STEREOISOMERIC Pd(II) COMPLEXES
59
lution and during time variation before the equilibꢀ
The molecule of [Pd(RꢀThr)(SꢀThr)] is cenꢀ
rium established; this provided more accurate identifiꢀ trosymmetric. The Pd environment is a square formed
cation of the signals from all species in solution.
As an example, Fig. 1 presents the H NMR spectra
of (a) pure cisꢀ[Pd(RꢀalloThr)(SꢀalloThr)] and (b),
by donor N atoms of the amino groups and O atoms of
two threonine anions (Fig. 3a). The Pd–O and Pd–N
distances are 1.981(4) and 2.019(5) Å, respectively
1
(
Table 4). The C–O distance for coordinated oxygen
(
c) the equilibrium mixture in the CH proton region,
3
13
of the COO group (1.280(7) Å) is considerably longer
than that for the nonꢀcoordinated atom (1.219(6) Å).
The asymmetric ꢀcarbon atoms of two coordinated
and Fig. 2 shows the C NMR spectrum of (a) pure
cisꢀ[Pd(RꢀalloThr)(SꢀalloThr)] and (b) the equilibꢀ
rium mixture. Note that in Fig. 1a, a signal from minor
α
13
threoninate anions have different absolute configuraꢀ
tions.
acetone impurity is recorded at 2.22 ppm. The C
NMR signals (Fig. 2) of both the individual comꢀ
pound and the equilibrium mixture exhibit additional
In the structure, the [Pd(RꢀThr)(SꢀThr)] moleꢀ
carbon signals (
) of the CH group bound to partially cules are stacked. The planes of the Pd squares in the
Δ
deuterated NH group (NHD).
neighboring stacks symmetrically related to each other
by a С2 axis are arranged at 79 angles relative to each
other and at 39 angle to the [010] direction. The
outerꢀsphere water molecules connect the [Pd(Rꢀ
Thr)(SꢀThr)] molecules by N ···O and O–H···
hydrogen bonds (Fig. 3b) to form layers parallel to the
2
.6°
From the signal intensity ratio in the spectra of
equilibrium mixtures, one can estimate the ratio of the
cis and trans isomers in the mixture, which is ~4 : 1,
and the diastereomer ratio for each geometric isomer,
which is ~1 : 1.
IR spectra. The solid phases of the complexes were
studied by IR spectroscopy. Table 3 presents the data
from IR spectra in the regions of the NH ꢀ and COO
characteristic bands for all of the obtained comꢀ
pounds.
.8°
–H
O
(
011) plane.
The cisꢀ[Pd(RꢀalloThr)(SꢀalloThr)]
· (CH ) CO
3 2
molecules are located in a general position of space
group 2 / . The Pd coordination sphere is a distorted
2
P
n
1
square formed by two N atoms of the amino groups
and two O atoms of the carboxy groups of the allothreꢀ
oninate anions (Fig. 4). The average Pd–O and Pd–N
For free amino acids SerH, ThrH, and alloThrH,
+
−
which exist as bipolar ions NH RCHCOO , the IR distances are 2.010(2) and 2.014(3) Å, respectively.
3
–1
spectra exhibited broad intense bands at ~3030 cm
corresponding to stretching vibrations of the hydroꢀ the opposing OPdO angle (95
The NPdN angle (97
.
75(5)
°
) is somewhat larger than
.
37(4) ). As in the strucꢀ
°
+
ture of transꢀ[Pd(RꢀThr)(SꢀThr)], the average C–O
distance for the coordinated oxygen atoms of the COO
group (1.2971(4) Å) exceeds substantially the average
C–O distance for nonꢀcoordinated atoms (1.2309(1) Å).
The chelate rings are little distorted relative to the
plane of the coordination square, the greatest deviaꢀ
tion being 0.33 Å. The asymmetric ꢀcarbon atoms of
two coordinated allothreoninate anions have different
absolute configurations.
Layers in which the complex molecules are hydroꢀ
gen bonded can be distinguished in the structure; aceꢀ
tone molecules form weak hydrogen bonds with the
amino groups of the allothreoninate anions from difꢀ
ferent layers, the shortest N1···O1S contact being
genꢀbonded N H 3 and OH groups, while at 1638–
–1
1
595 cm , the spectra showed
ν
as(CO) stretching
–
bands for the COO groups containing a contribution
+
of the
δ
d(NH3) bending mode.
For the amino acids bound in Pd(II) and Pt(II) bisꢀ
–
1
α
chelates, the
as
ν
(NH) mode occurs at ~3200 cm , andꢀ
–1
ν
(CO) is at ~1650 cm . For example, in the spectrum
of Pd(II) transꢀbischelate with glycine,
ν
as(CO) =
(NH) = 3230, 3120 cm [19, p. 260].
For all of the studied complexes with hydroxy
amino acids, (NH) and as(CO) bands were found,
–1
ν
–1
1
642 cm ,
ν
ν
which confirm the bidentate coordination of the
amino acids through the NH and OCO groups.
2
2.920(1) Å (Table 5).
It is noteworthy that the IR spectra of cisꢀbischelate
exhibit more bands in both the NH and COO regions,
as was to be expected [19, p. 262].
2
REFERENCES
Among the synthesized transꢀbischelates, there is a
1. L. M. Volshtein, Koord. Khim.
2. A. Jakovidis and N. Hadjiliadis, Coord. Chem. Rev.
35/136, 17 (1997).
3. L. F. Krylova and I. S. Kuprov, Zh. Neorg. Khim.
4), 605 (2001) [Russ. J. Inorg. Chem. 46 (4), 528
(2001)].
4. M. Watabe, M. Kai, and K. Goto, J. Inorg. Biochem.
97, 240 (2003).
5. L. F. Krylova, L. M. Kovtunova, and G. V. Romanenko,
1 (5), 595 (1975).
diastereomer pair, transꢀ[Pd(SꢀThr) ] and trans
ꢀ
2
[
Pd(RꢀThr)(SꢀThr)]. Their IR spectra differ in that,
1
for the mixedꢀligand diastereomer, the
as(CO) band at
ν
46
–1
1
630 cm is split into two components.
Xꢀray diffraction analysis. The structure of cis
Pd(SꢀSer) ] was reported previously [7]. The strucꢀ
(
ꢀ
[
2
tures of all other compounds are unknown. The crysꢀ
tals of transꢀ[Pd(RꢀThr)(SꢀThr)] were grown from an
aqueous solution and the crystals of cisꢀ[Pd(Rꢀalloꢀ
Thr)(SꢀalloThr) were obtained from a water–acetone
solution.
Zh. Strukt. Khim. 47 (4), 670 (2006).
6. L. D. Pettit and M. Bezer, J. Inorg. Biochem. 61, 97
(1985).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 1 2011
Krylova
