# Pt(II) and Pd(II) Complexes withβ-Alanine

Authors: L. F. Krylova; L. M. Kovtunova; G. V. Romanenko
Journal: Bioinorganic Chemistry and Applications
 (2008)

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## Abstract

A sequence of stages in the syntheses of isomeric bisamino acid complexes of Pt(II) withβ-aminopropionic acid (β-alanine = β-AlaH) has been studied by the P195t  NMR spectroscopy. The techniques have been developed of the synthesis of the cis- and trans-bischelates of Pt(II) and Pd(II) with β-alanine as well as of the halide complexes of trans-[M(β-AlaH)2Cl2] (M = Pt, Pd) and trans-K2[Pt(β-Ala)2I2] types. The NMR spectroscopy and IR spectroscopy (in the nuclei of P195t,C13,H1) and X-ray diffraction analysis have been used to examine the structures of the synthesized compounds.


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## Body

## 1. Introduction

The neoplastic activity of some Pt(II)
complexes was discovered in 1971 [1]. It has given an impulse to the growth of
platinum metal complexation. The study of the Pt(II) and Pd(II)
complexes with amino acids is very promising due to both of their biological
activity and their use in the solution of the fundamental problems in
coordination chemistry of planar complexes with multifunctional ligands. The Pt(II)
and Pd(II) complexes with α-alanine (NH2CH(CH3)COOH)
are widely described in the literature [2–8].Less attention has been paid to the
Pt(II) complexes with the simplestβ-amino acid (β-alanine, β-AlaH– NH2(CH2)2COOH).
The syntheses of two bisaminoacid complexes are described in [9]: those of trans-[Pt(β-Ala)2]
where β-alanine is a bidentate ligand (coordinated via
the NH2 and OCO groups) and of trans-[Pt(β-AlaH)2Cl2] where β-alanine
is a monodentate ligand (coordinated via the NH2 group). The trans-configuration of these complexes
has been proved by chemical methods. No physical methods have been applied to
verify their structures.The monoaminoacid complex K[Pt(NO2)2(β-Ala)]
with the bidentate β-alanine as well as the bisaminoacid complexes [Pt(NO2)2(β-AlaH)2]
and K2[Pt(NO2)2(β-Ala)2]
with the monodentate β-alanine were described in [10]. On the basis of the
Kurnakov reaction (thiourea test), it was concluded [10] that the bisaminoacid
complexes of Pt(II) appear to have the trans-configuration.
The Cambridge
crystallographic
database only contains some information about one Pt(II) complex with β-AlaH, [Pt(β-Ala)(C2H4)Cl], where β-Ala has a bidentate coordination to the Pt atom [11]. So far there has
been no evidence of β-AlaH bisaminoacid complexes of Pt(II)
with a cis-arrangement of ligands. To
the authors knowledge the Pd(II) complexes with β-AlaH
have never been investigated either.In this work, the195Pt
NMR spectroscopy has been used to study the successive stages of the synthesis
of bisaminoacid Pt(II) complexes with β-alanine,
which can exist in trans- and cis-configurations. On the basis of the
data obtained, we have developed the methods of synthesizing different Pt(II)
and Pd(II) bisaminoacid complexes with β-alanine.
The complexes in question have been characterized by 1H, 13C NMR, IR
spectroscopy, and X-ray diffraction analysis.


## 2. Experimental

### 2.1. Syntheses
of thetrans-[Pt(β-AlaH)2Cl2]
and trans-[Pt(β-Ala)2] Complexes

Thetrans-[Pt(β-AlaH)2Cl2] and trans-[Pt(β-Ala)2] complexes were synthesized using
the techniques suggested in [9], which were slightly modified for the purpose (see Section 3).


### 2.2. Synthesis
of thetrans-[Pd(β-AlaH)2Cl2]
Complex

0.887 g (5 mmol) of PdCl2 and 0.585 g (10 mmol) of NaCl were dissolved in 20 mL of water and heated in the
water bath until the dilution of PdCl2. A solution containing 1.78 g
(20 mmol) of β-AlaH and 0.800 g (20 mmol) of NaOH in 20 mL of
H2O was added to the solution of K2[PdCl4].
After cooling the solution as low as 0°C, 10 mL of concentrated HCl was added
to the reaction mixture. The orange precipitate fell out, which was filtered
off in an hour, washed with cold water, and dried at room temperature. The yield
was up to 85%.Anal. found (%); C 19.7, H 3.93, N 8.02, Cl
19.5, Pd 29.5. Calcd. for C6H14N2O4Cl2Pd
(%): C 20.3, H 3.94, N 7.88, Cl 20.0, Pd 29.9.


### 2.3. Synthesis
of thetrans-[Pd(β-Ala)2] Complex

1.0 g of thetrans-[Pd(β-AlaH)2Cl2] was dissolved in 10 mL of water then
the reaction mixture was treated with 1 M of NaOH till it became neutral to phenolphthaleine. A light yellow
precipitate fell out, which was filtered off and washed with cold water. At
first it was dried at room temperature and then at 110°C. The yield was up to 76%.Anal. found (%); C 25.5, H 4.17, N 9.88, Pd
37.9. Calcd. for C6H12N2O4Pd (%): C
25.5, H 4.25, N 9.92, Pd 37.7.


### 2.4. Synthesis
of thecis-[Pd(β-Ala)2] Complex

0.5 g of thetrans-[Pd(β-Ala)2] was dissolved in 20 mL of water. The reaction mixture
was heated with stirring at 80°C for 3 hours. After cooling the reaction
mixture as low as 0°C, a small amount of the starting trans-bischelate was filtered off. Then the cis-[Pd(β-Ala)2] was settled with acetone
from the filtrate solution (water:acetone ~1:4) and was filtered off. The solid cis-[Pd(β-Ala)2]
was dried at room temperature at first and then at 110°C. The yield was up to 60%.Anal. found (%); C 25.0; H 4.30; N 10.0; Calcd.
for C6H12N2O4Pd (%): C 25.5; H
4.25; N  9.92.


### 2.5. Synthesis
of thecis-[Pt(β-Ala)2] Complex

3.32 g (20 mmol) of KI in 25 mL of water was added to 2.08 g (5 mmol) of K2[PtCl4] in 25 mL of water. The
reaction mixture was heated in the water bath for 10 minutes. A solution of β-AlaH (0.89 g,
10 mmol) in water (25 mL) was added to the reaction mixture, which was heated
in the water bath for 2 hours. While heating the reaction mixture, 10 mL of 0.5 M of KOH was added by small portions. Then a
small amount of black precipitate was filtered off. The solution of AgNO3 (3.40 g,
20 mmol) in water (25 mL) was added to the orange solution of the filtrate
obtained, and the mixture was heated for ~5 minutes. The coagulated AgI
precipitate was filtered off. The reaction product was precipitated with
acetone (~100 mL) from the filtrate (V ~50 mL). The yield was up to 20%.Anal. found (%): Pt 53.1, N 7.65; Calcd. for C6H12N2O4Pt
(%): Pt 52.6, N 7.55.


### 2.6. Measurements

NMR spectra were recorded using a Bruker DPX-250 spectrometer
at the frequencies of 250 (1H), 62.9 (13C), and 53.6 (195Pt) MHz. Two solvents, D2O and acetone-d6, were used for the 1H
NMR spectrum: (a) in the D2O solution, the chemical shifts were
determined with reference to the signal of the CH3-group protons of the
DMSO, which was added as an internal standard (δ = 2.660 ppm); (b) in the acetone-d6 solution, the chemical shifts were determined with reference to the central
signal of the acetone residual protons (δ = 2.070 ppm). For the 13C NMR
spectrum the same solvents, D2O and acetone-d6, were used:
(a) in the D2O solution the chemical shifts were determined with
reference to the 13C signal of the DMSO, which was added as an internal
standard (δ =
40.2 ppm); (b) in the acetone-d6 solution the chemical shifts were
determined with reference to the signal of the methyl carbon atom of acetone-d6 (δ = 29.2 ppm). The chemical shift of the 195Pt NMR signals was recorded with
regard to the external standard, that is, 1 M of the Na2[PtCl6] water solution. All measurements
were performed at room temperature. The 195Pt and 13C NMR spectra were
recorded using proton decoupling.The IR spectra of crystalline samples packed in the KBr
pellets were measured using a Bruker Vector-22 one-beam FT spectrophotometer.X-ray diffraction analysis. Single-crystal data were collected
on a SMART APEX CCD (Bruker AXS) diffractometer (Mo Kα, λ = 0.71073 Å, T = 298 K, an absorption correction applied using the Bruker SADABS
program, version 2.10). The structures were solved by the direct methods and
refined by the full-matrix least squares in an anisotropic approximation for
all nonhydrogen atoms. The H atoms were located in difference electron density
syntheses and refined together with nonhydrogen atoms in an isotropic
approximation. All calculations on the structure solution and refinement were
carried out with the Bruker Shelxtl Version 6.14 software.Trans-[Pd(β-Ala)2]
C6H12N2O4Pd, M =
282.58, monoclinic crystals, space group P21/n, a = 5.750(1) Å, b = 8.910(2) Å, c = 9.020(2) Å, β = 104.692(3)°, V = 447.0(2) Å3; Z = 2, ρcalc = 2.100 g·cm−3, μ = 2.061 mm−1, 3281
reflections collected (3.27<θ<23.28°, Rint = 0.0242), including 639
reflections with I > 2σ(I), 86 refined parameters, R1 = 0.0156, wR2 = 0.0634.Trans-[Pt(β-Ala)2]
C6H12N2O4Pt, M =
371.26, monoclinic crystals, space group P21/c, a = 9.197(4) Å, b = 11.080(5) Å, c = 8.656(4) Å, β = 98.474(6)°, V = 872.4(7) Å3; Z = 4, ρcalc= 2.827 g·cm−3, μ = 160.7 cm−1, 6471
reflections collected (3.53<θ<23.33°, Rint = 0.0388), including
1253 reflections with I > 2σ(I), 134 refined parameters, R1 = 0.0290, wR2 = 0.0618.Cis-[Pt(β-Ala)2]
C6H12N2O4Pt, M = 371.26, monoclinic crystals,
space group P21/c, a = 17.673(3) Å, b = 10.232(3) Å, c = 10.457(2) Å, β = 100.043(4)°, V = 1862.0(6) Å3; Z = 8, ρcalc = 2.649 g·cm−3, μ = 150.6 cm−1, 6570
reflections collected (2.90<θ<23.33°, Rint = 0.0673), including
2608 reflections with I > 2σ(I), 258 refined parameters, R1 = 0.0381, wR2 = 0.0824.Trans-K2[Pt(β-Ala)2I2]•2H2O
C6H16I2K2N2O6Pt, M = 739.30, monoclinic crystals,
space group P21/c; a = 5.0414(7) Å, b = 24.174(3) Å, c = 7.0414(10) Å, β = 94.045(2)°, V = 856.0(2) Å3, Z = 2, ρcalc = 2.868 g·cm−3, μ = 123.1 cm−1, 6375
reflections collected (1.68<θ<23.29°, Rint = 0.0318), including
1231 reflections with I > 2σ(I), 121 refined parameters, R1 = 0.0203, wR2 = 0.0475.


## 2.1. Syntheses
of thetrans-[Pt(β-AlaH)2Cl2]
and trans-[Pt(β-Ala)2] Complexes

Thetrans-[Pt(β-AlaH)2Cl2] and trans-[Pt(β-Ala)2] complexes were synthesized using
the techniques suggested in [9], which were slightly modified for the purpose (see Section 3).


## 2.2. Synthesis
of thetrans-[Pd(β-AlaH)2Cl2]
Complex

0.887 g (5 mmol) of PdCl2 and 0.585 g (10 mmol) of NaCl were dissolved in 20 mL of water and heated in the
water bath until the dilution of PdCl2. A solution containing 1.78 g
(20 mmol) of β-AlaH and 0.800 g (20 mmol) of NaOH in 20 mL of
H2O was added to the solution of K2[PdCl4].
After cooling the solution as low as 0°C, 10 mL of concentrated HCl was added
to the reaction mixture. The orange precipitate fell out, which was filtered
off in an hour, washed with cold water, and dried at room temperature. The yield
was up to 85%.Anal. found (%); C 19.7, H 3.93, N 8.02, Cl
19.5, Pd 29.5. Calcd. for C6H14N2O4Cl2Pd
(%): C 20.3, H 3.94, N 7.88, Cl 20.0, Pd 29.9.


## 2.3. Synthesis
of thetrans-[Pd(β-Ala)2] Complex

1.0 g of thetrans-[Pd(β-AlaH)2Cl2] was dissolved in 10 mL of water then
the reaction mixture was treated with 1 M of NaOH till it became neutral to phenolphthaleine. A light yellow
precipitate fell out, which was filtered off and washed with cold water. At
first it was dried at room temperature and then at 110°C. The yield was up to 76%.Anal. found (%); C 25.5, H 4.17, N 9.88, Pd
37.9. Calcd. for C6H12N2O4Pd (%): C
25.5, H 4.25, N 9.92, Pd 37.7.


## 2.4. Synthesis
of thecis-[Pd(β-Ala)2] Complex

0.5 g of thetrans-[Pd(β-Ala)2] was dissolved in 20 mL of water. The reaction mixture
was heated with stirring at 80°C for 3 hours. After cooling the reaction
mixture as low as 0°C, a small amount of the starting trans-bischelate was filtered off. Then the cis-[Pd(β-Ala)2] was settled with acetone
from the filtrate solution (water:acetone ~1:4) and was filtered off. The solid cis-[Pd(β-Ala)2]
was dried at room temperature at first and then at 110°C. The yield was up to 60%.Anal. found (%); C 25.0; H 4.30; N 10.0; Calcd.
for C6H12N2O4Pd (%): C 25.5; H
4.25; N  9.92.


## 2.5. Synthesis
of thecis-[Pt(β-Ala)2] Complex

3.32 g (20 mmol) of KI in 25 mL of water was added to 2.08 g (5 mmol) of K2[PtCl4] in 25 mL of water. The
reaction mixture was heated in the water bath for 10 minutes. A solution of β-AlaH (0.89 g,
10 mmol) in water (25 mL) was added to the reaction mixture, which was heated
in the water bath for 2 hours. While heating the reaction mixture, 10 mL of 0.5 M of KOH was added by small portions. Then a
small amount of black precipitate was filtered off. The solution of AgNO3 (3.40 g,
20 mmol) in water (25 mL) was added to the orange solution of the filtrate
obtained, and the mixture was heated for ~5 minutes. The coagulated AgI
precipitate was filtered off. The reaction product was precipitated with
acetone (~100 mL) from the filtrate (V ~50 mL). The yield was up to 20%.Anal. found (%): Pt 53.1, N 7.65; Calcd. for C6H12N2O4Pt
(%): Pt 52.6, N 7.55.


## 2.6. Measurements

NMR spectra were recorded using a Bruker DPX-250 spectrometer
at the frequencies of 250 (1H), 62.9 (13C), and 53.6 (195Pt) MHz. Two solvents, D2O and acetone-d6, were used for the 1H
NMR spectrum: (a) in the D2O solution, the chemical shifts were
determined with reference to the signal of the CH3-group protons of the
DMSO, which was added as an internal standard (δ = 2.660 ppm); (b) in the acetone-d6 solution, the chemical shifts were determined with reference to the central
signal of the acetone residual protons (δ = 2.070 ppm). For the 13C NMR
spectrum the same solvents, D2O and acetone-d6, were used:
(a) in the D2O solution the chemical shifts were determined with
reference to the 13C signal of the DMSO, which was added as an internal
standard (δ =
40.2 ppm); (b) in the acetone-d6 solution the chemical shifts were
determined with reference to the signal of the methyl carbon atom of acetone-d6 (δ = 29.2 ppm). The chemical shift of the 195Pt NMR signals was recorded with
regard to the external standard, that is, 1 M of the Na2[PtCl6] water solution. All measurements
were performed at room temperature. The 195Pt and 13C NMR spectra were
recorded using proton decoupling.The IR spectra of crystalline samples packed in the KBr
pellets were measured using a Bruker Vector-22 one-beam FT spectrophotometer.X-ray diffraction analysis. Single-crystal data were collected
on a SMART APEX CCD (Bruker AXS) diffractometer (Mo Kα, λ = 0.71073 Å, T = 298 K, an absorption correction applied using the Bruker SADABS
program, version 2.10). The structures were solved by the direct methods and
refined by the full-matrix least squares in an anisotropic approximation for
all nonhydrogen atoms. The H atoms were located in difference electron density
syntheses and refined together with nonhydrogen atoms in an isotropic
approximation. All calculations on the structure solution and refinement were
carried out with the Bruker Shelxtl Version 6.14 software.Trans-[Pd(β-Ala)2]
C6H12N2O4Pd, M =
282.58, monoclinic crystals, space group P21/n, a = 5.750(1) Å, b = 8.910(2) Å, c = 9.020(2) Å, β = 104.692(3)°, V = 447.0(2) Å3; Z = 2, ρcalc = 2.100 g·cm−3, μ = 2.061 mm−1, 3281
reflections collected (3.27<θ<23.28°, Rint = 0.0242), including 639
reflections with I > 2σ(I), 86 refined parameters, R1 = 0.0156, wR2 = 0.0634.Trans-[Pt(β-Ala)2]
C6H12N2O4Pt, M =
371.26, monoclinic crystals, space group P21/c, a = 9.197(4) Å, b = 11.080(5) Å, c = 8.656(4) Å, β = 98.474(6)°, V = 872.4(7) Å3; Z = 4, ρcalc= 2.827 g·cm−3, μ = 160.7 cm−1, 6471
reflections collected (3.53<θ<23.33°, Rint = 0.0388), including
1253 reflections with I > 2σ(I), 134 refined parameters, R1 = 0.0290, wR2 = 0.0618.Cis-[Pt(β-Ala)2]
C6H12N2O4Pt, M = 371.26, monoclinic crystals,
space group P21/c, a = 17.673(3) Å, b = 10.232(3) Å, c = 10.457(2) Å, β = 100.043(4)°, V = 1862.0(6) Å3; Z = 8, ρcalc = 2.649 g·cm−3, μ = 150.6 cm−1, 6570
reflections collected (2.90<θ<23.33°, Rint = 0.0673), including
2608 reflections with I > 2σ(I), 258 refined parameters, R1 = 0.0381, wR2 = 0.0824.Trans-K2[Pt(β-Ala)2I2]•2H2O
C6H16I2K2N2O6Pt, M = 739.30, monoclinic crystals,
space group P21/c; a = 5.0414(7) Å, b = 24.174(3) Å, c = 7.0414(10) Å, β = 94.045(2)°, V = 856.0(2) Å3, Z = 2, ρcalc = 2.868 g·cm−3, μ = 123.1 cm−1, 6375
reflections collected (1.68<θ<23.29°, Rint = 0.0318), including
1231 reflections with I > 2σ(I), 121 refined parameters, R1 = 0.0203, wR2 = 0.0475.


## 3. Results and Discussion

### 3.1. Synthesis
of the Pt(II)trans-Isomers (Scheme 1)

The solutions ofβ-AlaH neutralized with an alkali and K2[PtCl4]
were used as the reagents for the synthesis of trans-isomers. The molar ratio of the reagents K2[PtCl4]:β-AlaH:KOH was as follows 1:4.5:2. The structures of complexes were
detected by the 195Pt NMR spectroscopy at each stage of the synthesis.According to the data of [9], the
first stage of the synthesis is heating of the reaction mixture for 5 hours. We
have shown that after heating the aqueous solution of K2[PtCl4]
with the neutralized β-AlaH for 2 hours, the reaction mixture does
not contain the starting reagents. Instead, it contains three forms (I, II, and
III) of the Pt(II) complexes (Scheme 1), complex II being predominant
(~80%). The signal assignment in the 195Pt NMR spectra was carried
out using the data of [12].Scheme 1
Sequence of reactions of K2[PtCl4] with β-alanine.The second stage comprises the
interaction of complexes with HCl. Just after the addition of HCl to the
reaction mixture, it is detected that the solution contains complexes IV, V, and
VI, complex V prevailing (~75%).Complex IV is formed from complex I
as a result of the ring opening and the insertion of Cl− ions at the
site of cleavage of the Pt–OCO bond. Complex V is formed from complex II via the
ring opening and the insertion of the Cl− ion. Complex VI is formed from complex
III via the protonation of the β-alaninate ions of complex III.
The subsequent heating of the reaction mixture in the water bath for ~20 minutes
only results in one complex (complex IV) in the solution. During this period,
complex VI converts into complex V, while complex V transforms into the trans-dichloride IV due to the
replacement of β-AlaH with the Cl− ion on the coordinate Cl-Pt-β-AlaH. The given replacement takes place in accordance with the kinetic
effect of the trans-influence of
ligands. That is, the trans-effect of
Cl exceeds that of the NH2, the group of β-alanine
[13].At the next stage, the yellow
precipitate of thetrans-[Pt(β-AlaH)2Cl2](IV) gradually settles from the
solution. The titration of complex IV with the KOH solution leads to the formation
of yellow K2[Pt(β-Ala)2Cl2] solution,
which is then heated to form a white precipitate of trans-[Pt(β-Ala)2](I).


### 3.2. Synthesis oftrans-Isomers of the Pd(II) Complexes

The problems of isolation of the
individual geometrical isomers of the Pd(II) bisaminoacid complexes withα-amino acids are related
to the trans-cis isomerization
processes. For the first time we described these processes for Pd(II)
bischelates with glycine and α-alanine in [5, 14].The decrease of temperature from
100°C to 0°C at the appropriate
stages of the synthesis rules out the isomerization processes and allows us to
use the same approaches to the synthesis of the Pd(II) complexes as is
the case with the Pt(II) complexes.The interaction of Na2[PdCl4]
with the neutralized β-AlaH in an aqueous solution is likely to
result in the formation of complexes similar to the complexes I, II, and III
(Scheme 1). The treatment with HClconc leads to the trans-[Pd(β-AlaH)2Cl2]
as the only product. The formation of a trans-isomer
as the only product is possible due to the kinetic effect of the trans-influence of ligands as is the
case with the Pt complexes [13].The titration of thetrans-[Pd(β-AlaH)2Cl2]
with an alkaline solution leads to the ring closure and the formation of the trans-[Pd(β-Ala)2].
The ring closure reaction was conducted at room temperature because the trans-bischelate product precipitated
immediately. As the cis-bischelate
readily dissolves in water, it cannot be present in the solid precipitate of the trans-[Pd(β-Ala)2]
as an impurity.The treatment of thetrans-[Pd(β-Ala)2]
with HCl at ~0°C leads to the opening of amino acid cycles and the formation of
the trans-[Pd(β-AlaH)2Cl2].


### 3.3. Synthesis
of thecis-[Pd(β-Ala)2] Complex

Due to its high solubility in water,
thecis-[Pd(β-Ala)2]
complex can hardly be isolated as a solid. That is why the procedures that we
have developed for the synthesis of the Pd(II) cis-bischelates with valine [15] are not applicable for the
preparation of the solid cis-[Pd(β-Ala)2] phase. The kinetic and thermodynamic data for the trans-cis isomerization of the Pd(II)
bischelates with valine are reported in [15]. It can be supposed that the
equilibrium and rate constants of the isomerization reaction are almost similar
for the bischelates where amino acids are bonded to Pd(II) via the NH2 or OCO groups. Thus for the synthesis of the cis-[Pd(β-Ala)2], we have used the kinetic
and thermodynamic data of [15].Thetrans-[Pd(β-Ala)2] was heated with water at 80°C until the starting
precipitate was completely diluted. The trans-isomer
isomerized, and the cis-isomer stayed
in solution. At 80°C the equilibrium constant of the trans-cis process was lower
than at
low temperatures because the reaction is exothermal (see [15]). So the reaction
mixture was abruptly cooled to ~0°C in order to increase the concentration of
the cis-bischelate. Moreover after cooling,
the starting trans-bischelate, which
did not isomerize, precipitated and was filtered off. The solid cis-[Pd(β-Ala)2]
was settled with acetone from the aqueous filtrate solution.The treatment of thecis-[Pd(β-Ala)2]
with HCl did not allow us to form the cis-[Pd(β-AlaH)2Cl2] as is the case with the trans-isomers. Even a highly diluted
solution of HCl resulted not only in the opening of the amino acid cycles, but
also in completing the substitution of the amino acid ligands and the formation
of PdCI42−. Similar processes were observed for the Pd(II)
complexes with valine [15] and for the Pd(II) complexes with aminobutyric acid
[16].


### 3.4. Synthesis
of thecis-Isomers of the Pt(II) Complexes  (Scheme
2)

For the synthesis of thecis-bischelate, we have used K2[PtI4],
which is formed by the reaction of K2[PtCl4]
with KI.Scheme 2
Sequence of reactions of K2[PtI4] with β-alanine.We supposed that the heating of K2[PtI4] with β-AlaH
at pH ~6-7 (pH was kept at this level by adding KOH) led to the formation of cis-K2[Pt(β-Ala)2I2]. The formation of the cis-isomer was expected to be in
agreement with the kinetic effect of the trans-influence
(TI) of the ligands (TI (I−)≫TI(NH2)).Further heating of thecis-K2[Pt(β-Ala)2I2] does not lead to the ring closure as is
the case with the trans-dichlorides.
Instead, it leads to the isomerization of the cis-K2[Pt(β-Ala)2I2]
and the formation of the trans-K2[Pt(β-Ala)2I2]. After heating for 10 hours, the
solution only contains one form of δ(195Pt) = −3408 ppm. This new form
was isolated as a single crystal and identified by the X-ray diffraction
analysis, which confirmed that it was the trans-K2[Pt(β-Ala)2I2].To synthesize thecis-[Pt(β-Ala)2],
a solution of AgNO3 was added to the solution of the cis-K2[Pt(β-Ala)2I2]. The resulting AgI precipitate was
filtered off. The filtrate solution contained only one form of the cis-[Pt(β-Ala)2]
complex (δ(195Pt)
= −1923 ppm).In addition to the main product, thecis-[Pt(β-Ala)2],
the solution contained KCl and KNO3. We added acetone to the
reaction mixture (water:acetone ~1:2) to separate the desired product from
inorganic salts. Cis-[Pt(β-Ala)2] was the only substrate that precipitated under such
conditions.PMR Spectra (Table1)
The PMR spectrum ofβ-AlaH (Figure 1(a)) in D2O contains two triplets of two CH2 groups. The spectrum corresponds to an A2X2 four-spin system with magnetically equivalent protons in each CH2 group [17, page 54].
Figure1 shows that the coordinate β-alanine (spectra b, c, and d) has a more complex spectrum than the incoordinate
β-alanine (spectrum a) in the region of CH2 protons. The
spectrum contains more lines, and their intensities are distorted. This
indicates that the protons of both CH2 groups are magnetically
nonequivalent. Therefore, these spectra cannot be interpreted using first
order rules [17, page 57].
It should be noted that the
spectrum of thetrans-[Pd(β-AlaH)2Cl2] is similar to that of the trans-[Pt(β-AlaH)2Cl2].
For both spectra (Figure 1(b)), it is impossible to evaluate the chemical
shifts of the individual CH2 groups from the spectra. In order to do
that we should employ a six-spin system of AA′BB′X2 type, where AA′
and BB′ are magnetically nonequivalent protons of the two CH2 groups, and X2 are magnetically equivalent NH2 protons.
In this system, the protons of the CH2 group, which is related to NH2 group, are additionally split
at the NH2 protons. After the suppression of interaction with the NH2 protons, the PMR spectrum (Figure 1(c)) corresponds to an AA′BB′ four-spin system,
is symmetric, and allows us to estimate the chemical shifts of the CH2 groups on the center of each multiplet [17, page 200].
Figure1(d) shows the PMR spectrum
of the cis-[Pt(β-Ala)2]
in D2O. The spectrum only contains the signals of two CH2 groups (the NH2 protons are deuterated in D2O and do not display
in the spectrum). The PMR spectra of bischelates as well as those of
dichlorides allow us to evaluate the chemical shifts of the individual CH2 groups on the centers of multiplets.
The spectrum of thecis-[Pt(β-Ala)2]
also shows that the weak-field signal of the CH2 group combined with
the NH2 group is split at 195Pt (broadened doublet).
It should be noted that for the Pt
and Pdcis-bischelates we succeeded
in recording the signals of the NH2 protons in D2O
because the NH2 protons are deuterated in the trans-bischelates faster than in the cis-bischelates.Table 1
NMR spectral data forβ-AlaH and the Pt(II) and Pd(II) complexes
with β-AlaH.
Complex (solvent)195Pt NMR,
δ, ppm1H NMR, δ, ppm13C NMR, δ, ppmNH2CH2–NH2CH2–COOCOOHCOO−CH2–NH2CH2–COONH3+–(CH2)2–COO− (D2O)——3,102,48179,137,3034,29Trans-[Pt(β-AlaH)2Cl2]
(acetone-d6)−22484,29J2H–Pt = 50 Hz2,982,91172,941,9033,36Trans-[Pd(β-AlaH)2Cl2]
(acetone-d6)—3,452,932,87172,740,5734,01Trans-[Pt(β-Ala)2]
(D2O)−1708—2,812,44———Cis-[Pt(β-Ala)2]
(D2O)−19305,17*J2H–Pt = 60 Hz2,76J2H–Pt = 45 Hz2,43180,241,87J2C–Pt = 30 Hz36,36J3C–Pt = 22 HzTrans-[Pd(β-Ala)2]
(D2O)——2,492,38181,738,4837,82Cis-[Pd(β-Ala)2]
(D2O)—4,34*2,592,46180,639,8637,04* Residual NH2 protons.(a) PMR spectra in the region of CH2 protons recorded in D2O for β-AlaH; (b) PMR spectra in the region of CH2 protons recorded in acetone-d6 for trans-[Pt(β-AlaH)2Cl2]; (c) PMR spectra in the region of CH2 protons recorded in acetone-d6 with NH2 proton coupling suppression for trans-[Pt(β-AlaH)2Cl2]; (d) PMR spectra in the region of CH2 protons recorded in D2O for cis-[Pt(β-Ala)2]. X: broadened signal of the H2O admixture in acetone (spectra b and c); V: DMSO reference in D2O (spectrume d); : broadened doublet of splitting at 195Pt (spectrume d).
(a)(b)(c)(d)195Pt NMR
spectra (Table 1)
The195Pt signal in the
spectrum of the trans-[Pt(β-AlaH)2Cl2] is found in the region of δ⁢~−2200 ppm, as is
the case with the other similar compounds with α-amino acids. The difference between the
chemical shifts of the cis- and trans-bischelate complexes is up to 200 ppm, the signals of the trans-bischelates
lying in a weaker field. Such differences are also observed for the bischelates
with α-amino
acids [18].
It should be noted that the signals
ofcis- and trans-bischelates with β-alanine lie in a stronger field compared to
the signals of similar α-amino acid complexes, the difference being up to 60–70 ppm.13C
NMR spectra
(Table 1)
The spectrum of thetrans-[Pt(β-Ala)2]
could not be recorded because of the very low solubility of this compound in
water.
Table1 shows that the 13C signals of the
protonated COOH group in the trans-[M(β-AlaH)2Cl2] (M = Pt, Pd) lie in a stronger field
than the signals of the coordinate COO groups in the cis- and trans-bischelate
complexes of Pt(II) and Pd(II).IR spectra
(Table2)
As is known, for free amino acids,
which exist as bipolar NH3+CH(R)COO− ions,
there is a broad band of up to 3400 cm−1 in the region of the N = H (ν˜ (NH))
stretching vibrations, while the C = O (ν˜ (CO)) stretching vibrations
display in the region of 1600 cm−1.
For the coordinatedα-amino acids in the Pt(II)
and Pd(II) bischelate complexes, the ν˜ (CO) is recorded in the
region of 1650 cm−1, while the ν˜ (NH)
is found at 3200 cm−1. For example, for the Pt(II) trans-bischelate with glycine, the ν˜ (CO)
is equal to 1643 cm−1, and the ν˜ (NH)
is equal to 3230 and 3090 cm−1. For the similar Pd(II) complex,
the ν˜ (CO) equals 1642 cm−1,
and the ν˜ (NH)
equals 3230 and 3120 cm−1 [19].
For all complexes presented in this
work, the split lines of NH antisymmetric stretching vibrations in the region of
~3200 cm−1 were found as well as NH symmetric stretching vibrations
at ~3100 cm−1, that correspond to the coordinated NH2 group.
In the region of the C = O stretching vibrations for the Pt(II) and Pd(II) bischelates,
theν˜ (CO) is in the range of 1617–1640 cm−1,
which shows that the OCO group is coordinate.
For thetrans-K2[Pt(β-Ala)2I2]
complex with the incoordinate COO group, the ν˜ (CO) is equal to 1602 cm−1,
as is the case with free amino acids.
For thetrans-[M(β-AlaH)2Cl2] complexes (where
M = Pt, Pd) containing the monodentate ligands of β-AlaH,
which is coordinated via the NH2 group and contains the protonated COOH group, the stretching
vibrations, the ν˜ (C = O), reach up to 1710 cm−1, as for
similar compounds with α-amino acids [19].Table 2
IR spectral data for the Pt(II) & Pd(II) complexes withβ-Alanine.
Complexν˜ (NH), cm−1ν˜ (C = O), cm−1Trans-[Pt(β-AlaH)2Cl2]32853254170732083127Trans-[Pd(β-AlaH)2Cl2]3319326017113128Trans-[Pt(β-Ala)2]32683215161731843090Trans-[Pd(β-Ala)2]322530381628Cis-[Pt(β-Ala)2]323530471640Cis-[Pd(β-Ala)2]3233308016343037Trans-K2[Pt(β-Ala)2I2]3246319016023069X-ray
diffraction data (Table3)
In thetrans-[Pd(β-Ala)2] centrosymmetric
molecule (Figure 2(a)), the Pd–O and
Pd–N distances are 2.004 and 2.026 Å. The deviations of atoms from the plane of
the chelate ring may be as high as 0.88 Å (for α-C). The chelate angle is 94.35°, which corresponds to
the transannular distance O⋯N 2.958 Å. The hydrogen bonds between the NH2 groups and the incoordinate atoms of carboxyl O groups link the molecules into
a framework (Figure 2(b)).
In the structure
of thetrans-[Pt(β-Ala)2], both crystallographically independent
molecules are also centrosymmetric. The Pt(II) atom is surrounded by a
square formed by the N donor atoms of the amino groups and the O atoms of the
two alaninate anions (Figure 3(a)). The average
Pt–O and Pt–N bond lengths are 1.996 and 2.028 Å, respectively. As in the trans-[Pd(β-Ala)2] , the C–O
distances for the coordinate O atom of the deprotonated OH group are
appreciably longer than those for the incoordinate atoms (1.29 and 1.23 Å on
the average). The independent molecules differ in the configuration of the
chelate rings. The maximal deviation of nonhydrogen atoms from the plane of the
coordination square is 0.26 Å in the Pt1 molecule and 1.09 Å in the Pt2
molecule (Figure 3(a)). The N–Pt–O
chelate angle in the Pt2 molecule, which is “more planar,” is
95.7(3)°; this is much larger than in the Pt1 molecule (94.0(3)°).
The molecules in
the structure are hydrogen bonded into a framework by N–H⋯O type bonds (Figure 3(b)).
In
the crystallographically independentcis-[Pt(β-Ala)2] molecules
the metal atom also has square planar surroundings (Figure 4(a)). The
average values of the Pt–O and Pt–N bond lengths are 2.015 and 1.997 Å,
respectively. The maximal deviation of nonhydrogen atoms from the coordination
square plane is 0.58 Å in the Pt1 molecule and 0.54 Å (Figure 4(a)) in the Pt2
molecule. The hydrogen bonds link the molecules into layers (Figure 4(b)).
In thetrans-K2[Pt(β-Ala)2I2]•2H2O complex,
the coordination trans-square of Pt
is formed by two I atoms and by the N atoms of the β-alaninate ions. The Pt–I distance is 2.5902(5) Å, and the Pt–N distance
is 2.047(5) Å. The N⋯O distance in β-Ala is 4.197 Å. The carboxylate groups of the β-alaninate ions link the [Pt(β-Ala)2I2] fragments
with K+
ions, thus
forming polymer layers in the structure (Figure 5). The environment of the K
ion includes three O atoms of the
carboxylate groups, two O atoms of the water molecules (dK–O = 2.780(4) − 2.863(5) Å), and two I ions (dK–I = 3.797(1) and 4.285(2) Å), because of which the
layers are linked into a framework.Table 3
Selected stereochemical data for the studied compounds.
Trans-[Pd(β-Ala)2]Trans-[Pt(β-Ala)2]Cis-[Pt(β-Ala)2]K2[Pt(β-Ala)2I2]•2H2OPt–O2.004(2)2.004(2)1.997(5)1.996(6)1.994(7)2.033(7)—2.019(7)2.014(8)Pt–N2.026(2)2.026(2)2.031(7)2.026(8)1.979(9)2.015(8)2.047(5)1.986(9)2.009(7)Pt–Hal———2.5902(5)K–I———3.797(1)4.285(2)K–O———2.780(4)2.820(5)2.808(5)2.863(5)2.851(4)∠ NPtO94.35(8)94.0(3)95.1(3)95.0(3)—96.1(3)94.9(3)C–O1.291(3)1.232(2)1.290(11)1.235(11)1.291(15)1.188(15)1.249(7)1.255(7)1.308(13)1.186(14)1.281(10)1.221(11)1.259(14)1.252(14)1.317(13)1.219(14)C–N1.463(3)1.486(11)1.461(14)1.525(15)1.461(15)1.539(14)1.468(14)Molecular structure oftrans-[Pd(β-Ala)2], atomic numbering, and deviations of atoms (Å) from the plane of the coordination square (a); view of the framework in the structure of complex (b).
(a)(b)Molecular structure of Pt1 and Pt2 intrans-[Pt(β-Ala)2] (a); structure projected on the (001) plane (b).
(a)(b)Molecular structure of Pt1 and Pt2 incis-[Pt(β-Ala)2] and deviations of atoms (Å) from plane of the coordination square (a); structure of a layer (b).
(a)(b)Atomic numbering scheme in an independent fragment (a); structure of the layer (b), and structure of the framework (c) intrans-K2[Pt(β-Ala)2I2]•2H2O.
(a)(b)(c)


## 3.1. Synthesis
of the Pt(II)trans-Isomers (Scheme 1)

The solutions ofβ-AlaH neutralized with an alkali and K2[PtCl4]
were used as the reagents for the synthesis of trans-isomers. The molar ratio of the reagents K2[PtCl4]:β-AlaH:KOH was as follows 1:4.5:2. The structures of complexes were
detected by the 195Pt NMR spectroscopy at each stage of the synthesis.According to the data of [9], the
first stage of the synthesis is heating of the reaction mixture for 5 hours. We
have shown that after heating the aqueous solution of K2[PtCl4]
with the neutralized β-AlaH for 2 hours, the reaction mixture does
not contain the starting reagents. Instead, it contains three forms (I, II, and
III) of the Pt(II) complexes (Scheme 1), complex II being predominant
(~80%). The signal assignment in the 195Pt NMR spectra was carried
out using the data of [12].Scheme 1
Sequence of reactions of K2[PtCl4] with β-alanine.The second stage comprises the
interaction of complexes with HCl. Just after the addition of HCl to the
reaction mixture, it is detected that the solution contains complexes IV, V, and
VI, complex V prevailing (~75%).Complex IV is formed from complex I
as a result of the ring opening and the insertion of Cl− ions at the
site of cleavage of the Pt–OCO bond. Complex V is formed from complex II via the
ring opening and the insertion of the Cl− ion. Complex VI is formed from complex
III via the protonation of the β-alaninate ions of complex III.
The subsequent heating of the reaction mixture in the water bath for ~20 minutes
only results in one complex (complex IV) in the solution. During this period,
complex VI converts into complex V, while complex V transforms into the trans-dichloride IV due to the
replacement of β-AlaH with the Cl− ion on the coordinate Cl-Pt-β-AlaH. The given replacement takes place in accordance with the kinetic
effect of the trans-influence of
ligands. That is, the trans-effect of
Cl exceeds that of the NH2, the group of β-alanine
[13].At the next stage, the yellow
precipitate of thetrans-[Pt(β-AlaH)2Cl2](IV) gradually settles from the
solution. The titration of complex IV with the KOH solution leads to the formation
of yellow K2[Pt(β-Ala)2Cl2] solution,
which is then heated to form a white precipitate of trans-[Pt(β-Ala)2](I).


## 3.2. Synthesis oftrans-Isomers of the Pd(II) Complexes

The problems of isolation of the
individual geometrical isomers of the Pd(II) bisaminoacid complexes withα-amino acids are related
to the trans-cis isomerization
processes. For the first time we described these processes for Pd(II)
bischelates with glycine and α-alanine in [5, 14].The decrease of temperature from
100°C to 0°C at the appropriate
stages of the synthesis rules out the isomerization processes and allows us to
use the same approaches to the synthesis of the Pd(II) complexes as is
the case with the Pt(II) complexes.The interaction of Na2[PdCl4]
with the neutralized β-AlaH in an aqueous solution is likely to
result in the formation of complexes similar to the complexes I, II, and III
(Scheme 1). The treatment with HClconc leads to the trans-[Pd(β-AlaH)2Cl2]
as the only product. The formation of a trans-isomer
as the only product is possible due to the kinetic effect of the trans-influence of ligands as is the
case with the Pt complexes [13].The titration of thetrans-[Pd(β-AlaH)2Cl2]
with an alkaline solution leads to the ring closure and the formation of the trans-[Pd(β-Ala)2].
The ring closure reaction was conducted at room temperature because the trans-bischelate product precipitated
immediately. As the cis-bischelate
readily dissolves in water, it cannot be present in the solid precipitate of the trans-[Pd(β-Ala)2]
as an impurity.The treatment of thetrans-[Pd(β-Ala)2]
with HCl at ~0°C leads to the opening of amino acid cycles and the formation of
the trans-[Pd(β-AlaH)2Cl2].


## 3.3. Synthesis
of thecis-[Pd(β-Ala)2] Complex

Due to its high solubility in water,
thecis-[Pd(β-Ala)2]
complex can hardly be isolated as a solid. That is why the procedures that we
have developed for the synthesis of the Pd(II) cis-bischelates with valine [15] are not applicable for the
preparation of the solid cis-[Pd(β-Ala)2] phase. The kinetic and thermodynamic data for the trans-cis isomerization of the Pd(II)
bischelates with valine are reported in [15]. It can be supposed that the
equilibrium and rate constants of the isomerization reaction are almost similar
for the bischelates where amino acids are bonded to Pd(II) via the NH2 or OCO groups. Thus for the synthesis of the cis-[Pd(β-Ala)2], we have used the kinetic
and thermodynamic data of [15].Thetrans-[Pd(β-Ala)2] was heated with water at 80°C until the starting
precipitate was completely diluted. The trans-isomer
isomerized, and the cis-isomer stayed
in solution. At 80°C the equilibrium constant of the trans-cis process was lower
than at
low temperatures because the reaction is exothermal (see [15]). So the reaction
mixture was abruptly cooled to ~0°C in order to increase the concentration of
the cis-bischelate. Moreover after cooling,
the starting trans-bischelate, which
did not isomerize, precipitated and was filtered off. The solid cis-[Pd(β-Ala)2]
was settled with acetone from the aqueous filtrate solution.The treatment of thecis-[Pd(β-Ala)2]
with HCl did not allow us to form the cis-[Pd(β-AlaH)2Cl2] as is the case with the trans-isomers. Even a highly diluted
solution of HCl resulted not only in the opening of the amino acid cycles, but
also in completing the substitution of the amino acid ligands and the formation
of PdCI42−. Similar processes were observed for the Pd(II)
complexes with valine [15] and for the Pd(II) complexes with aminobutyric acid
[16].


## 3.4. Synthesis
of thecis-Isomers of the Pt(II) Complexes  (Scheme
2)

For the synthesis of thecis-bischelate, we have used K2[PtI4],
which is formed by the reaction of K2[PtCl4]
with KI.Scheme 2
Sequence of reactions of K2[PtI4] with β-alanine.We supposed that the heating of K2[PtI4] with β-AlaH
at pH ~6-7 (pH was kept at this level by adding KOH) led to the formation of cis-K2[Pt(β-Ala)2I2]. The formation of the cis-isomer was expected to be in
agreement with the kinetic effect of the trans-influence
(TI) of the ligands (TI (I−)≫TI(NH2)).Further heating of thecis-K2[Pt(β-Ala)2I2] does not lead to the ring closure as is
the case with the trans-dichlorides.
Instead, it leads to the isomerization of the cis-K2[Pt(β-Ala)2I2]
and the formation of the trans-K2[Pt(β-Ala)2I2]. After heating for 10 hours, the
solution only contains one form of δ(195Pt) = −3408 ppm. This new form
was isolated as a single crystal and identified by the X-ray diffraction
analysis, which confirmed that it was the trans-K2[Pt(β-Ala)2I2].To synthesize thecis-[Pt(β-Ala)2],
a solution of AgNO3 was added to the solution of the cis-K2[Pt(β-Ala)2I2]. The resulting AgI precipitate was
filtered off. The filtrate solution contained only one form of the cis-[Pt(β-Ala)2]
complex (δ(195Pt)
= −1923 ppm).In addition to the main product, thecis-[Pt(β-Ala)2],
the solution contained KCl and KNO3. We added acetone to the
reaction mixture (water:acetone ~1:2) to separate the desired product from
inorganic salts. Cis-[Pt(β-Ala)2] was the only substrate that precipitated under such
conditions.PMR Spectra (Table1)
The PMR spectrum ofβ-AlaH (Figure 1(a)) in D2O contains two triplets of two CH2 groups. The spectrum corresponds to an A2X2 four-spin system with magnetically equivalent protons in each CH2 group [17, page 54].
Figure1 shows that the coordinate β-alanine (spectra b, c, and d) has a more complex spectrum than the incoordinate
β-alanine (spectrum a) in the region of CH2 protons. The
spectrum contains more lines, and their intensities are distorted. This
indicates that the protons of both CH2 groups are magnetically
nonequivalent. Therefore, these spectra cannot be interpreted using first
order rules [17, page 57].
It should be noted that the
spectrum of thetrans-[Pd(β-AlaH)2Cl2] is similar to that of the trans-[Pt(β-AlaH)2Cl2].
For both spectra (Figure 1(b)), it is impossible to evaluate the chemical
shifts of the individual CH2 groups from the spectra. In order to do
that we should employ a six-spin system of AA′BB′X2 type, where AA′
and BB′ are magnetically nonequivalent protons of the two CH2 groups, and X2 are magnetically equivalent NH2 protons.
In this system, the protons of the CH2 group, which is related to NH2 group, are additionally split
at the NH2 protons. After the suppression of interaction with the NH2 protons, the PMR spectrum (Figure 1(c)) corresponds to an AA′BB′ four-spin system,
is symmetric, and allows us to estimate the chemical shifts of the CH2 groups on the center of each multiplet [17, page 200].
Figure1(d) shows the PMR spectrum
of the cis-[Pt(β-Ala)2]
in D2O. The spectrum only contains the signals of two CH2 groups (the NH2 protons are deuterated in D2O and do not display
in the spectrum). The PMR spectra of bischelates as well as those of
dichlorides allow us to evaluate the chemical shifts of the individual CH2 groups on the centers of multiplets.
The spectrum of thecis-[Pt(β-Ala)2]
also shows that the weak-field signal of the CH2 group combined with
the NH2 group is split at 195Pt (broadened doublet).
It should be noted that for the Pt
and Pdcis-bischelates we succeeded
in recording the signals of the NH2 protons in D2O
because the NH2 protons are deuterated in the trans-bischelates faster than in the cis-bischelates.Table 1
NMR spectral data forβ-AlaH and the Pt(II) and Pd(II) complexes
with β-AlaH.
Complex (solvent)195Pt NMR,
δ, ppm1H NMR, δ, ppm13C NMR, δ, ppmNH2CH2–NH2CH2–COOCOOHCOO−CH2–NH2CH2–COONH3+–(CH2)2–COO− (D2O)——3,102,48179,137,3034,29Trans-[Pt(β-AlaH)2Cl2]
(acetone-d6)−22484,29J2H–Pt = 50 Hz2,982,91172,941,9033,36Trans-[Pd(β-AlaH)2Cl2]
(acetone-d6)—3,452,932,87172,740,5734,01Trans-[Pt(β-Ala)2]
(D2O)−1708—2,812,44———Cis-[Pt(β-Ala)2]
(D2O)−19305,17*J2H–Pt = 60 Hz2,76J2H–Pt = 45 Hz2,43180,241,87J2C–Pt = 30 Hz36,36J3C–Pt = 22 HzTrans-[Pd(β-Ala)2]
(D2O)——2,492,38181,738,4837,82Cis-[Pd(β-Ala)2]
(D2O)—4,34*2,592,46180,639,8637,04* Residual NH2 protons.(a) PMR spectra in the region of CH2 protons recorded in D2O for β-AlaH; (b) PMR spectra in the region of CH2 protons recorded in acetone-d6 for trans-[Pt(β-AlaH)2Cl2]; (c) PMR spectra in the region of CH2 protons recorded in acetone-d6 with NH2 proton coupling suppression for trans-[Pt(β-AlaH)2Cl2]; (d) PMR spectra in the region of CH2 protons recorded in D2O for cis-[Pt(β-Ala)2]. X: broadened signal of the H2O admixture in acetone (spectra b and c); V: DMSO reference in D2O (spectrume d); : broadened doublet of splitting at 195Pt (spectrume d).
(a)(b)(c)(d)195Pt NMR
spectra (Table 1)
The195Pt signal in the
spectrum of the trans-[Pt(β-AlaH)2Cl2] is found in the region of δ⁢~−2200 ppm, as is
the case with the other similar compounds with α-amino acids. The difference between the
chemical shifts of the cis- and trans-bischelate complexes is up to 200 ppm, the signals of the trans-bischelates
lying in a weaker field. Such differences are also observed for the bischelates
with α-amino
acids [18].
It should be noted that the signals
ofcis- and trans-bischelates with β-alanine lie in a stronger field compared to
the signals of similar α-amino acid complexes, the difference being up to 60–70 ppm.13C
NMR spectra
(Table 1)
The spectrum of thetrans-[Pt(β-Ala)2]
could not be recorded because of the very low solubility of this compound in
water.
Table1 shows that the 13C signals of the
protonated COOH group in the trans-[M(β-AlaH)2Cl2] (M = Pt, Pd) lie in a stronger field
than the signals of the coordinate COO groups in the cis- and trans-bischelate
complexes of Pt(II) and Pd(II).IR spectra
(Table2)
As is known, for free amino acids,
which exist as bipolar NH3+CH(R)COO− ions,
there is a broad band of up to 3400 cm−1 in the region of the N = H (ν˜ (NH))
stretching vibrations, while the C = O (ν˜ (CO)) stretching vibrations
display in the region of 1600 cm−1.
For the coordinatedα-amino acids in the Pt(II)
and Pd(II) bischelate complexes, the ν˜ (CO) is recorded in the
region of 1650 cm−1, while the ν˜ (NH)
is found at 3200 cm−1. For example, for the Pt(II) trans-bischelate with glycine, the ν˜ (CO)
is equal to 1643 cm−1, and the ν˜ (NH)
is equal to 3230 and 3090 cm−1. For the similar Pd(II) complex,
the ν˜ (CO) equals 1642 cm−1,
and the ν˜ (NH)
equals 3230 and 3120 cm−1 [19].
For all complexes presented in this
work, the split lines of NH antisymmetric stretching vibrations in the region of
~3200 cm−1 were found as well as NH symmetric stretching vibrations
at ~3100 cm−1, that correspond to the coordinated NH2 group.
In the region of the C = O stretching vibrations for the Pt(II) and Pd(II) bischelates,
theν˜ (CO) is in the range of 1617–1640 cm−1,
which shows that the OCO group is coordinate.
For thetrans-K2[Pt(β-Ala)2I2]
complex with the incoordinate COO group, the ν˜ (CO) is equal to 1602 cm−1,
as is the case with free amino acids.
For thetrans-[M(β-AlaH)2Cl2] complexes (where
M = Pt, Pd) containing the monodentate ligands of β-AlaH,
which is coordinated via the NH2 group and contains the protonated COOH group, the stretching
vibrations, the ν˜ (C = O), reach up to 1710 cm−1, as for
similar compounds with α-amino acids [19].Table 2
IR spectral data for the Pt(II) & Pd(II) complexes withβ-Alanine.
Complexν˜ (NH), cm−1ν˜ (C = O), cm−1Trans-[Pt(β-AlaH)2Cl2]32853254170732083127Trans-[Pd(β-AlaH)2Cl2]3319326017113128Trans-[Pt(β-Ala)2]32683215161731843090Trans-[Pd(β-Ala)2]322530381628Cis-[Pt(β-Ala)2]323530471640Cis-[Pd(β-Ala)2]3233308016343037Trans-K2[Pt(β-Ala)2I2]3246319016023069X-ray
diffraction data (Table3)
In thetrans-[Pd(β-Ala)2] centrosymmetric
molecule (Figure 2(a)), the Pd–O and
Pd–N distances are 2.004 and 2.026 Å. The deviations of atoms from the plane of
the chelate ring may be as high as 0.88 Å (for α-C). The chelate angle is 94.35°, which corresponds to
the transannular distance O⋯N 2.958 Å. The hydrogen bonds between the NH2 groups and the incoordinate atoms of carboxyl O groups link the molecules into
a framework (Figure 2(b)).
In the structure
of thetrans-[Pt(β-Ala)2], both crystallographically independent
molecules are also centrosymmetric. The Pt(II) atom is surrounded by a
square formed by the N donor atoms of the amino groups and the O atoms of the
two alaninate anions (Figure 3(a)). The average
Pt–O and Pt–N bond lengths are 1.996 and 2.028 Å, respectively. As in the trans-[Pd(β-Ala)2] , the C–O
distances for the coordinate O atom of the deprotonated OH group are
appreciably longer than those for the incoordinate atoms (1.29 and 1.23 Å on
the average). The independent molecules differ in the configuration of the
chelate rings. The maximal deviation of nonhydrogen atoms from the plane of the
coordination square is 0.26 Å in the Pt1 molecule and 1.09 Å in the Pt2
molecule (Figure 3(a)). The N–Pt–O
chelate angle in the Pt2 molecule, which is “more planar,” is
95.7(3)°; this is much larger than in the Pt1 molecule (94.0(3)°).
The molecules in
the structure are hydrogen bonded into a framework by N–H⋯O type bonds (Figure 3(b)).
In
the crystallographically independentcis-[Pt(β-Ala)2] molecules
the metal atom also has square planar surroundings (Figure 4(a)). The
average values of the Pt–O and Pt–N bond lengths are 2.015 and 1.997 Å,
respectively. The maximal deviation of nonhydrogen atoms from the coordination
square plane is 0.58 Å in the Pt1 molecule and 0.54 Å (Figure 4(a)) in the Pt2
molecule. The hydrogen bonds link the molecules into layers (Figure 4(b)).
In thetrans-K2[Pt(β-Ala)2I2]•2H2O complex,
the coordination trans-square of Pt
is formed by two I atoms and by the N atoms of the β-alaninate ions. The Pt–I distance is 2.5902(5) Å, and the Pt–N distance
is 2.047(5) Å. The N⋯O distance in β-Ala is 4.197 Å. The carboxylate groups of the β-alaninate ions link the [Pt(β-Ala)2I2] fragments
with K+
ions, thus
forming polymer layers in the structure (Figure 5). The environment of the K
ion includes three O atoms of the
carboxylate groups, two O atoms of the water molecules (dK–O = 2.780(4) − 2.863(5) Å), and two I ions (dK–I = 3.797(1) and 4.285(2) Å), because of which the
layers are linked into a framework.Table 3
Selected stereochemical data for the studied compounds.
Trans-[Pd(β-Ala)2]Trans-[Pt(β-Ala)2]Cis-[Pt(β-Ala)2]K2[Pt(β-Ala)2I2]•2H2OPt–O2.004(2)2.004(2)1.997(5)1.996(6)1.994(7)2.033(7)—2.019(7)2.014(8)Pt–N2.026(2)2.026(2)2.031(7)2.026(8)1.979(9)2.015(8)2.047(5)1.986(9)2.009(7)Pt–Hal———2.5902(5)K–I———3.797(1)4.285(2)K–O———2.780(4)2.820(5)2.808(5)2.863(5)2.851(4)∠ NPtO94.35(8)94.0(3)95.1(3)95.0(3)—96.1(3)94.9(3)C–O1.291(3)1.232(2)1.290(11)1.235(11)1.291(15)1.188(15)1.249(7)1.255(7)1.308(13)1.186(14)1.281(10)1.221(11)1.259(14)1.252(14)1.317(13)1.219(14)C–N1.463(3)1.486(11)1.461(14)1.525(15)1.461(15)1.539(14)1.468(14)Molecular structure oftrans-[Pd(β-Ala)2], atomic numbering, and deviations of atoms (Å) from the plane of the coordination square (a); view of the framework in the structure of complex (b).
(a)(b)Molecular structure of Pt1 and Pt2 intrans-[Pt(β-Ala)2] (a); structure projected on the (001) plane (b).
(a)(b)Molecular structure of Pt1 and Pt2 incis-[Pt(β-Ala)2] and deviations of atoms (Å) from plane of the coordination square (a); structure of a layer (b).
(a)(b)Atomic numbering scheme in an independent fragment (a); structure of the layer (b), and structure of the framework (c) intrans-K2[Pt(β-Ala)2I2]•2H2O.
(a)(b)(c)


## 4. Conclusion

First, the techniques have been developed of the synthesis of bisaminoacid
complexes Pt(II) and Pd(II): (1) the interaction of K2[PtCl4] or Na2[PdCl4]
with β-alanine
resulted in the trans-isomers only;
(2) the synthesis of the cis-[Pt(β-Ala)2] can be done by the interaction of K2[PtI4]
with β-alanine; (3) for the synthesis of the cis-[Pd(β-Ala)2],
we have used the kinetic and thermodynamic data for the trans-cis isomerization of
the Pd(II) bischelates with α-amino acid. Second, the investigation of
the NMR, IR spectral, and crystal structures have been reported for the
individual isomers: the trans-[M(β-AlaH)2Cl2] and the cis-[M(β-Ala)2] (M = Pt, Pd).



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*Source: 983725-2008-05-26.xml*