Formation of HoIII trinuclear clusters and GdIII monodimensional polymers induced by ortho and para regioisomers of pyridyl-functionalised a-diketones: Synthesis, structure, and magnetic properties

Article abstract of DOI:10.1002/ejic.200801006

Reaction of GdCl₃(H₂O)₆ and 1,3-bis(pyridin-4-yl)propane-1,3-dione in methanol with an excess of triethylamine produced a monodimensional polymeric chain [Gd(p-dppd) ₃-(H₂O)]_∞, whereas treatment of HoCl ₃(H₂O)₆ with 1,3-bis(pyridin-2-yl)propane-1,3- dione yielded a trinuclear cluster [Ho₃(o-dppd) ₃(μ₃-OH)₂(H₂O)₄Cl ₂]Cl₂. The compounds were characterised by elemental analysis, IR spectroscopy and magnetism, and their structures were investigated by X-ray crystallography. The 8.20-μ_B magnetic-moment value of the polymeric [Gd(p-dppd)₃(H₂O)]_∞, between 300 and 20 K, and the magnetisation isotherms (2-20 K; fields 0-5 T), are in agreement with essentially uncoupled single-ion Gd³⁺ f⁷ centres, a small decrease in μ_eff below 20 K being indicative of zero-field splitting. A temperature-dependent dc-susceptibility and magnetisation investigation of the trinuclear (tri-angular) [Ho ₃(o-dppd)₃(μ₃-OH)₂(H ₂O)₄Cl₂]Cl₂ revealed that spin-orbit and ligand-field effects on the Ho³⁺ centres, leading to thermal depopulation of Zeeman levels and consequent decreases in μ_eff values with decreasing temperature, are occurring rather than weak intra-cluster antiferromagnetic coupling. Frequency- and temperature-dependent acsusceptibility studies on this homometallic Ho³⁺ cluster did not show clear evidence for slow magnetisation reversal, characteristic of single-molecule magnetism (SMM), and this contrasts with such behaviour recently reported, elsewhere, for a Dy³⁺ triangle having the same core structure but with different chelating {O,O} ligands. Wiley-VCH Verlag GmbH & Co. KGaA, 2009.

Full text of DOI:10.1002/ejic.200801006

FULL PAPER
DOI: 10.1002/ejic.200801006
Formation of HoIII Trinuclear Clusters and GdIII Monodimensional Polymers
Induced by ortho and para Regioisomers of Pyridyl-Functionalised β-Diketones:
Synthesis, Structure, and Magnetic Properties
Philip C. Andrews,[a] Glen B. Deacon,[a] René Frank,[a] Benjamin H. Fraser,[a]
Peter C. Junk,*[a] Jonathan G. MacLellan,[a] Massimiliano Massi,[a]
Boujemaa Moubaraki,[a] Keith S. Murray,[a] and Morry Silberstein[b]
Keywords: β-Diketonate ligands / Coordination polymers / Cluster compounds / Molecular magnets / Ketones / N,O
ligands / Chelates
Reaction of GdCl3(H2O)6 and 1,3-bis(pyridin-4-yl)propane-
1,3-dione in methanol with an excess of triethylamine pro-
duced a monodimensional polymeric chain [Gd(p-dppd)3-
(H2O)]ϱ, whereas treatment of HoCl3(H2O)6 with 1,3-bis(pyr-
angular) [Ho3(o-dppd)3(µ3-OH)2(H2O)4Cl2]Cl2 revealed that
spin-orbit and ligand-field effects on the Ho3+ centres, lead-
ing to thermal depopulation of Zeeman levels and conse-
quent decreases in µeff values with decreasing temperature,
are occurring rather than weak intra-cluster antiferromag-
netic coupling. Frequency- and temperature-dependent ac-
susceptibility studies on this homometallic Ho3+ cluster did
not show clear evidence for slow magnetisation reversal,
characteristic of single-molecule magnetism (SMM), and this
contrasts with such behaviour recently reported, elsewhere,
for a Dy3+ triangle having the same core structure but with
different chelating {O,O} ligands.
idin-2-yl)propane-1,3-dione yielded
a trinuclear cluster
[Ho3(o-dppd)3(µ3-OH)2(H2O)4Cl2]Cl2. The compounds were
characterised by elemental analysis, IR spectroscopy and
magnetism, and their structures were investigated by X-ray
crystallography. The 8.20-µB magnetic-moment value of the
polymeric [Gd(p-dppd)3(H2O)]ϱ, between 300 and 20 K, and
the magnetisation isotherms (2–20 K; fields 0–5 T), are in
agreement with essentially uncoupled single-ion Gd3+ f7
centres, a small decrease in µeff below 20 K being indicative
of zero-field splitting. A temperature-dependent dc-suscep-
tibility and magnetisation investigation of the trinuclear (tri-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
as catalysis,[5] single-molecule magnets,[6] and luminescent
materials.[7] The most relevant examples of synthetic design
of lanthanoid clusters concern the use of functionalised β-
diketones as ligands.[5,8] The general method consists of tre-
ating a mixture of a lanthanoid salt and the relevant dike-
tone ligand with an excess of triethylamine in methanol.
The base serves to deprotonate both the ligand and the
water molecules coordinated to the metal centre, thus
initiating the formation of hydroxo-bridged polynuclear
species encapsulated in a shell of β-diketonate ligands.
Depending on the relative size of both the ligand and the
lanthanoid cation, this synthetic procedure yielded the for-
mation of dimeric,[9] tetranuclear,[8,10] pentanuclear,[5,10c]
nonanuclear,[11] dodecanuclear,[12] and tetradecanuclear[7c]
lanthanoid hydroxo diketonate clusters.
Introduction
Due to the sometimes unpredictable coordination nature
of the lanthanoid elements, polynuclear lanthanoid clusters
continue to fascinate the synthetic chemistry community. A
multitude of structures have been reported in the last dec-
ade, the majority of which were obtained serendipitously
rather than by a rational synthetic design.[1] These cluster
compounds were normally obtained by means of “con-
trolled hydrolysis” of simple lanthanoid salts[2] using a vari-
ety of ligands, such as amino acids[1a] and carboxylates,[1e]
alkoxides,[3] amides[4] and many more. More recently, meth-
odologies focussed on obtaining specific classes of polynu-
clear lanthanoid clusters were intensively studied. This im-
pulse was mainly driven in view of the potential applica-
tions of these compounds in a wide range of fields such
As part of our work related to the synthesis and charac-
terisation of polynuclear lanthanoid hydroxo clusters, we
have prepared β-diketones functionalised with pyridine
rings bearing the nitrogen atom either in position 2Ј or 4Ј,
namely 1,3-bis(pyridin-2-yl)propane-1,3-dione (o-dppdH)
[a] School of Chemistry, Monash University,
Melbourne, Victoria 3800 Australia
E-mail: peter.junk@sci.monash.edu.au
[b] School of Medicine Nursing and Health Sciences, Monash Uni-
versity,
and
1,3-bis(pyridin-4-yl)propane-1,3-dione
(p-dppdH)
Melbourne, Victoria 3800 Australia
(Scheme 1). We therefore attempted the preparation of clus-
ters by treatment of lanthanoid chloride salts with either o-
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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HoIII Trinuclear Clusters and GdIII Monodimensional Polymers
dppdH or p-dppdH in methanol in a 1:2 ratio with an excess ligand and Gd salt. The compound was then dissolved in
of base. From GdCl3(H2O)6 and HoCl3(H2O)6 two new ethanol and vapour diffusion of hexane into the solution
structurally characterised compounds have been obtained: produced suitable crystals for X-ray diffraction. The com-
the monodimensional polymer [Gd(p-dppd)3(H2O)]ϱ (1) pound was analysed by means of elemental analysis and IR
and the trinuclear cluster [Ho3(o-dppd)3(µ3-OH)2(H2O)4- spectroscopy. Elemental analysis on the bulk sample reveals
Cl2]Cl2 (2). The latter is a novel structure in lathanoid hy- the presence of four extra water molecules in the lattice,
droxo diketonate cluster chemistry, although this trinuclear some of which are replaced by ethanol when crystals are
cage motif has been known to form using other different grown from the ethanolic solution. Hydration of the prod-
classes of ligands, e.g. hydrido and funtionalised pyr- uct was confirmed by the broad IR band at 3500–
idines,[4] vanillin,[6c,6f] and aryl oxides.[3c,3d] The results 2500 cm–1, and the band at 1514 cm–1 was attributed to the
herein demonstrate how simple regio-control of the position C=O bond in the diketonate ligand.
of the extra donor atom in the β-diketonate ligands allows
templating of the resulting structure. The magnetic proper-
ties of the compounds are also described in some detail and
comparisons are made, for 2 with recent studies on a struc-
turally related trinuclear DyIII cluster.[6c]
Scheme 2. Synthetic pathway for the polymer 1 and the cluster 2.
Treatment of a mixture of 1 equiv. of HoCl3(H2O)6 and
1 equiv. of o-dppdH in methanol with an excess of triethyl-
amine yielded a trinuclear cage 2 (Scheme 2). The same
conditions for the preparation of 1 were used. Due to the
polar and ionic nature of the cluster, the usual extraction
of the product by toluene or dichloromethane was not pos-
sible.[10] Therefore, the unreacted o-dppdH ligand was re-
moved by washing the crude product with acetonitrile,
whereas any unreacted Ho salts were removed by dissolving
the compound in pyridine and filtering off any undissolved
residue. After this treatment, we were able to obtain suitable
crystals for X-ray diffraction by slow evaporation of a
methanol solution of 2. The compound was again analysed
by means of elemental analysis and IR spectroscopy. Ele-
mental analysis shows loss of all lattice solvent molecules
from the bulk after several hours under reduced pressure.
The C=O band is shifted to 1519 cm–1, with respect to the
usual values of C=O double bonds, due to the partial
double bond character of the diketonate carbonyl group.
Scheme 1. Synthetic pathway for the ligands o-dppdH and p-dppdH.
Results and Discussion
Synthesis and Characterisation of the Polymer 1 and
Trinuclear Cluster 2
The ligands o-dppdH and p-dppdH were synthesised fol-
lowing a modified literature procedure,[13] as reported in
Scheme 1. They were prepared by the Claisen condensation
between the ethyl esters of picolinic acid or isonicotinic acid
and the corresponding 2-acetylpyridine or 4-acetylpyridine.
Both reactions were carried out in dry THF, using NaH to
generate the corresponding sodium enolates in the presence
of the esters. The method does not require the generation
of a base in situ as an extra step, such as sodium ethanoate
in toluene, and works efficiently in conditions that are not
strictly anhydrous.
X-ray Crystal Structures
Treatment of a mixture of 1 equiv. of GdCl3(H2O)6 and
Figure 1 shows the molecular structure of polymer
2 equiv. of p-dppdH in methanol with an excess of triethyl- [Gd(p-dppd)3(H2O)]ϱ (1) which crystallises in the mono-
amine yielded the monodimensional polymer 1 (Scheme 2). clinic space group P21/c. The polymer is composed of linear
Although the stoichiometry of the reaction was set to a chains of trisubstituted neutral complexes. Overall the Gd
metal/ligand ratio of 1:2 in order to form a polynuclear centres are octacoordinate, bonded by three chelating
cluster, a trisubstituted complex, which polymerised by the (O,OЈ) diketonate groups, one water molecule and a bridg-
ligand pyridyl nitrogen, was instead obtained. Rather than ing pyridyl-N atom from another unit. Gd–O(diketonate)
performing the reaction at room temperature, we used re- bonds are slightly asymmetrical but lie within the expected
flux conditions as it was previously observed that the clus- range for this type of interaction (shortave 2.33 Å and lon-
ters were the thermodynamically favoured products. The gave 2.39 Å, Table 1). Internal ligand O–Gd–O bite angles
crude product was added to a 1:10 mixture EtOH/H2O vary little, ranging from 70.38(14)–71.47(12)°. The water
where it precipitated out leaving in solution any unreacted molecule binds to the Gd at a distance of 2.380(4) Å and
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P. C. Junk et al.
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lies trans to the interaction of ligand 2 with the Gd centre
[the (H2)O–Gd–C(H) angle is 175.53(15)°] but essentially
within the [O(3)–Gd–O(4)] plane (RMS deviation from
planarity for all four atoms is 0.0087 Å). The respective pla-
nes of ligands 1 and 3 with Gd form angles of 80.68(14)°
and 86.72(14)° on either side of the (ligand 2)–Gd–O(H2)
plane and at an angle of 158.86(22)° to each other. The
overall chain-structure is linked together by N(pyridyl)–Gd
bonds of 2.624(4) Å with four near identical angles to the
closest Gd–O bond of each ligand and to the water mole-
cule [range of angles 71.11(13)°–73.85(13)°]. Although the
polymeric chains are unidimensional, they are interlocked
through intermolecular face-to-face π-stacking. Two sym-
metry-generated rings align above and below the ring con-
taining N(1) with average distances between adjacent pyr-
idyl rings of 3.51 Å [to ring containing N(6)*] and 3.67 Å
[to ring containing N(5)**]. Moreover, the water molecule
bound to the Gd centre completes a hydrogen-bonded net-
work through interactions with the pyridyl-N atoms of two
parallel, neighbouring chains, N(3) and N(1) as shown in
Figure 2. Cavities within the network are filled by two sol-
vent molecules per monomeric unit. One is occupied by an
ethanol molecule, disordered over two positions with equal
occupancies, and the second is occupied by ethanol or water
(major component of disorder 80% EtOH). One pyridyl
substituent on each of the β-diketonate ligands is disor-
dered over two positions (refined occupancy of major com-
Figure 1. Molecular structure of complex 1 showing 30% ellipsoids
with all H atoms and lattice solvent molecules removed.
Table 1. Selected bond lengths [Å] and angles [°] for 1.
Gd(1)–O(1)
Gd(1)–O(2)
Gd(1)–O(3)
Gd(1)–O(4)
O(1)–Gd(1)–O(2)
O(3)–Gd(1)–O(4)
2.335(4)
2.387(4)
2.368(4)
2.338(4)
71.13(12)
71.47(12)
70.38(14)
94.05(14)
74.59(13)
142.28(13)
146.22(13)
80.07(14)
Gd(1)–O(5)
Gd(1)–O(6)
Gd(1)–O(7)
Gd(1)–N(4)*
O(6)–Gd(1)–O(7)
O(1)–Gd(1)–N(4)* 71.11(13)
O(2)–Gd(1)–N(4)* 126.31(13)
O(3)–Gd(1)–N(4)* 73.85(13)
O(4)–Gd(1)–N(4)* 138.97(13)
O(5)–Gd(1)–N(4)* 73.81(13)
O(6)–Gd(1)–N(4)* 138.86(15)
O(7)–Gd(1)–N(4)* 71.54(13)
2.408(4)
2.327(4)
2.380(4)
2.624(4)
82.85(15)
ponent: 68.3%, 76.5% and 80.0% for ligands 1, 2 and 3, O(5)–Gd(1)–O(6)
O(1)–Gd(1)–O(7)
respectively). The two disordered components of ligand 3
O(2)–Gd(1)–O(7)
also account for the site disorder of the neighbouring lattice
O(3)–Gd(1)–O(7)
solvent EtOH(major)/H2O(minor) mentioned previously.
O(4)–Gd(1)–O(7)
O(5)–Gd(1)–O(7)
The disorder was allowed to freely refine to near 80% and
was then fixed at this value for all further refinements. The
donor–acceptor distances involved in the hydrogen bonding
network are 2.770(8) Å for O(7)···N(3)* [2.66(2) Å for O(7)···
N(3A)*; the minor component of disorder] and 2.727(6) Å
for O(7)···N(1)*. There is one further weak H-bond involv-
ing the disordered ethanol, O(9)···N(5), at 2.905(14) Å.
There is no significant bonding to the other component of
this disorder when the ethanol is oriented in the opposite
direction.
* Symmetry transformation used to generate equivalent atoms:
x + 1, y , z
Compound [Ho3(o-dppd)3(µ3-OH)2(H2O)4Cl2]Cl2 (2)
¯
crystallises in the triclinic space group P1 and is reported in
Figure 3 and Table 2. This novel trinuclear complex shows
remarkable differences from its previous β-diketonate clus-
ter analogues, and these can be ascribed to the addition
(and position) of a donor N atom in the pyridyl diketonate
ligand. Unlike its regioisomer in 1 (p-dppdH), the position
of the N in o-dppdH allows intramolecular donation which
results in the formation of this unusual arrangement.
Each diketonate ligand binds to two Ho atoms through
µ-η2(N,O);η2(O,OЈ) bonding, leaving one pyridyl-N atom
per ligand free. One O per ligand [O(2,4,6)] forms a planar
Figure 2. Polymeric structure of complex 1 with all H atoms re-
moved except those on the attached water molecule.
six-membered central ring with the three Ho centres, RMS and corresponding angles in Table 3. Each β-diketonate li-
deviation of fitted atoms 0.0146 Å (RMS deviation of fitted gand again binds asymmetrically to the Ho centres. One O
atoms when both ligand O atoms and the coordinated N atom per ligand [O(2,4,6)] bridges between two Ho atoms
are included is 0.1861 Å). The three Ho3+ centres form an to form the central (HoO)3 ring with an average Ho–O
equilateral triangle, as evidenced by the Ho–Ho distances bond length of 2.36 Å. The second oxygen atom per ligand
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HoIII Trinuclear Clusters and GdIII Monodimensional Polymers
[O(1,3,5)] bonds to only one Ho atom with a marginally Table 2. Selected bond lengths [Å] and angles [°] for 2.
shorter bond length, averaging 2.30 Å, reflecting the lower
Ho(1)–O(1)
2.300(8)
2.351(8)
2.371(9)
2.378(8)
2.376(8)
2.362(9)
2.506(10)
2.670(3)
2.354(8)
2.317(10)
2.327(9)
2.355(9)
71.7(3)
Ho(2)–O(8)
Ho(2)–O(10)
Ho(2)–O(11)
Ho(2)–N(2)
Ho(3)–O(4)
Ho(3)–O(5)
Ho(3)–O(6)
Ho(3)–O(7)
Ho(3)–O(8)
Ho(3)–O(12)
Ho(3)–N(4)
Ho(3)–Cl(1)
2.394(8)
2.337(8)
2.325(8)
2.505(11)
2.360(8)
2.290(9)
2.318(8)
2.371(8)
2.363(8)
2.346(8)
2.512(10)
2.585(6)
connectivity of two for the O atoms. The bonding pyridyl-
N atoms [N(2,4,6)] of each ligand have nearly identical
Ho–N bond lengths; range 2.505(11) Å–2.512(10) Å. Intra-
ligand O–Ho–O bite angles for Ho(1), Ho(2) and Ho(3)
are 71.7(3), 72.8(3) and 73.1(3)° respectively with O–Ho–N
angles of 65.3(3), 64.7(3) and 65.0(3)°. As shown in Fig-
ure 4, the two hydroxy O atoms lie perpendicular to the
centre of the (HoO)3 ring [distances above and below the
centroid are 1.191 Å to O(7) and 1.208 Å to O(8)] with the
six Ho–O(H) distances ranging from 2.355(9) Å–
2.394(8) Å. Unusually not all the chloride anions are dis-
placed from the Ho centres by the hydroxo ligands, a fea-
ture not displayed by any of the previously reported β-dike-
tonate clusters.[5,7c,8–12] Two Ho cations, Ho(1) and Ho(3)
are connected to different Cl atoms in the first coordination
sphere at distances of 2.670(3) Å and 2.585(6) Å respec-
tively. All three metals are octacoordinate with their coordi-
nation spheres being completed by either one [or two in
the case of Ho(2)] molecules of water with average Ho–O
distances of 2.34 Å. This trinuclear cluster possesses an
overall 2+ charge and it is counterbalanced by two more
distant Cl– anions which are not in close contact with any
of the metal centres [the closest Ho···Cl distance is
4.5744(42) Å].
Ho(1)–O(2)
Ho(1)–O(6)
Ho(1)–O(7)
Ho(1)–O(8)
Ho(1)–O(9)
Ho(1)–N(6)
Ho(1)–Cl(2)
Ho(2)–O(2)
Ho(2)–O(3)
Ho(2)–O(4)
Ho(2)–O(7)
O(1)–Ho(1)–O(2)
O(8)–Ho(1)–O(7)
O(6)–Ho(1)–N(6)
O(9)–Ho(1)–Cl(2)
O(3)–Ho(2)–O(4)
O(7)–Ho(2)–O(8)
O(2)–Ho(2)–N(2)
O(12)–Ho(3)–Cl(1) 146.4(3)
Ho(1)–O(2)–Ho(2) 97.7(3)
Ho(2)–O(4)–Ho(3) 98.1(3)
Ho(3)–O(6)–Ho(1) 98.6(3)
Ho(2)–O(7)–Ho(3) 97.1(3)
Ho(2)–O(7)–Ho(1) 97.0(3)
Ho(3)–O(7)–Ho(1) 97.0(3)
Ho(3)–O(8)–Ho(1) 97.3(3)
Ho(3)–O(8)–Ho(2) 96.2(3)
Ho(1)–O(8)–Ho(2) 96.0(3)
60.6(3)
65.3(3)
146.7(3)
72.8(3)
60.6(3)
64.7(3)
O(10)–Ho(2)–O(11) 146.7(3)
O(5)–Ho(3)–O(6)
O(8)–Ho(3)–O(7)
O(4)–Ho(3)–N(4)
73.1(3)
60.8(3)
65.0(3)
Table 3. Ho–Ho distances [Å] and corresponding angles [°] in the triangu-
lar core of 2.
Ho(1)–Ho(2)
Ho(1)–Ho(3)
Ho(2)–Ho(3)
Ho(2)–Ho(1)–Ho(3)
Ho(1)–Ho(2)–Ho(3)
Ho(2)–Ho(3)–Ho(1)
O(7)–O(8) 2.398(11)
3.5435(15)
3.5560(18)
3.5409(14)
59.84(3)
60.26(4)
59.91(3)
2.398(11)
tended hydrogen-bonded network which can be seen in Fig-
ure 4 and relevant distances are given in Table 4. The hydro-
gen bonding is located above and below the Ho3 plane,
where either face of the molecule is free of the steric hin-
drance of the pyridyl rings. The presence of free faces in the
molecular structure is also unusual behaviour in diketonate
cluster chemistry, as in previously reported structures the
polymetallic core has always been completely surrounded
by the organic ligands.[9,10,12] As previously stated, all the
molecular units are arranged with their Ho3 planes parallel.
In addition to the hydrogen-bonded network, intermo-
lecular π-stacking (perpendicular to the plane of the mole-
cule) occurs between either the delocalised backbone of the
diketonate moiety and a pyridyl ring or between two pyridyl
rings. We located 32 unique contacts from six different π-
stacking arrangements with distances below 3.9 Å and aver-
aging 3.649 Å. There is no lateral interaction parallel to the
Figure 3. Molecular structure of cluster 2 showing 30% ellipsoids
with all H atoms and lattice solvent molecules removed.
Large solvent-accessible voids within the lattice are occu- Ho3 plane, as seen in 1, despite the presence of one un-
pied by five distinct molecules of water and one further bound pyridyl-N atom per diketonate ligand. In two of the
water molecule which is disordered with a molecule of unbound rings the free N atoms [N(3) and N(5)] face “in-
methanol. This disorder freely refined to 50% occupancies wards” in the same direction as the coordinated N atoms.
of the respective fragments and was therefore constrained In the other ligand, N(1) faces away from the central core
at this value for all further refinements. The lattice solvents, and H-bonds to the C–H on the β-diketonate backbone of
together with the two chloride counteranions, form an ex- the same ligand, C(1)···N(1), with a distance of 2.884(17) Å.
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P. C. Junk et al.
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the long intra-chain ligand-bridging pathways or the H-
bonded inter-chain pathways (Figure 2), anticipated to be
very weak or zero, measurements of µeff were made down
to 2 K, in a field of 1 T. In Figure 5 it can be seen that the
moments remain independent of temperature down to ca.
20 K, then decrease rapidly to reach 6.77 µB (χMT =
5.73 cm3 mol–1 K) at 2 K, the decrease probably being due
8
to zero-field splitting of the S7/2-derived ligand-field
ground state rather than to very weak antiferromagnetic
coupling, 2J values for the latter being usually observed in
the range – (0.04 to 0.21 cm–1) even when better superex-
change-pathway ligands than p-dppd are present.[15] The
–1
corresponding plot of χM vs. temperature, for 1, is essen-
tially Curie-like with C = 9.0 cm3 mol–1 K and θ = –0.83 K
(Figure 5), again indicative of monomer-like behaviour but
such C and θ values have often been ascribed to weak anti-
ferromagnetic coupling.[15] Magnetisation isotherms, mea-
sured between 2 and 20 K under fields of 0 to 5 T (Support-
ing Information), further confirm this situation, the 2 K
plot showing near saturation with M = 8.2 NµB in the 5 T
field, a value a bit higher than normal for a S = 7/2 system.
Figure 4. Molecular structure of cluster 2 showing H-bonding net-
work.
Table 4. Hydrogen bonds distances [Å] for 2.
D–H···A
d(H···A)
d(D···A)
O(11)–H(11B)···O(14)
O(10)–H(10A)···Cl(3)
O(7)–H(7A)···Cl(3)
O(10)–H(10B)···O(16)
O(9)–H(9B)···Cl(3)
O(9)–H(9A)···Cl(4)
O(11)–H(11A)···Cl(4)*
O(12)–H(12B)···Cl(4)*
C(1)–H(1)···N(1)
1.85(7)
2.21(3)
2.46(10)
1.96(6)
2.42(14)
2.44(8)
2.24(4)
2.27(4)
2.55
2.650(13)
3.036(10)
3.248(9)
2.781(16)
3.120(10)
3.206(10)
3.056(9)
3.036(10)
2.884(17)
* Symmetry transformations used to generate equivalent atoms:
–1
Figure 5. Plot of effective magnetic moment (ο) and χM (ᮀ) vs.
x + 1, y, z
temperature, per Gd, for 1, in a field of 1 Tesla. The solid line is
fitted to the Curie–Weiss Law using the parameters given in the
text.
The striking feature of both structures is represented by
the fact that the pyridine nitrogen atoms are able to displace
oxygen donor ligands, most likely water or hydroxide. Al-
though lanthanoid cations have a marked preference for
oxygen from H2O and OH– (especially in non-anhydrous
environments) we have in fact encountered in our studies a
similar preference for weaker donors, where lanthanoid cat-
ions form a rod-like metal-organic framework coordinating
neutral diols or amines, which is induced by heating the
lanthanoid complex in water.[14]
The plot of effective magnetic moment, per Ho3, vs. tem-
perature for complex 2 is given in Figure 6. The applied dc
field was 1 T. There is a gradual decrease in µeff from
17.83 µB (χMT = 39.74 cm3 mol–1 K) [µeff per Ho = 10.31 µB]
at 295 K to ca. 17 µB at 100 K, then more rapidly to reach
8.89 µB (χMT = 9.88 cm3 mol–1 K) [µeff per Ho = 5.14 µB] at
2 K. Use of a 0.1 T field in the region 70–2 K showed essen-
tially the same µeff values, apart for small differences at 2 K,
as did the 1 T data indicating that field induced crossing
of the lowest levels is minimal in this case. The Ho3+ f10
configuration, with a 5I8 free-ion ground state, typically
leads to observed values of ca. 10.4 µB in monomeric sys-
Magnetic Properties
Complex 1 has a room-temperature magnetic moment of tems, and this compares well to the calculated g[J(J + 1)]0.5
8.20 µB (χMT = 8.40 cm3 mol–1 K) which is a little higher value of 10.6 µB. Thus the ligand-field (Stark) levels ema-
than values normally observed for mononuclear Gd3+ com- nating from the spin-orbit J = 8 ground level are populated
pounds that generally display close to free-ion f7 (orbitally at room temperature. The next higher J level is at energy
8
non degenerate S7/2 ground state) behaviour for which the much greater than kT. We have not made quantitative cal-
expression g[J(J + 1)]0.5 yields 7.94 µB (χMT = 7.88 culations of ligand-field splittings in the present distorted
cm3 mol–1 K). To probe for any spin-spin coupling through eight-coordinate geometry, but early calculations by Lea et
748
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 744–751

HoIII Trinuclear Clusters and GdIII Monodimensional Polymers
al.[16a] showed that a ligand field of cubic symmetry pro- monomer.[16b] Any antiferromagnetic coupling, within the
duced splittings into a singlet, two non-magnetic doublets trinuclear cluster must be very weak at best. What is clear
and four triplets. The observed decrease in µeff values with is that there is no maximum in χM and no rapid S-shaped
decreasing temperature, for 2, strongly suggests that the de- rise in M, prior to saturation (above 2 T) of the kind re-
crease is due to thermal depopulation of the low-lying Zee- cently found in the Dy triangular analogue.[6c]
man levels originating from the above-mentioned ligand-
field levels, and is not due to weak antiferromagnetic coup-
ling. Indeed, very similar values of µeff, per Ho, were ob-
served for a monomeric HoIII complex even at the 2 K re-
gion where the effects of any magnetic exchange coupling
would be noted.[16b] The apparent lack of exchange coup-
ling in 2 contrasts with the weak antiferromagnetic coup-
ling noted in a GdIII cluster[6f] and the non-collinear Ising-
like antiferromagnetic exchange observed in a DyIII clus-
ter,[6d,6e] both of which have the same [M3L3(µ3-OH)2] core
structure as in 2. The DyIII compound has yielded a very
interesting non-magnetic ground state system as well as,
surprisingly, slow relaxation of the magnetisation, the latter
originating from low lying excited magnetic states.[6d,6e,6f]
Figure 7. Plots of isothermal magnetisation, per Ho3, at tempera-
tures of 2 (top), 3, 4, 5.5, 10 and 20 K (bottom). The solid lines
are just guides to the eye and are not calculated plots. (Note that
1 T = 10000 Oe).
To probe for possible single-molecule magnetic behav-
iour (SMM) in 2 we measured the (dynamic) ac in-phase
χMЈ susceptibilities and out-of-phase χMЉ values, as a func-
tion of frequency (50 to 1500 Hz), between 10 and 2.4 K.
Very weak frequency-dependent χMЉ values were noted in
the 4–2 K region, at the temperature limit of the instrument
but no firm conclusions can be drawn from this in the ab-
sence of data below 2 K. Further, the frequency dependence
was barely detectable in the χMЈ plot, the latter showing
Curie–Weiss behaviour as in the dc plot in this low-tem-
perature region.
Figure 6. Plot of effective magnetic moment (ο) vs. temperature,
per Ho3, for 2, in a field of 1 Tesla [the data in a field of 0.1 Tesla
(᭹) are also shown]. The solid lines are guides to the eye and are
not fitted curves.
Conclusions
In order to probe further the low-lying Zeeman energy
levels in 2, the magnetisation (M) isotherms were deter-
In summary we have shown in this work how the intro-
mined in fields up to 5 T, over the temperature range 2– duction of an extra nitrogen donor atom in dipyridyl β-
20 K, the data being shown in Figure 7. It can be seen that diketone ligands has favoured the formation of either lan-
at the lowest temperature of 2 K, and highest field of 5 T, thanoid polymeric or hydroxo cluster species. The type of
the M value is 15.65 NµB and far from being saturated. In- product obtained is efficiently templated by the position of
deed, the 3, 4 and 5.5 K values, in the 5 T field, are close the pyridine nitrogen. When the nitrogen is in position 2Ј,
to the value at 2 K, such behaviour normally, in d-block a novel trinuclear hydroxo cluster is obtained, whereas ni-
clusters, indicating that low-lying levels are close to the trogen in position 4Ј induces the formation of a monodi-
ground level and that Zeeman population effects, and/or mensional polymer. Despite the high oxophilic nature of
zero-field splitting effects, are playing a part. A spin-only lanthanoid cations, coordination of the pyridine rings is
value of S, for three Ho3+ ions, would be close to 12 NµB made possible by performing the reactions in refluxing con-
but this ignores the orbital (L) contribution, and, as in re- ditions rather than room temperature. Magnetic suscep-
cent pentanuclear and trinuclear DyIII (single-ion spin of tibility and magnetisation studies, using dc and ac methods,
5/2) cluster,[6a,6c] the observed 2 K/5 T value of M, in 2, is reveal an absence of spin-spin coupling in 1 and 2, the data
higher than the spin-only value. The shapes of the magneti- for the trinuclear cluster, 2, being explainable in terms of
sation curves at temperatures 2–5.5 K are consistent with the low-lying energy levels originating from spin-orbit and
closely spaced Zeeman levels from single-ion HoIII centres, ligand-field splittings of the constituent HoIII single ions,
the 2 K curve being very similar to that reported for a HoIII with any antiferromagnetic exchange contribution being
Eur. J. Inorg. Chem. 2009, 744–751
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
749

P. C. Junk et al.
FULL PAPER
hydrous THF and NaH (60% dispersion in paraffin oil, 2.00 g,
50.0 mmol) was carefully added. Then, the corresponding ethyl pic-
olinate or ethyl isopicolinate (6.24 g, 41.3 mmol) was added and
the mixture was vigorously stirred and heated at 60 °C for 12 h.
More portions of THF were added as the mixture thickened. The
solvent was eventually removed under reduced pressure and the
resulting solid was added to a 1:5 mixture of glacial acetic acid
and water. The remaining solid was filtered and recrystallised from
methanol.
close to zero. The magnetic behaviour of 2 is markedly dif-
ferent to the non-collinear Ising exchange recently observed
for a DyIII cluster having the same core and bridging motif,
but with a different O-bridging chelator than o-dppd–. It is
likely that magnetic anisotropy differences between the
HoIII and DyIII centres will influence the spin structure in
the triangular core of the cluster as well as the relative mag-
nitudes of ligand-field and magnetic-exchange contri-
butions.
1,3-Bis(pyridin-2-yl)propane-1,3-dione (o-dppdH): Yield 6.72 g
(72%), m.p. 100–101 °C. 1H NMR (200 MHz, [D6]acetone, dike-
tone tautomer, only small traces of enol tautomer are present in
the spectrum): δ = 4.89 (s, 2 H), 7.61 (ddd, J = 7.6, J = 4.7, J =
1.3 Hz, 2 H), 8.04 (td, J = 7.6, J = 1.7 Hz, 2 H), 8.18 (ddd, J =
7.6, J = 1.0 Hz, 2 H), 8.78 (m, 2 H) ppm. 13C NMR (50 MHz, [D6]-
DMSO, diketone tautomer, only small traces of enol tautomer are
present in the spectrum): δ = 48.01, 121.86, 127.85, 137.75, 149.68,
Experimental Section
General: All solvents and reagents were purchased from Aldrich
and used as received unless otherwise specified. THF was dried
prior to use with a M-Braun MB SPS-800 purification system.
Ethyl picolinate and ethyl isopicolinate were prepared according to
previously published procedures.[17] 1H NMR spectra were re-
corded at 200 MHz with a Bruker AC 200 spectrometer. 13C NMR
spectra were recorded in the DEPT mode, proton broad band de-
coupled at 50 MHz with a Bruker AC 200 spectrometer. All the
spectra were referenced using the solvent signal. Electrospray ioni-
sation spectra (ESI) were generated with a Micromass Platform II
QMS spectrometer. Electron impact spectra (EI) were recorded
with a Shimadzu QP5050A GCMS system. Attenuated total reflec-
tion (ATR) spectra were obtained with a Bruker Equinox 55 spec-
trometer, equipped with a Specac Diamond ATR source. Elemental
microanalyses were performed by the Campbell Microanalytical
Laboratory (Department of Chemistry, University of Otago, Dune-
din, New Zealand). Melting points were measured with a Stuart
Scientific melting point apparatus SMP3 in an open capillary. Mag-
netic measurements were carried out using a Quantum Design
MPMS 5 Squid magnetometer (for dc susceptibilities and magnet-
isations), and a Quantum Design PPMS instrument with an ac
susceptibility attachment (for ac in-phase and out-of-phase suscep-
tibilities) as described previously.[18] Crystalline samples of com-
pounds 1 and 2 were mounted upon glass fibres in highly viscous
oil at 123(2) K and data were collected with an Enraf–Nonius
Kappa CCD diffractometer [graphite-monochromated Mo-Kα X-
ray radiation (λ = 0.71073 Å)] and corrected for absorption using
the SORTAV[19] package. The SHELX[20] suite of programs was
employed for structural solution and refinements using the graphi-
cal interface X-Seed.[21] For compound 1, each of the pyridyl sub-
stituents of the β-diketonate ligands were modelled as disordered
over two positions (refined occupancy of major component: ligand
A 68.37%, ligand B 76.64% and constrained for ligand C 80.00%).
The two disorder components for ligand C also related to a site
disorder of a neighbouring lattice solvent EtOH(major)/H2O-
(minor). A second lattice solvent molecule of ethanol was present
and disordered over two positions with equal occupancies. The
minor components of disorder within the main residue and the
lattice solvent were refined isotropically. In compound 2 one pyr-
idyl substituent was disordered over two sites (refined occupancy
of major component 64.38%) and one lattice molecule of methanol
was disordered with a molecule of water with equal occupancies.
Neither of these molecules nor the minor component of the pyridyl
disorder could sustain anisotropic refinement and were therefore
refined isotropically. The solvent accessible voids in the structure
almost certainly contained molecules of water however we were
unable to model them satisfactorily with the current data.
151.88, 196.57 ppm. IR (Diamond ATR): ν = 3136 (w), 3050 (w),
˜
2995 (w), 2922 (w), 2852 (w), 1650 (s), 1577 (s), 1550 (s), 1241 (s),
1279 (s), 736 (s) . cm–1 MS (ESI): calcd. for C13H11N2O2 [MH+]
227.0; found 227.0.
1,3-Bis(pyridin-4-yl)propane-1,3-dione (p-dppdH): Yield 7.01 g
(75%), m.p. 156–157 °C. 1H NMR (200 MHz, [D6]acetone, enol
tautomer, only small traces of the diketone tautomer are present in
the spectrum): δ = 7.46 (s, 1 H), 8.03 (d, J = 2.9 Hz, 4 H), 8.84 (d,
J = 2.9 Hz, 4 H) ppm. 13C NMR (50 MHz, [D6]acetone, enol tauto-
mer, only small traces of the diketone tautomer are present in the
spectrum): δ = 95.93, 121.46, 142.43, 151.75, 185.56 ppm. IR (Dia-
mond ATR): ν = 3095 (w), 3035 (w), 1611 (s 1579 s), 1539 (s),
˜
1408 (s), 1368 (m), 1278 (m), 783 (s ) . cm–1. MS (ESI): calcd. for
C13H11N2O2 [MH+] 227.0; found 227.1.
{[Gd(p-dppd)3(H2O)]·4(H2O)}ϱ (1): GdCl3·6H2O (0.50 g, 1.4 mmol)
and p-dppdH (0.61 g, 2.7 mmol) were dissolved in 100 mL MeOH.
NEt3 (1.8 mL, 13.2 mmol) was added dropwise to the solution,
which was refluxed for 48 h. The solvent was finally evaporated
and the resulting solid was added to a 1:10 EtOH/H2O mixture
(50 mL). The leftover solid was filtered off and dried under reduced
pressure yielding the title compound as a yellow solid. Yield 0.83 g
(67%). Crystals suitable for X-ray diffraction could be obtained by
diffusion of n-hexane into an ethanolic solution of the title com-
pound after several days. IR (Diamond ATR): ν = 2500–3500 [s
˜
(br)], 3034 (w), 1591 (s), 1538 (s), 1514 (s), 1421 (m), 1392 (s), 772
(m) cm–1. C39H37GdN6O11: calcd. C 50.75, H 4.04, N 9.11; found
C 51.05, H 3.87, N 8.87. Magnetic moment at 295 K, µeff = 8.20 µB.
{[Ho3(o-dppd)3(µ3-OH)2(H2O)4Cl2]Cl2} (2): HoCl3·6H2O (0.84 g,
2.2 mmol) and o-dppdH (1.00 g, 4.4 mmol) were dissolved in
100 mL MeOH. NEt3 (3.0 mL, 21.5 mmol) was then added drop-
wise and the solution was heated to reflux for 24 h. The solvent
was removed under reduced pressure and 80 mL of acetonitrile
were added to the crude product. The leftover solid was filtered off
and subsequently dissolved in pyridine. The mixture was filtered
again and pyridine was removed from the filtrate under reduced
pressure yielding the title compound as a brown crystalline solid.
Yield 0.78 g (70%). Needle shape crystals suitable for X-ray diffrac-
tion were harvested from slow evaporation of a MeOH solution
after a few days. IR (Diamond ATR): ν = 2500–3500 [s (br)], 1607
˜
(m), 1593 (m), 1580 (m), 1562 (m), 1519 (s), 1444 (s), 1395 (s), 765
(m) cm–1. C39H37Cl4Ho3N6O12: calcd. C 33.03, H 2.63, N 5.93;
found C 33.45, H 2.86, N 5.60. Magnetic moment at 295 K, µeff
17.83 µB, per Ho3; µeff = 10.31 B.M. per Ho3+
=
.
Synthesis of the Diketones o-dppdH and p-dppdH: 2-Acetyl- or 4- Crystal Data for 1: C42.60H40.20GdN6O9 [corresponding to
acetylpyridine (5.00 g, 41.3 mmol) was dissolved in 200 mL of an-
1·(EtOH)1.8(H2O)0.2], M = 937.46 gmol–1, monoclinic, P21/c, a =
750
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 744–751

HoIII Trinuclear Clusters and GdIII Monodimensional Polymers
9.53390(10) Å, 18.9281(3) Å, 23.0918(4) Å, β =
[4] D. M. Lyubov, C. Doring, G. K. Fukin, A. V. Cherkasov, A. S.
Shavyrin, R. Kempe, A. A. Trifonov, Organometallics 2008, 27,
2905–2907.
[5] P. W. Roesky, G. Canesco-Melchor, A. Zulys, Chem. Commun.
2004, 6, 738–739.
[6] a) T. M. Gamer, Y. Lan, P. W. Roesky, A. K. Powell, R. Clerac,
Inorg. Chem. 2008, 47, 6581–6583; b) N. Mahé, O. Guillou, C.
Daiguebonne, Y. Gérault, A. Caneschi, C. Sangregorio, J. Y.
Chane-Ching, P. E. Car, T. Roisnel, Inorg. Chem. 2005, 44,
7743–7750; c) J. Tang, I. Hewitt, N. T. Madhu, G. Chastanet,
W. Wernsdorfer, C. E. Anson, C. Benelli, R. Sessoli, A. K.
Powell, Angew. Chem. Int. Ed. 2006, 45, 1729–1733; d) J. Lu-
zon, K. Bernot, I. J. Hewitt, C. E. Hanson, A. K. Powell, R.
Sessoli, Phys. Rev. Lett. 2008, 100, 247205-1 to 247205-4; e)
L. F. Chibotaru, L. Ungur, A. Soncini, Angew. Chem. Int. Ed.
2008, 47, 4126–4129; f) J.-P. Costes, F. Dahan, F. Nicodème,
Inorg. Chem. 2001, 40, 5285–5287.
b
=
c
=
93.4862(12)°, V = 4159.40(11) Å3, Z = 4, Dcalcd. = 1.497 gcm3, µ =
1.656 mm–1, T = 123(2) K, θmax = 25.0°, F(000) = 1895, crystal
dimensions: 0.18ϫ0.14ϫ0.13 mm, reflections collected/unique:
45250/7331, Rint = 0.0805, final R1 = 0.0430, wR2 = 0.1073
[IϾ2σ(I)], GooF = 1.032.
Crystal Data for 2: C79H100Cl8Ho6N12O36 [corresponding to
–1
¯
2·(MeOH)0.5(H2O)5.5], M = 3066.89 gmol , triclinic, P1, a =
10.2491(5) Å, b = 17.4612(8) Å, c = 17.8448(11) Å, α = 62.557(2)°,
β = 74.375(2)°, γ = 78.991(4)°, V = 2721.1(3) Å3, Z = 1, Dcalcd.
=
1.872 gcm3, µ = 4.586 mm–1, T = 123(2) K, θmax = 25.0°, F(000) =
1484, crystal dimensions: 0.11ϫ0.11ϫ0.09 mm, reflections col-
lected/unique: 24254/9548, Rint = 0.1006, final R1 = 0.0673, wR2 =
0.1499 [IϾ2σ(I)], GooF = 1.012.
CCDC-697913 (for 1) and -697914 (for 2) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[7] a) M. K. Thompson, M. Vuchkov, I. A. Kahwa, Inorg. Chem.
2001, 40, 4332–4341; b) L.-Z. Zhang, W. Gu, B. Li, X. Liu, D.-
Z. Liao, Inorg. Chem. 2007, 46, 622–624; c) R. Wang, D. Song,
S. Wang, Chem. Commun. 2002, 368–369.
[8] L. G. Hubert-Pfalzgraf, L. Cauro-Gamet, A. Brethon, S. Dani-
ele, P. Richard, Inorg. Chem. Commun. 2007, 10, 143–147.
[9] S. V. Eliseeva, O. V. Kotova, F. Gumy, S. N. Semenov, V. G.
Kessler, L. S. Lepnev, J.-C. Buenzli, N. P. Kuzmina, J. Phys.
Chem. A 2008, 112, 3614–3626.
[10] a) V. Baskar, P. W. Roesky, Z. Anorg. Allg. Chem. 2005, 631,
2782–2785; b) V. Baskar, P. W. Roesky, Dalton Trans. 2006,
676–679; c) S. Datta, V. Baskar, H. Li, P. W. Roesky, Eur. J.
Inorg. Chem. 2007, 4216–4220.
[11] G. Xu, Z.-M. Wang, Z. He, Z. Lu, C.-S. Liao, C.-H. Yan, Inorg.
Chem. 2002, 41, 6802–6807.
[12] P. C. Andrews, T. Beck, C. M. Forsyth, B. H. Fraser, P. C. Junk,
M. Massi, P. W. Roesky, Dalton Trans. 2007, 48, 5651–5654.
[13] V. Montoya, J. Pons, X. Solans, M. Font-Bardia, J. Ros, Inorg.
Chim. Acta 2005, 358, 2763–2769.
Supporting Information (see also the footnote on the first page of
this article): Plots of isothermal magnetisation, per Gd, for com-
plex 1 (Figure S1) and temperature dependence of the out-of-phase,
χMЈЈ, and in-phase, χMЈЈ, (Insert) components of the ac molar mag-
netic susceptibility of 2 under zero dc field (Figure S2).
Acknowledgments
The authors want to thank Dr. Craig Forsyth (Monash University)
for the help provided regarding the crystal structures. This work
was supported by the Australian Research Council and Bayer
Schering Pharma.
[14] a) P. C. Andrews, C. M. Forsyth, B. H. Fraser, P. C. Junk, M.
Massi, M. Silberstein, CrystEngComm 2007, 9, 282–285; b) T.
Fiedler, M. Hilder, P. C. Junk, U. H. Kynast, M. M. Lezhnina,
M. Warzala, Eur. J. Inorg. Chem. 2007, 291–301.
[15] a) H. Lueken, P. Hannibal, K. Handrick, Chem. Phys. 1990,
151–161; b) S.-S. Bao, .-F. Ma, Y. Wang, L. Fang, C.-J. Zhu,
Y.-Z. Li, L.-M. Zheng, Chem. Eur. J. 2007, 13, 2333–2343.
[16] a) K. R. Lea, M. J. M. Leask, W. P. Wolf, J. Phys. Chem. Solids
1962, 23, 1381–1405; b) J.-P. Sutter, M. L. Kahn, O. Kahn, Adv.
Mater. 1999, 11, 863–865; c) V. S. Mironov, Y. G. Galyametdi-
nov, A. Ceulemans, C. Görller, K. Binnemans, J. Chem. Phys.
2002, 116, 4673–4685.
[17] T. C. Bruice, J. Am. Chem. Soc. 1957, 79, 902–905.
[18] L. M. Wittick, K. S. Murray, B. Moubaraki, S. R. Batten, L.
Spiccia, K. J. Berry, Dalton Trans. 2004, 1003–1011.
[19] R. H. Blessing, J. Appl. Cryst. 1997, 30, 421.
[20] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
[21] L. J. Barbour, J. Supramol. Chem. 2003, 1, 189–191.
Received: October 14, 2008
[1] a) R. Wang, Z. Zheng, T. Jin, R. T. Staples, Angew. Chem. Int.
Ed. 1999, 38, 1813–1815; b) D.-S. Zhang, B.-Q. Ma, T.-Z. Jin,
S. Gao, C.-H. Yan, T. C. W. Mak, New J. Chem. 2000, 24, 61–
62; c) R. Anwander, Angew. Chem. Int. Ed. 1998, 37, 599–602;
d) D. Freedman, J. H. Melman, T. J. Emge, J. G. Brennan, In-
org. Chem. 1998, 37, 4162–4163; e) X. Gu, D. Xue, Inorg.
Chem. 2007, 46, 3212–3216; f) G. Gieser, P. Unfried, Z. Zák,
J. Alloys Compd. 1997, 257, 175–181; g) A. Ruiz-Martinez, D.
Casanova, S. Alvarez, Dalton Trans. 2008, 19, 2583–2591.
[2] a) Z. Zheng, Chem. Commun. 2001, 2521–2529; b) A. Babai,
A.-V. Mudring, Z. Anorg. Allg. Chem. 2006, 632, 1956–1958.
[3] a) M. R. Bürgstein, P. W. Roesky, Angew. Chem. Int. Ed. 2000,
39, 549–551; b) G. B. Deacon, T. Feng, D. C. R. Hockless, P. C.
Junk, B. W. Skelton, A. H. White, Chem. Commun. 1997, 341–
341; c) G. B. Deacon, G. B. Fallon, C. M. Forsyth, S. C. Harris,
P. C. Junk, B. W. Skelton, A. H. White, Dalton Trans. 2006,
802–812; d) G. B. Deacon, C. M. Forsyth, R. Harika, P. C.
Junk, J. W. Ziller, W. J. Evans, J. Mater. Chem. 2004, 14, 3144–
3149.
Published Online: January 14, 2009
Eur. J. Inorg. Chem. 2009, 744–751
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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