Synthesis and molecular structure of the first binuclear {(bis-N-isophthaloyl ureato)copper(II)pyridine}2 complex derived from the {(bis-N-isophthaloyl-selenoureato)copper(II)}2 complex by O for Se atom exchange

Article abstract of DOI:10.1016/j.inoche.2010.09.041

The bipodal ligand 3,3,3′,3′-tetraethyl-1,1′- isophthaloyl-bis(selenourea) (H₂L¹) forms a 2:2 copper(II) complex [Cu₂(L¹)₂] , the crystal and molecular structure and EPR spectrum of which are reported

Full text of DOI:10.1016/j.inoche.2010.09.041

Inorganic Chemistry Communications 14 (2011) 99–102
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis and molecular structure of the first binuclear {(bis-N-isophthaloyl ureato)
copper(II)pyridine}2 complex derived from the {(bis-N-isophthaloyl-selenoureato)
copper(II)}2 complex by O for Se atom exchange
Axel Rodenstein a, James A. Odendal b, Reinhard Kirmse a, Klaus R. Koch b,
⁎
a
Universität Leipzig, Institute of Inorganic Chemistry, Johannisallee 29, D-04103 Leipzig, Germany
b
Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag XI, Matieland, 7602, South Africa
a r t i c l e i n f o
a b s t r a c t
The bipodal ligand 3,3,3′,3′-tetraethyl-1,1′-isophthaloyl-bis(selenourea) (H2L1) forms
a 2:2 copper(II)
Article history:
Received 23 June 2010
Accepted 30 September 2010
Available online 2 November 2010
complex [Cu2(L1)2] , the crystal and molecular structure and EPR spectrum of which are reported. Treatment
of [Cu2(L1)2] with excess pyridine results in the formation of a novel (bis-N-acylureato)copper(II) 1:2
pyridine adduct [Cu2(L2)2(py)2], characterized by single crystal X-ray diffraction and EPR spectroscopy, as a
consequence of facile Se replacement by O presumably due to hydrolysis of water present in the mixture. The
latter complex forms a one-dimensional supramolecular architecture in the solid state, stabilized via
π-stacking interactions between alternate Cu-coordinated pyridine molecules.
Keywords:
Crystal structures of {(bis-N-isophthaloyl-
selenoureato)copper(II)}2
{(bis-N-isophthaloyl-ureato)-
copper(II)}2•2pyridine
EPR spectroscopy
© 2010 Elsevier B.V. All rights reserved.
Se by O atom exchange
Bipodal 1,3-aryl linked bis-acylthioureas such as 3,3,3′,3′-tetraethyl-
1,1′-isophthaloylbis(thiourea) result in the facile formation of 2:2
planar metallamacrocyclic complexes of Ni(II) and Pt(II), Pd(II) [1],
shown as a general structure (I) below. The corresponding trans-
dichloro-, dibromo- and diiodo-Pt(IV) complexes with such ligands
have been prepared by selective oxidation of the 2:2 Pt(II) complexes
and structurally characterized [2]. In the context of supramolecular
chemistry 2:2 Ni(II) complexes have recently received much recent
attention [3], in view of their tendency to form a variety of
interesting adducts with heterocyclic nitrogen bases such as pyridine,
4-(dimethylamino)pyridine, pyrazine, 4,4′-bipyridine or 4,4′-trans-
azopyridine resulting in 3D supramolecular assemblies with potential
applications as sensors. Subsequently, related 1,3- and 1,4-aryl linked
bis-β-diketone derivatives of inter alia Cu(II) and Fe(III) complexes (II)
have been prepared, and their supramolecular adducts with for example
pyrazine, 4,4′-bipyridine and related molecules have been studied [4].
The synthesis and characterization (based mainly on NMR and EPR
spectroscopic evidence) of the corresponding [Ni2(L1)2] and [Cu2(L1)2]
complexes (III), derived from bipodal acyl-selenourea ligands such as
3,3,3′,3′-tetraethyl-1,1′-isophthaloyl-bis(thiourea) (H2L1) have been
recently reported [5].
undergoes an interesting Se by O atom-exchange reaction in the bound
ligand (L1) when [Cu2(L1)2] is treated with excess pyridine, to result in a
novel five-coordinate (bis-N-acylureato)copper(II)-bis-pyridine complex
[Cu2(L2)2(py)2] (Scheme 1). The ligand 3,3,3′,3′-tetraethyl-1,1′-isophtha-
loyl-bis(selenourea) (H2L1) and its [Cu2(L1)2] complex were synthesized
in the absence of light according to a recently published procedure [5]. The
highly light-sensitive products were isolated in good yields as a pale red
solid (H2L1), and brown crystals of [Cu2(L1)2] respectively [6]. The ligand
3,3,3′,3′-tetraethyl-1,1′-isophthaloyl-bis(selenourea) was characterized
by means of conventional spectroscopic methods, with the 77Se{1H} NMR
spectrum of H2L1 showing a single resonance at δ(77Se)=496 ppm in
CDCl3 relative to (CH3)2Se. In the 13C{1H} NMR spectrum of H2L1 the
symmetrical satellites corresponding to 1JCSe =219 Hz about the 13C peak
at 180 ppm peak confirm the presence of the C=Se unit. The NH group
was detected as a broad band at 3190 cm−1 in the IR spectrum and as a
broad singlet in the 1H NMR spectrum of H2L1.
The brown, paramagnetic complex [Cu2(L1)2] is prepared by the
reaction of H2L1 with copper(II)acetate •H2O in ethanol in the absence of
light in 76% yield and re-crystallized from chloroform/acetonitrile [6].
The ESI(TOF) mass spectrum of [Cu2(L1)2] supports the molecular
structure by a base peak at 1100.9 amu associated with a [M+H]+
species. Suitable crystals of [Cu2(L1)2] were characterized by single
crystal X-ray diffraction [7] showing this complex to be a 2:2
metallamacrocyclic complex with Ci as shown in Fig. 1a. Interestingly,
in this 2:2 complex the Se atoms coordinated to the copper lie
significantly above and below the mean plane defined by the Cu1,O1,
O2 and Cu1a,O1a,O2a atoms. Essentially as shown in Fig. 1b, the two Se
We here report the crystal and molecular structures of a (bis-N-acyl-
selenoureato)copper(II) complex, cis-[Cu2(L1-Se,O)2] (Fig. 1a), which
⁎
Corresponding author. Tel.: +27 218083020; fax: +27 218083342.
E-mail address: krk@sun.ac.za (K.R. Koch).
1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.09.041

100
A. Rodenstein et al. / Inorganic Chemistry Communications 14 (2011) 99–102
Fig. 1. a) Molecular structure of [Cu2(L1)2]. Selected bond lengths (Å): Cu1–O1 1.947(3), Cu1–Se1 2.366(1), Cu1–O2 1.953(3), and Cu1–Se 2 2.359(1). Atoms are described by
thermal ellipsoids at the 50% probability level. b) Shown also is a representation of the structure (H atoms and ethyl chains deleted for clarity) to illustrate Se atoms above and below
the plane of the complex.
atoms significantly protrude above the mean plane of the metallama-
crocyclic complex, with the dihedral angles defined by C1–N1–C2–Se1/
C21–N3–C22–Se2 (and the symmetry related ones) being 8.6(1)°,
resulting in the Se atoms being relatively exposed to a possible reaction
with ambient water as indicated in Scheme 1 (vide infra).
Although the intra-molecular metal–metal distance Cu1–Cu1a of
7.69(1)Å in [Cu2(L1)2] is comparatively large, the presence of an
electron spin interaction might be anticipated [8]. This is confirmed by
the EPR spectrum of [Cu2(L1)2], which shows a hyperfine structure
(hfs) septet due to intra-molecular exchange interactions between the
two Cu2+ centres (Fig. 2). The isotropic g value of 2.077 and a Cu hfs
coupling constant of 39.2·10−4 cm−1 is consistent with a (CuO2Se2)2
coordination unit [5,8]. Inter-molecular exchange interactions can
most probably be excluded in view of the low concentration of [Cu2
(L1)2] in this solution (c≈10−3 M). The expected 77Se hfs splitting
could unfortunately not be detected in view of the relatively broad
I
II
III
R'
R'
R'
R2N
R2N
N
M
N
N
M
N
R2N
R2N
N
M
N
N
M
N
NR2
NR2
NR2
NR2
O
O
O
O
S
S
O
O
O
O
Se
Se
O
O
O
O
O
O
S
S
O
O
Se
Se
M
M
R'
M = Cu(II), Ni(II)
M = Cu(II), Fe(III)
M = Pt(II), Pd(II), Ni(II)
py
N
NEt2
Et2N
Et2N
N
Et2N
Et2N
N
N
Cu
N
NEt2
pyridine
O
O
O
O
O
O
O
Se
Se
O
O
EtOH
dark
Se
Se
O
O
2 HL1 + 2 Cu(CH3COO)2 x H2O
Cu
N
Cu
N
Cu
N
O
NEt2
NEt2
py
Scheme 1. Structural motifs of known 2:2 metallamacrocyclic complexes and synthesis of Cu(II) complexes herein.

A. Rodenstein et al. / Inorganic Chemistry Communications 14 (2011) 99–102
101
EPR lines obtained. Superposition of lines might be expected based on
the presence of a hyperfine quartet structure resulting from
“monomeric” Cu2+ centres. In the latter case the same g0 value as
found for the Cu2+–Cu2+ pair is expected, although the 63,65Cu hfs
coupling constant a0 will be approximately twice as large as that of the
Cu2+–Cu2+ pair. This phenomenon of a typical chemical equilibrium
of copper complexes with chalcogenoureato ligands in solution
was recently described [5,8]. The weak signals at low-field, 292 mT,
and at high-field, 335 mT, arise from decomposition products.
Dissolution of [Cu2(L1)2] in excess pyridine (as solvent) results in a
green solution, from which an unexpected product consisting of blue
crystals of [Cu2(L2)2(py)2] can be isolated after a two day period at room
temperature. Evidently the selenium donor atoms of the coordinated L1
are replaced by an oxygen donor atom forming a novel bis-N-acylureato
ligand system L2 which remains bound to Cu(II). Apparently, the ligand
L1-fragment of the relatively unstable (bis-N-acylselenoureato)copper
(II) complex, [Cu2(L1)2] undergoes O for Se atom replacement under
theseconditions, presumably asa result of hydrolysis of water presentin
this solution. This process is presumably accompanied by the formation
Fig. 2. X-band EPR spectra of [Cu2(L1)2] in toluene and [Cu2(L2)2(py)2] in pyridine at
T=370 K. The S=½ specie is highlighted with “*” and S=1 with “+”. Experimental
error: g0 = 0.002; a0 = 0.5.
Fig. 3. a) Molecular structure of [Cu2(L2)2(py)2] [7]. Selected bond lengths (Å): Cu1–O1 1.946(1), Cu1–O2 1.919(1), Cu1–O5 1.938(1), Cu1–O6 1.930(1), Cu1–N9 2.262(1), Cu2–O3
1.932(1), Cu2–O4 1.922(1), Cu2–O7 1.922(1), Cu1–O8 1.935(1), and Cu2–N10 2.296(1). b) One-dimensional supramolecular arrangement of [Cu2(L2)2(py)2]. The π-stacking
interactions are represented in a distance of 3.34(1)Å between the pyridine rings. Atoms are described by thermal ellipsoids at the 50% probability level.

102
A. Rodenstein et al. / Inorganic Chemistry Communications 14 (2011) 99–102
of intermediate [H2Se]‡, which decomposes immediately to form
elemental red selenium, which can be identified as a by product of this
reaction. The possible mechanism of this reaction is as yet unclear and it
has not been studied in any detail. The blue crystals isolated from this
mixture is a novel pyridine adduct [Cu2(L2)2(py)2] as characterized by
single crystal X-ray diffraction, the molecular structure of which is shown
in Fig. 3 [7]. Unfortunately the solid complex [Cu2(L2)2(py)2] rapidly loses
pyridine on exposure to air at ambient temperatures, which is indicative of
only weak pyridine coordination to copper(II) in this compound.
submitted to the Cambridge Crystallographic Data Centre with
reference numbers CCDC 780953 and CCDC 780954 at www.ccdc.ac.
uk/data_request/cif.
References
[1] K.R. Koch, S.A. Bourne, A. Coetzee, J. Miller, Dalton Trans. (1999) 3157–3161;
K.R. Koch, O. Hallale, S.A. Bourne, J. Miller, J. Bacsa, J. Mol. Struct. 561 (2000)
185–196.
[2] A.N. Westra, S.A. Bourne, K.R. Koch, Dalton Trans. (2005) 2916–2924.
[3] a) S.A. Bourne, O. Hallale, K.R. Koch, Cryst. Growth Des. 5 (2005) 307;
b) O. Hallale, S.A. Bourne, K.R. Koch, New J. Chem. 29 (2005) 1416;
The coordination sphere of copper(II)atom in [Cu2(L2)2(py)2] displays
a square pyramidal 5-coordinate geometry involving two chelating O,O
donor atom sets of N-acylureato fragments of L2 bound equatorially to Cu
(II) with the coordinated pyridine molecules in apical positions anti to one
another. The bound pyridine molecule on alternate sides of the planar [Cu2
(L2)2] unit, generate an infinite one-dimensional supramolecular chain
stabilized through π-stacking interactions between adjacent pyridine
moieties in the crystal lattice shown in Fig. 3b. The crystal and molecular
structure of [Cu2(L2)2(py)2] described here is remarkably similar to the
corresponding [Cu2(L)2(py)2]·py derived from 1,3-aryl linked bis-β-
diketone (L) derivatives reported by Clegg et al. [4]. The pyridine adducts
of related bis-β-diketonatocopper(II) complexes previously been de-
scribed also show loss of pyridine from the solid complex [4,9].
c
O. Hallale, S.A. Bourne, K.R. Koch, Cryst. Eng. Comm. 7 (2005) 161.
[4] J.K. Clegg, L.F. Lindoy, J.C. McMurtrie, D. Schilter, Dalton Trans. (2005) 857;
J.K. Clegg, L.F. Lindoy, B. Moubaraki, K.S. Murray, J.C. McMurtrie, Dalton Trans.
(2004) 2417.
[5] A. Rodenstein, J. Griebel, R. Richter, R. Kirmse, Z. Anorg. Allg. Chem. 634 (2008) 1735.
[6] Synthesis of H2L1 A solution of isophthaloyl dichloride (0.83 g, 4.17 mmol) in
15 mL of acetone was added to a solution of KSeCN (1.20 g, 8.33 mmol) in 25 mL
of acetone, which was not dried before. The mixture was stirred at room
temperature for 15 min. During this time, an orange suspension was formed.
Thereafter, diethylamine (0.61 g, 8.33 mmol) was added dropwise. The mixture
was heated to reflux for 2 h, after which it was allowed to cool. A red solution with
an orange–red precipitate was obtained. The mixture was transferred to a beaker
containing 150 mL water and 5 mL hydrochloric acid and was left to stand in the
fridge overnight. The solid was filtered off and washed with water. Recrystalli-
zation from ethanol gave pale red, light sensitive crystals of H2L. Yield 1.50 g
(74%). 1H NMR (300 MHz, CDCl3): δ [ppm]: 1.25 (t, 3J=6.9 Hz, 12H, CH3); 1.33
(t, 3J=6.9 Hz, 12H, CH3); 3.54 (q, 3J=6.9 Hz, 4H, CH2); 4.06 (q, 3J=6.9 Hz, 4H,
CH2); 7.49 (t, 3J=7.8 Hz, 1H, ar–H); 7.98 (d, 3J=7.8 Hz, 2H, ar–H); 8.35 (s, 1H,
ar–H); 9.64 (s, 2H, NH). 13C-{1H} NMR (75 MHz, CDCl3): δ [ppm]: 11.6 (s, CH3);
12.9 (s, CH3); 48.2 (s, CH2); 50.9 (s, CH2); 127.3 (s, ar–C); 129.4 (s, ar–C); 132.7
(s, ar–C); 132.8 (s, ar–C); 162.0 (s, C=O); 180.6 (s, C=Se, 2JCSe=219.1 Hz).
77Se-{1H} NMR (76 MHz, CDCl3): δ [ppm]: 495.9 (s, C=Se); IR (KBr) [cm−1]: ν
(N–H) 3189 (w), ν (C=O) 1694 (s), ν (C=Se) 1530 (s). Synthesis of [Cu2(L1)2]:
H2L (0.49 g, 1.00 mmol), dissolved in 25 mL ethanol, was added to a solution of Cu
(CH3COO)2·H2O (0.20 g, 1.00 mmol) in 40 mL of ethanol. The colour of the
solution turned immediately to brown and after stirring the reaction solution at
60 °C for 15 min, a microcrystalline solid was obtained. The solid was filtered off
and washed with water. The product was recrystallized from a chloroform/
acetonitrile mixture. Yield 0.42 g (76%). M.p. 160 °C (decomposition); positive
ESI-MS (m/z): 1100.9[M+H]+; IR (KBr) [cm−1]: ν(CO)1588(s), ν(CSe)1492
(s); Calculation for C36H48Cu2N8O4Se4: C, 39.32; H, 4.40; N, 10.19. Found: C, 39.10;
H, 4.38; N, 10.07. Synthesis of [Cu2(L2)2(py)2]: [Cu2(L1)2] (0.10 g, 0.09 mmol) was
dissolved in 1 mL pyridine. The colour of the solution turned to green. The mixture
was left to stand 2 days at room temperature. Thereafter, blue crystals of the product
and a red solid of the byproduct were obtained. The product, which is unstable
beyond the solvent, was characterized by X-ray diffraction and EPR spectroscopy.
[7] Structure determination of [Cu2(L1)2]: C36H48Cu2N8O4Se4 (M=1099.74); triclin-
ic, space group P-1 (No. 2); T=100(2)K, a=8.3300(15)Å, b=10.2834(19)Å,
c=12.1590(20)Å, α=81.280(2)°, β=80.142(2)°, γ=87.315(2)°, V=1014.1(3)
Å3, Z=1, Dc =1.801 Mg/m3, μ(MoKα)=4.687 mm−1, brown prism from CHCl3/
CH3CN, 0.11×0.05×0.03 mm3,Θ range for data collection 1.72–24.70°, F(000)=
546; 8875 collected, 3438 unique, and 2753 observed (IN2σ(I)) diffractions, 244
parameter, final R1 =3.63% for observed diffractions, wR2 =9.14% for all data,
GOF=1.045, residual electron density +1.953 and −0.769 e·Å−3. Structure
determination of [Cu2(L2)2(py)2]:The low temperature X-ray structure was
obtained immediately after isolation. C46H58Cu2N10O8 (M=1006.10); triclinic,
space group P-1 (No.2); T=100(2)K, a=12.4854(5)Å, b=12.8161(5)Å,
c=15.4141(6)Å, α=74.810(1)°, β=87.576(1)°, γ=86.650(1)°, V=2375.3(2)
Å3, Z=2, Dc =1.407 Mg/m3, μ(MoKα)=0.958 mm−1, blue prism from pyridine,
0.20×0.04×0.01 mm3,Θ range for data collection 1.65–28.19°, F(000)=940;
27534 collected, 10,655 unique, and 9241 observed (IN2σ(I)) diffractions, 595
parameter, final R1 =2.84% for observed diffractions, wR2 =7.78% for all data,
GOF=1.030, residual electron density +0.408 and −0.268 e·Å−3. Diffraction
data were collected on a Bruker-Nonius SMART Apex diffractometer equipped
with fine-focus sealed tube and a 0.5 mm Monocap collimator (monochromated
The paramagnetic copper(II) complex [Cu2(L2)2(py)2] was examined
by EPR spectroscopy in pyridine solution. The formation of ‘CuO4N’
coordination units in [Cu2(L2)2(py)2] is accompanied by drastic changes in
the EPR spectrum compared to the ‘CuSe2O2’ core of [Cu2(L1)2] in
toluene solution; the g0 value of the former increases significantly while a0
decreases significantly with respect to the Se,O coordinated Cu2+ centres
in the planar [Cu2(L1)2] (Fig. 2). This indicates noticeable changes in the
spin-density distribution within the Se,O chelated coordination sphere of
[Cu2(L1)2] compared to the ‘CuO4N’ coordination sphere of [Cu2(L2)2
(py)2] in the pyridine solution. Spin-exchange interactions were not
observed in the broad EPR spectrum of the [Cu2(L2)2(py)2] with the ‘CuO4/
CuO4N’ core in pyridine solution. Presumably in pyridine solutions at
370 K, pyridine exchange processes may result in equilibria between [Cu2
(L2)2(py)2], [Cu2(L2)2(py)] and [Cu2(L2)2] in view of the relatively low
stability found for the isolated [Cu2(L2)2(py)2] complex (vide infra), which
may account for the broad poorly resolved EPR spectrum obtained; such
exchange processes in the solution are likely also to affect any equilibrium
between “dimeric” and “monomeric Cu2+ ”centres in such solution, while
pyridine coordination to the ‘CuO4’ core in [Cu2(L2)2] to result in [Cu2(L2)2
(py)2] isolated here, will certainly prevent inter-molecular spin-exchange.
Further study will be required to resolve such issues. Similar results have
been observed in previous EPR studies of pyridine adducts of substituted
2,4-pentanedionatocopper(II) complexes [10,11].
In conclusion, the novel binuclear [Cu2(L2)2(py)2] complex derived
from the relatively unstable cis-[Cu2(L1-Se,O)2] complex, which in the
presence of pyridine results in the relatively rapid elimination of red
selenium accompanied by the O for Se atom exchange to yield the first
example of a metallamacrocyclic copper(II) complex (isolated as a
five-coordinate Cu(II) bis-pyridine adduct) containing a bipodal
chelating N,N,N′′′,N′′′-tetraethyl-N′,N′′-isophthaloylbis(urea) anion
fragment as ligand. This [Cu2(L2)2(py)2] complex crystallizes in one-
dimensional supramolecular arrays in the solid state.
MoKα radiation, λ=0.71073 Å). Data were captured with
a CCD (Charge-
Coupled Device) area-detector with the generator powered at 40 kV and 30 mA. A
constant stream of nitrogen gas is produced by an Oxford Cryogenics Cryostat
(700 Series Cryostream Plus) coupled to the diffractometer for low temperatures
(100 K). The structures were solved by direct methods (SHELXS-97 [12])and refined by
full-matrix least-squares on F2 (SHELXL-97 [12]). All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were fixed and refined in their theoretical positions.
The molecular structures were visualized by Diamond, Version 3.2e [13].
[8] A. Rodenstein, J. Griebel, R. Richter, R. Kirmse, Z. Anorg. Allg. Chem. 634 (2008) 867.
[9] D.E. Fenton, C.M. Regan, U. Casellato, P.A. Vigato, M. Vivaldi, Inorg. Chim. Acta 58
(1982) 83.
Acknowledgements
Financial support from Stellenbosch University and the NRF (GUN
2046827) is acknowledged. A. Rodenstein gratefully acknowledges
the Leipzig and Stellenbosch University exchange programme for
assistance to visit Stellenbosch.
[10] J. Pradilla-Sorzano, J.P. Fackler Jr., Inorg. Chem. 13 (1974) 38.
[11] D. Attanasio, I. Collamati, C. Ercolani, J. Chem. Soc., Dalton Trans. (1974) 1319.
[12] G. Sheldrick, Acta Crystallogr. A 64 (2008) 112.
[13] K. Brandenburg, Diamond 3.2e, Crystal and Molecular Structure Visualization,
Bonn, 2010.
Appendix A. Supplementary material
X-ray crystallographic files in CIF format for the supplementary
crystallographic data for [Cu2(L1)2] and [Cu2(L2)2(py)2] have been