Functionalised β-diketone assisted self-assembly of a hexanuclear yttrium oxo-hydroxo cluster

Article abstract of DOI:10.1016/j.poly.2009.04.035

The reaction of YCl₃·6H₂O with ortho-hydroxydibenzoylmethane (HO-DBMH) in a 1:2 ratio, in methanol and in the presence of excess triethylamine as a base yielded a yellow precipitate which on crystallization from toluene or benzene /h

Full text of DOI:10.1016/j.poly.2009.04.035

Polyhedron 28 (2009) 2284–2286
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Functionalised b-diketone assisted self-assembly of a hexanuclear yttrium
oxo-hydroxo cluster
Ananda Kumar Jami, Pilli V.V.N. Kishore, Viswanathan Baskar *
School of Chemistry, University of Hyderabad, Hyderabad 500046, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of YCl Á6H O with ortho-hydroxydibenzoylmethane (HO-DBMH) in a 1:2 ratio, in methanol
3
2
Received 9 March 2009
Accepted 12 April 2009
Available online 6 May 2009
and in the presence of excess triethylamine as a base yielded a yellow precipitate which on crystallization
from toluene or benzene /hexane afforded pale yellow block-like crystals. Single crystal X-ray diffraction
of 1 revealed the formation of an interesting hexanuclear yttrium oxo-hydroxo cluster [Y
6 6
(O-DBM) (HO-
DBM) -OH) (MeOH) ]; the core resembles a butterfly framework flanked by a lanthanide atom on
each side. Ten phenolic b-diketone ligands are present in the cluster, which bridge the metal centers
in both chelating and chelating-bridging fashions.
4
(
l
3
2
4
Keywords:
Yttrium clusters
Self-assembly
Functionalised b-diketones
Oxo-hydroxo bridges
Synthesis and structural elucidation
Ó 2009 Elsevier Ltd. All rights reserved.
1
. Introduction
Multinuclear metal clusters, in particular lanthanide based clus-
2. Experimental
Yttrium trichloride hexahydrate was synthesized from the cor-
responding oxide by neutralizing with conc. HCl, followed by evap-
oration to dryness. The ligand 1-(2-hydroxyphenyl)-3-phenyl-1,3-
propanedione was prepared according to the literature method
[27]. Triethylamine and the solvents were used as purchased from
commercial sources without further purification. Elemental analy-
ses were carried out with a FLASH EA series 1112 CHNS analyzer. IR
spectra were recorded on a JASCO-5300 FT-IR spectrophotometer
ters, have generated a huge amount of interest in recent years ow-
ing to their wide ranging applications from precursors to magnetic
materials to catalysis [1–13]. Traditionally, lanthanide oxo-hydro-
xo clusters have been synthesized either by controlled hydrolysis
of air and moisture sensitive lanthanide precursors [14–16] or by
slow deprotonation of the coordinated water molecules of hydra-
3 2
tion in lanthanum salts like LnCl ÁxH O, in the presence of suitable
1
ligands by addition of a base [17–19]. b-Diketones have been used
as ligands extensively to synthesize a large number of lanthanide
clusters whose solid state structures vary from tetra- to tetra deca-
nuclear forms [17–23]. Although b-diketones have been investi-
gated in detail for their ligating ability towards lanthanides and
their solid state structures are well understood, the use of func-
tionalized b-diketones [24] and in particular phenolic b-diketones
(using KBr pellets). The H solution NMR spectrum was recorded
on a BRUCKER DRX 400 instrument. Single crystal X-ray data was
collected at 298(2) K on a BRUKER SMART APEX CCD area detector
system [k(Mo Ka) = 0.71073 Å] with a graphite monochromator,
and the data were reduced using SAINTPLUS. The structure was solved
using SHELXS-97 and refined using SHELXS-97 [28,29]. All non hydro-
gen atoms were refined anisotropically, except for the carbon
and oxygen atom of a methanol solvent molecule (C81–O32) which
was refined isotropically. As the solvents of crystallization, metha-
nol and water molecules, were heavily disordered, the hydrogen
atoms were not fixed for the solvents of crystallization found in 1.
[
25,26] as ligands towards lanthanides are rare. In this paper, we
present the synthesis and structural characterization of a hexanu-
clear cluster of yttrium and using HO-DBMH as a ligand. The single
crystal X-ray characterization technique revealed the formation of
6 6 4 3
a novel hexanuclear yttrium cluster, [Y (O-DBM) (HO-DBM) (l -
OH) (MeOH) ] (1).
2
4
2.1. Synthesis
The ligand, 1-(2-hydroxyphenyl)-3-phenyl-1,3-propanedione
(
H0-DBMH) (0.470 g, 1.96 mmol) and YCl
mmol) were dissolved in methanol (20 ml). Triethylamine
0.39 g, 3.92 mmol) was slowly added to the above reaction mix-
3
Á6H
2
0 (0.30 g, 0.98
(
*
Corresponding author. Tel.: +91 40 66794825; fax: +91 40 23012460.
E-mail addresses: vbsc@uohyd.ernet.in, baskarviswanathan@gmail.com
V. Baskar).
ture and stirred for 12 h at room temperature. The pale yellow pre-
cipitate that formed was filtered, washed with methanol (5 ml)
(
0
277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.04.035

A.K. Jami et al. / Polyhedron 28 (2009) 2284–2286
2285
and air dried. Further the precipitate was dissolved in toluene
15 ml) and stirred for 20 min, at which point the solution was
The yttrium atoms that make up the butterfly core are eight-
coordinate and the peripheral yttriums are seven-coordinate. The
(
again filtered. Slow evaporation of toluene at room temperature
yielded yellow crystals of 1 in 78% yield (0.39 g). The crystals lost
the solvent of crystallization rapidly and turned opaque. Better
quality crystals suitable for single crystal X-ray diffraction studies
were obtained by slow evaporation of 1 from benzene (Caution:
Benzene is a class A carcinogen and should be used with the proper
precautions) or by a benzene/hexane diffusion method after a
central butterfly core is held together by two l3-OH bridges, sim-
ilar to the ones found in the tetranuclear structures of ytterbium
and lutetium reported recently [20]. The yttrium to oxygen bond
distances (2.254–2.436 Å) and the Y–O–Y bond angles (95.44–
111.12°) fall in the ranges reported in the literature [17–19]. Se-
lected bond lengths and bond angles are given in Table 2.
Ten phenolic b-diketone ligands are found coordinated to the
metal centers in 1, displaying varying modes of binding.
week. Elemental analysis for C154
H 3.99; found: C 60.04, H 3.95. IR(KBr, cm ): 3580(m) (
H
122
O
36
Y
6
: Anal. calcd. C 60.01,
À1
2À
m
OH),
Six of these ligands are in the dianionic [O–DBM] form, while
À
3
1
8
057(m), 1597(s) (
392(m), 1296(m), 1248(s), 1203(m), 1138(m), 1024(m), 941(m),
60(m), 756(s), 719(m), 696(m), 625(s), 584(m), 520(m). H NMR
m
CO), 1547(w), 1516(s) (
m
C–C), 1483(m),
the other four are monoanionic [OH–DBM] . The six dianionic [O–
2À
DBM] ligands are found wrapped around the central butterfly
1
(
3
CDCl ) d (ppm): 2.65 (s, Me/coordinated solvent methanol), 4.54
Table 1
(
s, CH), 6.54–8.02 (m, Ph), 11.60 (broad peak, phenolic OH).
Crystallographic data for 1.
Formula
164 192 66 6
C H O Y
3
. Results and discussion
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
3752.64
triclinic
P1
15.8562(9)
16.2774(9)
19.7466(11)
99.3220(10)
93.9730(10)
95.9110(10)
4983.3(5)
1
1.250
1.805
298
19686/0/1055
0.965
ꢀ
The synthetic methodology used for the preparation of 1 was
adopted from recent literature reports [17–19]. Hydrated yttrium
chloride and the ligand, ortho-hydroxydibenzoylmethane (HO-
DBMH) were dissolved in methanol (20 ml) in a ratio 1:2, and tri-
ethylamine (excess) was added dropwise to the stirred reaction
mixture (Scheme 1). Halfway through the addition of the base, a
yellow precipitate was obtained. The reaction mixture was stirred
further for a period of 12 h and filtered to isolate the precipitate.
The precipitate was then washed thoroughly with methanol to
remove the unreacted starting materials and the product was air
dried. Pale yellow block-like crystals were obtained after a week
by slow diffusion of hexane into a toluene or benzene solution of
a
(°)
b (°)
(°)
c
3
V (Å )
Z
D
À3
calcd (Mg m
)
À1
l
(Mo-
a) (mm
)
T (K)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0802, wR2 = 0.2123
1
at room temperature. The products were characterized by stan-
R indices (all data)
Largest difference in peak and hole (e Å
R
1
= 0.2057, wR
2
= 0.2719
À3
)
1.086 and À0.501
dard analytical and spectroscopic techniques. The IR spectrum of
1
1
shows a peak corresponding to a C–O stretch at around
À1
À1
597 cm . A broad peak at 3580 cm can be attributed to the
1
presence of an OH group in the product. The H NMR spectrum
of 1 in CDCl shows a multiplet centered around 6.54–8.02 ppm,
3
corresponding to the aromatic groups of the phenolic b-diketone
ligand.
The solid state structure of 1 was established by single crystal
X-ray diffraction. The crystallographic data is given in Table 1.
Although we could crystallize 1 from both toluene and benzene
solutions by slow diffusion of hexane at room temperature, only
the crystals isolated from benzene were of sufficiently good quality
for single crystal X-ray diffraction analysis, in spite of several at-
tempts to isolate good quality crystals of 1 from toluene (Caution:
Benzene is a class A carcinogen and should be used with the proper
precautions). The neutral cluster 1 crystallises in the triclinic space
ꢀ
group P1. The core of the cluster consists of six yttrium centers
connected through oxo and hydroxo bridges. A sheath of organic
groups encapsulates the metal oxo-hydroxo core enabling the
product to dissolve in a wide range of organic solvents like chloro-
form, dichloromethane, benzene and toluene. The hexanuclear me-
tal core can be visualized in the following manner; a central
butterfly core (consisting of four yttriums) flanked by a yttrium
metal on each side (Fig. 1).
6
[YCl .6H O] + 10 HO-DBMH
3 2
1
8 Et N
- 18 Et NHCl
3
3
Sol: MeOH
- 34 H O
2
]
Y (O-DBM) (HO-DBM) (µ3-OH)2(MeOH)4]
6
6
4
Fig. 1. (a) Solid state structure of 1; hydrogen atoms and solvents of crystallization
are omitted for clarity (b) the yttium oxo core of the cluster 1 omitting carbon and
hydrogen atoms.
Scheme 1.

2
286
A.K. Jami et al. / Polyhedron 28 (2009) 2284–2286
Table 2
4
. Conclusion
Selected bond lengths (Å) and bond angles (°) in 1.
Bond lengths
Bond angles
We have been successful in synthesizing a hexanuclear yttrium
oxo-hydroxo cluster using a phenolic b-diketone as a ligand. The
hexanuclear framework reported here is quite unique and we
believe that changing yttrium to other paramagnetic lanthanides,
like dysprosium or gadolinium, will lead to the generation of
paramagnetic lanthanide oxo-hydroxo clusters possessing
interesting magnetic properties. Work is currently under progress
in this direction.
Y1–O1
Y2–O1
Y1–O2
2.362(6)
2.391(5)
2.435(5)
2.421(5)
2.436(5)
2.382(6)
2.361(5)
2.355(5)
2.276(7)
2.276(6)
2.299(5)
2.272(6)
2.254(7)
2.274(6)
2.277(6)
2.313(5)
2.248(7)
2.253(6)
2.266(6)
2.239(7)
2.358(7)
Y1–O1–Y2
Y1–O17–Y2
Y1–O2–Y2
Y1–O5–Y2
Y1–O1–Y2
Y1–O4–Y3
Y1–O7–Y3
109.34(21)
111.12(21)
95.44(17)
96.41(17)
100.65(19)
111.02(24)
110.57(24)
108.66(21)
*
*
*
Y2 –O2
*
Y1–O5
*
Y2 –O5
Y1–O17
Y2–O17
Y1–O18
Y1–O7
Y1–O4
Y2–O16
Y2–O6
Y2–O3
Y3–O4
Y3–O7
Y3–O15
Y3–O10
Y4–O9
Y3–O13
Y3–O15
*
Y2–O1–Y2
Supplementary data
CCDC 721333 contains the supplementary crystallographic data
for 1. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
core, displaying both chelating and chelating-bridging modes of
binding. The oxygens of the b-diketone part of the ligand chelate
to the central dimeric core of the butterfly unit. Further, one of
the oxygen atoms of the b-diketone part of each ligand also bridges
to a third yttrium metal atom (so does the symmetry related oxy-
gen) leading to the formation of the central butterfly framework
observed in 1. This core is linked to the peripheral metal centres
through the phenoxide groups, which act as bridging ligands, lead-
ing to the formation of a hexanuclear cluster. Each of the periphe-
ral yttrium centers are further chelated to two monoanionic OH-
DBM ligands. The varying modes of binding found in 1 are depicted
in Chart 1. Interestingly, other than the central metal dimer of the
butterfly unit, all the other metal centers are coordinated to a
methanol solvent molecule to saturate their coordination spheres.
It is of interest to mention here that a subtle change in the stoi-
chiometry of the reactants can lead to isolation of interesting new
structures in the solid-state. In a recent report, reaction of hydrated
lanthanum nitrate with H0-DBMH in methanol as solvent followed
by addition of triethylamine as a base in the ratio 1:3:3 has led to
the isolation of mononuclear complexes of lanthanides where the
phenolic part of the ligand is essentially non-coordinating [25].
In the present case, however, where the stoichiometry of the me-
tal/ligand/base is 1:2:4, hexanuclear clusters have been isolated
wherein the phenolic oxygen from the ligand acts as a bridging
VB thanks the Department of Science and Technology, New Del-
hi, India for financial support under the SERC-Fast track scheme.
We thank Dr. P. Raghavaiah for useful discussions in
crystallography.
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O
O
OH
O
O
O
M
M
M
M
Chart 1.