)
3.4628(8)
3.1506(8)
3.4406(11)
3.9418(5)
3.4687(9)
3.1352(9)
3.4195(10)
3.9104(8)
3.4433(6)
3.1209(6)
3.4008(7)
3.8876(5)
aAverage bond distances.
from the ligand H4L1. The Ni1ꢀO and Ni1ꢀN bond lengths cover
30 ranges 1.979(2)ꢀ2.036(2) Å and 1.960(3)ꢀ2.166(3) Å, which are
similar to the values reported in the literature.7e The Ni ion lies at
about 0.2257 Å above the average basal plane. The dihedral angle
formed by Ni1N1N2 and Ni1O3O11 is 161.275(87)°. The Ni2
ion has adopted a slightly distorted octahedral geometry with an
35 NO5 donor set, (Fig. 3). The equatorial positions of Ni2 are
occupied by NO3 donor atoms from the ligand H4L1 and H2L2,
and the axial positions are occupied by two oxygen atoms arising
from one water molecule and one hydroxyl group. The Ni2ꢀO
distances are in the range 2.007(2)ꢀ2.068(2) Å. The Ni2ꢀN bond
20
Fig. 2 Coordination environment of nickel and gadolinium in
[Ni2GdL(OH)(H2O)]2 (4); carbon and hydrogen atoms, and solvent
Two Ni ions exist in dissimilar environments. The Ni1 ion is 40 length is 2.025(3) Å. They are comparable with the range found
fiveꢀcoordinated with the N3O2 environment, and the
in the literature.7f The Ni2 ion lies at about 0.0467 Å above the
equatorial plane. The dihedral angle formed by Ni2N3O6 and
Ni2N9O10 is 175.4 (9)°. The two Ni ion pairs are connected
through hydroxyl group. The value of Ni1ꢁꢁꢁNi2 separation is
25 coordination polyhedron can be viewed as distorted square
pyramid geometry (Fig. 3). Two nitrogen atoms (N1, N2) and a
oxygen atom (O3) from the ligand H4L1 build the basal plane,
whereas the apical position is occupied by a nitrogen atom (N4) 45 3.4221(16) Å. The Ni1ꢀO11ꢀNi2 angle is 116.4 (1)°.
4
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from 490 to 495 nm along with an enhancement of excitation
wavelength. As some lanthanide ions was directly modulated by
the presence of the dꢀ metal ions.26 Compound 6 appears red shift
40 to 474 nm, which may be assigned to ligandꢀmetal charge
transfer.27 As shown in Fig. 5, the emission intensity generally
decrease in the order Tb(5) >Er(7) >Ho(6) >Gd(4) >Eu(3)
>Sm(2) >Pr(1), in accord with the lanthanide contraction, except
Tb(5).
(a)
(b)
(c)
5
Fig. 3 (a) Distorted square antiprismatic environment around the
gadolinium(Ⅲ) metal ion in 4. (b) Distorted octahedral environment
around the Ni2 atom in 4. (c) Distorted square pyramid environment
around the Ni1 atom in 4.
45
The Gd ion is coordinated by three phenolic oxygen atoms,
Fig. 5 Fluorescence spectra of ligand H6L and complexes 1ꢀ7
10 four carboxyl oxygen atoms from both ligands and a hydroxyl
group, resulting in an 8ꢀfold coordinated geometry. The
coordination polyhedron can be best described as a distorted
square antiprism. (Fig. 3). The GdꢀO bond lengths fall in the
range of 2.308(3)ꢀ2.413(2) Å, similar to values reported
15 previously.7e, f Each Gd ion is linked through phenoxo groups and
the hydroxyl group toward the two Ni ions, resulting in a
Ni2GdO4 core, these are further bridged by carboxyl groups to
adjacent core, thus affording a Ni4Gd2O10 dumbbell core (Fig. 4).
The NiꢁꢁꢁGd distances range from 3.1449(5) to 6.6161(6) Å. The
20 GdꢁꢁꢁGd distance is 3.9511(4) Å.
Thermogravimetric Analysis (TGA)
The TGA of compounds are depicted in Fig. 6. For 1, the weight
loss of 9.39% between 25 and 219 °C is attributed to the loss of
50 two coordinated and eight free water molecules (calcd 9.30%).
The decomposition of 1 occurs above 219 °C. For 2, the weight
loss of 9.56% in the range of 25ꢀ242 °C corresponds to the loss of
eight point five free and two coordinated water molecules (calcd
9.62%). The weight loss above 242 °C indicates the
55 decomposition of the framework. For 4, the weight loss of 9.22%
in the range of 25ꢀ206 °C corresponds to the loss of eight free and
two coordinated water molecules (calcd 9.14%). The residues
decompose after 206 °C. For 5, the weight loss of 9.2% in the
range of 25ꢀ220 °C corresponds to the loss of eight free and two
60 coordinated water molecules (calcd 9.13%), and above 220°C,
complex 5 is gradually decomposed. For 6, the weight loss of
9.76% between 25 and 227 °C is attributed to the loss of one
methanol molecule, two coordinated and seven free water
molecules (calcd 9.71%). The decomposition of 6 occurs above
65 227 °C. For 7, the weight loss of 8.71% in the range of 25ꢀ201 °C
corresponds to the loss of seven point five free and two
coordinated water molecules (calcd 8.64%).
Fig. 4 View of the [Ni2Gd]2 dumbbell core
An inspection of Table 3 reveals that the NiꢀOavg and NiꢀNavg
bond distances for all of the complexes are very similar and range
25 from 2.002 to 2.054 Å for NiꢀOavg and from 2.014 to 2.063 Å for
NiꢀNavg bonds. The LnꢀOavg bond distances generally decrease in
the order Pr(2.433) > Sm(2.394) > Eu(2.393) > Gd(2.371) >
Tb(2.359) > Ho(2.344) > Er(2.328), in accord with the lanthanide
contraction. It is also interesting to note that the LnꢀLn distances
30 found in 1-7 follow the lanthanide contraction and decrease
proceeding from 1 to 7 (Table 3).
Luminescence Properties
Fig. 6 TGA curves for 1-2 and 4-7
70 Magnetic Properties
The luminescence spectra of the ligand H6L and the complexes 1ꢀ
7 were studied at room temperature in the solid state. When
35 excited at 286 nm, ligand H6L exhibits a broad strong peak
around 489 nm. The spectra of 1ꢀ2, 4ꢀ5 and 7 were blue shifted
The temperatureꢀdependent magnetic susceptibility data of
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polycrystalline samples of 2, 3 and 4 have been recorded at an
applied magnetic field of 1000 Oe in the temperature range of 2ꢀ 35 allows us to estimate the magnetic interactions of NiꢁꢁꢁGd and
In 4, the introduction of magnetically isotropic GdIII ions
300 K. The curves of χMT versus T are shown in Fig. 7 for 2 and
3. For 2, at 300 K, the observed χMT value of 4.11 cm3 K molꢀ1 is
close to the expected value of 4.18 cm3 K molꢀ1 for two
uncoupled SmIII ions (6H5/2, S = 5/2, L = 0, and g = 2/7) and four
GdꢁꢁꢁGd. For 4, at room temperature, the χMT value of 20.92 cm3
K molꢀ1 is in good agreement with the expected value of 19.75
cm3 K molꢀ1 for two uncoupled GdIII ions (8S7/2, S = 7/2, and g =
2) and four noninteracting NiII ions (S = 1 and g = 2). Upon
5
uncoupled NiII ions (S = 1 and g = 2). Upon cooling the χMT 40 cooling, the χMT value decreases slowly up to 120 K, where it
value decrease regularly, approaching a minimum around 2 K
reaches a value of 20.62 cm3 K molꢀ1, and then decreases rapidly
down to 2 K, reaching a minimum value of 12.62 cm3 K molꢀ1.
To our knowledge, no formula in literatures is available to
reproduce the magnetic susceptibility of such a complex system.
with χMT = 1.64 cm3 K molꢀ1.The experimental χMT value for 3 at
10 room temperature (9.39 cm3 K molꢀ1) is higher than the
theoretical value (5.63 cm3
K
molꢀ1) calculated for four
uncoupled NiII ions (S = 1) and two EuIII ions (S = 0) in the 45 Therefore, its magnetic properties was preliminarily investigated.
7
ground state F0. This result is explained by the presence of the
first excited states that are sufficiently low in energy to be
15 thermally populated at 300 K. As these thermally populated levels
are much more magnetic than the ground state, the experimental
χMT product is higher than estimated. As shown in Figure 7,
lowering the temperature induces a continuous decrease of the
χMT product of 3 to a value of 0.16 cm3 K molꢀ1 at 2 K. This
20 behavior is the expected result of the progressive and finally total
depopulation of the magnetic excited states of the europium(III)
metal ions. However, it is difficult to comment on the interactions
of NiꢁꢁꢁLn and LnꢁꢁꢁLn in 2 and 3, with lanthanide ions having
intrinsic complicated magnetic characteristics, which include the
25 presence of spinꢀorbit coupling and magnetic anisotropy.28
We were able to successfully simulate the magnetic susceptibility
data using the threeꢀJ models as shown in Scheme 2. Using the
MAGPACK29 program and employing the Hamiltonian in eq 1
) )
(1)
ˆ
H = − 2J S S
∑
ij
i
j
50 afforded the parameters J1 = −4.35 cmꢀ1, J2 = −0.17 cmꢀ1, J3 =
−0.05 cmꢀ1, and g = 2.07. Previous literature reported that NiꢀOꢀ
Ni angles between any two NiII ions that are smaller than 98° are
expected to ferromagnetic coupling. Angles larger than 98° are
expected to lead to antiferromagnetic coupling between NiII
55 ions.30 J1 corresponds to the bridging angles larger than 98°, and
its value is negative. Obviously, our result (116.4 (1)°) is in very
good agreement with the literature report.30 As expected, the
interactions between metal ions in the hexanuclear moiety are all
antiferromagnetic.
60 Conclusions
The use of a specifically designed tripodal Schiffꢀbase ligand
[H6L = 3, 3', 3''ꢀ(1E, 1'E, 1''E)ꢀ(2, 2', 2''ꢀnitrilotris(ethaneꢀ2,1ꢀ
diyl) tris(azanꢀ1ꢀylꢀ1ꢀylidene))tris(methanꢀ1ꢀylꢀ1ꢀylidene)tris(2ꢀ
hydroxybenzoic acid), containing N3O3 and O6 inner and outer
65 pockets, respectively, allows the synthesis of a new family of
heterometallic hexanuclear Ni4Ln2 clusters. In all of these
compounds, the six metal ions are held together to form novel
Ni4Ln2O10 core, exhibit a relatively rare dumbbellꢀtype structure.
From the structural point of view, the nickel ions involved in the
70 hexanuclear complexes have different coordination spheres,
distorted octahedrons and squareꢀpyramids. The coordination
geometry around the lanthanide metal ion is distorted icosahedral.
To the best of our knowledge, all compounds are first constructed
from in situ NiIIꢀcatalyzed partial degradation of tripodal ligand,
75 which further expands studying models of the hydrolysis of the
imineꢀphenol Schiff base types. The LnꢀLn separation and Lnꢀ
Oavg bond distances follow the lanthanide contraction trend. The
luminescent intensity generally decrease in the order Tb(5)
>Er(7) >Ho(6) >Gd(4) >Eu(3) >Sm(2) >Pr(1), in accord with the
80 lanthanide contraction, except Tb(5). magnetic preperties of 2, 3
and 4 have been also measured and analyzed.
Fig. 7 χMT versus T plots for complex 2 (○) and 3 (□)
X
Scheme 2 Magnetic exchange interactions threeꢀJ models employed to
30
simulate the susceptibilities of compound 4.
Acknowledgements
We acknowledge the generous financial support of the National
Science Foundation of China (21271143), the Natural Science
85 Foundation of Henan Province (092300410031), the Open Project
of Key Lab Adv Energy Mat Chem (Nankai Univ) ( KLAEMCꢀ
OP201201), the Natural Science Foundation of Henan University
Fig. 8 χMT versus T plots for complex 4 (△), the red line is the simulation
of the experimental data.
6
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and S. P. Yan, Inorg. Chem., 2007, 46, 4530; (c) Y. G. Huang, X. T.
Wang, F. L. Jiang, S. Gao, M. Y. Wu, Q. Gao, W. Wei and M. C.
Hong, Chem. Eur. J., 2008, 14, 10340; (d) J. P. Costes, L. Vendier
and W. Wernsdorfer, Dalton Trans., 2011, 40, 1700.
(2010YBZR007 and 2010YBZR015).
Notes and references
70
10 (a) M. C. Yin, X. F. Lei, M. Li, L. J. Yuan and J. T. Sun, J. Phy.
Chem. Solids, 2006, 67, 1372; (b) H. L. Gao, B. Zhao, X. Q. Zhao, Y.
Song, P. Cheng, D. Z. Liao and S. P. Yan, Inorg. Chem., 2008, 47,
11057.
75 11 (a) B. Zhao, P. Cheng, Y. Dai, C. Cheng, D. Z. Liao, S. P. Yan, Z. H.
Jiang and G. L. Wang, Angew. Chem., Int. Ed., 2003, 42, 934; (b) B.
Zhao, P. Cheng, X. Y. Chen, C. Cheng, W. Shi, D. Z. Liao, S. P. Yan
and Z. H. Jiang, J. Am. Chem. Soc., 2004, 126, 3012; (c) B. Zhao, X.
Y. Chen, P. Cheng, D. Z. Liao, S. P. Yan and Z. H. Jiang, J. Am.
a Institute of Molecular & Crystal Engineering, College of Chemistry and
Chemical Engineering, Henan University, Kaifeng, China. Eꢀmail:
rjtao@henu.edu.cn
5
b Key Laboratory of Advanced Energy Materials Chemistry,
Nankai University, Tianjin, China.
c College of Chemistry and Materials Engineering, Wenzhou University,
Wenzhou, China. Eꢀmail: hp_xiao@yahoo.com.cn.
10 † Electronic Supplementary Information (ESI) available: UVꢀvis spectra
of the complexes 1ꢀ7. CCDC reference numbers 898018ꢀ898024. For ESI
and crystallographic data in CIF or other electronic format see
DOI: 10.1039/b000000x/
‡ Footnotes should appear here. These might include comments relevant
15 to but not central to the matter under discussion, limited experimental and
spectral data, and crystallographic data.
80
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A table of contents entry
A family of dumbbell Ni4Ln2 complexes