Synthesis and characterisation of palladium(II) and platinum(II) compounds containing pyrazole-derived ligands: Crystal structure of [PdCl 2(HL1)] (HL1 = 3-phenyl-5-(2-pyridyl)pyrazole)

Article abstract of DOI:10.1016/j.ica.2004.07.064

Reaction of the ligands 3-phenyl-5-(2-pyridyl)pyrazole (HL¹), 3,5-bis(2-pyridyl)pyrazole (HL²), 3-methyl-5-(2-pyridyl)pyrazole (HL³) and 3-methyl-5-phenylpyrazole (HL⁴) with [MCl ₂(CH₃CN)₂] (M = Pd(II), Pt(II)) or [PdCl ₂(cod)] gives complexes with stoichiometry [PdCl₂(HL) ₂] (HL = HL¹, HL², HL³), [Pt(L) ₂] (L = L¹, L², L³) and [MCl ₂(HL⁴)₂] (M = Pd(II), Pt(II)). The new complexes were characterised by elemental analyses, conductivity measurements, infrared and ¹H NMR spectroscopies. The crystal and molecular structure of [PdCl₂(HL¹)] was resolved by X-ray diffraction, and consists of monomeric cis-[PdCl₂(HL¹)] molecules. The palladium centre has a typical square planar geometry, with a slight tetrahedral distortion. The tetra-coordinated metal atom is bonded to one pyridine nitrogen, one pyrazolic nitrogen and two chloro ligands in a cis disposition. The ligand HL¹ is not completely planar.

Full text of DOI:10.1016/j.ica.2004.07.064

Inorganica Chimica Acta 358 (2005) 617–622
www.elsevier.com/locate/ica
Synthesis and characterisation of palladium(II) and platinum(II)
compounds containing pyrazole-derived ligands: crystal structure of
[PdCl2(HL1)] (HL1 = 3-phenyl-5-(2-pyridyl)pyrazole)
a
Jose Antonio Perez , Josefina Pons , Xavier Solans , Merce Font-Bardia , Josep Ros
a,
b
b
a
*
`
¨
a
` ` `
` `
`
Departament de Quımica, Unitat de Quımica Inorganica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
b
´
Cristal.lografia, Mineralogia i Diposits Minerals, Universitat de Barcelona, Martı i Franques s/n, 08028 Barcelona, Spain
Received 30 June 2004; accepted 28 July 2004
Available online 13 November 2004
Abstract
Reaction of the ligands 3-phenyl-5-(2-pyridyl)pyrazole (HL1), 3,5-bis(2-pyridyl)pyrazole (HL2), 3-methyl-5-(2-pyridyl)pyrazole
(HL3) and 3-methyl-5-phenylpyrazole (HL4) with [MCl2(CH3CN)2] (M = Pd(II), Pt(II)) or [PdCl2(cod)] gives complexes with stoi-
chiometry [PdCl2(HL)2] (HL = HL1, HL2, HL3), [Pt(L)2] (L = L1, L2, L3) and [MCl2(HL4)2] (M = Pd(II), Pt(II)). The new complexes
were characterised by elemental analyses, conductivity measurements, infrared and 1H NMR spectroscopies. The crystal and molec-
ular structure of [PdCl2(HL1)] was resolved by X-ray diffraction, and consists of monomeric cis-[PdCl2(HL1)] molecules. The pal-
ladium centre has a typical square planar geometry, with a slight tetrahedral distortion. The tetra-coordinated metal atom is bonded
to one pyridine nitrogen, one pyrazolic nitrogen and two chloro ligands in a cis disposition. The ligand HL1 is not completely planar.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Palladium complexes; Platinum complexes; Pyrazole complexes; Crystal structures
1. Introduction
Over the last few years, we have developed the coor-
dination chemistry of pyrazole-derived ligands as it has
become apparent that this chemistry is rich in structural
types, reactivity characteristics and ligands modes. Re-
cently, our investigations have been directed towards
the preparation of 3,5-substituted pyrazole ligands.
These ligands have one or two chelating arms attached
to the 3- and 5-positions of the pyrazole.
The chemistry of pyrazole and pyrazolate metal com-
plexes is described quite extensively in the literature [1–
5]. Previous studies showed the high catalytic activity,
under mild conditions, of some polynuclear hetero-
bridged pyrazolate complexes, thus encouraging the
exploration of the unusual and specific features of the
pyrazolate ligands [4,5]. Some authors have suggested
that introducing appropriate substituents at positions
3, 4 or 5 of the heterocyclic ring may modify the nucle-
ophilicity of N2 (sp2) and the acid character of pyrazole
[6,7].
We have reported the synthesis and characterisation
of polydentate ligands with nitrogen donors 3-phenyl-
5-(2-pyridyl)pyrazole (HL1) [8], 3-phenyl-5-(6-methyl-
0
2-pyridyl)pyrazole (HL1 ) [8], 3,5-bis(2-pyridyl)pyrazole
(HL2) [9,10], 3-(6-methyl-2-pyridyl)-5-(2-pyridyl)pyraz-
0
ole (HL2 ) [11] and 3,5-bis(6-methyl-2-pyridyl)pyrazole
00
(HL2 ) [11]. We have also studied their reactivity with
the divalent metal ions Co [8,11–13], Ni [10–12,14], Pd
[15], Cu [11,16–19], Zn [12] and Cd [12]. Some of these
ligands were previously studied by other authors, thus,
*
Corresponding author. Tel.: +34 93 581 2895; fax: +34 93 581 31
01.
E-mail address: josefina.pons@uab.es (J. Pons).
0020-1693/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.07.064

618
J.A. Perez et al. / Inorganica Chimica Acta 358 (2005) 617–622
in 1995 Munakata et al. [20] described three complexes
with HL2, two of Ag(I) and one of Cu(II), and in 2003
Catalano et al. [21] described Ru(II) complexes with
these ligands.
2.2. Synthesis
2.2.1. [MCl2(HL)] (M = Pd(II), HL = HL1 1, HL2 2,
HL3 3)
Here, we study the synthesis and structural determi-
nation of the Pd(II) and Pt(II) complexes of the ligands
3-phenyl-5-(2-pyridyl)pyrazole (HL1) [8], 3,5-bis(2-
pyridyl)pyrazole (HL2) [9,10], 3-methyl-5-(2-pyridyl)-
pyrazole (HL3) [22], and 3-methyl-5-phenylpyrazole
(HL4) [23]. The crystal structure of [PdCl2(HL1)] is de-
scribed and compared with those of closely related
structures.
A solution of 0.29 mmol of {PdCl2(CH3CN)2: 0.075
g; PdCl2(cod): 0.082 g} in 75 ml of CH3CN was treated
with a solution of 0.29 mmol of the corresponding lig-
and (HL1: 0.064 g; and HL2: 0.064 g; HL3: 0.046 g) in
10 ml of CH3CN. After 14 h of stirring, the solution
was concentrated until a crystalline precipitate ap-
peared, which was filtered off, washed with CH3CN (5
ml), and dried in vacuo.
2.2.1.1. Compound 1. Yield: 85%. C14H11N3Cl2Pd: Anal.
Calc. C, 42.17; H, 2.76; N, 10.54. Found: C, 42.17; H,
2. Experimental
2.64, N, 10.38%. Conductivity (Xꢀ1 cm2 molꢀ1
,
2.1. General methods
8.5 · 10ꢀ4 M in DMSO): 21. IR: (KBr, cmꢀ1) 3237
m(N–H), 3125–3050 m(C–H)ar, 1615–1547 (mC@C,
mC@N), 1467–1450 (dC@C, dC@N), 1030 d(C–H)ip,
767 d(C–H)oop; (polyethylene, cmꢀ1) 483 m(Pd–N), 360,
342 m(Pd–Cl). 1H NMR (DMSO-d6 solution, 250
All reactions were performed under a nitrogen atmos-
phere with the use of vacuum line and standard Schlenk
techniques. All reagents were commercial grade materi-
als and were used without further purification. All sol-
vents were dried and distilled under N2 by standard
methods just before use.
3
MHz) d: 9.55 [1H, s, N H], 8.93 [1H, d, J = 5.9 Hz,
Py], 8.31 [1H, t, J = 8.0 Hz, Py], 8.22 [1H, d, J = 8.0
3
3
3
Hz, Py], 7.90 [2H, d, J = 7.7 Hz, Ph], 7.73 [1H, s, Pz],
7.68 [1H, m, Py], 7.50 [3H, m, Ph].
Elemental analyses (C, N, H) were carried out by the
staff of the Chemical Analyses Services of the Universi-
`
tat Autonoma de Barcelona on a Carlo Erba CHNS
2.2.1.2. Compound 2. Yield: 78%. C13H10N4Cl2Pd: Anal.
Calc. C, 39.06; H, 2.50; N, 14.02. Found: C, 39.08; H,
EA-1108 instrument. Conductivity measurements were
performed at room temperature (r.t.) in 10ꢀ3 DMSO,
employing a CyberScan CON 500 (Euthech Instru-
ments) conductimeter. Infrared spectra were run on a
Perkin–Elmer FT spectrophotometer, series 2000 cmꢀ1
as KBr pellets or polyethylene films in the range 4000–
2.44, N, 13.82%. Conductivity (Xꢀ1 cm2 molꢀ1
,
9.1 · 10ꢀ4 M in DMSO): 35. IR: (KBr, cmꢀ1) 3325
m(N–H), 3000 m(C–H)ar, 1610–1565 (mC@C, mC@N),
1442 (dC@C, dC@N), 1099 d(C–H)ip, 772 d(C–H)oop
;
(polyethylene, cmꢀ1) 474 m(Pd–N), 359, 340 m(Pd–Cl).
1H NMR (DMSO-d6 solution, 250 MHz) d: 10.25 [1H,
s, N H], 9.83 [1H, d, 3J = 5.9 Hz, Py], 8.93 [1H,
3J = 5.2 Hz, Py], 8.62 [1H, d, 3J = 4.8 Hz, Py], 8.50
100 cmꢀ1
.
1H NMR spectra were recorded on a
NMR-FT Bruker 250 MHz spectrometer in DMSO or
CDCl3 solutions at room temperature. All chemical
shifts values (d) are given in ppm.
Samples of [PdCl2(CH3CN)2] [24], [PtCl2(CH3CN)2]
[25] and [PdCl2(cod)] [26] were prepared as described
in the literature. The compounds 3-phenyl-5-(2-pyr-
idyl)pyrazole (HL1) [8], 3,5-bis(2-pyridyl)pyrazole
(HL2) [9,10], 3-methyl-5-(2-pyridyl)pyrazole (HL3) [22],
and 3-methyl-5-phenylpyrazole (HL4) [23] were pre-
pared according to the published methods (Fig. 1).
3
3
[1H, d, J = 4.4 Hz, Py], 8.35 [1H, t, J = 7.9 Hz, Py],
3
8.25 [1H, d, J = 7.9 Hz, Py], 7.85 [1H, m, Py], 7.43
[1H, s, Pz], 7.28 [1H, m, Py].
2.2.1.3. Compound 3. Yield: 90%. C9H9N3Cl2Pd: Anal.
Calc. C, 32.11; H, 2.68; N, 12.48. Found: C, 32.28; H,
2.40, N, 12.33%. Conductivity (Xꢀ1 cm2 molꢀ1
,
8.6 · 10ꢀ4 M in DMSO): 28. IR: (KBr, cmꢀ1) 3438
m(N–H), 3069 m(C–H)ar, 2959–2851 m(C–H)al, 1614–
1569 (mC@C, mC@N), 1444 (dC@C, dC@N), 1040
d(C–H)ip, 779 d(C–H)oop; (polyethylene, cmꢀ1) 473
R
R'
N
N
1
m(Pd–N), 348, 329 m(Pd–Cl). H NMR (DMSO-d6 solu-
H
tion, 250 MHz) d: 13.78 [1H, s, N H], 8.85 [1H, ddd,
3J = 7,3, 5.8 Hz, Py], 8.23 [1H, ddd, J = 7.3 Hz, Py],
3
3
8.13 [1H, d, J = 7.3 Hz, Py], 7.62 [1H, m, Py], 7.05
[1H, s, N H], 7.05 [1H, s, Pz], 2.34 [3H, s, CH3].
HL1: R= Py, R’: Ph
HL2: R= Py
HL3: R=Py,
R’= Py
R’= Me
2.2.2. [MCl2(HL4)2] (M = Pd(II) 4, Pt(II) 5)
A solution of 0.58 mmol (0.092 g) of HL4 in 10 ml of
CH3CN was treated with a solution of 0.29 mmol of
HL4: R= Ph, R’=Me
Fig. 1. Pyrazole derived ligands.

J.A. Perez et al. / Inorganica Chimica Acta 358 (2005) 617–622
619
[MCl2(CH3CN)2] (Pd(II): 0.075 g; Pt(II) 0.101 g) dis-
solved in 75 ml of CH3CN. After 12 h of stirring at room
temperature, the solution was concentrated until a crys-
talline precipitate appeared. This precipitate was filtered
off, washed twice with CH3CN (10 ml), and dried in
vacuo.
3025 m(C–H)ar, 1611–1526 (mC@C, mC@N), 1478–1460
(dC@C, dC@N), 989 d(C–H)ip, 777 d(C–H)oop; (polyeth-
1
ylene, cmꢀ1) 473 m(Pt–N). H NMR (DMSO-d6 solu-
3
tion, 250 MHz) d: 9.74 [2H, d, J = 5.2 Hz, Py], 8.30
[4H, m, Py], 8.14 [1H, s, Pz], 7.72 [1H, m, Py].
2.2.3.3. Compound 8. Yield: 48%. C18H16N6Pt: Anal.
Calc. C, 42.27; H, 3.13; N, 16.44, Found: C, 42.53; H,
2.2.2.1. Compound 4. Yield: 82%. C20H20N4Cl2Pd: Anal.
Calc. C, 48.64; H, 4.05; N, 11.36. Found: C, 48.52; H,
3.01, N, 16.47%. Conductivity (Xꢀ1 cm2 molꢀ1
,
3.98, N, 11.16%. Conductivity (Xꢀ1 cm2 molꢀ1
,
9.6 · 10ꢀ4 M in DMSO): 29. IR: (KBr, cmꢀ1) 3072–
3012 m(C–H)ar, 2981 m(C–H)al, 1612–1548 (mC@C,
mC@N), 1452 (dC@C, dC@N), 1022 d(C–H)ip, 761
8.6 · 10ꢀ4 M in DMSO): 28. IR: (KBr, cmꢀ1) 3196
m(N–H), 3055 m(C–H)ar, 2989–2863 m(C–H)al, 1570–
1502 (mC@C, mC@N), 1477 (dC@C, dC@N), 1065
d(C–H)ip, 762 d(C–H)oop; (polyethylene, cmꢀ1) 463
m(Pd–N), 336 m(Pd–Cl). 1H NMR (CDCl3 solution,
250 MHz) d: 7.65 [1H, s, NH], 7.40 [2H, m, Ph], 7.30
[3H, m, Ph], 5.86 [1H, s, Pz], 2.64 [3H, s, CH3].
d(C–H)oop
; )
(polyethylene, cmꢀ1 471 m(Pt–N). 1H
NMR (DMSO-d6 solution, 250 MHz) d: 8.43 [1H, d,
3J = 5.1 Hz, Py], 8.01 [1H, t, 3J = 7.4 Hz, Py], 7.98
3
[1H, d, J = 7.4 Hz, Py], 7.42 [1H, m, Py], 6.81 [1H, s,
Pz], 2.25 [3H, s, CH3].
2.2.2.2. Compound 5. Yield: 63%. C20H20N4Cl2Pt: Anal.
Calc. C, 41.23; H, 3.43; N, 9.62%. Found: C, 41.59; H,
2.3. X-ray crystal structure
3.25, N, 9.23%. Conductivity (Xꢀ1 cm2 molꢀ1
,
Suitable crystals for X-ray diffraction of compound
[PdCl2(HL1)] (1) were obtained through crystallisation
from a DMSO. One crystal was mounted on an Enraf-
Nonius CAD4 four-circle diffractometer. Intensities
were collected at room temperature with monochroma-
1.03 · 10ꢀ3 M in DMSO): 21. IR: (KBr, cmꢀ1) 3194
m(N–H), 3039 m(C–H)ar, 2891–2851 m(C–H)al, 1560–
1502 (mC@C, mC@N), 1470–1417 (dC@C, dC@N),
1063 d(C–H)ip, 760 d(C–H)oop; (polyethylene, cmꢀ1
)
1
˚
452 m(Pt–N), 318 m(Pt–Cl). H NMR (CDCl3 solution,
250 MHz) d: 7.58 [2H, m, Ph], 7.32 [1H, s, N H], 7.30
[3H, m, Ph], 6.06 [1H, s, Pz], 2.48 [3H, s, CH3].
tised Mo Ka radiation (k = 0.71069 A), using x/2h scan-
technique. The structure was solved by direct methods
(
SHELXS-90) [27] and refined by full-matrix least-squares
methods (SHELXL-94) [28]. 15 H atoms were located
from a difference synthesis and refined with an overall
isotropic temperature factor and 14 H atoms were com-
puted and refined with an overall isotropic temperature
2.2.3. [Pt(L)2] (L = L1 6, L2 7, L3 8)
The appropriate ligand (0.58 mmol: HL1: 0.128 g;
HL2: 0.129 g; HL3: 0.092 g) dissolved in CH3CN (15
ml) was added to a solution of [PtCl2(CH3CN)2] (0.29
mmol; 0.101 g) in 75 ml of CH3CN. The resulting solu-
tion was stirred at room temperature for 10 h and con-
centrated on a vacuum line to one-fifth of the initial
volume; crystalline solids were obtained which were fil-
tered off, washed with CH3CN (10 ml), and dried in
vacuo.
factor using
a
riding model. The weigh was
2
2
x = [r2(I) + (0.0516P)2]ꢀ1, where P = (jFoj + 2jFCj )/3.
The final R(F) factor and Rw(F2) values as well as the
number of parameters refined and other details concern-
ing the refinement of the crystal structure are gathered in
Table 1.
2.2.3.1. Compound 6. Yield: 60%. C28H20N6Pt: Anal.
Calc. C, 52.90; H, 3.15; N, 13.23. Found: C, 52.64; H,
3. Results and discussion
3.05, N, 13.12%. Conductivity (Xꢀ1 cm2 molꢀ1
,
3.1. Synthesis and spectroscopic properties of the
complexes
8.8 · 10ꢀ4 M in DMSO): 16. IR: (KBr, cmꢀ1) 3062–
3016 m(C–H)ar, 1611–1556 (mC@C, mC@N), 1462–1444
(dC@C, dC@N), 1002 d(C–H)ip, 759 d(C–H)oop; (poly-
ethylene, cmꢀ1) 467 m(Pt–N). 1H NMR (DMSO-d6 solu-
The reaction of the ligands HL1, HL2 and HL3 with
[PdCl2(CH3CN)2] or [PdCl2(cod)] gives complexes
[PdCl2(HL)] (HL = HL1, HL2, HL3), whereas these
same ligands with [PtCl2(CH3CN)2] yield complexes
[Pt(L)2] (L = L1, L2, L3). The reaction of the ligand
HL4 and [MCl2(CH3CN)2] (M = Pd(II), Pt(II)) gives
complexes with stoichiometry [MCl2(HL4)2]. Stoichi-
ometries of all complexes are not dependent of the
M/L molar ratio (1M:1L or 1M:2L). All characterised
complexes in this publication are unpublished except
[PdCl2(HL3)], which has already been published [29].
3
tion, 250 MHz) d: 8.67 [1H, d, J = 5.3 Hz, Py], 8.10
[1H, m, Py], 7.85 [1H, d, J = 7.6 Hz, Py], 7.52 [2H, d,
3J = 7.1 Hz, Ph], 7.50 [3H, m, Ph], 7.42 [1H, s, Pz],
7.36 [1H, m, Py].
3
2.2.3.2. Compound 7. Yield: 53%. C28H20N6Pt: Anal.
Calc. C, 48.98; H, 2.82; N, 17.58. Found: C, 48.53; H,
2.95, N, 17.47%. Conductivity (Xꢀ1 cm2 molꢀ1
,
9.6 · 10ꢀ4 M in DMSO): 23. IR: (KBr, cmꢀ1) 3085–

620
J.A. Perez et al. / Inorganica Chimica Acta 358 (2005) 617–622
13C NMR spectra could not be recorded for either com-
Table 1
Crystallographic data for [PdCl2(HL1)] (1)
plex owing to the very low solubility in common sol-
vents. NMR data are reported in Section 2.
Formula
M
C14H11Cl2N3Pd
398.56
293(2)
1
The H NMR spectra of complexes 1–5 present one
Temperature (K)
Crystal system
Space group
Unit cell dimensions
broad signal between 13.78 and 7.32 ppm assigned to
the protons NH(pz) [32]. This signal is not observed in
complexes 6–8.
In complex 2 chemical shifts of Ha pyridyl protons are
consistent with the presence of both N-uncoordinated
(d = 8.93 ppm) and N-coordinated (d = 9.83 ppm) pyridyl
monoclinic
P21/c
˚
a (A)
8.421(7)
˚
b (A)
21.523(8)
8.699(6)
90
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
groups. This 0 same behaviour is observed in complex
116.92(7)
90
0
[Pd(L1 )2] (L1 = 3-phenyl-5-(6-methyl-2-pyridyl)pyrazo-
late) [15]. In contrast, the complex 7 chemical shifts of
two-Ha pyridyl protons displayed at 9.74 ppm are consist-
ent with the presence of coordinated pyridyl groups.
3
˚
U (A )
1405.8(16)
4
1.883
Z
Dcalc (g cmꢀ3
)
l (mmꢀ1
F(000)
)
1.691
784
3.2. Crystal and molecular structure of complex 1
Crystal size
h Range (ꢁ)
Index range
0.1 · 0.1 · 0.2
2.71–30.17ꢁ
ꢀ11 < h < 10, 0 < k < 30,
0 < l < 12
4389/4125 [0.0422]
96.7%
The crystal structure of complex 1 consists of mono-
meric cis-[PdCl2(HL1)] molecules (Fig. 2). The palladium
centre has typical square planar geometry (with a slight
tetrahedral distortion), in which the largest deviation
Reflections collected/unique [Rint
Completeness to 2h = 30.17
Data/restraints/parameters
Goodness-of-fit
]
4125/0/202
0.986
˚
from the mean coordination plane is ꢀ0.065(4) A (in
N2), very similar to that of [PdCl2(HL0)] (HL0 = 2-(3-
pyrazolyl)pyridine) [35]. There is a significant pseudo-
axial interaction between the Pd atom and a Cl atom of
an adjacent complex unit (non-bonded Pdꢁ ꢁ ꢁCl separa-
Final R1,xR2
R1 (all data), xR2
Residual electron density (e A
0.0390, 0.1072
0.0720, 0.1234
0.291 and ꢀ0.525
ꢀ3
˚
)
˚
Elemental analysis and conductivity measurements
confirm the named stoichiometries of all complexes.
Conductivity measurements in 10ꢀ3 M DMSO (between
16 and 35 Xꢀ1 cm2 molꢀ1) show the non-ionic behaviour
of the complexes (conductivity values for a non-
electrolyte are below 50 Xꢀ1 cm2 molꢀ1 in DMSO solu-
tion) [30,31]. The IR spectra in the range 4000–400
cmꢀ1, show that the ligand is coordinated to the Pd(II)
and Pt(II) ions. The most striking bands of the pyridine
and pyrazolic ligands (m(C@C), m(C@N))ar and d(C–
H)oop increase their frequency when they are part of
the complexes [32,33]. In the complexes 6–8 the pyrazole
is deprotonated because the band m(N–H) is not ob-
served, whereas in the complexes 1–5 the m(N–H) band
is observed between 3438 and 3194 cmꢀ1 [32]. In the
IR spectra in the region 600–100 cmꢀ1, the m(M–N)
(M = Pd(II), Pt(II)) bands are observed (483–463 cmꢀ1
for Pd(II) and 473–452 cmꢀ1 for Pt(II)). Moreover, the
spectra of the complexes 1–3 display two bands (360–
348 cmꢀ1 and 342–329 cmꢀ1) corresponding to stretch-
ing m(Pd–Cl), which are typical of compounds with a
cis disposition of the chloro ligands around the Pd(II),
whereas the complexes 4 and 5 display one band m(M–
Cl) (M = Pd(II), Pt(II)) (336–318 cmꢀ1), which is typical
of compounds with a trans disposition of the chloro lig-
ands around the metal [34].
tion 3.63(4) A), and hydrogen bonding between the pyraz-
olyl NH proton and a Cl atom of an adjacent complex unit
˚
(Hꢁ ꢁ ꢁCl separation 2.40(3) A). The metal atom is coordi-
nated to one HL1 ligand, via one pyrazole nitrogen and
one pyridine nitrogen, and to two chlorides in cis disposi-
tion. HL1 behaves as a bidentate ligand and uses only two
of its three donor nitrogen atoms, forming a five-
membered metallocycle, which has a planar configuration.
The selected bond lengths and angles of the molecules
are listed in Table 2. The bond distances Pd–Npy
˚
(2.041(3) A) are clearly longer than those of Pd–NPz
˚
(1.979(3) A). Both distances are consistent with previ-
˚
ously described values (1.960–2.125 A) [15,35–40] and
˚
(1.968–2.153 A) [15,35,38–40], respectively. The Pd–Cl
˚
bond lengths (2.2763(14), 2.2842(19) A) can be regarded
as normal compared with the distances found in the lit-
˚
erature (2.276–2.326 A) [15,35,41–45].
The N(2)–Pd(1)–N(1) bite angle, 79.16(14)ꢁ, is similar
to those found in related [PdCl(HL0)] (HL0 = 2-(3-pyraz-
olyl)pyridine) (79.82ꢁ) [35], [PdCl2(HL00)] (HL00 = 2-(20-
0
0
pyridyl)quinoxaline) (80.0ꢁ) [46] and [Pd(L1 )2] (L1 =
3-phenyl-5-(6-methyl-2-pyridyl)pyrazole) (79.2, 80.2)
[15].
The HL1 ligand is not completely planar. The pyridyl
and phenyl groups are slightly twisted with respect to
the pyrazole. The angles between rings are py–pz
1.43(4)ꢁ and ph–pz 0.48(3)ꢁ in this complex. These val-
ues are lower than the other published data
[8,11,14,16,17].
1H NMR spectra of complexes 1–3, 6–8 were re-
corded in DMSO-d6 and for complexes 4 and 5 in
CDCl3, and show the signals of the coordinated ligands.

J.A. Perez et al. / Inorganica Chimica Acta 358 (2005) 617–622
621
Fig. 2. ORTEP drawing of the complexe [PdCl2(HL1)] (1) showing the numbering scheme (ellipsoides are shown at the 50% probability level).
Table 2
In summary, the ligands (HL) when complexed to
Pd(II) and Pt(II) can act as in neutral or anionic forms
depending on the metallic centre, in contrast with the
behaviour of the ligand (HL4) which is not dependent
of the metallic centre [MCl2(HL4)].
1
˚
Selected bond lenghts (A) and angles (ꢁ) for [PdCl2(HL )] (1) with
estimated standard deviations (e.s.d.s) in parentheses
Pd(1)–N(2)
Pd(1)–N(1)
Pd(1)–Cl(2)
Pd(1)–Cl(1)
1.979(3)
2.041(3)
2.2763(14)
2.2842(19)
N(2)–Pd(1)–N(1)
N(2)–Pd(1)–Cl(2)
N(1)–Pd(1)–Cl(2)
N(2)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(1)
Cl(2)–Pd(1)–Cl(1)
79.16(14)
173.56(10)
94.75(11)
93.76(11)
171.60(10)
92.47(6)
5. Supplementary material
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 244281 for compound
[PdCl2(HL1)] (1). Copies of this information may be
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk or www:
htpp://www.ccdc.cam.ac.uk).
4. Conclusions
The ligands HL1, HL2, HL3 (HL) and HL4 react with
Pd(II) and Pt(II) ions to give new pyrazole-derived
compounds.
The study of the coordination of (HL) ligands to
Pd(II) has only revealed the formation of [PdCl2(HL)]
compounds in contrast with Pt(II) complexes, which dis-
play [Pt(L)2] stoichiometries.
Elemental analyses, conductivity measurements and
spectroscopic data for the complexes of Pd(II) data are
consistent with mononuclear structures where neutral
(HL) pyrazole ligands coordinate the metal centre in a
bidentate form. Whereas for the complexes of Pt(II),
they are consistent with mononuclear structures where
ionic (Lꢀ) pyrazolate ligands coordinate the metal cen-
tre in a bidentate form.
Acknowledgement
Support by the Spanish Ministerio de Educacio´n y
Cultura (Project BQU 2003-03582) is gratefully
acknowledged.
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