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www.elsevier.com/locate/poly
Polyhedron 24 (2005) 1701–1709
Layered crystal structure of the trans(O5O6) isomer of potassium(1,3-propanediamine-N,N 0-diacetato-N,N 0-di-3-propionato)
cobaltate(III) trihydrate, trans(O5O6)-K[Co(1,3-pddadp)] Æ 3H2O,stabilized by ionic, hydrogen bond and C@O dipolar interactions:
Conformational analysis of Co(III) complexes with the1,3-propanediamine-N,N 0-diacetate-N,N 0-di-3-propionate ligand
Sonja Grubisic a, Svetozar R. Niketic b, Dusanka D. Radanovic a,*,Urszula Rychlewska c,*, Beata War _zajtis c
a Institute of Chemistry, Technology and Metallurgy, University of Belgrade, Njegoseva 12, P.O. Box 815, 11001 Belgrade, Serbia and Montenegrob Department of Chemistry, Faculty of Science, University of Belgrade, Studentski trg 16, P.O. Box 158, 11001 Belgrade, Serbia and Montenegro
c Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
Received 18 March 2005; accepted 25 April 2005
Available online 27 July 2005
This article is dedicated to the memory of Dusan J. Radanovic, Professor of Inorganic Chemistry at the Faculty of Science, University of Kragujevac.
In this way we want to express our appreciation for his contribution to the development of coordination chemistry of cobalt(III)-edta-type complexes
Abstract
The hexadentate trans(O5O6)-K[Co(1,3-pddadp)] Æ 3H2O complex (where 1,3-pddadp represents the 1,3-propanediamine-N,N 0-
diacetate-N,N 0-di-3-propionate ion) has been characterized by single-crystal X-ray crystallography. The complex crystallizes in
the P2/c space group of the monoclinic crystal system. In the crystal structure of trans(O5O6)-K[Co(1,3-pddadp)] Æ 3H2O the potas-
sium ions and two solvent water molecules (O1W and O3W) are settled on a twofold axis of symmetry. The octahedral complex
units trans(O5O6)-[Co(1,3-pddadp)]� are bridged by carboxylate oxygen atoms with the potassium ions to build a two-dimensional
polymer structure, separated by layers formed by hydrogen bonded water molecules and carboxylate oxygens. The coordination
polyhedra around K1 and K2 are found to be distorted square antiprism and twisted bi-capped trigonal prism, respectively. Con-
formational analysis of the three possible geometrical isomers (trans(O5), trans(O5O6) and trans(O6)) of the [Co(1,3-pddadp)]� com-
plex, was performed using the Consistent Force Field (CFF) program, with the parameters developed previously for edta-type
complexes and new parameters for Co(III). Molecular mechanics (MM) calculations reproduced very well the crystallographically
characterized structures (trans(O5O6)-[Co(1,3-pddadp)]� and trans(O6)-[Co(1,3-pddadp)]
�).
� 2005 Elsevier Ltd. All rights reserved.
Keywords: Aminopolycarboxylate complexes; X-ray crystal structure; Force-field calculations; Layered materials; H-bonding; Carbonyl dipolar
interactions
0277-5387/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.04.035
* Corresponding authors. Tel.: +381 11 773 270; fax: +381 11 636 061 (D.D. Radanovic), Fax: +48 61 865 8008 (U. Rychlewska).
E-mail addresses: [email protected] (D.D. Radanovic), [email protected] (U. Rychlewska).
1702 S. Grubisic et al. / Polyhedron 24 (2005) 1701–1709
1. Introduction
In the second half of the last century many aminopo-
lycarboxylate ligands, structurally related to edta (the
ethylenediaminetetraacetate ion), have been prepared
and used to form hexadentate complexes with transitionmetal ions [1,2]. One such ligand is the 1,3-propanedi-
amine-N,N 0-diacetate-N,N 0-di-3-propionate ion (1,3-
pddadp), Fig. 1(a), having a lengthened diamine and
two carboxylate chains with respect to edta. In the reac-
tions between 1,3-pddadp and metal ions with hexaden-
tate coordination of this ligand, theoretically three
geometrical isomers are possible: trans(O5), trans(O5O6)
and trans(O6); where O5 and O6 refer to the five- and six-membered N–O rings, respectively, Fig. 1(b). The same
geometrical isomers are also possible for hexadentate
[M(eddadp)]n� (where eddadp is the ethylenediamine-
N,N 0-diacetate-N,N 0-di-3-propionate ion) complexes,
and for these complexes it was found that six-membered
b-alaninate rings serve better for the formation of less-
strained G rings, favoring the trans(O5) geometry [2–
13]. Contrary to this, all possible isomers of the[M(1,3-pddadp)]n� complex have been reported for
Cr(III) [14], but only two isomers (trans(O5O6) and
trans(O6) for Co(III) [15,16] and trans(O5) and trans-
(O5O6) for Rh(III) [17,18] and Ni(II) [19]) have been iso-
lated and characterized. In addition, only one dominant
isomer of the same complex (trans(O6)) of Cu(II) [20]
has been described. The so far available X-ray data are
limited to: trans(O6)-[Cr(1,3-pddadp)]� [14], trans (O6)-
[Co(1,3-pddadp)]� [16,21], trans(O5)-[Rh(1,3-pddadp)]�
[18], trans(O5O6)-[Rh(1,3-pddadp)]� [18], trans(O5)-
[Ni(1,3-pddadp)]2� [19] and trans(O6)-[Cu(1,3-pddadp)]2�
[20] complexes.
In the reaction of the 1,3-pddadp ligand with Co(III)
ion two geometrical isomers (trans(O5O6) and trans(O6))
of the hexadentate [Co(1,3-pddadp)]� complex have
been obtained, resolved and characterized [15]. The(+)546-trans(O5O6)-[Co(1,3-pddadp)]
� and (+)546-trans-
Fig. 1. Formula of the 1,3-pddadp ligand (a); and possible geometrical
isomers of the hexadentate [M(1,3-pddadp)]n� and/or [M(eddadp)]n�
complex (b); O5 and O6 refer to the five- and six-membered N–O rings,
respectively.
(O6)-[Co(1,3-pddadp)]� enantiomers, with a positive
CD peak at the lowest energy in the first spin-allowed
d–d absorption band region, were tentatively assigned
the K absolute configuration. The trans(O6) geometry
of [Co(1,3-pddadp)]� has been established in the crystal
structure of racemate trans(O6)-K[Co(1,3-pddadp)] Æ3H2O [16], as well as in the crystal structure of optically
pure compounds: (–)589-trans(O6)-K1/2(H5O2)1/2[Co(1,3-
pddadp)] Æ 2H2O [21] and (–)589-trans(O6)-Li[Co(1,3-
pddadp)] Æ 7H2O [21]. The crystallographic studies of
Co(III) amine carboxylates have been of particular
interest in connection with different kinds of ‘‘mysteries’’
of hydronium ions [21]. Namely, it has been found that
minor variations in composition and/or stereochemistryof Co(III) amine carboxylates are sufficient to influ-
ence the crystallization of the hydronium ion or the
mixed potassium–hydronium salts, as evidenced in the
crystal structure of (–)589-trans(O6)-K1/2(H5O2)1/2[Co-
(1,3-pddadp)] Æ 2H2O [21].
The characterization of the trans(O5O6) geometry of
the [Co(1,3-pddadp)]� complex using crystallographic
methods is described here first. In addition, molecularmechanics (MM) calculations were applied for establish-
ing the relative energies of the three geometrical isomers:
trans(O5), trans(O5O6) and trans(O6) of the [Co(1,3-
pddadp)]� complex.
2. Experimental
The investigated complex trans(O5O6)-[Co(1,3-
pddadp)]� was prepared according to the previously de-
scribed procedure [15]. Recrystallization of this complex
was accomplished from hot water by adding ethanol andcooling of the solution in a refrigerator.
2.1. Crystallographic data collection and refinement of the
structure
For the hexadentate trans(O5O6)-K[Co(1,3-pddadp)] Æ3H2O complex, X-ray analysis was performed on the ba-
sis of the reflection intensities measured at 293 K on aKM4CCD kappa-geometry diffractometer [22] using
graphite monochromated Mo Ka radiation.
Crystal data: KCoC13H24N2O11 (FW = 482.37),
monoclinic, space group P2/c, a = 14.591(3), b =
9.815(2), c = 12.922(3) A, b = 94.06(3)�, V = 1845.9(7)
A3, Z = 4, Dcalc = 1.736 g cm�3, k (Mo Ka) = 0.71073
A, T = 293 K, l = 1.218 mm�1, F(000) = 1000.
The structure was solved by direct methods usingSHELXS97 [23] and refined by least-squares techniques
with SHELXL97 [24] to R = 0.057 and Rw = 0.151. Aniso-
tropic thermal parameters were employed for the non-
hydrogen atoms. The positions of the hydrogen atoms
attached to the C-atoms were calculated at standardized
distances of 0.96 A. An attempt to localize water hydro-
S. Grubisic et al. / Polyhedron 24 (2005) 1701–1709 1703
gens on subsequent difference Fourier maps was not
fully successful. Moreover, one of the hydrogen atoms
connected to O4W formed a very short non-bonding
contact with its inversion related equivalent (H6W� � �H6W(2 � x, �y, �z) 1.21 A). Therefore, we have as-
sumed the presence of a disordered configuration, withhalf occupancy of one of the two O4W water hydrogens,
but the alternative position of this hydrogen atom could
not be determined on the subsequent difference Fourier
maps. We were also unable to locate one of the two
hydrogen atoms connected to O1W. During the struc-
ture determination process it became obvious that this
hydrogen must also be disordered, this time over the
two sites that are related by a twofold axis. The disordermodel for the H-atom positions allowed us to postulate
the presence, in the crystal, of statistically distributed,
anti-parallel homodromic hydrogen bonded water
chains (see Fig. 1S in the supplementary material). All
OW–H distances have been standardized to a value of
0.85 A. The hydrogen atoms were refined using a ‘‘riding
model’’ with isotropic temperature factors 30% higher
than the isotropic equivalent for the atom to which theH-atom was bonded. A Siemens Stereochemical Work-
station was used to prepare the drawings [25].
2.2. Molecular mechanics calculations
Conformational analysis of the three geometrical iso-
mers of the [Co(1,3-pddadp)]� complex was carried out
using the consistent force field (CFF) conformationalprogram [26] with force field parameters particularized
earlier [27,28]. The only new parameters are for the cobalt
atom and the values are given in Table 1. The conforma-
tional energy was calculated from the following equation:
Etotal ¼ REb þ REh þ REu þ REnb þ REe; ð1Þwhere the summations are over all energy contributions
from bond stretching (Eb), angle bending (Eh), torsionangle (Eu), non-bonded (Enb) and electrostatic interac-
Table 1
Additional CFF parameters for edta-type complexes
Bond stretching kr (kcal/mol A2) r0 (A)
M–O 500.00 1.910
M–N 500.00 1.895
Angle bending kh (kcal/mol rad2) h0 (rad)N–M–N 90.95 1.571
M–O–K 180.01 2.184
Electrostatic q (esu)
M 1.118
van der Waals e* (kcal/mol) r* (A)
M—N 0.033 4.02
C—M 0.030 4.10
M—O 0.032 3.94
M—Q 0.036 3.94
M—H 0.031 3.70
tions (Ee). The potential functions and parameters con-
stituting the energy terms in Eq. (1) have been described
previously [29], and we used essentially the same forms
in this study, except the type for the non-bonded poten-
tial function. In this work we used the Lennard–Jones
�12-6� rather then the Lennard–Jones �9-6� type functionand this approach proved to be quite adequate for the
present study. With this potential function we recalcu-
lated the conformations of the [Cr(ed3p)(H2O)] (ed3p
is the ethylenediamine-N,N,N 0-tri-3-propionate) and
[Cr(ed3a)(H2O)] (ed3a is the ethylenediamine-N,N,N 0-
triacetate) complexes and obtained practically the same
results as previously reported [27,28].
The force field is parameterized on the basis of thetwo different types of carbon atom (sp3 – (C) and sp2
– (C 0) carbons), two different types of oxygen atom (car-
bonyl (O 0) and coordinated (O) oxygens), one type of
hydrogen (H) and of nitrogen (N), as well as the central
metal atom (Co). Comprehensive preliminary calcula-
tions did not justify the distinction between aliphatic
carbons from glycinate, b-alaninate and 1,3-propanedi-
amine chelate rings. All the stable conformers werefound by energy minimization of the numerous theoret-
ically possible initial structures having all the permissible
conformations of 1,3-propanediamine and b-alaninaterings. By this strategy we believe that we have achieved
a comprehensive and reliable spanning of the three geo-
metrical isomers of [Co(1,3-pddadp)]�. The procedure
used in the generation of the initial structures is similar
to that in our previous paper [27].Geometry optimizations were carried out using the
combination of steepest-descent, Davidon–Fletcher–
Powell and Newton–Raphson methods [26]. The steepest-
descent and Davidon–Fletcher–Powell methods were
Fig. 2. Molecular structure of the complex anion trans(O5O6)-[Co(1,3-
pddadp)]� in trans(O5O6)-K[Co(1,3-pddadp)] Æ 3H2O.
Table 2
Selected bond distances (A) and bond angles (�) for trans(O5O6)-
K[Co(1,3-pddadp)] Æ 3H2O
Bond distances
K1–O4 2.697(3)
K1–O2i 2.832(4)
K1–O2Wii 3.037(5)
K1–O6ii 3.190(4)
K2–O1 2.843(3)
K2–O3 2.796(3)
K2–O5 2.998(3)
K2–O6ii 2.779(3)
Co1–O1 1.925(3)
Co1–O3 1.903(3)
Co1–O5 1.885(3)
Co1–O7 1.908(3)
Co1–N1 1.970(3)
Co1–N2 1.988(3)
Bond angles
O4–K1–O4iii 135.1 (2)
O4–K1–O2i 134.70(11)
O4–K1–O2iv 85.81(11)
O2i–K1–O2iv 68. 8(2)
O4–K1–O2Wii 67.39(14)
O2i–K1–O2Wii 79.75(13)
O2iv– K1–O2Wii 98.68(11)
O4–K1–O2Wv 113.39(12)
O2Wii– K1–O2Wv 178.1(2)
O4–K1–O6v 70.98(10)
O2i–K1–O6v 151.15(9)
O2Wii–K1–O6v 128.45(13)
O4–K1–O6ii 77.46(10)
O2i–K1–O6ii 107.29(10)
O2Wii–K1–O6ii 53.24(10)
O6v–K1–O6ii 89.40(13)
O6ii–K2–O6v 107.7(2)
O6ii–K2–O3 78.86(10)
O6v–K2–O3 83.67(10)
O3iii–K2–O3 150.19(13)
O6ii–K2–O1 122.32(9)
O6v–K2–O1 99.78(9)
O3–K2–O1 54.72(8)
O1–K2–O1iii 106.68(12)
O3–K2–O5iii 140.66(8)
O1–K2–O5iii 99.36(9)
O6ii–K2–O5 71.36(9)
O6v–K2–O5 137.06(9)
O3–K2–O5 53.59(8)
O1–K2–O5 54.54(8)
O5iii–K2–O5 139.08(12)
O5–Co1–O3 87.48(13)
O5–Co1–O7 176.21(13)
O3–Co1–O7 88.75(13)
O5–Co1–O1 89.41(12)
O3–Co1–O1 85.25(12)
O7–Co1–O1 90.62(13)
O5–Co1–N1 87.23(14)
O3–Co1–N1 92.22(14)
O7–Co1–N1 92.57(14)
O1–Co1–N1 175.89(14)
O5–Co1–N2 89.01(14)
O3–Co1–N2 169.43(14)
O7–Co1–N2 94.77(14)
Table 2 (continued)
Bond angles
O1–Co1–N2 84.75(13)
N1–Co1–N2 97.6(2)
i�x + 1, y � 1, �z + 0.5.ii�x + 1, �y + 1, �z.iii�x + 1, y, �z + 0.5.ivx, y � 1, z.vx, �y + 1, z + 0.5.
1704 S. Grubisic et al. / Polyhedron 24 (2005) 1701–1709
mostly used, in that order, for initial exploratory
searches and minimizations of conformations far from
equilibrium. The number of iterations varied widely in
the optimization experiments. In particularly difficult
cases it was necessary to alternate between these two
procedures more than once. To approach true minima
Newton–Raphson iterations were always employed.
Geometry optimizations were carried out down to anenergy rms gradient of <10�6 kJ/mol A.
ORTEP III for Windows [30] was used to depict the
energy-minimized structures.
3. Results and discussion
3.1. The crystal structure of the trans(O5O6)-K[Co(1,3-
pddadp)] Æ 3H2O complex
The ORTEP diagram of the trans(O5O6)-[Co(1,3-
pddadp)]� complex anion is presented in Fig. 2, where
the numbering scheme adopted for the respective atoms
is also given. Selected bond distances and valence angles
are listed in Table 2.
The Co(III) ion is encircled by all of the donatingatoms (2N and 4O) of the 1,3-pddadp ligand to form
an octahedral geometry. The complex anion [Co(1,3-
pddadp)]� represents a trans(O5O6) isomer with the
two (R) rings (glycinate R1 and b-alaninate R2) in the
trans positions and the two (G) rings (b-alaninate G1
and glycinate G2) coordinated in the equatorial plane
making a 5–6–6 ring system in the G-plane (Fig. 2).
The format for describing the various chelate ringsformed in these kinds of chelates was credited to Weak-
liem and Hoard [31]. We have compared the mode and
degree of puckering of the chelate rings observed in the
presented trans(O5O6)-[Co(1,3-pddadp)]� complex with
those for trans(O6)-[Co(1,3-pddadp)]� complexes [16]
having a 5–6–5 combination of the ring members in
the G-plane. The results are presented in the form of
Table 1S in the supplementary material. In both trans
(O5O6) and trans(O6) complexes of Co(III), the six-
membered diamine (T) ring adopts a nearly perfect
twist-boat conformation. The helicity of the six-mem-
bered diamine ring is d for the enantiomorph presented
in Fig. 2 of K configuration. The same is observed for
Fig. 3. Packing in the crystal structure of trans(O5O6)-K[Co(1,3-pddadp)] Æ 3H2O showing the separation of ionic and water layers. Atoms involved
in carbonyl dipolar interactions operating between the layers are marked by substantially bigger circles. H-atoms have been omitted for clarity.
1 U (calculated applying method 1 reported in [32]) is the average
value of the three pseudotorsion angles that are measured along the
line joining the centroids of two nearly parallel triangular faces of a
bi-capped trigonal prism and adopt absolute values in the range 0–60�.
S. Grubisic et al. / Polyhedron 24 (2005) 1701–1709 1705
the trans(O6)-[Co(1,3-pddadp)]� complex of K configu-
ration. In these two complexes the six-membered b-alan-inate rings coordinated in axial positions are very
distorted and their distortion from the ideal conforma-
tions is so severe that they cannot be uniquely describedby the commonly used conventions. Contrary to this,
the six-membered b-alaninate ring of equatorial orienta-
tion in trans(O5O6)-[Co(1,3-pddadp)]� adopts an almost
ideal half-chair form. The five-membered glycinate rings
coordinated in the G-plane display different conforma-
tional modes (envelope in the trans(O5O6) Co(III) com-
plex and twist in the trans(O6) Co(III) complex),
however, the degree of puckering of these rings is nearlythe same (20.6–23.6�). In the [Co(1,3-pddadp)]� com-
plexes of trans(O5O6) and trans(O6) geometry the six-
membered diamine rings (T rings) also exhibit nearly
the same degree of ring puckering (the average torsion
angle magnitude sums 41.7� and 44.1�, respectively).
Similar values for the average torsion angle moduli have
been observed in the [Co(1,3-pdta)]� (41.1�) (where 1,
3-pdta is the 1,3-propanediaminetetraacetate ion), [Rh-(1,3-pdta)]� (40.9�) and trans(O5O6)-[Rh(1,3-pddadp)]�
(42.5�) complexes in which the six-membered diamine
rings adopt the same twist-boat conformation [18]. The
equatorially coordinated glycinates in the trans(O5O6)-
[Co(1,3-pddadp)]� and trans(O6)-[Co(1,3-pddadp)]� com-
plexes are highly puckered, while that one coordinated
in the axial position in the trans(O5O6) isomer is nearly
planar. However, the six-membered b-alaninate ringsdisplay nearly the same degree of ring puckering, inde-
pendent of their axial or equatorial orientation, so they
seem to be the less easy to modify with respect to the
glycinates. The values of the average torsion angle mag-
nitudes cover a range from 31.8� to 35.7�. Similar behav-
ior of b-alaninate rings has also been observed in the
[Rh(1,3-pddadp)]� complexes of trans(O5) and trans-
(O5O6) geometry [18].
In the crystal structure of trans(O5O6)-K[Co(1,3-
pddadp)] Æ 3H2O, potassium ions (K1 and K2), as well
as O1W and O3W water solvent molecules, are settled
on a twofold axis of symmetry. K1 is octacoordinated
with six carbonyl oxygen atoms (O4, O2i, O6ii, O4iii,
O2iv and O6v; symmetry codes: i = �x + 1, y � 1, �z +
0.5; ii = �x + 1, �y + 1, �z; iii = �x + 1, y, �z + 0.5;iv = x, y � 1, z and v = x, �y + 1, z + 0.5) from six dif-
ferent but symmetry-related 1,3-pddadp ligands and
with two symmetry-related water molecules O2Wii and
O2Wv. The coordination polyhedron formed around
K1 is distorted in shape and can be described as a square
antiprism. K2 is surrounded by eight carboxylate oxy-
gen atoms (O1, O1iii, O3, O3iii, O5, O5iii, O6ii and
O6v) from four symmetry-related ligands. The two car-bonyl oxygen atoms O6ii and O6v are shared between
the K1 and K2 ions. The coordination polyhedron
around K2 is midway between bi-capped trigonal prism
and bi-capped trigonal antiprism with a twist angle U1
[32] of 30.7�.
1706 S. Grubisic et al. / Polyhedron 24 (2005) 1701–1709
The crystalline trans(O5O6)-K[Co(1,3-pddadp)] Æ3H2O complex is a two-dimensional polymer (Fig. 3).
It consists of (100) layers (see Fig. 2S in the supplemen-
tary material) built up of potassium ions, situated on
twofold symmetry axes, joined by bridging oxygen
atoms (O6 and its symmetrical equivalent) and by bridg-ing carboxylate groups (O3–C6–O4 and its twofold sym-
metry equivalent along the b-axis, and O5–C10–O6 and
its centrosymmetric equivalent along the c-axis). The
construction of the polymeric layer structure formed
by the potassium ions and their first coordination sphere
is further supported by hydrogen bonds between the
O2W water molecule coordinated to K1 and one of
the uncoordinated carboxylate oxygens (O2) (Fig. 3).The Co1 octahedra are situated on both sides of the
layer formed by cationic polyhedra, and are joined
exclusively to K2 polyhedra by sharing one of the trian-
gular faces of the Co1 octahedron. Consequently, the
approach of the complex anion by the complex cation
takes place from the side of the planar glycinate R1 ring.
The consecutive ionic layers are separated by layers
formed by hydrogen bonded non-coordinated watermolecules (O1W and O3W, situated on a twofold axis,
and O4W in a general position) and O7–C11–O8 car-
boxylate groups (Fig. 3). Two of these water molecules
(O1W and O4W) have one of the two hydrogen atoms
disordered (O1W around a twofold axis, O4W around
the centre of symmetry) in a way that allows formation
of antiparallel homodromic chains of hydrogen-bonded
water molecules, statistically distributed in the crystal,running along the c-axis, which are graphically illus-
trated in Fig. 1S in the supplementary material. Hydro-
gen bond distances and angles are listed in Table 2S in
Table 3
Strain analysis of edta-type chelates of Co(III)a
Complexes Rings in G-plane RD(Oh)b DRc
T (E)
With 1,3-propanediamine (T) ring
trans(O5O6)-[Co(1,3-pddadp)]� (1)f 5–6–6 36 +34
trans(O6)-[Co(1,3-pddadp)]� (2) 5–6–5 38 +28
[Co(1,3-pdta)]� (3) 5–6–5 34 +36
With ethylenediamine (E) ring
trans(O5)-[Co(eddadp)]� (4) 6–5–6 31 –11
trans(O5)-[Co(ed3ap)]� (5)f 5–5–6 29 –11
[Co(edtp)]� (6) 6–5–6 29 �14
[Co(edta)]� (7) 5–5–5 48 �12
a Abbreviations of ligands: 1,3-pddadp = 1,3-propanediamine-N,N0-diaceeddadp = ethylenediamine-N,N0-diacetate-N,N 0-di-3-propionate, ed3ap = eth
mine-N,N,N 0,N0-tetra-3-propionate and edta = ethylenediaminetetraacetate.b RD(Oh) is the sum of the absolute values of the deviations from 90� of tc DR(ring) is the deviation from the ideal of the corresponding chelate rings�
complexes having an approx. C2 molecular symmetry.d D(Co–O–C) (ring) is the mean value of the deviation of the correspondine RD(N) is the sum of the absolute values of the deviations from 109.5� of
two nitrogens is reported.f For the complexes (1) and (5) having C1 molecular symmetry two values
the supplementary material. Interactions between neigh-
bouring layers formed by the complex molecules in-
clude, besides hydrogen bonds, dipolar interactions
between antiparallel C11@O8 carbonyl groups around
the centre of symmetry (Fig. 3).
3.2. Strain analysis of Co(III)-edta-type chelates
The results of a comparative study of the strain char-
acteristics of a related series of Co(III)-edta-type che-
lates are given in Table 3. The major contributions to
strain were considered to be: (i) the octahedral angles
around the Co(III) ion, (ii) the ring angle sums of the
various kinds of rings, (iii) the Co–O–C bond angles,and (iv) the bond angles that the chelating nitrogen
atom makes with its connectors.
The greatest octahedral distortion has been observed
for the [Co(edta)]� (7) [31,33] complex (48�) having a
5–5–5 combination of the ring members in an equatorial
plane. Introducing the six-membered b-alaninate ring(s)in the [Co(edta)]� (7) [31,33] system causes a decrease of
octahedral strain as evidenced by RD(Oh) values calcu-lated for the trans(O5)-[Co(eddadp)]
� (4) [8] (31�),trans(O5)-[Co(ed3ap)]
� (5) [34] (29�) and [Co(edtp)]�
(6) [13] (29�) complexes. However, an increase of octahe-
dral strain was observed when some of the glycinate
rings in the [Co(1,3-pdta)]� (3) [35] complex are replaced
by six-membered b-alaninate rings, as can be seen from
the comparison of RD(Oh) values for the trans(O5O6)-
[Co(1,3-pddadp)]� (1) (36�) and trans(O6)-[Co(1,3-pddadp)]� (2) [16] (38�) complexes with that of
[Co(1,3-pdta)]� (3) [35] (34�). Mostly due to the strain
formed by chelation of in-plane glycinate rings, manifested
D(Co–O–C)d RD(N)e Ref.
R G R G
0, +36 �9, +44 +6, +19 +5, +24 18, 14 this work
+33 �11 +17 +4 16 [16]
+1 �12 +7 +5 15 [35]
–1 +38 +6 +18 13 [8]
±1 �13, +44 +4, +5 +5, +19 18, 12 [34]
+42 +41 +21 +21 18 [13]
�1 �9 +5 +3 18 [31,33]
tate-N,N 0-di-3-propionate, 1,3-pdta = 1,3-propanediaminetetraacetate,
ylenediamine-N,N,N0-triacetate-N0-3-propionate, edtp = ethylenedia-
he L–Co–L0 bite angles. All values rounded off to the nearest degree.
bond angle sum. A mean value of the two rings (R or G) is reported for
g rings� Co–O–C bond angle from 109.5�.the six bond angles made by the nitrogen atoms. A mean value for the
are reported.
S. Grubisic et al. / Polyhedron 24 (2005) 1701–1709 1707
in octahedral bond angles, the trans(O6)-[Co(1,3-
pddadp)]� [16] complex with a 5–6–5 ring system in
the G-plane is more strained than trans (O5O6)-
[Co(1,3-pddadp)]� having an in-plane 5–6–6 combina-
tion of the ring members. The strain formed around
the chelating nitrogen atoms in [Co(1,3-pddadp)]� com-plexes of trans(O5O6) and trans(O6) geometry is practi-
cally the same. As expected five-membered chelate
rings coordinated in-plane are much more strained than
those coordinated in axial positions. Of all the ethylene-
diamine rings observed in complexes (4–7), the greatest
strain was registered for the ethylenediamine ring in
the [Co(edtp)]� (6) [13] complex with the ligand ethy-
lenediamine-N,N,N 0,N 0-tetra-3-propionate, which isable to form only six-membered carboxylato rings. For
this ring the deviation from the ideal sum of chelate ring
bond angles is �14�. For the analyzed Co(III) chelates
the greatest strain among in-plane coordinated glyci-
nates was registered for the glycinate ring in the
trans(O5)-[Co(ed3ap)]� (5) complex for which the
total deviation sums �13�. The total deviation of six-
membered chelate rings is positive and is the greatestfor in-plane coordinated b-alaninate rings in the trans-
(O5O6)-[Co(1,3-pddadp)]� (1) and trans(O5)-[Co(ed-
3ap)]� (5) complexes (+44�). The in-plane b-alaninaterings of the trans(O5)-[Co(eddadp)]
� (4) complex are less
Table 4
Summary of molecular mechanics results
X-ray, trans(O6) X-ray, trans(O5O6)
Energy terms (kcal/mol)
Etotal
Eb
Eh
Eu
Enb
Ee
Selected average bond lengths (A)
M–N 1.964 1.979
M–O 1.906 1.906
C 0–O 1.279 1.288
Ca–C0 1.509 1.500
Ca–Cb 1.506 1.512
C–C 1.529 1.522
N–Ca 1.491 1.494
N–Cb 1.500 1.496
N–C 1.497 1.500
Selected average valence angles (�)N–M–O 89.4 89.7
M–O–C0 120.0 123.2
O–C0–Ca 116.9 117.4
C 0–Ca–Cb 112.9 115.9
Ca–Cb–N 114.3 115.4
Ca–N–M 103.4 105.5
Cb–N–M 115.3 112.8
N–M–N 98.0 97.6
M–N–C 111.1 110.6
N–C–C 113.7 115.6
C–C–C 117.5 118.0
strained, favoring the trans(O5) geometry, as expected
for [M(eddadp)]n� complexes [2–13]. The two N-geminal
b-alaninate rings (R and G) in [Co(edtp)]� (6) show the
same positive total deviation of ca. 41�. The bond angles
of the M–O–C fragment are expected to be between
109.5� and 120�, depending on the degree of covalencyof the M–O bond [13]. These bond angles in the b-alan-inate rings are as high as 130�. In general, these values
are larger for the G b-alaninate rings than for the R
b-alaninate rings and for Co(III) chelates are in the
range 18–24� versus 17–21�.
3.3. Molecular mechanics results
The energy minimization and geometry optimization
procedure resulted in several stable conformations for
each geometrical isomer, trans(O5), trans(O5O6) and
trans(O6), regardless of the initial conformation we
started with. The structural parameters for the resulting
most stable energy-minimized structures, as well as a
comparison with the X-ray structures, are presented in
Table 4. Ortep illustrations for each of the resultingstructures are shown in Fig. 4.
Calculated energies for trans(O5), trans(O5O6) and
trans(O6) isomers of [Co(1,3-pddadp)]� show that the
trans(O5O6) isomer represents the most stable one
trans(O5O6) trans(O6) trans(O5)
39 42 44
9 9 10
29 28 27
4 8 7
24 24 27
�27 �27 �27
1.977 1.967 1.983
1.904 1.902 1.900
1.272 1.273 1.272
1.512 1.517 1.515
1.519 1.522 1.523
1.524 1.536 1.523
1.506 1.503 1.508
1.502 1.508 1.509
1.495 1.489 1.493
88.7 88.0 87.8
123.7 120.8 122.1
118.9 117.9 118.1
113.7 109.4 111.5
116.5 116.7 117.2
107.6 105.7 108.0
112.7 114.4 112.2
99.7 100.7 98.8
111.1 110.2 111.4
116.3 115.0 116.2
118.0 118.6 117.6
Fig. 4. Ortep illustrations of the energy-minimized structures of the three isomers of [Co(1,3-pddadp)]�.
1708 S. Grubisic et al. / Polyhedron 24 (2005) 1701–1709
(Table 4), but the energy differences between isomers are
rather small and result mostly form torsional contribu-
tions to the total energy. The analysis of the torsional
contributions to the total strain shows that in trans(O5)
and trans(O6) isomers the strain is pronounced mainly inendocyclic torsions involving M–O and O–C 0 bonds
in the b-alaninate rings (G and R rings, respectively).
In addition, in these b-alaninate rings we also noticed
significant deviation from planarity of the coordinated
carboxylato moiety, as indicated by the M–O–C 0–O 0
torsion angles of nearly 160� for all chelate rings consid-ered. In the crystal structure of the trans(O6)-[Co(1,3-
pddadp)]� complex the mean M–O–C 0–O 0 torsion anglein the axially coordinated b-alaninate rings is 154�. Thismight be the reason for greater torsional contributions
to the total energy in the case of the trans(O5) and
trans(O6) isomers.
The geometries of the calculated structures are in
good agreement with the corresponding structures for
which X-ray data are available (the trans(O5O6)-
[Co(1,3-pddadp)]� complex presented here and the ear-lier reported trans(O6)-[Co(1,3-pddadp)]
� [16]). The
lowest energy conformer corresponds to the configura-
tion that has been found in the X-ray structure pre-
sented in this paper. The total energy of the minimized
structures for three geometrical isomers of [Co(1,3-
pddadp)]� increases in the order Etotal(trans(O5O6)) <
Etotal(trans(O6)) < Etotal(trans(O5)), Table 4.
4. Concluding remarks
For the ligands having the ethylenediamine fragment
and mixed five- and six-membered carboxylate arms
(ed3ap [34,36] and eddadp [2–13]) geometrical isomers
are possible that differ in the number (0, 1, or 2) of six-
membered rings lying in the equatorial plane (G-plane).These ligands generally minimize strain by forming iso-
mers that have six-membered ring(s) in the G-plane
[2,13]. In the so far well known reactions of Co(III),
[3,4,8] Cr(III), [6,10] Fe(III), [7] Rh(III) [5,9] and Ni(II)
[12] with the ligand ethylenediamine-N,N 0-diacetate-
N,N 0-di-3-propionate (eddadp) the trans(O5) geometry
(Fig. 1(b)) is favored due to the lower steric strain
formed by chelation of the two in-plane b-alaninaterings [2,13]. However, in the case of the 1,3-propanedi-
amine-N,N 0-diacetato-N,N 0-di-3-propionato (1,3-pdda-
dp) complex, especially with small metal ions such as
Co(III) (0.685 A), [37] the trans(O5) isomer should besterically disfavored because of the concentration of all
three six-membered rings in the equatorial plane. The
6–6–6 combination of the chelate rings in the girdle
plane has been observed in the trans(O5) isomer of the
1,3-pddadp complex containing the Rh(III) ion, with
an ionic radius of 0.805 A [18], but has not been so
far obtained for Co(III) [15,16], with an ionic radius of
0.685 A. Of the two isomers that have been isolatedfor the [Co(1,3-pddadp)]� system, i.e., trans(O5O6) and
trans(O6), the lowest energy conformer corresponds to
the trans(O5O6) configuration that has been found in
the X-ray structure presented here. In addition, it has
also been observed that the trans(O5O6) isomer of the
[Co(1,3-pddadp)]� complex is slightly more free from
octahedral strain with respect to the trans(O6) configura-
tion of the same complex.
Acknowledgments
We thank the Ministry of Science and EnvironmentalProtection of the Republic of Serbia for financial sup-
port of the scientific projects No. 1569 and No. 1254.
This work was funded in part by the Polish State
Committee for Scientific Research as scientific project
No. 4 T09A 185 25 during the years 2003–2006.
Appendix A. Supplementary data
Supplementary data are given in a form of Tables 1S–
2S and Figs. 1S–2S. The crystallographic cif files are
available from the CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK, fax: +44 1223 336 033, e-mail: deposit
@ccdc.cam.uk or on the web www: http://www.ccdc.
cam.ac.uk) on request, quoting the Deposition No.
CCDC 262196. Supplementary data associated with thisarticle can be found, in the online version at doi:10.1016/
j.poly.2005.04.035.
S. Grubisic et al. / Polyhedron 24 (2005) 1701–1709 1709
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