A redox-triggered structural rearrangement in an iodate-templated polyoxotungstate cluster cage

Article abstract of DOI:10.1039/c3cc45659e

The new tungstatoiodate, α-[H₅W₁₈O ₅₉(IO₃)]^6-, containing I^VO ₃^- within a {W₁₈O₅₄} metal oxide framework has been prepared and shown by X-ray crystallography and mass spectrometry to be derived from the fully oxidised [H₃W ₁₈O₅₆(IO₆)]^6- by two-electron reduction accompanied by a redox-triggered structural rearrangement where three I-O covalent bonds are broken.

Full text of DOI:10.1039/c3cc45659e

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A redox-triggered structural rearrangement in an
iodate-templated polyoxotungstate cluster cage†
Cite this: Chem. Commun., 2013,
4
9, 9731
a
a
a
a
De-Liang Long,* Jun Yan, Andreu Ruiz de la Oliva, Christoph Busche,
Received 25th July 2013,
a
b
a
Haralampos N. Miras, R. John Errington and Leroy Cronin*
Accepted 30th August 2013
DOI: 10.1039/c3cc45659e
www.rsc.org/chemcomm
6
À
V
3À
The new tungstatoiodate, a-[H
5
W
18
O
59(IO
3
)] , containing I O
Compound 1 was prepared from an aqueous solution of
within a {W18
O54} metal oxide framework has been prepared and Na WO , H IO (molar ratio 14 : 1) and triethanolammonium
2 4 5 6
+
À
shown by X-ray crystallography and mass spectrometry to be chloride (TEAH Cl ) under reflux and was precipitated as pale
6À
derived from the fully oxidised [H
reduction accompanied by a redox-triggered structural rearrange- revealed a Dawson-type D3h-symmetric {W18
ment where three I–O covalent bonds are broken. enclosing an IO unit with average I–O and (I)O–W distances of
.90(2) Å and 2.42(2) Å respectively. Two m -O atoms from the
Polyoxometalates (POMs) are attracting widespread attention capping {W } groups, with average O–W distances of 2.23(2) Å,
because of emerging and anticipated applications arising from and three m -O atoms bridging pairs of belt W centers make up
3
18
W O
56(IO
6
)] by two-electron brown crystals.§ X-ray crystallographic structural analysis¶
O54} cluster shell
3
1
3
3
2
1
–3
their uniquely diverse electronic and molecular properties.
the remaining internal oxygen sites. The overall W and O
The physical and electronic properties of POMs are intimately positions are very close to those in Dawson-type anions contain-
linked to their structural features, but systematic synthesis and the ing tetrahedral template heteroatoms, but in contrast to the
6
À 11
reactivity studies required to understand these relationships previously reported potassium salt of b*-[H
3 18 6
W O56(IO )] ,
remain a pressing challenge. Methods for metal substitution in in which the iodine is centrally located, the iodine in
3
À
6À
Lindqvist hexametalates [(RO)MW
5
O
18
]
(M = Ti, Sn) enabled us to a-[H
5
W
18
O
59(IO
3
)] in 1 is displaced to one side of the cluster
axis, with a deviation of 0.53(2) Å from the
W NMR spectra. Electronic centre (Fig. 1). The off-centre displacement of iodine lowers the
properties can also be tuned by encapsulation of ‘functional’ cluster symmetry and increases the number of possible isomers
show how the frontier orbital energies vary with metal substitution along the molecular C
3
1
83
4
and the remarkable effect on
3
À
6À
template anions in place of the ‘innocent’ anions such as PO
from six for standard Dawson-type clusters [W O (PO ) ] or the
4
18 54
11–13
4 2
2
À
4–7
6À
6À
and SO
utilizing redox-active templates, we have isolated new types of XO
and XO -based POM clusters. The thermochromic Dawson-type
a- and b-[Mo18
4
more commonly used in POM synthesis,
and by [H
new anion [H
, b , b *, b
contain [H
and the first crystallo-
4
W
19
O
62
]
and [H
59(IO
3
W
18
O
56(IO
6
)] systems
to eight for this
6
À
3
5
W
18
O
3
)] . The isomers can be defined as a, a*,
6
b
1
2
1
2
*, g, g*, based on the six isomers of the parent
and [H
4À 8
8À
6À
6À
11,13
O
54(SO
templates inside the cluster shell,
graphically characterized tungstatoperiodate, [H W O (IO )]
3
)
2
]
, and [W18
O
58(SO
3
)
2
(H
2
O)
2
]
4
W
19
O
62
]
3
W
18
O
56(IO
6
)] systems.
In the a, a*, g
2À
9,10
SO
3
6
À
,
3
18 56
6
1
1
was shown to be catalytically active. We present herein the
structure of a new type of {W } cluster, (C H NO ) -
1
8
6
16
3 5
Na[H
5
W
18
O
59(IO
3
)]Á5H
2
O 1, which is the first example of a
À
POM with encapsulated IO
oxidised {W18 56(IO
3
. Its formation from the fully
O
6
)} core involves two-electron reduction
and a redox-switched structural rearrangement.‡
a
WestCHEM, School of Chemistry, The University of Glasgow, Glasgow, G12 8QQ,
UK. E-mail: Deliang.Long@glasgow.ac.uk, Lee.Cronin@glasgow.ac.uk; Web: http://
6
À
+
www.croninlab.com; Fax: +44 (0)141-330-4888; Tel: +44 (0)141-330-6650
Fig. 1 Representation of the structure of b*-[H
(left), IO having octahedral geometry, and a-[H
three O atoms of IO being eclipsed with the three m
atom. The {W18 54} frameworks are shown in stick mode. The central iodine
3
W
18
O
56(IO
6
)] in its K salt
b
6À
School of Chemistry, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
6
5
W
18
O
59(IO
3
)]
in 1 (right),
†
Electronic supplementary information (ESI) available: Full mass spectrometric
3
2
-O atoms above the iodine
data, crystallographic data, bond valence calculation, electrochemistry and
thermogravimetric analysis. CCDC 951761. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c3cc45659e
O
atoms and interior oxo ligands are highlighted as large spheres (I: purple; O:
pink).
This journal is c The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 9731--9733 9731

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1
1
6 3 18 6
and g* isomers of the {W18O62} structure, the two ends are the reduction product of (TEAH) [H W O56(IO )], i.e. upon
geometrically equivalent, so movement of the central iodine extended heating, the initial periodate product is reduced to
+
atom towards either end would give a single isomer in each iodate product by the protonated organic amine TEAH . This
case. However, in the b and b* isomers the two ends are argument is based on the fact that purple iodine vapor is
inequivalent, so movement of the iodine in different directions produced from the system after longer reflux periods confirm-
generates the b
1
, b
2
, b
1
* and b
2
* isomers. The {W18
3
O59(IO )} ing that iodine can be reduced from higher oxidation states
structure in 1 is the a isomer in which the {W18
O
54} cluster shell during the reaction. Furthermore, an analogous reaction using
has a D3h symmetry with a horizontal mirror plane and the iodic rather than periodic acid under the same reaction condi-
three oxygen atoms bonded to iodine are eclipsed with the tions did not produce 1, which further supports the interme-
6
À
three m
2
-O atoms above the iodine atom (Fig. 1). The presence diacy of the fully oxidized [H
of 1.
The isomer configuration of the periodate cluster
3 18 6
W O56(IO )] in the formation
of iodine lowers the symmetry to C .
3
v
6
À
[
H W O (IO )]
in
1
and the periodate cluster
5
18 59
3
À
6
6À
+
[
H W O (IO )]
represent different redox states of the [H W O (IO )] in the previously reported K salt K [H W -
3
18 56
nÀ
6
3
18 56
6
6
3
18
11
{
IW18O
62
}
core, where n = 11 and 9 respectively and the
are localized on iodine. but that in (TEAH)
The difference between these two clusters was verified by use disorders of the IO
O
56(IO
6
)] was undoubtedly determined as b* by crystallography,
11
additional two electrons in
1
6
[H
3
W
18
O
56(IO
6
)] was not clear due to heavy
54} cluster shell in the
6
template and {W18
O
of mass spectrometry coupled with the X-ray single crystal crystal structure which result from either cluster packing disorder
structure determination and elemental analysis. Exchange of or irresolvable isomer co-crystallization. Evidently the a isomer
+
+
6À
the TEAH cations in 1 with tetrabutylammonium (TBA ) gave configuration of the iodate cluster [H W O (IO )] in 1 is clear,
(
5
18 59
3
1
4
TBA) [H W O (IO )] 2. Fig. 2 shows the mass spectrum of 2 but it is not possible to conclude whether the isomer configuration
6 5 18 59 3
in acetonitrile in which all major peaks are derived from is conserved from the parent cluster during the reaction while three
6
À
[
H
5
W
18
O
59(IO
3
3
3
)] and m/z values can be assigned as follows: I–O covalent bonds of the IO
6
template are broken to form IO
3
3
À
À
3À
2À
6À
1
2
2
720.3 {TBA
580.4 {TBA
822.2 {TBA
[H
[H
5
6
IW18
IW18
O
O
62]}
62]}
,
,
1800.7 {TBA
2701.6 {TBA
4
4
[H
[H
IW18
4
5
IW18
IW18
O
O
62]}
62]}
,
,
upon the reduction. The isopolytungstate [H
ably produced as an impurity in this reaction system. This is not
4
19 62
W O ]
is unavoid-
2
2
À
3À
5
[H
4
IW18
+
O62]} , 3683.5 {TBA
56(IO
9
[H
5
O
62
]
2
}
. In unexpected, as this anion is produced quantitatively from the same
6À
contrast, the TBA salt of [H
3
W
18
O
6
)]
in acetonitrile reaction mixture in the absence of periodic acid after heating under
shows a quite different mass spectrum in this m/z range, and reflux for three days.
2
À
peaks can be assigned as follows: 2570.8 {TBA [H IW O ]}
,
The compounds reported here are the first examples of
3
2
18 61
2À 11
18 62
2À
15
2
700.5 {TBA [H IW O ]} , 2822.1 {TBA [H IW O ]}
.
tungstatoiodates, and the synthesis of 1 represents the first
4
3
18 62
5
2
V
3À
The combined mass spectral and elemental analyses therefore time that the I O ion has been captured within a POM cage,
V
À
VII 5À
clearly show the relationship between the I O
3
and I
O
6
and the first incorporation of I(V) into a POM. Notably, this is
POMs, and confirm that 2 contains the redox active center with also the first example of a Dawson-like {W18} cluster cage
6
À
encapsulated iodine(V), i.e. [H
5
W
18
O
59(IO
3
)]
.
3
containing pyramidal XO templates to adopt an ‘olive’ shape
The main peaks in the mass spectrum of 2 can be assigned with a {XW18} composition. All previous examples of the {XW18
}
2
À
7À
18 60
to species of the type {(TBA)9 [H W O (IO )]} where n = 4, composition have ‘peanut’ shape, e.g. the [H SbW O ] and
Àn
n
18 59
3
2
IV
6À
16
IV
6À
5
or 6. Of these, the five-fold protonated form is predominant, [H Te W O ] anions. [H Te W O ] was produced by the
i.e. the most intense peak at 2701.6 in Fig. 2 corresponds to reduction of [H Te W O ] with the loss of two internal oxo
2
18 60
2
7À
18 60
VI
3
18 62
2
À
16a
{
(TBA)
4 5
[H IW18O62]} . These results suggest that addition of ligands. Interestingly, the non-hydrogen composition is retained
6
À
6À
6À
two electrons to [H
3
W
18
O
56(IO
6
)] is accompanied by addi- after reduction of [H
3
W
18
O
56(IO
6
)]
5 18
to [H W O59(IO )] ,
3
tional double protonation to balance the increased charge.
suggesting the possibility to design a reversible, proton-coupled
redox process. This also provides an opportunity to expand our
+
The TEAH salt of the periodate-templated cluster (TEAH)
6
-
1
1
[H
3
W
18
O56(IO
6
)] was synthesized from the same reaction design and synthesis of POMs with redox-switchable physical
mixture as 1 but with a shorter heating and reflux time (about properties, and complements our work on the reductive synthesis
3À
3
0 minutes compared with one hour for 1). From the reaction of capped Keggin-type structures e.g. [PMo O {Co(MeCN) }]
12 40 2
3À 17
sequence and the cluster structure similarity, we argue that 1 is and [PMo O (VO) ]
.
12
40
2
In summary, we have discovered a new type of tungstato-
6
À
iodate, [H
5 18 3
W O59(IO )] , which contains iodine(V) within a
{
18
W O
54} Dawson-type shell and is the first example of an a-isomer
of this family. We have characterized this polyanion using single
crystal structure analysis and confirmed the assignment of the
central atom of the template anion as iodine, as well as the degree
of cluster protonation using mass spectrometry. Electrochemical,
catalytic and DFT studies are being performed to compare with
conventional Dawson-type polyoxotungstates.
This work was funded by the EPSRC. The authors are grate-
ful to COST Action CM1203 ‘‘Polyoxometalate Chemistry for
6 5 18 3
Fig. 2 Negative mode mass spectrum of TBA [H W O59(IO )] 2 in acetonitrile. Molecular Nanoscience (PoCheMoN)’’ for supporting this work.
9
732 Chem. Commun., 2013, 49, 9731--9733
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Notes and references
C. P. Pradeep, N. Gadegaard and L. Cronin, J. Am. Chem. Soc.,
2009, 131, 1340; (c) J. Thiel, D. Yang, M. H. Rosnes, X. Liu,
5
À
‡
Caution: care should be taken when using IO
since there is a risk of explosion or combustion.
Synthesis of (TEAH) Na[H 59(IO
)]Á5H
10.0 g, 30.3 mmol) and triethanolamine hydrochloride (7.0 g,
7.7 mmol) were dissolved in water (20 mL) and H IO (0.5 g, 2.2 mmol)
6
based materials
C. Yvon, S. E. Kelly, Y.-F. Song, D.-L. Long and L. Cronin, Angew.
Chem., Int. Ed., 2011, 50, 8871.
4 B. Kandasamy, C. Wills, W. McFarlane, W. Clegg, R. W. Harrington,
A. Rodriguez-Fortea, J.-M. Poblet, P. G. Bruce and R. J. Errington,
Chem.–Eur. J., 2012, 18, 59.
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and L. Cronin, Angew. Chem., Int. Ed., 2012, 51, 2115.
X. K. Fang and P. K o¨ gerler, Angew. Chem., Int. Ed., 2008, 47, 8123;
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(a) P. J. S. Richardt, R. W. Gable, A. M. Bond and A. G. Wedd, Inorg.
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§
5
5
W
18
O
3
2
O
1: Na
2
WO
4
Á2H
2
O
(
3
5
6
in water (5 mL) was added. The solution pH was adjusted to 1.3 by
dropping in 6 M HCl and the solution was heated to reflux and stirred
5
for about 1.0 h until the solution turned to light brown and purple I
vapour just started to appear in the flask. Light brown crystalline
product was then isolated in three days. Yield: 3.2 g. Elemental analysis,
2
6
calc. for C30
Na 0.44%. Found: C 7.80, H 1.81, I 2.46, N 1.46, Na 0.76%. Cation exchange
to produce (TBA) [H 59(IO )] 2: (C 16NO Na[H 59(IO O 1
)]Á5H
1.0 g) was dissolved in water (20 mL). Tetrabutylammonium bromide (1.0 g)
5
H85IN NaO77W18 (dried sample): C 6.91, H 1.65, I 2.44, N 1.34,
7
6
5 18
W O
3
6
H
3
)
5
5
W
18
O
3
2
(
dissolved in water (10 mL) was added with stirring. The precipitate was
centrifuged and washed with water, ethanol and ether, and dried in
vacuum. Yield: 0.7 g. Elemental analysis, calc. for C96
8
9
D.-L. Long, P. K ¨o gerler and L. Cronin, Angew. Chem., Int. Ed., 2004,
43, 1817.
H
221IN
6
O
62
W18: C
(a) C. Fleming, D.-L. Long, N. McMillan, J. Johnson, N. Bovet,
V. Dhanak, N. Gadegaard, P. K ¨o gerler, L. Cronin and M. Kadodwala,
Nat. Nanotechnol., 2008, 120, 229–233; (b) R. Tsunashima, D.-L. Long,
T. Endo, S. Noro, T. Akutagawa, T. Nakamura, R. Q. Cabrera,
P. F. McMillan, P. K o¨ gerler and L. Cronin, Phys. Chem. Chem. Phys.,
2011, 181, 7295.
1
¶
9.58, H 3.78, I 2.16, N 1.43%. Found: C 19.80, H 3.73, I 2.21, N 1.50%.
Crystallographic data and structure refinements for (TEAH) Na
5
À1
[
H
5
W
18
O
59(IO
3
2 5 r
)]Á5H O 1: C30H95IN NaO82W18, M = 5297.29 g mol ;
3
block crystal: 0.19 Â 0.15 Â 0.05 mm ; T = 150(2) K; triclinic, space
group P1%, a = 14.1743 (3), b = 18.6898(4), c = 21.2836(5) Å, a = 89.751(2)1,
3
À3
b = 87.320(2)1, g = 70.905(2)1, V = 5321.9(2) Å , Z = 2, r = 3.306 g cm
,
À1
10 D.-L. Long, H. Abbas, P. K o¨ gerler and L. Cronin, Angew. Chem., Int.
Ed., 2005, 52, 3415.
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Angew. Chem., Int. Ed., 2006, 45, 4798.
m(Mo-K
a
) = 19.76 mm , F(000) = 4724, 86 475 reflections collected,
1
9 759 unique, 1101 refined parameters, R = 0.0591, wR = 0.1782. The
1 2
+
cluster is well defined in the asymmetric unit. One Na site is identified
by the coordination environment around the site. Four TEAH sites are
roughly modelled in the structure. The fifth TEAH molecule (or a little
more according chemical analysis) is believed to be located in the
heavily disordered solvent area. Crystal data were measured on a Oxford
+
+
1
1
Gemini A Ultra Atlas CCD diffractometer using Mo-K
.71073 Å) at 150(2) K. Twin data process and structure refinement were
a
radiation (l =
1
4 Why was cation exchange needed, see for example: D.-L. Long,
C. Streb, Y. F. Song, S. Mitchell and L. Cronin, J. Am. Chem. Soc.,
0
applied in this structure determination. CCDC 951761 (1) contains the
2008, 130, 1830.
crystallographic data.
1
5 W. Levason, Coord. Chem. Rev., 1997, 161, 33.
1
6 (a) J. Yan, D.-L. Long, E. F. Wilson and L. Cronin, Angew. Chem., Int.
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18, 3010; (e) B. Krebs, E. Droste, M. Piepenbrink and G. Vollmer, C.
R. Acad. Sci., Paris Ser. IIc, 2000, 3, 205.
1
(a) M. T. Pope and A. M u¨ ller, Angew. Chem., Int. Ed. Engl., 1991, 30, 34;
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(
2
3
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This journal is c The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 9731--9733 9733