Synthesis and structural characterization of nonanuclear lanthanide complexes

Article abstract of DOI:10.1021/ic025929u

A series of nonanuclear lanthanide oxo-hydroxo complexes of the general formula [Ln₉(μ₄-O)₂ (μ₃-OH)₈(μ-BA)₈- (BA)₈]^-[HN(CH₂ CH₃)₃]⁺· (CH₃OH)₂(CHCl₃) (BA = benzoylacetone; Ln = Sm, 1; Eu, 2; Gd, 3; Dy, 4; Er, 5) were prepared by the reaction of hydrous lanthanide trichlorides with benzoylacetone in the presence of triethylamine in methanol and recrystallized from chloroform/methanol (1:10) at room temperature. These five compounds are isomorphous. Crystal data for 1: cubic, Pn3n; T = 180 K; a = 33.8652(4) A; V = 38838.4(8) A³; Z = 6; D_calcd = 1.125 g cm^-3; R1 = 3.37%. Crystal data for 2: cubic, Pn3n; T = 180 K; a = 33.8252(8) A; V = 38700.9(16) A³; Z = 6; D_calcd = 1.133 g cm^-3; R1 = 4.97%. Crystal data for 3: cubic, Pn3n; T = 180 K; a = 33.7061(6) A; V = 38293.5(12) A³; Z = 6; D_calcd = 1.157 g cm^-3; R1 = 5.13%. Crystal data for 4: cubic, Pn3n; T = 180 K; a = 33.5900(7) A; V = 37899.2(14) A³; Z = 6; D_calcd = 1.182 g cm^-3; R1 = 4.03%. Crystal data for 5: cubic, Pn3n; T = 180 K; a = 33.5054(8) A; V = 37613.6(16) A³; Z = 6; D_calcd = 1.202 g cm^-3; R1 = 4.86%. The core of the anionic cluster comprises two vertex-sharing square-pyramidal [Ln₅(μ₄-O)(μ₃- OH)₄]⁹⁺ units. The compounds were characterized by elemental analysis, IR, fast atom bombardment mass spectra, thermogravimetry, and differential scanning calorimetry. The thermal analysis indicated that the nonanuclear species were stable up to 150 °C. Luminescence spectra of 2 and magnetic properties of 1-5 were also studied.

Full text of DOI:10.1021/ic025929u

Inorg. Chem. 2002, 41, 6802−6807
Synthesis and Structural Characterization of Nonanuclear Lanthanide
Complexes
Gang Xu, Zhe-Ming Wang,* Zheng He, Zhi Lu1, Chun-Sheng Liao, and Chun-Hua Yan*
State Key Laboratory of Rare Earth Materials Chemistry and Applications, PKU-HKU Joint
Laboratory on Rare Earth Materials and Bioinorganic Chemistry, College of Chemistry, Peking
UniVersity, Beijing 100871, China
Received August 4, 2002
A series of nonanuclear lanthanide oxo−hydroxo complexes of the general formula [Ln9(µ4-O)2(µ3-OH)8(µ-BA)8-
(BA)8]-[HN(CH CH ) ]+‚(CH OH)2(CHCl3) (BA ) benzoylacetone; Ln ) Sm, 1; Eu, 2; Gd, 3; Dy, 4; Er, 5) were
2
3 3
3
prepared by the reaction of hydrous lanthanide trichlorides with benzoylacetone in the presence of triethylamine in
methanol and recrystallized from chloroform/methanol (1:10) at room temperature. These five compounds are
3
isomorphous. Crystal data for 1: cubic, Pn3hn; T ) 180 K; a ) 33.8652(4) Å; V ) 38838.4(8) Å ; Z ) 6; D
calcd
) 1.125 g cm-3; R1 ) 3.37%. Crystal data for 2: cubic, Pn3hn; T ) 180 K; a ) 33.8252(8) Å; V ) 38700.9(16)
Å ; Z ) 6; Dcalcd ) 1.133 g cm-3; R1 ) 4.97%. Crystal data for 3: cubic, Pn3hn; T ) 180 K; a ) 33.7061(6) Å;
3
V ) 38293.5(12) Å ; Z ) 6; Dcalcd ) 1.157 g cm-3; R1 ) 5.13%. Crystal data for 4: cubic, Pn3hn; T ) 180 K;
3
a ) 33.5900(7) Å; V ) 37899.2(14) Å ; Z ) 6; Dcalcd ) 1.182 g cm-3; R1 ) 4.03%. Crystal data for 5: cubic,
3
Pn3hn; T ) 180 K; a ) 33.5054(8) Å; V ) 37613.6(16) Å ; Z ) 6; Dcalcd ) 1.202 g cm-3; R1 ) 4.86%. The core
3
of the anionic cluster comprises two vertex-sharing square-pyramidal [Ln5(µ4-O)(µ3-OH)4]9+ units. The compounds
were characterized by elemental analysis, IR, fast atom bombardment mass spectra, thermogravimetry, and differential
scanning calorimetry. The thermal analysis indicated that the nonanuclear species were stable up to 150 °C.
Luminescence spectra of 2 and magnetic properties of 1−5 were also studied.
Introduction
metal ions in the presence of appropriate chelating ligands.4
Many classes of ligands are adequate to the task, including
polyketonates, polyamines, polyols, carboxylates, pyridonate,
and alkoxides.5-10 Hydrophilic groups, such as oxo and
hydroxo, bridge the metal ions to make up a cluster core,
whereas the hydrophobic groups take up positions in the
periphery, preventing the core from further aggregation and
thus forming a finite-sized polynuclear complex.
In recent years, self-assembly of nanoscale high-nuclearity
metal clusters via methods of coordination chemistry has
attracted increasing interest,1 because these supermolecules
exhibit novel structural characteristics2 as well as important
applications in both biology and materials chemistry, espe-
cially as potential precursors applied in magnetic, optical,
electronic, and catalytic processes for their size-dependent
physical properties.3 To obtain these high-nuclearity clusters,
a common synthetic strategy is to control the hydrolysis of
(4) Abbati, G. L.; Cornia, A.; Fabretti, A. C.; Caneschi, A.; Gatteschi, D.
Inorg. Chem. 1998, 37, 3759 and references therein.
(5) (a) Caneschi, A.; Cornia, A.; Fabretti, A. C.; Gatteschi, D. Angew.
Chem., Int. Ed. 1999, 38, 1295. (b) Abbati, G. L.; Cornia, A.; Fabretti,
A. C.; Malavasi, W.; Schenetti, L.; Caneschi, A.; Gatteschi, D. Inorg.
Chem. 1997, 36, 6443.
(6) Bhula, R.; Weatherburn, D. C. Angew. Chem., Int. Ed. Engl. 1991,
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(8) Steunou, N.; Bonhomme, C.; Sanchez, C.; Vaissermann, J.; Hubert-
Pfalzgraf, L. G. Inorg. Chem. 1998, 37, 901.
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Goldberg, D. P.; Caneschi, A.; Delfs, C. D.; Sessoli, R.; Lippard, S.
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90, 969.
* Authors to whom correspondence should be addressed. C.-H. Yan:
Tel and Fax, +86-10-62754179; E-mail, chyan@chem.pku.edu.cn.
(1) (a) Takeda, N.; Umemoto, K.; Yamaguchi, K.; Fujita, M. Nature
(London) 1999, 398, 794. (b) Olenyuk, B.; Whiteford, J. A.; Fechten-
ko¨tter, A.; Stang, P. J. Nature (London) 1999, 398, 796. (c) Fujita,
M. Chem. Soc. ReV. 1998, 27, 417.
(2) (a) Winpenny, R. E. P. Chem. Soc. ReV. 1998, 27, 447. (b) Caulder,
D. L.; Raymond, K. N. J. Chem. Soc., Dalton Trans. 1999, 1185. (c)
Mu¨ller, A.; Ko¨gerler, P. Coord. Chem. ReV. 1999, 182, 3.
(3) (a) Lauffer, R. B. Chem. ReV. 1987, 87, 901. (b) Sessoli, R.; Gatteschi,
D.; Caneschi, A.; Novak, M. A. Nature (London) 1993, 365, 141. (c)
Gatteschi, D.; Caneschi, A.; Sessoli, R.; Cornia, A. Chem. Soc. ReV.
1996, 25, 101. (d) Pope, M. T.; Muller, A. Angew. Chem., Int. Ed.
Engl. 1991, 30, 215.
6802 Inorganic Chemistry, Vol. 41, No. 25, 2002
10.1021/ic025929u CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/07/2002

Nonanuclear Lanthanide Complexes
Scheme 1. Two Coordination Modes of Ligand BA
Polynuclear lanthanide complexes are receiving much
attention due to their distinguished applications. Great efforts
have been focused on the europium(III) nanoclusters to
construct luminescent nanodevices.11 Similar interest in
gadolinium(III) nanoclusters with tunable electron relaxation
behavior can be conceived for magnetic resonance imaging
applications.12 As prominent precursors in sol-gel processes,
lanthanide oxo-alkoxide complexes have been studied
intensively,10b,13 whereas reports on polynuclear oxo-hy-
droxo lanthanide clusters are rather limited. Hexanuclear
complexes containing a [Ln6(µ6-O)(µ3-OH)8]8+ core were
synthesized via the direct hydrolysis of lanthanide nitrates
and perchlorates.14 Hubert-Pfalzgraf et al. reported the
synthesis of a nonanuclear [Na(EtOH)6][Y9O2(OH)8(AAA)16]
in the presence of â-diketonate allyl acetoacetate ligand under
an inert atmosphere.15 However, in contrast to the well-
established cluster chemistry of transition metals,16 the
analogous chemistry of lanthanide is still undeveloped.
Limited by current synthetic ability, the synthesis of poly-
nuclear lanthanide complexes can hardly be controlled and
Experimental Section
Chemicals and Measurements. Lanthanide(III) chlorides were
obtained by neutralizing corresponding oxides (Liyang Founder
Rare Earth Ltd. Co.; at least 99.99% purity) with concentrated
hydrochloric acid, followed by evaporation to near dryness. Other
reagents were commercial and were used as received.
Elemental analysis of C, H, and N was performed with a Carlo
Erba 1102 elemental analyzer. IR spectra were recorded on a Nicolet
Magna 750 FTIR spectrometer in the range 600-4000 cm-1 against
the neat samples and in the range 50-650 cm-1 against the samples
mulled in Nujol. Fast atom bombardment mass spectra (FAB MS)
(with a thioxo-glycerol matrix) were obtained using a ZAB-HS
mass spectrometer. The thermal stability was investigated by
thermogravimetry (TG) and differential scanning calorimetry (DSC)
with a thermal analyzer (DuPont 2100) in N2 at a heating rate of 2
°C/min, using R-Al2O3 as a reference. The luminescence and
excitation spectra were recorded using a Hitachi F-4500 spectro-
fluorometer with solid samples sealed in a glass tube. Variable-
temperature magnetization characterizations of complexes were
performed by using an Oxford MagLab 2000 system in the
temperature range 2-300 K. Diamagnetic corrections were esti-
mated from Pascal’s constants.
Preparation of Compounds. LnCl3‚6H2O (Ln ) Sm, Eu, Gd,
Dy, Er; 1.00 mmol) and benzoylacetone (HBA) (1.78 mmol)
were dissolved in ca. 15 mL of methanol. Triethylamine (3.75
mmol) was added dropwise to the above methanol solution,
and the mixture was stirred at room temperature for 24 h. Light
yellow (for Sm, Eu, Gd, and Dy) or pink (for Er) precipitates
were collected by filtration, washed with methanol, and dried in a
vacuum (yield: ca. 70%). The product was then dissolved in a
mixture of CHCl3/CH3OH (1:10 v/v). The mixture was then filtered,
and the filtrate was allowed to stand at room temperature. Cubic-
shaped crystals, suitable for X-ray analysis, were harvested after
10 days.
is usually performed by random self-organization.17
A
systematical work by Zheng et al. was to assemble poly-
nuclear lanthanide-hydroxo complexes, containing the cu-
bane-like [Ln4(µ3-OH)4]8+ cluster as a building block, with
R-amino acids as the supporting ligands under near physi-
ological pH conditions.18
In the present case, we found an easy and systematic access
to the nonanuclear lanthanide oxo-hydroxo clusters by a
partial hydrolysis of the trace water in a methanol reaction
mixture in air. To achieve this synthetic goal, we focused
on the â-diketonate ligand, benzoylacetone (HBA), which
featured different coordination modes (Scheme 1). Although
the reaction of lanthanide salts with HBA had already been
explored and usually produced mononuclear complexes,19
we succeeded in fabricating a series of nanoscale nonanuclear
lanthanide oxo-hydroxo clusters [Ln9(µ4-O)2(µ3-OH)8(µ-
BA)8(BA)8]-[HN(CH2CH3)3]+‚(CH3OH)2(CHCl3) (BA )
benzoylacetone; Ln ) Sm, 1; Eu, 2; Gd, 3; Dy, 4; Er, 5),
whose structures and unique features are described here.
(11) (a) Parker, D.; Williams, J. A. G. J. Chem. Soc., Dalton Trans. 1996,
3613. (b) de Sa´, G. F.; Malta, O. L.; Donega´, C. D.; Simas, A. M.;
Longo, R. L.; Santa-Cruz, P. A.; de Silva, E. F. Coord. Chem. ReV.
2000, 196, 165.
(12) (a) Caravan, P.; Ellison, J. J.; McMurry, T. J.; Lauffer, R. B. Chem.
ReV. 1999, 99, 2293. (b) Li, W. H.; Fraser, S. E.; Meade, T. J. J. Am.
Chem. Soc. 1999, 121, 1413.
(13) (a) Hubert-Pfalzgraf, L. G. New J. Chem. 1995, 19, 727. (b) Evans,
W. J.; Sollberger, M. S. J. Am. Chem. Soc. 1986, 108, 6095.
(14) (a) Wang, R. Y.; Carducci, M. D.; Zheng, Z. P. Inorg. Chem. 2000,
39, 1836. (b) Zhang, D. S.; Ma, B. Q.; Jin, T. Z.; Gao, S.; Yan, C. H.;
Mak, T. C. W. New J. Chem. 2000, 24, 61.
(15) Hubert-Pfalzgraf, L. G.; Miele-Pajot, N.; Papiernik, R.; Vaissermann,
J. J. Chem. Soc., Dalton Trans. 1999, 4127.
(16) For novel examples, see: (a) Watton, S. P.; Fuhrmann, P.; Pence, L.
E.; Caneschi, A.; Cornia, A.; Abbati, G. L.; Lippard, S. J. Angew.
Chem., Int. Ed. Engl. 1997, 36, 2774. (b) Pohl, I. A. M.; Westin, L.
G.; Kritikos, M. Chem. Eur. J. 2001, 7, 3438. (c) Dearden, A. L.;
Parsons, S.; Winpenny, R. E. P. Angew. Chem., Int. Ed. 2001, 40,
151. (d) Xu, Z. Q.; Thompson, L. K.; Miller, D. O. Chem. Commun.
2001, 1170.
(17) Anwander, R. Angew. Chem., Int. Ed. 1998, 37, 599 and references
therein.
(18) Representative work: Zheng, Z. P. Chem. Commun. 2001, 2521 and
references therein.
[Sm9(µ4-O)2(µ3-OH)8(µ-BA)8(BA)8]-[HN(CH2CH3)3]+‚
(CH3OH)2‚(CHCl3). Anal. Found: C, 46.26; H, 4.11; N, <0.3.
Calcd for C169H177Cl3NO44Sm9: C, 46.28; H, 4.08; N, 0.32. FTIR
(cm-1): 3346m, 1599s, 1570s, 1518s, 1486m, 1451m, 1379s,
1306w, 1280m, 999w, 961w, 761w, 716m, 690w. Far-IR (Nujol
mull, cm-1): 600w, 558m, 517m, 403sh, 372m, 319m, 190m.
Positive ion FAB MS: m/z 102 [HN(CH2CH3)3]+. µeff
250K
) 3.8
µB, calcd 4.7 µB (RT).
[Eu9(µ4-O)2(µ3-OH)8(µ-BA)8(BA)8]-[HN(CH2CH3)3]+‚
(CH3OH)2‚(CHCl3). Anal. Found: C, 45.92; H, 3.76; N, 0.33.
Calcd for C169H177Cl3NO44Eu9: C, 46.12; H, 4.06; N, 0.32. FTIR
(cm-1): 3347m, 1599s, 1570s, 1518s, 1486m, 1450m, 1375s,
1308w, 1280m, 1000w, 963w, 757w, 715m, 690w. Far-IR (Nujol
mull, cm-1): 600w, 561m, 549m, 402sh, 376m, 318m, 175m.
Positive ion FAB MS: m/z 102 [HN(CH2CH3)3]+. µeff
250K
) 8.3
µB, calcd 10.4 µB (RT).
[Gd9(µ4-O)2(µ3-OH)8(µ-BA)8(BA)8]-[HN(CH2CH3)3]+‚
(CH3OH)2‚(CHCl3). Anal. Found: C, 45.38; H, 3.60; N, <0.3.
Inorganic Chemistry, Vol. 41, No. 25, 2002 6803

Xu et al.
Table 1. Crystallographic Data of 1-5
1
2
3
4
5
formula
fw
µ(Mo KR), Å
T, K
C
169H177Cl3NO44Sm9
C
169H177Cl3NO44Eu9
C
169H177Cl3NO44Gd9
C
169H177Cl3NO44Dy9
C169H177Cl3NO44Er9
4385.62
0.71073
180
4400.11
0.71073
180
4447.72
0.71073
180
4494.97
0.71073
180
4537.81
0.71073
180
space group
a, Å
Pn3hn
Pn3hn
Pn3hn
Pn3hn
Pn3hn
33.8652(4)
38838.4(8)
6
33.8252(8)
38700.9(16)
6
33.7061(6)
38293.5(12)
6
33.5900(7)
37899.2(14)
6
33.5054(8)
37613.6(16)
6
V, Å3
Z
D
calcd, g cm-3
1.125
2.088
3.37
9.13
1.133
2.235
4.97
11.78
1.157
2.385
5.13
12.93
1.182
2.709
4.03
9.88
1.202
3.060
4.86
11.22
µ, mm-1
R1, %a
wR2, %b
2
2
a R1 ) ∑(||Fo| - |Fc||)/∑Fo. b wR2 ) [∑(|Fo| - |Fc| )2/∑(Fo)2]1/2
.
Calcd for C169H177Cl3NO44Gd9: C, 45.63; H, 4.02; N, 0.31. FTIR
(cm-1): 3568w, 3354m, 1598s, 1570s, 1521s, 1486m, 1452m,
1384vs, 1305w, 1280m, 999w, 962w, 771w, 714m, 690w. Far-IR
(Nujol mull, cm-1): 600w, 561m, 553sh, 519m, 403sh, 382m,
Results and Discussion
Synthesis. Generally, the examples of well-characterized
finite-sized lanthanide clusters are limited and the syntheses
are hard to reproduce. Recent reports of Anwander17 and
Zheng18 suggest that the hydrolysis of the lanthanide ions
supported by suitable ligands may be used as a general
approach to form lanthanide clusters. In this investigation,
we sought polynuclear lanthanide oxo-hydroxo complexes
via the hydrolysis of lanthanide chlorides in alcohol systems
in the presence of â-diketone HBA.
320m, 171m. Positive ion FAB MS: m/z 102 [HN(CH2CH3)3]+.
300K
µeff
) 23.6 µB, calcd 23.8 µB (RT).
[Dy9(µ4-O)2(µ3-OH)8(µ-BA)8(BA)8]-[HN(CH2CH3)3]+‚
(CH3OH)2‚(CHCl3). Anal. Found: C, 44.99; H, 3.83; N, <0.3.
Calcd for C169H177Cl3NO44Dy9: C, 45.15; H, 3.98; N, 0.31. FTIR
(cm-1): 3576w, 3358m, 1597s, 1570s, 1513s, 1486m, 1451m,
1379s, 1306w, 1281m, 999w, 963w, 761w, 713m, 689w. Far-IR
(Nujol mull, cm-1): 601w, 563m, 552sh, 410sh, 391m, 320m,
The syntheses of 1-5 were accomplished by mixing
hydrous lanthanide chlorides with a stoichiometric amount
of HBA (Ln:HBA ) 9:16) in methanol and subsequently
adding a quantity of triethylamine dropwise. The choice of
methanol in this study was based empirically on the
consideration of slowing down the hydrolysis rate of lan-
thanide ions. Usually, 24 h was needed to obtain a sufficient
precipitation. When triethylamine was first added to the
methanol mixture, it preferentially captured the proton from
HBA to form [HN(CH2CH3)3]+. Therefore, the ligand BA
was ready to chelate and/or bridge the lanthanide ions. As
the amount of triethylamine exceeded that of the HBA, the
small quantity of crystal water of lanthanide chlorides began
to hydrolyze to produce oxo and hydroxo, which could bridge
the lanthanide ions and make up a cluster core, while the
hydrophobic groups of BA took up positions in the periphery.
Consequentially, a nonanuclear lanthanide oxo-hydroxo
cluster was obtained as a result of the interplay of kinetics
and thermodynamics. These compounds were insoluble in
water and extremely soluble in CH2Cl2, CHCl3, ClCH2CH2-
Cl, CH3CN, and DMF, while they had poor solubility in
alcohols, making the purification of products easy by washing
with methanol. Block crystals could be recrystallized from
chloroform/methanol and were stable in the presence of the
mother liquid. Under the above conditions, we were able to
synthesize 1-5 many times. Moreover, the crystals could
also be obtained by recrystallizing from CHCl3/CH3OH, CH2-
Cl2/CH3OH, ClCH2CH2Cl/CH3OH, or CHCl3/CH3CH(OH)-
CH3 or even from CH3CN. Compared with the previous
reports, the synthesis route presented here provides an easy
way to obtain lanthanide complexes with high nuclearity and
high purity.
300K
172m. Positive ion FAB MS: m/z 102 [HN(CH2CH3)3]+. µeff
) 31.6 µB, calcd 31.9 µB (RT).
[Er9(µ4-O)2(µ3-OH)8(µ-BA)8(BA)8]-[HN(CH2CH3)3]+‚
(CH3OH)2‚(CHCl3). Anal. Found: C, 44.76; H, 3.88; N, <0.3.
Calcd for C169H177Cl3NO44Er9: C, 44.72; H, 3.94; N, 0.31. FTIR
(cm-1): 3345m, 1599s, 1570s, 1516s, 1486m, 1454m, 1386vs,
1306w, 1282m, 999m, 963m, 761w, 713m, 689w. Far-IR (Nujol
mull, cm-1): 601w, 565m, 552sh, 522m, 413sh, 398m, 322m,
300K
175m. Positive ion FAB MS: m/z 102 [HN(CH2CH3)3]+. µeff
) 28.3 µB, calcd 28.8 µB (RT).
X-ray Structure Determination. Intensity data for the five
compounds were collected at 180 K on a Nonius KappaCCD
diffractometer with graphite-monochromated Mo KR radiation
(λ ) 0.71073 Å). Cell parameters were obtained by the global
refinement of the positions of all collected reflections. Intensities
were corrected for Lorentz and polarization effects and empirical
absorption. The structures were solved by direct methods, and
refined by full-matrix least squares on F2 using the SHELX-97
package.20 All non-H atoms of the nonanuclear anion were refined
anisotropically. Locations of H atoms of OH groups were justified
by difference Fourier synthesis. H atoms were added geometrically
and refined using the riding model. The solvent molecules and the
[HN(CH2CH3)3]+ cation could not be revealed by the X-ray
analysis, and they were treated as C atoms positioned from the
difference Fourier map, with large isotropic thermal factors, in the
structure refinement. These atoms are not close to the well-defined
anion within 3.4 Å. Thus the solvent molecules and the [HN(CH2-
CH3)3]+ cation are severely disordered in the lattice. Even the X-ray
data collected at 120 K cannot resolve them. Details of crystal-
lographic data are summarized in Table 1.
(19) (a) Il’inskii, A. L.; Porai-Koshits, M. A.; Aslanov, L. A.; Lazarev, P.
I. Zh. Strukt. Khim. 1972, 13, 277. (b) Butman, L. A.; Aslanov, L. A.;
Porai-Koshits, M. A. Zh. Strukt. Khim. 1970, 11, 46.
(20) Sheldrick, G. M. SHELX-97, PC Version; University of Go¨ttingen:
Go¨ttingen, Germany, 1997.
Crystal Structure. Single-crystal X-ray diffraction analy-
sis revealed that compounds 1-5 were isomorphous. They
6804 Inorganic Chemistry, Vol. 41, No. 25, 2002

Nonanuclear Lanthanide Complexes
Figure 1. The structure of the nonanuclear anion for 1 with atomic labeling scheme. H atoms are omitted for clarity. (a) The hourglass-like [Ln9(µ4-O)2-
(µ3-OH)8] core. (b) The whole anion.
are actually ionic species composed of a nanoscaled nona-
nuclear [Ln9(µ4-O)2(µ3-OH)8(µ-BA)8(t-BA)8]- anion with a
counterion of protonated triethylamine ([HN(CH2CH3)3]+)
and several solvent molecules. The structure of the anion is
shown in Figure 1. The large anion has a nonanuclear [Ln9-
(µ4-O)2(µ3-OH)8] core and 16 peripheral BA ligands. In the
core (Figure 1a), the metal skeleton can be regarded as two
square-based pyramidal pentanuclear units assembled via the
apical metal (Ln2). As the two square-pyramids are twisted
at 45° to each other, the anion is of crystallographic D4d
symmetry. Each triangular face of the square pyramids is
capped by one µ3-OH group, so that the central Ln2 ion is
surrounded by eight µ3-OH groups and displays a square-
antiprism geometry and also shows a crystallographic D4d
symmetry. The distance of the µ3-OH to the triangular metal
face is ca. 1.0 Å. Four Ln1 metal ions in each square base
are planar and are linked by one µ4-O, which is slightly above
the basal face. The shift of the µ4-O [0.253(6)-0.275(8) Å
for 1-5] above the Ln4 basal plane is significantly shorter
than that observed in the tetradecanuclear [Ln14(µ4-OH)2(µ3-
OH)16(o-O2NC6H4O)24 (Ln ) Er, Yb)]21 [0.52 Å], whereas
the in-planar µ4-oxo was observed for [Y9(µ4-O)2(µ3-OH)8-
(AAA)16],15 [M4L2(NO3)4(MeOH)2(µ4-O)] [M ) Gd, Tb; L
) 1,3-bis(2-hydroxy-3-methoxy-benzylamino)propan-2-ol],22
and [Er8(µ4-O)(µ3-OH)12(thd)12] (Hthd ) 2,2,6,6-tetrameth-
ylheptane-3,5-dione).23 The Ln9 core is surrounded by 16
peripheral BA ligands (Figure 1b), which are divided into
two classes, eight terminal chelate (t-BA) and eight bridging
chelate (µ-BA), according to the coordination behavior of
the ligand (Scheme 1). Each Ln1 ion, at the corner of the
square bases, is chelated by one t-BA, and further coordinated
by two µ-BAs, which link the metal ion with two neighbor
metal ions at the corners. Thus Ln1 is coordinated by eight
oxygen atoms, two (O3, O4) from the t-BA, three (O5, O6,
O5#1) from two µ-BAs, two (O2, O2#1) of µ3-OHs, and
Table 2. Selected Bond Lengths (Å) of 1-5
bond
1
2
3
4
5
Ln1-Ln1
Ln1-Ln2
3.6971(3) 3.6725(4) 3.6462(4) 3.6038(3) 3.5657(4)
3.7761(2) 3.7590(3) 3.7430(3) 3.7025(2) 3.6726(3)
2.342(3)- 2.333(4)- 2.323(4)- 2.296(4)- 2.284(4)-
Ln1-O(BA)
Ln1-O2
2.476(3)
2.459(4)
2.456(4)
2.423(3)
2.411(4)
2.358(3)
2.371(3)
2.337(3)
2.358(3)
2.332(4)
2.340(4)
2.309(3)
2.309(3)
2.284(4)
2.290(4)
Ln1-O1
Ln2-O2
Ln2-O1
2.6264(6) 2.6090(8) 2.5921(9) 2.5626(8) 2.5363(9)
2.464(3)
2.978(6)
2.455(3)
2.969(7)
2.444(4)
2.981(8)
2.415(3)
2.957(7)
2.396(4)
2.945(8)
one µ4-O, in a distorted bicapped (O1 and O4) trigonal prism
with a coordination environment of C2V symmetry. It is worth
noting that the distances of Ln-O and Ln-Ln decrease
gradually as Ln varies from Sm to Er, in accordance with
the decrease on the radii of the lanthanide ions (Table 2).
The Ln-O distances follow the order Ln1-O(t-BA) ≈ Ln1-
µ3-OH < Ln2-µ3-OH ≈ Ln1-O(µ-BA) < Ln1-µ4-O <
Ln2-µ4-O, while the Ln‚‚‚Ln distances simply follow Ln1‚‚‚
Ln1 < Ln1‚‚‚Ln2. For 2 (Ln ) Eu), the Eu-O bond lengths
ranging from 2.333(4)-2.6090(8) Å are comparable with
those Eu-O distances, 2.321(12)-2.691(10) Å, in the [Eu5-
(µ4-OH)(µ3-OH)4(DBM)10] (DBM ) dibenzoylmethide),24
whereas the Ln1‚‚‚Ln1 distance is longer and the Ln1‚‚‚Ln2
distance is shorter than those in the latter pentanuclear Eu5
compound. In 5 (Ln ) Er), the distances of Ln-O and Ln‚‚‚
Ln are consistent with those in the similar nonanuclear Y9
species15 as the radii of Y and Er are almost the same.
The Ln9 core (Figure 1a) looks like an hourglass, and the
whole anion (Figure 1b) is of somewhat solid wheel-shape
with an underside diameter of 2.22 nm and a width of 1.56
nm. The middle of the “wheel” shrinks with a diameter of
1.67 nm. The planes of phenyl groups are ca. 38° and 42°
inclined with respect to the square plane of four Ln1 for
t-BA and µ-BA, respectively. There are six anions in each
unit cell, and the packing arrangement of the anions leads
to the formation of large hexagonal channels along the body
diagonal directions (Figure 2). The channel changes its
(21) Bu¨rgstein, M. R.; Roesky, P. W. Angew. Chem., Int. Ed. 2000, 39,
549.
(22) Lam, A. W. H.; Wong, W. T.; Wen, G. H.; Zhang, X. X.; Gao, S.
New J. Chem. 2001, 25, 531.
(23) Boeyens, J. C. A.; Villiers, J. P. R. D. J. Cryst. Mol. Struct. 1972, 2,
(24) Xiong, R. G.; Zuo, J. L.; Yu, Z.; You, X. Z.; Chen, W. Inorg. Chem.
Commun. 1999, 2, 490.
197.
Inorganic Chemistry, Vol. 41, No. 25, 2002 6805

Xu et al.
Figure 3. Combined TG-DSC run of 1.
Figure 2. The packing of the nonanuclear anion (space-filling model) of
1 down the [111] direction, showing the hexagonal channel along the body
diagonal direction in the lattice. Colors used: green and red for C, purple
for Sm, and orange for O.
diameter (expanding and shrinking) in its running direction,
and the minimum diameter is ca. 7 Å with van der Waals
volume excluded. It is large enough for the solvent molecules
and cations to move freely. In the lattice, the channels extend
along the four body diagonal directions of the unit cell. This
results in the severe disorder of the small components, which
cannot be resolved by X-ray analysis even at 120 K, and in
easy loss of the solvent for the crystals.
IR, FAB MS, and TG-DSC Characterizations. The IR
spectra of the as-precipitated powder and the as-recrystallized
crystal are identical, which implies the same purity of the
two. A broad absorption appears at around 3350 cm-1, the
typical stretching of alcohol hydroxyl, indicating the presence
of methanol. A weak peak around 3580 cm-1, previously
reported and assigned to the stretching of µ3-OH,25 was
observed in these compounds and was probably obscured
by the broad absorption of alcohol hydroxyl. Metal coordina-
tion results in appreciable shifts of the asymmetric stretching
frequency of the diketone moiety of the BA ligand, from
1603, 1571 to about 1599, 1570, 1518 cm-1, which happens
to be coincident with those of the benzene moiety. A strong
sharp absorption around 1380 cm-1 is assigned to the bending
of CH3 belonging to the methyl ketone.26 The identity of
the complexes was supported by the positive ion FAB MS
study; a m/z value of 102 was observed for the [HN(CH2-
CH3)3]+ counterion, which suggests the [Ln9O2(OH)8(BA)16]
species is a monovalent anion. Although the crystals undergo
rapid solvent loss once they leave the mother liquid, the
compounds are stable according to thermal stability study.
The TG trace of 1 (Figure 3) shows a weight loss of 5%
before 50 °C, which corresponds to the loss of absorbed
solvent (methanol and/or chloroform). No chemical decom-
position is observed up to 150 °C. A weight loss of ca. 2.3%
appears in the temperature range 150-190 °C, which
indicates the loss of one [N(CH2CH3)3] molecule per unit
Figure 4. Fluorescence spectrum (λex ) 465 nm) and excitation spectrum
(inset) of 2.
formula. Correspondingly, one endothermic peak appears
in the DSC curve around 166 °C, with an enthalpy of
approximate -50 kJ mol-1. As the temperature exceeds
190 °C, the complex begins to decompose. Similar thermal
behaviors are observed for 2-4. Therefore, the nonanuclear
species seem to be stable up to at least 150 °C.
Luminescence Spectroscopy of 2. The luminescence
spectrum of the powder of complex 2 (Figure 4) at room
temperature indicates that the cluster exhibits very strong
5
7
red luminescence, which may arise from a D0 f FJ (J )
0-4) transition, a typical characteristic of Eu3+.27 The main
5
7
emission occurs, as expected, in the D0 f F2. Although
5
7
5
7
the D0 f F0 and D0 f F1 transitions are also present,
they are 60 and 10 times less intense, respectively, which
are in accordance with those observed in the Eu(btfa)3‚bipy.28
The 5D0 f 7F0 transition is a singlet. The existence of a single
peak at about 578 nm indicates the presence of only one
single emitting species corresponding to the Eu1 of C2V
symmetry,27 which is 8 times more than the Eu2 of D4d
symmetry in the nonanuclear cluster.
(27) (a) Vicentini, G.; Zinner, L. B.; Zukerman-Schpector, J.; Zinner, K.
Coord. Chem. ReV. 2000, 196, 353. (b) Lessmann, J. J.; Horrocks,
W. D. Inorg. Chem. 2000, 39, 3114.
(28) Batista, H. J.; de Andrade, A. V. M.; Longo, R. L.; Simas, A. M.; de
Sa´, G. F.; Ito, N. K.; Thompson, L. C. Inorg. Chem. 1998, 37, 3542.
(25) Dube´, T.; Gambarotta, S.; Yap, G. Organometallics 1998, 17, 3967.
(26) Infrared and Raman Spectra of Inorganic and Coordination Com-
pounds, 4th ed.; Nakamoto, K., Ed.; Wiley-Interscience: New York,
1986; p 260.
6806 Inorganic Chemistry, Vol. 41, No. 25, 2002

Nonanuclear Lanthanide Complexes
Magnetic Properties. The temperature dependences of
effective magnetic moment, µeff, of complexes 1-5 in the
temperature range 2-300 K were studied. For complex 3
(µ4-OH)2(µ3-OH)16(o-O2NC6H4O)24 (Ln ) Er, Yb)]21 can all
be regarded as being composed of one or more [Ln5(µ4-O)-
(µ3-OH)4]9+ units. The ligands utilized in these compounds
as well as in this study are â-diketone or its analogue, which
feature different coordination modes and seem to play an
important role in the formation of the polynuclear lanthanide
clusters. Moreover, the number of the square-pyramidal units
in the cluster seems to have some relationship with the steric
restriction of the ligand, i.e., the smaller ligand chosen, the
larger complex gained. The novel example, the Ln14(OH)18
cluster,21 can be described as a chain of two face-sharing
square-antiprisms which contains four square-pyramidal
units. From the discussion above, polynuclear lanthanide
oxo-hydroxo clusters with designed nuclear number of
5n - 1 (n g 2) can be probably deduced and obtained with
specific ligands under appropriate reaction conditions.
-1
(Ln ) Gd), the plot of øM vs T obeys the Curie-Weiss
law [ø ) C/(T - θ)] with Curie constant, ø, of 77.3 cm3 K
mol-1, and with Weiss constant, θ, of -4.06. The µeff value
per molecule of 3 is 23.6 µB at room temperature, close to
the expected value of 23.8 µB for nine free noninteracting
Gd3+ ions,29 decreases gradually to 22.8 µB at 50 K, and
then drops rapidly below 50 K to 15.2 µB at 2 K. The
dramatic decrease of µeff at low temperature is mainly
attributed to the weak intra- and intermolecular antiferro-
magnetic coupling between the Gd3+ ions30 and may also
8
partially arise from the very small splitting of the S7/2
multiplet at zero field.22 Similar varieties of the temperature
dependence of µeff can also be found in complexes 4 and 5.
The decrease of µeff at low temperature is primarily due to
the splitting of the ligand field of the Ln3+ ion because of
strong spin-orbital coupling, and partly contributed to by
the possible antiferromagnetic interaction between the Ln3+
ions. However, for complexes 1 and 2, there is a continuous
decrease in µeff as the temperature drops, which mainly
indicates the feature of single Ln3+ ion.
Conclusion
A series of nonanuclear lanthanide oxo-hydroxo com-
plexes with â-diketonate ligands have been assembled which
contain two pentanuclear square-pyramidal units. The [Ln5-
(µ4-O)(µ3-OH)4]9+ core containing cluster may be a common
structural motif in lanthanide polynuclear complexes as well
as useful precursors for various advanced material processes.
The structural integrity and the highly ordered arrangement
of lanthanide centers in these nanosized clusters promise their
applications as structural and functional building blocks for
a variety of lanthanide-containing materials.
[Ln5(µ4-O)(µ3-OH)4]9+ Unit. It is interesting to compare
the structure of nonanuclear clusters with other related
complexes. The nonanuclear core contains two [Ln5(µ4-O)-
(µ3-OH)4]9+ units and is constructed by sharing the apical
lanthanide ion of the pentanuclear square-pyramidal units.
Admittedly, the square-pyramidal core is extremely different
from the cubane-like tetranuclear [Ln4(µ3-OH)4]8+ unit18 and
appears to be another common structural motif in lanthanide
oxo-hydroxo clusters, as demonstrated by present work and
others.15,21,24 The hexanuclear octahedral oxo-hydroxo [Ln6-
(µ6-O)(µ3-OH)8]8+ cluster14 may also be considered as two
square-pyramidal units sharing their base. The reported
pentanuclear [Eu5(µ4-OH)(µ3-OH)4(DBM)10],24 nonanuclear
[Y9(µ4-O)2(µ3-OH)8(AAA)16],15 and tetradecanuclear [Ln14-
Acknowledgment. The authors gratefully acknowledge
the financial support of the NSFC (No. 29831010), the
MOST of China (No. G1998061310), and the Founder
Foundation of Peking University.
Supporting Information Available: Emission spectrum data
5
7
(λex ) 465 nm) of the D0 f FJ transitions in compound 2 and
the temperature dependence of the effective magnetic moment of
1-5. X-ray crystallographic data in CIF format for the five
compounds in Table 1. This material is available free of charge
via the Internet at http://pubs.acs.org.
(29) Kahn, O. Molecular Magnetism; VCH Publishers: New York, 1993.
(30) (a) Panagiotopoulos, A.; Zafiropoulos, T. F.; Perlepes, S. P.; Bakal-
bassis, E.; Massonramade, I.; Kahn, O.; Terzis, A.; Raptopoulou, C.
P. Inorg. Chem. 1995, 34, 4918. (b) Costes, J. P.; Dahan, F.; Dupuis,
A.; Lagrave, S.; Laurent, J. P. Inorg. Chem. 1998, 37, 153.
IC025929U
Inorganic Chemistry, Vol. 41, No. 25, 2002 6807