Polyoxovanadium(IV) sulfite compounds: Synthesis, structural, and physical studies

Article abstract of DOI:10.1002/anie.200390129

An unexplored family of polyoxometalates has evolved through the synthesis and structural characterization of vanadium(IV) sulfite heteropolyanions. The hexanuclear vanadium(IV) compound, which is ferromagnetic down to 2 K, exhibits a unique structural motif for such metal species, with a central cubic {M₄O₂(OH)₂} fragment and metal centers at two of the corners of the cluster (see figure).

Full text of DOI:10.1002/anie.200390129

Angewandte
Chemie
Vanadium Sulfite Polyoxometalates
Polyoxovanadium(iv) Sulfite Compounds:
Synthesis, Structural, and Physical Studies**
Manolis J. Manos, Haralampos N. Miras,
Vassilis Tangoulis, J. Derek Woollins,
Alexandra M. Z. Slawin,* and
Themistoklis A. Kabanos*
Dedicated to Professor Dieter Rehder
on the occasion of his 60th birthday
The current interest in polyoxometalate chemistry is repre-
sentative of the diverse nature of this family of inorganic
clusters, which exhibit a wide variety of compositions and
have considerable structural versatility,[1] as well as important
magnetic,[2] optical,[1] and catalytic properties.[1] Much atten-
tion has been paid to heteropolyanions that contain tetrahe-
dral phosphate groups.[3] While a number of research groups
have focussed on polyoxomolybdenum and vanadium phos-
phates, fewer studies have been carried out on polyoxoanions
that incorporate the pyramidal sulfite anion.[4,5] The sulfite
anion has C3v symmetry and contains a nonbonding, but
stereochemically active pair of electrons, and their metal
complexes may potentially display nonlinear optical (NLO)
properties,[6] which are observed in the metal-selenites[7] and
metal-iodates.[8] Herein, we report the isolation, X-ray crystal
structures, and some properties of the first vanadium sulfite
species (nBu4N)2[(VIVO)6(m4-O)2(m3-OH)2(m3-SO3)4(H2O)2]
(1), (NH4)2[(VIVO)6(m4-O)2(m3-OH)2(m3-SO3)4(H2O)2] (2),
and (NH4)[VIVO(SO3)1.5(H2O)]¥2.5H2O (3). Compounds 1
and 2 are polyoxovanadium(iv) sulfite heteropolyanions that
exhibit a unique structural motif with a central cubic
{VI4VO2(OH)2} fragment and two vanadium(iv) ions located
at two of the corners of the cluster. Compound 3 exhibits an
open-framework structure. Open-framework materials have
recently received great interest because of their applications
in shape-selective catalysis, separation science, and ion-
exchange.[9]
Figure 1. a) Ball-and-stick representation of 1a. Average bond lengths
(ä): V O 1.577(6), V-O (m3-OH ) 2.202(3), V-O (m4-O2À) 2.073(4), V-O
(m3-SO32À) 2.024(3), V-O(H2O) 2.052(2), S-O (m3-SO32À) 1.532(8),
V(1)¥¥¥V(1A) 2.933(1), V(2)¥¥¥V(2A) 3.185(2); b) Ball-and-stick represen-
tation of the hydrogen-bonded dimer formed between two adjacent 1a
anions.
À
¼
2 NH4VVO3 þ 4 ðNH4Þ2SO3
þ 4 H O MgO 2 NH ½ðVIVOÞðSO3Þ1:5ðH2Oފ Á 2:5 H2O 3
ƒƒ!
2
4
þ ðNH4Þ2SO4 þ 6 NH3
ð2Þ
In the latter reaction, absence of MgO results in the
isolation of 2. The role of MgO in the formation of 3 remains
as yet unknown. Our reason for adding MgO to the reaction
was to attempt to replace the V(3) and V(3A) atoms in 2 (see
Figure 1) with MgII ions, to modify the complicated magnetic
properties of compound 2.
X-ray structural analysis of 1[10] revealed the presence of
the [(VIVO)6(m4-O)2(m3-OH)2(m3-SO3)4(H2O)2]2À anion (1a;
Figure 1a) as well as two Bu4Nþ counterions. The core of
the hexanuclear anion 1a consists of a distorted cubane unit,
{VI4VO2(OH)2}, which is comprised of four, triply edge-sharing
The reaction of [VIVOCl2(thf)2] in an HCl solution (37%
HCl in water, 1:3v/v, approximately pH 1) with an aqueous
solution (approximately pH 9) containing Na2SO3 and
Bu4NBr (final pH value of the solution was approximately
2.5) resulted in the formation of compound 1 [Eq. (1)].
[*] Dr. T. A. Kabanos, M. J. Manos, H. N. Miras
Department of Chemistry
Section of Inorganic and Analytical Chemistry
University of Ioannina, 45110 Ioannina (Greece)
Fax: (þ30)651-0-98795
6 ½VIVOCl2ðthfÞ2Š þ 4 NaSO3 þ 2 Bu4NBr þ 6 H2O
! ðBu4NÞ2½ðVIVOÞ6O2ðOHÞ2ðSO3Þ4ðH2OÞ2Š þ 8 NaCl þ 4 HCl
þ 2 HBr þ 12 THF
ð1Þ
E-mail: tkampano@cc.uoi.gr
Dr. A. M. Z. Slawin, Prof. J. D. Woollins
Department of Chemistry, University of St.Andrews
St. Andrews, Fife KY16 9ST (UK)
Fax: (þ44)1334-463384
Compound 2 was isolated by replacing sodium sulfite and
tetra-n-butylammonium bromide in the above synthetic
procedure with ammonium sulfite. The synthesis of com-
pound 3 was achieved by treating NH4VVO3, in an HCl
solution (37% HCl in water, 1:4 v/v, approximately pH 1),
with (NH4)2SO3 in the presence of magnesium oxide (final
pH value was approximately 3) [Eq. (2)].
E-mail: jdw3@st-andrews.ac.uk
Dr. V. Tangoulis
Department of Science of Materials, University of Patra, 26504 Patra
(Greece)
[**] We thank the central laser facility of the University of Ioannina for
the NLO measurements.
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Communications
IV
¼
V O6 octahedra, each having an oxo group (V O 1.58 ä) in a
À
position trans to a long V O bond (2.36 ä); the four
equatorial V O bonds are similar in length, at approximately
À
2.02 ä. The two square-pyramidal O5 VIV units are coordi-
nated to the vanadium ions of the core through one m4-O2À
and two m3-SO32À bridges. The two m4-oxygen atoms O(4) and
O(4A) connect the network of six vanadium(iv) ions and
possess almost a trigonal pyramidal geometry. There are
moderate-to-strong hydrogen bonds between the two hydro-
gen atoms of O(12)[11a] and the sulfite oxygen atoms O(7’) and
O(9’), along with the symmetry-related interactions between
the hydrogen atoms of O(12’) and the sulfite oxygen atoms
O(7) and O(9) (Table 1). These combine to form a hydrogen-
bonded dimer of two adjacent anions about a center of
symmetry (Figure 1b). There is further bonding between the
hydrogen atoms of O(12A) and O(7’’)/O(9’’) and, by symme-
try, the hydrogen atoms of O(12’A) with O(7’’’)/O(9’’’), etc.,
which links the dimeric units in 1D chains along the a axis. In
addition, the hydroxylic hydrogen atoms H(O(5)) and
H(O(5A)) form weak hydrogen bonds with the sulfite oxygen
atoms O(6) and O(6A), respectively (Table 1). Although the
{M4(m4-O)2(m3-OH)2} cubane core has been reported in the
literature,[12] the connection of the {VI4V(m4-O)2(m3-OH)2} unit
with two other metals through the oxygen atoms of the core
represents a novel motif, not only for vanadium species, but
for any metal. In addition, there are no known examples
where the {M4O4} cubane core is connected to two other
metals.
Figure 2. Structural buildingunit of 3 and the atomic numbering
scheme. Selected interatomic distances (ä): V(1)-O(1) 1.580(7), V(1)-
O(5) 1.984(6), V(1)-O(4A) 2.024(5), V(1)-O(2) 2.029(6), V(1)-O(3A)
2.057(5), V(1)-O(7) 2.280(7), S(1)-O(4) 1.548(6), S(1)-O(3) 1.548(6),
S(1)-O(2) 1.551(7), S(2)-O(6) 1.506(11), S(2)-O(5) 1.549(6).
our knowledge, the preparation of 3 represents the first
example of the isolation of an open-framework compound
under mild conditions.
The temperature dependence of the susceptibility data for
compound 1 is shown in Figure 3in the form of cT versus T,
where an overall ferromagnetic behavior is revealed. The cT
value of 2.24 cm3 molÀ1 K at room temperature is higher than
the value expected for six uncorrelated S ¼ 1/2 spins, and
increases with decreasing temperature to a maximum value of
3.1 cm3 molÀ1 K at 2 K.
The structure of 2[10] is similar to that of 1. However, 2
crystallizes in the noncentrosymmetric space group P21, while
1 crystallizes in the centrosymmetric I2/a space group. This
demonstrates the crucial role of the counterion concerning
the formation of noncentrosymmetric structures.[8a] The NLO
properties of compound 2 were studied in aqueous solution
using 1 cm- and 1 mm-thick glass cells. Under laser irradiation
at 590 nm, with a 5 ns pulse duration, the NLO properties of 2
were found to be limited; experiments using lasers in the
picosecond time domain are underway. Compound 3 crystal-
lizes in the orthorhombic space group Pbcm[10] and exhibits a
two-dimensional open-framework structure. The crystallo-
graphically unique vanadium ion of 3 resides in a distorted
octahedron comprised of four equatorial sulfite oxygen
atoms, as well as an oxygen atom from a water molecule
and an oxo group, which occupy the axial positions (Figure 2).
The 2D structure of 3 can be described as a layered net of
isolated VO6 octahedra, each sharing four corners with four
adjacent SO3 trigonal pyramids. The connectivity between the
VO6 octahedra and the SO3 pyramids creates eight- and four-
ring ™windows∫. Each eight-ring results from four VO6
Figure 3. Temperature dependence of magnetic susceptibility given by
measurements of cMT at 0.1 T over a temperature range of 2 300 K
2À
octahedra linked by four SO3 pyramids. In contrast, the
four-rings are formed from two VO6 octahedra that are
connected through two SO3 pyramidal units. To the best of
Experimental Section
1: An aqueous solution (approximately 10 mL, pH 9) containing
Na2SO3 (1.5 g, 12.0 mmol) and Bu4NBr (7.5 g, 24.0 mmol) was added
in one portion to a stirred solution of [VIVOCl2(thf)2][12] (1.5 g,
5.5 mmol) in an HCl solution (37% HCl in water, 1:4 v/v, 15 ml,
pH ~ 1). Upon addition of Na2SO3 and Bu4NBr the light-blue color of
the solution immediately changed to dark blue and the pH value of
the solution changed to approximately 2.5. Blue-green orthogonal
Table 1: Hydrogen bonds for 1.
À
À
D H¥¥¥A
d(D H)
d(H¥¥¥A)
d(D¥¥¥A)
a (DHA)
À
O12 H(12D)¥¥¥O7’
0.976(5)
0.976(5)
0.976(5)
1.794(15)
1.916(16)
2.33(4)
2.702(3)
2.825(3)
2.675(2)
153(3)
154(3)
100(2)
À
O12 H(12E)¥¥¥O9’
À
O5 H¥¥¥O6
426
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Angew. Chem. Int. Ed. 2003, 42, No. 4

Angewandte
Chemie
crystals of 1 were isolated from the resulting solution after one day.
Sect. C 1999, 55, 1980; d) P. S. Halasyamani, D. O©Hare, Chem.
À
Yield: 0.48 g (40% based on V). IR: n˜ ¼ 2964 [n(CBut H)], 1000, 1021,
Mater. 1998, 10, 646, and references therein; e) W. T. A. Harri-
son, L. L. Dussack, A. J. Jacobson, J. Solid State Chem. 1996, 125,
234.
987, 953[ n(V O)], 823, 636, 508 cm [n(SO32À)]; UV/Vis (H2O):
À1
¼
l/nm (e/dm3 molÀ1 cmÀ1) ¼ 238(sh, 14258) 862 (547); TGA: percent-
age weight loss (temperature (8C)) ¼ 6.8 (187, assigned to H2O), 36.5
(208, assigned to CxHy and NH3), 3.6 (306, assigned to SOx); elemental
analysis calcd (%) for C32H78N2O24S4V6 (1308.83): C 29.37, H 6.00, N
2.14, S 9.80, V 23.35; found: C 29.68, H 6.04, N 2.17, S 9.63, V 23.50.
2: Compound 2 was prepared in 60% yield in a similar fashion to
[8] a) R. E. Sykora, K. M. Ok, P. S. Halasyamani, T. E. Albrecht-
Schmitt, J. Am. Chem. Soc. 2002, 124, 1951; b) A. C. Bean, S. M.
Pepper, T. E. Albrecht-Schmitt, Chem. Mater. 2001, 13, 1266;
c) A. C. Bean, C. F. Campana, O. Kwon, T. E. Albrecht-Schmitt,
J. Am. Chem. Soc. 2001, 123, 8806; d) R. E. Sykora, D. M. Wells,
T. E. Albrecht-Schmitt, Inorg. Chem. 2002, 41, 2697.
[9] A. K. Cheetham, G. Fÿrey, T. Loiseau, Angew. Chem. 1999, 111,
3466, Angew. Chem. Int. Ed. 1999, 38, 3268, and references
therein.
1, except that (NH4)2SO3 was used instead of Na2SO3 and Bu4NBr.
À1
¼
IR: n˜ ¼ 3239 [n(N-H)], 1019, 989, 953[ n(V O)], 895, 644, 492 cm
[n(SO32À)]; UV/Vis (H2O): l/nm (e/dm3 molÀ1 cmÀ1) ¼ 380 (1757), 266
(9034), 889 (580); TGA: percentage weight loss (temperature (8C)):
6.2 (170, assigned to H2O), 3.9 (352, assigned to NH3), 24.1 (501,
assigned to SOx); elemental analysis calcd (%) for H14N2O24S4V6
(860.01): H 1.64, N 3.26, S 14.92, V 35.54; found: H 1.75, N 3.10, S
15.10, V 35.85.
[10] Crystal data for 1: C32H78N2O24S4V6, Mw ¼ 1308.83, monoclinic,
space group I2/a, a ¼ 20.48910(10), b ¼ 16.6679(4), c ¼
18.0218(3) ä, b ¼ 111.3460(10)8, V¼ 5732.42(17) ä3, Z ¼ 4,
1calc ¼ 1.517 MgmÀ3
,
T¼ 293(2) K; R1(final) ¼ 0.0274, wR2 ¼
3: Solid MgO (7.0 g, 174 mmol) was added in one portion to a
stirred solution of NH4VO3 (1.5 g, 12.8 mmol) in diluted HCl (37%
HCl in water, 1:4 v/v, 20 mL, pH ~ 1.5). Upon addition of MgO, the
yellow color of the solution did not change. Solid (NH4)2SO3 (1.5 g,
15.3mmol) was then added to the solution, the color of which
immediately turned blue, and the pH value changed to approximately
3.0. Blue hexagonal crystals of 3 were precipitated from the solution
0.0693. Crystal data for 2: H14N2O24S4V6, MW ¼ 860.01, mono-
clinic, space group P21, a ¼ 7.596(3), b ¼ 20.033(9), c ¼
7.624(3) ä, b ¼ 91.157(8)8, V¼ 1159.9(9) ä3, Z ¼ 2, 1calc
¼
2.463Mgm À3, T¼ 293(2) K; R1(final) ¼ 0.1226, wR2 ¼ 0.3021.
The structure of 2 was determined using different crystals under
a variety of conditions (including two determinations at 125 K);
the reported data are the best that were obtained. Crystal data
for 3: H11NO9S1.5V, M ¼ 268.13, orthorhombic, space group
Pbcm, a ¼ 7.0680(17), b ¼ 12.536(3), c ¼ 19.968(5), V¼
1769.2(7) ä3, Z ¼ 8, 1calc ¼ 2.013Mgm À3, T¼ 293(2) K. R1(fi-
nal) ¼ 0.0586, wR2 ¼ 0.1140. CCDC-179446 (1) contains the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB21EZ, UK; fax:
(þ 44)1223-336-033; or deposit@ccdc.cam.ac.uk). Further de-
tails on the crystal structure investigations for 2 and 3 may be
obtained from the Fachinformationszentrum Karlsruhe, 76344
Eggenstein-Leopoldshafen, Germany (fax: (þ 49)7247-808-666;
e-mail: crysdata@fiz-karlsruhe.de), on quoting the depository
numbers CSD-412712 and -412713.
after 2 days. Yield: 2.06 g (60% based on V). IR: n˜ ¼ 3262 [n(NH4þ)],
1019, 987, 953[ n(V O)], 904 cm [n(SO32À)]; UV/Vis (H2O): l/nm
À1
¼
(e/dm3 molÀ1 cmÀ1) ¼ 896 (2230), 235(sh, 6750); TGA: percentage
weight loss (temperature (8C)): 26.8 (270, assigned to H2O), 6.3(361,
assigned to NH3) 35.8 (519.9, assigned to SO2); elemental analysis
calcd (%) for H11NO9S1.5V (268.13): H 4.13, N 5.22, S 17.94, V 19.00;
found: H 4.20, N 5.10, S 18.05, V 18.80.
Received: August 19, 2002
Revised: October 29, 2002 [Z50002]
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