Cationic–anionic palladium complexes: effect of hydrogen bond character on their stability and biological activity

Article abstract of DOI:10.1134/S0036023617110043

The solution state of palladium cationic–anionic complexes (AmH_n)_k[PdCl₄] prepared for the first time, where Am is morpholine, methylmorpholine, aminoethylmorpholine, 5-aminovaleric acid, L-1-phenyl-2-methylaminopropanol, and m-xylilenediamine, has been studied by electronic absorption spectroscopy, NMR, and pH measurements. The agreement of obtained results for the state of the complexes in water and NaCl solutions with IR and X-ray diffraction data for these complexes has allowed us to substantiate the principle for designing patent formulation (C₅H₁₂NO)₂[PdCl₄], a new type of palladium complexes, palladium(II) cationic–anionic complexes showing high antitumor and antimetastatic activity. Crystallographic data for six obtained complexes have been presented.

Full text of DOI:10.1134/S0036023617110043

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2017, Vol. 62, No. 11, pp. 1469–1478. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © I.A. Efimenko, A.V. Churakov, N.A. Ivanova, O.S. Erofeeva, L.I. Demina, 2017, published in Zhurnal Neorganicheskoi Khimii, 2017, Vol. 62, No. 11,
pp. 1476–1485.
PHYSICAL METHODS
OF INVESTIGATION
Cationic–Anionic Palladium Complexes: Effect of Hydrogen Bond
1
Character on Their Stability and Biological Activity
I. A. Efimenkoa, *, A. V. Churakova, N. A. Ivanovaa, O. S. Erofeevaa, and L. I. Deminab
aKurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia
bFrumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, 119991 Russia
*e-mail: ines@igic.ras.ru
Received April 20, 2017
Abstract⎯The solution state of palladium cationic–anionic complexes (AmHn)k[PdCl4] prepared for the
first time, where Am is morpholine, methylmorpholine, aminoethylmorpholine, 5-aminovaleric acid, L-1-
phenyl-2-methylaminopropanol, and m-xylilenediamine, has been studied by electronic absorption spec-
troscopy, NMR, and pH measurements. The agreement of obtained results for the state of the complexes in
water and NaCl solutions with IR and X-ray diffraction data for these complexes has allowed us to substanti-
ate the principle for designing patent formulation (C5H12NO)2[PdCl4], a new type of palladium complexes,
palladium(II) cationic–anionic complexes showing high antitumor and antimetastatic activity. Crystallo-
graphic data for six obtained complexes have been presented.
DOI: 10.1134/S0036023617110043
crystal. Both these parameters determine complex sta-
bility in solutions; this information is required to
design formulation for use in medical practice.
In recent decades, the studies of molecular crystals
composed of organic and organometallic (coordina-
tion) compounds or ions, which in solid state are
supermolecules or supramolecular structures resulting
from noncovalent interactions, are in progress [1–4].
Among noncovalent interactions, hydrogen bond
is the main binding force in the formation of supramo-
lecular systems and plays important role in chemistry,
biology, and material science [5–7].
In our publications [8, 9] and patents [10–14] pre-
ceding to this paper, we showed the possibility to use
hydrogen bonds to design a new class of biologically
active compounds based on palladium cationic–
anionic complexes (AmHn)k[PdCl4] (n, k = 1, 2) show-
ing radioprotecting, immunomodulating, and antitu-
mor properties. Molecules of different classes of organic
compounds—amines, amides, imides, azoles, etc.—
were studied as amino-containing ligands.
Palladium cationic–anionic complexes with mor-
pholine and L-1-phenyl-2-methylaminopropanol
derivatives producing NH+···Cl– hydrogen bonds with
the protons of H2PdCl4 proved to be the most interest-
ing compounds of such a type in the context of medi-
cal application, especially those showing antitumor
activity at the level competitive or higher than that of
Cisplatin [17, 18]. The strength of this hydrogen bond
is governed, on the one hand, by amine pKa and, on
the other hand, by the number and character of intra-
molecular and intermolecular hydrogen bonds in
Physiological salt solution, aqueous 0.9% NaCl solu-
tion, is the only solvent that prevents hydrogen bond
cleavage and [PdCl4]2– ion hydrolysis. In this work, we
studied the stability of palladium cationic–anionic com-
plexes with methylmorpholine (C5H12NO)2[PdCl4] (1),
morpholine (C4H10NO)[PdCl4] (2), aminoethylmor-
pholine (C6H16N2O)[PdCl4] (3), 5-aminovaleric acid
(C5H12NO2)2[PdCl4] (4), L-1-phenyl-2-methylami-
nopropanol (C10H16NO)2[PdCl4] (5), and m-xylilenedi-
amine (C8H14N2)[PdCl4] (6), and previously described
piperazine complex (C4H12N2)[PdCl4] (7) [19].
The structure of complexes 1–6 and their hydrogen
bonds were studied by X-ray diffraction analysis; com-
plex stability was considered in the context of obtained
parameters, which considerably affects the choice of
compounds for biological testing.
EXPERIMENTAL
Initial compounds and methods of investigation. Pal-
ladium cationic–anionic complexes [AmHn]k[PdCl4]
were synthesized using the following chemicals as
initial compounds: PdCl2 (pure grade, Reakhim);
amines: 4-methylmorpholine С5Н11NO (1), mor-
pholine C4H9NO (2), 4-(2-aminoethyl)morpholine
C6H14N2O (3), δ-valerolactam (2-piperidone) C5H9NO
(4), L-1-phenyl-2-methylaminopropanol hydrochlo-
rideC10H15NO · HCl (5), m-xylilenediamine C8H12N2 (6),
1
This paper is a continuation of review [8].
1469

1470
EFIMENKO et al.
piperazine C4H10N2 (7) (Fluka); hydrochloric acid ences. The crystallographic data for 1–6 are deposited
with the Cambridge Crystallographic Data Center.
(HCl), and acetone (Khimmed).
Analysis for C, H, N was carried out on a Carlo
Erba Instruments CHNS OEA 1108 analyzer. Palla-
dium content in complexes was determined by weight
method, chlorine content was found by volumetric
analysis.
IR absorption spectra were registered in the region
225–4000 cm–1 on a Nicolet NEXUS Fourier-transform
IR spectrometer. Samples were obtained as Nujol mulls.
The prepared suspension was placed between KRS-5
plates.
Electronic absorption spectra were measured using
a Specord M40 spectrophotometer in quartz cuvettes
10 mm thick in the spectral region 200–900 nm. Spec-
trophotometric study of complex solutions was con-
ducted at ambient temperature in physiological solu-
tion (0.9% NaCl), in diluted solution (down to 0.45%
NaCl), and in water at complex concentration 0.2 wt %.
Analysis of obtained spectral parameters and their com-
parison with literature data for [PdCl4]2– and [Pd2Cl6]2–
anions [20, 21] provided a possibility to assign electron
transitions observed in the spectra of compound 2.
Solution pH was measured on an OP-110-type
MINI-DIGI pH meter with accuracy 0.01. An
OP-0808P combined pH-sensitive electrode was used.
The measurements were conducted at ambient tempera-
ture. Buffer solutions RK-21 with pH 2.07 and RK-71
with pH 7.03 were used for electrode preparation.
Synthesis of Palladium Cationic–Anionic Complexes
Complexes 1–3 with protonated nitrogen-contain-
ing ligands were synthesized by procedures described
in [14], complex 5 was obtained by procedure reported
in [17, 18], complex 7 was prepared by procedure [19].
[C5H12NO2]2[PdCl4] (4). The complex was
obtained by reacting 1.43 g (8.07 mmol) of palladium
dichloride in a mixture of 20 mL of H2O and 3 mL of
HCl with a solution of 1.60 g (16.14 mmol) of δ-valero-
lactam in a mixture of 15 mL of H2O and 2 mL of HCl.
Dissolution in acid medium causes the ring opening of
δ-valerolactam to give 5-aminovaleric acid (Am, 5-AVA)
whose amino group produces NН···Cl hydrogen
bonds due to protonated amino group of the cation
and the Cl– ions in [PdCl4]2– anion. The mixture was
concentrated on water bath until crystallization began,
cooled, and the crystals formed were separated by fil-
tration. They were dried at 80°C until constant weight.
The final product is a brown crystalline powder, 2.32 g,
yield 59% (toward involved palladium). For
C10H24N2O4PdCl4; anal. calcd., %: Pd, 21.96; С1,
29.27. Found, %: Pd, 21.64; С1, 29.20.
[C8H14N2][PdCl4] (6). A solution of 0.5645 g
(3.18 mmol) of PdCl2 in a mixture of 10 mL of H2O
and 1 mL of HCl was added to a solution of 0.4336 g
(3.18 mmol) of m-xylilenediamine C8H12N2 in a mix-
ture of 7 mL of H2O and 1 mL of HCl. The resultant
mixture was concentrated on a water bath until crystalli-
zation beginning. Next, three 5-mL portions of H2O
were added, the solution being concentrated each time
until crystallization beginning. The resultant crystalline
precipitate was separated by filtration, washed with ace-
tone, and dried at 80°C until constant weight. Yield 1.23 g
(93.9%). A single crystal selected from crystallizing mat-
ter had composition [C8H14N2][PdCl4] ⋅ Н2O. For
C8H14N2PdCl4; anal. calcd., %: Pd, 27.43; Cl, 36.92.
Found, %: Pd, 27.54; Cl, 36.70.
1H and 13C NMR spectra were recorded on a Bruker
DPX-30 and a Varian VXR-400 spectrometers with the
use of D2O at ambient temperature. Tetramethylsilane
was used as an internal reference for chemical shift
determination (δ, ppm).
X-ray diffraction analysis of crystals 1–6 was per-
formed on a Bruker SMART APEX II automated dif-
fractometer (MoKα radiation, λ = 0.71073 Å, graphite
monochromator) using ω scanning with 0.5° step.
Absorption was corrected using equivalent reflections
intensities [22]. The structures were solved by direct
methods, all non-hydrogen atoms were refined on F2
by full-matrix anisotropic least-squares techniques
(SHELXTL [23]). In crystal 3, [PdCl4]2– anion is
rotationally disordered over two sites with occupancy
coefficients of 0.55/0.45. For compounds 1, 2, and 5,
all hydrogen atoms were added in ideal positions and
refined using the Riding model. In structures 3 and 4,
all ammonium and hydroxyl hydrogen atoms were
found from difference Fourier maps and refined iso-
tropically, other hydrogen atoms (connected to car-
bons) were added in ideal positions and refined using
the Riding model. In structure 6, all hydrogen atoms
were located with difference Fourier maps and refined
isotropically except for solvate water molecule. Details
of structural studies are presented in Table 1.
IR spectral characteristics of complexes 1–7 are
presented in Table 2.
RESULTS AND DISCUSSION
The aim of this study is to substantiate the choice of
solvent for palladium cationic–anionic complexes
(AmHn)k[PdCl4] necessary for designing stable medi-
cal formulation to study biological, in particular anti-
tumor, activity of certain complexes of this class. All
compounds studied in the work include [PdCl4]2–
anion whose chloride ions are connected via hydrogen
bonds with nitrogen-containing ligands. We showed
previously in the work [8] that stable (AmHn)k[PdCl4]
complexes with protonated nitrogen-containing cat-
ions formed in acid medium when amine pKa is not
lower 7. When amine pKa is within 6–7, the palladium
X-ray diffraction studies were performed at the
Shared Facility Center, Kurnakov Institute of General
and Inorganic Chemistry, Russian Academy of Sci-
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EFIMENKO et al.
Table 2. Characteristic bands in IR spectra of (AmHn)k[PdCl4], cm–1
δ(
n = 2, 3
+),
NHn
+
+
ν (NH+)
Complex
ν(Pd–Cl),
ν(
)
ν(
)
NH2
NH3
1
2
3
326
323
321
3044
3088 as
3057 s
1571
3100–2900 br
3186
3152
3106
3038
1593
1578
4
5
323
323
3073
3035
1578
3116 br
3041
1593
1582
6
327
2948
7 [19]
327, 290
3200
Table 3. Dependence of pH for solutions of K2PdCl4, compounds 2, and 5 on NaCl concentration in water
Solvent
Complex
Time, h
c = 10–4
M
water
0.005 M NaCl
0.15 M NaCl
0
3.95
3.34
3.20
4.0
4.80
3.90
3.53
4.50
3.53
3.49
4.55
3.60
3.28
5.86
5.83
5.63
5.55
4.02
3.95
5.76
4.43
4.35
K2PdCl4
3
24, precipitate
0
2
5
3
3.43
3.24
4.01
3.35
3.30
24, precipitate
0
3
24, precipitate
pH values: distilled water, 6.30; 0.005 M NaCl solution, 6.28; 0.15 M NaCl solution, 6.06.
cationic–anionic complexes in acid medium, if with complex dissolution in water, it is accompanied
formed, immediately transform into aminate com-
plexes Am2PdCl2 (in accordance with Anderson rear-
rangement), while the formation of only aminate
complexes is possible at pKa < 6 even in acid medium.
Only data on K2[PdCl4] hydrolysis in water are avail-
able in the literature [25].
by change in solution pH from 3.95–4.00 (corre-
spondingly to the complexes noted above) and com-
pletes after 24 h at solution pH 3.20–3.30 when
Pd(OH)4 precipitates from solutions.
To study effect of chloride ions on hydrolysis pro-
cesses, we considered pH changes of K2[PdCl4], 2,
and 5 solutions at concentration 10–4 mol/L in 0.9%
aqueous NaCl solution corresponding to NaCl con-
centration in blood plasma (Table 3). It was found that
no pH change occurs for 3 h in the case of K2[PdCl4],
whereas pH decreases from 5.55 to 3.95 for solution of 2
and from 5.76 to 4.35 for solution of 5, i.e., the cleav-
age of NH···Cl hydrogen bonds leads to acceleration of
[PdCl4]2– anion hydrolysis in complexes 2 and 5. To
No information on the behavior of tetrachloropal-
ladate ions with nitrogen-containing cations in water
and the effect of Cl– anions in solution on the hydro-
lysis of [PdCl4]2– anion is available in the literature.
We obtained primary information on the comparative
behavior of 10–4 mol/L aqueous solutions of
K2[PdCl4], 2, and 5 by the example of change of solu-
tion pH in time (Table 3). Hydrolysis reaction begins
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CATIONIC–ANIONIC PALLADIUM COMPLEXES
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Table 4. Time dependence of electronic absorption spectra for solutions of compound 1 on NaCl concentration in water
Absorption intensity ε, L/mol cm
NaCl concentration
in water, %
Absorption band, nm
5 min
4 days
6 days
0.9
0.45
0
463
441
424
135
153
211
135
150
379
135
151
344 (Pd pptn.)
study in more detail the state of [PdCl4]2– anion and
protonated cation in (AmHn)k[PdCl4] upon change in
NaCl concentration, we used methylmorpholinium
tetrachloropalladate (1), which showed antitumor and
antimetastatic activity considerably higher than that of
Cisplatin [8].
new potentially biologically active compounds is con-
fined by the volume of solution introduced in animal,
we studied the stability of 0.2 wt % solutions of com-
plex 1 in physiological salt solution. The initial com-
plex concentration in 0.2% solution (20 mg of the
complex in 10 mL of physiological salt solution) was
determined from the current rules for dose determina-
tion for primary biological activity screening, which
equals to 1/3 of LD50 = 60 mg/kg (in this case deter-
mined as chronical). Our study showed that solution
does not change its characteristics even after one-year
storage at ambient temperature. A 0.2% solution of
complex 1 in aqueous 0.9% NaCl solution was quali-
fied as a pharmaceutical form of this compound,
which was confirmed by the patent [27].
The stability of other five complexes (2–6) was
studied concurrently, the complexes proved to be less
stable than 1 (Table 7). Since pKa values for the initial
nitrogen-containing ligands of these complexes are
within 9.64–9.95, while compound 2 has рКа = 7.41,
the stability of 1 can be explained only by structural fac-
tors, i.e., the character of NН···Cl hydrogen bonds sys-
tem that provides persistence of molecule 1 in solution.
The structure of complexes and ligand coordina-
tion modes were established at the first stage of the
work by IR spectroscopy with the use of comparative
analysis of the spectra for free ligands (Am), the spec-
tra of (AmHn)k[PdCl4] complexes (1–7) with proton-
ated forms of these ligands, and the spectrum of initial
K2[PdCl4].
The large contour complexity of ν(N–H) and
ν(Pd–Cl) bands in the spectra of complexes 1–7 indi-
cates the nonequivalence of hydrogen bonds formed in
(AmHn)k[PdCl4] complexes, i.e., the number of bands
related to hydrogen bonds in IR spectrum increases
with the number of functional groups in the ligand.
Electronic absorption spectra of 2.506 × 10–3 mol/L
solutions of compound 1 in 0.9% aqueous NaCl solu-
tion display three absorption bands at 463, 280, and
221 nm. The first band is caused by d–d transition,
while intraligand π–π* transitions of methylmorpho-
line make a considerable contribution to two other
bands in the UV region. Therefore, we will consider
only changes for the band at 463 nm. The analysis of
time dependence of electronic absorption spectra for
solutions of complex 1 showed (Table 2) that this com-
pound is extremely stable in physiological salt solution:
its spectrum remains unchanged for 6 months. In 0.45%
NaCl solution, the band is shifted to 441 nm in the first
several minutes after dissolution and remains constant up
to 4 days. Six days later, the spectrum shows emergence
of a new band at 626 nm (ε = 1 L/mol cm), but the posi-
tion of the band at 441 nm remains unchanged. The
electronic absorption spectrum of freshly prepared
aqueous solution of complex 1 differs from its spectra
in 0.9 and 0.45% NaCl solutions. The band of d–d
transition shifts to 424 nm with increase in ε intensity
up to 344 (in 6 days), while the band at 626 nm appears
even after 4 days and after 6 days its intensity reaches
ε = 344. Hydrolysis reaction in water is accompanied
by the precipitation of palladium metal (Table 4);
thus, we revealed the conditions of change in Pd(II)
coordination environment in anion depending on
NaCl concentration in solution.
The use of NMR method [26] allowed us to obtain
the spectra of resonance absorption for nuclei com-
prising the initial ligand and its cationic form LH+ in
compound 1 and to determine the type of functional
The number of bands of Pd–Cl stretching vibra-
tions is known to vary with ligand coordination mode
in complex and to be determined by the local symme-
try of the closest environment in the coordination
sphere of the metal atom. For the square planar
[PdCl4]2– anion of D4h symmetry, selection rules
require the presence in IR spectrum of only one band
of Pd–Cl stretching vibrations of symmetry class Eu.
13
groups containing the studied nucleus (1H, C) from
the chemical shifts of these resonance signals. NMR
spectra were measured in water (for L) and 0.9% NaCl
solution in D2O (for compound 1). NMR data indi-
cate (Tables 5 and 6) the retention of protonated form
of N-methylmorpholine in solution for both N-meth-
ylmorpholinium hydrochloride (b) and morpholin-
ium tetrachloropalladate (c). Thus, these data confirm
the stability of solutions of 1 in physiological salt solu-
tion even at its low concentrations (2.5 × 10–3 mol/L).
The corresponding ν(Pd–Cl) band at 336 cm–1
observed in the spectrum of K2[PdCl4] is shifted in the
spectra of complexes 1–7 to the low-frequency region
Since toxicity determination in preclinical testing of by 10–15 cm–1 and has unsymmetrical broadened pro-
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1474
EFIMENKO et al.
1
Table 5. H NMR data for (a) N-methylmorpholine, (b) N-methylmorpholinium hydrochloride, and (c) compound 1 in
0.9% NaCl in D2O
Chemical shift δ (ppm)
N–CH
O–CH
equatorial
Compound
N–CH
axial
equatorial
axial
N-Methylmorpholine (a)
2.12 singlet
2.86 singlet
Broadened signal
2.37
3.13 multiplet
Triplet
3.61
N-Methylmorpholinium
3.42
3.74
4.06
doublet
hydrochloride (b) LHCl
doublet
doublet
1 (c) (LH)2[PdCl4]
2.88
singlet
3.16 multiplet
3.45
doublet
3.76
doublet
4.06
doublet
Ha
Ha
He
He
N CH3
(a) L =
(b) LHCl, (c) (LH) [PdCl ].
2 4
O
He
He
Ha
Ha
Table 6. 13C NMR data for (a) N-methylmorpholine, (b) N-methylmorpholinium hydrochloride, and (c) compound 1 in
0.9% NaCl in D2O
Chemical shift δ (ppm)
Compound
N–CH3
N–CH2
O–CH2
N-Methylmorpholine (a)
N-Methylmorpholinium hydrochloride (b) LHCl
1 (c) (LH)2[PdCl4]
42.13
40.53
40.62
51.27
50.52
50.58
63.48
61.19
61.23
Table 7. Electronic absorption spectra for complexes 1–7 ( λ, nm (ε, L/mol cm)
1
2
3
4
5
6
7
5-aminovaleric
acid
(C5H12NO2)2[
PdCl4]
pKa1 = 10.8
pKa2 = 4.3
m-
4-
L-1-phenyl-2-
methylamino-
propanol
C10H15NO
pKa = 9.96
piperazine
4-(2-
xylilenediamine
C8H12N2
pKa1 = 9.64
pKa2 = 8.49
methylmorpho morpholine
Time, h
C4H10N2
pKa1 = 9.83
pKa2 = 5.56
aminoethyl)-
morpholine
C6H14N2O
line
С5Н11NO
pKa = 7.41
C4H9NO
pKa = 8.83
0
1
3
464 (151)
463 (155)
464 (156)
464 (156)
463 (218)
462 (208)
462 (236)
462 (255)
390 (367)
386 (671)
386 (813)
386 (664)
462 (223)
463 (247)
463 (253)
462 (260)
462 (153)
460 (152)
457 (155)
455 (152)
435 (158)
460 (243)
452 (238)
442 (241)
427 (247)
418 (296)
415 (301)
415 (312)
415 (330)
24
file (Table 2). Spectral changes in the region 2000–
3500 cm–1 caused by the formation of Cl···HN hydro-
gen bonds of protonated ligand molecule explain not
only the decrease of Pd–Cl bond energy but also the
reduction of local symmetry D4h. The reduction of
In this paper, we describe cationic–anionic com-
plexes where cation is represented by the protonated
forms of primary, secondary, and tertiary amines,
which causes certain differences in the spectral regions
related to the stretching and deformational vibrations
symmetry leads to the broadening of ν(Pd–Cl) band, of protonated nitrogen-containing groups. The gen-
and in certain cases to resolution into two bands as in
complex 7, which is characteristic of С2v symmetry.
eral feature for all protonated nitrogen-containing
ligands in complexes 1–7 is the shift of the bands of
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CATIONIC–ANIONIC PALLADIUM COMPLEXES
(a)
1475
C10H24N2O4PdCl4 (1)
С8H20N2O2PdCl4 (2)
Cl(2C)
O(2)
C(22)
O(1)
Cl(1C)
Pd(1A)
C(23)
C(25)
C(24)
H(1)
N(1)
N(2)
H(2)
Cl(1B)
Cl(2)
Pd(1)
C(21)
Cl(3)
H(2)
Cl(2B)
Cl(2D)
C(11A)
C(14A)
Cl(1)
Cl(4)
Cl(1D)
H(1A)
N(1A)
Pd(1B)
Cl(1E)
C(15A)
O(1A)
C(13A)
C(12A)
Cl(2E)
С6H16N2OPdCl4 (3)
O(1)
C(2)
Cl(4A)
Cl(5A)
C(3)
C(1)
Cl(1A)
C(4)
Cl(3A)
Pd(2)
Cl(1)
Cl(5)
Cl(2A)
N(1)
C(5)
Pd(1)
Cl(3)
C(6)
Cl(4)
Cl(2)
N(2)
(b)
b
0
c
a
Fig. 1. (a) Structures of complexes 1, 2, 3 and (b) crystal packing of complex 2.
N–H stretching vibrations to the low-frequency symmetric, respectively. The emergence of two hydro-
region by 200–250 cm–1 as compared with the spectra
of free ligands caused by hydrogen bonding in the
complexes. The spectrum of compound 1 exhibits one
gen atoms at the nitrogen atom results in the emer-
gence of deformational vibration δ(
+) character-
NH2
ized by the band at 1571 cm–1. Further spectra compli-
cation is observed for the complexes with protonated
primary amino groups. Thus, the spectrum of com-
pound 4 shows the bands of stretching vibrations of
ν(NH+) band at 3044 cm–1, whereas the protonated
+
secondary amino group
in the spectrum of com-
NH2
plex 2 is characterized by two bands of stretching
vibrations at 3088 and 3057 cm–1, asymmetric and NH3+ group at 3186, 3152, 3106, and 3038 cm–1 and
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 62 No. 11 2017

1476
EFIMENKO et al.
(a)
C10H24N2O4PdCl4 (4)
C20H32N2O2PdCl4 (5)
N(1)
Cl(1)
Cl(2)
C(15)
C(14)
C(13)
O(12)
Cl(21)
C(12)
Cl(3)
Pd(1)
Cl(2B)
Pd(2)
C(11)
O(11)
Cl(22)
N(2)
H(1)
C(25)
Cl(4)
O(1)
H(1A)
H(1B)
C(11)
Cl(2A)
Cl(11)
C(23)
C(22)
C(24)
N(1)
C(10)
O(22)
C(14)
C(16)
C(19)
C(21)
O(21)
C(13)
C(18)
Pd(1)
Cl(1B)
Cl(12)
C(15)
C(12)
C(17)
Cl(1A)
С8H14N2OPdCl4 · H2O (6)
Cl(1)
C(7)
Cl(2A)
Pd(1)
N(1)
C(1)
C(6)
C(5)
C(8)
C(3)
C(2)
N(2)
C(4)
Cl(2)
Cl(1A)
O(1)
Cl(4)
Cl(3A)
Pd(2)
Cl(4A)
Cl(3)
(b)
Fig. 2. (a) Structures of complexes 4, 5, 6 and (b) crystal packing of complex 4.
Table 8. Hydrogen bond parameters in complexes 1–7
Type A
ω(N–H···Cl), deg
Type B
Compound
d(H···Cl), Å
d(H···Cl), Å
ω(N–H···Cl), deg
1
2
3
4
5
6
2.48–2.52
2.55–2.59
2.72–2.83
2.67–2.72
–
2.61–2.73
2.64–3.18
136.6–140.2
132.2–147.0
124–130
131–136
–
137–140
–
–
–
–
–
2.32–2.28
2.38–2.42
2.39–2.53
1.99–2.73
–
161–168
169–171
147–169
154–176
–
7 [19]
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CATIONIC–ANIONIC PALLADIUM COMPLEXES
1477
two bands of deformational vibrations at 1593 and for one year, which differs compound 1 from com-
1578 cm–1. In complex 5, the OH group of the ligand
is also involved in intramolecular hydrogen bonding.
The spectrum displays two ν(ОН) bands at 3446 and
3398 cm–1, which indicate the contribution of two
ligands incorporated in the complex upon binding to
plexes 2–7 of (AmHn)k[PdCl4] series.
It should be also noted that H-bonded supramo-
lecular networks appear in complex 4 due to the pairs
of ОН···О hydrogen bonds produced by the free car-
boxylate groups of two 5-AVA molecules, similarly to
[PdCl4]2– anion. Crystal water molecule in com- networks revealed in palladium(II) pyrazolate com-
plex with N-acetylglycine [28].
pounds 6 and 7 (according to X-ray crystallography)
causes hydrogen bond variety. The spectrum of com-
plex 6 exhibits two ν(ОН) bands at 3561 and 3478 cm–1
because each hydrogen atom of water molecule pro-
vides different contribution to hydrogen bonding with
[PdCl4]2– anion. It was shown that the oxygen atom of
+
Thus, our study showed that the selection of bio-
logically active (AmHn)k[PdCl4] complexes is deter-
mined by the sum of parameters including amine
nature, its basicity parameters (pKa values) [15, 16],
and the structural features of complexes determined
by the ability of protonated amine to form hydrogen
bonds with the chlorine atoms of [PdCl4]2– anion.
water molecule also forms hydrogen bond with
NH3
group. The variety of intramolecular and intermolec-
ular hydrogen bonds appears in the spectrum of com-
pound 6 as the bands at 2669, 2591, and 2454 cm–1.
ACKNOWLEDGMENTS
This conclusion is confirmed well by the data of
X-ray diffraction study for single crystals of com-
pounds 1–6. The crystallographic analysis of single crys-
tals showed that all structures include one or two crystal-
lographically independent square-planar [PdCl4]2–
anions (Figs. 1, 2). These anions are located in general
positions in structures 1 and 5, in inversion centers in
structures 2 and 4, one of independent anions is on the
twofold axis, while another occupies inversion center
in crystals 3 and 6. The length of Pd–Cl bonds are
within 2.292(4)–2.324(6) Å, while cis ClPdCl angles
differ from right angle no more than by 7.5°. In the
structures 2 and 4, these anions are united in layers
due to two secondary Pd–Cl···Pd interactions that
complete the coordination polyhedron of the metal to
strongly extended octahedron. For these interactions,
Cl···Pd distances are within 3.174–3.674 Å. No such
contacts between anions are observed in the four other
compounds.
This work was supported by the Presidium of the
Russian Academy of Sciences (grant no. I.14P) and
the Presidential Grant Program “Leading Scientific
Schools” (grant no. 596.20143).
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No. 11
2017