New mononuclear mercury(II) complexes of a bifunctionalized ylide containing five-membered chelate ring: Spectral and structural characterization

Article abstract of DOI:10.1016/j.ica.2010.05.004

The reaction of a new bifunctionalized ylide, Ph₂PCH ₂PPh₂C(H)C(O)(C₆H₄Cl) (2) with mercury(II) halides in equimolar ratios using dry methanol as solvent yielded the P, C-chelated complexes, {HgX

Full text of DOI:10.1016/j.ica.2010.05.004

Inorganica Chimica Acta 363 (2010) 3654–3661
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Inorganica Chimica Acta
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New mononuclear mercury(II) complexes of a bifunctionalized ylide containing
five-membered chelate ring: Spectral and structural characterization
a
a
b
Seyyed Javad Sabounchei a, , Sepideh Samiee , Sadegh Salehzadeh , Zabihollah Bolboli Nojini ,
*
Mehdi Bayat a, Elisabeth Irran c, Marina Borowski c
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
b Department of Chemistry, Faculty of Science, Shahid Chamran University, Ahvaz, Iran
c Institut für Chemie-Anorganische Festkörperchemie, Technische Universität Berlin, Strabe des 17, Juni 135, D-10623 Berlin, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of a new bifunctionalized ylide, Ph2PCH2PPh2@C(H)C(O)(C6H4Cl) (2) with mercury(II)
halides in equimolar ratios using dry methanol as solvent yielded the P, C-chelated complexes, {HgX2
[Ph2PCH2PPh2C(H)C(O)(C6H4Cl)]} where X = Cl (3), Br (4), I (5). The structures of complexes 4 and 5 have
been characterized crystallographically. Single crystal X-ray analyses reveal the presence of mononuclear
complexes containing Hg atom in a distorted tetrahedral environment. Characterization of the obtained
compounds was also performed by elemental analysis, IR, 1H, 31P, and 13C NMR. A theoretical study at DFT
(B3LYP) level using standard CEP-31G basis set showed that the experimentally determined structure of
the complex 5 is about 0.6–15.75 kcal molꢀ1 more stable than its other bonding modes.
Ó 2010 Elsevier B.V. All rights reserved.
Received 3 December 2009
Received in revised form 6 April 2010
Accepted 5 May 2010
Available online 12 May 2010
Keywords:
Bifunctionalized ylide
Mercury(II) halides
X-ray crystal structure
1. Introduction
ongoing study we have chosen to investigate the bonding modes
adopted by bifunctionalized ylide when ligated to Hg(II). Herein,
The coordination and organometallic chemistry of
a-keto
we report the reactivity of the ligand Ph2PCH2PPh2@C(H)C(O)
stabilized phosphorus ylides has been investigated extensively
(C6H4Cl), towards mercury(II) halides.
and their ambidenticity explained in terms of a delicate balance
between electronic and steric factors [1–6]. The
a-keto stabilized
2. Experimental
ylides derived from bisphosphines, viz., Ph2P(CH2)nPPh2@C(H)C(O)R
(n = 1, 2) (R = Me, Ph or OMe) [7] and PhC(O)C(H)@PPh2(CH2)2
PPh2@C(H)C(O)Ph [8] form an important class of such ligands which
can exist in ylidic and enolate forms. These ligands can therefore
engage in different types of bonding as illustrated in Chart 1 for
Ph2PCH2PPh2@C(H)C(O)C6H4Cl.
The bonding mode (f) had been previously observed for Rh(I),
Pd(II), Pt(II), Hg(II) [7–17]. In addition, Rh(I) and Hg(II) were
shown to exhibit the P-bonding mode (a) [14,17]. Hg(II) forms
C-coordinated complexes with Ph3P@C(H)C(O)Ph [18,19] and
Ph3P@C(H)CO(OEt) [20], whereas, regiospecific O-coordination of
the acetyl oxygen observed with Ph3P@C(COPh)(COMe) [21]. The
remarkable change in reactivity arises from a subtle variation in
the molecular electronic structures of the ylide due to the presence
of additional keto stabilization. Although HgBr2 and HgI2 form 1:1
dimeric halobridged complexes with the above ylide, HgCl2 forms a
1:2 monomeric square planar complex [21]. The reactivity and
coordination chemistry of carbonyl stabilized phosphorus ylides
is an important research field of our group [22–24]. As part of this
2.1. Physical measurements and materials
All reactions were carried out under an atmosphere of dry nitro-
gen. Methanol was distilled over magnesium powder and diethyl
ether (Et2O) over a mixture of sodium and benzophenone just
before use. All other solvents were reagent grade and used without
further purifications. Melting points were measured on a SMP3
apparatus. IR spectra were recorded on a Shimadzu 435-U-04 FT
spectrophotometer from KBr pellets. 1H, 13C and 31P NMR spectra
were recorded on 300 MHz Bruker and 90 MHz Jeol spectrometer
in DMSO-d6 or CDCl3 as solvent at 25 °C. Chemical shifts (ppm)
are reported according to internal TMS and external 85% phospho-
ric acid. Coupling constants are given in Hz. Elemental analysis for
C, H and N atoms were performed using a Perkin–Elmer 2400
series analyzer.
2.2. X-ray crystallography
Suitable crystals were obtained from dimethylsulfoxide solu-
tion by the slow evaporation of the solvent over several days. All
* Corresponding author. Tel.: +98 8118272072; fax: +98 8118273231.
E-mail address: jsabounchei@yahoo.co.uk (S.J. Sabounchei).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.05.004

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3655
Chart 1. The possible bonding modes of Ph2PCH2PPh2C(H)C(O)C6H4Cl to metal M.
measurements were made on an Oxford Diffraction Xcalibur S Sap-
phire system at 150(2) K, using graphite monochromated Mo K
basis set. This basis set includes effective core potentials (ECP) for
both the mercury and phosphorus atoms as well as halide (Cl, Br
and I) ions. A starting molecular-mechanics for isomers II–V for
the ab initio calculations was obtained using the HYPERCHEM 5.02
program [30]. Calculations were performed on a Pentium-PC com-
puter with a 4400 MHz processor.
a
radiation (k = 0.7107 Å). Structure solution and refinement were
carried out using SHELXS-97 and SHELXL-97, respectively [25,26] The
structure was solved by direct methods and refined by full matrix
least-squares methods on F2. All non-hydrogen atoms were refined
anisotropically. All hydrogen were included in calculated positions.
2.4. Preparation of compounds
2.3. Computational method
2.4.1. Preparation of [Ph2PCH2PPh2CH2C(O)(C6H4Cl)]Br (1)
The geometry of the metal complexes 4 and 5 as determined by
X-ray crystal structure analysis (Figs. 1 and 2) were fully optimized
at DFT (B3LYP) [27,28] level of theory using the GAUSSIAN 03 set of
programs [29]. The observed geometry of compounds 4 and 5
was used as a basis of DFT calculations for compound 3. The geom-
etries of other available coordinated isomers for complex 5 (Fig. 3,
isomers I–V) were also optimized at the B3LYP level of theory. The
atomic coordinates of 4 and 5 in their crystal structures were used
for corresponding DFT calculations on isomer I using the CEP-31G
Bis(diphenylphosphino)methane (dppm) (0.2 g, 0.52 mmol)
was dissolved in 5 ml of chloroform and then a solution of 4-chlor-
ophenacyl bromide (0.12 g, 0.52 mmol) in the same solvent (5 ml)
was added dropwise to the above solution. The resulting yellow
solution was stirred for 2 h. The solution was concentrated under
reduced pressure to 2 ml, and diethyl ether (20 ml) was added.
The yellow solid formed was filtered off, washed with diethyl ether
(2 ꢁ 10 ml) and dried under reduced pressure. Yield: 0.28 g, 87%.
M.p. 170–172 °C. Anal. Calc. for C33H28BrOP2Cl: C, 64.15; H, 4.57.

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Fig. 1. ORTEP view of the X-ray crystal structure of [HgBr2(Ph2PCH2PPh2C(H)C(O)C6H4Cl)] (4).
cmꢀ1): 3450, 3051, 2926, 1581, 1503 (C@O), 1436, 1403, 1383,
1174, 1102, 1012, 902, 846, 740, 695. 1H NMR (CDCl3): dH = 3.65
2
(d, 2H, CH2, JP–H = 14.33); 4.32 (br, 1H, CH); 7.24–7.69 (m, 24H,
2
Ph). 31P NMR (CDCl3): dP = ꢀ29.90 (d, PPh2, JP–P = 64.00); 11.35
2
(d, PCH, JP–P = 63.82). 13C NMR (CDCl3): dC = 24.99 (dd, CH2,
1
1JP–C = 57.60, 57.72); 50.73 (d, CH, JP–C = 110.55); 128.15–137.82
(Ph); 184.05 (s, CO).
2.4.3. Preparation of {HgCl2[Ph2PCH2PPh2C(H)C(O)(C6H4Cl)]} (3)
General procedure for complexes: To a solution of HgCl2 (0.1 g
0.37 mmol) in dry methanol (10 ml), a solution of 2 (0.2 g,
0.37 mmol) also in dry methanol (10 ml) was added dropwise at
0 °C and stirred for 2 h. The separated solid was filtered, and
recrystallised in dichloromethane. Yield: 0.17 g, 56%. M.p. 205–
208 °C. Anal. Calc. for C33H27Cl3HgOP2: C, 49.03; H, 3.37. Found:
C, 48.66; H, 3.87%. IR (KBr, cmꢀ1): 3439, 2887, 1710, 1603 (C@O),
1438, 1327, 1182, 1107, 779, 748, 691. 1H NMR (DMSO-d6):
dH = 4.63 (br, 2H, CH2); 5.16 (br, 1H, CH); 7.40–7.91 (m, 24H, Ph).
2
31P NMR (DMSO-d6): dP = 6.66 (br, PPh2); 25.12 (d, PCH, JP–P
=
40.14). 13C NMR (DMSO-d6): dC = 24.99 (br, CH2); 34.24 (br, CH);
Fig. 2. ORTEP view of the X-ray crystal structure of [HgI2(Ph2PCH2PPh2C(H)-
C(O)C6H4Cl)] (5).
119.14–140.31 (Ph); 191.96 (s, CO).
2.4.4. Preparation of {HgBr2(Ph2PCH2PPh2C(H)C(O)(C6H4Cl)]} (4)
Yield: 0.21 g, 62%. M.p. 200–202 °C. Anal. Calc. for
Found: C, 63.89; H, 4.71%. IR (KBr, cmꢀ1): 3337, 3045, 2836, 1674
C
33H27Br2HgOP2Cl: C, 44.17; H, 3.03. Found: C, 43.94; H, 3.04%. IR
(KBr, cmꢀ1): 3475, 2888, 1709, 1605 (C@O), 1562, 1485, 1438,
1357, 1326, 1181, 1105, 1052, 1015, 845, 779, 749, 722, 691. 1H
NMR (DMSO-d6): dH = 4.65 (t, br, 2H, CH2); 5.26 (br, 1H, CH);
7.45–7.73 (m, 24H, Ph). 31P NMR (DMSO-d6): dP = 1.35 (br, PPh2);
(C@O), 1587, 1486, 1436, 1365, 1209, 1160, 1113, 997, 806, 740,
2
691. 1H NMR (CDCl3): dH = 4.28 (d, 2H, PCH2P, JP–H = 14.96); 5.95
2
(d, 2H, PCH2CO, JP–H = 12.81); 7.27–8.52 (m, 24H, Ph). 31P NMR
2
(CDCl3): dP = ꢀ29.42 (d, PPh2, JP–P = 65.15); 20.93 (d, PCH2CO,
1
2JP–P = 64.40). 13C NMR (CDCl3): dC = 21.54 (dd, PCH2P, JP–C
=
24.47 (d, PCH, JP–P = 42.24). 13C NMR (DMSO-d6): dC = 23.51 (br,
2
1
52.22, 51.85); 36.11 (d, PCH2, JP–C = 61.43); 117.64–140.95 (Ph);
CH2); 34.24 (br, CH); 120.62–140.33 (Ph); 190.52 (s, CO).
2
191.17 (d, CO, JP–C = 69.5).
2.4.5. Preparation of {HgI2(Ph2PCH2PPh2C(H)C(O)(C6H4Cl)]} (5)
2.4.2. Preparation of [Ph2PCH2PPh2@C(H)C(O)(C6H4Cl)] (2)
Yield: 0.29 g, 78%. M.p. 197–199 °C. Anal. Calc. for C33H27I2
The resulting phosphonium salts (1) (0.52 mmol) were treated
with triethyl amine (0.52 ml) in toluene (16 ml). The triethyl amine
hydrobromide was filtered off. Concentration of the toluene layer
to 3 ml and subsequent addition of petroleum ether (25 ml) results
in the precipitation of ligands as free-flowing white solids. They
were further purified by crystallization from toluene/petroleum
ether. Yield: 0.24 g, 85%. M.p. 150–152 °C. Anal. Calc. for
HgOP2Cl: C, 39.98; H, 2.75. Found: C, 40.45; H, 3.06%. IR (KBr,
cmꢀ1): 3420, 3052, 2889, 1711, 1606 (C@O), 1581, 1561, 1484,
1437, 1324, 1180, 1103, 1015, 874, 844, 777, 748, 690. 1H NMR
2
(DMSO-d6): dH = 4.68 (t, 2H, CH2, JP–H = 11.91), 5.34 (br, 1H, CH),
7.45–7.962 (m, 24H, Ph). 31P NMR (DMSO-d6): dP = ꢀ7.07 (br,
2
PPh2), 26.67 (d, PCH, JP–P = 48.95). 13C NMR (DMSO-d6):
1
dC = 23.52 (d, CH2, JP–C = 51.62); 123.14–136.95 (Ph); 191.50 (s,
C33H27OP2Cl: C, 73.81; H, 5.07. Found: C, 74.02; H, 5.14%. IR (KBr,
CO); (CH, was not seen).

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3657
Fig. 3. Illustration of the five possible isomers for complex 5.
attributable to the ylidic proton [16]. This compound shows upfield
shifts compared to that of phosphonium of the phosphonium salt
(1), suggesting some increasing of electron density in the P–C
bond.
3. Results and discussion
3.1. Synthesis
The 31P chemical shift values for the complexes appear to be
shifted downfield with respect to the parent ylide, also indicating
that coordination of the ylide has occurred. In the 31P NMR spectra
the signal due to phosphonium group appears as a doublet at
25.12, 24.47 and 26.67 ppm for 3, 4 and 5, respectively. The coor-
dination of phosphine is clearly evident from the strong downfield
shifts of the signal due to PPh2 group at 6.66, 1.35 and ꢀ7.07 ppm
for 3, 4 and 5, respectively, when compared to that of same signal
in the free ylide (d ꢀ29.90). In the 1H NMR spectra, the signals due
to the methinic protons for complexes are broad. Similar behavior
was observed earlier in the case of ylide complexes of platinum(II)
chloride [31]. The expected lower shielding of 31P and 1H nuclei for
the PCH group upon complexation in the case of C-coordination
were observed in their corresponding spectra. The most interesting
aspect of the 13C spectra of the complexes is the upfield shift of the
signals due to the ylidic carbon. Such an upfield shift observed in
The ligand (2) was synthesized by treating 4-chlorophenacyl
bromide (prepared by reacting 4-chloroacetophenone with bro-
mide in glacial acetic acid) with dppm and removal of the proton
from the phosphonium salt (Scheme 1). Reactions of HgX2 with
the ylide in a 1:1 stoichiometry afforded the P, C-chelated com-
plexes (Scheme 2).
3.2. Spectroscopy
The 31P NMR spectrum of 1 exhibits two doublets at 20.98 and
ꢀ29.39 ppm that indicate the PCH2CO and PPh2 groups, respec-
tively. The 1H NMR spectrum exhibits a doublet at 5.95 ppm, with
2
a coupling constant JP–H of 12.81 Hz, relative to a CH2 group of a
4-chlorophenacyl bromide system bonded to a phosphonium
moiety.
The 31P NMR spectrum of 2 shows two doublets at 11.35 and
ꢀ29.90 ppm, which are assigned to the PCH and PPh2 groups,
respectively. The 1H NMR spectrum shows a broad at 4.32 ppm
[PdCl (
was attributed to the change in hybridization of the ylidic carbon
g
3-2-XC3H4) (C6H5)3PCHCOR] (X = H, CH3; R = CH3, C6H5)

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Scheme 1. The synthesis route for preparation of bifunctionalized ylide (2).
Scheme 2. Reaction of bifunctionalized ylide (2) with Hg(II) halides.
[32]. Similar upfield shifts of 2–3 ppm with reference to the parent
ylide were also observed in the case of [(C6H5)3PC5H4HgI2]2 [33].
The 13C shifts of the CO group in the complexes are around
190 ppm, relative to 184.05 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 Hg was ob-
served 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 the ylide complexes of Hg(II)
[33] and Ag(I) [34], which had been explained by fast exchange
of the ylide with the metal.
The X-ray analysis reveals the P, C-chelate mode of coordination
of the ligand, Ph2PCH2PPh2@C(H)C(O)C6H4Cl to Hg(II) atom in
complexes 4 and 5. The Hg(II) centre in complexes 4 and 5 is
four-coordinate with sp3 hybridization. The Hg atom is bonded to
one ylidic C atom, one P atom of the PPh2 unit and two terminal
halogen atoms. The angles subtended by the ligand at the Hg(II)
centre in
4 and 5 vary from 90.30(8) to 117.89(3)(4) and
89.43(10) to 116.26(3)(5) indicating a distorted tetrahedral envi-
ronment. The stabilized resonance structures for the parent ylide
are destroyed by the complex formation, thus, the C(26)–C(27)
bond lengths 1.439(5) Å (4) and 1.460(6) Å (5) are longer than
the corresponding distances found in the similar uncomplexed
phosphorane [Ph2PCH2PPh2C(H)C(O)Ph] (1.404(3) Å) [15]. On the
other hand, the bond length of P–C(H) in the similar ylide
[Ph2PCH2PPh2C(H)C(O)Ph] is 1.705(2) Å [15] which shows that
the corresponding bonds are considerably elongated to
1.761(4) Å (4) and 1.754(4) Å (5).
The IR data confirm the complete formation of the carbonylic
ylide with the disappearance of the phosphonium CO band at
1674 cmꢀ1 and the presence of a new strong CO band relative to
a carbonyl stabilized ylide at 1503 cmꢀ1 [16]. The
m(CO), which is
sensitive to complexation, occurs at 1503 cmꢀ1 in the parent ylide,
as in the case of other resonance stabilized ylides [35]. Coordina-
tion of the ylide through C-coordination causes an increase in
The two terminal Hg–Br distances in
4 (2.5675(4) and
m
(CO) [22–24] while for O-coordination a lowering of
m
(CO) is ex-
2.6009(4) Å) are shorter than the corresponding distances in
[HgBr2(PPh3)2] (2.559(2) and 2.545(3) Å) [37]. The Hg–I distances
in 5 (2.7270(14) and 2.7483(3) Å) are in agreement with the values
reported in [HgI2(PPh3)2] (2.733(1) and 2.763(1) Å) [38].
pected [36]. The infrared absorption bands observed for the three
complexes around 1600 cmꢀ1 indicate coordination of the ylide
through carbon. Thus, the spectral data indicate the bidentate
coordination of the ligand (2) through both phosphine group and
ylidic carbon atom.
The Hg–P distances in 4 (2.4984(9) Å) and 5 (2.5429(12) Å) are
less than those of found in [HgBr2(PPh2CH2PPh2C(H)C(O)Ph)]
(2.546(3) Å) and [HgI2(PPh2CH2PPh2C(H)C(O)Ph)] (2.5688(19) Å)
[15]. The Hg–P bond lengths in 4 and 5 are consistent with the
values reported for the majority of Hg(II)–phosphine complexes
[39]. However, this distance is longer when compared to those in
the polymeric complex {HgI2[PPh2CH2CH2PPh2C(H)C(O)Ph]}n
(2.472(2) Å) [17], and P, P-coordinated monomeric complexes
HgCl2(dppeO)2 (2.453(2) Å) and HgBr2(dppeO)2 (2.456(2) Å) [40].
The Hg–C distances in 4 (2.412(3) Å) and 5 (2.424(5) Å) are
comparable to analogous distances in [HgBr2(PPh2CH2PPh2C(H)
3.3. X-ray crystallography
Table 1 provides the crystallographic results and refinement
information for complexes 4 and 5. The molecular structures are
shown in Figs. 1 and 2. Selected bond lengths (Å) and angles (°)
are given in Table 2. Fractional atomic coordinates and equivalent
isotropic displacement coefficients (Ueq) for the non-hydrogen
atoms of the complexes are shown in Supplementary material.

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3659
Table 1
Table 3
Crystal data and refinement details for complexes 4 and 5.
A comparison between the calculated energies for the five possible isomers of
compound 5.
Compound
4
5
E (Hartree)
D )
E (kcal molꢀ1
Empirical formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
33H27Br2ClHgOP2
C33H27ClHgI2OP2
991.33
150(2)
0.71073
monoclinic
P21/c
13.1440(2)
16.2491(3)
15.9487(3)
90
897.35
150(2)
P, C-coordinated (I)
P, O-coordinated (II)
C-coordinated (III)
P-coordinated (IV)
O-coordinated (V)
ꢀ422.897069
ꢀ422.8961062
ꢀ422.8950892
ꢀ422.8828843
ꢀ422.8719609
0
0.604
1.242
8.901
0.71073
monoclinic
P21/c
13.0756(3)
16.1069(3)
15.6853(3)
90
106.478(2).
90
3167.77(11)
4
15.755
b (Å)
c (Å)
a
(°)
C-coordinated Hg(II)–phosphorus ylide complexes which lie in
the range, 1.786(10)–1.806(10) Å [18–20]. Furthermore, the C@O
distances of 1.248(9) and 1.244(16) Å in 4 and 5, respectively, are
found to be close to that of the same distance in the similar ylide
[Ph2PCH2PPh2C(H)C(O)Ph] (1.249(2) Å). All these data perhaps
indicate that the interaction of carbon atom in present P, C-
chelated ligand is not as strong as that in similar C-coordinated
ligands.
b (°)
106.7339(19)
90
3262.05(10)
4
c
(°)
V (Å3)
Z
Absorption coefficient
7.592
6.816
(mmꢀ1
)
h Range for data collection 2.99–25.00
(°)
Index ranges
2.95–25.00
ꢀ11 6 h 6 15
ꢀ19 6 k 6 19
ꢀ18 6 l 6 18
14 034
ꢀ15 6 h 6 15
ꢀ18 6 k 6 19
ꢀ18 6 l 6 18
14 806
3.4. Theoretical studies
Reflections collected
Independent reflections
5564 [0.0241]
5724 [0.0328]
For complex 5 we can consider five different isomers (see Fig. 3,
I–V). In two cases, corresponding ylide acts as a bidentate ligand
[R(int)
]
Absorption correction
semi-empirical from
equivalents
semi-empirical from
equivalents
Maximum and minimum
transmission
0.5482 and 0.2091
0.5210 and 0.4487
Refinement method
Full-matrix least-
squares on F2
5564/0/361
Full-matrix least-
squares on F2
5724/0/361
Data/restraints/
parameters
Goodness-of-fit on F2
0.958
0.948
Final R indices [I > 2
r
(I)]
R1 = 0.0237,
wR2 = 0.0417
R1 = 0.0377,
wR2 = 0.0432
R1 = 0.0295,
wR2 = 0.0452
R1 = 0.0452,
wR2 = 0.0474
0.821 and ꢀ0.973
R indices (all data)
Largest diff. peak and hole 0.734 and ꢀ0.807
(e Åꢀ3
)
Table 2
Selected bond lengths (Å) and bond angles (°) for 4 and 5.
4
5
Bond lengths
Hg(1)–C(26)
Hg(1)–P(1)
Hg(1)–X(1)a
Hg(1)–X(2)a
O(1)–C(27)
P(2)–C(26)
C(26)–C(27)
2.412(3)
2.4984(9)
2.5675(4)
2.6009(4)
1.242(4)
1.761(4)
1.439(5)
2.424(5)
2.5429(12)
2.7270(14)
2.7483(3)
1.234(5)
1.754(4)
1.460(6)
Bond angles
C(26)–Hg(1)–P(1)
C(26)–Hg(1)–X(1)a
C(26)–Hg(1)–X(2)a
P(1)–Hg(1)–X(1)a
P(1)a–Hg(1)–X(2)a
X(1)–Hg(1)–X(2)a
C(1)–P(1)–Hg(1)
C(2)–P(1)–Hg(1)
C(8)–P(1)–Hg(1)
C(26)–P(2)–C(1)
90.30(8)
112.59(10)
108.92(8)
116.59(2)
117.89(3)
109.059(14)
100.92(11)
116.79(12)
116.44(12)
111.17(16)
89.43(10)
111.54(10)
113.79(9)
113.18(3)
116.26(3)
111.04(12)
100.89(14)
117.30(16)
117.31(15)
111.8(2)
a
X in the compounds 4 and 5 is Br and I, respectively.
C(O)Ph)] (2.415(12) Å) and [HgI2(PPh2CH2PPh2C(H)C(O)Ph)]
(2.418(8) Å) [15]. The Hg–C bond distances in 4 and 5 are longer
than those of found in mononuclear or dinuclear Hg(II)–phosphoy-
lide compounds (2.223(8)–2.310(6) Å) [22–24], indicating
relatively weak Hg–C bonds in these complexes. The P–C(H) dis-
tance is found to be shorter than the corresponding distances in
Fig. 4. Calculated molecular structures of complexes (a) 3 and (b) 4.

3660
S.J. Sabounchei et al. / Inorganica Chimica Acta 363 (2010) 3654–3661
coordinated through P and C atoms or P and O atoms, Fig. 3, iso-
mers I and II, respectively, to the metal ion. However, in remaining
three cases, the ylide acts as a monodentate ligand coordinated
through C, P, or O atoms, Fig. 3, isomers III, IV and V, respectively,
to the metal ion. For compound 5 the isomer I is the unique isomer
which was characterized by X-ray crystal structure analysis. The
optimized structures of isomers IꢀV are also shown in Fig. 3. As
can be seen in the Table 3 the isomer I is the most stable one be-
tween all five possible isomers for compound 5. Thus, it seems that
the complexes 4 and 5 have adopted the most stable structure in
the solid state (see description of X-ray crystal structure for 4
and 5).
Table 4
A comparison between the selected calculated bond lengths (Å) and bond angles (°) for
compounds 3, 4 and 5 and corresponding experimental values for complexes 4 and 5.
Cl–
Br–
I–
CEP-31G
CEP-31G
X-ray
CEP-31G
X-ray
It is clear than I is the most stable structure, probably due to the
chelate effect. The structures IV and V are the highest in energy,
and are not reachable at room temperature. However, the struc-
tures I, II and III differ only on a small amount of energy (0.6
and 1.2 kcal molꢀ1), therefore these structures can be considered
as isoenergetic. Thus, the latter three structures should be present
in solution at room temperature, in equilibrium, since the thermal
energy is enough to promote the change from one to another one.
This fact is in very good agreement with the NMR data, since no
199Hg satellites were observed in the 31P, 1H and 13C NMR spectra,
meaning that the Hg–P and Hg–C bonds probably are breaking and
forming quickly.
Bond lengths
Hg(1)–C(26)
Hg(1)–P(1)
Hg(1)–X(2)
Hg(1)–X(1)
2.463
2.885
2.547
2.506
2.490
2.901
2.666
2.620
2.412
2.507
2.949
2.831
2.787
2.424
2.498
2.601
2.568
2.543
2.748
2.727
Bond angles
P(1)–Hg(1)–C(26)
P(1)–Hg(1)–X(2)
P(1)–Hg(1)–X(2)
C(26)–Hg(1)–X(2)
C(26)–Hg(1)–X(2)
X(1)–Hg(1)–X(2)
85.247
114.435
109.821
102.477
107.770
127.638
83.571
103.139
110.208
116.149
110.852
124.352
90.296
116.597
117.889
112.583
108.928
109.060
82.657
103.403
111.828
116.895
112.104
122.055
89.426
113.180
116.261
113.799
111.541
111.041
The geometry of complexes 3, 4 and 5 were also fully optimized
at density functional (B3LYP) level of theory (see Figs. 3 (I) and 4).
A comparison between the calculated bond lengths (Å) and bond
angles (°) with corresponding experimental values is presented
in Table 4. The calculated structures for both complexes 4 and 5
in the gas phase agree well with the structures determined by
X-ray crystallography.
Table 5
Calculated energies for HOMO and LUMO molecular orbitals, hardness and energy gap
between the HOMO and LUMO of 3, 4 and 5 complexes.
X
HOMO (hartree)
LUMO (hartree)
g
(eV)
Gap (eV)
Cl–
Br–
I–
ꢀ0.23002
ꢀ0.22174
ꢀ0.21084
ꢀ0.07384
ꢀ0.07479
ꢀ0.07700
2.12
1.99
1.82
4.25
3.99
3.64
The calculated energies for HOMO and LUMO of 3, 4 and 5 com-
plexes are also given in Table 5. The hardness
fined as Eq. (1):
g of a molecule is de-
Fig. 5. Illustration of Calculated HOMO (a, c, and e) and LUMO (b, d, and f) molecular orbitals for compounds 3, 4 and 5, respectively.

S.J. Sabounchei et al. / Inorganica Chimica Acta 363 (2010) 3654–3661
3661
ðI ꢀ AÞ
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¼
ð1Þ
2
where I and A are the ionization potential and the electron affin-
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late the hardness of the present molecules using Eq. (2) [41].
ðELUMO ꢀ EHOMO
Þ
g
¼
ð2Þ
2
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We note that hard molecules have a large HOMOꢀLUMO gap
and soft molecules have a small one [42]. The result of CEP-31G
calculation show that both the HOMO and LUMO are demonstrated
with negative charges (see Table 5). Furthermore, the calculated
energy gap between the latter orbitals for the complex 5 contain-
ing iodine is smaller than that for other complexes. Thus, the latter
complex is softer than the other complexes described here. This is
completely consistent with this fact that a hard group makes mol-
ecule hard and a soft groups makes it soft. The HOMO and LUMO
for all three mononuclear complexes are illustrated in Fig. 5.
4. Conclusion
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The present study describes the synthesis and characterization
of a series of chelate mercury(II) complexes derived from mercuric
halides and a bifunctionalized phosphorus ylide. On the basis of
the physicochemical and spectroscopic data we propose that
ligands herein exhibit monodentate P, C-coordination to the metal
centre, which is further confirmed by the X-ray crystal structure of
the complexes. The Hg–C bond in these complexes is longer than
normal Hg–Cylide bond found in mononuclear and binuclear com-
plexes. The result of theoretical study showed that the experimen-
tally determined structure of the complex 5 is more stable than its
other bonding modes.
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We are grateful to the Bu-Ali Sina University for a grant,
Mr. Zebarjadian and Darvishi for recording the NMR spectra.
Appendix A. Supplementary material
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CCDC 703482 and 703480 contain the supplementary crystallo-
graphic data for 4 and 5. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif. Supplementary data associated with
this article can be found, in the online version, at doi:10.1016/
j.ica.2010.05.004.
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