Syntheses, crystal structures and nonlinear optical properties of MS4Pd(dppp) (M = Mo, W)

Article abstract of DOI:10.1016/S0020-1693(00)00104-3

The title compounds [MS₄Pd(dppp)] [M = Mo (1), W (2); dppp = Ph₂PCH₂CH₂CH₂PPh₂] were synthesized for nonlinear optical studies by the reaction of (Et₄N)₂MS₄ (M = Mo, W) and (dppp)PdCl₂ in the CH₂Cl₂-CH₃CN. Single-crystal X-ray analyses revealed that the two compounds consisted of a distorted tetrahedral MS₄ (M = Mo, W) unit with a Pd atom and two S atom bridges. The Pd atom has a cis-quasisquare coordination geometry with two P donors of dppp and two S donors of MS₄. The nonlinear optical properties of 1 and 2 were investigated by a Z-scan technique with 7 ns laser pulses at 532 nm. It was observed that the nonlinear absorption for 1 is very small, but it has considerable large nonlinear refractive index; no nonlinear optical behavior was observed for 2, although it shows a similar structure to that of compound 1. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00104-3

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Inorganica Chimica Acta 305 (2000) 14–18
Syntheses, crystal structures and nonlinear optical properties of
MS4Pd(dppp) (M =Mo, W)
b
a
c
He-gen Zheng a, Wei-lian Tan , Guo-cheng Jin , Wei Ji b, Qiong-hua Jin ,
Xiao-ying Huang d, Xin-quan Xin *
a,
a State Key Laboratory of Coordination Chemistry Institute, Nanjing Uni6ersity, Nanjing 210093, PR China
b Department of Physics, National Uni6ersity of Singapore, Singapore 119260, Singapore
c Department of Chemistry, Capital Normal Uni6ersity, Beijing 100037, PR China
d State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou 350002, PR China
Received 10 November 1999; accepted 28 February 2000
Abstract
The title compounds [MS4Pd(dppp)] [M =Mo (1), W (2); dppp =Ph2PCH2CH2CH2PPh2] were synthesized for nonlinear optical
studies by the reaction of (Et4N)2MS4 (M =Mo, W) and (dppp)PdCl2 in the CH2Cl2ꢀCH3CN. Single-crystal X-ray analyses
revealed that the two compounds consisted of a distorted tetrahedral MS4 (M =Mo, W) unit with a Pd atom and two S atom
bridges. The Pd atom has a cis-quasisquare coordination geometry with two P donors of dppp and two S donors of MS4. The
nonlinear optical properties of 1 and 2 were investigated by a Z -scan technique with 7 ns laser pulses at 532 nm. It was observed
that the nonlinear absorption for 1 is very small, but it has considerable large nonlinear refractive index; no nonlinear optical
behavior was observed for 2, although it shows a similar structure to that of compound 1. © 2000 Elsevier Science S.A. All rights
reserved.
Keywords: Crystal structures; Optical properties; Palladium complexes; Thiometallate complexes
structures and NLO properties of two new palladium-
containing cluster compounds: [MoS4Pd(dppp)] (1) and
[WS4Pd(dppp)] (2).
1. Introduction
The chemistry of Mo (W)ꢀCu (Ag)ꢀS cluster com-
pounds have been of interest for the past two decades
[1]. Many of these compounds have been extensively
studied because of their relevance to biological systems
and catalytic processes [2,3]. Up to now, a number of
Mo(W)ꢀCu (Ag)ꢀS compounds have been synthesized
from the reactions of MS42− (M =Mo, W) anions with
soft cations Cu+, Ag+, Au+ in the presence of Ph3P,
Ph3As and Py ligands [4–6]. In our laboratory, we
discovered that some Mo(W)ꢀCu(Ag)ꢀS clusters dis-
play very strong nonlinear optical (NLO) effects [4–10].
In order to explore this field further, we have synthe-
sized a series of new Mo(W)ꢀPdꢀS cluster compounds.
In this article, we report the synthesis, X-ray crystal
2. Experimental
2.1. Materials
All solvents were AR grade. (Et4N)2MS4 (M =Mo,
W) were synthesized according to the literature meth-
ods [11], and (dppp)PdCl2 was prepared similar to the
literature method [12].
2.2. Physical measurements
IR spectra were recorded on a Fourier Nicolet FT-
170SX spectrophotometer with pressed KBr pellets and
the electronic spectra of the two clusters were measured
* Corresponding author. Tel.: +86-25-3593132; fax: +86-25-
3317761.
E-mail address: xxin@netra.nju.edu.cn (X.-q. Xin)
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00104-3

H.-g. Zheng et al. / Inorganica Chimica Acta 305 (2000) 14–18
15
with a Hitachi U-3410 spectrophotometer. Carbon and
hydrogen analyses were performed on a PE 240C Ele-
mental Analyser.
translation stage that was controlled by the computer
to move along the Z axis with respect to the focal
point. For determining both the sign and magnitude of
the nonlinear refraction, a 1.0-mm diameter aperture
was placed in front of the transmission detector and the
transmittance was recorded as a function of the sample
position on the Z axis (closed-aperture Z -scan). For
measuring the nonlinear absorption, the Z -dependent
sample transmittance was taken without the aperture
(open-aperture Z -scan).
2.3. Nonlinear optical (NLO) measurements
The dimethylformanide (DMF) solutions of clusters
1 and 2 were contained in a 1-mm thick quartz cuvette
with concentrations of 5.0 and 2.7×10−4 M for clus-
ters 1 and 2, respectively. The samples were irradiated
by a Q-switched frequency-doubled Nd:YAG laser,
which produced linearly polarized 7 ns (FWHM) opti-
cal pulses at 532 nm. The laser was operated at pulse
repetition rate of 10 Hz. The spatial profiles of the
optical pulses were nearly Gaussian after passing
through a spatial filter. The laser beam was then di-
vided by a beam splitter into two parts: one was used as
a reference for the incident energy and the other was
focused onto the sample by a focusing mirror of 25-cm
focal length. The minimum beam radius of the focused
laser beam was measured to be 3095 mm. Both inci-
dent and transmitted pulse energies were measured
simultaneously by two energy detectors (Rjp-735 energy
probes, Laser Precision), which were link to a computer
by an IEEE interface. The NLO properties of the
samples were determined by performing the Z -scan
measurements [13]. The samples were mounted on a
2.4. Syntheses of compounds 1 and 2
2.4.1. Preparation of [MoS4Pd(dppp)] (1)
(Et4N)2MoS4 (0.242 g, 0.5 mmol) and Pd(dppp)Cl2
(0.250 g, 0.5 mmol) were added to 30 ml of CH2Cl2 and
CH3CN (1:1 v/v). The obtained mixture was stirred for
12 h at room temperature (r.t.) and then filtered. The
solid was dried in air after washing with CH2Cl2,
distilled water, EtOH and ether, respectively. Single
orange crystals were obtained by diffusing ethyl ether
into the DMF solution (0.297 g, yield 80%). Anal. Calc.
for C27H26MoPdP2S4: C, 43.65; H, 3.53; Found: C,
43.1; H, 3.85%. IR spectra (KBr pellet): MoꢀSt, 488.0;
MoꢀSb, 442 cm−1
.
2.4.2. Preparation of [WS4Pd(dppp)] (2)
The method was similar to that for 1, (Et4N)2WS4
(0.286 g, 0.5 mmol) and Pd(dppp)Cl2 (0.250 g, 0.5
mmol) were added to 30 ml of CH2Cl2 and CH3CN (1:1
v/v). The obtained mixture was stirred for 12 h at r.t.
and yellow crystals were obtained (0.316 g, yield 76%).
Anal. Calc. for C27H26P2S4WPd: C, 39.03; H, 3.15;
Found: C, 39.09; H, 3.20%. IR spectra (KBr pellet):
Table 1
Crystal data and data collection parameters
Formula
Mo1Pd1S4P2C27H W1Pd1S4P2C27H
26
26
Formula weight
Crystal system
Space group
743.03
830.96
monoclinic
P 21/c (no. 14)
10.884(5)
11.473(2)
23.527(3)
94.63(2)
2928(1)
4
monoclinic
P 21/c
WꢀSt, 484.0; WꢀSb, 452 cm−1
.
,
a (A)
10.863(2)
11.485(1)
23.595
94.71(1)
2933.9(9)
4
,
b (A)
,
c (A)
2.5. Crystal data and structure determination
i (°)
3
,
V (A )
Suitable crystals of compounds 1 and 2 were
mounted in random orientation on a glass fiber for
X-ray determination. Data were collected on a Enraf–
Nonius CAD4 diffractometer using Mo Ka radiation at
296 K. Details concerning the intensity and data collec-
tion are given in Table 1. The data were corrected for
Lorentz and polarization factors, and the absorption
Z
T (K)
293
293
Dcalc (g cm−3
)
1.685
1.881
v (mm−1
)
1.423
5.01
Crystal size (mm)
0.85×0.25
0.36×0.25
×0.08
ꢀ–2q
×0.22
ꢀ–2q
Scan type
No. of observations
4495
4630
was corrected by using empirical scan data and DIFABS
.
(I\3.0|(I))
316
(I\3.0|(I))
316
The structures of the compounds were determined by
direct methods. The structures of the compounds were
refined by full-matrix least-squares fits with isotropic
temperature factors for the remaining non-hydrogen
atoms to final R =0.033, Rw=0.041 for compound 1
and R =0.035, Rw=0.043 for compound 2. All calcula-
tions were carried out on a MICRO-VAX II computer
with a TEXSAN program package [14].
No. of variables
R
Rw
Goodness-of-fit
Maximum shift in final cycle
Largest peak in final
difference map (e A
0.033
0.035
0.041
0.043
1.05
1.10
0.001
0.002
0.46, −0.67
1.32, −1.26
(near to W
atom)
−3
,
)

16
H.-g. Zheng et al. / Inorganica Chimica Acta 305 (2000) 14–18
3. Results and discussion
3.1. Structures of compounds 1 and 2
The two title compounds are isomorphous and crys-
tallize in the monoclinic space group P 21/c. Therefore,
the structure of compound 2 will be mainly described in
here. The crystal of compound 2 is a neutral compound
consisting of a distorted tetrahedral WS4 with a palla-
dium atom and two sulfur atom bridges (Fig. 1). The
selected bond lengths and bond angles are given in
Tables 2 and 3, respectively. The palladium atom has
a cis-quasisquare coordination geometry with two
phosphorus donors of dppp and two sulfur donors
,
of WS4. The terminal WꢀS distances (average 2.150 A)
are similar to those found in [NEt4][PdWS4-
(S2CNC4H8)] [15], but the WꢀS bridge distances (2.224
,
A) are slightly shorter than those observed in
Fig. 1. Crystal structure of [WS4Pd(dppp)].
,
[NEt4][PdWS4(S2CNC4H8)] (2.236 A). The PdꢀP dis-
,
tances (2.287 A) are longer than those for (dppp)PdCl2
[12]. PdꢀS bond lengths (average 2.364 A) are slight
,
Table 2
,
Selected bond lengths (A) and angles (°) for compound 1
Bond lengths
PdꢀP1
PdꢀS2
MoꢀS2
P1ꢀC1
C2ꢀC3
2.294(1)
2.360(1)
2.228(1)
1.819(5)
1.514(7)
PdꢀP2
PdꢀMo
MoꢀS3
P2ꢀC3
2.291(1)
2.9102(7)
2.153(1)
1.826(4)
PdꢀS1
MoꢀS1
MoꢀS4
C1ꢀC2
2.351(1)
2.219(1)
2.134(1)
1.516(6)
Bond angles
P2ꢀPdꢀP1
92.00(5)
133.45(4)
132.74(3)
48.66(3)
110.28(6)
110.38(5)
52.47(3)
78.66(4)
P2ꢀPdꢀS1
P1ꢀPdꢀS1
S1ꢀPdꢀS2
S4ꢀMoꢀS3
S4ꢀMoꢀPd
S3ꢀMoꢀPd
S2ꢀMoꢀPd
167.00(5)
84.30(5)
96.98(5)
109.78(6)
121.53(5)
128.69(4)
52.68(3)
P2ꢀPdꢀS2
P1ꢀPdꢀS2
S1ꢀPdꢀMo
S4ꢀMoꢀS1
S3ꢀMoꢀS1
S1ꢀMoꢀS2
MoꢀS1ꢀPd
87.24(5)
177.40(5)
48.46(3)
110.63(6)
110.71(6)
104.98(5)
79.07(4)
P2ꢀPdꢀMo
P1ꢀPdꢀMo
S2ꢀPdꢀMo
S4ꢀMoꢀS2
S3ꢀMoꢀS2
S1ꢀMoꢀPd
MoꢀS2ꢀPd
Table 3
,
Selected bond lengths (A) and angles (°) for compound 2
Bond lengths
PdꢀP1
PdꢀS2
WꢀS2
P1ꢀC1
C2ꢀC3
2.287(2)
2.368(2)
2.230(2)
1.822(7)
1.49(1)
PdꢀP2
PdꢀW
WꢀS3
P2ꢀC3
2.286(2)
2.9259(6)
2.163(2)
1.827(7)
PdꢀS1
WꢀS1
WꢀS4
C1ꢀC2
2.360(2)
2.217(2)
2.137(2)
1.53(1)
Bond angles
P2ꢀPdꢀP1
P2ꢀPdꢀW
P1ꢀPdꢀW
S2ꢀPdꢀW
S4ꢀWꢀS2
S3ꢀWꢀS2
S1ꢀWꢀPd
WꢀS2ꢀPd
91.89(7)
133.55(5)
132.74(5)
48.43(4)
110.43(8)
110.33(7)
52.46(5)
78.98(6)
P2ꢀPdꢀS1
P1ꢀPdꢀS1
S1ꢀPdꢀS2
S4ꢀWꢀS3
S4ꢀWꢀPd
S3ꢀWꢀPd
S2ꢀWꢀPd
167.18(7)
84.63(7)
96.43(7)
109.81(8)
121.49(7)
128.70(5)
52.59(5)
P2ꢀPdꢀS2
P1ꢀPdꢀS2
S1ꢀPdꢀW
S4ꢀWꢀS1
S3ꢀWꢀS1
S1ꢀWꢀS2
WꢀS1ꢀPd
87.55(6)
177.54(7)
48.14(5)
110.56(8)
110.74(8)
104.88(7)
79.40(7)

H.-g. Zheng et al. / Inorganica Chimica Acta 305 (2000) 14–18
17
peaks are located at 486 and 390 nm for compounds 1
and 2, respectively. The Z -scan results for compounds 1
are shown in Fig. 3, where the filled circles were the
Z -scan data measured without the aperture and the
open circles were the results obtained from the division
of the closed aperture Z -scan data by the open aperture
Z -scan data. To obtain the NLO parameters, we em-
ployed a Z -scan theory [13], which considers nonlinear-
ities of third-order nature. The total absorption
coefficient can be written as h=h0+h2I, where h0 and
h2 are the linear and nonlinear absorption coefficients,
respectively, and I is the irradiance of the laser beam
within the sample. The total refractive coefficient can
be expressed as n=n0+n2I, where n0 and n2 are the
linear and nonlinear refractive indices. The good fits
between the theory and our experimental data suggest
that the observed NLO phenomena are effectively a
third-order process. In Fig. 3, it was observed that
compound 1 shows a negative sign for n2. This indicates
that the laser beam propagating in compound 1 under-
goes a self-defocusing process. Table 4 lists the mea-
sured nonlinear absorption coefficient, h2 and nonlinear
refractive index, n2 for compound 1. It should be noted
that the Z -scan measurements reported here could not
reveal the origin of the measured h2 and n2 values for
compound 1. Excited state effects, two-photon absorp-
tion, third-order bound-electronic effect and nonlinear
scattering are the possible mechanism behind the ob-
served nonlinearities [17–19]. The observed self-defo-
cusing property possess by compound 1 shows that it
can be a promising material for applications such as
protection of optical sensors. It is also interesting to
compare this compound with other different structural
clusters. Table 4 shows that compound 1 is comparable
with most of the other clusters in terms of the effective
n2 value. It should also be pointed out that compound
2 has very weak NLO properties, although it shows a
similar structure to that of compound 1.
Fig. 2. Electronic spectrum of [MoS4Pd(dppp)] (5.0×10−4M) (
)
–
and [WS4Pd(dppp)] (2.7×10−4 M) (- - -) in DMF. The optical path
is 1 mm.
Fig. 3. The normalised Z -scan data [MoS4Pd(dppp)] (5.0×10−4M)
in DMF solution with 532 nm, 7 ns laser pulses. The optical path is
1 mm. The peak incident irradiance of the pulses at focus is 240 MW
cm−2. The experimental data were measured without ( ) an aper-
ture. The open circles (ꢀ) were obtained by dividing the Z -scan data
collected with the aperture by those collected without the aperture;
they have been vertically displaced by −0.4 for clarity. The solid
curves are the theoretical fits based on the Z -scan theory.
4. Supplementary material
Supplementary data have been deposited with the
Cambridge Crystallographic Data Centre (CCDC Nos.
135112 and 135113). Copies of this information may be
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
,
longer than in [{(allyl)Pd}2WS4] (average 2.34 A) [16].
The WꢀSꢀPd angles (average 79.19°) are larger and the
,
WꢀPd distance (2.9259 A) bond length is longer than
those in [NEt4][PdWS4(S2CNC4H8)] (77.58° and 2.8669
,
A, respectively).
3.2. NLO properties of compounds [MoS4Pd(dppp)] (1)
and [WS4Pd(dppp)] (2)
Acknowledgements
The electronic spectra of compounds 1 and 2 in
DMF are depicted in Fig. 2. It was noted that both
compounds have relatively low linear absorption in the
visible and near-IR region. The lowest absorption
This research was supported by the National Natural
Science Foundation of China and the National Univer-
sity of Singapore.

18
H.-g. Zheng et al. / Inorganica Chimica Acta 305 (2000) 14–18
Table 4
The NLO parameters for cluster compounds a
Compound
Structure
ho (cm−1 M−1) (×103)
h2 (cm W−1 M−1) (×10−5
)
n2 (cm2 W−1 M−1) (×10−10
)
[MoS4Pd(dppp)] b
[WS4Pd(dppp)] b
[MoOS3Cu3I(py)5] c
[WOS3Cu3I(py)5] c
[Et4N][Mo2O2S6Cu6I6] d
[WOS3Cu2(PPh3)3] e
linear
linear
nested
nested
twin-nested
butterfly
5.50
7.57
0.04
2.10
0.74
2.50
2.0
−1.1
2.5
15.0
2.0
−1.3
16.0
−3.0
6.70
a Note: ho is the linear absorption coefficient, h2 is the nonlinear absorption coefficient and n2 is the nonlinear refractive index. The dashed lines
represent negligible nonlinearity coefficients.
b This work.
c Ref. [5].
d Ref. [20].
e Ref. [21].
Inorg. Chim. Acta 72 (1983) 205.
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