Synthesis, spectroscopic properties and structural characterisation of Pd(II) and Pt(II) complexes with 1,3,5-pyrazole derived ligands. Rotation around the metal-N bond

Article abstract of DOI:10.1016/j.ica.2004.12.060

Reactions of ligands 1-ethyl-5-methyl-3-phenyl-1H-pyrazole (L¹) and 5-methyl-1-octyl-3-phenyl-1H-pyrazole (L²) with [PdCl ₂(CH₃CN)₂ and K₂PtCl₄ gave complexes trans-[MCl₂(L)₂] (L = L¹, L ²). The new complexes were characterised by elemental analyses, conductivity measurements, infrared, ¹H and ¹³C{ ¹H} NMR spectroscopies and X-ray diffraction. The NMR study of the complex [PdCl₂(L¹)₂], in CDCl₃ solution, is consistent with a very slow rotation of ligands around the Pd-N bond, so that two conformational isomers can be observed in solution (syn and anti). Different behaviour is observed for complexes [PdCl₂(L ²)₂] and [PtCl₂(L)₂] (L = L ¹, L²), which present an isomer in solution at room temperature (anti). The crystal structure of [PdCl₂(L ¹)₂] complex is described, where the Pd(II) presents a square planar geometry with the ligands coordinated in a trans disposition.

Full text of DOI:10.1016/j.ica.2004.12.060

Inorganica Chimica Acta 358 (2005) 2312–2318
www.elsevier.com/locate/ica
Synthesis, spectroscopic properties and structural characterisation of
Pd(II) and Pt(II) complexes with 1,3,5-pyrazole derived
ligands. Rotation around the metal–N bond
a
Vanessa Montoya , 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 15 October 2004; accepted 10 December 2004
Abstract
Reactions of ligands 1-ethyl-5-methyl-3-phenyl-1H-pyrazole (L1) and 5-methyl-1-octyl-3-phenyl-1H-pyrazole (L2) with
[PdCl2(CH3CN)2 and K2PtCl4 gave complexes trans-[MCl2(L)2] (L = L1, L2). The new complexes were characterised by elemental
analyses, conductivity measurements, infrared, 1H and 13C{1H} NMR spectroscopies and X-ray diffraction. The NMR study of the
complex [PdCl2(L1)2], in CDCl3 solution, is consistent with a very slow rotation of ligands around the Pd–N bond, so that two con-
formational isomers can be observed in solution (syn and anti). Different behaviour is observed for complexes [PdCl2(L2)2] and
[PtCl2(L)2] (L = L1, L2), which present an isomer in solution at room temperature (anti). The crystal structure of [PdCl2(L1)2] com-
plex is described, where the Pd(II) presents a square planar geometry with the ligands coordinated in a trans disposition.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Pyrazole ligands; Palladium complexes; Platinum complexes; Crystal structure
1. Introduction
platinum(II) compounds with 1-hydroxyalkyl-3,5-dim-
ethylpyrazole [23,24] and 1-hydroxyalkylpyrazole li-
gands [24,25]. A similar study has been carried out
with complexes with N1-polyether-3,5-dimethylpyrazole
ligands [26]. NMR studies of these complexes have
proved the existence of conformational diastereoisomers
in solution, anti and syn, due to the relative disposition
of the hydroxyalkylic or polyether chains, in which the
ratio of both isomers was shown to be dependent on ste-
ric factors caused by the lengths of the N1-substituent
[23,25,26].
Research on the coordination chemistry of pyrazole-
derived ligands has progressed very rapidly over the last
two decades. Mukherjee published an extensive review
in [1], which complements those presented by La Mon-
ica and Ardizzoia in [2] and by Trofimenko in [3–6].
The N1-substituted pyrazolic ligands have been
extensively investigated in our laboratory in recent
years: N-aminoalkylpyrazoles
phinoalkylpyrazoles [13–15],
[7–12],
N-thioetherpyrazoles
N-phos-
[16–22], N-hydroxyalkylpyrazoles [23–25] and N-poly-
etherpyrazoles [26–29].
In particular, we have reported the synthesis and
structural characterisation of new palladium(II) and
In order to see whether the hindered rotation
around the metal–N bond solution is caused by the
bulk substituents in 3,5-disposition, by the lengths
of the N1-substituents or by the nature of the metal,
the related Pd(II) and Pt(II) complexes with N1-al-
kyl-5-methyl-3-phenylpyrazole were prepared and
studied.
*
Corresponding authors. Fax: +34 93 581 31 01.
E-mail address: josefina.pons@uab.es (J. Pons).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.12.060

V. Montoya et al. / Inorganica Chimica Acta 358 (2005) 2312–2318
2313
L2) dissolved in 5 ml of acetonitrile. After 48 h of stir-
ring at room temperature, the solution was concentrated
until a crystalline precipitate appeared. The complex
precipitate as a orange needles, which were recrystallised
in a dichloromethane + hexane mixture. The solid was
filtered off, washed with diethyl ether (5 ml) and dried
in vacuo.
4
5
3
6
7
9
8
10
2
1
N
N
R
L1: R= ethyl
L2: R= octyl
1: (yield: 69%) Anal. Calc. for C24H28Cl2N4Pd: C,
52.42; H, 5.10; N, 10.19. Found: C, 52.31; H, 4.93; N,
10.12%. Conductivity (Xꢀ1 cm2 molꢀ1, 1.1 · 10ꢀ3 M in
acetone): 6. IR: (KBr, cmꢀ1): 3080 (mC–H)ar, 2979
(mC–H)al, 1557 (mC@C, mC@N)ar, 1452 (dC@C,
dC@N)ar, 768 (dC–H)oop; (polyethylene, cmꢀ1) 492
m(Pd–N), 341 m(Pd–Cl). 1H NMR (CDCl3 solution,
Fig. 1. Pyrazole derived ligands and the atom numbering scheme.
The syntheses of 1-ethyl-5-methyl-3-phenyl-1H-pyr-
azole (L1) and 5-methyl-1-octyl-3-phenyl-1H-pyrazole
(L2) have previously been reported in the literature
[30] (Fig. 1), and it is with these ligands that we obtained
and fully characterised the dichlorocomplexes with the
formula [MCl2(L)2] (M = Pd(II), L = L1 (1); M = Pd(II),
L = L2 (2); M = Pt(II), L = L1 (3); M = Pt(II), L = L2
(4)). The crystal structure of 1 is also reported.
3
250 MHz) d: isomer syn: 7.93 [d, J = 7.2 Hz, 2H, H1,
H5], 7.64–7.54 [m, 3H, H2, H3, H4], 5.89 [s, 1H, H6],
5.44, 5.32 [m, 2H, CH2–CH3], 2.04 [s, 3H, H7], 1.15 [t,
3J = 7.2 Hz, 3H, CH2–CH3] ppm. Isomer anti: 8.21[d,
3J = 7.7 Hz, 2H, H1, H5], 7.64–7.54 [m, 3H, H2, H3,
3
H4], 6.15 [s, 1H, H6], 4.86 [q,, J = 7.0 Hz, 2H, CH2–
3
CH3], 2.32 [s, 3H, H7], 1.47 [t, J = 7.0 Hz, 3H, CH2–
CH3] ppm. 13C NMR (CDCl3 solution, 62.9 MHz):
isomer syn: 153.6 (C9), 142.9 (C10), 132.5 (C8), 130.0–
128.8 (C1–C5), 107.4 (C6), 45.6 (CH2–CH3), 15.2
(CH2–CH3), 12.0 (C7) ppm. Isomer anti: 153.7 (C9),
142.9 (C10), 133.3 (C8), 130.0–128.8 (C1–C5), 108.4
(C6), 46.1 (CH2–CH3), 15.4 (CH2–CH3), 12.1 (C7) ppm.
2: (yield: 63%) Anal. Calc. for C36H52Cl2N4Pd: C,
60.22; H, 7.25; N, 7.80. Found: C, 60.28; H, 7.55; N,
7.67%. Conductivity (Xꢀ1 cm2 molꢀ1, 1.2 · 10ꢀ3 M in
acetone): 3. IR: (KBr, cmꢀ1): 3061 (mC–H)ar, 2924
(mC–H)al, 1554 (mC@C, mC@N)ar, 1456 (dC@C,
dC@N)ar, 772 (dC–H)oop; (polyethylene, cmꢀ1) 494
m(Pd–N), 348 m(Pd–Cl). 1H NMR (CDCl3 solution,
2. Experimental
2.1. General details
All reactions were carried out with the use of vacuum
line and Schlenk techniques. All reagents were commer-
cial grade materials and were used without further puri-
fication. All solvents were dried and distilled by
standard methods.
The elemental analyses (C, N, H) were carried out by
the staff of the Chemical Analyses Service of the Univer-
`
sitat Autonoma de Barcelons on a Carlo Erba CHNS
EA-1108 instrument. Conductivity measurements were
performed at room temperature (r.t.) 10ꢀ3 M in acetone
solutions employing a Crison, micro CM 2200 conduc-
timeter. Infrared spectra were run on a Perkin–Elmer
FT spectrophotometer series 2000 cmꢀ1 as KBr pellets
or polyethylene films in the range 4000–100 cmꢀ1 under
3
250 MHz) d: isomer anti: 8.21 [d, J = 6.8 Hz, 2H, H1,
H5], 7.61–7.49 [m, 3H, H2, H3, H4], 6.14 [s, 1H, H6],
4.79 [t, 3J = 7.3 Hz, 2H, CH2–(CH2)6–CH3], 2.31 [s,
3H, H7], 1.86 [m, 2H, CH2–CH2–(CH2)5–CH3], 1.33–
1.07 [m, 10H, CH2–CH2-(CH2)5–CH3], 0.92 [t,
3J = 6.5 Hz, 3H, (CH2)7–CH3] ppm. 13C NMR (CDCl3
solution, 62.9 MHz) d: isomer anti 154.3 (C9), 143.5
(C10), 133.3 (C8), 130.0–128.9 (C1–C5), 108.4 (C6), 51.3
(CH2–(CH2)6–CH3), 32.2–23.1 (CH2-(CH2)6–CH3) 14.5
((CH2)7–CH3), 12.5 (C7) ppm.
a nitrogen atmosphere. The H NMR, 13C{1H} NMR,
1
HMQC, and NOESY spectra were run on a NMR-FT
Bruker 250 MHz spectrometer (mixing time: 500 ms).
Chemical shifts (d) are given in ppm.
Samples of [PdCl2(CH3CN)2] [31] and K2PtCl4 were
prepared as described in the literature. 1-ethyl-5-
methyl-3-phenyl-1H-pyrazole (L1) and 5-methyl-1-oc-
tyl-3-phenyl-1H-pyrazole (L2) were prepared according
to the published methods [30] (Fig. 1).
2.2.2. [PtCl2(L)2] (L = L1 (3), L2 (4))
A solution of 0.32 mmol (0.135 g) of K2PtCl4 in 10 ml
of HCl 0.1 M was treated with a solution of 0.64 mmol
of the corresponding ligand (0.121 g of L1, 0.176 g of L2)
dissolved in 5 ml of H2O. After 72 h of stirring at room
temperature, the solution was concentrated until a crys-
talline solid appeared. This precipitate was filtered off,
washed twice with diethyl ether (5 ml) and dried in
vacuo.
2.2. Synthesis
2.2.1. [PdCl2(L)2] (L = L1 (1), L2 (2))
A
[PdCl2(CH3CN)2] in 20 ml of acetonitrile was treated
solution
of
0.32 mmol
(0.083 g)
of
3: (yield: 55%) Anal. Calc. for C24H28Cl2N4Pt: C,
45.13; H, 4.39; N, 8.78. Found: C, 45.09; H, 4.48; N,
with a solution of 0.64 mmol (0.121 g of L1, 0.176 g of

2314
V. Montoya et al. / Inorganica Chimica Acta 358 (2005) 2312–2318
8.98%. Conductivity (Xꢀ1 cm2 molꢀ1, 1.1 · 10ꢀ3 M in
acetone): 13. IR (KBr, cmꢀ1): 3058 (mC–H)ar, 2925
(mC–H)al, 1522 (mC@C, mC@N)ar, 1466 (dC@C,
dC@N)ar, 769 (dC–H)oop; (polyethylene, cmꢀ1) 494
m(Pt–N), 312 m(Pt–Cl). 1H NMR (CDCl3 solution,
Table 1
Crystallographic data for trans-[PdCl2(L1)2] (1)
Formula
C24H28Cl2N4Pd
Formula weight
Temperature (K)
˚
Wavelength (A)
549.80
293(2)
0.71073
3
250 MHz) d: isomer anti: 7.97 [d, J = 6.8 Hz, 2H, H1,
H5], 7.52–7.42 [m, 3H, H2, H3, H4], 6.52 [s, 1H, H6],
ꢀ
System, space group
Unit cell dimensions
triclinic, P1 (no. 2)
3
4.74 [q, J = 6.8 Hz, 2H, CH2–CH3], 2.44 [s, 3H, H7],
˚
a (A)
7.378(3)
8.747(2)
1.62 [t, 3J = 6.8 Hz, 3H, CH2–CH3] ppm. 13C NMR
(CDCl3 solution, 62.9 MHz) d: isomer anti: 152.6 (C9),
140.2 (C10), 132.6 (C8), 127.3–130.9 (C1–C5), 104.5
(C6), 45.06 (CH2–CH3), 15.8 (CH2–CH3), 11.5 (C7) ppm.
4: (yield: 59%) Anal. Calc. for C36H52Cl2N4Pt: C,
53.59; H 6.45; N 6.95. Found: C, 53.19; H, 5.99; N,
6.60%. Conductivity (Xꢀ1 cm2 molꢀ1, 1.0 · 10ꢀ3 M in
acetone): 26. IR (KBr, cmꢀ1): 3060 (mC–H)ar, 2929
(mC–H)al, 1551 (mC@C, mC@N)ar, 1470 (dC@C,
dC@N)ar, 763 (dC–H)oop; (polyethylene, cmꢀ1) 507
m(Pt–N), 309 m(Pt–Cl). 1H NMR (CDCl3 solution,
˚
b (A)
˚
c (A)
10.141(3)
72.91(2)
77.16(3)
a (ꢁ)
b (ꢁ)
c (ꢁ)
83.76(2)
609.3(3)
3
˚
U (A )
Z
1
1.499
Dcalc (g cmꢀ3
)
l (mmꢀ1
F(000)
Crystal size (mm3)
hkl Ranges
)
0.999
280
0.1 · 0.1 · 0.2
ꢀ10 to 10, ꢀ11 to 12, 0 to 14
2.14–29.97
3555/3555 [0.0000]
100.0%
2h Range (ꢁ)
3
Reflections collected/unique [Rint
Completeness to h = 29.97
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)] R1, w2
R indices (all data) R1,w2
]
250 MHz) d: isomer anti: d: 7.88 [d, J = 7.0 Hz, 2H,
H1, H5], 7.51–7.35 [m, 3H, H2, H3, H4], 6.43 [s, 1H,
None
3555/0/198
1.074
3
H6], 4.30 [t, J = 7.3 Hz, 2H, CH2–(CH2)6–CH3], 2.37
[s, 3H, H7], 1.95–1.87 [m, 2H, CH2–CH2–(CH2)5–
CH3], 1.38–1.31 [m, 10H, CH2–CH2-(CH2)5–CH3],
0.0314, 0.0814
0.0320, 0.0819
0.676 and ꢀ0.439
3
0.91 [t, J = 7.0 Hz, 3H, (CH2)7–CH3] ppm. 13C NMR
ꢀ3
˚
Largest diff. peak and hole (e A
)
(CDCl3 solution, 62.9 MHz) d: isomer anti 149.2 (C9),
141.5 (C10), 138.3 (C8), 129.1–126.6 (C1ꢀC5), 103.5
(C6), 49.7 (CH2–(CH2)6–CH3), 32.2–23.0 (CH2-(CH2)6–
CH3) 14.6 ((CH2)7–CH3), 11.7 (C7) ppm.
3. Results and discussion
2.3. X-ray crystal structure analyses
3.1. Synthesis and spectroscopic properties of the
complexes
Suitable crystals for X-ray diffraction of compound
trans-[PdCl2(L1)2] (1) were obtained through crystallisa-
tion from CHCl3. One crystal was mounted on an En-
raf-Nonius CAD4 four-circle diffractometer. Unit-cell
parameters were determined from automatic centring
of 25 reflections (12 < h < 21) and refined by least-
squares method. Intensities were collected with graphite
The complexes trans-[MCl2(L)2] (M = Pd(II): L = L1
(1), L2 (2); M = Pt(II): L = L1 (3), L2 (4)) were obtained
by reaction of [PdCl2(CH3CH)2] or K2PtCl4 with the
corresponding pyrazolic ligand (L), in an acetonitrile
solution in the case of Pd(II) or in a H2O/0.1 M HCl
solution with Pt(II) and in the 1M:2L ratio for both
cases. The ability of L1 and L2 to coordinate Pd(II)
and Pt(II) is comparable to that of the N-hydrox-
yalkylpyrazoles and N-polyetherpyrazoles [23–26]. The
elemental analyses are consistent with the formula
[MCl2(L)2] for the four compounds. Conductivity mea-
˚
monochromatised Mo Ka radiation (k = 0.71069 A),
using x/2h scan-technique. 3555 reflections were mea-
sured every two hours as orientation and intensity con-
trol, significant intensity decay was not observed.
Lorentz-polarisation but no absorption corrections were
made. The structure was solved by Patterson synthesis,
using SHELXS computer program [32], and refined by
full-matrix least-squares method with SHELX 97 com-
puter programs [33] using 3555 reflections (very negative
surements in acetone (between 3 and 26 Xꢀ1 cm2 molꢀ1
)
show the non-ionic behaviour of the complexes 1–4
(conductivity values for a non-electrolyte are below
100 Xꢀ1 cm2 molꢀ1 in acetone solution) [34,35].
The IR spectra in the range of 4000–400 cmꢀ1 show
that the ligands are coordinated to the Pd(II) or Pt(II).
The m(C@C), m(C@N) and d(C–H)oop bands of the pyr-
azolic ligands increase its frequency when are part of the
complex [30].
intensities were not assumed). The function minimised
2 2
P
2
was
wiFoj ꢀ jFcj j , where x = [r2(I) + (0.0664P)2 +
0.0341P]ꢀ1, and P = (jFoj + 2jFcj )/3. All H atoms were
located from a difference synthesis and refined with an
overall isotropic temperature factor. The final R(F) fac-
tor and Rw (F2) values as well as the number of param-
eters and other details concerning the refinement of the
crystal structure are gathered in Table 1.
2
2
The IR spectra of [MCl2(L)2] complexes in the region
600–100 cmꢀ1 were also measured. The presence of
bands at 500 cmꢀ1 assigned to m(Pd–N) or m(Pt–N)

V. Montoya et al. / Inorganica Chimica Acta 358 (2005) 2312–2318
2315
confirms the coordination of the ligand to the metallic
atom. These complexes display one well-defined m(Pd–
Cl) band at 341 cmꢀ1 (1) and 348 cmꢀ1 (2), and m(Pt–
Cl) bands at 312 cmꢀ1 (3) and 309 cmꢀ1 (4), respectively.
These bands clearly indicate that the chlorine atoms are
coordinated trans to the Pd(II) and Pt(II) [36].
The NMR spectra of 1–4 were acquired using CDCl3
as a solvent.
The 1H and 13C{1H} NMR spectra of complex 1
show two sets of signals for many protons, suggesting
the presence of conformational isomers in solution, in
an intensity ratio of approximately 1:1. Our previous
work also proved that the two species proposed in this
case are the anti and the syn isomers (respectively), con-
cerning the position of the hydroxyalkyl or polyether
chains [23,25,26] (Fig. 2).
A different behaviour is observed in complex 2, which
shows a unique NMR signal for each type of proton and
carbon. The only specie present is the anti conforma-
tional isomer, which was confirmed by NOESY experi-
ment. The presence of two conformers in complex 1
and one (anti) in complex 2 can be explained by the bulk
of alkylchain. Thus, when the N1-alkyl chain increases
its length, the less stable isomer (syn) decreases its con-
centration in solution.
The presence of two isomers in solution is not ob-
served in complexes [PtCl2(L)2] (L = L1 (3), L2 (4))
1
which show unique set of signals for each type of H
and 13C{1H} corresponding the anti conformational iso-
1
mer. The H NMR spectrum of [PdCl2(L2)2] at variable
temperature (243 K) did not show any splitting or
broadening of signals, which is in agreement with the
existence of one specie in solution. The anti nature of
the isomers was confirmed by a NOESY experiment,
which shows NOE interaction between H1 and –CH2–
CH2–(CH2)5–CH3 (Fig. 3). In these compounds, the
rotation around the Pt–N bond seems not to be possible
due to higher Pt–N bond stability in comparison with
Pd–N bonds.
The hindrance to rotation around metal–ligand
bonds is predominantly controlled by steric factor but
the influence of metal is not negligible [37]. It is well
known that Pd(II) is more reactive than Pt(II) in substi-
tution reactions but, interestingly, the palladium com-
plexes are found to interconvert more readily than
platinum analogues. [38]. NMR studies of rotational
N
N
Cl
N
N
Pd
Cl
Cl
Pd
N
N
Cl
N
N
Fig. 2. The conformational isomers existing in solution due to a
hindered rotation around the Pd–N bond at room temperature for
compound (1).
H2, H3, H4
H1
-CH2-(CH2)6-CH3
(ppm)
0.0
0.8
1.6
2.4
3.2
4.0
4.8
-CH2-CH2-(CH2)5-CH3
(ppm)
90.0
80.0
7. 00
6.00
5.00
4.00
Fig. 3. The 250 MHz 2D NOESY spectrum of [PdCl2(L2)2] (2) in CDCl3 at room temperature.

2316
V. Montoya et al. / Inorganica Chimica Acta 358 (2005) 2312–2318
Table 2
barriers for metal–N complexes have shown that in
Pt(II) complexes are higher than in Pd(II) complexes
[39]. These experimental observations were supported
by ab initio calculations of model complexes containing
Pd–N and Pt–N bonds, which reveal that the nitrogen
metal p–r interaction is stronger for Pt(II) complexes,
resulting in a higher energy rotation barrier [39]. Despite
the fact that pyrazole ligands are poor p-acceptors [40]
and weaker p-acceptors than pyridine derivatives (lar-
gely studied in rotational dynamic processes) [41], the
experimental findings suggest that the p-effects can be
significant in the control of the preferential formation
of the rotational diastereoisomers.
1
˚
Selected bond lengths (A) and bond angles (ꢁ) for trans-[PdCl2(L )2] (1)
with estimated standard deviations (e.s.d.s) in parentheses
Pd–N(1)
Pd–Cl
2.0281(16)
2.3078(9)
180.00(12)
88.72(5)
91.28(5)
180.00
N(1)–Pd–N(1)#1
N(1)–Pd–Cl#1
N(1)–Pd–Cl
Cl#1–Pd–Cl
Symmetry transformations used to generate equivalent atoms: #1
ꢀx + 1, ꢀy, ꢀz.
ment, by two trans chlorides and two nitrogen atoms
in the pyrazolic rings. The angles N–Pd–N and Cl–Pd–
Cl are exactly 180ꢁ, which means that the metallic atoms
lie in the centre of the plane determined by the two
nitrogen atoms and the two chlorides. The N1-substitut-
ing alkyl chains is in an anti disposition. Cis angles N–
Pd–Cl deviate from the ring angle in ꢁ1ꢁ the deviation
in the equivalent complexes trans-[MCl2(HL)2]
(HL = 1-(2-hydroxyethyl)pyrazole [25]) and 1-[2-(2-
methoxyethoxymethoxy)ethyl]-3,5-dimethylpyrazole [26]
is ꢁ1ꢁ, however for the ligands 1-(2-hydroxyethyl)-3,5-
dimethylpyrazole [23] and 1-[2-[2-(2-methoxyethoxy)-
ethoxy]ethyl]-3,5-dimethylpyrazole [26] are only around
0.5ꢁ and 0ꢁ, respectively.
Precedents in the literature show that the reactivity of
pyrazolic ligands with Pt(II) yields different results to
those obtained with Pd(II) [23–25].
3.2. Crystal and molecular structure of complex 1
The crystal structure of 1 consists of discrete centro-
symmetric [PdCl2(L1)2] molecules linked by van der
Waals forces. Table 2 lists selected distances and angles
for this complex. The molecular structure is illustrated
in Fig. 4.
The crystal structure is a monomeric molecule con-
taining Pd(II) coordinated in a square planar environ-
Fig. 4. ORTEP drawing of the complex [PdCl2(L1)2] (ellipsoids are shown at the 50% probability level).

V. Montoya et al. / Inorganica Chimica Acta 358 (2005) 2312–2318
2317
The ligand (L1) is not planar. The phenyl group
twisted with respect to the pyrazole. The angle dihedral
between ph and pz is 35.06ꢁ.
1223 336033; e-mail: deposit@ccdc.cam.ac.uk or
www.htpp://ccdc.cam.ac.uk).
The X-ray powder diffraction spectrum of 1 corrobo-
rates the presence of the single anti conformer in the so-
lid state.
The [PdCl2(Npz)2] core (containing terminal chlorine
ions) is found in 21 complexes described in the literature
(thirteen of the complexes found had trans geometry and
eight were cis) [16,22,23,25,26,42–56]. Both the Pd–N
Acknowledgement
´
Support by the Spanish Ministerio de Educacion y
Cultura (Project BQU2003-03582) is gratefully
acknowledged.
˚
distances (2.0281(16) A) and the Pd–Cl distances
˚
(2.3078(9) A) bond lengths are on the some order as
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