ARTICLE IN PRESS
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H. Perry et al. / Journal of Solid State Chemistry 183 (2010) 1165–1173
[23] the syntheses of a Mn derivative of 2-pyridylphosphonic
acid and a Zn derivative of 6-methyl-2-pyridylphosphonic acid
by hydrothermal methods. Mn(C5H4NPO3)2(H2O) and Zn(6-Me-
2-C5H4NPO3) are both layered compounds in which the pyridyl
groups occupy space between the layers.
GADDS MWPC three-circle X-ray diffractometer equipped with a
rotating Cu K anode operated at 40 kV and 40 mA. Single crystal
X-ray diffraction data for III and IV were collected on a Bruker
Smart APEX-II CCD diffractometer with a Mo K source operated
at 40 kV and 40 mA. Data reduction and cell refinement for all
compounds were performed with SAINT [32]. SADABS [33] was
used to obtain absorption corrected data. The structures were
solved by direct methods using SHELXTL [34].
a
a
Recently we explored the compounds formed by Zn, Mn, and
Cu with 4-pyridylphosphonic acid [24]. In the Zn compound, the
tetrahedral Zn atoms are bound to two Cl atoms and two
phosphonate O atoms. Two Zn atoms are bridged by O–P–O
linkages to form eight-membered rings, but the two Cl atoms
prevent edge-sharing of the rings and formation of ladders. The
pyridyl nitrogen atoms are protonated and engage in hydrogen
bonding with phosphonate oxygen atoms. The Mn compound
forms layers that are linked by pendant pyridyl groups, while the
Cu compound forms a 3-D network that contains interpenetrating
channels along all three crystallographic axes. The channels are
filled with solvent water molecules that contribute to the stability
of the compound.
Although pyridylphosphonic acids have yielded a panoply of
coordination polymers with divalent metals, there have been no
studies on the compounds they form with SnII. These compounds
may be of use in ion exchange and catalysis, as they contain
potentially active lone pairs. A variety of structural motifs have
been observed for SnII phosphonates, including chains [25], rings,
ladders (edge-sharing rings), and sheets [26]. Cheetham and
coworkers [27] have developed a system of nomenclature for the
inorganic units formed in these structure types, which describes
them in terms of the number of Sn and P atoms in the Sn–O–P–O
rings. The most prevalent rings are 4R’s and 3R’s, although 8R’s
and others have been observed. The Sn atoms in these structures
are typically bound to three oxygen atoms resulting in a trigonal
pyramidal geometric configuration. There have been examples
published in which the Sn atoms are 4-coordinate [28,29]; the
additional bond is typically an oxygen atom at a distance of
2.3. Syntheses
3-Pyridylphosphonic acid: Pd(PPh3)4 (2.0 mmol, 2.31 g) was
placed, with a stirbar, in a 500 ml Schlenk roundbottom flask to
which was then affixed a Vigreux column sealed with a septum. A
needle with a balloon attached as a pressure moderator was
inserted into the septum. The sealed system was then repeatedly
evacuated and flushed with dry nitrogen. Toluene (30 ml) was
added into the top of the condenser through the septum by
syringe, and the setup was placed in an oil bath at 90 1C with
stirring. Once the solid had dissolved, 3-bromopyridine (0.1 mol,
15.8 g), triethylamine (0.12 mol, 16.7 ml), and diethyl phosphite
(0.12 mol, 15.5 ml) were added sequentially in the same manner
as the toluene. The yellow solution was stirred and heated at
115 1C for 12 h, during which a white precipitate appeared. After
cooling, 100 ml acetone was added and the mixture was filtered to
remove the majority of the Et3NHBr. The solvent was then
removed under reduced pressure, and 50 ml acetone was added.
After cooling to ꢂ5 1C, the mixture was filtered again to remove
residual Et3NHBr, and the acetone removed under reduced
pressure. The clear brown oil was dissolved in CH2Cl2, dried over
MgSO4, and the solvent removed under reduced pressure. Column
chromatography on silica gel eluted with ethyl acetate afforded
13.9 g (65% yield) diethyl 3-pyridylphosphonate. The ester was
then hydrolyzed under acidic conditions according to published
procedures [24]. 3-Pyridylphosphonic acid was dried in vacuo and
used without further purification.
Diethyl 4-cyanophenylphosphonate: Pd(PPh3)4 (1.25 mmol,
1.44 g) and 4-bromobenzonitrile (50.0 mmol, 9.1 g) were placed,
with a stirbar, in a 500 ml Schlenk roundbottom flask to which
was then affixed a Vigreux column sealed with a septum. A needle
with a balloon attached as a pressure moderator was inserted into
the septum. The sealed system was then repeatedly evacuated
and flushed with dry nitrogen. Toluene (50 ml) was added into the
top of the condenser through the septum by syringe, and
the setup was placed in an oil bath at 100 1C with stirring.
A white precipitate slowly began to form. After ꢁ20 min, an
additional 10 ml toluene was added to loosen the mixture and
facilitate stirring. The mixture was refluxed for 20 h, then cooled
to ambient temperature before washing three times with 50 ml
portions of H2O. The clear yellow organic phase was dried over
MgSO4 and the solvent then removed under reduced pressure.
Column chromatography on silica gel eluted with hexanes/ethyl
acetate (1:1) afforded 7.2 g (79% yield) diethyl 4-cyanophenylpho-
sphonate. The diethyl ester was used directly in the hydrothermal
reaction without further purification.
˚
ꢁ2.4 A. Barrou and coworkers have synthesized a divalent Sn
compound in which the Sn atom is coordinated by two oxygen
atoms and two alkylamine nitrogen atoms [30]. However, prior to
the work presented herein, there has not been a SnII phosphonate
reported in which the Sn is additionally coordinated by a pyridyl
nitrogen atom.
2. Experimental
2.1. Materials and methods
(Tetrakis)triphenylphosphine
palladium,
triethylamine,
diethylphosphite, toluene, SnII oxalate, and 3-bromopyridine were
purchased from Sigma Aldrich. Water was distilled and deionized.
Toluene, triethylamine, and diethylphosphite were dried or
distilled prior to use. All other starting materials were used as
received. 4-Pyridylphosphonic acid [24] and 6-methyl-2-pyridyl-
phosphonic acid [31] were synthesized as described in the
literature. Thermogravimetric analyses (TGA) were performed
with a TA Instruments Q500-0215 analyzer. The samples were
heated from ambient temperature to 1000 1C at a rate of 10 1C per
minute under air. Elemental analyses were performed by
Robertson Microlit, Inc., Madison, New Jersey.
Tin 3-pyridylphosphonate, Sn(O3PC5NH4) (I): In a PTFE-lined
autoclave with an internal volume of 15 ml, SnC2O4 (0.5 mmol,
0.103 g), 3-pyridylphosphonic acid (0.5 mmol, 0.08 g), and 10 ml
H2O were heated at 180 1C for five days under autogenous
pressure. After cooling, colorless crystals were collected by
filtration, washed with water and ethanol, and dried in an oven
at 90 1C. Yield: 0.069 g, 62% based on Sn. Anal. Calcd. for
SnO3PC5NH4: C, 21.77%; H, 1.46%; N, 5.08%. Found: C, 21.78%; H,
1.06%; N, 5.18%.
2.2. X-ray crystallography
Single crystal X-ray diffraction data for I were collected at
110 K on a Bruker Smart CCD-1000 diffractometer with a Mo K
a
source operated at 40 kW and 40 mV. Single crystal X-ray
diffraction data for II were collected at 110 K on a Bruker-AXS