A planar anthracene–imidazolium/anthracene–benzimidazolium cation system in a spherical polyoxometalate matrix: Synthesis, crystallography and spectroscopy

Article abstract of DOI:10.1016/j.poly.2017.01.049

A series of ion–pair compounds, comprising of Lindqvist type isopolyanions viz., [Mo₆O₁₉]^2?and [W₆O₁₉]^2?as the counter anions and anthracene–imidazolium/anthracene–benzimidazolium as counter cations, have been described. Structures of the isolated stoichiometric solids have been unambiguously determined by single crystal X-ray diffraction analysis. In spite of the structural incompatibility between anthracene (planar) and the present polyoxometalate anions (spherical), coulombic and several intermolecular weak interactions, e.g. C–H?O, C–H?π, π–π, etc. compensate the destabilization energy raised due to presence of the structurally mis-matched components in the respective crystal lattices. Single-crystal- as well as powder X-ray-diffraction (PXRD) analyses reveal iso-structural relationship between the hexamolybdates- and hexatungstates-associated ion pair compounds. Conformational variation has been observed in the crystal structures containing benzyl benzimidazolium counter cations. Diffuse reflectance electronic absorption spectral studies are performed to understand the relatively intense color of the title compounds in their solid states in comparison to their respective solution states.

Full text of DOI:10.1016/j.poly.2017.01.049

Accepted Manuscript
A planar anthracene–imidazolium / anthracene-benzimidazolium cation system
in a spherical polyoxometalate matrix: synthesis, crystallography and spectro-
scopy
Tanmay Chatterjee, Tanmaya Kumar, Samar K. Das
PII:
S0277-5387(17)30086-4
DOI:
http://dx.doi.org/10.1016/j.poly.2017.01.049
POLY 12453
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
24 November 2016
26 January 2017
28 January 2017
Please cite this article as: T. Chatterjee, T. Kumar, S.K. Das, A planar anthracene–imidazolium / anthracene-
benzimidazolium cation system in a spherical polyoxometalate matrix: synthesis, crystallography and spectroscopy,
Polyhedron (2017), doi: http://dx.doi.org/10.1016/j.poly.2017.01.049
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A
planar anthracene–imidazolium
/
anthracene-
benzimidazolium cation system in a spherical
polyoxometalate matrix: synthesis, crystallography and
spectroscopy
Tanmay Chatterjee, Tanmaya Kumar and Samar K. Das*
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
Supplementary data associated with this article can be found, in the online
Version, at xxxxxxxxxxxxxxxxxxx
Corresponding author. Tel: +91-40-2301-1007; fax: +91-40-2301-2460.
E-mail address: skdsc@uohyd.ernet.in (S. K. Das)
1

Abstract
2
–
6 19
A series of ion–pair compounds, comprising of Lindqvist type isopolyanions viz., [Mo O ]
2
–
and [W
6
O
19
]
as the counter anions and anthracene–imidazolium / anthracene-
benzimidazolium as counter cations, have been described. Structures of the isolated
stoichiometric solids have been unambiguously determined by single crystal X–ray
diffraction analysis. In spite of the structural incompatibility between anthracene (planar) and
the present polyoxometalate anions (spherical), coulombic and several intermolecular weak
interactions, e.g. C–H···O, C–H···π, π–π etc. compensate the destabilization energy raised
due to presence of the structurally mis-matched components in the respective crystal lattices.
Single-crystal- as well as powder X-ray-diffraction (PXRD) analyses reveal iso-structural
relationship between the hexamolybdates- and hexatungstates-associated ion pair compounds.
Conformational variation has been observed in the crystal structures containing benzyl
benzimidazolium counter cations. Diffuse reflectance electronic absorption spectral studies
are performed to understand the relatively intense color of the title compounds in their solid
states in comparison to their respective solution states.
Keywords: Lindqvist isopolyanions / Coulombic interactions / Supramolecular interactions /
Stoichiometric solids / Conformational variation / Solid state electronic spectral studies
2

1
. Introduction
The term 'co-crystal', in a broader sense, denotes crystalline solids made from more than
one component held together by non–covalent intermolecular interactions. To–date, many
authors have defined the term in diverse ways although an accurate and universally accepted
definition of 'co-crystal' is not yet available [1]. Another characteristic feature of the co-
crystals is that they exhibit distinct physical properties (for example, solubility, thermal
stability, melting point etc.) than those of the co-crystal formers. Thus, after the
intermolecular association of more than one molecular component (not necessarily to be both
solids), a crystalline solid (necessarily to be solid) is formed, where the uniqueness / identity
of the constituents disappears and a modulation of their physico–chemical properties (in
solution state there might be a retention of their individuality) is observed [2].
Very often, in the case of co-crystals, a central molecule is focused which is co-
crystallized with various other secondary components (called as conformers [3]). At this
point, it should be remembered that, co-crystals do not involve only organic molecules, but
also ionic compounds, inorganic compounds / complexes as co-formers. The first co-crystal
(
all organic) was discovered by Wohler (1844) in the era before the invention of X–ray by
Rontgen (1895) [4-5]. Since then co-crystals turned out to be a subject of immense interest
and at present, majority of the co-crystals, reported in literature, incorporate active
pharmaceutical ingredients (APIs) as one component in achieving bioactive materials [6-8].
Besides co-crystals obtained from only neutral hosts or guests, ionic compounds are also
found to form co-crystals with definite stoichiometry. Few representative examples include
co-crystals containing both carboxylic acid and acid salt, phenolic acid and acid salt or
organic−inorganic co-crystals [3].
Several intermolecular forces, for example, hydrogen bonding, van der Walls,
electrostatic, π–stacking etc. govern molecular packing of the crystallizing substances in a
crystal lattice. The central aim of the supramolecular chemistry is to gain organized
arrangement / packing of the molecules in a crystal using these intermolecular interactions
[
9]. Apart from the co-crystals built from simple organic:organic or organic: inorganic
molecular components, recent interests have been grown to incorporate complex molecular
systems such as, molecules with curved and flat external surfaces in the crystal lattice.
Obtaining multi-dimensional and/or larger supramolecular ensembles using fullerenes as the
3

crystallizing substances has become a subject of extensive research to the structural chemists
crystallographers since the last two decades. The ubiquitous three–dimensional and higher
/
symmetrical shape of the fullerenes along with their exciting physical and chemical
properties (e.g., their facile electron accepting abilities) have drawn significant attention to
the structural chemists for choosing them as good candidates to build complex
supramolecular architectures [10-16] .
Polyoxometalates (POMs), on the other hand, are transition metal–oxide based cluster
anions comprising of metal ions bridged by oxygen atoms [17], which have received an
enormous attention by the contemporary chemists, because of their diverse physical and
chemical properties e.g., diversity in their shape, size, electrochemistry, acid–base chemistry,
charge distribution etc. including their participation in soft-oxometalate (SOM) chemistry
[
18-21]. The surface of these macro–anions bearing oxygen atoms, are of particular interest.
Interestingly, some features of the POM anions resemble that of the fullerenes e.g. (i) their
electron accepting nature [22] (the metal centers are in their higher oxidation states and thus
can be partially reduced by a secondary substance), (ii) their highly symmetrical shape etc.
Therefore, they can be introduced in supramolecular chemistry as the low–cost alternative to
the fullerenes despite the fact, that the POM anions have profound chances to form dative
linkages to the external metal centers (thus acting as ligands) via the terminal oxygen atoms
[
23]. Crystallization of the POM anions with supramolecular complexes of the macrocyclic
systems [24-25] or other counter cations [26] have been documented in literature that
illustrate the usage of the POM anions as building blocks in the context of crystal
engineering. However, co-crystallization of the POM anions with π–donor flat aromatic co-
formers is of great crystallographic challenge due to size incompatibility between the
interacting components. Aromatics containing flat π surfaces (e.g. anthracene, pyrene, etc.)
can interact with the surface of the POM anions via two possible ways as depicted in Scheme
1
. The planar aromatics mostly pack with each other through π–staking interactions in their
crystals. These π–staked aromatics could further associate with the POM macroanions
through C–H···O hydrogen bonding interactions as shown in Scheme 1a. Thus, in this way of
interaction, there are no direct contacts between the π cloud of the aromatics and the POM
anions. The other interaction mode, as shown in Scheme 1b, demonstrates direct contact
between the π surface of the flat aromatics and the electron accepting POM surfaces, thereby
including possibility of charge transfer interaction between the components that result in
partial oxidation and partial reduction of the aromatics and the POM anions respectively.
4

Scheme 1. Two possible ways of interactions between flat aromatics and POMs.
Kochi and co-workers first reported the π···POM interactions in a series of co-crystals,
made up of anthracene or pyrene based conformers [27]. The relevant publication comments
that, coulombic interactions between the POM anions and the alkylammonium or pyridinium
groups, attached to the polyaromatic hydrocarbons (anthracene and pyrene) via flexible
polymethylene chains, help the planar surfaces of the aromatics to come closer to the POM
surfaces, thus involving in the π···POM interactions. This has led to charge transfer from the
π–donors to the POM anions [27]. Similarly, Tan and Bu reported four hybrid compounds,
formed by electrostatic interactions between the POM and the anthracene donor having two
alkylimidazolium groups, that can be described as charge-transfer salts. They calculated the
energy level parameters, which reasonably matched with those of the commonly used organic
electroluminescence devices [28]. Keeping these works in mind, a series of hexamolybdate
and hexatungstate (iso-polyanions) based ion–pair compounds (Scheme 2: 10a-f, 11a-f, 12a-
e, 13a-e), which contain anthracene–imidazolium or anthracene–benzimidazolium species as
counter cations, have been synthesized and reported in this article.
We wish to analyze the structural and physical properties of the ion-pair compounds, 10a-
f, 11a-f, 12a-e, 13a-e (Scheme 2), constructed from anthracene-based counter cations bearing
th
a heavy atom (Br) at the 9 position of anthracene and polyoxometalate (POM) anions
VI
2−
[
M
6
O
19
]
(M = Mo and W). Coulombic association between the POM anion surfaces and
5

the imidazolium or benzimidazolium cationic counterparts have been observed whereas, the
anthracene moieties are involved in C–H···O, C–H···π or π···π interactions to optimize the
(
a)
(b)
R= Me (10a, 11a), n-Pr (10b, 11b),
i-Pr (10c, 11c), n-Bu (10d, 11d),
hexyl (10e, 11e),decyl (10f, 11f)
R
R
R
1
1
1
= R
= F, R
= Cl, R
= Br, R
= R = R
2
= R
3
= R
4
= R
4
5
= H (12a, 13a)
= R = H (12b, 13b)
= R = H (12c, 13c)
= R = H (12d, 13d)
= Me (12e, 13e)
2
= R
3
= R
5
2
= R
= R
= R
3
= R
4
5
R
1
2
3
= R
= R
4
5
R
1
2
3
4
5
(
c)
Scheme 2. (a) Anthracene-imidazolium ion-pair compounds (10a-f, 11a-f), (b) the anthracene-
benzimidazolium ion-pair compounds (12a-e, 13a-e), (c) the structural representation of
2
‒
6
hexametalateate ion, [Mo O19] .
lattice energy. We found that varying the alkyl chain length of the imidazolium cation (10a-
f, 11a-f: Scheme 2) or changing the substituents in benzimidazolium moieties (12a-e, 13a-e:
Scheme 2) causes a modification in hydrogen bonding situation to some extent, whereas in
the all the crystals, the nature of the π···π stacking interaction remains invariant. The
remaining part of this article deals with the detailed structural analysis and solid state
absorption spectroscopy of the title compounds that are electro–neutral in nature.
6

2
. Experimental
2
.1. Materials and physical methods
All the chemicals were received as reagent grade and used without any further purification.
2
.2 Characterization:
Elemental analyses were determined by FLASH EA series 1112 CHNS analyzer. Infrared
spectra of solid samples were obtained as KBr pellets on a JASCO-5300 FT-IR
spectrophotometer. Powder X-ray diffraction patterns were recorded on a Bruker D8-
Advance diffractometer using graphite monochromated CuKα1 (1.5406 Å) and Kα2 (1.54439
Å) radiations. The electronic absorption spectra have been recorded on a Cary 100 Bio
1
UV−visible spectrophotometer at room temperature. H NMR spectra have been recorded
in a Bruker AV 400 MHz spectrometer. The chemical shifts (δ) are reported in ppm with
respect to the solvent signals
.
Solution mass spectra (LCMS) were obtained on a LCMS-
2
010A Shimadzu spectrometer.
Synthesis.
–bromo–10–(bromomethyl)anthracene (2). Bromine (2 equivalents) was added drop wise to
9
a stirred solution of triphenylphosphine (1 equivalent) in acetonitrile at room temperature and
the pale yellow slurry was stirred for 15 min. Solid 9–anthracene methanol (1 equivalent) was
then added slowly and the reactants were allowed to react at room temperature until total
consumption of the starting material (TLC) after which, it was refrigerated overnight. The
product, which appeared as yellow precipitate, was isolated by filtration, washed with little
cold methanol and then dried under vacuum. It was further re–crystallized twice from
chloroform before use. Characterization data completely corroborated with the literature
reported data [29].
General procedure for the synthesis of the N–alkyl imidazoles (4a–f) and N–benzyl
benzimidazoles (7a–e). Imidazole (3) / benzimidazole (5) (10 mmol) was dissolved in 10 ml
of DMSO and solid NaOH (15 mmol) was then added it. The resulting pale yellow
suspension was stirred in air at room temperature for 1.5 h, after which, the alkyl bromides or
benzyl chlorides (15 mmol) were added and allowed to react until completion (TLC). Water
(
50 ml) was then added and the products were extracted with ethyl acetate. Combined organic
layers were washed several times with water, then with brine, dried over Na SO and
subjected to chromatographic purification over silica (100–200 mesh) using MeOH : EtOAc
2
4
5
:95 (v/v) as the mobile phase. Compounds 4a–f were isolated as yellow oils whereas, the
7

compounds 7a–e were white solid. Spectroscopic data of the N–alkyl imidazoles are in
accord with earlier literature and thus haven’t shown here [30].
1
N–benzyl–benzimidazole (7a). White solid; Yield = 77%; H NMR (400 MHz, CDCl
3
, TMS)
δ: 7.92 (s, 1H), 7.84 (d, J = 8 Hz, 1H), 7.21–7.37 (m, 6H), 7.15 (d, J = 8 Hz, 2H), 5.29 (s,
1
3
2
1
H). C NMR (100 MHz, CDCl
3
, TMS) δ: 143.9, 143.3, 135.5, 133.9, 129.0, 128.3, 127.0,
+
+
23.1, 120.4, 110.1, 48.8. LC–MS (positive mode) m/z = 209 (M +H) . Anal. Calcd. For
C
14
H
12
N
2
(208.26): C, 80.74; H, 5.81; N, 13.45. Found: C, 80.72; H, 5.84; N, 13.44.
1
N–(4–fluorobenzyl)–benzimidazole (7b). Off–white solid; Yield = 73%; H NMR (400 MHz,
1
3
CDCl
3
, TMS) δ: 7.91 (s, 1H), 7.76–7.82 (m, 1H), 6.90–7.33 (m, 7H), 5.26 (s, 2H). C NMR
(
100 MHz, CDCl , TMS) δ: 163.7, 161.3, 143.9, 143.1, 131.2, 128.9, 123.2, 122.4, 120.4,
3
+
+
1
16.1, 115.9, 110.0, 48.1. LC–MS (positive mode) m/z = 227 (M +H) . Anal. Calcd. For
C
14
H11FN
2
(226.25): C, 74.32; H, 4.90; N, 12.38. Found: C, 74.36; H, 4.87; N, 12.41.
1
1
–(4–chlorobenzyl)–benzimidazole (7c). Off–white solid; Yield = 73%; H NMR (400 MHz,
1
3
CDCl
MHz, CDCl
10.1, 48.3. LC–MS (positive mode) m/z = 244 (M +H) . Anal. Calcd. For C14
242.70): C, 69.28; H, 4.57; N, 11.54. Found: C, 69.27; H, 4.53; N, 11.57.
N–(4–bromobenzyl)–benzimidazole (7d). Pale–yellow solid; Yield = 75%; H NMR (400
MHz, CDCl , TMS) δ: 7.92 (s, 1H), 7.83 (d, J = 8 Hz, 1H), 7.43 (d, J = 8 Hz, 2H), 7.23–7.28
3
, TMS) δ: 8.05 (s, 1H), 7.82 (m, 2H), 7.00–7.37 (m, 6H), 5.30 (s, 2H). C NMR (100
3
, TMS) δ: 143.3, 142.9, 134.2, 133.9, 133.5, 129.2, 128.4, 123.4, 122.7, 120.2,
+
+
1
H11ClN
2
(
1
3
1
3
(
m, 3H), 7.01 (d, J = 8 Hz, 2H), 5.26 (s, 2H). C NMR (100 MHz, CDCl
3
, TMS) δ: 143.9,
1
43.1, 134.5, 133.7, 132.2, 128.7, 123.3, 122.3, 120.5, 109.9, 48.2. LC–MS (positive mode)
+
+
m/z = 288 (M +H) . Anal. Calcd. For C14
Found: C, 58.55; H, 3.83; N, 9.80.
H11BrN
2
(287.15): C, 58.56; H, 3.86; N, 9.76.
1
N–(2,3,4,5,6–pentamethylbenzyl)–benzimidazole (7e). White solid; Yield = 78%; H NMR
(
400 MHz, CDCl
3
, TMS) δ: 7.87 (s, 1H), 7.20–7.63 (m, 4H), 5.33 (s, 2H), 2.14–2.38 (m,
5H). C NMR (100 MHz, CDCl , TMS) δ: 144.2, 142.0, 136.2, 134.2, 133.5, 127.2, 122.8,
22.3, 120.4, 109.6, 44.4, 17.2, 16.9, 16.6. LC–MS (positive mode) m/z = 279 (M +H) .
1
3
1
1
3
+
+
Anal. Calcd. For C19
N, 10.08.
H
22
2
N (278.39): C, 81.97; H, 7.97; N, 10.06. Found: C, 81.93; H, 7.99;
General procedure for the synthesis of the ANT–Im or ANT–BenzIm bromide salts (8a–f and
a–e). A mixture of 9–bromo–10–(bromomethyl)anthracene (2) (1 mmol) and the relevant
9
N–alkyl imidazoles (4a–f) or N–benzyl benzimidazoles (7a–e) in THF (15 ml) was refluxed
at open condition for 24 h. By this time the products 8a–f and 9a–e appeared as yellow
8

precipitates which were isolated by filtration, washed with little THF, then with ether and
were air–dried. Yield: 85–89% (imidazolium salts) and 80–87% (benzimidazolium salts).
Bromide 8a. Yellow solid. Anal. Calcd. For C19
.48. Found: C, 52.76; H, 3.75; N, 6.51.
Bromide 8b. Yellow solid. Anal. Calcd. For C21
.09. Found: C, 54.82; H, 4.36; N, 6.05.
H
16Br
2
N
2
(432.25): C, 52.81; H, 3.73; N,
6
H20Br
2
N
2
(460.20): C, 54.81; H, 4.38; N,
6
2 2
Bromide 8c. Yellow solid Anal. Calcd. For C21H20Br N (460.20): C, 54.81; H, 4.38; N, 6.09.
Found: C, 54.84; H, 4.37; N, 6.07.
Bromide 8d. Yellow solid. Anal. Calcd. For C22
.91. Found: C, 55.74; H, 4.71; N, 5.89.
Bromide 8e. Yellow solid. Anal. Calcd. For C24
.58. Found: C, 57.37; H, 5.16; N, 5.60.
H
22Br
2
N
2
(474.23): C, 55.72; H, 4.68; N,
(502.28): C, 57.39; H, 5.22; N,
5
H26Br
2
N
2
5
2 2
Bromide 8f. Yellow solid. Anal. Calcd. For C28H34Br N (558.39): C, 60.23; H, 6.14; N, 5.02.
Found: C, 60.27; H, 6.11; N, 4.98.
Bromide 9a. Yellow solid. Anal. Calcd. For C29
.45. Found: C, 67.80; H, 4.27; N, 5.37.
Bromide 9b. Yellow solid. Anal. Calcd. For C29
.27. Found: C, 65.51; H, 3.99; N, 5.26.
Bromide 9c. Yellow solid. Anal. Calcd. For C29
.11. Found: C, 63.56; H, 3.84; N, 5.13.
Bromide 9d. Yellow solid. Anal. Calcd. For C29
.73. Found: C, 58.79; H, 3.55; N, 4.72.
Bromide 9e. Yellow solid. Anal. Calcd. For C34
.80. Found: C, 69.96; H, 5.53; N, 4.73.
H
22BrClN
2
(513.86): C, 67.78; H, 4.32; N,
(531.85): C, 65.49; H, 3.98; N,
(548.30): C, 63.53; H, 3.86; N,
(592.75): C, 58.76; H, 3.57; N,
(583.99): C, 69.93; H, 5.52; N,
5
H21BrClFN
2
5
2 2
H21BrCl N
5
H21Br
2
ClN
2
4
H32BrClN
2
4
General Procedure for the synthesis of ion-pair complexes (10 a-f, 11 a-f, 12 a-e, 13 a-e).
To a stirred solution of salts 8 a-f or 9 a-e (2 mmol) in acetonitrile is added the hexametalate
salt (1 mmol), to give an immediate precipitate, which is further stirred for 30-45 mins. at
room temperature. The molybdate salts (10 a-f, 12 a-e) were orange in colour, while the
tungstate salts (11a-f, 13 a-e) precipitated as yellow salts. They were then filtered and then
air dried.
–1
Hexamolybdate 10a. Orange yellow solid. IR (KBr, cm ): 3144.25 (C–H), 3097.96 (C–H),
9
2
56.78 (Mo=O), 898.91 (Mo–O–Mo). Anal. Calcd. For C38
8.81; H, 2.04; N, 3.54. Found: C, 28.66; H, 1.99; N, 3.61.
H32Br
2
N
4
Mo
6
O
19 (1584.12): C,
9

–1
Hexamolybdate 10b. Orange yellow solid. IR (KBr, cm ): 3152.17 (C–H), 3070.29 (C–H),
9
3
54.87 (Mo=O), 895.11 (Mo–O–Mo). Anal. Calcd. For C42
0.75; H, 2.46; N, 3.42. Found: C, 30.41; H, 2.39; N, 3.53.
2 4 6
H40Br N Mo O19 (1640.23): C,
–1
Hexamolybdate 10c. Orange yellow solid. IR (KBr, cm ): 3145.19 (C–H), 3092.58 (C–H),
9
3
49.19 (Mo=O), 890.17 (Mo–O–Mo). Anal. Calcd. For C42
0.75; H, 2.46; N, 3.42. Found: C, 30.57; H, 2.44; N, 3.56.
H40Br
2
N
4
Mo O19 (1640.23): C,
6
–1
Hexamolybdate 10d. Orange yellow solid. IR (KBr, cm ): 3141.15 (C–H), 3089.91 (C–H),
9
3
58.78 (Mo=O), 897.41 (Mo–O–Mo). Anal. Calcd. For C44
1.68; H, 2.66; N, 3.36. Found: C, 31.63; H, 2.63; N, 2.42.
2 4 6
H44Br N Mo O19 (1668.28): C,
–1
Hexamolybdate 10e. Orange yellow solid. IR (KBr, cm ): 3157.33 (C–H), 3068.97 (C–H),
9
3
41.48 (Mo=O), 891.96 (Mo–O–Mo). Anal. Calcd. For C48
3.43; H, 3.04; N, 3.25. Found: C, 33.35; H, 3.01; N, 3.30.
H52Br
2
N
4
Mo O19 (1724.39): C,
6
–
1
Hexamolybdate 10f. Orange yellow solid. IR (KBr, cm ): 3162.19 (C–H), 3091.17 (C–H),
9
3
57.12 (Mo=O), 893.22 (Mo–O–Mo). Anal. Calcd. For C56
6.62; H, 3.73; N, 3.05. Found: C, 36.53; H, 3.71; N, 3.12.
2 4 6
H68Br N Mo O19 (1836.60): C,
–
1
Hexatungstate 11a. Yellow solid. IR (KBr, cm ): 3150.04 (C–H), 3092.17 (C–H), 978.00
W=O), 802.46 (W–O–W). Anal. Calcd. For C38 19 (2111.52): C, 21.62; H,
.53; N, 2.65. Found: C, 21.59; H, 1.51; N, 2.68.
(
2 4 6
H32Br N W O
1
–
1
Hexatungstate 11b. Yellow solid. IR (KBr, cm ): 3157.12 (C–H), 3076.49 (C–H), 982.54
W=O), 799.35 (W–O–W). Anal. Calcd. For C42 19 (2167.63): C, 23.27; H,
.86; N, 2.58. Found: C, 23.22; H, 1.83; N, 2.62.
(
2 4 6
H40Br N W O
1
–
1
Hexatungstate 11c. Yellow solid. IR (KBr, cm ): 3147.97 (C–H), 3096.19 (C–H), 982.88
W=O), 789.79 (W–O–W). Anal. Calcd. For C42 19 (2167.63): C, 23.27; H,
.86; N, 2.58. Found: C, 23.24; H, 1.81; N, 2.65.
(
2 4 6
H40Br N W O
1
–
1
Hexatungstate 11d. Yellow solid. IR (KBr, cm ): 3148.83 (C–H), 3043.27 (C–H), 988.72
W=O), 801.91 (W–O–W). Anal. Calcd. For C44 19 (2195.68): C, 24.07; H,
.02; N, 2.55. Found: C, 24.03; H, 2.00; N, 2.61.
(
2 4 6
H44Br N W O
2
–
1
Hexatungstate 11e. Yellow solid. IR (KBr, cm ): 3142.26 (C–H), 3045.27 (C–H), 979.89
W=O), 800.22 (W–O–W). Anal. Calcd. For C48 19 (2251.79): C, 25.60; H,
.33; N, 2.49. Found: C, 25.51; H, 2.30; N, 2.52.
(
2 4 6
H52Br N W O
2
–
1
Hexatungstate 11f. Yellow solid. IR (KBr, cm ): 3134.19 (C–H), 3042.55 (C–H), 976.17
W=O), 785.60 (W–O–W). Anal. Calcd. For C56 19 (2364.00): C, 28.45; H,
.90; N, 2.37. Found: C, 28.41; H, 2.88; N, 2.39.
(
H68Br
2
N
4
W O
6
2
1
0

–1
Hexamolybdate 12a. Orange yellow solid. IR (KBr, cm ): 3146.83 (C–H), 3109.36 (C–H),
9
3
43.21 (Mo=O), 892.37 (Mo–O–Mo). Anal. Calcd. For C58
7.93; H, 2.41; N, 3.05. Found: C, 37.91; H, 2.37; N, 3.07.
2 4 6
H44Br N Mo O19 (1836.43): C,
–1
Hexamolybdate 12b. Orange yellow solid. IR (KBr, cm ): 3159.23 (C–H), 3091.41 (C–H),
9
3
55.25 (Mo=O), 889.56 (Mo–O–Mo). Anal. Calcd. For C58
7.20; H, 2.26; N, 2.99. Found: C, 37.11; H, 2.23; N, 3.04.
H42Br
2
F
2
N
4
Mo O19 (1872.41): C,
6
–1
Hexamolybdate 12c. Orange yellow solid. IR (KBr, cm ): 3153.15 (C–H), 3096.18 (C–H),
9
3
48.23 (Mo=O), 881.07 (Mo–O–Mo). Anal. Calcd. For C58
6.56; H, 2.22; N, 2.94. Found: C, 36.47; H, 2.19; N, 3.01.
2 2 4 6
H42Br Cl N Mo O19 (1905.32): C,
–1
Hexamolybdate 12d. Orange yellow solid. IR (KBr, cm ): 3158.11 (C–H), 3097.44 (C–H),
9
3
41.60 (Mo=O), 892.75 (Mo–O–Mo). Anal. Calcd. For C58
4.93; H, 2.12; N, 2.81. Found: C, 34.88; H, 2.09; N, 2.84.
H42Br
4
N
4
Mo O19 (1994.23): C,
6
–1
Hexamolybdate 12e. Orange yellow solid. IR (KBr, cm ): 3161.20 (C–H), 3091.28 (C–H),
9
4
45.28 (Mo=O), 898.10 (Mo–O–Mo). Anal. Calcd. For C68
1.32; H, 3.26; N, 2.83. Found: C, 41.25; H, 3.22; N, 2.89.
2 4 6
H64Br N Mo O19 (1976.70): C,
–
1
Hexatungstate 13a. Yellow solid. IR (KBr, cm ): 3139.85 (C–H), 3048.49 (C–H), 980.56
W=O), 788.21 (W–O–W). Anal. Calcd. For C58 19 (2363.83): C, 29.47; H,
.88; N, 2.37. Found: C, 29.39; H, 1.86; N; 2.38.
(
2 4 6
H44Br N W O
1
–
1
Hexatungstate 13b. Yellow solid. IR (KBr, cm ): 3144.18 (C–H), 3040.13 (C–H), 981.67
W=O), 792.63 (W–O–W). Anal. Calcd. For C58 19 (2399.81): C, 29.03; H,
.76; N, 2.33. Found: C, 28.95; H, 1.71; N, 2.36.
(
2 2 4 6
H42Br F N W O
1
–
1
Hexatungstate 13c. Yellow solid. IR (KBr, cm ): 3143.59 (C–H), 3049.97 (C–H), 976.23
W=O), 792.14 (W–O–W). Anal. Calcd. For C58 Cl 19 (2432.72): C, 28.64; H,
.74; N, 2.30. Found: C, 28.59; H, 1.72; N, 2.33.
(
H42Br
2
2 4 6
N W O
1
–
1
Hexatungstate 13d. Yellow solid. IR (KBr, cm ): 3141.72 (C–H), 3036.36 (C–H), 979.30
W=O), 790.85 (W–O–W). Anal. Calcd. For C58 19 (2521.63): C, 27.63; H,
.68; N, 2.22. Found: C, 27.58; H, 1.66; N, 2.25.
(
4 4 6
H42Br N W O
1
–
1
Hexatungstate 13e. Yellow solid. IR (KBr, cm ): 3137.54 (C–H), 3029.12 (C–H), 978.86
W=O), 793.45 (W–O–W). Anal. Calcd. For C68 19 (2504.10): C, 32.62; H,
.58; N, 2.24. Found: C, 32.53; H, 2.55; N, 2.26.
(
2 4 6
H64Br N W O
2
1
1

A General Procedure for Obtaining Single Crystals, Suitable for Single Crystal X-ray
Crystallography.
A small amount of the ion pair compound (30 mg), to be recrystallized, was dissolved in
minimum amount of DMSO by sonication to prepare a saturated solution in a small vial. This
open small vial was then placed into an another bigger vial containing diethyl ether and the
bigger vial was then capped / closed so that diethyl ether diffused into DMSO solution of the
ion pair compound. Single crystals, appeared during one week or so, were subjected to single
crystal X-ray crystallography for data collection.
2
.2. Crystal structure determination
Single-crystals suitable for structural determination of the compounds 10a, 10d, 11a-e, 13a-
e, were mounted on a three circle Bruker SMARTAPEX CCD area detector system under Mo
Kα (λ = 0.71073 Å) graphite monochromated X-ray beam with crystal-to-detector distance of
6
0
0 mm, and a collimator of 0.5 mm width. The scans were recorded with a ω scan width of
.3°. Data reduction was performed by SAINTPLUS [31], empirical absorption corrections
using equivalent reflections were performed by program SADABS [32]. Structure solutions
were done using SHELXS-97 [33] and fullmatrix least-squares refinement was carried out
using SHELXL- 97 [34] for all compounds. All the non-hydrogen atoms were refined
anisotropically. Hydrogen atoms on the C atoms were introduced on calculated positions and
were included in the refinement riding on their respective parent atoms. Crystal data and
structure refinement parameters for the compounds are summarized in Tables 1-5.
3
3
9
. Results and discussion
.1. Synthesis
–Anthracene methanol (1) has been used as the starting precursor to obtain the anthracene
based cations. Treatment of one equivalent triphenyl phosphine with two equivalents of
molecular bromine generates the Lewis acid–base adduct PPh ·Br that brominates the
3
2
alcohol function of 1 whereas, the remaining free molecular bromine brominates the
th
anthracene ring at the 9 position resulting in the formation of the desired brominated
precursor 9–bromo–10–bromomethyl–anthracene (2) [9]. N–alkyl–imidazoles (4a–f) and N–
benzyl–benzimidazoles (7a–e) have been synthesized from imidazole (3) and benzimidazole
(
5) respectively, by means of base mediated electrophillic substitution at nitrogen (see
Scheme 3). All the reactions have been carried out in air in DMSO using NaOH as the base.
1
2

Choice over the solvent and base is arbitrary in the present study as any other solvents like
THF, MeCN, toluene etc. or base like triethylamine, diisopropylamine, sodium hydride etc.
can also be conveniently used for these reactions.
Scheme 3. Synthesis of the N–alkyl–imidazoles and N–benzyl–benzimidazoles.
Sometimes, usage of a phase transfer catalyst, for example, 18–crown–6,
tetrabutylammonium bromide, benzenetriethylammonium chloride etc. help in smoother
progress of such reactions. However, in the present case, no phase transfer catalyst has been
used, as the monitoring of the reactions by TLC indicates clear progress of the same without
any catalyst. Similarly, reaction conditions, such as, dry solvent or heat etc. have not explored
any considerable improvement of the product yields, thereby the reactions were carried out in
air at an ambient condition. Addition of 1.5 equiv. of base in a DMSO solution of 3 or 5,
followed by slow addition of the corresponding electrophiles (alkyl bromides or benzyl
chlorides) at 20–25 ºC results in formation of the products (4a–f and/or 7a–3, Scheme 3).
They have been isolated in good yields after regular workups followed by purification
through column chromatography (silica gel, 100–200 mesh, MeOH : EtOAc = 5:95 v/v, see
experimental section). Purification of the N–alkyl imidazoles by distillation method has been
avoided because of their high boiling points and chances of product loss due to
decomposition at elevated temperature. All the isolated compounds have been characterized
1
13
by NMR ( H and C) spectroscopy, LC–MS and successful elemental analysis.
1
3

Scheme 4. Synthesis of the POM–anthracene ion–pair compounds.
Reactions between 9–bromo–10–(bromomethyl)anthracene (2) and the corresponding
N–alkyl imidazoles (4a–f) / N–benzyl benzimidazoles (7a–e) in THF under refluxing
condition have resulted in precipitation of the corresponding bromide salts 8a–f and 9a–e
respectively (see Scheme 4), that have been isolated by filtration. Stoichiometric ion–
exchange between these salts with [Bu
4
N]
2
[M O19] (2:1) (M = Mo, W) in acetonitrile renders
6
immediate precipitation of the hexamolybdate or hexatungstate salts of the anthracene
cations. Molybdate salts (10a–f, 12a–e, Scheme 4) are orange in color while tungstates
(
11a–f, 13a–e, Scheme 4) are yellow- colored. Single crystals, suitable for X–ray diffraction
analysis, have been grown by diffusion of diethyl ether into DMSO solutions of the
respective POM salts.
3
.3. Description of Crystal structures
The hexametalate POM cluster anions have isometric (almost spherical) shape and the
polyaromatic hydrocarbon anthracene is of highly anisometric (flat) shaped with π–electron
clouds above and below the plane of the molecule. Therefore, to co-crystallize these
structurally incompatible / mismatched molecular components (hexametalates and
anthracene), sufficient energy should be provided to overcome the destabilization that arises
due to presence of them in the same crystal lattice. In this regard, Coulombic forces have
1
4

been shown to play the major role towards the stabilization of the co-crystals, thus built from
2
7
the structurally mismatched components. Basically one cationic fragment should be
attached with the anthracene ring to associate the cation with the POM surface through
electrostatic / Coulombic forces and the anthracene ring, if possible, would orient itself to the
POM surface. Thus, in the present case, N–alkyl imidazolium or N–benzyl benzimidazolium
moieties have been used as the cationic anchors to the anthracene–based cations. The cationic
counterparts in all the cases are attached to the anthracene ring via a methylene spacer (–
2
CH –). Although the solids (10a–13e, Scheme 4), obtained by the ionic metathesis between
the POM cluster anions (tetrabutylammonium salt) and anthracene–based cations (bromide),
can best be considered as salts or ion–pair solids, we would like to use the phrase 'Coulombic
co-crystals' to describe them. The reason, we have used this term, is the Coulombic forces
that contribute towards the stabilization of such isometric : anisometric cocrystals (10a–13e,
Scheme 4). X-ray diffraction quality crystals have been grown using ether as the anti-solvent
(
precipitant) to the DMSO solutions of the respective solids.
Molecular structures of the crystallographically characterized solids have been presented
in Figures 1–2. Mainly the tungstate salts have been structurally characterized. For the
comparison purpose, two molybdates (10a and 10d) have been crystallographically
characterized. Crystals of molybdate- and tungstate-salts of the same countercation are found
to be isomorphous / isostructural, as observed from unit cell parameters of the compounds
1
0a and 11a (or 10d and 11d), that are almost identical, thereby making the molecules in the
concerned solids pack under same space symmetry. Thus, changing the metal centers of the
Lindqvist type isopolyanions from molybdenum to tungsten has not induced any significant
alteration of the molecular ensemble. This is clearly in accord with the expectation as both
2
–
2–
6 6
the [Mo O19] and [W O19] cluster anions have many similar features e.g. almost spherical
h
shape, octahedral symmetrical (O ) etc. The crystal structures of ion pair compounds 13a–e
are presented in Figure 3.
All crystal structures consist of two cations and one POM cluster anion.
Some of the crystals have been isolated as DMSO solvates. Structural analysis of the
relevant solids reveals some common features, which are summarized below.
(
a)
Asymmetric units of all the crystal structures consist of one anthracene–based mono–
cation and half of the POM cluster di–anion for electro-neutrality. All the molecules
are centrosymmetric with respect to the centre of inversion at the central oxygen
atom of the POM cluster anions. The full molecules are generated upon operation of
the inversion symmetry on the concerned asymmetric units. Therefore, the title solids
1
5

have maintained 2:1 stoichiometry between the cations and the anions and the
respective solids are considered as stoichiometric solids.
(
(
b)
c)
The imidazolium / benzimidazolium cationic counterparts in all the structures have
been observed to face toward one of the octrahedral facets of the POM cluster anions
due to Coulombic association between them.
The anthracene rings are away of the POM surfaces and pack with each other through
π···π stacking interactions. No π···POM interactions are observed in the relevant
crystals where the π–stacked anthracenes interact with the POM cluster anions only
by C–H···O weak hydrogen bonding interactions. Thus, the solids described in this
article cannot be considered as donor–acceptor π···POM solids even though they are
intensely colored contrast to their starting precursors in their solid states.
Two different space symmetry viz. P–1 (triclinic) and P2
for the crystal packing of the compounds containing anthracene–imidazolium counter cations
10a–11f). The crystals, containing methyl, i–propyl, hexyl and decyl alkyl chains in the
1
/c (monoclinic) have been observed
(
imidazolium cationic counterparts, feature packing of the molecules obeying the lower space
symmetry (P–1). But, in case of the n–propyl and butyl alkyl chains, the molecules tend to
crystallize under higher special symmetry (P2 /c). This symmetry alteration might be due to
1
variation of the hydrogen boding environments in the relevant solids. In all the cases,
molecules have crystallized with one cation and half of the POM cluster anion in the
asymmetric unit (Z' = ½). In the symmetric unit, the two cations are related to each other by
the inversion symmetry with respect to the central oxygen atom of the cluster anion.
Although the structural analysis of the solids 11a–f exhibit many similarities in packing of
the molecules, a little change in the intermolecular interactions has been observed with the
variation of the alkyl chain lengths in the cations. The imidazolium ring has a rotational
freedom around the C(15)–N(1) bond and this rotation determines the dihedral angle between
the anthracene and imidazolium planes. Variation of the alkyl chain lengths in the
imidazolium cations causes a change in this torsion angle in an irregular manner. There is a
partial overlapping between the anthracene rings in the relevant crystals as shown in Figure 4.
In the crystal structures of the compounds 10a, 11c and 11e, the imidazolium and anthracene
planes are oriented in such an angular span, that interactions between two inversion
symmetry related cations result in the formation of a π–stacked dimer (10a, 11c and 11e,
Figure 4). The crystals of other compounds of Figure 4 exclude such dimer formation due to
improper spatial orientation of the imidazole and the anthracene rings, although there is C–
H···π stacking interactions between the alkyl chain of one cation with the anthracene ring of
1
6

the other inversion related cation. No direct interaction between the π–cloud of the anthracene
ring and the POM surface is noticed in these solids. Thus, the lattice energy of such
Coulombic cocrystals incorporating both flat and spherical shaped molecular components are
minimized by the abundance of Coulombic association between the imidazolium cations and
POM anions, C–H···O weak hydrogen bonding interactions with the POM acceptors, C–
H···π and π···π stacking interactions between the various crystal components.
In all these solids, the anthracene cations have packed with each other through π···π
stacking interactions in a trans–fashion as far as orientations of the N–alkyl imidazolium
moieties and bromine atoms are concerned. A little change in the distance between centroids
of two such stacked anthracene rings has been observed with the variation of the alkyl chain.
These π–stacked anthracene rings have further interacted with the POM anions through C–
H···O supramolecular interactions in an alike fashion as mentioned in Scheme 1a.
Rotational freedom of C–C bond around the benzimidazolium plane in 13a-13e
The crystal structures, discussed so far, contain only one π–ring i.e. the anthracene ring
attached to the imidazolium moiety. The situation is bit different in the case of N–benzyl
benzimidazolium cations which consist of more number of π–rings. The imidazolium cation
consists only one π–ring-system, i.e. the anthracene ring but the benzimidazolium cations
comprise of three π–rings viz. the anthracene ring, benzimidazole ring and the phenyl ring of
the benzyl counterpart. Both the anthracene and the benzene ring of the benzyl fragment have
C–C rotational freedom around the benzimidazolium plane (Table 6). Thus, these cations are
more puckred compared to the alkylimidazolium cations. The only structural difference
between the benzimidazolium cations is the variation of bulkiness in the benzyl group. As
previously stated, PXRD analysis of the molydates and the tungstates have revealed
isostructurality between the two, only the tungstate analogous (13a–e) have been
crystallographically characterized. The solid 12a and 13a do not contain any substitution on
the benzyl ring whereas, in case of the others, bulkiness of the benzyl groups has been
increased by attaching F (12b, 13b), Cl (12c, 13c), Br (12d, 13d) and five methyl groups
(
12e, 13e). Depending upon the spatial spans of the anthracene and the phenyl (benzyl) rings,
the cations can be classified into three rotamers i.e. eclipsed, gauche and staggered as shown
in Table 6. If both of them are projected at the same side of the benzimidazolium plane, the
conformation of the concerned cation is eclipsed. Similarly, if the relevant C–C rotations
make them to flang on opposite direction of the mentioned plane, then the conformation of
the cation is staggered. For the gauche conformation, both the rings are on the same direction
1
7

of the benzimidazolium plane, but at a certain dihedral angle between 0 and 180º. Crystal
structures of the solids 13a–e have been presented in Figure 3.
As shown in Figure 3, structures of all the compounds 13a–e are characterized by one
cation and half of the POM cluster anion in the asymmetric unit (Z' = ½). In the relevant
crystals, two different orientations of the anthracene and the phenyl (benzyl) rings have been
observed with respect to the benzimidazolium plane. Several observed angular parameters in
the concerned crystal structures have been summarized in Table 6. Crystallographically
observed angular spans of the anthracene and the phenyl ring of the benzyl fragment have
been pictorially represented in Figure 5 that clearly depicts eclipsed and gauche orientations
of the concerned rings in the relevant crystals. However, alike all the crystals built from N–
alkyl imidazolium cations, the present case also demonstrate similar crystal packing features
and will not be discussed separately. For example, in all the crystals (13a–e), the anthracene
rings are stacked with each other via π···π stacking interactions, the benzimidazolium
cationic counterparts are oriented toward a facet of the POM anions due to Coulombic
association and the cations are further associated with the POM cluster anions via
supramolecular C–H···O hydrogen bonding interactions. Two representative crystal–packing
features have been displayed in Figure 6. Due to more bulkiness of the benzyl
benzimidazolium cations compared to the alkyl imidazolium cations, complete overlap
between the π–electron clouds of two anthracene rings have been forbidden and a partial
overlapping between the two rings have been observed in the relevant crystals. Thus,
changing the cation from alkyl imidazolium to benzyl benzimidazolium has not induced
much difference in the packing feature of the molecules in their respective crystals.
Spectroscopy
2
‒
It has already been mentioned that, the hexamolybdate ([Mo
6
O
19] ) salts are intense
2
‒
orange–red and the hexatungstate ([W O19] ) salts are intense yellow in color in their solid
6
states. Dissolution of the molybdates in DMF or in DMSO (these salts are not soluble in
other common organic solvents e.g. MeCN, MeOH etc.) causes disappearance of the orange-
red color and a pale yellow color persists in the solution. Absorption spectra of the resulting
solutions are found to be equivalent to that obtained from a 2:1 physical mixture of the
4 2 6
anthracene cations and [Bu N] [Mo O19]. Even the absorption properties of the solutions
remain invariant upon addition of large amount of the ionic counterparts. The corresponding
absorption spectra are characterized by discrete and broad absorptions due to the anthracene
cations and the hexamolybdate cluster anion in solution. The similar matter is observed for
the hexatungstate analogues. Contrast to the solution–state absorption spectra of the
1
8

concerned solids, the solid–state absorption spectra show remarkable difference. Absorption
spectra of the concerned solids have been obtained by the diffused reflectance technique by
dispersing the powdery samples in BaSO
e), [Bu N] [Mo 19] and [Bu N] [W 19] are transparent (solid–state) at wavelengths more
than 500 nm. The [Bu N] [W 19] cluster absorb at higher energy (λmax < 300 nm) than the
Bu N] [Mo 19] cluster (λmax ≈ 345 nm). Both of the cluster precursors exhibit structureless
4
. Both the various anthracene cations (8a-f and 9a-
4
2
6
O
4
2
6
O
4
2
6
O
[
4
2
6
O
absorption patterns. A structured broad absorption band (λmax ≈ 380 nm) features the solid–
state absorption spectra of the anthracene cations as shown in Figure 7. Also, the 2:1 physical
mixtures of the anthracene bromide salts and the POM tetrabutylammonium salts exhibit the
similar feature. The concerned ion–exchanged molybdates, described in this article, rather
feature a modulated absorption spectra i.e. appearance of a new band (or tail) in the visible
region of the spectra (λ > 500 nm). The yellow tungstates exhibit a tail initiating from ca.
5
50 nm. Again, in all the cases, the absorption spectra of the anthracene–POM salts exhibit
very distinct features than the same of their ionic parents. For example, the absorption bands
due to the hexametalate cluster anions and anthracene remain indistinctive in the absorption
spectra of the anthracene–POM solids demonstrated here. Therefore, commencement of the
new bands in the visible region is due to some sort of interaction between the molecular
components only in the solid state. In another words, it can be said that spectroscopic
identities of the anthracene and hexametalate counterparts vanish upon their ionic and
supramolecular association in the solid state and results in an intense color of the resulting
ion pair compounds in their solid states. This intense color of the ion pair compounds in their
solid state is probably due to the broad shoulder-like feature in the region of 450-550 nm in
their diffuse reflectance spectra (Figure 7). We assign this feature as solid state intra-ion-pair
transition.
4
. Conclusion
Surprisingly, crystallographic analyses on the present synthesized solids (10a–11f, 12a–
1
3e) have not revealed any π···POM interaction between anthracene and the POM cluster
anions. Single crystal- as well as powder X–ray diffraction analyses show that both the
molybdate and tungstate salts of the same counter cation are isostructural.
In conclusion, a series of hexametalate cluster based solids comprising of various
anthracene-imidazolium and anthracene-benzimidazolium cationic counterparts have been
synthesized and their structures have been determined through crystallography. Both the
hexamolybdates and hexatungstates of the same counter cation are isomorphous. All the
1
9

solids maintain 2:1 stoichiometry between the mono-cations and the di-anions and are
centrosymmetric with respect to the central oxygen atom of the octahedral symmetrical
POMs. The cationic counterparts (imidazolium and benzimidazolium) in all the solids project
toward surface of the POMs due to electrostatic interaction between the oppositely charged
species. Apart from coulombic association between the anthracenes and the POM,
supramolecular hydrogen bonding interactions are also observed to optimize the lattice
destabilization due to coexistence of the structurally mismatched molecular components in
the same crystal. Color of the molybdates are observed only in the solid state and probably no
adduct formation takes place in the solution state as revealed by the solid state as well as the
solution state UV-visible spectroscopy. Variation of the alkyl chain lengths in the
imidazolium cationic moiety or alteration of the substituent in the benzimidazolium moiety
does not change the intermolecular association of the components to a greater extent.
Possibly, due the shorter spacer, the anthracene ring could not interact with the POM surface,
which results in charge transfer interaction between the two. In the solid state, the title
compounds show an intense color (that is absent in both of their constituents, cations and
anions), which has been assigned to a solid state intra-ion-pair transition.
Acknowledgements
We thank SERB, Department of Science and Technology (DST), Government of India, for
financial support (Project No. SB/S1/IC-34/2013). We also thank UPE-II (UGC) for some
financial support.
Appendix A. Supplementary data
CCDC 1514215, CCDC 1514216 and CCDC 1514231 contain the supplementary
crystallographic data for compounds 10a, 11a and 10d respectively. CCDC 1514232 –
CCDC 1514241 contain the supplementary crystallographic data for compounds 11b-f and
1
3a-e respectively. Relevant crystal data can be obtained free of charge via
http://www.ccdc.cam.atc.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.
2
0

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(
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[
[
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Table 1 Crystal data and structure refinement parameters for compounds 10a and 10d
0a 10d
Mo Mo
1
Empirical formula
Formula weight
T (K), λ (Å)
Crystal system
Space group
a(Å)
C
42
H
44Br
2
6
N
4
O
21
S
2
C
48
H
55Br
2
6 4 21 2
N O S
1740.39
1824.55
298(2), 0.71073
triclinic
P-1
298(2), 0.71073
monoclinic
P21/c
10.705(5)
11.509(5)
12.013(6)
116.856(6)
99.2150(10)
90.529(7)
1317.1(10)
1, 2.194
11.0467(7)
12.3811(8)
22.1829(14)
90.00
99.2150(10)
90.00
2994.8(3)
2, 2.023
2.699, 1788
1.032
b(Å)
c(Å)
O
α( )
O
β( )
O
γ( )
V(Å )
3
-3
Z, dcalcd(g cm )
-1
µ(mm ), F(000)
3.062, 846
1.059
2
GooF on F
R
R
1
/wR
/wR
2
[I˃2σ(I)]
(all data)
0.0312/0.0801
0.0384/0.0836
0.0458/0.1069
0.0805/0.1214
0.772/-0.434
1
2
-3
Largest diff. peak/hole(e.Å ) 0.657/-0.553
2
7

Table 2 Crystal data and structure refinement parameters for compounds 11a-c
1a 11b
1
11c
Empirical formula
C
42
H44Br
2
N
4
C
46
H52Br
2
N
4
C
46
H52Br
2
N
4
O
21
S
2
W
6
O
21
S
2
W
6
O
21
S
2
W
6
Formula weight
T (K), λ (Å)
Crystal system
Space group
a(Å)
2267.85
2323.94
2323.96
298(2), 0.71073 298(2), 0.71073
triclinic
P-1
298(2), 0.71073
triclinic
P-1
monoclinic
P2 /c
1
10.799(3)
11.533(3)
12.016(3)
117.088(4)
93.323(4)
90.887(4)
1328.6(6)
1, 2.819
10.371(4)
12.851(5)
21.899(8)
90.00
93.172(7)
90.00
2914.2(19)
2, 2.642
13.313, 2128
1.373
10.1433(12)
11.7753(14)
13.1042(16)
67.945(2)
87.633(2)
86.138(2)
1447.1(3)
2, 2.585
13.405, 1070
1.204
b(Å)
c(Å)
O
α( )
O
β( )
O
γ( )
V(Å )
3
-3
Z, dcalcd(g cm )
-1
µ(mm ), F(000)
14.597, 1026
1.060
2
GooF on F
R
R
1
/wR
/wR
2
[I˃2σ(I)]
(all data)
0.0203/0.0509
0.0232/0.0520
0.0932/0.1750
0.1032/0.1792
1.852/-1.362
0.0399/0.0847
0.0442/0.0865
1.241/-1.134
1
2
-3
Largest diff. peak/hole(e.Å ) 0.685/-0.884
Table 3 Crystal data and structure refinement parameters for compounds 11d-f
11d
11e
11f
Empirical formula
C
48
H48Br
2
N
4
C
48
H52Br
2
N
4
C
56
H68Br
2
N
4
O
21
S
2
W
6
O
19
W
6
O
19
W
6
Formula weight
T (K), λ (Å)
Crystal system
Space group
a(Å)
2383.94
298(2), 0.71073
monoclinic
2251.86
2364.06
298(2), 0.71073
triclinic
P-1
298(2), 0.71073
triclinic
P-1
P2
1
/c
11.120(3)
12.375(3)
22.166(5)
90.00
99.222(4)
90.00
9.9087(11)
11.7099(13)
12.4878(13)
107.775(2)
90.262(2)
94.106(2)
1375.7(3)
1, 2.718
11.2164(16)
11.9454(17)
12.8091(18)
76.337(2)
85.806(2)
70.853(2)
1575.4(4)
1, 2.492
b(Å)
c(Å)
O
α( )
O
β( )
O
γ( )
V(Å )
3
3010.9(12)
2, 2.585
-3
Z, dcalcd(g cm )
2
8

-
1
µ(mm ), F(000)
12.887, 2156
1.022
14.020, 1034
0.990
12.250, 1098
1.317
2
GooF on F
R
R
1
/wR
/wR
2
[I˃2σ(I)]
(all data)
0.0316/0.0737
0.0429/0.0787
0.0431/0.0822
0.0694/0.0909
-0.771/0.176
0.0554/0.0909
0.0633/0.0933
1.073/-1.405
1
2
-3
Largest diff. peak/hole(e.Å ) 1.470/-1.161
Table 4 Crystal data and structure refinement parameters for compounds 13a-c
3a 13b
1
13c
Cl
Empirical formula
C
58
H44Br
2
N
4
C
66
H66Br
2
F
2
C
58
H
42Br
2
2
N
4
O
21
W
6
N
4
O
23
S
4
W
6
O
19
W
6
Formula weight
T (K), λ (Å)
Crystal system
Space group
a(Å)
2363.89
2712.39
2432.78
298(2), 0.71073
monoclinic
298(2), 0.71073 298(2), 0.71073
triclinic
P-1
triclinic
P-1
1
P2 /c
9.4925(12)
10.1101(12)
15.7024(19)
92.964(2)
100.955(2)
97.339(2)
1462.9(3)
1, 2.683
11.628(3)
11.924(3)
15.585(4)
92.288(4)
110.777(3)
109.182(3)
1878.1(7)
1, 2.398
11.8559(12)
12.5348(13)
25.243(3)
90.00
97.995(2)
90.00
3714.9(7)
2, 2.175
10.463, 2236
0.987
b(Å)
c(Å)
O
α( )
O
β( )
O
γ( )
V(Å )
3
-3
Z, dcalcd(g cm )
-1
µ(mm ), F(000)
13.192, 1086
1.219
10.407, 1270
1.115
2
GooF on F
R
R
1
/wR
/wR
2
[I˃2σ(I)]
(all data)
0.0355/0.0772
0.0377/0.0782
0.0670/-1.705
0.0593/0.1547
0.0634/0.1575
2.439/-3.877
0.0403/0.0790
0.0597/0.0841
1.196/-0.799
1
2
-3
Largest diff. peak/hole(e.Å )
Table 5 Crystal data and structure refinement parameters for 13d and 13e
13d
13e
Empirical formula
Formula weight
T (K), λ (Å)
Crystal system
Space group
a(Å)
C
58
H
42Br
4
W
6
N
4
O
19
C
68
H
2 6 4 19
64Br W N O
2521.70
298(2), 0.71073
monoclinic
2504.15
298(2), 0.71073
triclinic
P-1
P2
1
/c
12.1119(15)
11.357(8)
2
9