Structural, theoretical and multinuclear NMR study of mercury(II) complexes with a new ambidentate phosphorus ylide

Article abstract of DOI:10.1016/j.poly.2011.06.033

The reaction of the new ambidentate ylide, Ph₃PCHCOCH ₂COOC₂H₅ (EAPPY), with HgX₂ (X = Cl, Br and I) in equimolar ratios using methanol as the solvent leads to binuclear complexes of the type [EAPPY·H

Full text of DOI:10.1016/j.poly.2011.06.033

Polyhedron 30 (2011) 2486–2492
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Structural, theoretical and multinuclear NMR study of mercury(II) complexes
with a new ambidentate phosphorus ylide
a
a
a
Seyyed Javad Sabounchei a, , Sadegh Salehzadeh , Marjan Hosseinzadeh , Fateme Akhlaghi Bagherjeri ,
⇑
Hamid Reza Khavasi b
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
b Department of Chemistry, Shahid Beheshti University, G.C., Evin, Tehran 1983963113, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of the new ambidentate ylide, Ph3PCHCOCH2COOC2H5 (EAPPY), with HgX2 (X = Cl, Br and I)
in equimolar ratios using methanol as the solvent leads to binuclear complexes of the type [EAPPYꢀHgX2]2
(X = Cl (1), Br (2) and I (3)). Single crystal X-ray analysis reveals the presence of a centrosymmetric
dimeric structure containing the ylide and HgX2 (X = Br or I). The IR and NMR data of the product [(EAP-
PY)ꢀHgCl2]2 (1), formed by the reaction of mercury(II) chloride with the same ylide, are similar to those of
2 and 3. Analytical data indicate a 1:1 stoichiometry between the ylide and Hg(II) halide in each of the
three products. Theoretical studies indicate that the nature of the R group in ylides of the type Ph3PCH-
COR has a weak effect on the Hg–C(ylide) bond length in binuclear Hg2L2I4 complexes.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 24 February 2011
Accepted 21 June 2011
Available online 12 July 2011
Keywords:
Phosphorus ylide
Mercury(II) halides complexes
X-ray crystal structure
Theoretical studies
1. Introduction
[14] [APPY = Ph3CCOMe; L = PPh3, PBu3; L2 = bipy] contain stable
ylides O-linked to a soft metal center.
The organometallic chemistry of phosphorus ylides R3P = C (R0)
(R00) (R, R0, R00 = alkyl or aryl groups) has undergone great growth
over the last few years, mainly due to their interesting application
as reactants in organometallic and metal-mediated organic synthe-
sis [1–4]. Juxtaposition of the keto group and carbanion in the
phosphorus ylide EAPPY allows for resonance delocalization of
the ylidic electron density, providing additional stabilization to
We have recently focused on the synthesis of binuclear com-
plexes derived from mercury(II) salts and phosphorus ylides
[15,16]. The aims of our present work are to describe the prepara-
tion and spectroscopic characterization of Hg(II) binuclear com-
plexes. The X-ray crystal structures of complexes
2 and 3
demonstrate C-coordination of the ylide to a metal. We also report
here a theoretical study on binuclear Hg2L2I4 complexes in which
the ligands L are a series of ylides of the type Ph3PCHCOR.
the ylide species (Scheme 1). This so-called
a-stabilization pro-
vides EAPPY with the potential to act as an ambidentate ligand
and thus bond to a metal center through either the carbanion (b)
or the enolate oxygen (c). The enolate from (c) may assume either
a cis or trans arrangement, the geometry of which will be retained
upon bonding to the metal.
2. Experimental
2.1. Physical measurements and materials
In the compounds reported to date, coordination through car-
bon is more predominant and is observed with soft metal ions,
e.g., Hg(II), Pd(II), Pt(II), Ag(I), Au(I) and Au(III) [5–9] and only very
few examples of O-coordinated ylides are known [10–13]. Some of
these examples contain the ylide O-coordinated to a hard, very
oxophilic metal center, such as Sn(IV) [10,11] or group 4 metals
with a high oxidation number e.g., Ti(IV), Zr(IV) and Hf(IV) [12].
Only W(0) complexes of the type W(CO)5L (L = ylide) [13] and
Pd(II) complexes of the stoichiometry [Pd(C6F5)L2)(APPY)](ClO4)
All reactions were performed in air. Methanol was distilled over
magnesium powder and diethyl ether over a mixture of sodium
and benzophenone just before use. All other solvents were reagent
grade and used without further purifications. The ligand was syn-
thesized by the reaction of triphenylphosphine with a chloroform
solution of the phosphonium salt and concomitant elimination of
HCl by NaOH [17]. Melting points were measured on a Stuart
SMP3 apparatus. Elemental analysis for C, H and N were performed
using a Perkin-Elmer 2400 series analyzer. Fourier transform IR
spectra were recorded on a Shimadzu 435-U-04 spectrophotome-
ter and samples were prepared as KBr pellets. 1H, 31P and 13C
NMR spectra were recorded on 300 MHz Bruker and 90 MHz Jeol
spectrometers.
⇑
Corresponding author. Tel.: +98 8118272072; fax: +98 8118273231.
E-mail address: jsabounchei@yahoo.co.uk (S.J. Sabounchei).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.06.033

S.J. Sabounchei et al. / Polyhedron 30 (2011) 2486–2492
2487
2.4.2.2. Data for 1. Yield: 83%, m.p. 178–180 °C. Anal. Calc. for
48H46Cl4Hg2O6P2: C, 43.55; H, 3.50. Found: C, 43.28; H, 3.73%. IR
(KBr disk)
(cmꢁ1): 1671 (CO) and 800 (P+–Cꢁ). 1H NMR (DMSO-
d6, ppm) dH: 4.82 (br, 1H, CH), 7.66–7.76 (m, 15H, arom.), 3.73 (s,
(Ph)3P
O
(Ph)3P
O
(Ph)3P
C
m
3
3
R
R
O
R
2H, CH2), 4.05 (q, JHH = 6.98 Hz, 2H, CH2), 1.16 (t, JHH = 6.98 Hz,
3H, CH3). 31P NMR (DMSO-d6, ppm) dp: 20.49. 13C NMR (DMSO-
a
b
c
\
1
d6, ppm) dC: 51.63 (br, CH), 123.60 (d, JPC = 89.50 Hz, PPh3(i)),
2
3
Scheme 1. The canonical forms of EAPPY (R = CH2COOC2H5).
133.75 (d, JPC = 10.04 Hz, PPh3(o)), 130.04 (d, JPC = 12.07 Hz,
PPh3(m)), 134.05 (s, PPh3(p)), 60.85 (s, CH2), 14.52 (s, CH3), 48.51
(s, CH2), 168.42 (s, OCO), 191.93 (s, CO).
2.2. X-ray crystallography
2.4.2.3. Data for 2. Yield: 83%, m.p. 176–178 °C. Anal. Calc. for
The single crystal X-ray diffraction analysis of suitable crystals
of 2 and 3 were performed on a STOE IPDS-II diffractometer at
C48H46Br4Hg2O6P2: C, 38.39; H, 3.09. Found: C, 38.56; H, 3.21%. IR
(KBr disk)
d6, ppm) dH: 4.61 (br, 1H, CH), 7.64–7.73 (m, 15H, arom.), 3.60 (s,
m
(cmꢁ1): 1667 (CO) and 796 (P+–Cꢁ). 1H NMR (DMSO-
298 K, using graphite monochromated Mo K
0.71073 Å). The data collection was performed using the
a
radiation (k =
-scan
x
3
3
2H, CH2), 4.07 (q, JHH = 7.17 Hz, 2H, CH2), 1.17 (t, JHH = 7.17 Hz,
technique and using the STOE X-AREA software package [18]. The
crystal structures were solved by direct methods and refined by
full-matrix least-squares on F2 by SHELX [19] and using the
X-STEP32 crystallographic software package [20]. All non-hydro-
gen atoms were refined anisotropically. Hydrogen atoms were
inserted at calculated positions using a riding mode with fixed
thermal parameters. Residual densities of 2.485 and ꢁ2.228 e Åꢁ3
for 2 and 3.572 and ꢁ3.173 e Åꢁ3 for 3 are near to the heavy Hg
atoms (0.95 and 0.91 Å from Hg1 in 2 and 1.25 and 0.79 Å from
Hg1 in 3).
3H, CH3). 31P NMR (DMSO-d6, ppm) dp: 20.09. 13C NMR (DMSO-
d6, ppm) dC: 52.27 (br, CH), 123.09 (d, JPC = 87.77 Hz, PPh3(i)),
133.16 (d, JPC = 9.93 Hz, PPh3(o)), 129.51 (d, JPC = 11.80 Hz,
PPh3(m)), 133.38 (s, PPh3(p)), 60.39 (s, CH2), 14.01 (s, CH3), 47.95
(s, CH2), 167.99 (s, OCO), 190.03 (s, CO).
1
2
3
2.4.2.4. Data for 3. Yield: 81%, m.p. 165–167 °C. Anal. Calc. for
C48H46I4Hg2O6P2: C, 34.18; H, 2.75. Found: C, 34.02; H, 2.88%. IR
(KBr disk)
m
(cmꢁ1): 1657 (CO) and 786 (P+–Cꢁ). 31P NMR
(DMSO-d6, ppm) dp: 18.89. 1H NMR (DMSO-d6, ppm) dH: 4.40 (br,
1H, CH), 7.61–7.68 (m, 15H, arom.), 3.46 (s, 2H, CH2), 4.07 (q,
2.3. Computational methods
3
3JHH = 7.17 Hz, 2H, CH2), 1.17 (t, JHH = 7.17 Hz, 3H, CH3). 13C NMR
1
(DMSO-d6, ppm) dC: 52.02 (br, CH), 124.11 (d, JPC = 77.59 Hz,
The geometries of all the compounds were fully optimized at
the DFT (B3LYP) [21,22] level of theory using the GAUSSIAN 03 [23]
set of programs. Three different standard basis sets LanL2MB,
Lanl2DZ and CEP-121G were used in all calculations to study the
possible effect of the basis set. All the above basis sets include
effective core potentials (ECP) for mercury, phosphorus and halide
(Br and I) atoms. In the case of all Hg2L2X4 complexes and the cor-
responding free ligands, the atomic coordinates for DFT calcula-
tions were obtained from the data of the X-ray crystal structure
analyses [15,16,24,25].
PPh3(i)), 133.66 (d, 2JPC = 8.45 Hz, PPh3(o)), 129.95 (d,
3JPC = 11.77 Hz, PPh3(m)), 133.94 (s, PPh3(p)), 60.84 (s, CH2),
14.66 (s, CH3), 48.85 (s, CH2), 168.79 (s, OCO), 189.56 (s, CO).
3. Results and discussion
3.1. Spectroscopy
The infrared data of the ligands as well as the corresponding
metal complexes are listed in Table 1. The mCO absorption, which
is sensitive to complexation, occurs at 1546 cmꢁ1 in the parent
ylide, as in the case of other resonance-stabilized ylides [26]. Coor-
dination of the ylide through the carbon atom cause an increase in
2.4. Sample preparation
2.4.1. Synthesis of EAPPY
mCO, while for O-coordination a lowering of mCO is expected. The
To
a chloroform solution (10 mL) of triphenylphosphine
infrared spectra of complexes in the solid state show mCO in the
(0.262 g, 1 mmol) was added ethyl-4-chloroacetoacetate (0.164 g,
1 mmol) and the mixture was stirred for 12 h. The solid product
(phosphonium salt) was filtered off, washed with Et2O and dried
under reduced pressure. Further treatment with aqueous NaOH
solution led to elimination of HCl, giving the free ligand EAPPY.
Yield: 94%, m.p. 86–88 °C. Anal. Calc. for C24H23O3P: C, 73.84; H,
range 1657–1671 cmꢁ1, at higher frequencies with respect to the
þ—Cꢁ
free ylide. The mP
frequency, which is also diagnostic of the
coordination, occurs at 870 cmꢁ1 for EAPPY. In the present study,
Table 1
5.94. Found: C, 74.21; H, 6.22%. IR (KBr disk)
m
(cmꢁ1): 1546 (CO)
Assignment of characteristic FT-IR vibrations of the ligands and their complexes.
and 870 (P+–Cꢁ). 1H NMR (CDCl3, ppm) dH: 3.80 (d, 2JPH = 24.19 Hz,
IR bond (cmꢁ1
)
1H, CH), 7.51–7.73 (m, 15H, arom.), 3.33 (s, 2H, CH2), 4.16 (q,
Compound
mC@O
Ref.
3JHH = 7.17 Hz, 2H, CH2), 1.25 (t, JHH = 7.17 Hz, 3H, CH3). 31P NMR
3
(CDCl3, ppm) dP: 12.50. 13C NMR (CDCl3, ppm) dC: 52.50 (d,
Ph3PCHCOPh (BPPY)
Ph3PCHCON(CH3)2
Ph3PCHCOCH3 (APPY)
Ph3PCHCOCH2COOC2H5 (EAPPY)
1525
1530
1530
1546
[27]
[28]
[29]
a
1JPC = 107.30 Hz, CH), 126.58 (d, JPC = 90.56 Hz, PPh3(i)), 133.11
1
2
3
(d, JPC = 10.16 Hz, PPh3(o)), 128.86 (d, JPC = 12.21 Hz, PPh3(m)),
132.13 (s, PPh3(p)), 60.42 (s, CH2), 14.23 (s, CH3), 48.28 (d,
3JPC = 15.41 Hz, CH2), 170.68 (s, OCO), 184.02 (s, CO).
C-coordination
[(EAPPY)ꢀHgCl2]2
[(EAPPY)ꢀHgBr2]2
[(EAPPY)ꢀHgI2]2
1671
1667
1657
1605
1635
a
a
a
[28]
[5]
2.4.2. Synthesis of the Hg(II) halide dimeric complexes
Au[CH(PPh3)(CON)(CH3)2]Cl
BPPYꢀHgCl2
2.4.2.1. General procedure. To HgX2 (0.5 mmol) dissolved in 10 mL
of dried methanol was added the ylide EAPPY (0.195 g, 0.5 mmol)
at room temperature. The mixture was stirred for approximately
4 h. The white solid product was filtered, washed with Et2O and
dried under reduced pressure.
O-coordination
[(Sn(CH3)3ꢀBPPY]Cl
1480
[17]
a
This work.

2488
S.J. Sabounchei et al. / Polyhedron 30 (2011) 2486–2492
Table 3
þ—Cꢁ
the mP
values for all the complexes were shifted to lower fre-
quencies and were observed in the range 786–843 cmꢁ1, suggest-
ing some removal of electron density from the P–C bond [27,28].
In the 1H NMR spectra, the signals due to the methinic protons
were broad or unobserved, probably due to the very low solubility
Crystal data and refinement details for 2 and 3.
Empirical formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C48H46Br4Hg2O6P2
C48H46Hg2I4O6P2
1689.57
120(2)
1501.57
298(2)
0.71073
monoclinic
Pc
0.71073
of these complexes. The expected higher frequency shifts of the 31
P
triclinic
and 1H signals for the PCH group upon complexation were ob-
served in their corresponding spectra. The 31P{1H} NMR spectra
show only one sharp singlet between d 18.89 and 20.49 ppm for
these complexes. The 31P chemical shift values for the complexes
appear to higher frequency by about d 6–8 ppm with respect to
the parent ylide (d = 12.50 ppm), indicating coordination of the
ylide has occurred (Table 2).
ꢀ
P1
10.4551(9)
11.8372(9)
20.9539(17)
10.2208(7)
10.8141(7)
12.9264(8)
72.206(5)
72.207(5)
73.452(5)
1266.11(14)
1
b (Å)
c (Å)
a
(°)
b (°)
98.658(7)
c
(°)
V (Å3)
2563.7(4)
2
1.945
9.205
The appearance of one set of signals for the PCH group in both
the 31P- and 1H NMR spectra indicates the presence of only one
molecule for all complexes [5], as expected for C-coordination. It
must be noted that O-coordination of the ylides generally leads
to the formation of cis and trans isomers, giving rise to two differ-
ent signals in the 31P- and 1H NMR spectra [12,14].
Z
Calculated density (mg/m3)
Absorption coefficient
2.216
8.602
(mmꢁ1
F(0 0 0)
Crystal size (mm)
)
1424
0.15 ꢂ 0.11 ꢂ 0.10
784
0.29 ꢂ 0.23 ꢂ 0.21
1.70–29.18
ꢁ14 ꢃ h ꢃ 13
ꢁ14 ꢃ k ꢃ 14
ꢁ17 ꢃ l ꢃ 17
14 537/6741
[Rint = 0.0438]
98.7
h Range for data collection (°) 1.72–29.27
Limiting indices
The most interesting aspect of the 13C NMR spectra of the com-
plexes is the upfield shift of the signals due to the ylidic carbon.
ꢁ14 ꢃ h ꢃ 10
ꢁ16 ꢃ k ꢃ 16
ꢁ28 ꢃ l ꢃ 28
19 869/11 878
[Rint = 0.0927]
98.8
Such an upfield shift observed in PdCl(g
3-2-XC3H4)(C6H5)3PCHCOR
Reflections collected/unique
(X = H, CH3; R = CH3, C6H5) was attributed to the change in hybrid-
ization of the ylidic carbon [29]. Similar upfield shifts of d 2–3 ppm
with reference to the parent ylide were also observed in the case of
[(C6H5)3PC5H4HgI2]2 [30] and our synthesized complexes [27,31].
The 13C shifts of the CO group in the complexes are around
190 ppm, relative to 183.91 ppm noted for the same carbon in
the parent ylide, indicating much lower shielding of the carbon
of the CO group in these complexes. No coupling to metal ions
was observed at room temperature in the 1H-, 13C- and 31P NMR
spectra for all these complexes. Failure to observe satellites in
the above spectra was previously noted in ylide complexes of
Hg(II) [32], which had been explained by fast exchange of the ylide
with the metal.
Completeness (%)
Absorption correction
Maximum and minimum
transmission
numerical
0.401 and 0.310
numerical
0.956 and 0.915
Refinement method
full-matrix least-
squares on F2
11 787/3/561
1.130
R1 = 0.0759,
wR2 = 0.1738
R1 = 0.1088,
full-matrix least-
squares on F2
6741/0/280
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.099
Final R indices [I > 2
r
(I)]
R1 = 0.0334,
wR2 = 0.0876
R1 = 0.0344,
wR2 = 0.0882
3.572 and ꢁ3.173
R indices (all data)
wR2 = 0.2003
2.485 and ꢁ2.228
Largest difference in peak
and hole (e Åꢁ3
Flack parameter
)
0.013(15)
3.2. X-ray crystallography
Single crystal X-ray diffraction analysis showed that complex 2
crystallized in the trigonal chiral Pc space group with a flack
parameter of 0.013(15) throughout, with Z = 2, so that one merucry
dimer complex is crystallographically independent. On the other
The crystals of complexes 2 and 3 were grown by the slow evap-
oration of the dimethylsulfoxide solution over several days. The so-
lid state structures of complexes 2 and 3 have been established by
single crystal X-ray analysis, which revealed monoclinic and tri-
clinic systems, respectively. Table 3 provides the crystallographic
results and refinement for the complexes. The molecular structures
are shown in Figs. 1 and 2, and selected interatomic parameters are
collected in Table 4. It is to be noted that according to data collec-
tion at room temperature, the ethylacetoacetate side chain in 2,
has a high thermal parameter. We tried refining some of these
atoms in two positions with a reduced occupancy, but while this
model converged satisfactorily, there was no decrease in the R va-
lue and therefore we consider that our original refinement is the
best that can be achieved and should be reported.
ꢀ
hand, complex 3 crystallized in the P1 space group throughout,
with Z = 1, so that 1/2 of the complex is crystallographically inde-
pendent. The dimeric structures adopted by the mercury com-
plexes are in contrast to the O-coordinated trinuclear mercury(II)
complex of the phosphorus ylide Ph3PCHCOPh [33], but they are
similar to the structure of trans-di-l-iodo-diiodobis(tri-phenyl-
phosphoniumcyclopentadienylide) dimercury(II) reported by Bae-
nziger et al. [34] and the C-coordinated dinuclear mercury(II)
halide complexes of Ph3CHCOPh (BPPY) [5]. The C-coordination
of EAPPY is in stark contrast to the O-coordination of the phospho-
rus ylide, Ph3PC(COMe)(COPh) (ABPPY) to a Hg(II) center [35]. The
difference in the coordination mode of ABPPY and the present ylide
to Hg(II) can be rationalized in terms of the electronic properties
and steric requirements of the ylides.
Table 2
31P and 1H NMR data of the ligands and their mercury(II) halide complexes.
The nucleophilicity of the carbanion in ABPPY is less than for
EAPPY; this is due to the additional delocalization of the ylide elec-
tron density in ABPPY which is facilitated by the second carbonyl
group. This will reduce the ability of ABPPY to bind via the ylidic
carbon. Facchin and co-workers have studied the steric influences
on the coordination modes of ylide molecules to Pt(II) systems
[36]. This research group concluded that the preferred coordina-
tion takes place via the ylidic C-atom, but that steric hindrance
around the metal center or the ylidic C-atom will necessitate O-
coordination. Indeed, this trend is reflected here, both BPPY and
Compound
31P{1H} NMRa
CH
2J(P–H)
EAPPYb
12.50 (s)
20.49 (s)
20.09 (s)
18.89 (s)
3.80 (d)
4.82 (br)
4.61 (br)
4.40 (br)
24.19
c
[EAPPYꢀHgCl2]2
c
[EAPPYꢀHgBr2]2
c
[EAPPYꢀHgI2]2
s, Singlet; d, doublet; br, broad.
T = 298 K; TMS d = 0.00 ppm; shifts relative to internal TMS and external 85%
phosphoric acid.
a
b
Record in CDCl3.
Record in DMSO-d6.
c

S.J. Sabounchei et al. / Polyhedron 30 (2011) 2486–2492
2489
Fig. 1. Thermal ellipsoid plot of 2 (30% probability level) showing the numbering scheme. H atoms are omitted for clarity.
EAPPY are slightly less sterically demanding than ABPPY, and both
are C-coordinated to Hg(II).
tances are much longer than the sum of Van der Waals radii
(1.5 Å) of two mercury atoms [41], indicating the absence of any
significant bonding interactions between the mercury atoms in
the molecular structures. The adaptation of dimeric structures in
Hg(II) ylide complexes may be explained by both the preference
of Hg(II) to have four coordination and the stability of the 18 elec-
tron configuration around Hg(II).
The Hg(II) center forms four close contacts with sp3 hybridiza-
tion and has a four-coordinate environment with one short Hg–X,
one Hg–C bond and two asymmetric bridging Hg–X bonds at dis-
tances of 2.779(2) and 2.831(2) Å in
2 and 2.8411(3) and
3.0348(4) Å in 3. The significant shortening of the Hg–C bond length,
2.205(19) Å in 2 and 2.234(4) Å in 3, compared to analogous dis-
tances in [EPPYꢀHgBr2]2 [5,24] and in [(C5H4P(C6H5)3HgI2]2 [37]
(2.224(5) and 2.292(8) Å , respectively) must be attributed to the
use of mercury orbitals with high s character for bonding to the yli-
dic carbon. The use of non-equivalent hybrid orbitals with high s
character to bond to low electronegative atoms was proposed by
Bent in the concept of isovalent hybridization to account for the var-
iation in bond lengths and bond angles around a central atom [38].
3.3. Theoretical studies
In our previous works we have reported the relative stability of
trans-like isomers versus cis-like isomers for a number of binuclear
metal ylide complexes [15,31,42]. In addition we have compared C-
coordination versus O- and P-coordination for a number of ylides
[43]. The reaction of a solvent molecule with binuclear metal ylide
complexes producing the corresponding mononuclear complexes
also has been previously studied [42,44,45]. In this work we have
compared the structure and metal–ylide bond strength in a number
of binuclear metal ylide complexes. We were interested to compare
the characteristic bond distances in compounds 2 and 3 with those
in a number of metal complexes containing similar ylides. Also we
were interested to see how much the energy of reaction (1) is differ-
ent for various ylides. Thus we chose a number of binuclear com-
plexes of Hg(II) with similar ylides for which the X-ray crystal
structures and related CIFs were available (see Scheme 2).
The terminal Hg–X bond lengths, 2.490(3) Å in
2 and
2.6950(4) Å in 3, are comparable to the value of 2.578 Å observed
in the case of C22H21O2PHgBr2, which has a tetrahedral coordina-
tion environment around mercury with a bridging structure [24].
The two bridged Hg–X bonds fall within the range 2.779(2)–
2.859(2) Å for 2 and 2.8411(3)–3.0348(4) Å for 3 reported for other
structures [39] containing bromo and iodo bridged mercury.
The angles around mercury vary from 87.61(6)° to 140.9(4)° for
2 and 91.819(10)° to 125.83(10)° for 3, a much distorted tetrahe-
dral environment. This distortion must be due to the higher s char-
acter of the sp3 hybrid mercury orbitals involved in the above
bonds and the formation of a strong halogen bridge between the
Hg atoms, which requires the internal XHgX angle to be consider-
ably smaller.
The stabilized resonance structure for EAPPY is destroyed by the
complexes formation. Thus, the C(5)–C(6) bond length of 1.50(2) Å
in 2 and the C(20)–C(19) bond length of 1.483(5) Å in 3 are signif-
icantly longer than the corresponding bond found in a similar
uncomplexed phosphorane (1.407(8) Å) [40]. On the other hand,
the P(1)–C(6) bond length in 2 and C(19)–P(1) bond length in 3
in the similar ylide is 1.706 Å [14], which shows that the above
bond is considerably elongated to 1.776(17) and 1.792(4) Å,
respectively, in the complexes. The internuclear distances between
the mercury atoms were found to be 4.046(7), 4.091 and 4.014(1) Å
in the structures 2, 3 and [BPPYꢀHgBr2]2, respectively These dis-
2Hg2þ þ 2L þ 4Xꢁ ! Hg L2X4
ð1Þ
2
The optimized structures of all the complexes are shown in
Fig. 3. A comparison between the selected calculated bond lengths
(Å) for the complexes with the corresponding experimental values
are presented in Table 5. The calculated electronic energies (Har-
tree) for the studied complexes and their components using differ-
ent basis sets are given in Table 6. As can be seen in Table 5, the
calculated bond lengths using all basis sets are slightly longer than
the measured ones, but the results of CEP-121G calculations are
closer to the experimental data. Interestingly, the results of all cal-
culations, similar to experimental data, show that the longest P–
C(ylide) bond length exists in Hg2LE2I4. Also the results of LanL2MB
and LanL2DZ calculations show that, similar to the solid state, the
longest Hg–C(ylide) bond length exists in Hg2LE2I4. On the other

2490
S.J. Sabounchei et al. / Polyhedron 30 (2011) 2486–2492
Fig. 2. Thermal ellipsoid plot of 3 (50% probability level) showing the numbering scheme. H atoms are omitted for clarity. Symmetry code; a: ꢁx + 1, ꢁy + 1, ꢁz+.
Table 4
O
C
R
Selected bond lengths (Å) and bond angles (°) for 2 and 3.
O
CH3
CH2O
CH2
LA
LB
R =
Bond distances
2
C5–C6
C6–P1
C6–Hg1
C5–O3
C4–C5
3
CH
X
PPh3
X
X
X
1.50(2)
C20–C19
C19–P1
C19–Hg1
C20–O1
C21–C20
C13–P1
C1–P1
1.483(5)
1.792(4)
2.234(4)
1.217(5)
1.523(5)
1.801(4)
1.805(4)
1.796(4)
2.8411(3)
2.6950(4)
3.0348(4)
Hg
Hg
1.776(17)
2.205(19)
1.21(2)
Ph3P
CH
LC
LD
CH2O
CH3
1.51(3)
O
R
C7–P1
1.824(19)
1.803(19)
1.769(15)
2.831(2)
2.490(3)
2.779(2)
2.812(2)
2.859(2)
2.503(3)
CH2O
C13–P1
C19–P1
Br1–Hg1
Br2–Hg1
Br3–Hg1
Br1–Hg2
Br3–Hg2
Br4–Hg2
Hg2L2X4
C7–P1
X= Br L= LA
X= I
I1–Hg1
I2–Hg1
I1a–Hg1
L= LA, LB, LC, LD, LE
LE
O2N
Scheme 2. Schematic illustration of complexes studied here.
Bond angles
C5–C6–P1
C5–C6–Hg1
P1–C6–Hg1
O3–C5–C6
in the solid state with that in the gas phase. Thus it is probable that
in addition to the nature of coordinated ylide (which is not very
important), crystal packing has also an effect on the bond lengths
around the metal atom in these complexes. The calculated energies
for the formation of Hg2L2I4 complexes according to reaction (1)
and considering the different ylides are given in Table 7. As can
be seen, in the case of all basis sets the least amount of released en-
ergy is calculated for Hg2LE2I4. We remember that the latter com-
plex has the longest Hg–C(ylide) bond length in both the solid
state and gas phase. Except in the latter case, one can hardly find
an agreement between the trend for increasing the Hg–C(ylide)
bond length in the solid state and decreasing the energy of forma-
tion of the Hg2L2I4 complexes in the gas phase. Furthermore, the
difference between the maximum amount of released energy and
minimum one in the series of these complexes is about 15–
20 kcal/mol, depending on the type of basis set. Thus once again
it confirms that the nature of the R group in the coordinated ylide
has only a weak effect on the strength of the Hg–C(ylide) bond
length. The second reason for this fact that the changes in the en-
ergy of reaction (1) are not consistent with the changes in Hg–
C(ylide) bond length, is the difference in the relaxation energy of
the different ligands from their geometry in the complex to the
equilibrium geometry. Obviously, different ligands have different
strain energies in the complex and this affects the energy of reac-
tion (1).
113.0(13)
107.6(11
112.7(9)
123.0(16)
120.3(15)
116.6(15)
140.9(4)
99.3(5)
106.48(9)
88.82(6)
87.61(6)
103.67(9)
106.4(4)
140.5(4)
C20–C19–P1
C20–C19–Hg1
P1–C19–Hg1
O1–C20–C19
O1–C20–C21
C19–C20–C21
C19–Hg1–I2
C19–Hg1–I1
I2–Hg1–I1a
I1–Hg1–I1a
I2 Hg1–I1
112.5(3)
110.3(3)
109.52(18)
123.2(4)
120.4(4)
O3–C5–C4
C6–C5–C4
116.4(3)
C6–Hg1–Br2
C6–Hg1–Br1
Br2–Hg1–Br3
Br1–Hg1–Br3
Br1–Hg2–Br3
Br4–Hg2–Br1
C30–Hg2–Br1
C30–Hg2–Br4
125.83(10)
100.74(10)
103.469(12)
91.819(10)
112.036(11)
88.180(9)
Hg1–I1–Hg1a
See Figs. 1 and 2 for the atom numbering. Symmetry code; a: ꢁx + 1, ꢁy + 1, ꢁz + 1.
hand, both the experimental data and the CEP-121G calculations
show that amongst all the Hg2L2I4 complexes, the Hg2LA2I4 com-
plex 3 has the shortest Hg–C(ylide) bond length. However, a com-
parison of experimental data for Hg2L2I4 complexes indicates that
the difference between the shortest and longest Hg–C(ylide) bond
length in the solid state is about 0.058 Å. We note that the ylides
studied in this work are of the type Ph3PCHCOR. Thus the above re-
sults shows that the nature of the R group in the coordinated ylide
has a weak effect on the Hg–C(ylide) bond length. Except in the
case of the longest and shortest bond lengths in the series of
Hg2L2I4 complexes, one can hardly find an agreement between
the trends for increasing the bond lengths around the metal ion
Now let us study the effect of the coordinated halide ion on both
the Hg–C(ylide) bond length and energy of reaction (1). As can be

S.J. Sabounchei et al. / Polyhedron 30 (2011) 2486–2492
2491
Fig. 3. Optimized structures for the Hg2L2X4 complexes studied here at the B3LYP/CEP-121G level of theory.
Table 5
A comparison between selected calculated bond lengths with the corresponding experimental data for Hg2L2X4 complexes.
Compound
Hg2LA2Br4
Bond length (Å)
LanL2 MB
LanL2DZ
CEP-121G
X-Ray
Hg–C
2.331
2.811
3.026
2.991
1.974
2.498
2.706
2.985
2.853
1.848
2.319
2.634
3.058
2.780
1.879
2.205(19)a
2.490(3)
2.831(2)
2.779(2)
1.776(17)
Hg–Br (terminal)
Hg–Br (bridged)
Hg–Br (bridged)
P–C
Hg2LA2I4
Hg2LB2I4
Hg2LC2I4
Hg2LD2I4
Hg2LE2I4
Hg–C
2.333
3.005
3.179
3.310
1.972
2.518
2.874
3.067
3.150
1.848
2.367
2.809
2.948
3.218
1.878
2.234(4)a
2.695(4)
2.841(3)
3.035(4)
1.792(4)
2.270(8)b
2.709(9)
2.816(7)
3.079(8)
1.771(8)
Hg–I (terminal)
Hg–I (bridged)
Hg–I (bridged)
P–C
Hg–C
2.354
3.019
3.184
3.272
1.981
2.513
2.868
3.094
3.153
1.847
2.384
2.807
2.982
3.168
1.873
Hg–I (terminal)
Hg–I (bridged)
Hg–I (bridged)
P–C
Hg–C
2.337
3.035
3.220
3.306
1.971
2.504
2.879
3.066
3.145
1.833
2.382
2.821
2.931
3.187
1.863
2.276(7)c
2.735(5)
2.803(5)
3.019(5)
1.786(7)
2.263(6)d
2.672(9)
2.841(9)
3.130(8)
1.783(6)
2.292(5)e
2.685(7)
2.790(6)
3.192(6)
1.793(4)
Hg–I (terminal)
Hg–I (bridged)
Hg–I (bridged)
P–C
Hg–C
2.338
3.013
3.161
3.325
1.969
2.499
2.898
3.044
3.141
1.835
2.373
2.821
2.955
3.148
1.864
Hg–I (terminal)
Hg–I (bridged)
Hg–I (bridged)
P–C
Hg–C
2.355
3.017
3.146
3.301
1.984
2.528
2.867
3.029
3.193
1.850
2.378
2.804
2.906
3.302
1.881
Hg–I (terminal)
Hg–I (bridged)
Hg–I (bridged)
P–C
a
b
c
This work.
[22].
[21].
[13].
[12].
d
e

2492
S.J. Sabounchei et al. / Polyhedron 30 (2011) 2486–2492
Table 6
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033;
or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at doi:10.1016/
j.poly.2011.06.033.
Calculated electronic energies (Hartree) for the studied complexes and their
components using different basis sets.
Compound
LanL2MB
LanL2DZ
CEP-121G
Brꢁ
ꢁ13.2064239
ꢁ13.2371155
ꢁ13.4633275
ꢁ11.5372418
ꢁ152.7585572
ꢁ203.5430001
ꢁ217.9604358
ꢁ175.0982868
ꢁ204.5004601
ꢁ222.7987857
ꢁ768.39909
Iꢁ
ꢁ11.4491618
ꢁ11.4721101
Hg2+
ꢁ41.7410709
ꢁ41.7934727
References
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Table 7
Calculated energies (kcal/mol) for the formation of Hg2L2X4 complexes according to
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Compound
LanL2MB
LanL2DZ
CEP-121G
Hg2LA2Br4
Hg2LA2I4
Hg2LB2I4
Hg2LC2I4
Hg2LD2I4
Hg2LE2I4
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ꢁ1327.01
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bonding to the ylidic carbon with decreasing electronegativity of
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complexes is only 0.023 Å. Thus it seems that the halide ion has
also a weak effect on the Hg–C(ylide) bond length. Therefore, the
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4. Conclusions
The present study describes the synthesis and characterization
of some binuclear Hg(II) complexes of a new phosphorus ylide.
On the basis of the physico-chemical and spectroscopic data we
propose that the ligand herein exhibits monodentate C-coordina-
tion to the metal center. Both the experimental and theoretical
studies show amongst all the five binuclear Hg2L2I4 complexes
studied here, complex 3 (Hg2LA2I4) has the shortest Hg–C(ylide)
bond length in both the solid state and gas phase. However, the
nature of the R group in the ylides of the type Ph3PCHCOR has a
weak effect on the Hg–C(ylide) bond length in the above
complexes.
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We are grateful to the Bu-Ali Sina University for a grant and Mr.
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Appendix A. Supplementary data
CCDC 751708 and 778462 contain the supplementary crystallo-
graphic data for complexes 2 and 3. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data Centre, 12