Syntheses and coordination studies of 2-(diphenylphosphinomethyl)pyridine and its oxide towards mercury(II)

Article abstract of DOI:10.1016/j.poly.2012.01.001

Several coordination complexes of mercury(II) have been synthesized by the reaction of mercury(II) salts with 2-(diphenylphosphinomethyl)pyridine (L1) and its corresponding oxide (L2). The synthesized complexes were fully characterized by elemental analysis and multinuclear NMR spectroscopy techniques. The crystal structures were determined by single-crystal X-ray crystallography. Different geometries were observed around the metal center, including distorted trigonal-pyramidal (1,3), distorted tetrahedral (2) and distorted octahedral (4,5), with the degree of distortion depending on the steric effects and the chelating capability of 2-(diphenylphosphinomethyl)pyridine and its oxide.

Full text of DOI:10.1016/j.poly.2012.01.001

Polyhedron 34 (2012) 215–220
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Syntheses and coordination studies of 2-(diphenylphosphinomethyl)pyridine
and its oxide towards mercury(II)
⇑
Daniel A. Padron, Kevin K. Klausmeyer
Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Several coordination complexes of mercury(II) have been synthesized by the reaction of mercury(II) salts
with 2-(diphenylphosphinomethyl)pyridine (L1) and its corresponding oxide (L2). The synthesized com-
plexes were fully characterized by elemental analysis and multinuclear NMR spectroscopy techniques.
The crystal structures were determined by single-crystal X-ray crystallography. Different geometries
were observed around the metal center, including distorted trigonal–pyramidal (1,3), distorted tetrahe-
dral (2) and distorted octahedral (4,5), with the degree of distortion depending on the steric effects and
the chelating capability of 2-(diphenylphosphinomethyl)pyridine and its oxide.
Received 21 July 2011
Accepted 3 January 2012
Available online 10 January 2012
Keywords:
Mercury(II) complexes
N,P ligands
Ó 2012 Elsevier Ltd. All rights reserved.
31P NMR
X-ray diffraction
1. Introduction
The oxidized form, (L2, Fig. 1b), modifies the softer phosphorus
to a phosphoryl (P@O) group in which the oxygen moiety can act as
Hemilabile ligands have become the focus of intense research in
the past few decades due to their possible application in catalytic
reactions [1–5]. Our group has put considerable effort into the
study of the coordination chemistry of pyridyl containing phos-
phines, phosphinites, and phosphonites where the pyridyl ring is
substituted in various positions by the attendant phosphorus moi-
ety. This has resulted in a number of both discrete and polymeric
structures formed by the reaction of the ligand with various Ag+
salts. A part of these studies has been an examination of the influ-
ence of the coordinating ability of the anion present in the salt,
which effects a large influence on the solid state structure adopted
by the complex or polymer [6–12].
The bidentate ligand 2-(diphenylphosphinomethyl)pyridine
(L1, Fig. 1a) possesses a combination of a softer phosphine moiety
and a harder pyridine nitrogen functionality for which it can be in-
cluded in the hemilabile ligand category [6,13]. The chelating abil-
ity of this bifunctional ligand is well documented as it easily
conforms to the formation of a 5-membered ring [14–21]. The
bridging mode of this ligand has only been seen when reacted with
silver(I) as geometric constraints are overcome by the ability of
Ag(I) to form Ag–Ag interactions [6]. Only two instances of mono-
dentate binding have been seen thus far, once with Fe complexes,
and once with Ag in both of these cases the softer P binds to the
metal with pyridyl functionality dangling [6,22].
a hard donor. In this way the coordination mode of L1 and L2 can
depend on the ‘‘hardness’’ or ‘‘softness’’ of the transition metal ion
interacting with the ligand. As with L1 the expected normal bind-
ing mode is to chelate the metal center to form a 6-membered ring
[8,19]. An example is also known where only the N moiety is
bound with the P@O group dangling, in this example with PdCl2,
the P@O moiety is pointed away from the metal center [23].
Mercury(II) salts possess a soft metal center known to react
with tertiary phosphines to yield complexes with a range of
ligand-to-metal ratios, the most common being 1:1 and 2:1. The
2:1 complexes are tetra-coordinated and usually display mono-
meric tetrahedral structures in which the degree of distortion
depends on the electronic and steric properties of the phosphine.
On the other hand, 1:1 complexes exhibit a variety of molecular
structures ranging from discrete dimers to supramolecular net-
working assemblies [24–27].
In this research we describe the synthesis of several mercury(II)
complexes of 2-(diphenylphosphinomethyl)pyridine and its corre-
sponding oxide. The synthesized compounds have been charac-
terized by single crystal X-ray diffraction, multinuclear NMR
spectroscopy and elemental analysis.
2. Experimental
2.1. General remarks
⇑
All experiments were performed under nitrogen atmosphere
using Schlenk techniques. All air and light sensitive compounds
Corresponding author. Fax: +1 254 710 4272.
E-mail address: Kevin_Klausmeyer@baylor.edu (K.K. Klausmeyer).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.01.001

216
D.A. Padron, K.K. Klausmeyer / Polyhedron 34 (2012) 215–220
to leave an off-white powder. Colorless blocks were obtained by
(a)
(b)
slow diffusion of ether into a CH3CN solution of 4 at 5 °C. Yield
92% (0.197 g, 0.187 mmol). 1H NMR (CD3OD, 298.1 K): d 4.85 (d,
2H), 7.00 (m, 1H), 7.11 (m, 1H), 7.65 (m, 4H), 7.76 (m, 3H), 7.95
(m, 5H). 31P NMR (CD3CN, 298.1 K):
d
34.9, (s) ppm,
1J(31P–199Hg): 5981.29 Hz. Anal. Calc. for C38H32HgN2P2F6S2O6ÁH2O
(1053.34): C, 42.602; H, 3.19; N, 2.615. Found: C, 42.45; H, 3.02; N,
2.60%.
2.2.5. Synthesis of Hg(OTf)2(L2)2 (5)
A stirred solution of L2 (0.118 g, 0.402 mmol) in THF (5 mL) was
added to a solution of Hg(OTf)2 (0.100 g, 0.200 mmol) in THF
(5 mL). The resulting solution was allowed to stir for 5 min. A
white precipitate was formed and washes with THF (2 Â 30 mL)
were performed. The solvent was dried under vacuum to leave
an off-white powder. Colorless blocks were obtained by slow diffu-
sion of ether into a CH3CN solution of 5 at 5 °C. Yield 89% (0.193 g,
0.178 mmol). 1H NMR (CD3CN, 298.1 K): d 4.56 (d, 2H), 7.50 (m,
13H), 8.94 (d, 1H), 3J(1H–199Hg): 53.21 Hz. 31P NMR (CD3CN,
298.1 K): d 38.5, (s) ppm. Anal. Calc. for C38H32HgN2P2F6S2O8Á2H2O
(1085.34): C; 40.70; H, 3.23; N, 2.49. Found: C, 40.43; H, 2.85; N,
2.39%.
Fig. 1. Structure of (a) 2-(diphenylphosphinomethyl)pyridine (L1) and (b) 2-
(diphenylphosphinomethyl)pyridine oxide (L2).
were stored and handled in an inert atmosphere glovebox and used
as received. All solvents were reagent grade and distilled under in-
ert atmosphere from the appropriate drying agent prior to use. 1H
and 31P NMR spectra were recorded at 499.78 and 202.31 MHz,
respectively, at 25.0 °C/298.1 K, using a Varian VNMRS 500 MHz
Spectrometer. Elemental analyses were performed by Atlantic
Microlabs Inc. in Norcross, Georgia.
2.2. Synthesis
2.3. X-ray crystallography
2.2.1. Synthesis of [Hg(SCN)2(L2)]2 (1)
A solution of L2 (0.116 g, 0.394 mmol) in THF (5 mL) was added
to a solution of Hg(SCN)2 (0.480 g, 0.394 mmol) in THF (5 mL). The
resulting solution was allowed to stir for 15 min and then dried un-
der vacuum to leave an off-white powder. Colorless blocks were
obtained by slow diffusion of ether into a DMF solution of 1 at
5 °C. Yield 59% (0.284 g, 0.231 mmol). 1H NMR (CD3CN, 298.1 K):
d 4.21 (d, 2H), 7.53 (m, 13H), 8.53 (d, 1H). 31P NMR (CD3CN,
298.1 K) d 36.2, (s) ppm. Anal. Calc. for C40H32Hg2N6O2P2S4Á2.5THF
(1220.124): C, 42.88; H, 3.74; N, 6.00. Found: C, 42.97; H, 3.30; N,
6.16%.
Crystallographic data were collected on crystals with dimen-
sions 0.108 Â 0.119 Â 0.178 mm for 1, 0.231 Â 0.156 Â 0.142 mm
for 2, 0.108 Â 0.178 Â 0.221 mm for 3, 0.256 Â 0.133 Â 0.103 mm
for 4 and 0.105 Â 0.115 Â 0.147 mm for 5. Data were collected at
110 K on a Bruker X8 Apex using Mo Ka radiation (k = 0.71073 Å).
All structures were solved by direct methods after correction of
the data using SADABS [28,29]. Crystal data are presented in Tables
1 and 2, and selected interatomic distances and angles are given
in Table 3. All the data were processed using the Bruker AXS SHELXTL
software, version 6.10 [30]. Unless otherwise noted, all non-hydro-
gen atoms were refined anisotropically and hydrogen atoms were
placed in calculated positions.
2.2.2. Synthesis of Hg(SCN)2(L1)2 (2)
A solution of L1 (0.107 g, 0.386 mmol) in THF (5 mL) was added
to a solution of Hg(SCN)2 (0.0611 g,0.193 mmol) in THF (5 mL). The
resulting solution was allowed to stir for 20 min and then dried in
vacuum to leave an off-white powder. This was then dissolved in a
small amount of CH3CN and precipitated with ether. Colorless
blocks were obtained by slow diffusion of ether into a DMF solu-
tion of 2 at 5 °C. Yield 78% (0.132 g, 0.151 mmol). 1H NMR (THF-
d8, 298.1 K): d 4.53 (d, 2H), 7.54 (m, 13H), 8.62 (d, 1H). 31P NMR
(CD3OD, 298.1 K) d 35.0. Anal. Calc. for C38H32HgN4P2S2 (871.36):
C, 52.38; H, 3.370; N, 6.43. Found: C, 52.09; H, 3.78; N, 6.45%.
3. Result and discussion
3.1. General characterizations
3.1.1. Syntheses
The ligands L1 and L2 were synthesized according to a previ-
ously reported procedure [6,31]. Complexes 1–5 were synthesized
at room temperature and atmospheric pressure and were obtained
as white solids. The reaction of Hg(SCN)2 with an equimolar quan-
tity of L2 gave rise to the dimeric compound [Hg(SCN)2(L2)]2(1). In
contrast, the reaction of 2 equiv. of L1 with 1 equiv. of Hg(SCN)2
produced the monomeric complex Hg(SCN)2(L1)2(2). The complex
[HgCl2(L2)]2(3) was obtained by the reaction of HgCl2with an equi-
molar quantity of L2, producing a dimeric structure, as in the case
of complex 1. The reaction of 2 equiv. of L1 with 1 equiv. of
Hg(OTf)2 produced the complex Hg(OTf)2(L1)2(4) while the reac-
tion of 2 equiv. of L2 with 1 equiv. of Hg(OTf)2 yielded the com-
pound Hg(OTf)2(L2)2(5). Compounds 1–5 were purified by
washing the solid with THF, since the products were sparingly sol-
uble in this solvent. The presented compounds were very stable
under normal conditions, showing no signs of decomposition while
exposed to light or air at room temperature.
2.2.3. Synthesis of [HgCl2(L2)]2 (3)
A solution of L2 (0.059 g, 0.200 mmol) in THF (5 mL) was added
to a solution of HgCl2 (0.054 g, 0.200 mmol) in THF (5 mL). The
resulting solution was allowed to stir for 15 min and then dried
in vacuum to leave an off-white powder. This was then dissolved
in a small amount of CH3CN and precipitated with ether. Colorless
blocks were obtained by slow diffusion of ether into a THF solution
of 3 at 5 °C. Yield 80% (0.180 g, 0.160 mmol). 1H NMR (CD3CN,
298.1 K): d 4.24 (d, 2H), 7.52 (m, 13H), 8.49 (d, 1H). 31P NMR
(CD3CN, 298.1 K):
d
35.3, (s) ppm. Anal. Calc. for
C
36H32Cl4Hg2N2O2P2ÁH2O (1129.6): C, 37.67; H, 2.98; N, 2.44.
Found: C, 37.74; H, 2.71; N, 2.41%.
2.2.4. Synthesis of Hg(OTf)2(L1)2 (4)
A stirred solution of L1 (0.112 g, 0.405 mmol) in THF (5 mL) was
added to a stirred solution of Hg(OTf)2 (0.100 g, 0.201 mmol) in
THF (5 mL). A white precipitate was formed and washes with
THF (2 Â 30 ml) were performed. The solvent was dried in vacuum
3.2. Description of the crystal structures
Crystallographic data and refinement details for the complexes
reported herein were provided by X-ray diffraction studies. The

D.A. Padron, K.K. Klausmeyer / Polyhedron 34 (2012) 215–220
217
Table 1
Crystallographic data for compounds 1 through 3.
1
2
3
Empirical formula
Formula mass
a (Å)
b (Å)
c (Å)
C
20H16HgN3OPS2
C38H32HgN4P2S2
871.33
12.5734(10)
19.6504(15)
14.2674(15)
90
90
90
3525.1(5)
4
C44H48Cl4Hg2N2O4P2
1273.76
12.5791(7)
8.6549(4)
20.9536(10)
90
96.738(2)
90
2265.5(2)
2
610.06
8.4467(6)
9.7171(7)
13.9400(10)
76.694(3)
89.100(3)
71.610(4)
1054.57(13)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Crystal system
Space group
T (K)
triclinic
P1
110(2)
1.921
7.587
orthorhombic
Aba2
110(2)
1.642
4.609
monoclinic
P2(1)/n
110(2)
1.867
7.119
ꢀ
Dcalc (g/cmÀ3
)
l
(mmÀ1
2hmax (°)
)
28.28
28.24
28.28
Reflections measured
Reflections used
16424
5164
19700
9974
36763
5635
Data/restraints/parameters
R1 [I > 2r(I)]
5164/0/253
0.0229
0.0512
0.0256
0.0524
1.056
2268/1/214
0.0165
0.0438
0.0189
0.0451
1.099
5635/0/262
0.0220
0.0550
0.0250
0.0566
wR2 [I > 2
r
(I)]
R(F2o) (all data)
Rw(F20)(all data)
Goodness-of-fit (GOF) on F2
1.046
Table 2
fashion, Hg1-(l1,3-SCN)2-Hg1A, with a Hg1–Hg1A distance of
Crystallographic data for compounds 4 and 5.
5.945 Å. The geometry around the mercury centers can be de-
scribed as distorted trigonal–bipyramidal. The equatorial plane is
defined by a nitrogen donor from the L2 and two sulfur atoms from
two thiocyanate ions, where the O1–Hg1–N2A, N1–Hg1–S1 and
S1–Hg1–S2 angles are 119.2°, 139.7° and 100.6° (average = 119.8°),
respectively. The axial positions are occupied by one nitrogen atom
from a bridging counter-anion and an oxygen atom from the ligand
where the O1–Hg1–N2A angle is 154.4°. The distortions from a
regular trigonal–bipyramidal geometry may be attributed to the
formation of the mercury(II) thiocyanate metallacycle with rigid
NCS–Hg–NCS bond angles, and to the long range interaction be-
tween the soft Hg metal center and the hard oxygen donor, with
a Hg–O distance of 2.721 Å.
4
5
Empirical formula
Formula mass
a (Å)
b (Å)
c (Å)
C
38H32HgN2P2F6S2O6
C38H32HgN2P2F6S2O8
1085.31
30.2478(14)
25.6146(12)
20.7312(9)
90
93.707(2)
90
16028.6(13)
16
monoclinic
C2/c
110(2)
1.799
4.108
1053.31
20.289(2)
9.8162(12)
19.468(2)
90
a
(°)
b (°)
90
90
c
(°)
V (Å3)
3877.3(8)
4
orthorhombic
Pbcn
110(2)
1.804
4.238
28.29
39442
4801
Z
Crystal system
Space group
T (K)
Dcalc (g/cmÀ3
)
l
(mmÀ1
2hmax (°)
)
28.33
71806
19917
3.2.2. Structure of compound 2
Reflections measured
Reflections used
The crystal structure of complex 2, displayed in Fig. 3, was
obtained by the reaction of Hg(SCN)2 with L1 in a 2:1 ligand to
metal ratio. This compound is monomeric possessing a crystallo-
graphic C2 axis passing through the four-coordinate mercury
center. The geometry around the mercury atom consists of a dis-
torted tetrahedron with two L1 ligands coordinated through the
phosphorus atoms, and two monodentate thiocyanate anions
bound via the sulfurs to complete the coordination sphere of the
metal center. The steric hindrance caused by the bulky substitu-
ents on the phosphine ligands makes the P–Hg–P (127.7°) angle
much wider than the angle S–Hg–S (93.9°), which is formed by
the sulfur atoms on the smaller counter-anions and the mercury
center. The Hg–P (2.4688 Å) and Hg–S (2.6460 Å) distances fall in
the range of values previously reported in literature [26–28]. In
contrast to complex 1 above, the unoxidized ligand in complex 2
features a soft phosphorus moiety and forms a 2:1 complex with
the harder pyridyl nitrogen being unbound. In this case, complex
2 features two bulky units of the ligand bound to one metal center.
This sterically constrained environment prevents the thiocyanate
ions from adopting the sterically demanding bridging coordination
mode, limiting the counter-anions in the coordination sphere of 2
to act as terminal ligands. Regardless of initial reaction stoichiom-
etry, the 2:1 complex always results.
Data/restraints/parameters
R1 [I > 2r(I)]
4801/0/258
0.0227
0.0428
0.0444
0.0508
1.011
19917/0/1063
0.0329
0.0670
0.0544
0.0749
wR2 [I > 2
r
(I)]
R(F2o) (all data)
Rw(F20)(all data)
Goodness-of-fit (GOF) on F2
1.006
data is found in Tables 1 and 2. Figs. 2–6 display the molecular
structure of all compounds. A summary of selected bond lengths,
angles, and interatomic distances are given in Table 3. The mercury
coordination environments displayed in structures 1–5 differ
greatly from one structure to another, showing that the metal cen-
ter coordination mode depends on a combination of the counterion
present, and the soft or hard nature of the ligand donating atoms.
3.2.1. Structure of compound 1
Complex 1, shown in Fig. 2, was obtained by the reaction of
Hg(SCN)2 and L2 in a 1:1 ligand to metal ratio. The structure con-
sists of a centrosymmetric thiocyanate-bridged dimer with two
mercury centers. This nonplanar eight-membered ring is formed
by two bridging thiocyanate anions coordinated in a head-to-tail

218
D.A. Padron, K.K. Klausmeyer / Polyhedron 34 (2012) 215–220
Table 3
Selected bond lengths (Å) and angles (°) for compounds1 through 5.a
1
Hg(1)–N(1)
Hg(1)–N(2A)
Hg(1)–S(1)
Hg(1)–S(2)
Hg(1)–O(1)
2.361(3)
2.560(3)
2.4484(10)
2.4537(9)
2.7214(19)
N(1)–Hg(1)–S(1)
N(1)–Hg(1)–S(2)
S(1)–Hg(1)–S(2)
N(1)–Hg(1)–N(2A)
S(1)–Hg(1)–N(2A)
S(2)–Hg(1)–N(2A)
O(1)–Hg(1)–N(1)
O(1)–Hg(1)–S(1)
O(1)–Hg(1)–S(2)
O(1)–Hg(1)–N(2A)
P(1)–Hg(1)–P(1A)
P(1)–Hg(1)–S(1)
P(1A)–Hg(1)–S(1)
S(1A)–Hg(1)–S(1)
N(1)–Hg(1)–Cl(1)
N(1)–Hg(1)–Cl(2)
Cl(1)–Hg(1)–Cl(2)
N(1)–Hg(1)–O(1)
Cl(1)–Hg(1)–O(1)
Cl(2)–Hg(1)–O(1)
N(1)–Hg(1)–Cl(2A)
Cl(1)–Hg(1)–Cl(2A)
Cl(2)–Hg(1)–Cl(2A)
O(1)–Hg(1)–Cl(2A)
Hg(1)–Cl(2)–Hg(1A)
P(1A)–Hg(1)–P(1)
P(1A)–Hg(1)–N(1)
P(1)–Hg(1)–N(1)
N(1A)–Hg(1)–N(1)
O(1)–Hg(1)–N(1)
O(1)–Hg(1)–P(1)
O(1)–Hg(1)–N(1A)
O(1)–Hg(1)–P(1A)
O(1)–Hg(1)–O(1A)
N(2)–Hg(1)–N(1)
N(2)–Hg(1)–O(2)
N(1)–Hg(1)–O(2)
N(2)–Hg(1)–O(1)
N(1)–Hg(1)–O(1)
O(2)–Hg(1)–O(1)
N(4)–Hg(2)–N(3)
N(4)–Hg(2)–O(4)
N(3)–Hg(2)–O(4)
N(4)–Hg(2)–O(3)
N(3)–Hg(2)–O(3)
O(4)–Hg(2)–O(3)
N(4)–Hg(2)–O(11)
N(3)–Hg(2)–O(11)
O(4)–Hg(2)–O(11)
O(3)–Hg(2)–O(11)
O(2)–Hg(1)–O(5)
O(2)–Hg(1)–O(8)
N(1)–Hg(1)–O(8)
N(1)–Hg(1)–O(5)
N(2)–Hg(1)–O(8)
N(2)–Hg(1)–O(5)
O(1)–Hg(1)–O(8)
O(1)–Hg(1)–O(5)
O(8)–Hg(1)–O(5)
O(3)–Hg(2)–O(14)
O(4)–Hg(2)–O(14)
O(11)–Hg(2)–O(14)
N(3)–Hg(2)–O(14)
N(4)–Hg(2)–O(14)
119.20(7)
100.64(7)
139.71(4)
83.66(9)
96.42(7)
93.45(7)
77.28(7)
78.54(5)
106.71(5)
154.36(8)
127.57(10)
104.05(3)
111.10(3)
93.98(8)
116.36(7)
113.33(7)
130.30(3)
81.00(8)
94.44(5)
94.00(5)
85.15(6)
98.57(3)
84.45(2)
164.17(5)
95.55(2)
179.55(4)
105.06(5)
74.58(5)
76.85(11)
87.61(7)
90.21(5)
154.14(7)
90.04(5)
113.58(8)
177.34(12)
87.22(9)
92.03(9)
92.31(9)
88.26(9)
175.82(7)
176.43(11)
88.09(9)
92.97(9)
90.44(9)
88.41(9)
177.80(9)
103.46(9)
80.02(10)
85.92(8)
96.01(8)
73.00(8)
107.45(8)
85.73(10)
96.46(10)
96.93(10)
80.88(10)
76.73(08)
102.82(8)
177.76(9)
99.11(8)
79.05(8)
164.18(9)
95.74(10)
81.12(10)
2
3
Hg(1)–P(1)
Hg(1)–S(1)
2.4707(12)
2.6439(17)
Fig. 2. Thermal ellipsoid of 1 with an atomic numbering scheme. Ellipsoids are
shown at the 50% level. Hydrogen atoms have been removed for clarity.
Hg(1)–N(1)
Hg(1)–Cl(1)
Hg(1)–Cl(2)
Hg(1)–O(1)
Hg(1)–Cl(2A)
2.309(2)
2.3887(8)
2.4172(7)
2.510(2)
2.9738(7)
4
Hg(1)–P(1)1
Hg(1)–N(1)
Hg(1)–O(1)
2.3854(7)
2.631(2)
3.102(2)
5
Hg(1)–N(2)
Hg(1)–N(1)
Hg(1)–O(2)
Hg(1)–O(1)
Hg(1)–O(8)
Hg(1)–O(5)
Hg(2)–N(4)
Hg(2)–N(3)
Hg(2)–O(4)
Hg(2)–O(3)
Hg(2)–O(11)
Hg(2)–O(14)
2.120(3)
2.122(3)
2.520(2)
2.541(2)
2.126(3)
2.135(3)
2.511(2)
2.520(2)
2.631(3)
2.715(3)
2.674(3)
2.745(3)
Fig. 3. Thermal ellipsoid of 2 with an atomic numbering scheme. Ellipsoids are
shown at the 50% level. Hydrogen atoms have been removed for clarity.
Fig. 4. Thermal ellipsoid of 3 with an atomic numbering scheme. Ellipsoids are
shown at the 50% level. Hydrogen atoms and one molecule of THF have been
removed for clarity.
a
Symmetry transformations used to generate equivalent atoms. For 1: Àx + 2,
Ày, Àz + 1. For 2: Àx + 1, Ày + 1, z. For 3: Àx + 1, Ày + 1, Àz. For 4: Àx + 1, y, Àz + 1/2.
For 5: Àx, y, Àz + 1/2.
Two of the chloride atoms act as bridging connectors and one as
a simple terminal ligand. The axial positions are occupied by the
hard oxygen donor and one of the bridging chloride anions with
Cl2A–Hg1–O1 angle of 164.2°, while the equatorial plane is formed
by the nitrogen donor and two chloride anions coordinated to the
mercury center with Cl2–Hg1–Cl1, Cl1–Hg1–N1 and Cl2–Hg1–N1
angles of 130.8°, 116.4° and 113.3°, respectively (an average angle
of 120.16°). The bridging region shows a high degree of asymmetry
with bond distances of 2.974 and 2.417 Å for the bridging Hg–Cl
and 2.3886 Å for the terminal Hg–Cl. The two bridged Hg–Cl bond
3.2.3. Structure of compound 3
The reaction of HgCl2 with L2 in a 1:1 stoichiometry afforded
the complex with a halo-bridged dimeric structure 3 as shown in
Fig. 4. The geometry around the mercury atom presents a heavily
distorted trigonal–bipyramid that is defined by the nitrogen and
oxygen donors from the bidentate L2 and three chloride anions.

D.A. Padron, K.K. Klausmeyer / Polyhedron 34 (2012) 215–220
219
This allows the coordination of two ligand moieties via the soft
phosphorus and nitrogen atoms in a five-membered chelated ring
fashion (Hg1–S1 = 2.6460 Å for complex 2 and Hg1–O1 = 3.102 Å
for complex 2).
3.2.5. Structure of compound 5
Complex 5 was obtained from the reaction of 1 equiv. of
Hg(OTf)2 with 2 equiv. of L2. The product displays a 2:1 ligand to
metal ratio as shown in Fig. 6. Two independent molecules are
present in the asymmetric unit with only slight differences in the
bond lengths around the Hg centers (Fig. S2). As in the case of com-
plex 4, the geometry around the metal center in complex 5 can be
described as a distorted octahedron supported by two six-mem-
bered chelating rings and the weak interaction between the triflate
oxygen atoms and the mercury(II). In contrast to complex 4, the
six-membered ring in complex 5 allows a more flexible structure
which more closely approximates the geometry of an ideal octahe-
dron. The angles N1–Hg1–N2 and O1–Hg1–O2 are 177.34° and
175.82°, respectively, and the angles N1–Hg1–O1 and N2–Hg1–
O2 are 88.26° and 87.22°, respectively. Furthermore, the flexibility
in structure 5, given by the six-membered rings, makes the bite an-
gle of the ligand more obtuse than in complex 4, which bears a
five-membered chelate ring.
Fig. 5. Thermal ellipsoid of 4 with an atomic numbering scheme. Ellipsoids are
shown at the 50% level. Hydrogen atoms have been removed for clarity.
3.3. NMR spectra
All the products were characterized by multinuclear NMR spec-
troscopy techniques. The TMS (internal) reference was used for 1
H
NMR and H3PO4 (external) for 31P NMR. The spectra were recorded
as acetonitrile-d3, methanol-d4 or THF-d8 solution, depending on
the solubility of the compounds. The 1H NMR spectra of com-
pounds 1–5 are similar with small variations in the chemical shift
compared to the free ligand spectrum. In complex 4, a chemical
shift upfield was observed, causing overlapping of the signals cor-
responding to the hydrogen adjacent to the nitrogen in the pyridyl
substituent and the rest of the aromatic hydrogen atoms in the
ligand. This chemical shift suggests that the pyridyl moiety may
not be coordinated to the mercury center while in solution;
although the coordination is observed in solid state. For complex
5 we observe 3J(1H–199Hg) coupling to the bound pyridyl which
supports that the pyridyl is bound in solution [37–39]. The 31P
NMR spectra of these complexes show the presence of only one
phosphorus-containing species in solution. For 2 and 4 the shift
from free ligand is from À13.7 to 35.0 and 34.9 ppm, respectively,
the magnitude of this shift to lower field is consistent with previ-
ous work with other phosphines and mercury [37,40,41]. In com-
plex 4, where the phosphorus atom is directly coordinated to the
Hg atom, the spectrum showed the expected satellites due to
1J(31P–199Hg) coupling (199Hg, 16.84% natural abundance, nuclear
spin I = 1/2). The solubility of complex 2 was very poor in common
organic solvents, and were unable to detect the corresponding sa-
tellite speaks. For complexes 1, 3 and 5, which have the oxidized
ligand L2, only a slight shift is observed from the free ligand reso-
nance. This is likely due the weaker interaction of the P@O group
with the metal as compared to the much softer P moiety of L1.
Chemical shift and proton integration values are provided in the
Section 2.
Fig. 6. Thermal ellipsoid of 5 with an atomic numbering scheme. Ellipsoids are
shown at the 50% level. Hydrogen atoms have been removed for clarity.
lengths are typical for mercury structures containing chloro-bridg-
ing moieties [32,33]. The terminal Hg–Cl bond length, 2.3886 Å, is
comparable to 2.4015 Å, observed in the case of [HgCl(Ph3P)
(
l
-Cl)]2, and 2.375 Å, reported for the complex [HgCl(Ph2Ppym)
-Cl)]2 as well as other previous works [32–36].
(l
3.2.4. Structure of compound 4
Complex 4, the product from the reaction of Hg(OTf)2 with L1 in
a 2:1 ligand to metal ratio, is shown in Fig. 5. The crystal structure
exhibits a distorted octahedral geometry with a linear P–Hg–P
angle of 179.55° and an N–Hg–N angle of 76.85°. The bite angle
of the ligand (74.58°) featured in this complex constrains the envi-
ronment around the metal center which pushes the geometry
away from ideal octahedral. Contrary to complex 2, in which the
strongly coordinated thiocyanate anions deny the access of a sec-
ond ligand unit due to steric congestion, complex 4 features
weakly coordinated triflate oxygen atoms to the soft mercury(II).
4. Conclusions
Several complexes of Hg(II) and 2-(diphenylphosphino-
methyl)pyridine and its oxide have been synthesized and their
structures determined by single-crystal X-ray crystallography.
The ligand has shown the capability to coordinate to the mercury
center in a monodentate or chelating fashion, dependent on both

220
D.A. Padron, K.K. Klausmeyer / Polyhedron 34 (2012) 215–220
[3] S. Kitagawa, S. Noro, ChemCommun (2006) 701.
the sterically demanding phosphine substituents and the coordina-
tion properties of the counterion. Due to the soft nature of mer-
cury, the coordination of L1 and L2 through the softer donor
atoms (phosphorus and nitrogen, respectively), was preferred
when the ligands acted in a monodentate fashion. This coordina-
tion behavior of the ligand suggests that the harder moiety of the
ligand, either nitrogen in L1 or phosphoryl (P@O) in L2, could
reversibly bind the soft mercury center when in the presence of
a harder Lewis acid. Different geometries were observed around
the metal center, including distorted tetrahedral and distorted tri-
gonal–pyramidal, with the degree of distortion depending on the
steric effects and the chelating capability of the ligand. We are
continuing to study the coordination properties of this versatile
phosphine ligand and its two possible oxidized products (one bear-
ing a P@O and a nitrogen moieties and the other fully oxidized,
bearing a P@O and N–O moieties) toward mercury salts and other
transition metals.
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CCDC 834887, 834888, 834891, 834890, and 834889 contains
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conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
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data associated with this article can be found, in the online version,
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