Solvent-induced reversible single-crystal-to-single-crystal transformations observed in lanthanide complexes

Article abstract of DOI:10.1039/c3dt50737h

In this work, a rare 0D→0D single-crystal-to-single-crystal transformation (SCSC) is observed in lanthanide compounds, which is triggered by the removal or retake of solvent molecules. This advantage prompted us to explore the magnetic property of them, and some interesting magnetic properties are obtained.

Full text of DOI:10.1039/c3dt50737h

Dalton
Transactions
View Article Online
View Journal | View Issue
COMMUNICATION
Solvent-induced reversible single-crystal-to-single-
crystal transformations observed in lanthanide
complexes†
Cite this: Dalton Trans., 2013, 42, 8545
Received 19th March 2013,
Accepted 11th April 2013
Yan Zhu,a Feng Luo,*a Ming-biao Luo,a Xue-feng Feng,a Stuart R. Batten,b
Gong-ming Sun,a Shu-juan Liua and Wen-yuan Xua
DOI: 10.1039/c3dt50737h
www.rsc.org/dalton
In this work, a rare 0D→0D single-crystal-to-single-crystal trans- 1,10-phenanthroline, HL = 2-methylbenzoic acid) via solvo-
formation (SCSC) is observed in lanthanide compounds, which is (hydro) thermal reaction of DyCl3, phen, HL, and Na2CO3 in
triggered by the removal or retake of solvent molecules. This C2H5OH/H2O. The phase purity was confirmed by XRD studies
advantage prompted us to explore the magnetic property of (see ESI, Fig. S1†). The dimeric molecular structure of 1 and
them, and some interesting magnetic properties are obtained.
coordination geometries of the Dy(III) ions are shown in Fig. 1
and S2.† The asymmetric unit contains two crystallographically
independent Dy(III) sites which generate two crystallographi-
cally independent dimers. The dimer formed by Dy1 and the
symmetry-related Dy1A (symmetry code A = 1 − x, 2 − y, 1 − z)
is located in a face of the unit cell, while the dimer containing
Dy2 and the symmetry-related Dy2B (symmetry code B = −x,
−y, −z) lies on a corner. The bridges for these dimeric struc-
tures are four L− carboxylate groups. For both Dy1 and Dy2 the
coordination sites are occupied by six L− oxygen atoms and
two phen nitrogen atoms, creating local square antiprismatic
geometries. Notably, the Dy1–Dy1A dimer differs from the
Dy2–Dy2B dimer in that the former is surrounded by two water
molecules and two C2H5OH molecules, which interact through
typical O–H⋯O hydrogen bonds with O⋯O contacts of ca.
2.9 Å or 2.8 Å, respectively. The intradimer metal-to-metal dis-
tances are ca. 4.12 Å for Dy1–Dy1A and 4.19 Å for Dy2–Dy2B.
In the crystal packing, the distances between adjacent dimeric
structures are at least ca. 11 Å.
The existence of solvent molecules led us to explore possi-
ble SCSC transformations. As expected, upon calcination at
160 °C under vacuum 1 undergoes a SCSC transformation to
yield a solvent-free phase with the formula of Dy2(phen)2(L)6
(2). The structure of it can be well solved by single crystal X-ray
diffraction. The phase purity of the resulting bulk samples
were confirmed by EA and XRD measurements. To confirm its
stability, we measured its crystal parameters every week for a
month, and found that under ambient conditions this solvent-
free phase is quite stable. However, when immersed in
C2H5OH/H2O it can tardily transform into 1, supportive of a
reversible SCSC transformation between 1 and 2. Alternatively,
this solvent-free phase can also be prepared by hydrothermal
reaction of DyCl3, phen, HL, and Na2CO3.
Recenty, single-crystal-to-single-crystal transformations (SCSC)
have attracted extensive interest, due to their potential appli-
cations in molecular switches and sensors, as well as their
inherent structural interest.1–4 However, this special pheno-
menon is often hindered, as the loss of single crystal integrity
during the transformation is common. To date only a handful
of examples have been reported. In some cases, structural
dynamism in metal–organic frameworks in response to exter-
nal stimuli,5 or ligand formed in situ, or photochromism,6
were observed. Especially in other cases, dynamic magnetic
properties, such as variation of magnetic behavior from ferro-
magnetic interaction to antiferromagnetic interaction, or
transformation from single chain magnetism to metamagnet-
ism, can be achieved.6–8
Generally speaking, the SCSC is often accompanied by the
change of dimension, for example, 0D→1D, 1D→2D, 2D→3D.
However, the case referring to 0D→0D SCSC is still highly
rare.9 Moreover, in most afore-mentioned SCSC, these com-
pounds are based on transition metal ions. By contrast, the
research of SCSC based on lanthanide compounds is relatively
scarce.10 With the big advancement of magnetic research in
lanthanide compounds,11 it is believed that taking full advan-
tage of this SCSC will bring some interesting magnetic pro-
perties in lanthanide compounds.
To this end we prepared a dinuclear dysprosium com-
pound, namely [Dy2(phen)2(L)6]·(H2O)0.5(C2H5OH) (1, phen =
aCollege of Biology, Chemistry and Material, Science, East China Institute of
Technology, Fuzhou, 344000 Jiangxi, China. E-mail: ecitluofeng@163.com
bSchool of Chemistry, Monash University, Vic 3800, Australia
†Electronic supplementary information (ESI) available: Experimental procedure,
figures, and cif files. CCDC 859338, 859339, 932127 and 932128. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3dt50737h
In general, the structures of both 1 and 2 are largely
similar. In particular, the asymmetric units of each involve two
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 8545–8548 | 8545

View Article Online
Communication
Dalton Transactions
crystallographically independent Dy(III) sites, and these con-
struct two independent dimers. The most significant mole-
cular change upon desolvation, curiously, is that two of the
four bridging 2-methylbenzoate ligands in each dimer change
from coordinating once to each metal to a bridging mode
where one of the oxygen atoms takes on an additional Dy–O
interaction across the dimer to become μ2 (Dy–O = 2.753(3)
and 2.806(3) Å, vs. 3.080(3) and 3.187(3) Å for the closest such
distances in 1). This leads to a number of other significant
differences, including (i) the Dy(III) coordination number, such
that a nine-coordinate environment observed in 2 (Fig. 1 and
S3†); (ii) the Dy(III) coordination geometry (a monocapped
square antiprismatic coordination geometry is observed in 2);
(iii) the dimers in 2 are located on the side and face of the unit
cell; and (iv) changes in the intradimer metal-to-metal distance
(ca. 4.0 Å in 2) and the intermolecular distances (at least ca.
10 Å in 2). Both structures contain alternating layers of all Dy1
and all Dy2 dimers, and in 1 the solvent molecules lie between
these layers. However, upon loss of solvent, presumably via the
interlayer spaces, the packing arrangements of the dimers
within these layers also change.
By analyzing the two structures it is clear that the reversible
transformation between 1 and 2 involves changes of lattice
parameters, bond cleavage/formation, and changes in the
coordination geometries of the Dy(III) sites. Given these signifi-
cant structural changes, in conjunction with the possibility of
SMM behavior derived from the Dy2 structure, interesting mag-
netic properties are expected in this case.
Fig. 2 shows the χMT versus T plots of 1 and 2 at 2.7–300 K
under an applied field of 1000 Oe. The χMT values of
29.08 cm3 mol−1 K (1) and 29.23 cm3 mol−1 K (2) at room
temperature are consistent with the expected value (28.32 cm3
mol−1 K) for two magnetically isolated Dy(III) ions with JDy
=
15/2, gDy = 4/3. The outline of χMT suggests similar magnetic
behavior for 1 and 2: first paramagnetic behavior, and then
weak antiferromagnetic interactions and/or magnetic an-
isotropy. The magnetic behavior observed in 1 and 2 is consist-
ent with that observed in the literature.12
To test SMM properties, temperature-dependent ac
measurements were performed on 1 and 2 under a 3 Oe ac
field. For 1, as shown in Fig. 3, the in-phase (χ′) signal appears
frequency-independent, whereas the out-of-phase (χ′′) shows a
clear frequency-dependent signal, suggestive of SMM behavior
in 1. However no peaks in either χ′ or χ′′ can be found. As
Fig. 1 Views of the SCSC transformation between 1 and 2, the local environ-
ment surrounding the dinuclear structures, and the coordination geometries of
Dy(III) sites. The hydrogen atoms are omitted for clarity. The atoms are colored as
follows: C/green, N/blue, O/red, Dy/purple. Note: we give here the N⋯N dis-
tances in 1 of one chelate phen ligand, for example 2.706(1) Å for Dy2 and
2.695(1) Å for Dy1, to highlight the differences in the Dy1 and Dy2 sites, while
in 2 the Dy–O (capped atom) bond lengths are distinct, 2.806(5) Å for Dy1 and
2.753(5) Å for Dy2.
Fig. 2 The χMT vs. T plots of 1/black and 2/blue.
8546 | Dalton Trans., 2013, 42, 8545–8548
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Communication
Fig. 5 Left: The ln τ vs. T−1 plot of 2 using the ac susceptibility data (dc/2000
Oe, ac/3 Oe) and the fitting by Arrhenius law marked in red. Right: The Cole–
Cole plot of 2 at dc = 0 Oe, ac = 3 Oe; the solid line is a least-squares fitting of
the data to the generalized Debye model.
peak, while at high frequency one distinct inflexion around
5 K is observed. However, at low temperature χ′′ still increases,
indicating the presence of the quantum tunneling effect. As
employed above, an external magnetic field of 2000 Oe was uti-
lized. Under these conditions, field-dependent slow magnetic
relaxation, visible frequency-dependent χ′ and χ′′, and clear
peaks in both χ′ and χ′′ are observed. Most importantly, at low
temperature the χ′′ product decreases under both low and high
frequencies, except under 1 Hz, strongly suggesting that this
external magnetic field is enough to suppress the quantum
tunneling effect. Magnetization relaxation times (τ) were
deduced from the relationship ωτ = 1 at the maxima of the χ′′
vs. T plot.14 The χ′′ peak positions were created by fitting the χ′′
vs. T data at 50–1488 Hz to a Lorentzian function. Then the
energy barrier and relaxation time were deduced by fitting the
plot of ln τ vs. 1/T by Arrhenius law, giving Ueff = 42.3 K, τ0 =
5.6×10−7 s (Fig. 5). This order of magnitude of energy barrier
and relaxation time, comparable with most Dy(III) SMMs,
suggests considerable magnetic anisotropy and exceeds the
corresponding value observed in 1.13 To determine the type of
magnetic relaxation, the Cole–Cole semicircular plot of χ′ vs. χ′′
at low temperatures was constructed (Fig. 5). Fitting the data
by means of a generalized Debye model gives a small α value
of 0.1–0.2, confirming one relaxation process operating at low
temperatures.14
Fig. 3 The χ’ and χ’’ versus T plots (dc/0 Oe, ac/3 Oe, and dc/2000 Oe, ac/3
Oe) of 1.
observed in most Dy(III) SMMs, this frequency-independent χ′
value and absence of χ′ and χ′′ peaks is possibly due to the
quantum tunneling effect that often prevents isolation of an
effective energy barrier at zero-field.13 A common method to
improve this situation is to apply an external magnetic field.
Thus, an external field of 2000 Oe was employed, and more
clearly field-dependent χ′ and χ′′ was observed. This was
accompanied by an increase in the χ′′ value and the ratio of χ′′/
χ′, suggesting that the slow magnetic relaxation is improved
and the quantum tunneling effect is effectively suppressed.
Nevertheless, the absence of a maximum in χ′′ still forces us to
estimate the order of magnitude of the energy barrier and the
relaxation time that is a characteristic parameter for evaluating
the slow magnetic relaxation of SMMs.
For 2, under zero dc field below 8 K strong frequency-
dependent χ′ and χ′′ are observed, confirming the SMM charac-
ter of 2 (Fig. 4). The χ′′ at low frequency below 500 Hz has no
It is well known that the magnetic coupling between lantha-
nide ions is very weak and usually has negligible effect on
SMM properties.14 Therefore, the nature of the individual
lanthanide ions should be responsible for the recently develo-
ped lanthanide-based SMMs.15 To exploit lanthanide-based
SMMs, as indicated recently by Long et al.,11c consideration of
coordination geometry or so-called ligand field factor is
crucial. In this regard, the distinct slow magnetic relaxation
and field-dependent slow magnetic relaxation observed in 1
and 2 is closely related to the significant change in coordi-
nation geometry, from nine-coordinated monocapped square
antiprism to eight-coordinated square antiprism.
In summary, we report here the synthesis, structure, SCSC,
and magnetic studies of two dinuclear Dy(III) compounds. The
most significant change in this SCSC is the Dy–O bond clea-
vage and formation, which results in the differing coordi-
nation geometries for Dy(III) sites in 1 and 2. The magnetic
Fig. 4 The χ’ and χ’’ vs. T plots (dc/0 Oe, ac/3 Oe, and dc/2000 Oe, ac/3 Oe)
of 2.
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 8545–8548 | 8547

View Article Online
Communication
Dalton Transactions
studies reveal similar magnetic behaviors for 1 and 2. Further
magnetic studies revealed slow magnetic relaxation and field-
dependent slow magnetic relaxation for both 1 and 2, respect-
ively, indicative of SMM behavior. Further insight into the
dynamic magnetic properties revealed relatively larger mag-
netic anisotropy for compound 2. These results are thus sup-
portive of SCSC transformations being used to modulate
magnetic behavior and SMM properties, and provide a unique
method to target fine-tuned SMM properties.
B. Kuchta, G. Férey, C. Serre and R. Denoyel, Angew. Chem.,
Int. Ed., 2010, 49, 7526.
6 (a) G. J. Halder, C. J. Kepert, B. Moubaraki, K. S. Murray
and J. D. Cashion, Science, 2002, 298, 1762; (b) S. Ohkoshi,
K. Arai, Y. Sato and K. Hashtmoto, Nat. Mater., 2004, 3,
857.
7 (a) D. Maspoch, D. Rruiz-molina, K. Wurst, N. Domingo,
M. Cavallini, F. Biscarini, J. Tejada, C. Rovira and
J. Veciana, Nat. Mater., 2003, 2, 190; (b) Y. Sato, S. Ohkoshi,
K. Arai, M. Tozawa and K. Hashimoto, J. Am. Chem. Soc.,
2003, 125, 14590.
8 (a) M. Kurmoo, H. Kumagai, K. W. Chapman and
C. J. Kepert, Chem. Commun., 2005, 3012; (b) X. N. Cheng,
W. X. Zhang and X. M. Chen, J. Am. Chem. Soc., 2007, 129,
15738; (c) N. Motokawa, S. Matsunaga, S. Takaishi,
H. Miyasaka, M. Yamashita and K. R. Dunbar, J. Am. Chem.
Soc., 2010, 132, 11943.
Acknowledgements
This work was supported by the Foundation of Jiangxi Edu-
cational Committee (no. GJJ13472), the NSF of China
(21203022, 21261001).
9 Y. M. Song, F. Luo, M. B. Luo, Z. W. Liao, G. M. Sun,
X. Z. Tian, Y. Zhu, Z. J. Yuan, S. J. Liu, W. Y. Xu and
X. F. Feng, Chem. Commun., 2012, 48, 1006.
Notes and references
1 (a) N. L. Toh, M. Nagarathinam and J. J. Vittal, Angew. 10 S. K. Ghosh, J. P. Zhang and S. Kitagawa, Angew. Chem., Int.
Chem., Int. Ed., 2005, 44, 2237; (b) C. J. Kepert, Chem. Ed., 2007, 46, 7965.
Commun., 2006, 695; (c) S. Kitagawa, R. Kitaura and 11 (a) D. Schmitt, J. Phys., 1986, 47, 677; (b) J. Z. Sievers, Phys.
S.-i. Noro, Angew. Chem., Int. Ed., 2004, 43, 2334;
(d) B. Zhang, Z.-M. Wang, M. Kurmoo, S. Gao, K. Inoue and
B, 1982, 45, 289; (c) J. D. Rinehart and J. R. Long, Chem.
Sci., 2011, 2, 2078.
H. Kobayashi, Adv. Funct. Mater., 2007, 1, 577; 12 Y. Wang, X. Li, T. W. Wang, Y. Song and X. Z. You, Inorg.
(e) Z.-M. Wang, B. Zhang, H. Fujiwara, H. Kobayashi and
M. Kurmoo, Chem. Commun., 2004, 416.
2 (a) G. Xu, G. C. Guo, M. S. Wang, Z. J. Zhang, W. T. Chen
Chem., 2010, 49, 969.
13 P. H. Lin, T. J. Burchell, R. Clérac and M. Murugesu, Angew.
Chem., Int. Ed., 2008, 47, 8848.
and J. S. Huang, Angew. Chem., Int. Ed., 2007, 46, 3249; 14 (a) F. Luis, M. J. Martínez-Pérez, O. Montero, E. Coronado,
(b) P. C. Jhang, N. T. Chuang and S. L. Wang, Angew. Chem.,
Int. Ed., 2010, 49, 4200.
3 (a) Q. Chu, D. C. Swenson and L. R. MacGillivray, Angew.
Chem., Int. Ed., 2005, 44, 3569; (b) D. Liu, Z. G. Ren,
H. X. Li, J. P. Lang, N. Y. Li and B. F. Abrahams, Angew.
Chem., Int. Ed., 2010, 49, 4767.
4 C. Avendano, Z. Zhang, A. Ota, H. Zhao and K. R. Dunbar,
Angew. Chem., Int. Ed., 2011, 50, 6543.
5 (a) G. J. Halder and C. J. Keppert, J. Am. Chem. Soc., 2005,
127, 7891; (b) I. Beurroies, M. Boulhout, P. L. Llewellyn,
S. Cardona-Serra, C. Martí-Gastaldo, J. M. Clemente-Juan,
J. Sesé, D. Drung and T. Schurig, Phys. Rev. B: Condens.
Matter, 2010, 82, 060403; (b) R. Giraud, W. Wernsdorfer,
A. M. Tkachuk, D. Mailly and B. Barbara, Phys. Rev. Lett.,
2001, 87, 057203; (c) W. Wernsdorfer, T. Ohm,
C. Sangregorio, R. Sessoli, D. Mailly and C. Paulsen, Phys.
Rev. Lett., 1999, 82, 3903.
15 (a) A. K. Powell, Angew. Chem., Int. Ed., 2010, 49, 5185;
(b) J. D. Rinehart, M. Fang, W. J. Evans and J. R. Long, Nat.
Chem., 2011, 3, 5.
8548 | Dalton Trans., 2013, 42, 8545–8548
This journal is © The Royal Society of Chemistry 2013