Synthesis, crystal structures and properties of two Pd(II) and Pt(II) complexes involving 3,5-diphenylpyrazole and NO2 donor ligands

Article abstract of DOI:10.1016/j.inoche.2007.02.028

A pyrazolate bridged binuclear Pd(II) complex [Pd₂(μ-dppz)₂(Hida)₂] · CH₃OH · 2H₂O (1) (dppz = 3,5-diphenylpyrazolate) with monoprotonated iminodiacetate (Hida) and a mononuclear Pt(II) complex containing Hdppz and 2,6-pyridinedicarboxylate (2,6-dipic) [Pt(Hdppz)(2,6-dipic)] · CH₃OH (2) have been synthesized and characterized by elemental analysis, ¹H NMR, ESI-MS and single crystal X-ray diffraction studies. The molecular packing for 1 shows a 2D network while that for 2 constitutes a left-handed 1D helix. Moderate luminescence property and antimicrobial activity against Bacillus subtilis have been noted for both.

Full text of DOI:10.1016/j.inoche.2007.02.028

Inorganic Chemistry Communications 10 (2007) 671–676
www.elsevier.com/locate/inoche
Synthesis, crystal structures and properties of two Pd(II) and
Pt(II) complexes involving 3,5-diphenylpyrazole and NO2 donor ligands
a
b
a,
*
Jishnunil Chakraborty , Manas K. Saha , Pradyot Banerjee
a
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India
b
Department of Chemistry, University of Houston, Houston, TX 77054, USA
Received 5 January 2007; accepted 27 February 2007
Available online 12 March 2007
Abstract
A pyrazolate bridged binuclear Pd(II) complex [Pd2(l-dppz)2(Hida)2] Æ CH3OH Æ 2H2O (1) (dppz = 3,5-diphenylpyrazolate) with
monoprotonated iminodiacetate (Hida) and a mononuclear Pt(II) complex containing Hdppz and 2,6-pyridinedicarboxylate (2,6-dipic)
[Pt(Hdppz)(2,6-dipic)] Æ CH3OH (2) have been synthesized and characterized by elemental analysis, 1H NMR, ESI-MS and single crystal
X-ray diffraction studies. The molecular packing for 1 shows a 2D network while that for 2 constitutes a left-handed 1D helix. Moderate
luminescence property and antimicrobial activity against Bacillus subtilis have been noted for both.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Binuclear Pd(II) complex; Mononuclear Pt(II) complex; 2D and helical network; Luminescence; Antimicrobial activity
The coordination chemistry of neutral pyrazole (HRpz)
or anionic pyrazolate (Rpz) ligands has been enormously
developed over many years [1] and thoroughly reviewed
[2–5]. Recently, unprecedented compounds showing new
bonding modes for the pyrazolate ligands have been
reported [6–10]. In spite of this, the number of palladium
and platinum complexes is rather small. Only a few
examples of mononuclear complexes: ([Pd(Hpz)4]Cl2 [11],
[Pd(dmpz)2(Hdmpz)2] [12], [Pt(pz)2(Hpz)2] [11,13], [Pt
(Hpz)4]Cl2 [13]), binuclear complexes: ([Pd2(l-dmpz)2-
(dmpz)2(Hdmpz)2] [14], [Pd2(l-3-tBupz)2(3-tBupz)2(H3–
tBupz)2] [11], [Pd2((l-pz)2(Hpz)4](BF4)2 [15]) and trinuclear
complexes: ([{Pd(l-pz)2}3] [11], [{Pd(l-4-Mepz)2}3] [11],
[{Pt(l-pz)2}3] [11,16]) containing only pyrazoles (HRpz)
and/or pyrazolates (Rpz) as ligands have been reported till
now. We have reported recently an unsymmetrical binu-
clear palladium(II) complex [(Hdmpz)2Pd2(l-dmpz)2(2,6-
dipicolinate)] [17], where the terminal Hdmpz ligands
bonded to one Pd(II) center act as a hydrogen bond donor
and a free-carboxylate group of the 2,6-dipicolinate moiety
acts as the hydrogen bond acceptor. The hydrogen bonds
of the type N–H–O form a 1D zigzag network. With an
aim to construct such hydrogen bonded low dimensional
as well as higher dimensional networks, we have attempted
to synthesize Pd(II) and Pt(II) complexes with another kind
of substituted pyrazole, 3,5-diphenylpyrazole (Hdppz) and
carboxylic acids such as iminodiacetic acid and 2,6-pyridin-
edicarboxylic acid. The syntheses, structural characteriza-
tion, luminescence property and antimicrobial activity of
a dppz bridged binuclear palladium(II) complex and a
mononuclear Hdppz coordinated platinum(II) complex
are reported herein.
The reaction of PdCl2(CH3CN)2 with 3,5-dimethylpy-
razole and monosodium salt of iminodiacetic acid in
1:1:1 molar ratio in DMF–MeOH–H2O mixture at 50 ꢁC
afforded the formation of a binuclear pyrazolate bridged
Pd(II)-iminodiacetate complex [Pd2(l-dppz)2(Hida)2] Æ
CH3OH Æ 2H2O (1), where the Hida binds the palladium
center in a bidentate fashion leaving one free carboxylate
group protonated. No external base was employed to
deprotonate the Hdppz moiety. Complex 2 was obtained
*
Corresponding author. Fax: +91 33 2473 2805.
E-mail address: icpb@mahendra.iacs.res.in (P. Banerjee).
1387-7003/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2007.02.028

672
J. Chakraborty et al. / Inorganic Chemistry Communications 10 (2007) 671–676
by the reaction of PtCl2(dmso)2 with Hdppz and monoso-
dium salt of 2,6-pyridinedicarboxylic acid in a 1:1:1 molar
ratio in MeOH–H2O medium at 50 ꢁC. This compound can
be formulated as [Pt(Hdppz)(2,6-dipic)] Æ CH3OH.
ladium complexes Pd2L4 (L = 3-phenyl-5-(6-methyl-(2-pyr-
˚
idyl)) pyrazolate (3.097(2) A) [20], [(Hdmpz)2Pd2(l-dmpz)2
˚
(2,6-dipic)] (3.397 A) [17], [{Pd2(l-3,5-dmpz)(3,5-dmpz)
(3,5-Hdmpz)}2] (3.4020 A) [14], [Pd(l-3,5-dmPz)(g3-
˚
1
˚
The H NMR spectrum of 1 shows the signals of –CH2
C3H4)]2 (3.343 A)[21], [Pd2Cl2(l-3,5-dmpz)2(PMe2Ph)2]
˚
protons of the ida unit as well as the signals in the aromatic
region confirming the presence of dppz moiety. Compound
2 shows signals in the aromatic region showing the pres-
ence of both 2,6-dipic and the Hdppz moieties. The pat-
terns of the 1H NMR spectra are consistent with the
presence of the complex structure in solution [18a,18b].
Compounds 1 and 2 have been characterized by ESI-MS
positive measurements in acetonitrile [18] (Figures S1 and
S2 in supporting information).
The single-crystal X-ray structures for both complexes
have been determined [19]. The molecular graphics and
selected bond lengths and angles are depicted in Figs. 1
and 3 and more elaborately in the supporting information
(Tables S1, S2 and S3).
(3.115(1) A) [22] and [{Pd2(CH2C6H4P(o-tolyl)2–jC,
4
0
˚
P)2(l3-3,5-dmpz-N,N ,C )2Ag(l-ClO4)}2] (3.2297(7) A) [4]
˚
but is almost identical to 3.029(1) A in {[(phen)Pd]2L2}
(NO3)2 [23], where phen = 1,10-phenanthroline and L =
dppz. Each palladium center is in an almost square-planar
coordination environment. The central six-member [Pd(l-
dppz)2Pd] core is non-planar with Pd–Ndppz distances
˚
between 2.009(2) and 2.036(2) A comparable to other
Pd(II) complexes with the same bridging ligand [23]. The
almost similar bond lengths within the pyrazolate rings
suggest substantial delocalization upon deprotonation.
The N–Pd–N angles are 86.68(9)ꢁ and 86.17(9)ꢁ between
the diphenylpyrazolate groups. The Pd2N4 six-member ring
reveals a boat like conformation [14,15,20]; the dihedral
angle formed by the best least-squares coordination planes
of the metals is 63.14ꢁ. The metal atoms are situated at the
vertices of the boat and the angle between the planes con-
taining the Pd–N–N–Pd fragments is 82.49ꢁ. The mean
deviation of the plane constructed by the four nitrogen
The asymmetric unit (Fig. 1) shows that 1 is a binuclear
Pd(II) complex containing two dppz and two Hida units.
The coordination environments for both the palladium
centers are same. The two 3,5-dmpz units bridge the metal
centres in an exobidentate fashion. The Pd–Pd separation
˚
˚
is 3.030 A which is shorter than that observed in other pal-
atoms N1, N2, N4 and N3 is 0.025 A. The displacement
Fig. 1. ORTEP drawing of 1. Thermal ellipsoids are at 30% probability level. All hydrogen atoms and solvent molecules have been omitted for clarity.
˚
Selected bond lengths (A) and angles (ꢁ): Pd1–Pd2, 3.030; Pd1–O1, 2.005(2); Pd2–O5, 2.006(2); Pd1–N1, 2.009(2); Pd1–N3, 2.013(2); Pd1–N5, 2.049(3);
Pd2–N2, 2.013(2); Pd2–N4, 2.036(2); Pd2–N6, 2.050(3); O1–Pd1–N1, 175.66(10); O1–Pd1–N3, 91.86(9); O1–Pd1–N5, 81.59(11); N1–Pd1–N3, 86.68(9);
O5–Pd2–N2, 176.77(10); O5–Pd2–N4, 94.27(9); O5–Pd2–N6, 84.35(10); N2–Pd2–N4, 86.17(9).

J. Chakraborty et al. / Inorganic Chemistry Communications 10 (2007) 671–676
673
˚
of Pd1 towards this plane is 1.192 A while that for Pd2
N6 bond angles are 81.59(11)ꢁ and 84.35(10)ꢁ, respectively.
It may be noted that in this complex the metal–nitrogen
bond length is longer than that of the metal–oxygen reflect-
ing the greater trans influence of N-atom compared to O-
atom of the ligand.
˚
towards the same plane is 1.230 A. The dppz ligands are
planar within experimental error. The bow angles between
the planes N1–N2–N4–N3 and N1–Pd1–N3, N2–Pd2–N4
are 54.61ꢁ and 56.33ꢁ, respectively, creating an ‘open book’
disposition for the square-planar environment of the palla-
dium centers. The dihedral angle between the dppz bridged
ligands N1–C7–C8–C9–N2 and N3–C22–C23–C24–N4 is
88.21ꢁ, larger than the dihedral angle between the Pd1–
N1–N2–Pd2 and Pd1–N3–N4–Pd2 planes (82.49ꢁ). The
dihedral angle between the phenyl rings attached to
the N1–N2–C9–C8–C7 dppz unit is 28.15ꢁ while that for
the phenyl rings attached to the N3–N4–C24–C23–C22
dppz unit is 18.55ꢁ. On the other hand, the dihedral angle
between the phenyl rings situated at the same side of two
dppz moieties is larger and found to be 66.80ꢁ and
78.62ꢁ. These large magnitudes reflect that the restricted
rotation of the phenyl rings attached to the N1–N2–C9–
C8–C7 dppz unit is due to the presence of the Hida moie-
ties. The ligand NaHida coordinates both the metal centers
in a bidentate fashion (N,O) while the other carboxylate
group remains free. The noncoordinated oxygen atoms
O3 and O8 of the free carboxylate groups must be proton-
ated for internal charge balance. The other carboxylate
group remains nonchelating and protonated. The Pd–N
The molecular packing of 1 (Fig. 2) shows an infinite 2D
network formed by the intermolecular hydrogen bonding
between the hydrogen atom of free carboxylic acid and
˚
the MeOH solvent molecule (O3–O9 = 2.590(4) A), and
between the imino group and a carboxylate moiety of the
˚
adjacent unit (N5–O2 = 3.049(4) A). The carboxylate O2
and methanol O9 atoms provide the hydrogen bond accep-
tor sites for the hydrogen atoms H5A and H3A (from N5
and O3, respectively), respectively, from two neighboring
formula units. A strong O1–O9 interaction is also present
˚
(2.684 A). In addition there is an intramolecular hydrogen
bonding between the imino group and the carboxylate moi-
˚
ety (N6–O4 = 3.058(4) A). The shortest distance between
˚
two Pd(II) centers lying in two adjacent sheets is 7.208 A.
The X-ray crystal structure of 2 (Fig. 3) shows that the
3,5-diphenylpyrazole moiety coordinates the platinum cen-
ter in a monodentate fashion leaving the noncoordinated
pyrazole nitrogen atom protonated. There is a solvent
MeOH molecule outside the coordination sphere. The
2,6-dipic2ꢀ unit coordinates the central platinum atom in
a tridentate fashion via the ring nitrogen atom and two
oxygen atoms, one from each of the two carboxylate
groups producing a Pt(N2O2) coordination environment.
The molecule is essentially planar with a mean deviation
˚
bond lengths are 2.049(3) and 2.050(3) A which are consid-
erably smaller than that observed in trans-[Pd(Hida)2]
˚
(2.061(4) A) previously reported by us [24]. The Pd–O bond
˚
distances are 2.005(2) and 2.006(2) A, which are close to
˚
the literature values [25]. The O1–Pd1–N5 and O5–Pd2–
from planarity of 0.046 A. The geometry around the Pt(II)
Fig. 2. A perspective view of the packing of complex 1.

674
J. Chakraborty et al. / Inorganic Chemistry Communications 10 (2007) 671–676
Fig. 3. ORTEP drawing of 2. Thermal ellipsoids are at 30% probability level. All hydrogen atoms and solvent molecule have been omitted for clarity.
˚
Selected bond lengths (A) and angles (ꢁ): Pt–O1, 2.029(2); Pt–O3, 2.049(2); Pt–N1, 1.918(3); Pt–N2, 2.027(3); O1–Pt–O3, 163.33(10); O1–Pt–N1, 82.06(11);
O1–Pt–N2, 95.63(11); O3–Pt–N1, 81.27(11); O3–Pt–N2, 101.01(11); N1–Pt–N2, 175.11(13).
center is very slightly distorted; the N1 and N2 atoms lie
nated ligand molecules play key roles in the formation
of the helices by acting as structure-directing agents to
induce a helical array. The angles N2–N3–O5 and O5–
O4–C1 in the helix are 116.72 and 107.85ꢁ, respectively.
The unit cell packing shows the presence of two helices
located at the center of the b- and c-axes.
˚
0.046 and 0.036 A, respectively, above the mean Pt(N2O2)
˚
plane, whilst O1 and O3 lie 0.025 and 0.023 A, respectively,
below it. The principal distortion in the Pt(N2O2) coordina-
tion geometry is non-linear in the 2,6-dipic O–Pt–O angle
(O1–Pt–O3 = 163.33(10)ꢁ) which is consistent with another
2,6-dipic coordinated Pt(II) complex Pt(2,6-dipic)(H2O)
[26]; the N1–Pt–N2Hdppz bond is nearly linear (175.11(13)ꢁ).
The Pt–N2,6-dipic bond distance is slightly shorter
The absorption spectrum of complex 1 in DMF solution
is dominated by the intense band with the maximum at
254 nm in the ultraviolet region (e = 1.32 · 104 Mꢀ1 cmꢀ1
)
(1.918(3) A) than the Pt–NHdppz distance (2.027(3) A).
The Hdppz moiety and the 2,6-dipic unit are not in the
same plane. The dihedral angle between the planes contain-
ing individual units is 84.14ꢁ.
which is assigned to a spin-allowed p–p* transition. At
longer wavelength in the range 350–425 nm, a shoulder is
obtained which may be attributed to a metal-to-ligand
charge transfer (MLCT) transition. Complex 2 in acetoni-
trile medium also exhibits a strong band centered at
285 nm with molar absorption coefficient of 6.17 ·
103 Mꢀ1 cmꢀ1. In addition, the lower energy band in the
range 325–400 nm is assigned to be the spin allowed MLCT
transition. In the fluorescence emission spectrum of the
solution of 1 in DMF (5.0 · 10ꢀ6 M) at room temperature
on excitation at 274 nm, the emission peaks are observed at
333 and 640 nm in the visible region which are independent
of the concentration of the solution. The luminescence
spectrum of complex 2 in acetonitrile solution exhibits sim-
ilar emission pattern with that of complex 1. Excitation at
254 nm reveals two emission peaks centered at 338 and
644 nm. The same type of emission peaks observed in both
the complexes may be assigned to the p–p* and MLCT
transitions for the shorter and longer wavelengths, respec-
tively (see Figure S4).
˚
˚
The packing feature of complex 2 shows that the indi-
vidual molecules are packed together by noncovalent
interactions that lead to the formation of a one-dimen-
sional network (see Figure S3). The hydrogen atom of
the Hdppz moiety is involved in hydrogen bonding inter-
actions with the solvent MeOH molecule (N3–H3A–O5).
In addition, there is an appreciable degree of interaction
present between the same methanol oxygen atom and the
carboxylate oxygen atom of another asymmetric unit
˚
(O5–O4 = 2.699 A). Interestingly, complex 2 forms left-
handed helical supramolecular chains involving the inter-
˚
molecular hydrogen bonding (N3–O5 = 2.683(4) A) as
well as O–O interactions. The tilt angle between the pla-
nar Hdppz and a carboxylate ligand could be responsible
for the formation of such helical structure. The ball and
stick model extending along the crystallographic b-axis
displays such helicates (Fig. 4) which may have resulted
from metal–ligand interactions coupled with stereoelec-
tronic characteristics of the ligands and conditions pre-
vailing during the synthesis. An inspection of the
structure of 2 leads to the belief that the metal coordi-
The antimicrobial activities of compounds 1 and 2 were
determined against Bacillus subtilis in a medium of nutri-
ent. 0.1 mL of cell suspension (5.0 · 105 cfu/mL) from
18 h cell culture of bacteria grown on nutrient agar at
37 ꢁC was added per 5 mL of the medium. The compounds

J. Chakraborty et al. / Inorganic Chemistry Communications 10 (2007) 671–676
675
Appendix A. Supporting information
CCDC 632402 and 632403 contain the supplementary
crystallographic data for 1 and 2. These data can be
obtained free of charge via <http://www.ccdc.cam.ac.uk/
conts/retrieving.html>, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk. Full crystallographic details including per-
tinent bond distances and angles for compounds 1 and 2.
Tables of structural refinements and bond distances and
angles are included in the supplementary information.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.inoche.2007.
02.028.
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Fig. 4. A view of the 1D helical propagation in complex 2.
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[18] (a) Compound 1: IR spectrum (KBr disk, m/cmꢀ1): 1722 (medium,
were dissolved in a mixture of 1:1 DMSO and absolute eth-
anol. Control sets containing only PdCl2(CH3CN)2,
PtCl2(DMSO)2, NaHida, NaH2,6-dipic and Hdppz were
also prepared. All the tubes were incubated at 37 ꢁC for
24 h for the growth of the bacteria. The lowest concentra-
tions of the compounds that resulted in complete inhibition
of the visible growth after incubation were recorded as
MIC (minimum inhibitory concentration). No activity of
the constituents was detected. The MIC’s of the com-
pounds 1 and 2 against B. subtilis have been found to be
100 and 50 lg/mL, respectively. These are in accord with
the value found for [(Hdmpz)2Pd2(l-dmpz)2(2,6-dipicoli-
nate)] previously reported by us [17]. Complexes 1 and 2
are coordinately saturated, and are believed to show anti-
microbial activity through physical interactions in which
the first step could be an adsorption reaction involving
noncovalent interactions. It may be noted that both the
complexes are neutral, hence no electrostatic interaction
could be conceived.
1
m
COOH), 1612 (strong, mCOOꢀ); H NMR (300 MHz, [d6]dmso, 25 ꢁC,
TMS as the internal standard): d = 8.29 (d, 4H; phdppz–H1,5), 7.88 (d,
4H; ph0dppz-H1,5), 7.37 (t, 4H; phdppz–H2,4), 7.21 (t, 4H; ph0dppz–H2,4),
7.67 (m, 4H; phdppz–H3,3, ph0dppz–H3,3), 3.88, 3.89 (AB pattern, 4H; –
CH2 ring acetate), 2.89 (AB pattern, 4H; –CH2 free acetate), 6.39 (s,
2H; Hida–NH), 12.83 (s, 2H; Hida–CO2H); this spectral pattern
reflects that same conformational rigidity exists in solution yielding
unsymmetrical proton distribution of phenyl protons; elemental
analysis: calc. for
C39H42N6O11Pd2, C, 47.62%; H, 4.27%; N,
8.55%; found: C, 47.90%; H, 3.44%; N, 8.56%; ESI-MS (m/Z):
[1 + Na]+ 938.3; X-ray quality crystals were grown from a DMF–
MeOH–H2O medium after 15 days.;
(b) Compound 2: IR spectrum (KBr disk, m/cmꢀ1): 1684, 1653
(strong, mCOOꢀ); 1H NMR (300 MHz, CD3CN, 25 ꢁC, TMS as the
internal standard): d = 7.77 (d, 2H; phHdppz–H1,5), 7.74 (d, 2H;
Acknowledgement
We would like to thank Prof. A.K. Guha, Department
of Biological Chemistry, IACS, Kolkata for his advice in
the study of antimicrobial activity.
ph0Hdppz–H1,5), 7.47 (m, 3H; phHdppz–H2,3,4), 7.46 (m, 3H; ph0
–
Hdppz
H2,3,4), 7.80 (s, 1H; Hdppz-H4), 7.07 (s, 1H; Hdppz–NH), 8.31 (dd,
3H; ph2,6-dipic–H1,2,3); elemental analysis: calc. for C23H19N3O5Pt, C,

676
J. Chakraborty et al. / Inorganic Chemistry Communications 10 (2007) 671–676
´
45.09%; H, 3.10%; N, 6.86%; found: C, 45.06%; H, 2.89%; N, 6.78%;
ESI-MS (m/Z): [2 + Na]+ 603.4; X-ray quality crystals were grown
from a MeOH–H2O medium after six days.
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[19] Crystal data: For complex 1: C39H34N6O11Pd2, Mr = 975.40, T = 77 K,
˚
ꢀ
˚
k = 0.71073 A, triclinic, space group P1 (No. 2), a = 10.3792(12) A,
˚
˚
b = 11.8281(14) A, c = 16.637(2) A, a = 96.964(6)ꢁ, b = 93.036(7)ꢁ,
99.668(7)ꢁ, V = 1993.0(4) A , Z = 2, Dcalc = 1.625 g/cm3, F(000) =
3
˚
948, R1(I > 2r(I)) = 0.0469 and wR2 (all data) = 0.098; the water
molecule O11 is disorded; for complex 2: C23H15 N3O5Pt, Mr = 608.46,
˚
´ˇ
T = 77 K, k = 0.71073 A, monoclinic, space group P21/c (No. 14),
˚
˚
˚
˚
a = 5.9103(5) A, b = 32.029(4)A, c = 11.1916(13)A, b = 98.012(5)ꢁ,
Chem. 28 (2003) 765.
3
V = 2097.9(4) A , Z = 4, Dcalc
=
1.926 g/cm3, F(000) = 1168,
[26] D.M.L. Goodgame, T.E. Muller, D.J. Williams, Polyhedron 14
¨
R1(I > 2r(I)) = 0.032 and wR2 (all data) = 0.0709.
(1995) 2557.