Four mono-/bi-nuclear palladium(II) complexes of triphenylphosphine and heterocyclic-N/NS ligands: Synthesis, structural characterization and luminescence properties

Article abstract of DOI:10.1016/j.poly.2011.10.001

The reactions of palladium(II) chloride, PPh₃ and heterocyclic-N/NS ligand in a mixture of CH₃CN (5 ml) and CH ₃OH (5 ml) produced [PdCl₂(PPh₃)(L1)] ·(CH₃CN) (1) (L1 = ADMT = 3-amino-5,6-dimethyl-1,2,4-triazine) , [PdCl₂(PPh₃)(L2)] (2) (L2 = 3-CNpy = 3-cyanopyridine), [PdCl(PPh₃)(L3)]₂·(CH₃CN) (3), [PdCl(PPh₃)₂(HL3)]Cl (4) (HL3 = Hmbt = 2-mercaptobenzothiazole). The coordination geometry around the Pd atoms in these complexes is a distorted square plane. In 3, L3 acts as a bidentate ligand, bridging two metal centers, while in 4, HL3 appears as monodentate ligand with one nitrogen donor atom uncoordinated. Complexes 1-4 are characterized by IR, luminescence, NMR and single crystal X-ray diffraction analysis. All complexes exhibit luminescence in solid state at room temperature.

Full text of DOI:10.1016/j.poly.2011.10.001

Polyhedron 31 (2012) 472–477
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Polyhedron
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Four mono-/bi-nuclear palladium(II) complexes of triphenylphosphine and
heterocyclic-N/NS ligands: Synthesis, structural characterization and
luminescence properties
a
a
a
a
a
b
Qiong-Hua Jin a, , Li-Na Cui , Zhong-Feng Li , Yu-Han Jiang , Man-Hua Wu , Sen Gao , Cun-Lin Zhang
⇑
a Department of Chemistry, Capital Normal University, Beijing 100048, China
b Beijing Key Laboratory for Terahertz Spectroscopy and Imaging, Key Laboratory of Terahertz Optoelectronics, Ministry of Education, Department of Physics,
Capital Normal University, Beijing 100048, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of palladium(II) chloride, PPh3 and heterocyclic-N/NS ligand in a mixture of CH3CN (5 ml)
and CH3OH (5 ml) produced [PdCl2(PPh3)(L1)]Á(CH3CN) (1) (L1 = ADMT = 3-amino-5,6-dimethyl-1,2,4-tri-
azine), [PdCl2(PPh3)(L2)] (2) (L2 = 3-CNpy = 3-cyanopyridine), [PdCl(PPh3)(L3)]2Á(CH3CN) (3), [PdCl(PPh3)2
(HL3)]Cl (4) (HL3 = Hmbt = 2-mercaptobenzothiazole). The coordination geometry around the Pd atoms
in these complexes is a distorted square plane. In 3, L3 acts as a bidentate ligand, bridging two metal
centers, while in 4, HL3 appears as monodentate ligand with one nitrogen donor atom uncoordinated.
Complexes 1–4 are characterized by IR, luminescence, NMR and single crystal X-ray diffraction analysis.
All complexes exhibit luminescence in solid state at room temperature.
Received 12 June 2011
Accepted 3 October 2011
Available online 15 October 2011
Keywords:
Palladium
Triphenylphosphine
3-Amino-5,6-dimethyl-1,2,4-triazine
2-Mercaptobenzothiazole
3-Cyanopyridine
Ó 2011 Elsevier Ltd. All rights reserved.
Luminescence
1. Introduction
Heterocyclic NS ligands are frequently used as bridging ligands
for adjacent transition-metal sites in the design of luminescent
Studies on the complexes with phosphines and heterocyclic-
N/NS mixed-ligand are extensive, because of their varied structures
and photophysical properties [1,2]. In this paper, our research
focuses on the palladium(II) complexes of ADMT (3-amino-5,6-di-
methyl-1,2,4-triazine), 3-CNPy (3-cyanopyridine) and Hmbt
(2-mercaptobenzothiazole).
The heterocyclic-N ligand 3-amino-5,6-dimethyl-1,2,4-triazine
is a multifunctional ligand because the triazine ring can act as
nitrogen donor, and NH2 group can act as nitrogen donor or
hydrogen donor. The only reported complex containing ADMT is
[Al(CH3)2]5[ADMT][Al(CH3)3], in which all the four nitrogen atoms
of ADMT coordinate to aluminum atoms [3]. The palladium(II)
complex of ADMT has not yet been reported.
materials, because the well match of their orbital energies can
produce great delocalization of the spin electron density toward
bridging atoms [7,8]. The rare earth and d10 metal complexes of
2-mercaptobenzothiazole, such as Ln(mbt)3, [Ag6(mbt)6] and
[Zn4(l4-O)(mbt)6], exhibit intensive luminescence properties
[9,10]. But the reported palladium(II) complexes of mbt
[Pd2(mbt)4]Á1.5DMSO [11] and [Pd2(mbt)4]ÁCH2Cl2 [12] are not
luminescent.
The luminescence of palladium(II) complexes has received rare
attention because the low spin d8 palladium(II) complexes are well
known quenchers [13]. Recently, we found that the heterocyclic-N
ligand can enhance the luminescence of the d10 metal-phosphine
complexes in the solid state at ambient temperature [14]. In this
paper, we expanded our study to palladium(II)–PPh3 complexes
with different heterocyclic-N/NS co-ligands, and found that the
coexistence of PPh3 and heterocyclic-N/NS ligands remarkably
change the luminescence property of d8 palladium(II) complexes.
Herein, four palladium(II) complexes [PdCl2(PPh3)(L1)]Á(CH3CN)
(1), [PdCl2(PPh3)(L2)] (2), [PdCl(PPh3)(L3)]2Á(CH3CN) (3) and
[PdCl(PPh3)2(HL3)]Cl (4) (L1 = ADMT; L2 = 3-CNpy; HL3 = Hmbt)
are synthesized, and all the complexes exhibit luminescence in
solid state at room temperature, which makes them more
intriguing.
The heterocyclic nitrogen ligand 3-cyanopyridine is widely
used as
a conjugated ligand in synthesizing supramolecular
compounds, such as [{Cu(3-CNPy)2(H2O)}2{Cu(3-CNPy)2(H2O)2}
{W(CN)8}2]Á6H2O [4] and Fe(3-CNPy)2[Ag(CN)2]2Á2/3H2O [5].
[PdCl2(3-CNPy)2] is the only reported palladium(II) complex
of 3-CNpy [6].
⇑
Corresponding author.
E-mail address: jinqh@mail.cnu.edu.cn (Q.-H. Jin).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.10.001

Q.-H. Jin et al. / Polyhedron 31 (2012) 472–477
473
2.3. Crystal structure determination and refinement
2. Experimental
Crystals of 1–4 suitable for single-crystal X-ray diffraction were
2.1. Materials and measurements
mounted on a Bruker Smart 1000 CCD diffractometer equipped
with a graphite-monochromated Mo K
a (k = 0.71073 Å) radiation
All chemical reagents are commercially available and used
without furthermore treatment. FT-IR spectra (KBr pellets) were
measured on a Perkin-Elmer Infrared spectrometer. C, H and N ele-
mental analysis were carried out on a Elementar Vario MICRO
CUBE (Germany) elemental analyzer.
at 293(2) K. Semi-empirical absorption corrections were applied
using SABABS program. The program SAINT [15] was used for integra-
tion of the diffraction profiles. All structures were solved by direct
methods using the SHELXS program of the SHELXTL-97 package and re-
fined with SHELXL [16]. Metal atom centers were located from the E-
maps and other non-hydrogen atoms were located in successive
difference Fourier syntheses. The final refinements were performed
by full matrix least-squares methods with anisotropic thermal
parameters for non-hydrogen atoms on F2. The hydrogen atoms
were generated geometrically and refined with displacement
parameters riding on the concerned atoms. Crystallographic data
and experimental details for structural analysis are summarized
in Table 1, and selected bond lengths and angles of 1–4 are sum-
marized in Table 2.
2.2. Preparation of the complexes
2.2.1. Synthesis of [PdCl2(PPh3)(L1)]Á(CH3CN) (1)
Triphenlyphosphine (PPh3) (0.3 mmol, 0.0788 g) and L1
(0.3 mmol, 0.0372 g) were added into the stirring solution of PdCl2
(0.3 mmol, 0.0532 g) in a mixture of CH3CN (5 ml) and CH3OH
(5 ml). Six hours later, the yellow precipitate was filtered off. Sub-
sequent slow evaporation of the yellow filtrate resulted in the for-
mation of yellow crystals of the title complex. Anal. Calc. for
C
25H26Cl2N5PPd: C, 49.7; H, 4.3; N, 11.6. Found: C, 49.6; H, 4.3;
N, 11.5%. Selected IR absorptions (KBr disc, v/cmÀ1): 3405m,
3299m, 1628s, 1534m, 1481m, 1435s, 1395m, 1714s, 1143m,
1096m, 1026w, 998w, 748m, 708m, 694s, 534s, 511m. 1H NMR
(DMSO, 600 MHz, ppm): 7.8–7.4 (m, 15H, phenyl-H), 3.3 (s, 2H,
H2O), 2.8–2.0 (m, 9H, CH3CN–H, ADMT–CH3–H).
3. Results and discussion
3.1. Synthesis and characterization of complexes 1–4
Four Pd(II) complexes [PdCl2(PPh3)(L1)]Á(CH3CN) (1), [PdCl2
(PPh3)(L2)] (2), [PdCl(PPh3)(L3)]2Á(CH3CN) (3) and [PdCl(PPh3)2
(HL3)]Cl (4) are obtained by the one-pot reaction of the metal salts
with the heterocyclic-N/NS ligand and PPh3 (Scheme 1). The reac-
tion of PdCl2, PPh3 with L (L = L1 or L2) in CH3CN and MeOH with
molar ratio 1:1:1 of Pd:P:L gave rise to complexes 1 and 2. Interest-
ingly, the reaction of PdCl2, PPh3 with HL3 in CH3CN and MeOH
produced the compound 3 or 4, depending on the molar ratio of
Pd:P:HL3 we choose (the ratio is 1:1:1 for 3 and 3:3:4 for 4). The
molar ratio of Pd:P:L in complexes 1–3, agrees with that in the
starting materials, while the molar ratio of Pd:P:L of complex 4 is
not as expected.
2.2.2. Synthesis of [PdCl2(PPh3)(L2)] (2)
Complex 2 has been prepared following a procedure similar to
that reported for 1 by adding PPh3 (0.2 mmol, 0.0525 g) and L2
(0.2 mmol, 0.0208 g) into a mixture of CH3CN (5 ml) and MeOH
(5 ml) containing PdCl2 (0.2 mmol, 0.0355 g). After slow evapora-
tion of the yellow filtrate at ambient temperature for 1 week, a
red strip shaped complex was obtained. Anal. Calc. for
C
24H19Cl2N2PPd: C, 53.0; H, 3.5; N, 5.2. Found: C, 53.0; H, 3.4; N,
5.0%. Selected IR absorptions (KBr disc, v/cmÀ1): 3443m, 1632w,
1599w, 1481m, 1434s, 1191m, 1098s, 1027w, 998w, 810m,
747m, 709m, 690s, 535s, 514m, 500m. 1H NMR (DMSO, 600 MHz,
ppm): 8.0–7.3 (m, 19H, phenyl-H, py-H), 3.4 (s, 2H, H2O), 2.6–2.5
(m, DMSO–H).
All the four complexes are air-stable. They are insoluble in
diethyl ether but soluble in the common polar solvents such as
methanol, ethanol, dichloromethane, acetonitrile, dimethylsulfox-
ide and dimethylformamide.
The complexes have been characterized by the elemental anal-
yses, together with IR, NMR and the single crystal X-ray diffraction.
In the four IR spectra, the following absorptions can be assigned to
C@N ring stretching vibrations: the absorptions at 1481 and
1435 cmÀ1 (for 1), 1481 and 1434 cmÀ1 (for 2), 1479 and
1433 cmÀ1 (for 3) and 1478 and 1434 cmÀ1 (for 4). The absorptions
of the range 3211–3405 in the spectrum of 1 can be assigned to
NH2 stretching vibrations. The absorption at 2237 cmÀ1 in the
spectrum of 2 can be assigned to conjugated C„N stretching vibra-
tion. The P–C vibrations of the PPh3 moiety are found around
2.2.3. Synthesis of [PdCl(PPh3)(L3)]2Á(CH3CN) (3)
Follow the same procedure as 1, with L1 replaced by HL3
(0.3 mmol, 0.0502 g). The crystal was obtained by slow evapora-
tion of the red filtrate for 2 days, which was filtered off and washed
with Et2O to give complex 3 as a red crystal. Anal. Calc. for
C52H41Cl2N3P2Pd2S4: C, 52.9; H, 3.5; N, 3.6. Found: C, 52.8; H, 3.4;
N, 3.5%. Selected IR absorptions (KBr disc, v/cmÀ1): 3052w,
1571w, 1479m, 1448w, 1433s, 1383s, 1314m, 1246m, 1096s,
1028s, 1012s, 998m, 744s, 725m, 707m, 692s, 616m, 528s, 511m,
494m. 1H NMR (DMSO, 600 MHz, ppm): 9.0–7.1 (m, 38H, phenyl-
H), 4.4 (s, 1H, SH–H), 2.5 (m, DMSO–H), 2.08 (s, 3H, CH3CN–H).
690 cmÀ1
.
2.2.4. Synthesis of [PdCl(PPh3)2(HL3)]Cl (4)
3.2. Single crystal X-ray studies
Details of synthesis of 3 also apply to 4, by adding PPh3
(0.3 mmol, 0.0788 g) and HL3 (0.4 mmol, 0.0669 g) into a mixture
of CH3CN (5 ml) and MeOH (5 ml) containing PdCl2 (0.3 mmol,
0.0532 g). Slow evaporation of the red filtrate for 12 days resulted
in the red crystals of the title complex. Anal. Calc. for
3.2.1. Crystal structure of complexes 1 and 2
The asymmetric unit of each crystal structure comprises
[PdCl2(PPh3)(L)] (L = L1 for 1 and L = L2 for 2) molecule. The palla-
dium(II) atom in each unit is bonded to one nitrogen of L1 or L2,
one phosphorous of PPh3 and two chloride atoms in a slightly dis-
torted square-planar coordination (Figs. 1 and 2). In complex 1, L1
C
43H35Cl2NP2PdS2: C, 59.4; H, 4.1; N, 1.6. Found: C, 59.4; H, 4.0;
N, 1.6%. Selected IR absorptions (KBr disc, v/cmÀ1)
:
3437m,
1653m, 1497m, 1432s, 1386w, 1095m, 1081m, 1027s, 1012s,
749s, 692s, 526s, 511m. 1H NMR (DMSO, 600 MHz, ppm): 9.1 (s,
1H, SH–H), 9.0–7.0 (m, 34H, phenyl-H), 3.3 (s, 2H, H2O), 2.5 (s,
DMSO–H).
acts as a monodentate ligand, while in [Al(CH3)2]5[ADM-
T][Al(CH3)3], L1 (L1 = ADMT) adopts tetradentate coordination
fashion [3]. In complex 2, L2 is a monodentate ligand, just like in
other reported similar complexes [4,5].

474
Q.-H. Jin et al. / Polyhedron 31 (2012) 472–477
Table 1
Crystal data for complex 1–4.
Compound
Formula
1
2
3
4
C
PPd
25H26Cl2N5
C24H19Cl2N2
PPd
C52H41Cl2N3
P2Pd2S4
C43H35Cl2N
P2PdS2
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
603.78
monoclinic
P2(1)/c
16.2949(15)
10.6440(10)
17.0161(16)
117.135(2)
2626.5(4)
4
543.68
monoclinic
P2(1)/n
9.6810(16)
13.5181(16)
12.2169(13)
13.6608(15)
2250.9(4)
4
1181.76
monoclinic
P2(1)/n
16.1700(17)
13.2351(11)
24.7630(20)
108.459(1)
5026.8(8)
4
869.08
monoclinic
P2(1)/c
13.9240(13)
15.0671(16)
21.9602(20)
120.460(2)
3971.3(4)
4
b (°)
V (Å3)
Z
Dcalc (g/cm3)
1.529
0.994
1.604
1.147
1.562
1.091
1.454
0.819
l
(mmÀ1
)
R1 and wR2
T (K)
0.0386/0.1031
298(2)
0.0317/0.0989
298(2)
0.0597/0.2612
298(2)
0.0501/0.1027
298(2)
Table 2
All bond distances are within the expected values. The Pd–N
bonds (2.023(3) Å for 1, 2.141(3) Å for 2) agree with the corre-
sponding distances in compounds [Pd(py)4]Cl2Á1/2H2O [21] and
[Pd(dmba)(N10-9AA)(PPh3)] [18]. In complex 1, the hydrogen bond
N4H4B. . .Cl1 helps to stabilize the structure. Here the distance
N4. . .Cl1 is 3.287 Å and the angle N4–H4B–Cl1 is 160.9°.
Selected bond lengths (Å) and angles (°) for complex 1–4.
Complex 1
Pd(1)–N(1)
Pd(1)–P(1)
Pd(1)–Cl(1)
2.023(3)
2.374(7)
2.305(1)
2.368(1)
91.6(9)
178.2(9)
87.1(4)
89.1(9)
P(1)–Pd(1)–Cl(2)
Cl(1)–Pd(1)–Cl(2)
C(12)–P(1)–Pd(1)
C(6)–P(1)–Pd(1)
C(18)–P(1)–Pd(1)
C(3)–N(1)–Pd(1)
N (2)–N(1)–Pd(1)
179.1(4)
92.1(4)
107.2(1)
115.5(1)
114.9(1)
123.7(3)
116.2(2)
Pd(1)–Cl(2)
N(1)–Pd(1)–P(1)
N(1)–Pd(1)–Cl(1)
P(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(2)
3.2.2. Crystal structure of complexes 3 and 4
The structure of [PdCl(PPh3)(L3)]2Á(CH3CN) (3) consists of one
dimeric unit and one CH3CN solvent molecule (Fig. 3). Each palla-
dium atom is bonded to one thiolate bridging sulfur, one bridging
nitrogen, one phosphorus of triphenylphosphine and one chloride
in a distorted square-planar geometry. The two planar units
(Pd1–N1–P1–Cl1–S4 and Pd2–N2–P2–Cl2–S2) are joined via two
bridging mbt ligands to form an eight-membered ring. The Pd. . .Pd
distance 3.6728(1) Å, which is much longer than the corresponding
distance in other Pd–L3 complexes, such as complex
[Pd2(mbt)4]Á1.5DMSO (Pd. . .Pd distance 2.747(2) Å) [11] and
[Pd2(mbt)4]ÁCH2Cl2 (Pd. . .Pd distance 2.756(5) Å) [12], shows that
there exists no Pd–Pd bond in the complex.
The angles (85.9(9)–94.2(2)°) in the coordination sphere of the
metal atom show deviation from the ideal 90°, which is similar to
the compounds 3d, 5a, 5c, 6a, 6b and 7a in [19]. Due to the steric
stress between two L3 ligands located on the same side of the
Pd. . .Pd axis, the square-planar structure in 3 is much more dis-
torted than the corresponding structure in complexes 1 and 2.
The values of the bite angles N–Pd–S are 92.3(2)° (N1–Pd1–S4)
and 89.0(2) (N2–Pd2–S2), which are similar to those found for
Complex 2
Pd(1)–N(1)
Pd(1)–P(1)
Pd(1)–Cl(1)
2.141(3)
2.253(1)
2.287(1)
2.308(1)
179.3(1)
88.4(1)
P(1)–Pd(1)–Cl(2)
Cl(1)–Pd(1)–Cl(2)
C(12)–P(1)–Pd(1)
C(7)–P(1)–Pd(1)
C(19)–P(1)–Pd(1)
C(5)–N(1)–Pd(1)
C(1)–N(1)–Pd(1)
89.2(4)
178.3(5)
106.2(1)
117.2(1)
113.4(1)
123.9(3)
119.1(3)
Pd(1)–Cl(2)
N(1)–Pd(1)–P(1)
N(1)–Pd(1)–Cl(1)
P(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(2)
91.6(4)
90.8(1)
Complex 3
Pd(1)–N(1)
Pd(1)–P(1)
Pd(1)–Cl(1)
Pd(1)–S(4)
Pd(2)–N(2)
Pd(2)–Cl(2)
Pd(2)–P(2)
2.049(7)
2.278(2)
2.291(2)
2.371(2)
2.018(7)
2.296(3)
2.298(3)
2.365(3)
94.2(2)
176.1(2)
87.5(9)
92.3(2)
173.3(9)
85.9(9)
175.2(2)
92.4(2)
Cl(2)–Pd(2)–P(2)
N(2)–Pd(2)–S(2)
Cl(2)–Pd(2)–S(2)
P(2)–Pd(2)–S(2)
C(1)–N(1)–Pd(1)
C(2)–N(1)–Pd(1)
C(8)–N(2)–Pd(2)
C(9)–N(2)–Pd(2)
C(21)–P(1)–Pd(1)
C(27)–P(1)–Pd(1)
C(15)–P(1)–Pd(1)
C(39)–P(2)–Pd(2)
C(45)–P(2)–Pd(2)
C(33)–P(2)–Pd(2)
C(1)–S(2)–Pd(2)
C(8)–S(4)–Pd(1)
92.3(1)
89.0(2)
86.3(1)
176.8(9)
123.3(6)
124.6(6)
122.9(6)
124.1(6)
112.8(3)
115.7(3)
109.6(3)
112.7(4)
112.4(3)
116.4(3)
106.4(3)
105.7(3)
Pd(2)–S(2)
N(1)–Pd(1)–P(1)
N(1)–Pd(1)–Cl(1)
P(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–S(4)
P(1)–Pd(1)–S(4)
Cl(1)–Pd(1)–S(4)
N(2)–Pd(2)–Cl(2)
N(2)–Pd(2)–P(2)
other dinuclear complexes such as [Pd(SCN)(
(87.9(2)° and 90.2(1)°, [Pd(N3)( -med)]2 (92.4(1)° and 93.5(1)°),
[PdCl( -med)]2 (91.5(1)° and 92.1(9)°) [20] and [Pd(
l
-med)]2Á0.5CH3CN
l
l
l-
Complex 4
Pd(1)–S(2)
Pd(1)–P(1)
Pd(1)–Cl(1)
med)(PPh3)]2 (84.1(9)°) [18]. [Hmed = N-2-mercaptoethyl)-3,5-
dimethylpyrazole].
2.319(1)
2.361(1)
2.341(1)
2.374(1)
177.9(5)
92.3(5)
88.4(5)
91.4(5)
87.8(5)
P(1)–Pd(1)–P(2)
C(1)–S(2)–Pd(1)
C(8)–P(1)–Pd(1)
C(14)–P(1)–Pd(1)
C(20)–P(1)–Pd(1)
C(38)–P(2)–Pd(1)
C(26)–P(2)–Pd(1)
C(32)–N(1)–Pd(1)
174.5(5)
103.8(2)
118.3(2)
114.3(2)
108.6(2)
106.6(2)
114.2(2)
118.8(2)
In the crystal structure of complex 4, the unit cell consists of
one [PdCl(PPh3)2(HL3)]+ cation and one chloride anion. The metal
center allows the formation of a distorted planar square with four
vertex occupied by two phosphorus atoms of two PPh3, one thio-
late-sulfur atom of mbt and one chloride. The perspective view
of 4 is shown in Fig. 4.
Pd(1)–P(2)
S(1)–Pd(1)–Cl(1)
S(2)–Pd(1)–P(1)
Cl(1)–Pd(1)–P(1)
S(2)–Pd(1)–P(2)
Cl(1)–Pd(1)–P(2)
In complex 4, the bridging coordination of HL3 is broken, leav-
ing the thiazole-nitrogen uncoordinated. The Pd–S bond distance
(Pd1–S2 = 2.319(1) Å) is shorter than those in complex 3 (Pd1–
S4 = 2.371(2), Pd2–S2 = 2.365(3) Å), but both the Pd–P distances
(Pd1–P1 = 2.361(1), Pd1–P2 = 2.374(1) Å) and the Pd–Cl distance
(Pd1–Cl1 = 2.341(1) Å) are much longer than the corresponding
distances in complex 3 (Pd1–P1 = 2.278(2), Pd2–P2 = 2.298(3),
Pd1–Cl1 = 2.291(2), Pd2–Cl2 = 2.296(3) Å). This can be attributed
The angles around Pd(II) atoms in the coordination sphere,
which are in the range 87.1(4)–92.1(4)° for 1 and in the range
88.4(1)–91.6(4)° for 2, are close to the expected value 90° and sim-
ilar to the corresponding angles in compounds [(PPh3)Pd(HL)Cl]ClÁ
2CH3CN, [(PPh3)Pd(HL)I]ClÁ1/2H2O (HL = 4-amino-5-methyl-2H-
1,2,4-triazole-3(4H)-thione) [17].

Q.-H. Jin et al. / Polyhedron 31 (2012) 472–477
475
H2N
L1
PPh3
N
.
Cl
CH3
CH3
CH3CN
Pd
Cl
N
N
Cl
L2
Ph3P Pd
Cl
N
CH3CN/CH3OH(1:1)
CN
Cl
PdCl2+PPh3
Cl
Pd
Pd PPh3
HL3
PPh3
.
CH3CN
N
N
S
S
S
S
Cl
HL3
Ph3P Pd PPh3
S
S
N
(L1= 3-Amino-5,6-dimethyl-1,2,4-triazine, L2=3-cyanopyridine), HL3=2-Mercaptobenzothiazole
Scheme 1. The routine of synthesis for complexes 1–4.
Fig. 1. Perspective view of complex 1. All the hydrogen atoms are omitted for
clarity.
to the need to accommodate the bulky triphenylphosphine groups.
The Pd–P distances are similar to those observed in complex
Pd(CO2CH3)(ONO2)(PPh3)2 (Pd–P1 = 2.349(3), Pd–P2 = 2.364(3) Å)
[21].
Fig. 2. Perspective view of complex 2. All the hydrogen atoms are omitted for
clarity.
3.3. Emission spectra of complexes
shows two emission peaks (416 and 438 nm for 3, 419 and
438 nm for 4). The emission peaks of compounds 3 and 4 are
blue-shifted with respect to the free ligand PPh3 and are red-
shifted with respect to the free ligand HL3. So it is easy to conclude
that the emission spectra of compounds 3 and 4 can be assigned to
ILCT (intra-ligand charge transfer) based on both HL3 and PPh3
ligands. The shifts of the emission bands of compounds 1–4 can
be attributed to the coordination action of L1, L2, HL3 and PPh3
on palladium(II) atoms. For all the four palladium complexes, the
absence of the low-energy emission is likely due to a higher energy
difference between the metal and ligand orbitals. Though it seems
that the emission spectra of 1 and 2 are not related to the hetero-
cyclic N ligand (L1 or L2), the presence of L1 (or L2) is very
In this work, photoluminescence spectra in the solid state at
room temperature of complexes 1–4 and free ligands L1, L2 and
HL3 have been measured (Figs. S1–S7). Free ligands PPh3, L1, L2
and HL3 display emission with maxima at 447 nm [22], 400 nm
(kex = 329 nm for L1), 405 nm (kex = 333 nm for L2) and 402 nm
(kex = 337 nm for HL3), respectively. All the compounds 1–4 pos-
sess fluorescence properties. Compounds 1 and 2 show emission
with maxima at 439 nm and 437 nm, respectively. The resem-
blance of the emission spectrum of the compound 1 or 2 with that
of the free ligand PPh3 indicates that the luminescence of the com-
pound 1 or 2 is PPh3-based emission. Each of compounds 3 and 4

476
Q.-H. Jin et al. / Polyhedron 31 (2012) 472–477
From the 31P NMR spectra we can see that 1, 2 and 4 phospho-
rous signal splittings are 24.7 and 25.0 ppm for 1, 26.9 and
27.1 ppm for 2 and 24.5, 26.2 and 27.2 ppm for 4. In the 31P NMR
spectrum of 3, only one single resonance signal is found
(26.1 ppm). The 31P spectra reveal that the structures of complexes
1, 2, 4 in solvent DMSO-d6 are not consistent with observed solid
state structures. Binuclear Pd(II) complex 3 is stable in DMSO-d6
solution, while mononuclear Pd(II) complexes 1, 2 and 4 are unsta-
ble. The instability of compounds 1, 2, 4 in DMSO-d6 is probably
the result of substitution of N/NS ligands or chlorine atoms by
the molecules of the solvent DMSO [24]. This hypothesis is consis-
tent with the fact that the strong coordination ability of DMSO-d6
with metal Pd(II) atom cleaves the metal-nitrogen (sulfur or chlo-
ride) bond leaving free ligand molecules [25]. Magnetic resonance
investigation of complexes containing PPh3 and N/NS ligands pro-
vides some important information about the structure and stability
of these compounds. But the unknown dissociated byproducts
bring about complicated NMR spectral patterns [26].
Fig. 3. Perspective view of complex 3. All the hydrogen atoms are omitted for
clarity.
4. Conclusion
In conclusion, we have synthesized and characterized three
mononuclear and one binuclear Pd(II)–PPh3 complexes containing
different heterocyclic N/NS ligands, including 3-amino-5,6-di-
methyl-1,2,4-triazine (ADMT), 3-cyanopyridine (3-CNpy) and 2-
mercaptobenzothiazole (Hmbt). Complex 1 is the first Pd(II) com-
plex of ADMT. We found that ADMT and 3-CNpy act as monoden-
tate ligands. Hmbt acts as a bidentate NS-bridging ligand through
its thiolate-sulfur and thiazole-nitrogen atoms, while its deproto-
nated species mbt acts as a monodentate ligand. Complexes 3
and 4 are obtained from the same starting materials with different
molar ratio of Pd:Hmbt. All the four Pd(II) complexes exhibit lumi-
nescence properties. The coexistence of PPh3 and heterocyclic-N/
NS ligands remarkably enhances the luminescence property of d8
palladium(II) complexes. In solution, mononuclear complexes (1,
2 and 4) show complicated 31P NMR spectra, which are attributed
to the reaction of DMSO solvent toward Pd(II) atoms.
Acknowledgements
This work has been supported by the National Science Founda-
tion of China (Grant No. 21171119, 20871085), Program for Excel-
lent Talents of Beijing City (Project No. 2010D005016000002), the
Project sponsored by SRF for ROCS and SEM, the subsidy of Beijing
Personnel Bureau, National Keystone Basic Research Program (973
Program) under Grant Nos. 2007CB310408, 2006CB302901, State
Key Laboratory of Functional Materials for Informatics, Shanghai
Institute of Microsystem and Information Technology, Chinese
Academy of Sciences.
Fig. 4. Perspective view of complex 4. All the hydrogen atoms are omitted for
clarity.
important for the products to have luminescence. From the lumi-
nescence of complexes 1–4 and similar compounds [23], we can
know that the coexistence of PPh3 and heterocyclic-N/NS ligands
brings remarkable change in luminescence property of d8 palla-
dium(II) complexes.
Appendix A. Supplementary data
CCDC 807177, 807180, 807178 and 807179 contain the supple-
mentary crystallographic data for the compounds 1–4. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 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.2011.10.001.
3.4. NMR spectra of complexes
The 1H NMR and 31P NMR spectra of complexes 1–4 were mea-
sured at room temperature in DMSO solution. In the 1H NMR spec-
tra of complexes 1–4, the broad multiplet assigned to signals of
aromatic protons are in the range 7.4–7.8 ppm, 7.3–8.0 ppm, 7.1–
9.0 ppm, and 7.0–9.0 ppm, respectively. In 1H NMR spectra of com-
plex 1, there is another broad multiplet in the range 2.0–2.8 ppm,
which is assigned to triazine–methyl protons and acetonitrile pro-
tons. There is a singlet at 2.1 ppm in complex 3, which is attributed
to acetonitrile protons. The 1H NMR spectrum of complex 4 shows
the singlet at 9.1 ppm, which is attributed to the signal of mer-
capto-proton.
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