Synthesis and structural studies of diorganotin(IV)-based coordination polymers bearing silaalkylphosphonate ligands and their transformation into colloidal domains

Article abstract of DOI:10.1021/ic500682t

The contribution of silaalkylphosphonic acids Me₃SiCH ₂P(O)(OH)₂ (1) and Me₃SiC(CH₃) ₂P(O)(OH)₂ (2) as ligands was demonstrated for the first time by the isolation of new diorganotin(IV) phosphonates Et₂Sn{OP(O) (OH)CH₂SiMe₃}(OSO₂Me) (3), (Et ₂Sn)₆{O₃PC(CH₃)₂SiMe ₃}₄(OSO₂Me)₄ (4), and Et ₂Sn(O₃PCH₂SiMe₃) (5). X-ray crystallographic studies of 1-4 are presented. The structures of 1 and 2 adopt extended motifs by virtue of P-OH···O=P-type hydrogen bonding interactions. The molecular structure of 3 is composed of a dimer formed by bridging hydrogen phosphonate groups, while the sulfonate group appended on each tin atom acts in a μ₂-bridging mode to afford the formation of one-dimensional coordination polymer featuring alternate eight-membered [-Sn-O-P-O-]₂ and [-Sn-O-S-O-]₂ rings. The asymmetric unit of 4 is composed of two crystallographically unique trinuclear tin phosphonate clusters with a Sn₃(μ₃-PO₃)₂ core linked together by coordinative association of a μ₂-sulfonate group, while the remaining sulfonates are involved in the construction of a two-dimensional self-assembly. The identity of 1-5 in solution was established by IR and multinuclear (¹H, ¹³C, ³¹P, ¹¹⁹Sn) NMR spectroscopy. The presence of silaalkyl group in 5 imparts unusual solubility in hydrocarbon, aromatic, and ether solvents. As a consequence, the formation of colloidal particles of 5 featuring rodlike morphology was achieved by ultrasonication of a solution in ethanol-chloroform mixture.

Full text of DOI:10.1021/ic500682t

Article
pubs.acs.org/IC
Synthesis and Structural Studies of Diorganotin(IV)-Based
Coordination Polymers Bearing Silaalkylphosphonate Ligands and
Their Transformation into Colloidal Domains
Ravi Shankar,*,† Nisha Singla,† Meenal Asija,† Gabriele Kociok-Kohn,‡ and Kieran C. Molloy‡
̈
†Department of Chemistry, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India
‡Department of Chemistry, University of Bath, Bath BA2 7AY, U.K.
S
* Supporting Information
ABSTRACT: The contribution of silaalkylphosphonic acids
Me3SiCH2P(O)(OH)2 (1) and Me3SiC(CH3)2P(O)(OH)2
(2) as ligands was demonstrated for the first time by the
isolation of new diorganotin(IV) phosphonates Et2Sn{OP-
(O)(OH)CH2SiMe3}(OSO2Me) (3), (Et2Sn)6{O3PC-
(CH3)2SiMe3}4(OSO2Me)4 (4), and Et2Sn(O3PCH2SiMe3)
(5). X-ray crystallographic studies of 1−4 are presented. The
structures of 1 and 2 adopt extended motifs by virtue of P−
OH···OP-type hydrogen bonding interactions. The molec-
ular structure of 3 is composed of a dimer formed by bridging
hydrogen phosphonate groups, while the sulfonate group
appended on each tin atom acts in a μ2-bridging mode to
afford the formation of one-dimensional coordination polymer
featuring alternate eight-membered [−Sn−O−P−O−]2 and [−Sn−O−S−O−]2 rings. The asymmetric unit of 4 is composed of
two crystallographically unique trinuclear tin phosphonate clusters with a Sn3(μ3-PO3)2 core linked together by coordinative
association of a μ2-sulfonate group, while the remaining sulfonates are involved in the construction of a two-dimensional self-
assembly. The identity of 1−5 in solution was established by IR and multinuclear (1H, 13C, 31P, 119Sn) NMR spectroscopy. The
presence of silaalkyl group in 5 imparts unusual solubility in hydrocarbon, aromatic, and ether solvents. As a consequence, the
formation of colloidal particles of 5 featuring rodlike morphology was achieved by ultrasonication of a solution in ethanol−
chloroform mixture.
organotin(IV) phosphonate diesters as molecular entities has
been reported.6 These studies have provided a great deal of
insight into the reactivity behavior of these complexes both at
metal and the ligand centers. The contribution in this area from
our group relates to synthesis and structural characterization of
several mixed-ligand diorganotin(IV) coordination polymers of
general composition R2Sn{OP(O)(OH)R1}(OSO2R2) and
(R2Sn)3(O3PR1)2(OSO2R2)2 (R = Me, Et, n-Bu; R1, R2 =
alkyl or Ph). Among these families, incorporation of sulfonate
groups as the appended donor functionality on tin-
phosphonate framework and its ubiquitous (μ2, μ3) bonding
affinity toward tin has opened up interesting opportunities to
construct novel structural motifs.7
In recent years, there have been persistent efforts directed
toward evolving synthetic methods to transform infinite
coordination polymers (ICPs) into nano/colloidal size domains
and unfolding their promising applications in catalysis, gas
sorption, biomedical imaging, biosensing, etc.8 To this end,
transition metal based 1D and layered coordination frameworks
INTRODUCTION
■
The contribution of phosphonate ligands in both monoanionic
[RP(O)(OH)O]− and dianionic [RPO3]2− forms has been
well-recognized in the construction of organotin(IV) phospho-
nates featuring structurally variable coordination frameworks
ranging from cluster entities to two-/three-dimensional (2D/
3D) polymeric motifs. Among the known examples of
organotin clusters,1 the skeletal framework is often composed
of oxo-/hydroxotin species as the constructing units bearing
phosphonate groups as the complexing ligand. The structure of
Bu2Sn{OP(O)(OH)Me}2 in the solid state is best described as
a one-dimensional (1D) polymer resulting from strong and
weak Sn ← O contacts [Sn−O = 2.165, 3.18 Å] of the
hydrogen phosphonate ligands,2 while Me3Sn{OP(O)(OH)-
Ph} adopts a helical polymeric motif.3 The contribution of
tridentate [RPO3]2− ligand has been exemplified in n-
Bu2Sn(O3PPh), (Me3Sn)4(O3PPh)2, and (Me3Sn)2(O3PPh).
MeOH and Me2Sn(O3PPh), wherein formation of 1D/2D
polymeric structures are particularly noticeable.4 The complex
Ph3Sn{OP(O)(OMe)Me}, derived from phosphonate ester, is
a unique example of a cyclic hexamer with five-coordinated tin
atoms.5 The synthesis and structural chemistry of several
Received: March 25, 2014
© XXXX American Chemical Society
A
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Table 1. Summary of Crystallographic Data for 1−4
crystal data
empirical formula
1
2
3
4
C4H13O3PSi
168.20
C6H17O3PSi
196.25
C9H25O6PSSiSn
439.10
C52H132O24P4S4Si4O6
2218.19
fw
temperature (K)
wavelength (Å)
cryst syst
space group
a, Å
150(2)
150(2)
150(2)
150(2)
0.710 73
0.710 73
0.710 73
triclinic
0.710 73
orthorhombic
orthorhombic
monoclinic
P21/n
P212121
Pnab
P1
̅
8.6436(3)
6.1752(2)
10.6670(2)
21.5869(3)
19.7660(3)
21.8682(3)
90
b, Å
6.6929(2)
13.0947(3)
10.3127(3)
12.1930(4)
67.8301(13)
87.0945(14)
66.139(2)
c, Å
21.5021(6)
14.9488(3)
α, deg
90
90
β, deg
90
90
104.8080(10)
90
γ, deg
V, Å3
90
90
888.68(5)
2088.07(7)
913.79(5)
9021.0(2)
4
Z
4
8
2
ρ calcd. (Mg/m3)
1.257
1.249
1.596
1.633
μ (mm−1
)
0.392
0.344
1.680
1.912
F(000)
crystal size (mm3)
360
848
444
4464
0.300 × 0.200 ×
0.150
0.200 × 0.150 ×
0.150
0.200 × 0.150 ×
0.150
0.250 × 0.200 ×
0.200
θ (deg)
3.433 to 27.519
14 469
3.651 to 27.461
27 912
2.984 to 27.581
15 658
3.551 to 27.334
86 132
reflns colld
unique reflens
2032
2385
4113
19 598
completeness to θ
max. and min. transmn.
R(int)
25.242° (99.3%)
0.946 and 0.853
0.0661
25.242° (99.6%)
0.954 and 0.866
0.0630
25.242° (99.1%)
0.732 and 0.782
0.0326
25.242° (96.6%)
0.859 and 0.797
0.0835
data/restraints/parameters
GOF on F2
2032/1/93
1.093
2385/0/113
1.099
4113/1/182
1.079
19598/6/933
1.041
final R indices [I > 2σ(I)]
R indices (all data)
absolute structure parameter
largest diff. peak and hole (e Å−3
R1 = 0.0272, wR2 = 0.0618
R1 = 0.0297, wR2 = 0.0633
0.00(5)
R1 = 0.0345, wR2 = 0.0832
R1 = 0.0448, wR2 = 0.0888
R1 = 0.0254, wR2 = 0.0563
R1 = 0.0292, wR2 = 0.0581
R1 = 0.0370, wR2 = 0.078
R1 = 0.0622, wR2 = 0.088
)
0.305 and −0.260
0.287 and −0.304
0.727 and −0.976
0.855 and −1.036
that exhibit weak noncovalent interactions in the solid state are
particularly attractive candidates, as these interactions can be
depleted in the presence of an external stimuli via a wet
chemical approach and facilitate the formation of nanorods/
nanowires9 and nanosheets.10 Among the metal-phosphonate
family, realization of nano structures, however, still remains a
formidable challenge in view of their tendency to form densely
packed solid phases. The added complexity arising from their
insoluble nature restricts structure tailorability by a wet
chemical method. Maeda et al. have recently described the
synthesis of a lanthanum−organophosphonate nanosheet by
exfoliation of the layered structure derived from 1,3,5-
benzenetriphosphonate ligand.11 Several layered tin(IV)
phosphonates, Sn(O3PR)2 and Sn(O3PRPO3) (R = alkyl or
aryl), have been synthesized by solvothermal approach and are
known to exhibit porous characteristics as a result of
aggregation of nanosized particles.12
To broaden the scope of organotin(IV) phosphonates in the
development of nano-structured materials, we focused our
attention to explore the potential of silaalkylphosphonic acids
as ligands. It is important to emphasize that coordination
chemistry of these ligands still remains in a state of dormancy
despite a few early reports on the synthesis of sila-substituted
phosphonic acids.13 As part of our ongoing interest in metal
coordination frameworks derived from oxyphosphorus-based
ligands,7,14 we surmised that incorporation of these ligands in
the coordination assemblies might offer a possibility to
modulate structural motifs as a result of steric and electronic
attributes of silaalkyl groups. Herein we report a detailed study
on the synthesis and structural aspects of two new
silaalkylphosphonic acids, namely, Me3SiCR2P(O)(OH)2 [R
= H (1), CH3 (2)] and diorganotin(IV) coordination polymers
E t 2 S n { O P ( O )( O H ) C H 2 S i M e3 } ( O S O 2 Me ) ( 3 ) ,
(Et2Sn)6{O3PC(CH3)2SiMe3}4(OSO2Me)4 (4), and Et2Sn-
(O3PCH2SiMe3) (5) derived therefrom. Interestingly, intro-
duction of the silaalkyl group in 5 imparts unusual solubility in
hydrocarbon, aromatic, and ether solvents and facilitates the
formation of colloidal particles with rodlike morphology.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Phosphonic Acids.
As a prerequisite, the synthesis of diethyltrimethylsilylmethyl-
phosphonate, Me3SiCH2P(O)(OEt)2 (1a), was achieved by
following the procedure reported by Eaborn et al.13a The
reaction involves Arbuzov rearrangement in triethylphosphite
in the presence of (chloromethyl)trimethylsilane.
Me3SiCH2Cl + P(OEt)3
N2
⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ Me3SiCH2P(O)(OEt)2 + C2H5Cl
140−150°C
(1a)
The active methylene group adjacent to silicon in 1a undergoes
deprotonation in the presence of a strong base such as n-butyl
lithium in tetrahydrofuran (THF) at −60 °C, and subsequent
addition of methyl iodide affords the formation of diethyl(2-
trimethylsilyl)-2-propylphosphonate, Me3SiC(CH3)2P(O)-
B
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Table 2. Selected Bond Lengths (Å) and Angles (deg) of 1
Si−C(3)
Si−C(4)
P−O(3)
P−O(1)
1.859(2)
Si−C(2)
Si−C(1)
P−O (2)
P−C(1)
O2−H2
1.863(2)
1.869(3)
1.8916(18)
1.5574(15)
1.7708(17)
0.83(3)
1.5060(13)
1.5544(12)
0.90(2)
O1−H1
P−C(1)−Si
O(1)−H(1)···O(3)
118.50(10)
2.5579(19)
a
b
O(2)−H(2)···O(3)
2.5910(19)
a
b
Symmetry transformations used to generate equivalent atoms: −x + 1, y − 1/2, −z + 1/2. Symmetry transformations used to generate equivalent
atoms: −x, y − 1/2, −z + 1/2.
Table 3. Selected Bond Lengths (Å) and Angles (deg) of 2
Si−C (3)
Si−C (4)
P−O(3)
P−O(1)
1.859(2)
Si−C(2)
Si−C(1)
P−O (2)
P−C(4)
O3−H2
1.859(2)
1.861(2)
1.5543(12)
1.7864(16)
0.83(2)
1.9226(16)
1.5682(12)
1.5108(11)
0.81(3)
O2−H1
P−C(4)−Si
O(2)−H(1)···O(1)
112.63(8)
2.5771(17)
a
b
O(2)−H(2)···O(3)
2.6346(16)
a
b
Symmetry transformations used to generate equivalent atoms: −x + 3/2, y, −z + 1. Symmetry transformations used to generate equivalent atoms:
−x + 1, −y, −z + 1.
Figure 1. (a) ORTEP view of asymmetric unit of 1. The thermal ellipsoids are set at 40% probability. (b) 2D layered structure of 1 featuring OH···O
hydrogen bonding (view along c axis). The Me3Si group and hydrogen atoms of CH2 are omitted for clarity.
(OEt)2 (2a), as the major product along with minor amounts
of Me3SiCH(CH3)P(O)(OEt)2 (∼5%), which can be separated
by column chromatography. The acid hydrolysis of the
phosphonate esters 1a and 2a proceed under reflux conditions
to afford the corresponding phosphonic acids 1 and 2 as white
crystalline solids in nearly quantitative yield.
Single crystals suitable for X-ray crystallography were grown
from a solution of 1 and 2 separately in diethyl ether. The
crystal data are summarized in Table 1, while selected bond
lengths and angles are shown in Tables 2 and 3, respectively.
The molecular structures (Figures 1 and 2) reveal that sterically
demanding trimethylsilyl group imposes considerable strain,
and this is reflected in wide Si−C−P bond angles [118.50(10)°
(1); 112.63(8)° (2)], greater than the expected tetrahedral
angle of 109.5°. In addition, elongation in the Si−C bond
[1.8916(18) (1); 1.9226(16) Å (2)] also occurs to relieve the
steric strain. These features are in conformity with structural
studies of 1,3-disilapropane reported earlier.16 The involvement
of P−OH and PO groups in OH···O hydrogen bonding
extends the molecular structure of 1 into a layered motif
featuring fused noncentrosymmetric 14-membered rings. On
the other hand, the structure of 2 adopts a ribbonlike 1D motif,
which is commonly observed in alkylphosphonic acids.17 The
O···O bond distance associated with hydrogen bonds in 1 and 2
lies in the range of 2.557−2.634 Å, whereas the hydrogen bond
angles (O−H···O) vary between 165(4) and 176(2)°.
Me3SiCR2P(O)(OEt)2
⎯d⎯⎯il⎯u⎯t⎯e⎯⎯H⎯C⎯→l Me3SiCR2P(O)(OH)2 + 2C2H5OH
120°C,30h
R = H(1), CH3(2)
For 1 and 2, medium-intensity IR absorption at 2360 cm−1 is
suggestive of hydrogen bonded P−OH groups, while character-
istic absorptions due to νPO3 and νSi−Me appear at 1205 and
1260 cm−1, respectively. The 1H and 13C NMR spectra provide
distinct JP−H and JP−C coupling information (Supporting
Information, Figures S1 and S2) and establish the identity of
each compound. In conformity with earlier reports,15 electro-
spray ionization mass (ESI-MS) spectra (positive ion mode)
reveal the existence of hydrogen bonded aggregates in solution
along with the expected molecular ion peak at m/z 191.0276
[M + Na]+ and 197.0747 [M + H]+ for 1 and 2, respectively.
Synthesis and Characterization of Diorganotin(IV)
Coordination Polymers. Following our earlier approach,7
C
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Figure 2. (a) ORTEP view of asymmetric unit of 2. The thermal ellipsoids are set at 40% probability. (b) 1D ribbonlike structural motif of 2 showing
O−H···O hydrogen bonding interactions (view along b axis). The Me3Si and CH3 groups are omitted for clarity.
the reaction between equimolar quantities of diethyltin-
(methoxy)methanesulfonate Et2Sn(OMe)OSO2Me and silaal-
kylphosphonic acid (1 or 2) proceeds under mild conditions
(CH2Cl2, room temperature (rt), 8 h) to afford the isolation of
Et2Sn{OP(O)(OH)CH2SiMe3}(OSO2Me) (3) and
(Et2Sn)6{O3PC(CH3)2SiMe3}4(OSO2Me)4 (4). The chemo-
selective reactivity of Sn−OMe group in the precursor tin
complex toward the phosphonic acids is in accord with more
basic character of the methoxide group as compared to the
alkanesulfonate group. The synthesis of Et2Sn(O3PCH2SiMe3)
(5) was achieved by azeotropic dehydration reaction between
equimolar quantities of diethyltin oxide and phosphonic acid 1
in toluene under reflux conditions. The compounds 3−5 are
obtained as white crystalline solids. While 3 and 4 are readily
soluble in polar organic solvents such as methanol, dichloro-
methane, chloroform, etc., the solubility of 5 in hydrocarbon,
aromatic, and ether solvents is quite unusual among this family
of organotin(IV) phosphonates.
Table 5. Selected Bond Lengths (Å) and Angles (deg) of 4
Sn1−O1
Sn1−O24
Sn1−C1
Sn2−O6
Sn2−O2
Sn2−C5
Sn3−O3
Sn3−C9
Sn4−O7
Sn4−O17
Sn4−C15
Sn5−O8
Sn5−O22
Sn5−C19
Sn6−O19
2.099(3)
2.535(3)
2.116(4)
2.141(3)
2.009(3)
2.123(4)
2.139(3)
2.119(5)
2.083(3)
2.418(3)
2.129(4)
2.160(3)
2.304(3)
2.125(4)
2.290(3)
2.121(5)
89.66(11)
87.30(11)
157.48(18)
167.69(11)
118.92(15)
138.5(2)
109.53(17)
85.18(11)
91.1(1)
Sn1−O4
Sn1−O20
Sn1−C3
Sn2−O13
Sn2−C7
Sn3−O5
Sn3−O16
Sn3−C11
Sn4−O10
Sn4−C13
Sn4−O14
Sn5−O11
Sn5−C17
Sn6−O12
Sn6−O9
Sn6−C23
2.094(3)
2.549(3)
2.117(5)
2.276(3)
2.121(5)
2.025(3)
2.320(3)
2.127(4)
2.125(3)
2.110(4)
2.623(3)
2.015(3)
2.136(4)
2.134(3)
2.008(3)
2.129(5)
88.48(11)
94.54(12)
107.92(16)
132.43(18)
173.71(11)
111.74(19)
88.99(12)
94.7(1)
a
b
Sn6−C21
a
O24 −Sn1−O1
O4−Sn1−O1
Single crystals suitable for X-ray crystallography were grown
by diffusion of diethyl ether into a solution of 3 or 4 in
methanol−chloroform mixture. The crystal data are summar-
ized in Table 1, while selected bond lengths and angles are
given in Tables 4 and 5, respectively. The structural motif of 3
b
a
b
O4−Sn1−O20
C3−Sn1−C1
O24 −Sn1−O20
O−Sn2−C5
C7−Sn2−C5
O6−Sn2−O13
C7−Sn2−O2
C11−Sn3−C9
O5−Sn3−C11
O7−Sn4−O17
O14−Sn4−O17
O8−Sn5−O22
O11−Sn5−C17
O12−Sn6−O19
O9−Sn−C21
O16−Sn3−O3
O5−Sn3−C9
O10−Sn4−O7
O10−Sn4−O14
C13−Sn4−C15
O11−Sn5−C19
C17−Sn5−C19
O9−Sn6−C23
C21−Sn6−C23
Table 4. Selected Bond Lengths (Å) and Angles (deg) of 3
a
157.26(17)
112.13(17)
140.1(2)
110.8(2)
134.6(2)
Sn−O(6)
Sn−O(4)
Sn−O(1)
2.1000(15)
2.0987(14)
2.4606(16)
0.830(17)
152.89(9)
89.55(6)
Sn−C(3)
Sn−O(3)
Sn−C(1)
2.122(2)
2.5456(16)
2.112(2)
2.632(2)
81.69(5)
84.18(6)
b
171.49(12)
107.57(18)
163.03(12)
114.15(17)
c
O(5)−H(5)
C3Sn−C1
O(5)−H(5)···O(2)
b
a
O3 Sn−O6
a
a
O6 Sn−O4
O1Sn−O4
Symmetry transformations used to generate equivalent atoms: x, y, z
b
b
− 1. Symmetry transformations used to generate equivalent atoms: x
+ 1/2, −y + 1/2, z − 1/2.
O3 Sn−O1
104.57(6)
a
Symmetry transformations used to generate equivalent atoms: 2 − x,
b
−y, 1 − z. Symmetry transformations used to generate equivalent
c
The structure of 4 represents a hitherto unknown polymeric
motif despite apparent similarity with respect to the presence of
trinuclear tin phosphonate clusters with a Sn3P2O6 core, which
has been observed earlier in a few related examples in this
family.7a,e The asymmetric unit is composed of a hexanuclear
tin assembly of composition [(Et2Sn)3(OSO2Me)2(O3PR)2]2
with two crystallographically unique trinuclear tin phosphonate
clusters [Sn−O(P) = 2.008−2.160 Å] being associated with
each other by the involvement of a methanesulfonate (S2)
group [Sn3−O16(S2) = 2.320(3), Sn4−O17 = 2.418(3) Å].
The remaining sulfonate groups (S1, S3, and S4) perform in
bridging bidentate fashion to drive the structure to a 2D
coordination assembly in the ac plane (Figure 4). The tin atoms
Sn2, Sn3, Sn5, and Sn6 in the layered structure adopt a
distorted trigonal bipyramidal geometry with an SnC2O
atoms: 1 − x, 1 − y, 1 − z. Symmetry transformations used to
generate equivalent atoms: 1 − x, −y, 1 − z.
represents 1D coordination polymer featuring alternate [−Sn−
O−P−O−]2 and [−Sn−O−S−O−]2 eight-membered rings by
virtue of bridging bidentate mode of both phosphonate and
sulfonate ligands similar to that observed for analogous
organotin complex Et2Sn{OP(O)(OH)Ph}(OSO2Me), re-
ported earlier.7b Thus, a more detailed discussion on the
structural attributes is not warranted. The coordination
assembly extends to a 2D motif (Figure 3b) as a result of
hydrogen bonding interactions between uncoordinated oxygen
atom O(2) of the sulfonate and P−OH groups [O5−H5 =
0.830(17), O5−H5···O2iii = 2.632(2) Å].
D
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Figure 3. (a) Asymmetric unit of 3. All the hydrogen atoms (except H5) are omitted for clarity. (b) 2D structural motif of 3 (view along c axis). The
Si and all the carbon atoms are omitted for clarity. Hydrogen bonding interactions are shown by dashed lines.
equatorial atom set (Σ360 0.2−0.73°), and the axial positions
are occupied by oxygen atoms [∠O−Sn−O = 163.03(12)−
173.71(11)°]. On the other hand, the tin atoms Sn1 and Sn4
adopt a distorted octahedral geometry with SnO4 occupying the
basal plane [Σ360 0.02−0.03°] and trans position of ethyl
groups [∠C−Sn−C = 157.26(17)−157.48(18)°]
chemical process. Thus, a solution of as-synthesized sample in
ethanol−chloroform mixture (5:1) upon ultrasonication results
in the formation of colloidal particles capable of scattering an
incident laser light beam (Tyndall effect). The choice of solvent
is found to be crucial since other combinations of solvents, such
as methanol−chloroform, n-propanol−chloroform, and meth-
anol−hexane, did not yield the desired effect. The morphology
of colloidal particles was examined by scanning electron
microscopy (SEM) and atomic force microscopy (AFM)
studies. The SEM micrograph (Figure 6a) reveals that colloidal
particles possess rodlike morphology, the largest dimension
being on the order of 2 μm × 160 nm. A close view of the AFM
image (tapping mode) shows that these colloidal particles are
formed by aggregation of microcrystallites, and the height
profile provides a dimension on the order of 40−60 nm (Figure
6b). The powder X-ray diffraction pattern of the sample
obtained from the colloidal solution [see Supporting
Information, Figure S4b] closely resembles that of the as-
synthesized sample, suggesting structural integrity in the
colloidal domain. Since the polymer 5 does not possess any
functionality capable of forming hydrogen bonding interactions,
it is reasonable to assume that bulk morphology of the as-
synthesized sample in solid state (see Supporting Information,
Figure S5) is predominately held by van der Waals interactions
arising from silaalkyl chains, which can be depleted by proper
choice of the solvent under sonicated conditions for which
there exists enough precedence in literature.18 In light of these
results, we considered it appropriate to examine hydrolytic
stability of 5 for possible applications. The bulk sample was
kept in contact with deionized water for 24 h and was finally
washed with acetone. The powder X-ray diffraction pattern of
the dried sample remains essentially unchanged, with no new
peak, and a little loss of intensity of lower 2θ values [see
Supporting Information, Figure S4c].
Spectroscopic Studies. The identities of 3−5 were
established by IR and multinuclear (1H, 13C, 31P, 119Sn)
NMR spectral studies, and the relevant data are summarized in
the Experimental Section. For 3 and 4, the observed IR
absorptions in the region of 940−1200 cm−1 are overlapping
νSO3 and νPO3 stretching modes and, thus, are not informative
in evaluating the coordination modes of these ligands. The 31P
and 119Sn NMR spectra of 3 reveal a single resonance at δ 28.6
and −250, respectively. The lack of observed 2JSn−O−P coupling
suggests fluxional behavior of the compound in solution.
However, the 119Sn NMR spectrum of 4 reveals a triplet
centered at δ −237 (2JSn−O−P = 147.6 Hz) due to heteronuclear
coupling with two neighboring phosphorus centers (see
Supporting Information, Figure S3) and conforms to the
presence of trinuclear tin phosphonate moiety in the structural
framework as observed in solid state. For 5, the 119Sn NMR
spectral profile exhibits a quartetlike resonance centered around
δ −282, while two distinct peaks at δ 17.1 (major) and 17.0
(minor) in the 31P NMR spectrum are flanked by partially
2
resolved tin satellites of unequal intensity with JSn−O−P
coupling on the order of 141 Hz (Figure 5). These spectral
attributes find a close analogy with those reported earlier for n-
Bu2Sn(O3PPh) by Biesemans et al.2 On the basis of detailed
NMR studies, it has been shown that each tin atom in the
molecule is associated with three phosphonate groups. These
results are in conformity with X-ray crystal structure of this
compound, which adopts a 1D ladderlike structure by virtue of
μ3-bonding mode of the phosphonate groups.4a
Synthesis of Colloidal Particles from Et2Sn-
(O3PCH2SiMe3) (5). The preferential solubility of 5 in
nonpolar solvents including hydrocarbons has interesting
ramifications in miniaturization of the bulk sample by a wet
CONCLUSIONS
■
The silaalkylphosphonic acids 1 and 2 are shown to be
potentially useful ligands in the isolation of diorganotin
E
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Inorganic Chemistry
Article
Figure 4. (a) Asymmetric unit of 4. All the hydrogen atoms are omitted for clarity. (b) Extended 2D layered structure (view along b axis). The Si and
all the carbon atoms are omitted for clarity.
at 110−120 °C and further flame-dried under vacuum prior to use.
(Chloromethyl)trimethylsilane, triethylphosphite, n-butyl lithium (1.6
M in hexane), and methyl iodide (Aldrich) were used as supplied.
Literature methods were used to prepare diethyltinoxide19 and
diethyltin(methoxy)methanesulfonate.7e
coordination polymers with interesting structural motifs. The
structural attributes of 3 and 4 are important additions to the
family of stable mixed-ligand diorganotin coordination frame-
works reported earlier from our group. For 5, the presence of
silaalkylphosphonate ligand significantly enhances the solubility
in hydrocarbons, aromatics, and ether solvents. Taking
advantage of this property, we have successfully utilized a wet
chemical approach to achieve colloidal particles of 5 featuring
rodlike morphology. Further studies are in progress to
understand the properties associated with nano/colloidal
sized organotin phosphonates.
1H, 13C{1H}, 31P{1H}, and 119Sn{1H} NMR spectra were recorded
on a BRUKER DPX-300 spectrometer at 300, 75.48, 121.50, and
1
119.92 MHz, respectively. H and 13C chemical shifts are quoted with
respect to the residual protons of the solvents (CDCl3), while 31P and
119Sn NMR data are given using 85% H3PO4 and tetramethyltin as the
external standards, respectively. IR spectra were recorded on Nicolet
protege 460 ESP spectrometer using KBr optics. Elemental analysis
(C, H) was performed on a PerkinElmer model 2400 CHN elemental
analyzer. The electron spray mass (ESI-MS) spectra were recorded
using a Micromass Quattro II triple quadrupole mass spectrometer.
The samples dissolved in chloroform−acetonitrile were introduced
into the ESI source through a syringe pump at the rate of 5 L min−1.
The ESI capillary was set at 3.5 kV, and the cone voltage was 40 V.
Phase determination was done by using the powder XRD technique
EXPERIMENTAL SECTION
■
All operations were carried out using standard Schlenk line techniques
under dry nitrogen atmosphere. Solvents were freshly distilled over
phosphorus pentaoxide (dichloromethane and hexane) and over
magnesium cake (methanol, ethanol). Glassware was dried in an oven
F
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Article
Figure 5. (a) 119Sn and (b) 31P NMR spectrum of Et2Sn(O3PCH2SiMe3) (5).
Figure 6. (a) SEM micrograph, (inset) demonstration of Tyndall effect, and (b) AFM image of 5.
using Cu Kα radiation on a Bruker D8 advance machine. A scanning
electron microscope (SEM) EVO-50 from Carl Zeiss AG, Germany,
was used to take images of the spin-coated samples. Tapping mode
atomic force microscopy (AFM) was carried out on a Bruker
Dimension Icon AFM. The images were acquired in air by using an
MPP-11100−10 probe (Bruker; tip radius and resonance frequency
are 8 nm and 75 kHz, respectively).
Synthetic Methods. Synthesis of Trimethylsilylmethylphos-
phonic Acid (1). Diethyltrimethylsilylmethylphosphonate 1a was
synthesized by following the known procedure13a using
(chloromethyl)trimethylsilane (3.5 g, 28.66 mmol) and triethylphos-
phite (4.76 g, 28.66 mmol) as the reagents. The hydrolysis of 1a (4.0
g) was performed using 120 mL of approximately 3 N HCl solution
under refluxed conditions for 24−30 h. The product was extracted in
diethyl ether and dried over sodium sulfate. The solution was
concentrated and kept overnight under refrigeration to afford the
isolation of 1 as white crystalline solid.
Hz). 31P{1H} NMR (CDCl3): δ 32.9. 29Si{1H} NMR (CDCl3): δ
−0.19. Anal. Calcd for C8H21O3PSi (224.09): C, 42.84; H, 9.44.
Found: C, 42.79; H, 9.52%.
Me3SiCH2P(O)(OH)2 (1). Yield: 2.36 g, 79.0%. 1H NMR (CDCl3): δ
7.95 (br, 2H, P−OH), 1.18 (d, 2H, P−CH2, 2JP−H = 23.9 Hz), 0.16 (S,
1
9H, Si−CH3). 13C{1H} NMR (CDCl3): 14.4 (d, P−CH2, JP−C
=
110.4 Hz), −0.51 (S, Si−CH3). 31P {1H} NMR (CDCl3): δ 39.1.
29Si{1H} NMR (CDCl3): δ 0.13. IR (KBr, cm−1): 1255 (νSi−Me), 1198,
1132 (νPO3), 2298 (br, νP−OH), hydrogen bonded. ESI-MS (m/z):
191.0276 [M + Na]+, 213.0095 [M−H + 2Na]+, 381.0466 [2M−H +
2Na]+, 403.0282 [2M−2H + 3Na]+, 549.0835 [3M−H + 2Na]+,
593.0479 [3M−3H + 4Na]+, 739.1039 [4M−2H + 3Na]+, 761.0855
[4M−3H + 4Na]+. Anal. Calcd for C4H13O3PSi (168.04): C, 28.56; H,
7.79. Found: C, 28.51; H, 7.84%.
Synthesis of (2-Trimethylsilyl)-2-propylphosphonic Acid (2). To a
solution of 1a (5.0 g, 22.32 mmol) in dry THF was added 1.1 equiv of
n-BuLi at −60 °C. After stirring for 3−4 h at rt, methyl iodide (1.5
equiv) was added at −60 °C, and the reaction mixture was stirred for
15 h at room temperature. The solution was poured into a saturated
aqueous solution of NH4Cl. The organic layer was separated, dried
over sodium sulfate, and subjected to column chromatography over
silica gel using a mixture of hexane and ethyl acetate (9:1) to afford the
phosphonate diester 2a as a colorless liquid. The transformation of 2a
Me3SiCH2P(O)(OEt)2 (1a). bp 120−122 °C/20 mm. Yield: 4.1 g,
1
65.0%. H NMR (CDCl3): δ 4.03 (m, 4H, P−OCH2), 1.29 (t, 6H,
3
2
PO−CH2CH3, JH−H = 7.2 Hz), 1.12 (d, 2H, P−CH2, JP−H = 21.9
Hz), 0.13 (S, 9H, Si−CH3). 13C{1H} NMR (CDCl3): 60.9 (d, P−O−
CH2, JP−O−C = 6.3 Hz), 16.2 (d, P(OCH2)CH3, JP−O−C = 6.45 Hz),
14.4 (d, P−CH2, 1JP−C = 127.65 Hz), −0.48 (S, Si−CH3, 1JSi−C = 50.32
2
3
G
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Article
to the corresponding phosphonic acid 2 was achieved by following the
procedure similar to that described above for 1.
with SAINT.24 The measured intensities were reduced to F2 and
corrected for absorption with SADABAS.25 Structure solution,
refinement, and data output were carried out using the SHELXTL
program.26 All the non-H atoms were refined anisotropically. H atoms
were placed in geometrically calculated positions by using a riding
model unless stated otherwise. Images were created using the
Diamond program.27 In compound 4, one trimethylsilyl group is
disordered over two sites in the ratio of 1:1, and three ethyl groups are
disordered in the ratio of 2:1. The atom C24A in one disordered ethyl
group was refined with restrained atomic displacement parameters
(ADP).
Me3SiC(CH3)2P(O)(OEt)2 (2a). bp 70−72 °C/0.07 mm. Yield: 3.9 g,
1
78.0%. H NMR (CDCl3): δ 4.03 (m, 4H, P−OCH2), 1.28 (t, 6H,
3
3
PO−CH2CH3, JH−H = 7.2 Hz), 1.14 (d, 6H, P−C(CH3)2, JP−H
=
18.6 Hz), 0.08 (S, 9H, Si−CH3). 13C{1H} NMR (CDCl3): 60.8 (d, P−
2
1
OCH2, JP−O−C = 6.15 Hz), 23.3 (d, P−C(CH3), JP−C = 134.8 Hz),
19.1 (d, P−CH2, 2JP−C = 5.6 Hz), 16.3(d, P(OCH2)CH3, 3JP−O−C = 6.5
Hz), −1.5 (S, Si−CH3). 31P{1H} NMR (CDCl3): δ 38.4. 29Si{1H}
NMR (CDCl3): δ −0.26. Anal. Calcd for C10H25O3PSi (252.13): C,
47.59; H, 9.99. Found: C, 47.53; H, 10.01%.
Me3SiC(CH3)2P(O)(OH)2 (2). Yield: 2.4 g, 77.0%. 1H NMR (CDCl3):
3
δ 7.40 (br, 2H, P−OH), 1.20 (d, 6H, P−C(CH3)2, JP−H = 18.6 Hz),
ASSOCIATED CONTENT
0.14 (S, 9H, Si−CH3). 13C{1H} NMR (CDCl3): 23.2 (d, P−C(CH3)2,
1JP−C = 136.6 Hz), 19.1 (d, P−C(CH3)2, 2JP−C = 5.6 Hz), −2.0 (S, Si−
CH3). 31P{1H} NMR (CDCl3): δ 45.2. 29Si{1H} NMR (CDCl3): δ
0.03. IR (KBr, cm−1): 1251 (νSi−Me), 1205, 1134 (νPO3), 2358 (br,
νP−OH), hydrogen bonded. ESI-MS (m/z): 197.0747 [M + H]+,
393.1427 [2M + H]+, 589.2137 [3M + H]+, 785.2891 [4M + H]+,
981.3614 [5M + H]+, 1177.4359 [6M + H]+. Anal. Calcd for
C6H17O3PSi (196.06): C, 36.72; H, 8.73. Found: C, 36.68; H, 8.81%.
Synthesis of 3−5. The solution containing diethyltin(methoxy)-
methanesulfonate (0.52 g, 1.74 mmol) and 1 (0.30 g, 1.74 mmol) or 2
(0.35 g, 1.74 mmol) in dichloromethane was stirred for 8 h at room
temperature. Thereafter, the solvent was removed under vacuum, and
n-hexane was added to afford, in each case, a white solid, which was
filtered and dried under vacuum. The synthesis of 5 was achieved by
azeotropic dehydration reaction between diethyltin oxide (0.52 g, 1.74
mmol) and 1 (0.30 g, 1.74 mmol) in toluene under refluxed
conditions. The product was precipitated using methanol.
■
S
* Supporting Information
Selected NMR spectra, powder X-ray diffraction pattern,
scanning electron micrograph, and crystallographic data for
the structural analysis (in CIF format). This material is available
free of charge via the Internet at http://pubs.acs.org. Related
crystallographic information can be obtained free of charge
from the CCDC via www.ccdc.cam.ac.uk/data_request/cif
(CCDC Nos. 991294−991297 for 1−4).
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: shankar@chemistry.iitd.ac.in.
Notes
The authors declare no competing financial interest.
1
Et2Sn{OP(O)(OH)CH2SiMe3}(OSO2Me) (3). Yield: 0.65 g, 88.0%. H
NMR (CDCl3): δ 2.77 (S, 3H, SCH3), 1.66 (br, 4H, SnCH2), 1.34 (t,
ACKNOWLEDGMENTS
3
2
■
6H, Sn(CH2)CH3, JH−H = 8.1 Hz), 1.21 (d, 2H, P−CH2, JP−H =12
Hz), 0.11 (S, 9H, Si−CH3). 13C{1H} NMR (CDCl3): δ 39.3 (S, S−
The work was supported by CSIR Grant No. [01(2651)/12/
EMR-II]. N.S. is grateful to CSIR for providing Senior Research
Fellowship.
1
1
CH3), 20.7 (S, Sn−CH2, JSn−C = 648 Hz), 17.3 (d, P−CH2, JP−C
=
2
129.7 Hz), 9.2 (S, Sn(CH2)CH3, JSn−C = 35.46 Hz), −0.26 (S, Si−
CH3). 31P{1H} NMR (CDCl3): δ 28.6. 119Sn{1H} NMR (CDCl3): δ
−250. IR (KBr, cm−1): 1208, 1194, 1118, 1057 (νSO3 + νPO3), 1240
(νSi−Me), 2362 (νP−OH), hydrogen bonded. Anal. Calcd for C9H25O6-
PSSiSn (439.99): C, 24.62; H, 5.74. Found: C, 24.54; H, 5.81%.
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