Oligomeric arylstibonates

Article abstract of DOI:10.1246/bcsj.20140160

Three oligomeric arylstibonates [H₅(p-ClC₆H₄Sb)₁₆O₃₆]^3-, [H₄(p-ClC₆H₄Sb)₁₆O₃₆]^4-, and [Na₂(p-ClC₆H

Full text of DOI:10.1246/bcsj.20140160

Oligomeric Arylstibonates#
Zun-qi Liu,1 Yoshiki Ozawa,*2 and Atsushi Yagasaki*1
1Department of Chemistry, Kwansei Gakuin University, Sanda, Hyogo 669-1337
2Department of Material Science, University of Hyogo, Harima Science Garden City, Hyogo 678-1297
E-mail: yagasaki@kwansei.ac.jp
Received: June 4, 2014; Accepted: July 28, 2014; Web Released: August 4, 2014
Three oligomeric arylstibonates [H5(p-ClC6H4Sb)16O36]3¹, [H4(p-ClC6H4Sb)16O36]4¹, and [Na2(p-ClC6H4Sb)12O24-
(OH)6(H2O)3]4¹ have been synthesized as tetra-n-butylammonium salts and structurally characterized. The Sb16C16O36
core of the [H5(p-ClC6H4Sb)16O36]3¹ and [H4(p-ClC6H4Sb)16O36]4¹ anions is made up from arrays of close-packed O and
C atoms and Sb atoms that occupy the octahedral interstices between the close-packed layers. The layers of close-packed
O and C atoms are stacked in a sequence ABACA, resulting in an hch packing. The [Na2(p-ClC6H4Sb)12O24(OH)6-
(H2O)3]4¹ anion has an “opened-up” δ-Keggin structure.
A while back, we reported the synthesis and structure of
octaantimonate [Sb8O12(OH)20]4¹, a molecular oxide of anti-
mony.1 It was anticipated back then that the isolation and struc-
tural characterization of [Sb8O12(OH)20]4¹ as a tetra-n-butyl-
ammonium (TBA) salt soluble in nonaqueous solvents would
open up a gateway to the unexplored chemistry of the molecular
oxide of antimony. Unfortunately, however, this anticipation
is yet to be materialized. A silyl derivative of tetraantimonate
was reported in 2001,2 but that is about the only fruit that the
isolation of [Sb8O12(OH)20]4¹ has brought forth so far.
without further purification: activated charcoal (Taihei), P2O5,
SbCl3, CuBr, NaNO2, pyridine, ethanol, and concentrated sul-
furic acid (Kishida), p-chloroaniline, Na2CO3, concentrated
hydrochloric acid, and aqueous 10% (0.41 M) TBAOH (Wako).
Molecular sieves (Kishida) were activated at 300 °C before use.
Et2O (Wako) was dried over 4 ¡ molecular sieves and CH3CN
(Kishida) and CD3CN (ISOTEC) over 3 ¡ molecular sieves
before use.
Analytical Procedures. Elemental analysis was performed
by Toray Research Center Inc., Shiga, Japan. IR spectra were
recorded from mineral oil (Nujol) mulls between KBr plates on
a Shimadzu FTIR-8400 spectrometer. Absorptions are describ-
ed as follows: very strong (vs), strong (s), medium (m), weak
(w), and shoulder (sh). 1H NMR spectra were recorded at
299.963 MHz and referenced internally against TMS.
Preparation of p-Chlorophenylstibonic Acid. This com-
pound was prepared by slightly modifying the procedures
described by Doak and Steinman.5 To a solution of p-chloro-
aniline (6.38 g, 50.0 mmol) in 125 mL of ethanol cooled in
an ice-bath was added 2.75 mL (51.6 mmol) of concentrated
sulfuric acid with stirring. The colorless suspension that formed
was stirred for 15 min, after which period 11.4 g (50.0 mmol) of
SbCl3 was added to the suspension. The mixture was stirred for
another 10 min and then a solution of NaNO2 (3.50 g, 50.7
mmol, in 5.0 mL of H2O) was added to this mixture dropwise
over 10 min. The resulting thick suspension was stirred for
30 min before 1.00 g of CuBr (6.97 mmol) was added. After the
mixture was stirred for 24 h at ambient temperature, 125 mL of
H2O was added to the mixture. It was then refluxed for 3 h
and allowed to cool to ambient temperature. The precipitate
was collected by filtration, washed with 3 © 20 mL of H2O,
and dried under vacuum over P2O5 for 12 h to yield 14.6 g
(45.7 mmol, 91.4% on Sb) of crude product. The crude product
was then dissolved in 700 mL of 1:1 mixture of ethanol and
concentrated hydrochloric acid. The pyridine reagent (25 mL),
which was prepared by diluting 20 mL of concentrated hydro-
chloric acid with 5 mL of pyridine, was added to this brown
The biggest obstacle in pursuing the chemistry of molecular
oxide of antimony is the lack of a probe that enables us to
monitor the reaction in solution. NMR is by far the most
powerful tool when it comes to monitoring the reaction in
solution, and both 121Sb and 123Sb are NMR-active nuclei.
However, their large quadrupolar moments render Sb NMR
virtually useless in synthetic investigations.3 This is in marked
contrast to the case for the molecular oxide of vanadium, whose
chemistry has made great progress during the last score of years
as 51V NMR became easily accessible.4 In order to extricate
ourselves from the stagnant research of the molecular oxide
chemistry of antimony, we turned our eyes to arylstibonate. The
preparation of arylstibonate is relatively straightforward and
1
its reaction can readily be followed by H NMR.5 Once we
establish the synthesis of a certain polyarylstibonate, we would
then be able to apply the knowledge acquired there to the
inorganic antimonate to further develop the chemistry of the
molecular oxide of antimony. Recent reports of Baskar et al.6,7
and Nicholson et al.8,9 on the formation of oligomeric aryl-
stibonates suggest this strategy would work. During our effort
to prepare a TBA salt of p-chlorophenylstibonate, i.e., TBA-
[(p-ClC6H4)Sb(OH)5], we obtained three different oligomeric
arylstibonates. Here we report their syntheses and structures.
Experimental
Reagents, Solvents, and General Procedures.
The
followings were purchased from commercial sources and used
Bull. Chem. Soc. Jpn. 2014, 87, 1245–1251 | doi:10.1246/bcsj.20140160
© 2014 The Chemical Society of Japan | 1245

solution with stirring to precipitate the pyridinium salt of
[p-ClC6H4SbCl5] . The precipitate was collected by filtration,
of H2O. The mixture was allowed to stand for 3 days at ambient
temperature. Somewhat hygroscopic crystals that formed were
collected by filtration and dried under vacuum to yield 0.052 g
of the product (0.012 mmol, 26%).10 Anal. Calcd for TBA4-
[H6Na2(p-ClC6H4Sb)12O33(OH2)3]¢7H2O (C136Cl12H218N4Na2-
O40Sb12): C, 36.45; Cl, 9.49; H, 4.90, N, 1.25; Sb, 32.6%.
Found: C, 36.25; Cl, 9.19; H, 4.78, N, 1.22; Sb, 32.6%. IR
(Nujol mull, 1100-400 cm¹1): 1088 (m), 1067 (m), 1014 (m),
881 (w), 813 (m), 723 (vs), 700 (m), 653 (m), 633 (m), 618 (m),
601 (s), 528 (m), 526 (m), 500 (s), 489 (m), 462 (m), 438 (w).
1H NMR (CD3CN): ¤ 0.87 (t, CH3CH2CH2CH2N, 48H), 1.25
(m, CH3CH2CH2CH2N, 32H), 1.34 (m, CH3CH2CH2CH2N,
32H), 2.86 (m, CH3CH2CH2CH2N, 32H), 6.46 (s, SbOH, 6H),
6.93 (d, ClC6H4, 12H), 7.05 (d, ClC6H4, 6H), 7.23 (d, ClC6H4,
6H), 7.68 (d, ClC6H4, 12H), 7.96 (d, ClC6H4, 6H), 8.23 (d,
ClC6H4, 6H). Single-crystals used for X-ray structural analysis
were prepared in the same manner except that the final drying
process was omitted.
Crystal Structure Determinations. Single-crystal diffrac-
tion data for TBA3[H5(p-ClC6H4Sb)16O36]¢5CH3CN, TBA2-
[H4(p-ClC6H4Sb)16O36(H3O)2]¢6H2O¢CH3CN, and TBA4-
[Na2(p-ClC6H4Sb)12O24(OH)6(H2O)3]¢3H2O¢4.5CH3CN were
measured on a Rigaku R-AXIS RAPID diffractometer using
Mo Kα radiation. The structures were solved by direct method
and refined by full-matrix least squares using the SHELX-2013
program suite.11 Crystallographic parameters are summarized
in Table 1. Selected interatomic distances in TBA3[H5(p-
¹
washed with 3 © 10 mL of concentrated hydrochloric acid, and
dried under open air for 48 h to yield 22.5 g (45.9 mmol, 100%)
of yellow pyridinium salt. The pyridinium salt was then redis-
solved in 1.80 L of aqueous 1% Na2CO3 solution. Activated
charcoal (1.0 g) was added to this yellow cloudy solution and
the mixture was stirred for 2 h. The activated charcoal was
removed by filtration and 575 mL of 1.0 M hydrochloric acid
was added dropwise with stirring to the colorless clear filtrate
to yield white precipitate. The precipitate was collected by
filtration, washed with 3 © 20 mL of H2O, and dried under
vacuum over P2O5 for 12 h to yield 10.5 g (32.9 mmol, 65.8%)
of p-chlorophenylstibonic acid.
Synthesis of TBA3[H5(p-ClC6H4Sb)16O36].
p-Chloro-
stibonic acid (2.3 g, 7.2 mmol) was mixed with 6.5 mL of
aqueous 10% TBAOH (2.7 mmol) and stirred for 43 h in a
poly(ethylene terephthalate) vial. The solid left undissolved
was then collected by filtration and dried under vacuum over
P2O5 for 6 h to yield 2.6 g of crude product. The solution of
0.20 g of this product in 2.0 mL of CH3CN was refluxed for
80 h. The solution was allowed to cool to ambient temperature,
and the microcrystals that precipitated were collected by filtra-
tion. These microcrystals, which weighed 0.12 g after drying
under vacuum over P2O5 for 30 min, was dissolved in 2.0 mL
of CH3CN by briefly heating the mixture. The solution was
allowed to stand at ambient temperature for 3 days, and the
block-shaped crystals that formed were collected by filtration,
dried under vacuum to yield 0.093 g (0.018 mmol, 53%) of the
compound. IR (Nujol mull, 1100-400 cm¹1): 1088 (m), 1069
(m), 1015 (m), 957 (w), 887 (w), 816 (s), 792 (m), 765 (m),
726 (vs), 666 (vs), 623 (m), 604 (m), 554 (w), 506 (s), 490 (s),
446 (m). 1H NMR (CD3CN): ¤ 0.92 (t, CH3CH2CH2CH2N,
36H), 1.28 (m, CH3CH2CH2CH2N, 24H), 1.46 (m, CH3CH2-
CH2CH2N, 24H), 2.96 (m, CH3CH2CH2CH2N, 24H), 6.7-8.4
(m, ClC6H4, 64H), 8.05 (br, SbOH, 1H), 8.65 (s, SbOH, 2H),
9.04 (s, SbOH, 2H). Single-crystals used for X-ray structural
analysis were prepared in the same manner except that the final
drying process was omitted.
ClC6H4Sb)16O36]¢5CH3CN,
TBA2[H4(p-ClC6H4Sb)16O36-
(H3O)2]¢6H2O¢CH3CN, and TBA4[Na2(p-ClC6H4Sb)12O24-
(OH)6(H2O)3]¢3H2O¢4.5CH3CN are listed in Tables 2, 3,
and 4. The structures of [H5(p-ClC6H4Sb)16O36]3¹, [H4(p-
ClC6H4Sb)16O36(H3O)2]2¹, and [Na2(p-ClC6H4Sb)12O24(OH)6-
(H2O)3]4¹ anions are shown in Figures 1, 2, and 3. Crystallo-
graphic data have been deposited with Cambridge Crystallo-
graphic Data Centre: Deposition numbers CCDC-987797-
987799. Copies of the 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, U.K.; Fax: +44 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk).
Synthesis of TBA2[H4(p-ClC6H4Sb)16O36(H3O)2].
p-
Chlorostibonic acid (2.3 g, 7.2 mmol) was mixed with 6.5 mL
of aqueous 10% TBAOH (2.7 mmol) and stirred for 43 h in a
poly(ethylene terephthalate) vial. The solid left undissolved
was then collected by filtration and dried under vacuum over
P2O5 for 6 h to yield 2.6 g of crude product. To the solution of
this product (0.20 g in 2.0 mL of CH3CN) was added 0.10 mL
of H2O. The mixture was allowed to stand at ambient tem-
perature for 1 month. Block-shaped crystals that formed were
collected by filtration and dried under vacuum to yield 0.016 g
(0.0033 mmol, 9.6%) of the product. Single-crystals used for
X-ray structural analysis were prepared in the same manner
except that the final drying process was omitted.
Synthesis of TBA4[Na2(p-ClC6H4Sb)12O24(OH)6(H2O)3].
p-Chlorostibonic acid (2.3 g, 7.2 mmol) was mixed with 6.5 mL
of aqueous 10% TBAOH (2.5 mmol) and stirred for 43 h in a
poly(ethylene terephthalate) vial. The solid left undissolved
was then collected by filtration and dried under vacuum over
P2O5 for 6 h to yield 2.6 g of crude product. To the solution of
this product (0.20 g) in 2.0 mL of CH3CN was added 0.10 mL
Results and Discussion
The TBA salt of [H5(p-ClC6H4Sb)16O36]3¹ was obtained in a
moderate yield by reacting p-chlorophenylstibonic acid with
aqueous TBAOH, dissolving the solid thus obtained in CH3CN,
and refluxing the solution for almost 4 days. X-ray structural
analysis revealed that the single crystals of TBA3[H5(p-
ClC6H4Sb)16O36]¢5CH3CN are composed of TBA cations,
CH3CN molecules of crystallization, and discrete [H5(p-
ClC6H4Sb)16O36]3¹ anions shown in Figure 1. The antimony-
oxygen framework of the [H5(p-ClC6H4Sb)16O36]3¹ anion is the
same as that of [H2(p-XC6H4Sb)16O36]6¹ (X = H, Cl, and Br)
anion reported by Baskar and co-workers.6,7 The structure is
composed of four (ArSb)3O10 units (Ar = aryl group) reminis-
cent of the M3O13 group frequently encountered in polymolyb-
dates and -tungstates12 and two (ArSb)2O8 units. The four
(ArSb)3O10 units form a ring sharing four vertices. Each
(ArSb)2O8 unit caps this ring from front and back sharing edges
with two diagonal (ArSb)3O10 units and vertices with the other
1246 | Bull. Chem. Soc. Jpn. 2014, 87, 1245–1251 | doi:10.1246/bcsj.20140160
© 2014 The Chemical Society of Japan

Table 1. Crystallographic Data for TBA3[H5(p-ClC6H4Sb)16O36]¢5CH3CN (1), TBA2[H6(p-ClC6H4Sb)16O36(H3O)2]¢
6H2O¢CH3CN (2), and TBA4[Na2(p-ClC6H4Sb)12O24(OH)6(H2O)3]¢3H2O¢4.5CH3CN (3)
1
2
3
Empirical formula
C154H192Cl16N8O36Sb16
C130H161Cl16N3O44Sb16
C145H223.5Cl12N8.5Na2O36Sb12
fw
5246.34
C2/c
37.8176(12)
17.7720(5)
32.5851(11)
90
121.763(1)
90
18620(1)
4
4984.81
4594.19
P21/n
22.5182(6)
31.8969(11)
28.2014(9)
90
103.381(1)
90
19706(1)
4
ꢀ
P1
Space group
a/¡
b/¡
16.2147(8)
18.5629(10)
18.5929(11)
59.768(1)
83.106(1)
86.357(1)
4800.2(5)
1
c/¡
¡/degree
¢/degree
γ/degree
V/¡3
Z
T/K
-/¡
150(2)
0.71073
1.871
150(2)
0.71073
1.724
150(2)
0.71073
1.549
¹3
μcalcd/g cm
¹1
®/mm
2.578
2.497
1.846
R [Fo2 > 2·(Fo )]a)
0.0869
0.1989c)
2
0.0929
0.0935
0.2761e)
2
2
Rw [all data]b)
0.2540d)
2
2 2
a) R = -««Fo« ¹ «Fc««/-«Fo«. b) Rw = [-w(Fo ¹ Fc ) /-w(Fo )]1/2 where w = 1/[·2(Fo ) + (aP)2 + bP] and P =
(Fo2 + 2Fc )/3. c) a = 0.0610, b = 276.1790. d) a = 0.1069, b = 0. e) a = 0.1189, b = 144.7196.
2
Table 2. Selected Distances in TBA3[H5(p-ClC6H4Sb)16-
O36]¢5CH3CNa)
Table 3. Selected Distances in TBA2[H6(p-ClC6H4Sb)16-
O36(H3O)2]¢6H2O¢CH3CNa)
Sb1-O1
Sb1-O2
Sb1-O4
Sb1-O6
Sb1-O7
Sb2-O1
Sb2-O2
Sb2-O3
Sb2-O8
Sb2-O9
Sb3-O1
Sb3-O3
Sb3-O4
Sb3-O10
Sb3-O11
Sb4-O5
Sb4-O7
Sb4-O12
Sb4-O13¤
Sb4-O14¤
2.059(7)
1.973(8)
1.972(7)
2.061(7)
2.032(7)
2.098(7)
1.964(8)
1.953(7)
1.961(7)
2.096(8)
2.114(7)
1.977(7)
1.970(7)
2.144(7)
1.935(8)
1.969(8)
2.047(7)
1.976(7)
1.947(7)
2.132(7)
Sb5-O5
Sb5-O6
Sb5-O14¤
Sb5-O15¤
Sb5-O16¤
Sb6-O8
1.957(7)
2.069(7)
2.104(7)
1.967(7)
1.938(7)
1.987(8)
2.120(7)
1.920(8)
1.952(6)
2.128(7)
2.121(8)
1.968(8)
1.929(7)
1.951(7)
2.133(7)
2.092(8)
2.072(7)
1.975(7)
2.056(7)
1.983(8)
Sb1-O1
Sb1-O2
Sb1-O4
Sb1-O10
Sb1-O13
Sb2-O1
Sb2-O2
Sb2-O3
Sb2-O12
Sb2-O18
Sb3-O1
Sb3-O3
Sb3-O4
Sb3-O9
Sb3-O16
Sb4-O9
Sb4-O10
Sb4-O11
Sb4-O15
Sb4-O17¤
Sb5-O5
Sb5-O6
2.053(7)
1.974(7)
1.989(7)
2.081(7)
2.088(8)
2.109(7)
1.977(7)
1.989(7)
1.963(7)
1.977(8)
2.120(8)
1.953(7)
1.955(7)
1.944(7)
2.077(7)
1.931(7)
2.095(7)
1.960(8)
1.979(7)
2.146(7)
2.097(7)
1.939(7)
Sb5-O7
1.989(8)
2.131(7)
1.971(8)
2.118(7)
1.951(8)
1.968(8)
2.115(8)
1.954(7)
1.920(7)
2.111(7)
1.986(7)
1.968(7)
2.095(7)
2.060(7)
1.982(7)
2.001(8)
2.088(7)
1.949(7)
2.37(2)
Sb5-O10
Sb5-O11
Sb6-O5
Sb6-O6
Sb6-O8
Sb6-O13
Sb6-O14
Sb7-O12
Sb7-O13
Sb7-O14
Sb7-O15¤
Sb7-O17
Sb8-O5
Sb6-O9
Sb6-O13
Sb6-O17¤
Sb6-O18¤
Sb7-O10
Sb7-O11
Sb7-O16
Sb7-O17
Sb7-O18
Sb8-O9
Sb8-O10
Sb8-O12¤
Sb8-O14
Sb8-O15
Sb8-O7
Sb8-O8
Sb8-O16¤
Sb8-O18¤
O21£O11
O21£O12¤
O21£O18¤
2.57(2)
2.64(2)
a) Atoms labeled with a prime are related to those without it
by the crystallographic inversion center at (1/4, 3/4, 0). See
also Figure 1.
a) Atoms labeled with a prime are related to those without it
by the crystallographic inversion center at (0, 0, 0). See also
Figure 2.
two (See also the figure in the Graphical Abstract.). Crystallo-
graphically, the anion only has a center of symmetry. However,
it closely approximates the ideal 2/m symmetry if all C, H,
and Cl atoms except those directly bonded to the Sb atoms
are disregarded. The entire Sb16C16O36 structure is made up
of arrays of close-packed O and C atoms and Sb atoms that
occupy the octahedral interstices between the close-packed
layers. The layers of close-packed O and C atoms are stacked in
a sequence ABACA, resulting in an hch packing. The mixing of
hexagonal and cubic close-packing has also been observed for
the [(IMo7O26)2]6¹ 13 and Keggin structures.14
Charge neutrality requires the [H5(p-ClC6H4Sb)16O36]3¹
anion to be penta-protonated, as the formula suggests. Where
are these protons? Unfortunately, the protons could not be
located directly from the X-ray diffraction data in the current
study. However, their locations can reasonably be inferred from
Bull. Chem. Soc. Jpn. 2014, 87, 1245–1251 | doi:10.1246/bcsj.20140160
© 2014 The Chemical Society of Japan | 1247

Table 4. Selected Distances in TBA4[Na2(p-ClC6H4Sb)12O24(OH)6(H2O)3]¢3H2O¢4.5CH3CNa)
Sb1-O1
Sb1-O4
Sb1-O7
Sb1-O13
Sb1-O16
Sb2-O1
Sb2-O7
Sb2-O8
Sb2-O19
Sb2-O24
Sb3-O1
Sb3-O4
Sb3-O8
Sb3-O14
Sb3-O17
Sb4-O2
Sb4-O5
Sb4-O9
Sb4-O14
Sb4-O17
Sb5-O2
Sb5-O9
Sb5-O10
Sb5-O20
Sb5-O21
2.066(6)
1.996(6)
1.974(6)
1.965(6)
2.080(6)
2.115(6)
2.012(7)
2.001(6)
1.933(7)
1.938(6)
2.087(6)
1.965(7)
1.990(6)
1.966(6)
2.064(7)
2.069(6)
1.988(6)
1.971(7)
1.968(7)
2.082(6)
2.119(7)
2.027(6)
2.004(7)
1.936(6)
1.953(6)
Sb6-O2
Sb6-O5
Sb6-O10
Sb6-O15
Sb6-O18
Sb7-O3
2.079(6)
1.970(6)
1.976(7)
1.956(7)
2.057(7)
2.063(6)
1.973(7)
1.968(6)
1.980(6)
2.084(7)
2.133(6)
2.017(6)
1.995(8)
1.966(7)
1.952(7)
2.080(7)
1.977(6)
1.991(6)
1.967(6)
2.068(6)
2.131(7)
1.977(6)
1.977(6)
1.985(6)
1.988(7)
Sb11-O18
Sb11-O21
Sb11-O22
Sb11-O27
Sb11-O28
Sb12-O16
Sb12-O23
Sb12-O24
Sb12-O29
Sb12-O30
Na1-O13
Na1-O14
Na1-O15
Na1-O31
Na1-O32
Na1-O33
Na2-O1
2.140(7)
1.961(7)
1.953(7)
1.983(7)
1.984(7)
2.132(7)
1.970(6)
1.964(7)
1.982(7)
1.975(7)
2.393(7)
2.389(8)
2.388(7)
2.560(9)
2.542(9)
2.579(10)
2.476(7)
2.482(7)
2.479(8)
2.815(7)
2.857(8)
2.825(8)
2.849(7)
2.788(8)
2.833(7)
Sb7-O6
Sb7-O11
Sb7-O15
Sb7-O18
Sb8-O3
Sb8-O11
Sb8-O12
Sb8-O22
Sb8-O23
Sb9-O3
Sb9-O6
Sb9-O12
Sb9-O13
Sb9-O16
Sb10-O17
Sb10-O19
Sb10-O20
Sb10-O25
Sb10-O26
Na2-O2
Na2-O3
Na2-O19
Na2-O20
Na2-O21
Na2-O22
Na2-O23
Na2-O24
a) See also Figure 3.
Figure 1. Structure of the [H5(p-ClC6H4Sb)16O36]3¹ anion.
Atoms of the aryl groups other than the ipso carbons are
omitted for clarity. Ellipsoids are drawn to encompass 50%
probability levels. Atoms labeled with a prime are related
to those without it by the crystallographic inversion center
at (1/4, 3/4, 0).
Figure 2. Structure of the [H4(p-ClC6H4Sb)16O36(H3O)2]2¹
anion. Atoms of the aryl groups other than the ipso carbons
are omitted for clarity. Ellipsoids are drawn to encompass
50% probability levels. Atoms labeled with a prime are
related to those without it by the crystallographic inversion
center at (0, 0, 0). O21 and O21¤ are the oxygen atoms of
hydronium cations. See text in the Results and Discussion.
a comparison of bond lengths and bond valence sums.15,16 The
Sb-O bonds involving O18 is anomalously long for a doubly
bridging oxygen. In addition, the bond valence sum for O18
is 1.2 and significantly smaller than the ideal value of 2. These
facts suggest that the two O18 atoms in the structure are
protonated. These oxygens are the only doubly bridging O
atoms in the structure that are trans to the aryl groups. All the
other oxygens trans to the aryl groups are triply bridging. The
bond valence sums for O6 and O7 are also low; 1.4 for O6 and
1.5 for O7. There are two O6’s and O7’s in the structure. It is
highly likely that the remaining three protons are attached to
three of those four oxygens.
A different compound was obtained when the solid obtained
by reacting p-chlorophenylstibonic acid with aqueous TBAOH
was dissolved in wet CH3CN that contains ca. 5% water and
allowed to stand at ambient temperature for one month. X-ray
1248 | Bull. Chem. Soc. Jpn. 2014, 87, 1245–1251 | doi:10.1246/bcsj.20140160
© 2014 The Chemical Society of Japan

Table 5. The 2/m-Averaged Bond Lengths (¡) of [H5(p-
ClC6H4Sb)16O36]3¹ (a), [H4(p-ClC6H4Sb)16O36]4¹ (b),
[H2(C6H5Sb)16O36]6¹ (c), [H2(p-ClC6H4Sb)16O36]6¹ (d),
and [H2(p-BrC6H4Sb)16O36]6¹ (e)a),b)
a
b
c
d
e
Sb1A-OA1
Sb1A-OB
Sb1A-OC11
Sb1B-OA1
Sb1B-OC11
Sb1B-OC12
Sb1B-OD1
Sb1B-OE
Sb2A-OA2
Sb2A-OC21
Sb2A-OE
Sb2B-OA2
Sb2B-OB
Sb2B-OC21
Sb2B-OC22
Sb2B-OD2
Sb3-OB
2.06
2.08
1.98
2.12
1.97
1.97
1.95
2.06
2.06
1.97
2.05
2.11
2.12
1.97
1.97
1.95
2.12
1.93
1.98
1.95
2.13
2.05
2.09
1.98
2.12
1.97
1.97
1.95
2.03
2.06
1.99
2.02
2.11
2.13
1.98
1.95
1.96
2.11
1.93
1.98
1.98
2.13
2.04
2.05
1.99
2.13
2.01
2.01
1.97
1.95
2.11
2.03
1.98
2.12
2.14
1.95
1.96
1.95
2.11
1.91
1.98
1.99
2.13
2.06
2.07
2.00
2.11
2.00
2.04
1.95
1.94
2.09
2.02
1.95
2.10
2.14
1.98
1.95
1.95
2.10
1.93
1.98
1.96
2.12
2.06
2.07
1.99
2.11
1.99
2.04
1.96
1.94
2.08
2.02
1.95
2.10
2.12
1.99
1.95
1.94
2.11
1.93
1.98
1.95
2.13
Figure 3. Structure of the [Na2(p-ClC6H4Sb)12O24(OH)6-
(H2O)3]4¹ anion. Atoms of the aryl groups other than the
ipso carbons are omitted for clarity. Ellipsoids are drawn to
encompass 50% probability levels.
structural analysis revealed that this compound is composed
of TBA cations, H2O and CH3CN molecules of crystallization,
and oligomeric arylstibonate anions [H4(p-ClC6H4Sb)16O36]4¹
Sb3-OD1
Sb3-OD2
Sb3-OF
.
As can be seen from Figure 2, the [H4(p-ClC6H4Sb)16O36]4¹
anion has the same antimony-oxygen framework as the [H5(p-
ClC6H4Sb)16O36]3¹ anion mentioned above and also closely
approximates the maximal 2/m symmetry. However, its pro-
tonation state is different. The [H4(p-ClC6H4Sb)16O36]4¹ anion
has only four protons attached to its Sb16O36 core. Here again
the locations of those protons can reasonably be inferred from a
comparison of bond lengths and bond valence sums.15,16 The
bond valence sums for O17 and O16 are 1.3 and 1.4, respec-
tively. These values allow us to conclude that the protons are
attached to these four oxygens.
Sb3-OG
a) a, b This work. c Ref. 6. d, e Ref. 7. b) See also Figure 4.
There are only two TBA cations per [H4(p-ClC6H4Sb)16-
O36]4¹ anion in the crystals. Charge neutrality requires two
more protons. It is highly likely that those two protons are on
water molecules. The distances between O21 and O11, O12¤,
and O18¤ are significantly shorter than 2.8 ¡, indicating hydro-
gen bonding. Thus O21 (and hence O21¤) is assumed to be an
oxygen of a hydronium cation. It is probably more appropriate
to formulate this anion as [H4(p-ClC6H4Sb)16O36(H3O)2]2¹
.
The O11, O12, and O18 are located at the bottom of a pit made
from aryl groups. The hydronium cation sits in this pit. The
Figure 4. Labeling scheme for the 2/m-idealized Sb16-
C16O36 unit. The 2-fold axis goes through OF and OG. The
atoms Sb1A, Sb2A, OA1, OA2, and OC22 are on the mirror
plane.
same pit is occupied by a Na+ ion in [H2(C6H5Sb)16O36]6¹ 6
.
The assumption that O21 is an oxygen of a hydronium cation
is not inconsistent with this observation.
Table 5 compares the 2/m-averaged Sb-O distances of
different hexadecastibonates. The atom labeling scheme used
in the table is shown in Figure 4. Table 5 shows that the Sb-O
bonds in different hexadecastibonates are very similar. It tells
us that all hexadecastibonates reported in Refs. 6 and 7 are
actually diprotonated, although the stibonate in Ref. 6 is
formulated as a nonprotonated anion and those in Ref. 7 are
formulated as fully protonated neutral [H8(p-XC6H4Sb)16O36]
by the authors of the respective papers. The Sb3-OG bond
lengths are virtually the same for all the compounds listed in
Table 5 and anomalously long for a doubly bridging oxygen.
This makes us conclude that OG oxygens are protonated in all
five hexadecastibonates. No such elongation is observed for
the bonds to the other doubly bridging oxygens in [H2(p-
ClC6H4Sb)16O36]6¹ and [H2(p-BrC6H4Sb)16O36]6¹. No anom-
aly is observed for triply bridging OA and OB oxygens in those
anions, either. It is highly unlikely that any oxygens other
than OG are protonated in [H2(p-ClC6H4Sb)16O36]6¹ and [H2(p-
BrC6H4Sb)16O36]6¹. The remaining protons required for charge
neutrality are probably on the dimethylpyrazol molecules in the
crystals; i.e., the compounds reported as dimethylpyrazol sol-
Bull. Chem. Soc. Jpn. 2014, 87, 1245–1251 | doi:10.1246/bcsj.20140160
© 2014 The Chemical Society of Japan | 1249

vates of fully protonated [H8(p-XC6H4Sb)16O36] (X = Cl and
Br) in Ref. 7 actually are dimethylpyrazolium salts of [H2(p-
XC6H4Sb)16O36]6¹
.
Table 5 also shows the effect of the protonation of OE in
[H5(p-ClC6H4Sb)16O36]3¹ and [H4(p-ClC6H4Sb)16O36(H3O)2]2¹
anions. The Sb-OE bonds in those stibonates are longer than
the corresponding bonds in [H2(p-XC6H4Sb)16O36]6¹. Slightly
shorter average Sb-OE bond lengths of [H4(p-ClC6H4Sb)16-
O36(H3O)2]2¹ than those of [H5(p-ClC6H4Sb)16O36]3¹ can
be explained by the fact that three OE atoms are protonated
in the latter while only two are protonated in the former.
Figure 5. Polyhedral representation of the Sb12O30C12 unit
of the [Na2(p-ClC6H4Sb)12O24(OH)6(H2O)3]4¹ anion (left)
and the M12O40 unit of the δ-Keggin structure (right). The
O atom indicated by an arrow and those related to this atom
by a 3-fold symmetry are protonated in the Mn5(ArSb)12
compound.
Notable differences are also observed for Sb1B-OC12 and Sb2A
-
OC21. These bonds are longer in [H2(p-XC6H4Sb)16O36]6¹ than
in [H5(p-ClC6H4Sb)16O36]3¹ and [H4(p-ClC6H4Sb)16O36-
(H3O)2]2¹. This can be attributed to the hydrogen-bonding
of these oxygens to dimethylpyrazolium cations in [H2(p-
XC6H4Sb)16O36]6¹ (X = Cl and Br) and interactions with Na+
C atoms closely approximates 3m symmetry. The Sb12O30C12
unit is made up from two rings, each of which is built from six
SbO5C octahedra. The octahedra are connected sharing edges in
the bottom ring to form a Sb6O18C6 moiety that is isostructural
with the M6O24 ring of the Anderson-type polyoxoanions12 and
cations and a water molecule in [H2(C6H5Sb)16O36]6¹
.
Yet another compound was obtained when the solid obtained
by reacting p-chlorophenylstibonic acid with aqueous TBAOH
was dissolved in wet CH3CN that contains ca. 5% water and
allowed to stand at ambient temperature for three days. X-ray
structural analysis revealed that this compound is composed of
TBA cations, H2O and CH3CN molecules of crystallization,
and discrete [Na2(p-ClC6H4Sb)12O24(OH)6(H2O)3]4¹ anions
that have the structure shown in Figure 3. Three water mole-
cules coordinate to Na1. These water molecules form hydrogen
bonds to the water molecules coordinated to Na1 of another
dodecastibonate anion, forming a [Na2(p-ClC6H4Sb)12O24-
[α-Mo8O26]4¹ 17,18
In the top ring the octahedra are connected
.
sharing vertices. Alternatively, the structure can be perceived
as an “opened-up” δ-Keggin structure (Figure 5).19,20 Three
(ArSb)3O10 units are connected to form a δ-Sb9 unit. Three
SbO5C octahedra further connect these (ArSb)3O10 units by
sharing vertices. If we flip those SbO5C octahedra up to make
another (ArSb)3O10 unit on the top of the anion, we would end
up with a complete δ-Keggin structure. The δ-Keggin struc-
ture has been observed for the Mn5(ArSb)12 compound6 and
[BaCoH4(ArSb)12O28].21 It is interesting to note that bond
valence sum calculations suggest that the oxygen indicated
by an arrow in Figure 5 and those related to this atom by a 3-
fold symmetry are protonated in the δ-Keggin framework of
[BaCoH4(ArSb)12O28]. These doubly bridging oxygens also
forms significantly shorter bonds to the peripheral Mn atoms
(average 1.99 ¡) than the other doubly bridging oxygens in the
structure (average 2.21 ¡) in Mn5(ArSb)12.
8¹
(OH)6(H2O)3]2 dimer.9 This Na+ cation is bound on the
surface of the molecular oxide anion, but the other Na+ cation
in the structure, Na2, is located inside the dodecastibonate
cage. There is a CH3CN molecule right above this Na+ cation
and in the center of the pocket formed by the six aryl groups
surrounding it. Another CH3CN molecule exists alongside this
CH3CN molecule and close to O19 and O24. The pocket
formed by the six aryl groups seems to be a little too large for a
single CH3CN molecule. Bond valence sum calculations15,16
revealed that oxygens O25 through O30 all have a low value of
0.9, suggesting those six oxygens are protonated.
References
The current dodecastibonate anion has the same antimony-
oxygen framework as the those reported by Baskar et al.6 and
Nicholson et al.8,9 but different degree of protonation and com-
plexation with alkaline metal cations. In our dodecastibonate,
there are no protons other than those six described above.
However, the dodecastibonates reported by Nicholson et al.
have two or three more protons. Our dodecastibonate anion
contains only two Na+ ions. On the other hand, there are three
Na+ ions attached to the dodecastibonate reported by Baskar
et al.6 The K analog and mixed Rb/Na salt reported by
Nicholson et al.9 also contain three alkaline metal cations in the
structure. In all of those compounds, two of the cations occupy
the same sites as the Na+ ions in our dodecastibonate, but the
one that corresponds to Na2 in Figure 3 are coordinated by a
water molecule. The third alkaline metal cation in those struc-
tures occupies the site where the second CH3CN molecule sits
in our structure.
#
Dedicated to the memory of Prof. Lage Pettersson who
passed away in October 2013.
H. Nakano, Y. Ozawa, A. Yagasaki, J. Am. Chem. Soc.
1995, 117, 12007.
1
2
2634.
3
Y. Kusaka, Y. Ozawa, A. Yagasaki, Inorg. Chem. 2001, 40,
C. Brevard, P. Granger, Handbook of High Resolution
Multinuclear NMR, Wiley, New York, 1981. p. 170.
4
5
Y. Hayashi, Coord. Chem. Rev. 2011, 255, 2270.
G. O. Doak, H. G. Steinman, J. Am. Chem. Soc. 1946, 68,
1987.
6
V. Baskar, M. Shanmugam, M. Helliwell, S. J. Teat, R. E. P.
Winpenny, J. Am. Chem. Soc. 2007, 129, 3042.
A. K. Jami, M. S. R. Prabhu, V. Baskar, Organometallics
2010, 29, 1137.
7
8
C. J. Clark, B. K. Nicholson, C. E. Wright, Chem.
Commun. 2009, 923.
Although the anion has no vigorous crystallographic sym-
metry, its Sb12O30C12 framework made up from Sb, O, and ipso
9
B. K. Nicholson, C. J. Clark, C. E. Wright, T. Groutso,
Organometallics 2010, 29, 6518.
1250 | Bull. Chem. Soc. Jpn. 2014, 87, 1245–1251 | doi:10.1246/bcsj.20140160
© 2014 The Chemical Society of Japan

10 The Na+ cations in the compound are from p-chlorostibonic
acid. p-Chlorostibonic acid prepared by the method of Doak
and Steinman is known to contain a small amount of Na. See
Ref. 8.
16 N. E. Brese, M. O’Keeffe, Acta Crystallogr., Sect. B 1991,
47, 192.
17 J. Fuchs, H. Hartl, Angew. Chem., Int. Ed. Engl. 1976, 15,
375.
11 G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112.
12 M. T. Pope, Heteropoly and Isopoly Oxometalates,
Springer, Berlin, 1983.
13 D. Honda, T. Ozeki, A. Yagasaki, Inorg. Chem. 2004, 43,
6893.
14 J. W. Linnett, J. Chem. Soc. 1961, 3796.
15 I. D. Brown, D. Altermatt, Acta Crystallogr., Sect. B 1985,
41, 244.
18 V. W. Day, M. F. Fredrich, W. G. Klemperer, W. Shum,
J. Am. Chem. Soc. 1977, 99, 952.
19 L. C. W. Baker, J. S. Figgis, J. Am. Chem. Soc. 1970, 92,
3794.
20 M. T. Pope, Heteropoly and Isopoly Oxometalates,
Springer, Berlin, 1983, p. 26.
21 B. K. Nicholson, C. J. Clark, S. G. Telfer, T. Groutso,
Dalton Trans. 2012, 41, 9964.
Bull. Chem. Soc. Jpn. 2014, 87, 1245–1251 | doi:10.1246/bcsj.20140160
© 2014 The Chemical Society of Japan | 1251