N-2-[4,6-dimethylpyridyl]-N′-phenylthiourea (HDMPyPt) transition metal complexes

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N-2-[4,6-DIMETHYLPYRIDYL]-N′-PHENYLTHIOUREA
(HDMPyPt) TRANSITION METAL COMPLEXES
Hoda A. Bayoumi a , Eman M. Shoukry b & Mohsen M. Mostafa c d
a Chemistry Department , University College for Girls, Ain Shams University , Egypt
b Chemistry Department, Faculty of Science , Al-Azhar University for Girls , Egypt
c Umm Al-Quraa University , P.O. Box 6503-25, Makkah All Mukarramah, Kingdom of Saudi
Arabia
d Chemistry Department, Faculty of Science , Mansoura University , Egypt
Published online: 20 Aug 2006.
To cite this article: Hoda A. Bayoumi , Eman M. Shoukry & Mohsen M. Mostafa (2001) N-2-[4,6-DIMETHYLPYRIDYL]-N′-
PHENYLTHIOUREA (HDMPyPt) TRANSITION METAL COMPLEXES, Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry, 31:4, 579-597, DOI: 10.1081/SIM-100104788
To link to this article: http://dx.doi.org/10.1081/SIM-100104788
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(4), 579–597 (2001)
N-2-[4,6-DIMETHYLPYRIDYL]-
N0-PHENYLTHIOUREA (HDMPyPt)
TRANSITION METAL COMPLEXES
1
Hoda A.Bayoumi, Eman M.Shoukry, and
2
3,
*
Mohsen M.Mostafa
1Chemistry Department, University College for Girls,
Ain Shams University, Egypt
2Chemistry Department, Faculty of Science,
Al-Azhar University for Girls, Egypt
3Chemistry Department, Faculty of Science,
Mansoura University, Egypt
ABSTRACT
Several types of new metal complexes of N-2-[4,6-dimethyl-
pyridyl]-N0-phenylthiourea (HDMPyPT) have been prepared
from M(OAc)2 [M ¼ Cu(II), Zn(II), Ni(II), Co(II), UO2(VI)],
HAuCl4, Na2[PdCl4] and metal chlorides [M ¼ Co(II),
Sm(III), Nd(III)]. HDMPyPT behaves in a monodentate
fashion via the pyridyl nitrogen in all of the complexes except
the Cu(II), Pd(II), and Au(III) complexes. The participation
of the thioketo and=or thioenol groups, in addition to the
pyridyl nitrogen, has been confirmed in the latter three
*Corresponding author. Current address: Umm Al-Quraa University, Makkah All
Mukarramah, Kingdom of Saudi Arabia, P.O. Box 6503-25. E-mail: mmostafa84@
hotmail.com
579
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

580
BAYOUMI, SHOUKRY, AND MOSTAFA
complexes. The role of the methyl groups in positions 4 and 6
as well as the pH of the reaction mixture has been investi-
gated. Also, the effect of anions (ClÀ and OAcÀ) attached to
the metal salts on the structure of the complexes has been
studied. The stereochemistry of the metal complexes has been
1
determined from spectral (IR, UV-Vis., H NMR and mass)
and magnetic measurements. The results suggest a square-
planar geometry for the Pd(II) and Au(III) complexes, a tet-
rahedral structure for one of the Co(II) complexes and octa-
hedral geometry for the other metal complexes. The amount
of solvents inside or outside the coordination sphere has been
determined using TGA and DTA measurements.
INTRODUCTION
In a previous paper1 we reported the role of the methyl group attached to
the pyridyl ring in position 3as well as the pH of the reaction mixture on the
bonding and stereochemistry of the prepared solid complexes. As extension
of our work, we have now synthesized and characterized a series of new metal
complexes derived from a similar ligand containing methyl groups in posi-
tions 4 and 6 with the aim to substantiate our earlier observation that the
attachment of a methyl group to the pyridyl moiety at any position prevents
the participation of the CS group either in the thioketo and=or thioenol
forms. The only exception for participation of the thioketo group in bonding
occurred when using excess metal salt or by raising the pH of the reaction
mixture close to the pK2 value (9.3) of the free ligand (HDMPyPT) using
NaOAc. Also, we have extended our work1,2 to include some lanthanide and
actinide ions, in addition to first, second and third row transition metal ions.
The aim of using different metal salts with different anions (ClÀ, OAcÀ) is to
study their effect on the structure of the isolated solid complexes.
In this paper, we have studied the behaviour of N-2-[4,6-dimethylpyridyl]-
N0-phenylthiourea (HDMPyPT), the structure of which is shown in Fig. 1,
towards some metal acetates and chlorides using conventional physical and
chemical methods to elucidate the stereochemistry of the solid complexes.
EXPERIMENTAL
HDMPyPT was prepared by boiling under reflux a solution of 2-amino-
4,6-dimethylpyridine (12.2 g, 0.1 mol) and phenyl isothiocyanate (13.5 mL,
0.1 mol) in absolute EtOH (50 mL) for 1 h. The isolated white crystals were

TRANSITION METAL COMPLEXES
581
Figure 1. Structure of the ligand HDMPyPT.
filtered, washed several times successively with absolute EtOH and Et2O and
finally dried in a vacuum desiccator over anhydrous CaCl2; yield, 23.9 g. The
1
purity of HDMPyPT was checked by elemental analyses and H NMR and
mass spectra.
Metal Complexes
Preparation of M(II) Complexes
A solution of metal acetate (1 mmole) [Cu(OAc)2 Á H2O, Co(OAc)2 Á 4H2O;
Ni(OAc)2.4H2O. and Zn(OAc)2 Á 2H2O] or CoCl2.6H2O in aqueous ethanol
solution (50%) was added to 2 mmol HDMPyPT (0.5 g) in absolute
EtOH (50 mL). The pH of the Cu(II) complex was adjusted to 8.9 while the
pH of the other complexes remained in the 4–5 range.
Preparation of M(III) Complexes
A solution of metal chloride [SmCl3 Á 6H2O or NdCl3 Á 6H2O] in aqueous
ethanol solution (50%) was added to 2 mmol HDMPyPT (0.5 g) in absolute
EtOH (50 mL). The pH of the metal (III) complexes remained in the 4–5
range.
Preparation of UO2(VI) Complex
A solution of 4 mmol of UO2(OAc)2 Á 2H2O (1.7 g) in 25 mL of an aqueous
ethanol solution (50%) was added to 1 mmol of HDMPyPT (0.26 g) in
absolute ethanol (20 mL). The pH of the solution was adjusted to 7.5.

582
BAYOUMI, SHOUKRY, AND MOSTAFA
Preparation of Pd(II) Complexes
Two Pd(II) complexes having the general formulae [Pd3(HDMPyPT)2-
Cl6(EtOH)2] Á 5=2EtOH and [Pd2(HDMPyPT)Cl4(H2O)2] Á 2H2O were
obtained using different ratios of EtOH-H2O mixtures. 4 mmol of
Na2[PdCl4] (1.2 g) in 25 mL of aqueous ethanol solution (50%) was added to
1 mmol of HDMPyPT (0.26 g) in absolute ethanol (25 mL). The former
complex was isolated in EtOH (80%) at pH 8.3while the latter was pre-
cipitated using aqueous EtOH (50%) and at pH 8.3.
Preparation of Au(III) Complex
A solution of 4 mmol of HAuCl4 (1.4 g) in 25 mL of an aqueous
ethanol solution (50%) was added to 1 mmol of HDMPyPT (0.26 g) in
absolute ethanol (20 mL). The pH of the solution was adjusted to 8.3
using NaOAc.
In all cases, the reaction mixtures were heated under reflux for 2 h. The
resulting solid complexes (66–95%) were filtered hot, washed several times
with absolute EtOH followed by Et2O and finally dried in a vacuum
desiccator. All of the metals except Au(III) were determined by ignition of
the complexes in a muffle oven at 800 ꢀC to the corresponding metal oxide
followed by dissolution in HClO4. The metal content was determined by
complexometric titration using xylenol orange as indicator3,4. Uranium was
determined gravimeterically as U3O8.
Physical Measurements
All the instruments used in this study were similar to those described
in our previous work1. The pK values were determined by pH titration using
a Metrohm 686 titroprocessor equipped with a 665 Dosimat (Switzerland
Herisaue) at Cairo University. The mass spectra of the ligand, Pd(II) and
Au(III) complexes were recorded on a Finnigan MAT SSQ 7000 mass
spectrometer at National Research Center, Cairo, Egypt.
RESULTS AND DISCUSSION
Analytical results and some physical properties of HDMPyPT and its
metal complexes are given in Table I.

584
BAYOUMI, SHOUKRY, AND MOSTAFA
Synthesis
The complex compounds were prepared according to the following
equations:
2HDMPyPT þ CoðOAcÞ2
EtOH ð50%Þ
Reflux 1 h
½CoðHDMPyPTÞ2ðOAcÞ2ðH2OÞ2ꢁÁH2O
!
2HDMPyPT þ CuðOAcÞ2
EtOH ð50%Þ
Reflux 1 h
½CuðHDMPyPTÞðOAcÞ2ðEtOHÞðH2OÞꢁ
!
pH¼8:9
EtOH ð50%Þ
Reflux 1h
2HDMPyPTþMðOAcÞ2
½MðHDMPyPTÞ4ðOAcÞ2ꢁÁxH2O
!
M¼NiðIIÞ or ZnðIIÞ; x¼3in case of Ni ðIIÞ
EtOHð50%Þ
Reflux1h
2HDMPyPTþSmCl3
½SmðHDMPyPTÞCl3ðEtOHÞ2ꢁÁ2EtOH
!
pH¼4:0
EtOHð50%Þ
Reflux1h
!
2HDMPyPTþNdCl3
½Nd2ðHDMPyPTÞCl5ðH2OÞ2ꢁClÁ2EtOH
pH¼5:0
EtOH ð50%Þ
Reflux 1 h
2HDMPyPT þ CoCl2
½NdðHDMPyPTÞClðH2OÞꢁCl
!
pH¼5:0
4HDMPyPT þ UO2ðOAcÞ2
EtOH ð50%Þ
Reflux 2 h
½UO2ðHDMPyPTÞðOHÞ4ðH2OÞꢁ Á 5H2O
!
pH¼7:5
4HDMPyPT þ Na2PdCl4
EtOH ð50%Þ
Reflux 2 h
½Pd3ðHDMPyPTÞCl6ðEtOHÞꢁ Á 5=2H2O
!
pH¼8:3
EtOHð50%Þ
Reflux2h
!
4HDMPyPTþNa2PdCl4
4HDMPyPT þ HðAuCl4Þ
½Pd2ðHDMPyPTÞCl4ðH2OÞ2ꢁÁ2H2O
pH¼8:3
EtOH ð50%Þ
Reflux 1h
½Au2ðHDMPyPTÞ2Cl6ꢁ Á 2H2O
!
pH¼8:3
All of the prepared complexes are of a bright colour, except the Cu(II),
Pd(II) and Au(III) complexes. They are quite stable in air, insoluble in most
common organic solvents but soluble in DMF and DMSO. The brightness

TRANSITION METAL COMPLEXES
585
of the colour is quite similar to the complexes derived from N-2-[3-
methylpyridyl]-N0-phenylthiourea (HMPyPT)1 and indicates the involve-
ment of the pyridyl nitrogen only. Our previous study5 revealed that the
involvement of the thioketo (CS) and=or thioenol (SH) groups in bonding
results in the isolated complexes being deeply coloured. The brightness of
the complexes under investigation suggests that neither the thioketo nor the
thioenol groups are taking part in complexation, and that participation of
the pyridyl nitrogen in bonding prevails. On the other hand, the deep colour
of the Cu(II), Pd(II), and Au(III) complexes suggests the involvement of the
thioketo and=or thioenol groups in addition to the pyridyl nitrogen towards
one or more metal ions5,6. Also, the deep colour suggests that the Cu(II),
Pd(II) and Au(III) ions act as soft acids and consequently HDMPyPT acts
as a soft base(6) coordinating via the thioketo or thioenol groups. On
contrary, the brightness of colour due to participation of pyridyl nitrogen of
HDMPyPT is explained on the basis that the other metal ions act as hard
acids and hence the ligand participates via the pyridyl nitrogen and acts as a
hard base(6). The molar conductivities of the complexes in DMSO and=or
DMF at 25 ꢀC are in the 2.4–12.3 OÀ1 cm2 molÀ1 range (Table II), indicating
the non-electrolytic nature7 of all complexes, except [Co(HDMPyPT)2Cl-
(H2O)]Cl (39.0 OÀ1 cm2 molÀ1
,
DMSO) and [Nd2(HDMPyPT)Cl5
(H2O)5]Cl Á 2EtOH (26.6 OÀ1 cm2 molÀ1, DMSO). The comparatively high
values for the two latter complexes suggest a 1:1 electrolyte and the presence
of one chloride ion in the outer coordination sphere. Therefore, the possi-
bility of involvement of water molecules in coordination is considered. In
both cases, the colour of the two complexes changes to yellow on dissolu-
tion in DMSO. This suggests that DMSO substitutes the water molecules in
both cases and completes the coordination number to six in case of the
Co(II) ion only.
IR and pH Studies
The most important IR assignments of HDMPyPT as well as its bonding
sites (Table III) have been determined by careful comparison of the spectra
of the ligand with those of its metal complexes and by considering our
previous publications1,2. The IR spectrum of HDMPyPT in KBr shows a
strong band at 3225 cmÀ1 together with a weak band at 3045 cmÀ1, assigned
to n(NH) and n(N0H) vibrations, respectively. These two bands are observed
at 3218 and 3096 cmÀ1 in Nujol mulls. The shift of the N0H band to higher
wave number (51 cmÀ1) suggests a weakening of the hydrogen bond between
N0H and the pyridyl nitrogen (Fig. 1) in Nujol mull.

586
BAYOUMI, SHOUKRY, AND MOSTAFA

588
BAYOUMI, SHOUKRY, AND MOSTAFA
The NH band remains more or less at the same position indicating that
this group does not participate in hydrogen bonding. On comparing the
positions of those two bands with our earlier work with N-2-pyridyl-N0-
phenylthiourea (HPyPT)2 and N-2-[3-methylpyridyl]-N0-phenylthiourea
(HMPyT)1, we observed that the effect of the methyl groups in positions
4 and 6 is much greater on the strength of hydrogen bonding than when at
position 3(HMPyPT). Consequently, the hydrogen bond is much stronger
in HDMPyPT than in HMPyPT and HPyPT as indicated by the value of the
shift of the N0H band to lower energy. The existence of two methyl groups in
positions 4 and 6 increases the basicity of the pyridyl nitrogen and hence the
hydrogen bond between the N0H and pyridyl nitrogen is strengthened.
The IR spectral date show that the strength of the hydrogen bond decreases
in the following order: HPyPT < HMPyPT < HDMPyPT based on the shift
of the N0H band in KBR.
The two bands observed at 1246 and 760 cmÀ1 are attributed to n(CS)
vibrations and the four bands at 1631, 1567, 1534 and 1495 cmÀ1 are assigned
to n(C¼C) and n(C¼N) vibrations of the pyridyl and phenyl groups. All of
the above bands were observed at 1632, 1595, 1565, 1533, 1246 and 761 cmÀ1
in Nujol mulls. The shifts of the second, third and fourth bands to higher
wave numbers are taken as evidence for the deletion of the hydrogen bonding
between the pyridyl nitrogen and the N0H groups in Nujol mulls.
On comparison of the ligand IR spectrum with the spectra of its metal
complexes (Table III), except for the Cu(II), Pd(II) and Au(III) complexes,
we observed that the ligand behaves in a monodentate fashion via the pyridyl
nitrogen only. This behaviour is supported as discussed in our earlier work1.
By contrast, the participation of thioketo and=or thioenol groups in bonding,
in addition to the pyridyl nitrogen, is observed for the Cu(II), Pd(II), and
Au(III) complexes. The shift to lower energy (16–22 cmÀ1) of the CS band
suggests the involvement of this groups in bonding. Further evidence for the
involvement of the CS and=or SH groups in bonding in case of the Cu(II),
Pd(II) and Au(III) complexes is obtained from the pK2 values obtained by a
potentiometric method8. The results show two pK’s, at 4.5 (pK1) and 9.3
(pK2), for HDMPyPT. The pK2 value of HDMPyPT lies between the values
of HPyPT (8.4) and HMPyPT (10.5). On adjusting the pH of the Cu(II)
complex solution to 8.9 and to 8.3for the Pd(II) and Au(III) solutions, we
observed that the thioketo group participates without deprotonation in case
of the Pd(II) and Au(III) complexes while the SH group is bonded to the
Cu(II) ion without deprotonation. Accordingly, we have gained a good
insight in the involvement of the CS group in bonding. Firstly, if the pH of
the solution is much greater than the pK2 value, the thioketo group parti-
cipates in bonding via deprotonation of the thioenol group as reported earlier
in our previous work2. Secondly, the CS group does not get involved in

TRANSITION METAL COMPLEXES
589
bonding if the pH of the solution during complex formation is much lower
than the pK2 value. Thirdly, the CS group participates in bonding without
deprotonation if the pH lies between 7.5 and 8.5. Finally, the participation of
the CS group as SH without deprotonation occurs if the pH lies very closely
to the pK2 value, as in case of the Cu(II) ion (pH ¼ 8.9).
Several complexes with 1:2, 1:4 and 2:1 (metal : ligand) ratios were
obtained by the reaction of HDMPyPT with metal acetates, [Zn(OAc)2,
Co(OAc)2, Ni(OAc)2, and UO2(OAc)2], in aqueous ethanolic solution (50%)
without raising the pH of the solution (pH < 5), except for UO2(OAc)2 where
the pH of the solution was raised to 7.5 using NaOAc. HDMPyPT coordi-
nates via the pyridyl nitrogen in all metal acetate complexes. The only
exception is the Cu(II) complex in which the ligand coordinates through the
pyridyl nitrogen and the SH group without deprotonation. The absence of
the CS group, together with the appearance of new two bands at 2540 and
1698 cmÀ1 assigned to (SH) and (C¼N*) vibrations, respectively, is taken as
evidence for the involvement of these groups in bonding as shown in Fig. 2.
These two bands are obscured in the spectra of all other complexes. Another
piece of evidence for the involvement of the SH group in bonding is obtained
by comparison of the UV spectra of HDMPyPT with that of the Cu(II)
complex. The UV spectrum of the ligand in DMSO shows two bands with a
low-intensity band at 26,525 cmÀ1 and 25,189 cmÀ1 assigned to n ! p*
transitions of the C¼N and C¼S groups, respectively. The absence of the
latter band due to n ! p* transition in the spectrum of the Cu(II) complex in
DMSO (10À4 M) together with the appearance of a new band at 23,529 cmÀ1
assigned to the n ! p* transition of the azomethine group (C¼N*) suggests
the formation of a thioenol structure (Fig. 2.). The observation of this band
at longer wave number is mainly due to the conjugation of the azomethine
(C¼N*) group with the ring C¼N of the pyridyl group.
Figure 2. Structure of [Cu(HDMPyPT)(OAc)2(EtOH)H2O)].

590
BAYOUMI, SHOUKRY, AND MOSTAFA
The acetate group acts in a monodentate manner since the difference
between the nas and ns vibrations (167–180 cmÀ1) lies in the permissible
range as reported elsewhere9.
The IR spectrum of the UO2(VI) complex in KBr shows characteristic
bands at 925, 870 and 243cm À1 assigned to n3, n1 and n4 vibrations of the
O¼U¼O moiety10. The force constant (FUO) and the bond length (RUO
)
were calculated using a method reported in the literature11 and were found
to be 7.062 dynes=A and 1.74 A, respectively. The two new bands appearing
at 1150 and 525 cmÀ1 are assigned to n(OH)12 and n(UO)9 vibrations,
respectively. The existence of these two bands confirms the formation of a
dihydroxo bridge within the uranyl complex. It is important to point out
that this type of bridge is mainly due to the increase of the pH of the
solution using NaOAc as discussed earlier13. The UV spectrum in DMF
1
3
and=or Nujol mull shows a band at 22,570 cmÀ1 assigned to the Eg ! pu
transition14. There are no bands below 20,000 cmÀ1 suggesting that the
uranyl complex has more than four equatorial groups15.
1H NMR Spectra
1
The H NMR spectrum of HDMPyPT in DMSO-d6 (Table IV) shows
two singlets at 14.33 and 10.74 ppm downfield from TMS. These two signals
are observed at 13.70 and 9.10 ppm in DMSO-d6 for HMPyPT1. The higher
shift of the N0H signal in case of HDMPyPT than that observed for
HMPyPT is another evidence for the strength of hydrogen bonding between
the N0H and the pyridyl nitrogen in case of HDMPyPT than HMPyPT.
Also, the 1H NMR spectrum shows two singlets at 2.24 and 2.42 ppm
assigned to CH3 protons in positions 4 and 6. The multiplets in the 6.7–7.82
region are assigned to the protons of the pyridyl and phenyl groups.
1
The H NMR spectrum of [Zn(HDMPyPT)4(OAc)2] in DMSO-d6 shows
two singlet signals at 10.61 and 9.75 ppm downfield from TMS and assigned
to the N0 and N protons, respectively. The upfield shifts of those signals
indicate the absence of the hydrogen bond as well as the involvement of the
pyridyl nitrogen in coordination. Also, the observation of only one signal
for each of the N0 and N protons suggests that the four molecules of
HDMPyPT are identical and are located at the corners of the square-planar
geometry, as shown in Fig. 3, while the acetate groups complete the octa-
hedral geometry around the Zn(II) ion.
Moreover, the singlet signal at 3.38 ppm and the multiplet signals in the
6.68–7.78 regions are assigned to the protons of acetate, pyridyl and phenyl
groups, respectively. We believe that the structure of the Ni(II) complex is quite
similar to that of the Zn(II) complex since it has similar chemical analyses.

TRANSITION METAL COMPLEXES
591

592
BAYOUMI, SHOUKRY, AND MOSTAFA
Figure 3. Structure of [Zn(HDMPyPT)4(OAc)2].
Electronic and Mass Spectra, Thermal and Magnetic Studies
of the Complexes
The electronic spectrum of [Cu(HDMPyPT)(OAc)2(EtOH)(H2O)] in
Nujol shows a broad band centered at 12,005 cmÀ1 assigned to the
2
2E2g ! T2g transition in a distorted octahedral structure around the Cu(II)
ion16. The room temperature magnetic moment of the Cu(II) complex
(1.05 B.M.) indicates some sort of molecular association that could be
achieved through a direct copper–copper interaction17. The thermal analysis
curves (TGA, DTA) show a peak at 155 ꢀC exhibiting fast decomposition up
to 300 ꢀC and, subsequently, slow decomposition up to 800 ꢀC leaving a
residue of Cu2O.
The electronic spectrum of the Ni(II) complex, [Ni(HDMPyPT)4
(OAc)2] Á 3H2O, in Nujol shows two bands at 14,390 and 25,640 cmÀ1
3
1
3
3
assigned to the A2g ! T1g (n2) and A2g ! T1g(p) (n3) transitions16,
respectively, in an octahedral geometry around the Ni(II) ion. The low-
energy band due to 3A2g ! T1g (n1) and the ligand field parameters (Dq, B,
1
b) were found to be 8720, 872.0, 925 and 0.89, respectively. These values are
very close to those expected for octahedral symmetry18. Also, the value of
the magnetic moment (3.18 B.M.) is taken as additional evidence for the
existence of an octahedral geometry around the Ni(II) ion.
The values of the magnetic moments of [Co(HDMPyPT)2(OAc)2(H2O)2]
and [Co(HDMPyPT)2Cl(H2O)]Cl are 5.07 and 4.46 B.M., respectively,

TRANSITION METAL COMPLEXES
593
suggesting an octahedral geometry for the former while a tetrahedral
structure for the latter around the Co(II) ion. Also, the low E value
(10 L cmÀ1 molÀ1) for the former and the high e value (500 L cmÀ1 molÀ1
for the latter lends support for the proposed geometries. The electronic
)
spectrum of [Co(HDPyPT)2(OAc)2(H2O)2] Á H2O in DMSO shows a band at
4
4
19,230 cmÀ1 assigned to the T1g(F) ! T1g(p) (n3) transition and indicates
an octahedral geometry around the Co(II) ion. On the other hand, the
spectrum of [Co(HDMPyPT)2Cl(H2O)]Cl in DMSO shows a finestructure
4
for the n3 [4A2 ! T1(p)] transition, due to spin-orbit coupling19 as those
reported10 for [CoCl4]2À and [CoI4]2À. The finestructure is observed as three
well defined bands at 18,380, 16,750, and 15,360 cmÀ1. These results indicate
that the anions (ClÀ or OAcÀ) attached to the metal salts have an effect on
the stereochemistry of the prepared solid complexes.
The electronic spectrum of [Au2(HDMPyPT)2Cl6] Á 2H2O in Nujol shows
1
1
new bands at 32,845 and 44,050 cmÀ1 assigned to the A1g ! A2u and
1
1A1g ! Eu transitions20, respectively. These bands correspond fairly well to
1
a square-planar geometry around the Au(III) ion. The H NMR spectrum
of the Au(III) complex in DMSO-d6 shows two singlet signals at 13.83 and
10.34 ppm downfield from TMS which are assigned to the protons of N0 and
N, respectively. The shift of these two signals is very small. This indicates
that these groups are inactive toward coordination. The value of the
molecular ion (Mþ) obtained from the mass spectrum of the Au(III) com-
plex (calcd. 1157.5; found, 1157.3) confirms the suggested formula. Also, the
mass spectrum of [Au2(HDMPyPT)2Cl2] Á 2H2O shows that the complex
splits off the ligand (HDMPyPT) which then undergoes further fragmen-
tation as shown in the Fig. 4.
The diamagnetic nature of the two Pd(II) complexes, [Pd3(HDMPyPT)2-
Cl6(EtOH)2] Á 5=2EtOH and [Pd2(HDMPyPT)Cl4(H2O)2] Á 2H2O, is con-
sistent with the normal square-planar geometry around the Pd(II) ion16. The
1H NMR spectra in DMSO-d6 show two singlet signals at 11.10 and 9.5 ppm
for the former and at 10.85 and 9.8 ppm for the latter, which are assigned to
the protons at N0 and N, respectively. The upfield shift of the former signal is
attributed to the dissolution of the hydrogen bond while the downfield shift
of the latter signal indicates the participation of the thioketo and pyridyl
nitrogen groups in bonding, which leads to the decrease of the electron
density on the N atom, (Figs. 5 and 6). The two signals due to the protons of
N0 and N disappear upon adding D2O. The existence of EtOH in the former
and H2O molecules in the latter complex is confirmed by the results of the 1H
NMR spectra and thermal analyses (TGA, DTA). The results of the mass
spectra of these two complexes, together with their metal analyses, confirm
their structures. The molecular weight (Mþ) obtained from the mass
spectra for the former complex, [Pd2(HDMPyPT)2Cl6(EtOH)2] Á 5=2EtOH,

594
BAYOUMI, SHOUKRY, AND MOSTAFA
Figure 4. Mass fragmentation of [Au2(HDMPyPT)2Cl6] Á 2H2O.
coincides with that of the formula (calcd., 1254; found, 1253). The same
fragments have been observed in the mass spectra of the two Pd(II) com-
plexes which are closely similar to the Au(III) complex.
The electronic spectrum of [Pd3(HDMPyPT)2Cl6(EtOH)2] Á 5=2EtOH in
DMSO shows four bands at 19,340, 20,750, 25,970, and 37,450 cmÀ1
1
1
1
1
1
1
1
1
assigned to the A1g ! A2g, A1g ! B1g, A1g ! Eg, and A1g ! A2u
transitions, respectively, for a square-planar structure around the Pd(II) ion
(Fig. 5).
Also, the electronic spectrum of [Pd2(HDMPyPT)Cl4(H2O)2] Á 2H2O in
DMSO shows four bands at 19,120, 22,370, 26,110 and 35,715 cmÀ1
assigned to the same transitions discussed above for the square-planar

TRANSITION METAL COMPLEXES
595
Figure 5. Suggested structure of [Pd3(HDMPyPT)2Cl6(EtOH)2] Á 5=2EtOH.
Figure 6. Suggested structure of [Pd2(HDMPyPT)Cl4(H2O)2O] Á 2H2O.
Pd(II) complexes (Fig. 6.). The molecular weight (M þ ) obtained from the
mass spectrum of the Pd(II) complex, [Pd2(HDMPyPT)Cl4(H2O)2] Á 2H2O,
suggests the proposed formula (calcd., 684.1; found, 683.5).
Finally, the calculated magnetic moments for the Nd(III) and Sm(III)
complexes are 3.6 and 2.16 B.M., respectively, and very close to the Van

596
BAYOUMI, SHOUKRY, AND MOSTAFA
Vleck values21. The electronic spectra showed a shift in the f-f bands
towards lower energy as compared to the aquo ions22 due to the nephe-
lauxetic effect.
The spectrum of the Nd(III) complex in Nujol shows several sharp peaks
at 11,400, 11,535, 12,420, 13,385, 14,530, 15,730, 17,240, 19,010, and
4
4
19,455 cmÀ1 assigned respectively, to 4I9=2 ! F3=2
,
,
4I9=2 ! F5=2
,
,
4
4
4
4
4
4I9=2 ! F7=2
,
4I9=2 ! S3=2
,
4I9=2 ! F9=2
,
4I9=2 ! G5=2
4I9=2 ! G7=2
4
4
4
4I9=2 ! G9=2, and I9=2 ! G11=2 transitions23.
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Received: February 17, 2000
Accepted: February 13, 2001
Referee I: K. Moedritzer
Referee II: F. P. Gabbai