Platinum(II) and palladium(II) complexes of N-benzoyl-N′-propylthiourea (H2L): Synthesis and geometric isomer distribution of [M(H2L-S)2X2] (M = PtII or PdII; X = Cl-, Br- or I-); crystal structure of trans-[Pd(H2L-S)2Br2]

Article abstract of DOI:10.1039/a809543d

A systematic study of the synthesis and cis/trans isomer distribution for simple [M(H₂L-S)₂X₂] complexes (M = Pt^II or Pd^II; X = Cl, Br or I; H₂L = N-benzoyl-N′-propylthiourea) has shown that the pure cis-[Pt(H₂L-S)₂Cl₂] complex is obtained prior to recrystallization. The cis-[Pt(H₂L-S)₂Cl₂] complex undergoes facile isomerization in a variety of organic solvents, the equilibrium cis/trans distribution of which depends on solvent polarity. The corresponding bromo- and iodo-complexes of Pt^II tend toward mainly the trans isomers, as do the corresponding palladium(II) complexes. The crystal structure of trans-[Pd(H₂L-S)₂Br₂] has been determined which is the first example of a palladium(II) complex in which the potentially chelating ligand is bound through the S atom only.

Full text of DOI:10.1039/a809543d

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Platinum(II) and palladium(II) complexes of N-benzoyl-NЈ-propyl-
thiourea (H2L): synthesis and geometric isomer distribution of
[M(H2L-S)2X2] (M ؍ PtII or PdII; X ؍ Cl؊, Br؊ or I؊); crystal
structure of trans-[Pd(H2L-S)2Br2]
Klaus R. Koch,* Yali Wang and Anita Coetzee
Department of Chemistry, University of Cape Town, P Bag Rondebosch, Cape Town, 7701,
RSA
Received 7th December 1998, Accepted 27th January 1999
A systematic study of the synthesis and cis/trans isomer distribution for simple [M(H2L-S)2X2] complexes (M = PtII
or PdII; X = Cl, Br or I; H2L = N-benzoyl-NЈ-propylthiourea) has shown that the pure cis-[Pt(H2L-S)2Cl2] complex
is obtained prior to recrystallization. The cis-[Pt(H2L-S)2Cl2] complex undergoes facile isomerization in a variety
of organic solvents, the equilibrium cis/trans distribution of which depends on solvent polarity. The corresponding
bromo- and iodo-complexes of PtII tend toward mainly the trans isomers, as do the corresponding palladium()
complexes. The crystal structure of trans-[Pd(H2L-S)2Br2] has been determined which is the first example of a
palladium() complex in which the potentially chelating ligand is bound through the S atom only.
2
We have become interested in the co-ordination chemistry of a
O
H
3
group of deceptively simple ligands based on the N-alkyl-NЈ-
aroyl- (H2L) and N,N-dialkyl-NЈ-aroylthioureas (HL), in view
of their selective co-ordination of the platinum group metals.1
Of particular interest is the potential utility of these ligands in
the analytical chemistry of the platinum group metals (PGMs)
such as for example the chromatographic separation and
determination of the PGMs at trace level,2,3 as well as the on-
line preconcentration of PdII followed by its determination at
ultra-trace level by means of electrothermal atomic absorption
spectroscopy.4 We, and others, have previously shown that the
co-ordination of the N,N-dialkyl-NЈ-aroylthioureas usually
leads to very stable bidentate-S,O co-ordination to PdII,5 PtII 6
and RhIII.7 On the other hand the co-ordination chemistry of
N-alkyl-NЈ-aroylthioureas is strongly influenced by an intra-
molecular hydrogen-bond between the carbonyl atom of the
aroyl moiety and the thiourea NH group, resulting in co-
ordination through the S atom of the ligand.8 Despite the
analytical utility of these ligands, there is relatively little
detailed information in the literature concerning the synthesis
and structure of complexes of PtII and PdII with N-alkyl-NЈ-
aroylthioureas. Of interest in the case of d8 metal ions are the
factors which determine the distribution of cis/trans isomers of
complexes of PtII/PdII of for example N-benzoyl-NЈ-propyl-
thiourea. Recently we characterized the cis-[Pt(H2L-S)2Cl2]
complex by means of X-ray diffraction,8 and reported that the
corresponding trans isomer coexists in chloroform solution in
cis:trans mole ratio of 67:33 at 25 ЊC. As part of our continu-
ing interest in elucidating the fundamental co-ordination chem-
istry of N-alkyl-NЈ-aroylthioureas of the PGMs, we here report
a systematic study of the synthesis of [M(H2L-S)X2] complexes
(M = PtII or PdII; X = Cl, Br or I; H2L = N-benzoyl-NЈ-
propylthiourea) with reference to determining the distribution
of cis/trans isomers in the solid state, as well as in various
solvents.
N
S
N
H1
Experimental
Preparative methods
N-Benzoyl-NЈ-propylthiourea was prepared as previously
described8 and purified by recrystallization from chloroform–
ethanol mixtures.
[M(H2L-S)2X2] (M ؍ PtII or PdII; X ؍ Cl؊, Br؊ or I؊) com-
plexes. These complexes were prepared according to the follow-
ing standardized procedure from commercially available
K2[PtCl4] and K2[PdCl4] or PdCl2, which were used without
further purification. The complexes were characterized by
means of melting points (measured using a Reichert Thermo-
var microscope), elemental (C, H, and N) analysis, IR and
NMR spectroscopy.
[Pt(H2L-S)2Cl2]. A 0.25 mmol portion (103.8 mg) of K2-
[PtCl4] dissolved in 30 cm3 of a 1:2 (v/v) mixture of 1 M HCl–
1,4-dioxane or acetonitrile was added dropwise to 30 cm3 of a
well stirred solution containing 0.50 mmol H2L (111.2 mg) in
the same solvent, at the desired temperature (25, 60, 85 2 ЊC),
using a water-jacketed dropping funnel over a period of 5–15
min. The bright yellow mixture was then stirred at the desired
temperature for a fixed time interval (Table 1). On cooling, 200
cm3 cold water were added to complete the precipitation of the
complex, which was collected in high yield by centrifugation,
washed with cold water and ethanol, followed by drying at
60 ЊC under vacuum. If desired (see below), the complex was
recrystallized from mixtures of chloroform and ethanol, with
minimum losses followed by drying (Found: C, 37.24; H,
4.01; N, 7.71. C22H28Cl2N4O2PtS2 requires C, 37.18; H, 3.97; N,
7.88%).
We report the crystal structure of trans-[Pd(H2L-S)2Br2], the
first example of H2L co-ordinated to PdII only through the
S atom is this manner. For the purposes of this contribution,
we have adopted an arbitrary numbering scheme for the
N-benzoyl-NЈ-propylthiourea ligand which is consistent with
that used in the crystal structure of trans-[Pd(H2L-S)2Br2].
[Pt(H2L-S)2Br2] and [Pt(H2L-S)2I2]. The dibromo- and
diiodo-complexes were prepared by an identical procedure to
that for the dichloro-complexes, except that the corresponding
[PtBr4]2Ϫ and [PtI4]2Ϫ anions were generated in situ by addition
of a 25 fold molar excess of NaBr or NaI to the solution of
J. Chem. Soc., Dalton Trans., 1999, 1013–1016
1013

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Table 1 Conditions of synthesis and physical properties of recrystallized [Pt(H2L-S)2Cl2] complexes prepared by a standardized procedure
1H NMR shifts (δ)b
cis:trans
Reaction medium
(0.01 M HX ϩ solvent)
Ratio (%)c
X
t/h
T/ЊC
Yield (%)
Mpa/ЊC
cis-N(1)H
trans-N(1)H
(not equilibrium)
Cl
1
6
17
1
1
1
6
1
1
1
25
25
25
60
85
25
25
60
85
25
25
60
85
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
Acetonitrile
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
Acetonitrile
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
Acetonitrile
77
87
94
84
82
69
84
62
71
82
75
84
81
154–158, 162–165
152–153, 158–160
153–155, 160–163
154–155, 165–168
154–155, 165–169
162–164, 174–178
161–164, 176–179
161–164, 175–178
163–166, 175–178
172–173, 196–199
172–173, 196–198
172–173, 195–197
171–173, 196–197
11.80
11.80
11.80
11.80
11.80
11.49
11.49
11.50
11.50
11.36
11.36
11.36
11.36
11.55
11.55
11.56
11.55
11.56
11.31
11.31
11.32
11.32
10.99
10.99
10.99
10.99
74:26
75:25
75:25
75:25
75:25
40:60
42:58
42:58
42:58
8:92
Br
I
6
1
1
6:94
5:95
8:92
a For two distinct crystals. b Measured at 25 ЊC within 2 min of dissolution in CDCl3. c Estimated from the resonance integrals of the N(1)H signals in
solution described in footnote b; for the chloro-complexes the equilibrium distribution is different in this solvent.
2Ϫ
K2[PtCl4] and substituting the 1 M HCl by 10% (v/v) HBr or
HI, allowing this mixture to stir for 1 h prior to addition to the
solution of ligand, and proceeding as before (Found: C, 33.30;
H, 3.50; N, 6.97. C22H28Br2N4O2PtS2 requires C, 33.05; H, 3.53;
N, 7.01. Found: C, 29.75; H, 3.14; N, 6.26. C22H28I2N4O2PtS2
requires C, 29.57; H, 3.16; N, 6.27%).
[Pd(H2L-S)2Cl2] and [Pd(H2L-S)2Br2]. These complexes
were prepared by means of an identical method to that for the
platinum() complexes described above, using K2[PdCl4] or
PdCl2 as the source of PdII (Found: C, 42.89; H, 4.61; N, 9.16.
C22H28Cl2N4O2PdS2 requires C, 42.49; H, 4.54; N, 9.01. Found:
C, 37.51; H, 4.00; N, 7.85. C22H28Br2N4O2PdS2 requires C,
37.17; H, 3.97; N, 7.88%). Yields and other pertinent analytical
data are given in Table 1.
addition of the metal salt MX4 dissolved in a 1:1 mixture
of 0.1 M HX (X = Cl, Br or I) and 1,4-dioxane or acetonitrile
over a 15 min period to a well stirred solution of the required
amount of H2L (L:M mole ratio 2:1) at a predetermined
temperature. The reactions were carried out at fixed temper-
atures of 25, 60 and 85 ЊC for various reaction times of 1, 6 and
17 h, respectively. In general, the complex precipitates during
the reaction and high yields of analytically pure complex
[M(H2L-S)2X2] were obtained. These data are summarized in
Table 1.
[Pt(H2L)2X2] (X ؍ Cl؊, Br؊ or I؊) complexes
The recrystallized (chloroform–ethanol), analytically pure
[Pt(H2L-S)2Cl2] complex shows two distinct melting points at
154–158 and 165–169 ЊC irrespective of the solvent mixture,
temperature and reaction time used during the synthesis, sug-
gesting that isomerism takes place during the recrystallization
NMR and IR spectroscopy
1
The H and 195Pt NMR spectra were recorded in 5 mm tubes
1
process. Moreover, the H NMR spectrum of a fresh solution
in CDCl3 solution using a Varian Unity-400 spectrometer
operating at 400 and 85.85 MHz respectively; 1H spectra
were recorded at 25 ЊC, while 195Pt chemical shifts were meas-
ured at 30 ЊC relative to the usual reference of external H2PtCl6
[500 mg in 1 cm3 30% (v/v) D2O–1 M HCl].9 Infrared spectra
were recorded using a Perkin-Elmer 983 dispersive spec-
trometer, as freshly prepared Nujol mulls between polyethylene
plates.
of the recrystallized [Pt(H2L-S)2Cl2] complex (acquired within
2 min of dissolution) shows this to be a two component mixture
consisting of cis:trans isomers in the ratio of ca. 75%:25%
(Table 1). We have shown recently that the cis/trans isomer
distribution of bis(N-benzoyl-NЈ-propylthioureato)dichloro-
1
platinum() can conveniently be determined by means of H
and 195Pt NMR spectroscopy.8 Thus in the H NMR spectrum
1
of cis-bis(N-benzoyl-NЈ-propylthioureato)dichloroplatinum()
(characterized by X-ray diffraction) the 1H resonances of
N(1)H and N(2)H appear at δ 11.80 0.03 and 11.15 0.03
[partially resolved triplet 3J(H2-H3) ≈ 13 Hz] respectively, with
δ(195Pt) at Ϫ3231 2. The corresponding chemical shifts for
the trans isomer occur at δ(1H) 11.55 0.03, 11.11 0.03 and
δ(195Pt) Ϫ3052 2 respectively.
Crystal structure determination and refinement
Crystals of trans-[Pd(H2L-S)2Br2] of dimensions 0.30 × 0.25 ×
0.25 mm, crystallizing in the triclinic system, were chosen for
analysis. Data were collected at 173(2) K on an Enraf-Nonius
CAD4 diffractometer using graphite-monochromated Mo-Kα
radiation (λ = 0.7107 Å). A Lorentz-polarization correction
was applied to the data, as well as an empirical absorption
correction.10 The structure was solved by direct methods11 and
refined using full-matrix least squares12 on F2. Non-hydrogen
atoms were treated anisotropically while hydrogen atoms were
placed in geometrically calculated positions and linked to
common thermal parameters. Pertinent crystal and structure
refinement data are given in Table 3.
To test the possibility that isomerization occurs during the
recrystallization of [Pt(H2L-S)2Cl2], we examined the 1H NMR
spectrum of a freshly made CDCl3 solution (25 ЊC) of an unre-
crystallized, but analytically pure, sample of [Pt(H2L-S)2Cl2]
(mp 154–157 ЊC). The infrared spectrum of this solid confirms
the cis configuration, since only two strong ν(Pt–Cl) stretching
bands at 304 and 321 cmϪ1 are observed, consistent with liter-
1
ature values for mononuclear cis complexes.13 The H NMR
spectrum acquired within 2 min of dissolution of unrecrystal-
lized [Pt(H2L-S)2Cl2] shows only one set of N(1)H and N(2)H
resonances corresponding to the cis-[Pt(H2L-S)2Cl2] complex
as shown by the first spectrum in the array in Fig. 1. On stand-
ing in CDCl3 solution (at 25 ЊC) an additional set of 1H reson-
ances appears in the spectrum over time, corresponding to the
trans isomer, the system reaching an equilibrium distribution
CCDC reference number 186/1333.
See http://www.rsc.org/suppdata/dt/1999/1013/ for crystallo-
graphic files in .cif format.
Results and discussion
A standardized procedure for the synthesis of [M(H2L-S)2X2]
(M = PtII or PdII) was adopted, consisting of the dropwise
1
after 3–4 h, as shown by the partial H NMR spectrum as a
function of time in Fig. 1. From these spectra an equilibrium
1014
J. Chem. Soc., Dalton Trans., 1999, 1013–1016

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Table
Cl2]
2
Measured equilibrium values for the cis-[Pt(H2L-S)2-
trans-[Pt(H2L-S)2Cl2] system in various solvents at 25 ЊC as
a function of solvent polarity
Relative
permittivity, D
Equilibrium
constant, K
Solvent
Nitromethane-d3
Dimethylformamide-d7
Acetone-d6
Tetrahydrofuran-d8
Chloroform-d3
Benzene-d6
38.6
36.7
20.5
7.39
4.7
0.16
0.23
0.28
0.39
0.47
0.88
2.27
however, the isomer distribution in CDCl3 found for [Pt(H2L-
S)2Br2] and [Pt(H2L-S)2I2] remains invariant irrespective of
whether these complexes are recrystallized or not. In the case of
[Pt(H2L-S)2Br2] we find a distribution of ca. 42% cis:68% trans
(mp 161–166 and 175–179 ЊC), while for the [Pt(H2L-S)2I2]
complexes the distribution is ca. 5% cis and 95% trans (mp
171–173 and 195–199 ЊC). Evidently the dibromo- and diiodo-
complexes in CDCl3 appear to reach an equilibrium isomer dis-
tribution (K = 1.41 0.06 and 15.4 3.8, respectively) during
the synthesis in the water–dioxane/acetonitrile phase, whereas
the dichloro-complexes undergo facile isomerization in various
solvents at room temperature (Table 2). These various assign-
ments are independently confirmed by the 195Pt NMR reson-
ances of the dibromo- and diiodo-complexes, which show 195Pt
resonances at δ Ϫ3693, Ϫ3678 and Ϫ4693, Ϫ4870 for the cis-
and trans-[Pt(H2L-S)2Br2] or [Pt(H2L-S)2I2] complexes respect-
ively. The 195Pt shift assignments are based on the relative
resonance intensities of these signals, which mirror those of the
Fig. 1 Portion of the 1H NMR spectrum of a freshly dissolved sample
of unrecrystallized cis-[Pt(H2L-S)2Cl2] in CDCl3 at 25 ЊC as a function
of time. The first spectrum in the array was recorded 1.9 min after
dissolution, while the last spectrum was recorded ca. 24 h later, at
steady state. The isomerization of cis to trans is clearly evident.
constant,†
K = {trans-[Pt(H2L-S)2Cl2]/cis-[Pt(H2L-S)2Cl2]}
trans-[Pt(H2-
defined for the system cis-[Pt(H2L-S)2Cl2]
1
corresponding H NMR spectra. Moreover the 195Pt chemical
L-S)2Cl2] can easily be estimated from the relative resonance
integrals of the cis and trans N(1)H resonances; in CDCl3
solution we find K = 0.47 0.02 at 25 ЊC. Several repeated
preparations of [Pt(H2L-S)2Cl2] under different conditions of
temperature, reaction time and solvent composition confirm
that all unrecrysallized samples have essentially the pure cis
configuration, but on dissolution undergo facile isomerization.
Table 2 shows the measured equilibrium isomer distribution
constants of [Pt(H2L-S)2Cl2] in a number of deuteriated sol-
vents of differing polarity at 25 ЊC. It is clear that an inverse
correlation between K and the relative permittivity, D, of the
solvent14 is observed. The cis isomer is favored in solvents of
highest polarity, while in benzene-d6 with lowest D in this series
the trans isomer predominates; these trends are similar to
observations made for [Pd(PR3)2Cl2] by Jenkins and Shaw15
and Redfield and Nelson16 some years ago. An interesting, if
poorly understood aspect of the cis/trans isomerization of
[Pt(H2L-S)2Cl2] is that the rate of equilibration also depends on
the nature of the solvents. Qualitatively, we find that the relative
rates of isomerization are greatest in benzene-d6 (lowest D), the
process being complete within the time of preparing a solution
shift of trans-[Pt(H2L-S)2I2] is upfield relative to the cis isomer,
in contrast to the corresponding dichloro- and dibromo-com-
plexes, which is consistent with similar trends generally found in
other uncharged mononuclear platinum() complexes involving
two halide ions and two uncharged ligands.9
[Pd(H2L-S)2X2] (X ؍ Cl؊ or Br؊) complexes
It was only possible to prepare the dichloro and dibromo
[Pd(H2L-S)2X2] complexes by a similar synthetic method as
used for the corresponding platinum() analogues. Moreover
the isomer distribution observed for the palladium() com-
plexes differs substantially from that observed for the corre-
sponding platinum() complexes. The unrecrystallized, pure
[Pd(H2L-S)2Cl2] complex is presumed to be a single isomer, in
view of the sharp melting point (149–152 ЊC). However, from
1
the H NMR spectrum of a fresh CDCl3 solution of unrecrys-
tallized [Pd(H2L-S)2Cl2], it appears that trans-[Pd(H2L-S)2Cl2]
predominates with a equilibrium constant K = 2.33 at 25 ЊC
[assignment is based on the relative resonance integral ratio of
the N(1)H peaks at δ 12.18 to 11.62 which are assigned to the
cis and trans complexes respectively, by comparison with
1
and recording a H NMR spectrum (<2 min), while it takes
more than 24 h to reach equilibrium in CD3NO2 (highest D).
We are currently studying the kinetics of isomerism of [Pt-
(H2L-S)2Cl2] in more detail, the results of which will be
published elsewhere.
1
the corresponding platinum() complexes]. Moreover, the H
NMR spectra of the palladium() complexes remain invariant
for 24 h, suggesting that the isomer distribution rapidly reaches
equilibrium on dissolution of the substance. By contrast to the
platinum() complexes, the intramolecular hydrogen-bonded
N(2)H resonances of cis-[Pd(H2L-S)2Cl2] (δ 11.39) and trans-
[Pd(H2L-S)2Cl2] (δ 11.26) are substantially broadened so that
the 3J coupling between the α-CH2 moiety of the propyl group
is unresolved, something which might cast doubt on the
unambiguous assignment of cis and trans configuration of
these isomers.
As might be expected, substitution of the ClϪ by BrϪ or IϪ
ions is likely to significantly affect the K values of isomer distri-
bution in [Pt(H2L-S)2X2], in view of the increasing trans effect
in the order Cl < Br < I.17 Results in Table 1 essentially confirm
this expectation, showing that the trans complex is strongly
favored in the order I > Br > Cl. By contrast to [Pt(H2L-S)2Cl2]
Substitution of the ClϪ ion by the BrϪ ion leads to the form-
ation of the pure trans-[Pd(H2L-S)2Br2] complex (mp 176–
178 ЊC), for which the 1H N(1)H resonance appears at δ 11.17,
the N(2)H resonance being just visible as a shoulder of the
latter peak. There is no evidence of any cis isomer in CDCl3,
† The attainment of an equilibrium distribution is confirmed by the
invariance of the respective resonance integrals for these complexes for
at least 72 h at 25 ЊC. In determining the K values by means of 1H NMR
spectroscopy care was taken to ensure that the system was fully relaxed
and that resonance integrals accurately reflected the concentrations of
the cis/trans isomers.
J. Chem. Soc., Dalton Trans., 1999, 1013–1016
1015

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Table
3 Crystal and structure refinement data for trans-bis(N-
and the carbonyl oxygen atom (O11) of the co-ordinated ligand
at 2.601(4) Å effectively locks the ring C1–N1–C11–O11–H2–
N2 into a planar structure, the atoms of this ring deviating from
planarity by not more than 0.026 Å. The structure, bond
lengths and angles of the co-ordinated H2L in trans-[Pd-
(H2L-S)2Br2] are remarkably similar to that of the unbound
ligand,18 as well as that of the co-ordinated ligand in the corre-
sponding cis-platinum complex.8 This mode of co-ordination
of N-benzoyl-NЈ-alkylthiourea once again highlights the
importance and relative stability of the intramolecular hydro-
gen bond between the thiourea NH moiety and the carbonyl
oxygen atom of these ligands in determining the preferred
mode of S atom co-ordination.
benzoyl-NЈ-propylthioureato)dibromopalladium()
Empirical formula
Formula weight
C22H28Br2N4O2PdS2
710.84
T/K
Crystal system
Space group
293(2) K
Triclinic
P1
¯
a/Å
b/Å
c/Å
α/Њ
8.768(1)
8.9525(9)
9.8668(8)
104.034(8)
113.016(8)
99.226(9)
662.7(1)
β/Њ
γ/Њ
U/Å3
µ/mmϪ1
3.849
Z
1
Conclusion
Independent reflections
Goodness of fit on F2
Final R1, wR2 [I > 2σ(I)]
(all data)
1744 [R(int) = 0.0137]
1.093
0.0254, 0.0724
0.0306, 0.0739
From our studies some interesting and fairly significant conclu-
sions can be drawn which have relevance to the synthesis of
simple mononuclear complexes of PtII and PdII with N-benzoyl-
NЈ-propylthiourea and related ligands. In the case of PtII only
the pure cis-[Pt(H2L-S)2Cl2] complex is obtained by our method
of synthesis; this complex undergoes relatively rapid partial
isomerization in solution to yield a cis/trans distribution which
is dependent on solvent polarity. In contrast the corresponding
palladium() complexes are predominantly trans, and appear
to have reached an equilibrium cis/trans distribution on dis-
solution, something consistent with the greater lability of
palladium() complexes in general. The corresponding bromo-
and iodo-complexes of PtII and PdII are mainly trans, as illus-
trated by the crystal structure of the trans-[Pd(H2L-S)2Br2]
complex.
Acknowledgements
We thank the University of Cape Town and the Foundation for
Research Development for financial assistance. The loan of
platinum and palladium salts from Johnson Matthey plc is
gratefully acknowledged.
Fig. 2 The molecular structure of trans-[Pd(H2L-S)2Br2], with the
numbering scheme used. Only those hydrogen atoms involved in intra-
molecular hydrogen bonding are shown (see text). Selected bond
lengths and angles: Pd–S 2.3164(10), Pd–Br 2.4415(5), S–C(1) 1.689(4),
N(1)–C(11) 1.379(5), N(2)–C(21) 1.315(5), N(2)–C(21) 1.460(5) and
C(11)–O(11) 1.220(5) Å; S(A)–Pd–S 180, S(A)–Pd–Br 94.54(3) and
S–Pd–Br 85.46(3)Њ.
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1
nor does the H NMR spectrum change with time. The trans
stereochemistry of this complex, and thus by inference of
the corresponding dichloro-complexes, was confirmed by the
crystal structure of [Pd(H2L-S)2Br2] described below.
6 K. R. Koch, A. Irving and M. Matoetoe, Inorg. Chim. Acta, 1993,
206, 193.
7 W. Bensch and M. Schuster, Z. Anorg. Allg. Chem., 1992, 615, 93.
8 K. R. Koch and S. Bourne, J. Chem. Soc., Dalton Trans., 1993, 2071.
9 P. S. Pregosin, Coord. Chem. Rev., 1982, 44, 247.
10 A. T. C. North, D. C. Phillips and F. S. Mathews, Acta Crystallogr.,
Sect. A, 1968, 24, 351.
11 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
12 G. M. Sheldrick, SHELXL 97, Suite of programs for crystal
structure determinations, 1997.
13 D. M. Adams and J. B. Cornell, J. Chem. Soc. A, 1967, 884.
14 J. Burgess, Metal Ions in Solution, Ellis Horwood, Chichester, 1978,
p. 32.
15 J. M. Jenkins and B. L. Shaw, J. Chem. Soc. A, 1966, 770.
16 D. A. Redfield and J. H. Nelson, Inorg. Chem., 1973, 12, 15.
17 J. E. Huheey, Inorganic Chemistry, 2nd edn., Harper & Row,
London, 1978, p. 491.
Crystal structure of trans-bis(N-benzoyl-NЈ-propylthioureato)-
dibromopalladium(II)
The structure of the trans-[Pd(H2L-S)2Br2] complex is shown in
Fig. 2, while the crystal and structure refinement data, are given
in Table 3. Inspection of the structure shows the expected
square-planar co-ordination with two ligands H2L bonded
through the S atom with Pd–S 2.316(1) Å. The bond lengths
Pd–Br are 2.442(1) Å, while the bond angles S(A)–Pd–Br
94.54(3) and S–Pd–Br 85.46(3)Њ deviate significantly from 90Њ,
the distortion presumably being induced by the two weak
hydrogen bonds between N1(H) ؒ ؒ ؒ Br(A) [and N1A(H) ؒ ؒ ؒ Br]
at 3.294 Å (van der Waals radii N–Br ≈ 3.45 Å). Similar weak
N(H) ؒ ؒ ؒ Cl hydrogen bonds, and the resultant mild distortion
of bond angles from 90Њ, have previously been observed for the
cis-bis(N-benzoyl-NЈ-propylthioureato)dichloroplatinum()
complex.8 An additional hydrogen bond between the N(2)H
18 A. Drago, Yu Shepelev, F. Fajardo, F. Alvarez and R. Pomes, Acta
Crystallogr., Sect. C, 1989, 45, 1192.
Paper 8/09543D
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J. Chem. Soc., Dalton Trans., 1999, 1013–1016