Organooxotin cages, {[(n-BuSn)3(μ3-O)(OC6H 4-4-X)3]2[HPO3]4}, X = H, Cl, Br, and I, in double O-capped structures: Halogen-bonding-mediated supramolecular formation

Article abstract of DOI:10.1021/om050269x

The reaction of n-BuSn(O)(OH) with H₃PO₃ and HOC ₆H₄-4-X (X = H, Cl, Br, and I) afforded the hexanuclear organooxotin cages {[(n-BuSn)₃(μ₃-O)(OC ₆H₄-4-X)₃]₂[HPO₃] ₄}, where X = H (1), Cl (2), Br (3), and I (4), in moderate yields. These cages possess double O-capped structures. The oxotin cages 1-4 contain two tritin motifs that are joined by four tripodal [HPO₃]^2- ligands. The three tin atoms in each tritin subunit are held together by a μ₃-capping oxygen atom. In addition three phenolate oxygen atoms act as μ₂-bridging ligands between two tin atoms. The molecular structures of 1-4 are intimately related to other organooxotin cages such as the O-capped cluster, the drum, and the football cage. The crystal structures of 2-4 reveal intermolecular halogen-bonding-mediated [X- - -O (X = Cl, Br), I- - -I, and I- - π] supramolecular assemblies.

Full text of DOI:10.1021/om050269x

4926
Organometallics 2005, 24, 4926-4932
Organooxotin Cages,
{[(n-BuSn)3(µ3-O)(OC6H4-4-X)3]2[HPO3]4}, X ) H, Cl, Br,
and I, in Double O-Capped Structures:
Halogen-Bonding-Mediated Supramolecular Formation
Vadapalli Chandrasekhar,*,† Viswanathan Baskar,† Kandasamy Gopal,† and
Jagadese J. Vittal‡
Department of Chemistry, Indian Institute of Technology, Kanpur-208 016, India, and
Department of Chemistry, National University of Singapore, Singapore 117543
Received April 9, 2005
The reaction of n-BuSn(O)(OH) with H3PO3 and HOC6H4-4-X (X ) H, Cl, Br, and I) afforded
the hexanuclear organooxotin cages {[(n-BuSn)3(µ3-O)(OC6H4-4-X)3]2[HPO3]4}, where X )
H (1), Cl (2), Br (3), and I (4), in moderate yields. These cages possess double O-capped
structures. The oxotin cages 1-4 contain two tritin motifs that are joined by four tripodal
[HPO3]2- ligands. The three tin atoms in each tritin subunit are held together by a µ3-capping
oxygen atom. In addition three phenolate oxygen atoms act as µ2-bridging ligands between
two tin atoms. The molecular structures of 1-4 are intimately related to other organooxotin
cages such as the O-capped cluster, the drum, and the football cage. The crystal structures
of 2-4 reveal intermolecular halogen-bonding-mediated [X- - -O (X ) Cl, Br), I- - -I, and I- - -
π] supramolecular assemblies.
Introduction
munication, we have recently reported the formation of
a new structural form of an organooxotin cage, {[(n-
BuSn)3(µ3-O)(OC6H5)3]2[HPO3]4} (1), in a three-compo-
nent reaction that involves the organotin precursor, a
phosphorus-based acid, and a co-ligand, phenol.2b Herein,
we report the complete details of these investigations.
Accordingly, the following account describes the syn-
thesis and structural characterization of the double
O-capped clusters {[(n-BuSn)3(µ3-O)(OC6H4-4-X)3]2-
[HPO3]4}, where X ) H (1), Cl (2), Br (3), and I (4). We
also demonstrate, in the crystal structures of 2-4, the
halogen-bonding-mediated [X- - -O (X ) Cl, Br), I- - -I,
and I- - -π] supramolecular formation of organooxotin
compounds.
The remarkable structural adaptability of the stan-
noxane and distannoxane units has been initially dem-
onstrated by the research group of Holmes.1 Subse-
quently, a rich structural chemistry of the rings, cages,
and clusters containing stannoxane and distannoxane
motifs has emerged from our laboratory2,3 as well as
those of other research groups drawn across the world.4-7
Most of the organooxotin cages are essentially two-
component reactions and involve the use of n-BuSn(O)-
(OH) and a protic acid such as carboxylic, phosphinic,
phosphonic, or sulfonic acid.8 In a preliminary com-
* To whom correspondence should be addressed. E-mail: vc@iitk.ac.in.
Phone: (+91) 512-259-7259. Fax: (+91) 512-259-0007/7436.
† Indian Institute of Technology.
(4) (a) Swamy, K. C. K.; Said, M. A.; Nagabrahmanandachari, S.;
Poojary, D. M.; Clearfield, A. J. Chem. Soc., Dalton Trans. 1998, 1645.
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D. J. Chem. Soc., Dalton Trans. 2000, 4021. (c) Mehring, M.; Paulus,
I.; Zobel, B.; Schu¨rmann, M.; Jurkschat, K.; Duthie, A.; Dakternieks,
D. Eur. J. Inorg. Chem. 2001, 153. (d) Beckmann, J.; Dakternieks, D.;
Duthie, A.; Mitchell, C. Organometallics 2003, 22, 2161.
(5) (a) Xiang, J.; Toyoshima, S.; Orita, A.; Otera, J. Angew. Chem.,
Int. Ed. 2001, 40, 3670. (b) Otera, J. Acc. Chem. Res. 2004, 37, 288. (c)
Kemmer, M.; Biesemans, M.; Gielen, M.; Martins, J. C.; Gramlich, V.;
Willem, R. Chem. Eur. J. 2001, 7, 4686. (d) Chaniotakis, N.; Jurkschat,
K.; Mu¨ller, D.; Perdikaki, K.; Reeske, G. Eur. J. Inorg. Chem. 2004,
2283.
(6) (a) Garc´ıa-Zarracino, R.; Ramos-Qui_ones, J.; Ho¨pfl, H. Inorg.
Chem. 2003, 42, 3835. (b) Ma, C.; Jiang, Q.; Zhang, R.; Wang, D. J.
Chem. Soc., Dalton Trans. 2003, 2975. (c) Garc´ıa-Zarracino, R.; Ho¨pfl,
H. Angew. Chem., Int. Ed. 2004, 43, 1507; J. Am. Chem. Soc. 2005,
127, 3120. (d) Prabusankar, G.; Murugavel, R. Organometallics 2004,
23, 5644.
(7) (a) Zheng, G.-L.; Ma, J.-F.; Su, J.-M.; Yan, L.-K.; Yang, J.; Li,
Y.-Y.; Liu, J.-F. Angew. Chem., Int. Ed. 2004, 43, 2409. (b) Zheng, G.-
L.; Ma, J.-F.; Yang, J.; Li, Y.-Y.; Hao, X.-R. Chem. Eur. J. 2004, 10,
3761. (c) Dea´k, A.; Ta´rka´nyi, G. Chem. Commun. 2005, 4074.
(8) (a) Chandrasekhar, V.; Nagendran, S.; Baskar, V. Coord. Chem.
Rev. 2002, 235, 1. (b) Chandrasekhar, V.; Gopal, K. Appl. Organomet.
Chem. 2005, 19, 429. (c) Chandrasekhar, V.; Gopal, K.; Sasikumar,
P.; Thirumoorthi, R. Coord. Chem. Rev. 2005, 249, 1745.
‡ National University of Singapore.
(1) (a) Chandrasekhar, V.; Day, R. O.; Holmes, R. R. Inorg. Chem.
1985, 24, 1970. (b) Day, R. O.; Holmes, J. M.; Chandrasekhar, V.;
Holmes, R. R. J. Am. Chem. Soc. 1987, 109, 940. (c) Holmes, R. R.;
Schmid, C. G.; Chandrasekhar, V.; Day, R. O.; Holmes, J. M. J. Am.
Chem. Soc. 1987, 109, 1408. (d) Swamy, K. C. K.; Day, R. O.; Holmes,
R. R. J. Am. Chem. Soc. 1987, 109, 5546. (e) Holmes, R. R. Acc. Chem.
Res. 1989, 22, 190. (f) Day, R. O.; Chandrasekhar, V.; Swamy, K. C.
K.; Holmes, J. M.; Burton, S. D.; Holmes, R. R. Inorg. Chem. 1988, 27,
2887.
(2) (a) Chandrasekhar, V.; Nagendran, S.; Bansal, S.; Powell, D. R.
Angew. Chem., Int. Ed. 2000, 39, 1833. (b) Chandrasekhar, V.; Baskar,
V.; Vittal, J. J. J. Am. Chem. Soc. 2003, 125, 2392. (c) Chandrasekhar,
V.; Nagendran, S.; Gopal, K.; Steiner, A.; Zacchini, S. Chem. Commun.
2003, 862. (d) Chandrasekhar, V.; Baskar, V.; Boomishankar, R.;
Gopal, K.; Zacchini, S.; Bickley, J. F.; Steiner, A. Organometallics 2003,
22, 3710.
(3) (a) Chandrasekhar, V.; Baskar, V.; Steiner, A.; Zacchini, S.
Organometallics 2004, 23, 1390. (b) Chandrasekhar, V.; Nagendran,
S.; Azhakar, R.; Ravikumar, M.; Srinivasan, A.; Ray, K.; Chan-
drashekar, T. K.; Madhavaiah, C.; Verma, S.; Priyakumar, U. D.;
Sastry, G. N. J. Am. Chem. Soc. 2005, 127, 2410. (c) Chandrasekhar,
V.; Gopal, K.; Nagendran, S.; Singh, P.; Steiner, A.; Zacchini, S.;
Bickley, J. F. Chem. Eur. J. 2005, 11, 5437. (d) Chandrasekhar, V.;
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11556.
10.1021/om050269x CCC: $30.25 © 2005 American Chemical Society
Publication on Web 09/15/2005

Organooxotin Cages
Organometallics, Vol. 24, No. 21, 2005 4927
Chart 1. Monoorganooxotin Cages: O-Capped Cluster, Drum, and Football Cage
Results and Discussion
and the in situ generation of the reactants [HPO3]2- and
[C6H5O]-.2b The cages 1-4 are thermally stable solids
with high decomposition points (vide infra, see Experi-
mental Section). The 31P{1H} NMR spectra of 1-4 show
a single resonance with nearly the same chemical shift
(0.54-0.58 ppm). A strong 1J(P-H) coupling is observed
in each case (688-690 Hz). The 119Sn NMR show upfield
resonances and are consistent with the coordination
environment around the tin atoms (1C, 5O).8
Molecular Structures of 2-4. The molecular struc-
tures of 1-4 are very similar and show spherical cage-
like architectures. The structure of 1 has been previ-
ously reported by us in a preliminary communication.2b
The molecular structure of 2 is shown in Figure 1 and
is discussed below. The molecular structures of 3 and 4
are given in the Supporting Information.
The structure of 2 reveals that its asymmetric unit
contains two molecules (Figure 1). All the tin atoms
present in 2 have a coordination number of six (1C, 5O);
this coordination is derived from one alkyl group, one
µ3-capping oxygen atom, two µ2-capping phenolate
oxygen atoms, and two phosphonate oxygen atoms. The
molecular structure of 2 can be described as a spherical
cage that contains two centrosymmetrically related
Sn3O4 subunits. Each of these subunits contains three
mutually perpendicular Sn2O2 four-membered rings
(Figure 1). One oxygen atom (O4) of this core is
µ3-bridging and is involved in the capping of Sn1, Sn2,
and Sn3 atoms; the other three oxygen atoms (O1, O2,
and O3) are derived from the phenoxide ligand and
bridge only two tin atoms. The Sn-O distances involv-
Synthesis. Three related structural forms in orga-
nooxotin cages, viz., the O-capped cluster, the drum, and
the football cage, are formed in three different reactions
involving n-BuSn(O)(OH). Thus, the reaction of n-BuSn-
(O)(OH) with diphenylphosphinc acid affords the tri-
nuclear O-capped cluster {[n-BuSn(OH)O2PPh2]3O}+-
{Ph2PO2}- (Chart 1).1b On the other hand the reaction
of n-BuSn(O)(OH) with many carboxylic acids and also
phosphates such as (PhO)2P(O)(OH) affords the hex-
americ drums, [n-BuSn(O)O2CR]6 or [n-BuSn(O)O2P-
(OPh)2]6.1e,f,8 The reactions of many aryl sulfonic acids
with n-BuSn(O)(OH) afford the dodecanuclear football
cages [(n-BuSn)12O14(OH)6]2+[RSO3-]2 (Chart 1).9a,b The
latter can also be obtained in alternative hydrolytic
reactions involving appropriate organotin precursors.9c-e
In contrast to these two-component reactions, the reac-
tion of n-BuSn(O)(OH) with H3PO3 in the presence of
phenols, HOC6H4-4-X (X ) H, Cl, Br, and I), affords the
hexanuclear double O-capped clusters 1-4 in moderate
yields (vide infra, see Experimental Section) (Scheme
1). As reported earlier by us, 1 can also be synthesized
in a reaction between n-BuSn(O)(OH) and (PhO)2P(O)H
which involves the hydrolytic scission of the P-O bond
(9) (a) Eychenne-Baron, C.; Ribot, F.; Sanchez, C. J. Organomet.
Chem. 1998, 567, 137. (b) Eychenne-Baron, C.; Ribot, F.; Steunou, N.;
Sanchez, C.; Fayon, F.; Biesemans, M.; Martins, J. C.; Willem, R.
Organometallics 2000, 19, 1940. (c) Banse, F.; Ribot, F.; Tole´dano, P.;
Maquet, J.; Sanchez, C. Inorg. Chem. 1995, 34, 6371. (d) Jaumier, P.;
Jousscaume, B.; Lahcini, M.; Ribot, F.; Sanchez, C. Chem. Commun.
1998, 369. (e) Dakternieks, D.; Zhu, H.; Tiekink, E. R. T.; Colton, R.
J. Organomet. Chem. 1994, 476, 33.

4928 Organometallics, Vol. 24, No. 21, 2005
Chandrasekhar et al.
Figure 1. View of the two molecules of 2 present in its asymmetric unit. The unlabeled atoms are symmetry related to
the labeled atoms. Selected bond distances (Å) and angles (deg) for one of the molecules: Sn1-O1 2.149(5), Sn1-O2 2.164-
(6), Sn1-O4 2.044(5), Sn1-O5 2.065(5), Sn1-O6 2.062(5), Sn1-C1 2.113(8), Sn2-O1 2.213(5), Sn2-O3 2.133(6), Sn2-
O4 2.044(5), Sn2-O9 2.068(5), Sn2-O10 2.061(6), Sn2-C5 2.102(8), Sn3-O2 2.209(5), Sn3-O3 2.169(5), Sn3-O4 2.026(5),
Sn3-O7 2.069(5), Sn3-O8 2.084(5), Sn3-C9 2.113(9), P1-O5 1.523(5), P1-O9 1.517(6), P1-O8* 1.504(6), P2-O6 1.520-
(6), P2-O7 1.519(6), P2-O10* 1.511(6); Sn1-O4-Sn2 108.5(2), Sn1-O4-Sn3 108.6(2), Sn2-O4-Sn3 111.4(2), O4-Sn1-
C1 169.3(3), O4-Sn2-C5 165.1(3), O4-Sn3-C9 164.1(3), Sn1-O1-Sn2 101.1(2), Sn1-O2-Sn3 100.2(2), Sn2-O3-Sn3
102.8(2), Sn1-O5-P1 127.3(3) Sn1-O6-P2 128.5(3), Sn2-O9-P1 128.0(3), Sn2-O10-P2* 142.0(4), Sn3-O7-P2 129.2-
(3), Sn3-O8-P1* 140.2(3), O5-P1-O8* 111.5(3), O9-P1-O8* 115.4(3), O5-P1-O9 111.5(3), O6-P2-O7 112.5(3), O6-
P2-O10* 112.2(3), O7-P2-O10* 113.0(3)°.
Scheme 1. Synthesis of Compounds 1-4
ing the capping µ3-oxygen are nearly similar, although
not equal: Sn1-O4 2.105(6), Sn2-O4 2.044(5), and
Sn3-O4 2.026(8) Å. In comparison, Sn-O distances
involving the phenoxide oxygen atoms are longer. Each
tin atom of the tritin subunit is further bound to two
oxygen atoms of the phosphonate ligands. Each of the
phosphonate ligands is involved in a tripodal bridging
coordination mode. None of the phosphonates act as
tin cages, viz., the O-capped cluster, the drum, and the
football cage (Scheme 2).2b It is immediately evident that
cages 1-4, as well as the drum and the football cage,
are structurally related to the O-capped cluster. The
latter itself can be considered as an incomplete cube,
with one of the vertexes of the cube remaining unoc-
cupied. The absence of one vertex atom results in a
Sn3O4 core for the O-capped cluster. Thus, the core
structure of the O-capped cluster is exactly the same as
what is found for 1-4. The bonding parameters in these
two types of oxotin structures are also quite comparable
(Table 1). The drum compound (Sn6O6 core) is a hex-
americ prism and can be thought of as forming from a
face-face condensation of the two incomplete cubes of
the O-capped cluster (Scheme 2). Because of such a
fusion, the core of the drum does not contain any µ2-
oxygen atoms; all the oxygen atoms of the core of the
chelating ligands. The four phosphonates, [HPO3]2-
,
effectively bridge the two tritin subunits and generate
the spherical cage-like architecture. The Sn-O and P-O
bond distances in the Sn-O-P structural units are
quite similar (av 2.068(10) and 1.516(8) Å respectively).
Comparison of the Molecular Structures of 1-4
with Other Related Organooxotin Cages. It is
relevant to compare the molecular structures of 1-4
with those of other three very closely related organooxo-

Organooxotin Cages
Organometallics, Vol. 24, No. 21, 2005 4929
Scheme 2. Structural Comparison of the Monoorganooxotin Cages 1-4 with Other Related Systems
Table 1. Comparison of Bond Distances in the Core Structures of Selected Monoorgano Oxotin Cages
average
Sn-O(µ3) (Å)
average
Sn-O(µ2) (Å)
average
Sn-O(P) (Å)
diametrically
opposite P-P (Å)
interpole
[O(µ3)-O(µ3)] (Å)
compound
ref
1
2.065(3)
2.058(5)
2.057(5)
2.063(3)
2.064(4)
2.062(7)
2.075(5)
2.101(5)
2.091(7)b
2.054(8)c
2.140(8)d
2.172(2)
2.172(6)
2.176(6)
2.177(4)
2.181(4)
2.172(7)
2.128(6)
2.072(2)
2.068(6)
2.064(6)
2.071(4)
2.073(4)
2.080(7)
2.122(6)
2.155(5)
6.337(1)
6.283(2)
6.275(3)
6.294(3)
6.294(4)
6.274(5)
3.778(4)
3.813(2)
3.848(2)
3.805(5)
3.827(6)
3.825(9)
2b
2a
this work
3a
this work
4
this work
O-capped cluster
drum
1b
1f
9c
football cage
2.096(8)
6.331(6)e
3.899(6)
a Two crystallographically independent molecules are present. b Sn is bonded with µ3-capped oxygen (O-capped) in the poles. c Pole tin
atoms bonded with µ3-oxygens that are part of the equator. d Equator tin atoms bonded with µ3-oxygens that are part of the equator.
e Average distance between the diametrically opposite tin atoms present in the equator.
drum are µ3-bridging. The bonding parameters (Sn-O)
of the drum are also comparable to that observed for
1-4 as well as the O-capped cluster (Table 1). If the
two Sn3O4 cores of the latter are joined to each other in
a back-back manner with the help of additional ligands,
one obtains the cages 1-4 or the football cage. Thus,
the formation of 1-4 involves the use of the tripodal
phosphonate ligands to join the Sn3O4 cores (Scheme
2). On the other hand the football cage is derived by
combining two such cores with the help a Sn6O12 unit.
The football cage and compounds 1-4 are, thus, struc-
turally quite similar. Further evidence for this struc-
tural similarity comes from examining some of their
bonding parameters. The football cage has been thought
of as an ellipsoidal sphere possessing two poles (Sn3O4)
and a central equator (Sn6O12). The interpole distance
is comparable with the distance of the diametrically
opposite tin atoms in the football cage (6.331(6) Å, Table
1). Thus, despite the apparent dissimilarities, many of
the oxotin cages are structurally quite close.
Halogen Bonding in the Crystal Structures of
2-4. We have shown recently that the hexameric
organooxotin drum [n-BuSn(O)OC(O)CH2Fc]6 (Fc )
ferrocenyl) and other organooxotin derivatives form
interesting noncovalent interaction-mediated (O-H- - -
O, C-H- - -O, C-H- - -π, π- - -π, etc.) supramolecular
assemblies in their solid state.2c,3c,d,10 In view of this
interest we have examined the crystal structures of 1-4
to detect the presence and effect of noncovalent interac-
tions. The crystal structure of 1 does not show any
hydrogen bonds (such as C-H- - -O) or other types of
noncovalent interactions. On the other hand the crystal
(µ3O-µ3O) is 3.899(6) Å in [(n-BuSn)12O14(OH)6]2+
-
[OH-]2.9c Interestingly, the interpole distance in 1-4
ranges from 3.778(4) (for 1) to 3.825(9) Å (for 4). The
distance between the diametrically opposite phosphorus
atoms in 1-4 ranges from 6.274(5) to 6.337(1) Å. This
(10) (a) Chandrasekhar, V.; Nagendran, S.; Bansal, S.; Cordes, A.
W.; Vij, A. Organometallics 2002, 21, 3297. (b) Chandrasekhar, V.;
Boomishankar, R.; Singh, S.; Steiner, A.; Zacchini, S. Organometallics
2002, 21, 4575. (c) Chandrasekhar, V.; Boomishankar, R.; Steiner, A.;
Bickley, J. F. Organometallics 2003, 22, 3342.

4930 Organometallics, Vol. 24, No. 21, 2005
Chandrasekhar et al.
Figure 2. View showing the Cl- - -O-mediated two-dimensional supramolecular network in 2. The halogen-bonding
parameters are Cl5- - -O6 3.303(9) Å, 164.32(2)°.
structures of 2-4 reveal robust halogen-bonding inter-
actions that lead to the generation of supramolecular
structures. The term halogen bonding (XB), as defined
in a recent leading review article,11 is a noncovalent
interaction and encompasses interactions of the type
D- - -X-Y (D ) donor, a Lewis base; X ) halogen, a
Lewis acceptor; Y ) C, N, or a halogen). Alternatively,
the interaction can be viewed as A- - -X-Y (A ) halogen
acceptor). The XB interaction energy varies over a wide
range from 5 to 180 kJ mol-1, with Cl- - -Cl interactions
being weak and I-- - -I-I interactions being quite
strong.12 In general it has been shown that XB can
prevail over hydrogen bonding in terms of being the
primary glue that selects and binds the modules in a
competitive supramolecular recognition process.13 Some
of these XB interactions such as X- - -O interactions are
highly directional multipolar interactions as reviewed
recently.14
Compounds 2-4 crystallize in the triclinic crystal
system (space group P1h). Compounds 2 and 3 have two
molecules in their asymmetric units. It can be noticed
from Figure 1 that the chlorophenoxide moiety present
in the pole of one of the molecules (in 2) protrudes into
the core of the other molecule within the same asym-
metric unit. A similar situation is found for 3 also.15
Thus, the molecules are well-positioned for systematic
(13) (a) Murray-Rust, P.; Motherwell, W. D. S. J. Am. Chem. Soc.
1979, 101, 4374. (b) Ramasubbu, N.; Parthasarathy, R.; Murray-Rust,
P. J. Am. Chem. Soc. 1986, 108, 4308. (c) Desiraju, G. R.; Parthasa-
rathy, R. J. Am. Chem. Soc. 1989, 111, 8725. (d) Lommerse, J. P. M.;
Stone, A. J.; Taylor, R.; Allen, F. H. J. Am. Chem. Soc. 1996, 118, 3108.
(e) Schwiebert, K. E.; Chin, D. N.; MacDonald, J. C.; Whitesides, G.
M. J. Am. Chem. Soc. 1996, 118, 4018. (f) Metrangolo, P.; Resnati, G.
Chem. Eur. J. 2001, 7, 2511. (g) Caronna, T.; Liantonio, R.; Logothetis,
T. A.; Metrangolo, P.; Pilati, T.; Resnati, G. J. Am. Chem. Soc. 2004,
126, 4500.
(11) Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati, G. Acc. Chem.
Res. 2005, 38, 386.
(12) (a) Corradi, E.; Meille, S. V.; Messina, M. T.; Metrangolo, P.;
Resnati, G. Angew. Chem., Int. Ed. 2000, 39, 1782. (b) Zordan, F.;
Brammer, L.; Sherwood, P. J. Am. Chem. Soc. 2005, 127, 5979. (c)
Weiss, R.; Schwab, O.; Hampel, F. Chem. Eur. J. 1999, 5, 968, and
references therein.

Organooxotin Cages
Organometallics, Vol. 24, No. 21, 2005 4931
Table 2. Crystal Data and Structure Refinement Parameters for Compounds 2-4
2
3
4
empirical formula
C
63.50H86Cl6O20P4Sn6
C
63.50H86Br6O20P4Sn6
C
36.50H47ClI4O11P2Sn3
fw
2218.04
2484.80
1622.80
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
223(2)
223(2)
223(2)
0.71073
0.71073
0.71073
triclinic
triclinic
triclinic
P1h
P1h
P1h
13.500(5)
13.5706(7)
16.0101(8)
20.7547(11)
109.512(1)
91.172(1)
13.3902(7)
14.2179(8)
16.9005(10)
81.364(1)
b (Å)
15.974(5)
c (Å)
20.487(7)
R (deg)
109.127(7)
90.972(8)
â (deg)
69.981(1)
γ (deg)
97.352(7)
97.496(1)
62.312(1)
V (Å3)
4132(2)
4204.1(4)
2676.8(3)
Z
2
2
2
density (calcd, Mg/m3)
1.783
1.963
2.013
absorp coeff (mm-1
F(000)
)
2.120
4.745
3.852
2178
2394
1526
cryst size (mm3)
θ range (deg)
index ranges
0.38 × 0.15 × 0.10
1.42 to 25.00
-16 e h e 15,
-18 e k e 18,
-24 e l e 22
23 991
0.45 × 0.30 × 0.15
1.04 to 25.00
-16 e h e 16,
-19 e k e 15,
-22 e l e 24
24 524
0.63 × 0.45 × 0.38
1.62 to 25.00
-15 e h e 14,
-16 e k e 16,
-20 e l e 9
15 472
no. of reflns collected
no. of indep reflns
14 467
[R(int) ) 0.0527]
99.5%
SADABS (Sheldrick, 1996)
full-matrix least
squares on F2
14 467/3/851
1.018
R1 ) 0.0491,
wR2 ) 0.1050
R1 ) 0.0732,
wR2 ) 0.1135
1.262 and -0.929
14 810
[R(int) ) 0.0352]
100.0%
SADABS (Sheldrick, 1996)
full-matrix least
squares on F2
14 810/325/873
1.015
R1 ) 0.0353,
wR2 ) 0.0686
R1 ) 0.0481,
wR2 ) 0.0705
1.197 and -1.270
9400
[R(int) ) 0.0344]
100.0%
SADABS (Sheldrick, 1996)
full-matrix least
squares on F2
9400/59/532
1.014
R1 ) 0.0628,
wR2 ) 0.1699
R1 ) 0.0777,
wR2 ) 0.1761
2.994 and -3.664
completeness to θ
absorp corr
refinement method
no. of data/restrains/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]a
R indices (all data)a
largest diff peak and hole (e Å-3
)
a R1 ) ∑||Fo| - |Fc| |/∑|Fo|; wR2 ) {∑[w(Fo - Fc )2]/[∑(Fo2)2]}1/2, where w ) 1/[σ2(Fo2) + (aP)2 + bP].
2
2
X- - -O interactions. It can be seen that from Figure 2
that the (four) chlorine atoms of one of the molecules of
the asymmetric unit of 2 interact with the phosphonate
oxygens (halogen acceptors) of the neighboring mol-
ecules. This leads to the formation of a regular two-
dimensional sheet containing alternate rows of chlorine-
donor and chlorine-acceptor clusters. The Cl- - -O
distances and the C-Cl- - -O angles involved in these
interactions are Cl5- - -O6 3.303(9) Å, 164.32(2)° and
Cl4- - -O7 3.269(11) Å, 164.11(3)°. These are consistent
with other Cl- - -O interactions known in the litera-
ture.11,16 The 2D grids formed by Cl- - -O interactions
are further interconnected by means of C-H- - -O
interactions to form a 3D supramolecular network.
Compound 3, which contains 4-bromophenoxide ligands,
shows a supramolecular pattern identical with that of
2. In the crystal structures of 2 and 3 the angle of
approach of the halogen toward the nucleophilic center
(phosphoryl oxygen) is almost linear and head on.13b The
formation of the supramolecular assembly in 4 is not a
consequence of I- - -O interactions, but is due to I- - -I
and I- - -π interactions.15
Unlike many reactions known for assembling organotin
compounds, the synthesis of 1-4 is a three-component
reaction and involves n-BuSn(O)(OH), H3PO3, and
4-substituted phenols. The molecular structures of 1-4,
which can be described as double O-capped structures,
reveal the presence of two centrosymmetrically related
Sn3O4 cores that are interconnected by four bridging
tripodal phosphonate ligands. The molecular structures
of 1-4 are intimately related to the other structural
forms known for organooxotin cages, viz., the O-capped
cluster, the drum, and the football cage. The crystal
structures of 2-4 show halogen-bonding-mediated su-
pramolecular formation.
Experimental Section
Reagents and General Procedures. All the reactions
were performed under a dry nitrogen atmosphere by employing
standard Schlenk techniques. Solvents were dried over sodium
benzophenone ketyl and were collected from the still at the
time of the reaction. The chemicals n-BuSn(O)(OH), HO-C6H4-
4-X (X ) Cl, Br, and I) (all from Aldrich), C6H5OH, and H3-
PO3 (from Sd-fine, India) were used as such. Melting points
were measured using a JSGW melting point apparatus and
are uncorrected. Elemental analyses were carried out using a
Thermoquest CE instruments model EA/110 CHNS-O elemen-
Conclusion
In conclusion, we report in this contribution the
formation of hexanuclear organooxotin cages, 1-4.
1
tal analyzer. H, 31P, and 119Sn NMR spectra were obtained
on a JEOL-JNM LAMBDA 400 model spectrometer using
CDCl3 solutions in room temperature with the chemical shifts
referenced to tetramethylsilane (for 1H), 85% H3PO4 (for 31P),
and tetramethyltin (for 119Sn), respectively. 31P and 119Sn NMR
were recorded under broad-band decoupled conditions.
(14) Paulini, R.; Mu¨ller, K.; Diederich, F. Angew. Chem., Int. Ed.
2005, 44, 1788.
(15) See Supporting Information.
(16) (a) Moorthy, J. N.; Venkatakrishnan, P.; Mal, P.; Dixit, S.;
Venugopalan, P. Cryst. Growth Des. 2003, 3, 581. (b) Thaimattam, R.;
Xue, F.; Sarma, J. A. R. P.; Mak, T. C. W.; Desiraju, G. R. J. Am. Chem.
Soc. 2001, 123, 4432, and references therein.
Synthesis. Compound 1 was synthesized by two synthetic
routes reported by us recently.2b The general synthetic proce-

4932 Organometallics, Vol. 24, No. 21, 2005
Chandrasekhar et al.
dure for the preparation of the other compounds (2-4) is as
follows. A stoichiometric mixture of the n-BuSn(O)(OH), H3-
PO3, and substituted phenols in toluene (60 mL) was heated
under reflux for 6 h. The water formed in the reaction was
removed by using a Dean-Stark apparatus. The reaction
mixture was filtered and reduced to one-tenth of its initial
volume in vacuo and kept for crystallization at room temper-
ature. After 3-4 weeks, colorless block-like crystals were
formed, which were separated by filtration. The crystals were
further purified by quickly washing with CH2Cl2 (3 mL). The
crystals were crushed and dried in vacuo for further analysis.
The stoichiometric ratios of the reactants, the yields of the
products 2-4, and the characterization data for these are given
below.
ppm): 0.50-0.73 (m, 18H, CH3 of n-Bu), 0.80-1.46 (m, 36H,
CH2 of n-Bu), 6.76-7.51(m, 24H, phenyl), 6.56 (d, 2H, free iodo
phenol), 7.43 (d, 2H, free iodo phenol), 7.13 (d, 4H, 1J(H-P) )
1
690 Hz). 31P NMR (162 MHz, ppm): 0.57 (d, J(P-H) ) 688
Hz). 119Sn NMR (150 MHz, ppm): -532.7 (m), -551.3 (m),
-563.6 (m).
X-ray Crystallography. Colorless block-like crystals suit-
able for single-crystal X-ray diffraction were loaded on a
Bruker AXS Smart Apex CCD diffractometer. The details
pertaining to the data collection and refinement are given in
Table 2. The structures were solved by direct methods and
refined by using full-matrix least-squares on F2 (SHELX97).18
The hydrogen on the phosphorus atom was located from the
difference maps, and their positions were refined. All the other
hydrogens were fixed at calculated positions. The compounds
2 and 3 crystallized with a molecule of toluene, and compound
4 crystallized with a molecule of CH2Cl2 (disordered) as solvent
of crystallization. The CCDC numbers for the crystal struc-
tures 1-4 are 192010, 268235, 268236, and 268237, respec-
tively. Figures and bonding parameters were obtained from
the DIAMOND 3.0 software package.19
2: n-BuSn(O)(OH) (1.69 g, 8.09 mmol), HO-C6H4-4-Cl (1.04
g, 8.09 mmol), and H3PO3 (0.45 g, 5.39 mmol). Yield: 0.40 g
(13%).17 Mp: 305 °C (dec). Anal. Calcd (%) for C60H82O20Cl6P4-
1
Sn6: C 33.17, H 3.80. Found: C 33.10, H 3.65. H NMR (400
MHz, ppm): 0.50-0.78 (m, 18H, CH3 of n-Bu), 0.80-1.50 (m,
36H, CH2 of n-Bu), 6.65-7.30 (m, 24H, phenyl), 7.14 (d, 4H,
1J(H-P) ) 690 Hz). 31P NMR (162 MHz, ppm): 0.58 (d, 1J(P-
H) ) 688 Hz). 119Sn NMR (150 MHz, ppm): -532.7 (m), -551.3
(m), -563.6 (m).
Acknowledgment. We are thankful to the Depart-
ment of Science and Technology, New Delhi, for finan-
cial support. K.G. thanks Council of Scientific and
Industrial Research, India, for Senior Research Fellow-
ship.
3: n-BuSn(O)(OH) (1.32 g, 6.32 mmol), HO-C6H4-4-Br (1.10
g, 6.32 mmol), and H3PO3 (0.34 g, 4.21 mmol). Yield: 0.32 g
(13%).17 Mp: 306 °C (dec). Anal. Calcd (%) for C60H82O20Br6P4-
1
Sn6: C 29.54, H 3.38. Found: C 29.45, H 3.20. H NMR (400
MHz, ppm): 0.50-0.72 (m, 18H, CH3 of n-Bu), 0.80-1.40 (m,
36H, CH2 of n-Bu), 6.83-7.35 (m, 24H, phenyl), 7.13 (d, 4H,
1J(H-P) ) 690 Hz). 31P NMR (162 MHz, ppm): 0.54 (d, 1J(P-
H) ) 688 Hz). 119Sn NMR (150 MHz, ppm): -532.7 (m), -551.3
(m), -563.6 (m).
4: n-BuSn(O)(OH) (1.32 g, 6.34 mmol), HO-C6H4-4-I (1.40
g, 6.34 mmol), and H3PO3 (0.35 g, 4.23 mmol). Yield: 0.80 g
(30%).17 Mp: 100 °C (slight change in morphology of the solid)
and 308 °C (major dec). Anal. Calcd (%) for C72H92O22I8P4Sn6:
C 26.52, H 2.78. Found: C 26.41, H 2.89. 1H NMR (400 MHz,
Supporting Information Available: ORTEP diagrams,
figures of supramolecular assemblies, and crystallographic
information files (CIF) for compounds 2-4. These materials
are available free of charge via the Internet at
http://pubs.acs.org.
OM050269X
(18) Sheldrick, G. M. SHELX97, Programs for the Solution and
Refinement of Crystal Structures; Institut fu¨r Anorganische Chemie
der Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1998.
(19) DIAMOND version 3.0; Crystal Impact GbR: Bonn, Germany,
2004.
(17) Yields are based on the crystals isolated from their reaction
mixture.