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: radanovic@helix.chem.bg.ac.yu (D.D. Radanovic), urszular@amu.edu.pl (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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