A new polymorph of a cobalt(III) Schiff base complex exhibits a one-dimensional C - H...O hydrogen-bonded extended structure with helical 21 symmetry

Article abstract of DOI:10.1107/S0108270107007494

In a new polymorph of acetato(2,2′-{imino-bis[(E)-propane-3,1- diylnitrilo-methyl-idyne]}diphenol-ato)-cobalt(III), [Co(C20H23N3O2)(C2H3O2)], in the space group P21/c, the Co^III ion is six-coordinate, with unequal Co - Ophenolate distances that average 1.908 (12) A and more similar Co - Nimine distances averaging 1.937 (4) A. The acetate ion occupies the sixth coordination site and forms an intra-molecular hydrogen bond (H...O = 1.95 A) with the Co-bound NH group of the penta-dentate chelate. The extended structure is a one-dimensional (aryl)C - H...O(carbonyl) hydrogen-bonded polymer with 21 (helical) symmetry and is thus distinct from the simple hydrogen-bonded stack of the P21/n polymorph [Matsumoto, Imaizumi & Ohyoshi (1983). Polyhedron, 2, 137-139]. International Union of Crystallography 2007.

Full text of DOI:10.1107/S0108270107007494

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
by Matsumoto et al. (1983) with cell constants a = 16.846ꢀ (4),
Ê
b = 9.417 (2) and c = 14.032 (4) A, and ꢀ = 111.29 (1) . As
Communications
discussed below, the present polymorph of (I) has both a
clearly different cell and an extended structure different from
that of the P21/n polymorph.
ISSN 0108-2701
A new polymorph of a cobalt(III)
Schiff base complex exhibits a one-
dimensional CÐHÁ Á ÁO hydrogen-
bonded extended structure with
helical 21 symmetry
Orde Q. Munro* and Santham Govender
School of Chemistry, University of KwaZulu-Natal, Peitermaritzburg, Private Bag
X01, Scottsville 3209, South Africa
Correspondence e-mail: munroo@ukzn.ac.za
The pentadentate ligand of (I) occupies ®ve of the six
coordination sites at the CoIII centre, with the phenolate O
atoms in a cis arrangement (Fig. 1). The two imine N atoms
(N1 and N3) are trans to each other and the acetate ligand
coordinates trans to phenolate atom O1. The CoÐNimine
Received 1 February 2007
Accepted 13 February 2007
Online 17 March 2007
In a new polymorph of acetato(2,20-{iminobis[(E)-propane-
3,1-diylnitrilomethylidyne]}diphenolato)cobalt(III), [Co-
(C20H23N3O2)(C2H3O2)], in the space group P21/c, the CoIII
ion is six-coordinate, with unequal CoÐOphenolate distances
that average 1.908 (12) A and more similar CoÐNimine
Ê
distances averaging 1.937 (4) A. The acetate ion occupies
Ê
distances are short [mean 1.937 (4) A], while the bond to the
secondary amine atom (N2) is considerably longer as a result
of additional steric strain associated with its sp3 hybridized
geometry (Table 1). The CoÐOphenolate distances average
Ê
Ê
1.908 (12) A, but differ by more than 4ꢁ. Since atom O1 forms
a shorter bond to CoIII than atom O2 and is possibly hydrogen
bonded to atoms H11B and H13A (Table 1), it is not unlikely
that these attractive intramolecular interactions favour a
somewhat shorter coordination interaction for this phenolate
the sixth coordination site and forms an intramolecular
Ê
hydrogen bond (HÁ Á ÁO = 1.95 A) with the Co-bound NH
group of the pentadentate chelate. The extended structure is a
hydrogen-
one-dimensional
(aryl)CÐHÁ Á ÁO(carbonyl)
bonded polymer with 21 (helical) symmetry and is thus
distinct from the simple hydrogen-bonded stack of the P21/n
polymorph [Matsumoto, Imaizumi & Ohyoshi (1983). Poly-
hedron, 2, 137±139].
Comment
Cobalt(II) complexes of pentadentate Schiff base ligands
formed by condensation of N-(3-aminopropyl)propane-1,3-
diamine and salicylaldehyde, or their structurally related
derivatives, are normally neutral ®ve-coordinate species with a
trigonal±bipyramidal coordination geometry (Cini & Orioli,
1982; Zanello et al., 1983). The cobalt(III) analogues, on the
other hand, are typically six-coordinate because of the coor-
dination of an anion (Anderson et al., 1998), or a neutral
ligand such as N-methylimidazole (Kistenmacher et al., 1974;
Padden, Krebs, Trafford et al., 2001), at the sixth site. Such
systems are attractive for applications that include roles as
molecular O2 transporters (Cini & Orioli, 1981, 1983; Lind-
blom et al., 1971) and porous O2/NO sensing polymers (Krebs
& Borovik, 1998; Sharma & Borovik, 2000; Padden, Krebs,
MacBeth et al., 2001).
Figure 1
The molecular structure of (I), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 70% probability level. H atoms
are shown only as the intersections and end-points of bonds represented
as cylinders. The most prominent intramolecular hydrogen bond is shown
as a dashed line.
As part of a more general project in our laboratory, we have
isolated crystals of a new polymorph of the title compound,
(I). The ®rst structure of (I) (space group P21/n) was reported
m150 # 2007 International Union of Crystallography
DOI: 10.1107/S0108270107007494
Acta Cryst. (2007). C63, m150±m152

metal-organic compounds
by the twofold screw axis (Fig. 2). An (aryl)CÐHÁ Á Á
O(carbonyl) interaction occurs between ortho atom H2 of one
of the phenolate groups and acetate carbonyl atom O4 of a
neighbouring molecule (Table 2). In the case of the P21/n
polymorph, the intermolecular hydrogen bonding is char-
Ê
acterized by a longer interaction distance (HÁ Á ÁO = 2.66 A)
and occurs between the acetate carbonyl O atom of one
molecule and the meta H atom of a phenolate group of a
neighbouring molecule (Matsumoto et al., 1983). This results
in a one-dimensional extended structure that is more like a
simple hydrogen-bonded stack than a spiral or helix, as it lacks
an axis of symmetry.
Despite the unique extended structures and crystal packing
arrangements for the two polymorphs of (I), the molecular
structures are similar and have virtually equivalent saturated
chelate ring conformations and coordination group geome-
Ê
tries (r.m.s. deviation < 0.05 A; Fig. 3). The key differences
between the molecular structures of the two polymorphs are
the relative orientations of the two phenoxy rings and, to a
lesser extent, the relative orientations of the acetate ions.
More speci®cally, the dihedral angle between the lower pair of
phenoxy rings in Fig. 3 is 8.4 (2)ꢀ, while that between the
upper right-hand pair of rings is somewhat smaller, at 5.4 (2)ꢀ.
Interestingly, the two six-membered chelate rings that include
the imine N atoms have different conformations in the two
polymorphs. One chelate ring has a regular chair conforma-
tion (back ring in Fig. 3), while the other chelate ring (left-
hand ring) is best described as having a twisted boat confor-
mation. Clearly, the latter twist is required to enable coordi-
nation of one of the phenolate O atoms (O1) in an axial
position relative to the three N atoms that occupy sites within
the equatorial plane about the CoIII ion (Fig. 1).
Figure 2
Part of the one-dimensional hydrogen-bonded extended structure of (I),
viewed approximately down the a axis of the unit cell (full contents have
been omitted for clarity). H atoms involved in intermolecular hydrogen
bonds are shown as spheres (isotropic displacement parameter radii). All
other atoms have displacement ellipsoids at the 50% probability level.
3
2
3
2
[Symmetry codes: (i) x 1,
y, z 12; (ii) 1 + x,
y, 12 + z.]
O atom. It is also likely that the secondary amine donor atom
(N2) has a trans elongating effect on the Co-bound phenolate
atom (O2), particularly as it is a better ꢁ-donor (stronger Lewis
base) than the acetate ligand trans to O1. Notwithstanding
possible differences in the intermolecular interactions for the
two phenolate groups, the combined effect of these intra-
molecular perturbations would account, at least partly, for the
signi®cant difference in the CoÐOphenolate bond lengths.
The conformation of (I) is characterized by a hinge-like
shape brought about by the non-orthogonal relative orienta-
tion of the two benzene rings [dihedral angle = 76.2 (2)ꢀ]. The
benzene rings are, furthermore, individually canted relative to
the mean plane passing through the metal ion and four
coplanar ligand donor atoms (N1±N3/O2); the dihedral angles
between this plane and the C1±C6 and C15±C20 planes are
66.5 (2) and 39.5 (2)ꢀ, respectively.
Somewhat surprisingly, the acetate ligand of (I) is ®rmly
bound to the CoIII ion. We have therefore been unable to
substitute the anion in dichloromethane solution by primary
amines such as butylamine or benzylamine, even using an
excess of these ligands. A possible explanation for the
substitution-inert anion, beyond the high ligand ®eld stabili-
zation energy for low-spin CoIII, is the fact that it is further
anchored within the complex via a hydrogen bond between
the carbonyl O atom and the amine N atom (Table 2 and
Fig. 1). This conclusion is consistent with the fact that an iodo
analogue of (I), which is presumably incapable of forming
strong intramolecular hydrogen bonds, has been used for the
synthesis of the corresponding N-methylimidazole adduct
(Padden, Krebs, MacBeth et al., 2001).
Figure 3
Root-mean-square ®t of the present molecular structure of (I) and the
P21/n polymorph [Co ion and six ligand donor atoms; r.m.s. deviation =
Ê
0.033 (4) A] reported by Matsumoto et al. (1983) [Cambridge Structural
In the packing of (I), each molecule belongs to an in®nite
one-dimensional hydrogen-bonded polymer chain generated
Database (Allen, 2002) refcode BUWWEV]. Only the bonds are shown
(as cylinders) in both structures for the sake of clarity.
ꢁ
Acta Cryst. (2007). C63, m150±m152
Munro and Govender [Co(C20H23N3O2)(C2H3O2)] m151

metal-organic compounds
Table 2
Hydrogen-bond geometry (A, ).
Experimental
ꢀ
Ê
A new two-step method for the synthesis of (I) was developed. N-(3-
Aminopropyl)propane-1,3-diamine (4 ml, 30.48 mmol) was dissolved
in dry ethanol (25 ml). Salicylaldehyde (6.5 ml, 60.97 mmol) was
added slowly to the solution, which turned yellow. On stirring at
ambient temperature (30 min), the colour of the solution changed
from yellow to bright orange. The solvent was then removed in vacuo
to yield the ligand (2,20-{iminobis[(E)-propane-3,1-diylnitrilome-
thylidyne]}diphenol) as an orange oil. UV±vis (CH2Cl2, ꢂmax, nm):
255.26, 316.00; IR (KBr pellet, ꢃ, cm 1): 2933 (m, CÐH), 1631 (s,
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
N2ÐH100Á Á ÁO4
C2ÐH2Á Á ÁO4i
0.91 (2)
0.95
0.99
0.99
0.99
1.95 (2)
2.51
2.50
2.46
2.50
2.8270 (17)
3.372 (2)
2.8496 (18)
2.9658 (19)
2.9183 (18)
160.3 (19)
150
100
111
105
C8ÐH8AÁ Á ÁO3
C11ÐH11BÁ Á ÁO1
C13ÐH13AÁ Á ÁO1
Symmetry code: (i) x 1; y ‡ 32; z
.
1
2
C
N), 1460 (m, CH2), 1278 (s, CÐO). The ligand (1.0450 g,
Ê
rotating group, with CÐH = 0.96 A and Uiso(H) = 1.5Ueq(C). Other H
3.079 mmol) was dissolved in dry tetrahydrofuran (14 ml, THF). A
solution of cobalt(II) acetate (0.7333 g, 2.944 mmol) dissolved in dry
methanol (20 ml) was added slowly to the stirred THF solution of the
ligand. An immediate colour change from bright yellow to brown
occurred. The solution was stirred for ca 2 h and then left to stand for
1 h prior to removal of the solvent in vacuo to afford a brown powder.
Compound (I) was recrystallized from a mixture of CH2Cl2 and
hexane (1:12) in a test tube over several days (isolated yield 0.7694 g,
57%).
atoms were positioned geometrically and re®ned using a riding
Ê
model, with CÐH = 0.97 A and Uiso(H) = 1.2Ueq(C) for methylene H
Ê
atoms, and CÐH = 0.93 A and Uiso(H) = 1.2Ueq(C) for aromatic H
atoms. Atom H100 attached to N2 (the secondary amine donor atom)
was located in a difference Fourier map and re®ned without
constraints.
Data collection: CrysAlis CCD (Oxford Diffraction, 2003); cell
re®nement: CrysAlis RED (Oxford Diffraction, 2003); data reduc-
tion: CrysAlis RED; program(s) used to solve structure: SHELXS97
(Sheldrick, 1997); program(s) used to re®ne structure: SHELXL97
(Sheldrick, 1997); molecular graphics: WinGX (Farrugia, 1999);
software used to prepare material for publication: WinGX.
Crystal data
3
Ê
[Co(C20H23N3O2)(C2H3O2)]
Mr = 455.39
Monoclinic, P21=c
Ê
a = 7.730 (2) A
b = 20.439 (3) A
c = 13.321 (2) A
ꢀ = 104.169 (18)ꢀ
V = 2040.6 (7) A
Z = 4
Mo Kꢄ radiation
1
ꢅ = 0.88 mm
T = 100 (2) K
Ê
The authors gratefully acknowledge ®nancial support from
the University of KwaZulu-Natal and the National Research
Foundation (NRF, Pretoria). Any opinions, ®ndings and
conclusions or recommendations expressed in this paper are
those of the authors and therefore the NRF does not accept
any liability in regard thereto.
Ê
0.27 Â 0.17 Â 0.06 mm
Data collection
Oxford Xcalibur2 CCD area-
detector diffractometer
Absorption correction: numerical
[CrysAlis RED (Oxford
Clark & Reid (1995)]
Tmin = 0.688, Tmax = 0.904
18148 measured re¯ections
6468 independent re¯ections
5817 re¯ections with I > 2ꢁ(I)
Rint = 0.019
Diffraction, 2003), using a multi-
faceted crystal model based
on expressions derived by
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: JZ3056). Services for accessing these data are
described at the back of the journal.
Re®nement
R[F2 > 2ꢁ(F2)] = 0.033
wR(F2) = 0.083
S = 1.05
6468 re¯ections
276 parameters
H atoms treated by a mixture of
independent and constrained
re®nement
References
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Anderson, J. R., Baklien, A., Djajamahadja, V., West, B. O. & Tiekink, E. R. T.
(1998). Z. Kristallogr. New Cryst. Struct. 213, 49±50.
3
Ê
Áꢆmax = 0.50 e A
3
Ê
0.63 e A
Áꢆmin
=
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Table 1
Selected geometric parameters (A, ).
ꢀ
Ê
C1ÐO1
1.3157 (15)
1.3157 (15)
1.8934 (10)
1.9222 (9)
1.9236 (10)
Co1ÐN1
Co1ÐN3
Co1ÐN2
O3ÐC21
O4ÐC21
1.9318 (11)
1.9410 (11)
1.9950 (11)
1.2914 (16)
1.2375 (17)
C20ÐO2
Co1ÐO1
Co1ÐO2
Co1ÐO3
Matsumoto, N., Imaizumi, M. & Ohyoshi, A. (1983). Polyhedron, 2, 137±139.
Oxford Diffraction (2003). CrysAlis CCD (Version 1.170.32) and CrysAlis
RED (Version 1.170.32). Oxford Diffraction Ltd, Abingdon, Oxfordshire,
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(2001). J. Am. Chem. Soc. 123, 1072±1079.
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Borovik, A. S. & Scarrow, R. C. (2001). Chem. Mater. 13, 4305±4313.
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O1ÐCo1ÐO2
O1ÐCo1ÐO3
O2ÐCo1ÐO3
O1ÐCo1ÐN1
O2ÐCo1ÐN1
O3ÐCo1ÐN1
O1ÐCo1ÐN3
O2ÐCo1ÐN3
91.14 (4)
176.17 (4)
85.12 (4)
92.02 (5)
88.54 (5)
88.71 (5)
86.04 (5)
90.28 (4)
O3ÐCo1ÐN3
N1ÐCo1ÐN3
O1ÐCo1ÐN2
O2ÐCo1ÐN2
O3ÐCo1ÐN2
N1ÐCo1ÐN2
N3ÐCo1ÐN2
93.14 (4)
177.71 (5)
92.80 (5)
175.88 (4)
90.96 (5)
90.13 (5)
91.19 (5)
È
Gottingen, Germany.
The methyl H atoms of the acetate ligand were identi®ed in a
difference Fourier synthesis, idealized and re®ned as part of a rigid
Zanello, P., Cini, R., Cinquantini, A. & Orioli, P. L. (1983). J. Chem. Soc.
Dalton Trans. pp. 2159±2166.
ꢁ
m152 Munro and Govender [Co(C20H23N3O2)(C2H3O2)]
Acta Cryst. (2007). C63, m150±m152