Synthesis and spectroscopic studies on copper(II) binuclear complexes of 1-phenylamidino-O-alkylurea (alkyl = n-propyl, n- and iso-butyl) with 1,3-diaminopropane or ethylenediamine

Article abstract of DOI:10.1021/ic051037t

Copper(II) binuclear complexes [Cu(II)(1-phenylamidino-O-n-propylurea)tn] ₂ (H₂O)₂(Cl₂)₂ (1), [Cu(II)(1-phenylamidino-O-n-butylurea)tn]₂(H₂O) ₂(Cl₂)₂(2), [Cu(II)(1-phenylamidino-O-i- butylurea)tn]₂(H₂O)₂(Cl₂) ₂(3), and [Cu(II)(1-phenyamidino-O-i-butylurea)en]₂(H ₂O)₂(Cl₂)₂ (4) have been reported. The binuclear complexes 3 and 4 crystallize in a monoclinic structure with unit cell dimensions a = 15.252(17) A, b = 14.682(10) A, c = 13.606(13) A, and β = 111.2(1)° and a = 15.278(35) A, b = 14.665(21) A, c = 13.603(27) A, and β = 111.1(1)°, respectively. The EPR spectra of all the solid complexes at room temperature consisted of fine-structure transitions (ΔM_s = 1) with zero-field splitting (ZFS) of 0.0500 cm^-1 and a half-field signal (ΔM_s = 2) at ca. 1600 G, suggesting the formation of binuclear complexes (S = 1). From the observed ZFS, we estimated the average Cu-Cu distance. From the temperature dependence of the EPR signal intensity, we evaluated the isotropic exchange interaction constant J. It appears that the exchange interaction between the two interacting spins of the binuclear complexes is ferromagnetic in nature. The formation of ferromagnetically coupled copper binuclear complexes was further confirmed from the high magnetic-moment values at room temperature. When the EPR spectra were recorded in the temperature range 300-400 K, it was observed that the triplet-state EPR signal completely and irreversibly disappeared at ca. 380 K with the appearance of a new signal attributable to the mononuclear complex (S = 1/2). Thermal studies of these complexes in this temperature range suggested the loss of two water molecules, which might be responsible for binding two mononuclear species. EPR, IR, and thermal studies indicate a long-range ferromagnetic exchange mediated through hydrogen bonding between copper(II) ions (S = 1/2).

Full text of DOI:10.1021/ic051037t

Inorg. Chem. 2006, 45, 2193−2198
Synthesis and Spectroscopic Studies on Copper(II) Binuclear
Complexes of 1-Phenylamidino-O-alkylurea (alkyl n-propyl, n- and
)
iso-butyl) with 1,3-Diaminopropane or Ethylenediamine
S. Pramodini Devi,† R. K. Hemakumar Singh,*,† and R. M. Kadam‡
Department of Chemistry, Manipur UniVersity, Imphal 795003, India, and Radiochemistry
DiVision, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
Received June 24, 2005
Copper(II) binuclear complexes [Cu(II)(1-phenylamidino-O-n-propylurea)tn]2 (H2O)2(Cl2)2 (1), [Cu(II)(1-phenylamidino-
O-n-butylurea)tn]2(H2O)2(Cl2)2(2), [Cu(II)(1-phenylamidino-O-i-butylurea)tn]2(H2O)2(Cl2)2(3), and [Cu(II)(1-phenyamidino-
O-i-butylurea)en]2(H2O)2(Cl2)2 (4) have been reported. The binuclear complexes 3 and 4 crystallize in a monoclinic
structure with unit cell dimensions a
)
15.252(17) Å, b
)
14.682(10) Å, c
)
13.606(13) Å, and â ) 111.2(1)
°
and a 15.278(35) Å, b 14.665(21) Å, c
)
)
)
13.603(27) Å, and â ) 111.1(1)°
, respectively. The EPR spectra
of all the solid complexes at room temperature consisted of fine-structure transitions (
∆
Ms
)
1) with zero-field
1
splitting (ZFS) of 0.0500 cm- and a half-field signal (
∆
Ms
)
2) at ca. 1600 G, suggesting the formation of
binuclear complexes (S
)
1). From the observed ZFS, we estimated the average Cu−Cu distance. From the
temperature dependence of the EPR signal intensity, we evaluated the isotropic exchange interaction constant J.
It appears that the exchange interaction between the two interacting spins of the binuclear complexes is ferromagnetic
in nature. The formation of ferromagnetically coupled copper binuclear complexes was further confirmed from the
high magnetic-moment values at room temperature. When the EPR spectra were recorded in the temperature
range 300
−400 K, it was observed that the triplet-state EPR signal completely and irreversibly disappeared at ca.
380 K with the appearance of a new signal attributable to the mononuclear complex (S
)
1/2). Thermal studies
of these complexes in this temperature range suggested the loss of two water molecules, which might be responsible
for binding two mononuclear species. EPR, IR, and thermal studies indicate a long-range ferromagnetic exchange
mediated through hydrogen bonding between copper(II) ions (S
) 1/2).
Introduction
investigations was to understand metal-metal interaction
among d-electron systems and also to gain insight into the
structural aspects, with a special emphasis on investigating
the nature of magnetic coupling in these complexes.
Electron paramagnetic resonance (EPR) spectroscopy has
been extensively used for the elucidation of the molecular
structures of several binuclear complexes, such as copper
DL-tartrates,1 vanadyl tartrates,2 citrates,3 copper hydroxyl-
carboxylate,4 and peptide5 complexes. The main goal of such
In recent years, many papers have been published on the
creation of supramolecular architectures based on [CuL2]2+
cations in which the copper(II) center is coordinated by
tetradentate bis(amidino-O-alkylurea) ligands, which have
extensive hydrogen-bonding potential (eight N-H donor
centers and two oxygen acceptor centers). In such cases, the
hydrogen-bonded supramolecular architects are used to link
cationic transition coordination complexes through non-
coordinated anions and generate 1-D chains and 2-D sheet
architectures. In [CuL2]Cl2‚2H2O, the chains are linked into
sheets through hydrogen-bonding contacts involving anions
and solvent molecules. Although hydrogen-bonding interac-
tions have long been considered to be of importance in
* To whom correspondence should be addressed. Fax: 91-0385-2435145.
Phone: 91-0385-2226460. E-mail: rkhemakumar@rediffmail.com (R.K.H.S.),
rmkadam2003@yahoo.co.in (R.M.K.)
† Manipur University.
‡ Bhabha Atomic Research Centre.
(1) Chasteen, N. D.; Belford, R. L. Inorg. Chem. 1970, 9, 169.
(2) Belford, R. L.; Chasteen, N.D.; So, H.; Tapscott, R.E. J. Am. Chem.
Soc. 1969, 91, 4675.
(3) Dunhill, R. H.; Smith, T. D. J. Chem. Soc. A 1968, 2189.
(4) Dunhill, R. H.; Pilbrow, J. R.; Smith, T. D. J. Chem. Phys. 1966, 45,
1474.
(5) Boas, J. F.; Pilbrow, J. R.; Hartzell, C. R.; Smith, T. D. J. Chem. Soc.
A 1969, 572.
10.1021/ic051037t CCC: $33.50
Published on Web 02/04/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 5, 2006 2193

Pramodini Devi et al.
Analytical, electronic spectra, and magnetic moment data of the
complexes are summarized below.
biological systems, it is only recently that the transition-metal
complexes containing ligands with versatile hydrogen-
bonding capabilities have been used to bind DNA bases and
other anions and to construct a network of coordinated
complexes connected through intermolecular interactions.6
In a continuation of our earlier investigations7,8 on bi-
nuclear complexes and with the aim of obtaining an improved
insight into the chemical and structural factors that govern
the formation of binuclear complexes, we have extended our
investigations to a number of newly synthesized copper(II)
complexes of 1-phenylamidino-O-alkylurea with 1,3-diami-
nopropane and 1,2-diaminoethane. We have also confirmed
the formation of ferromagnetically coupled binuclear com-
plexes [Cu(II)(1-phenylamidino-O-n-propylurea)tn]2(H2O)2-
(Cl2)2 (1), [Cu(II)(1-phenylamidino-O-n-butylurea)tn]2(H2O)2-
(Cl2)2 (2), [Cu(II)(1-phenylamidino-O-i-butylurea)tn]2(H2O)2-
(Cl2)2 (3), and [Cu(II)(1-phenylamidino-O-i-butylurea)en]2-
(H2O)2(Cl2)2 (4). The X-ray powder diffraction studies of
[Cu(II)(1-phenylamidino-O-i-butylurea)tn]2(H2O)2(Cl2)2 and
[Cu(II)(1-phenylamidino-O-i-butylurea)en]2(H2O)2(Cl2)2 sug-
gested monoclinic structures for these complexes. Thermal,
magnetic, and spectroscopic investigations on these com-
plexes are presented in this paper.
(i) [Cu(II)(1-phenylamidino-O-n-propylurea)tn]2(H2O)2(Cl2)2 (1).
Color, violet; yield ) 65%; mp ) 128 °C; λmax(DMF) ) 18 484
cm-1; µeff: 2.01 µB. Anal. Calcd. for C28H56Cl4Cu2N12O4: C, 37.62;
H, 6.27; N, 18.81; Cu, 14.22. Found: C, 37.80; H, 6.20; N, 19.11;
Cu, 14.30.
(ii) [Cu(II)(1-phenylamidino-O-n-butylurea)tn]2(H2O)2(Cl2)2 (2).
Color, violet; yield ) 75%; mp ) 129 °C; λmax(DMF) ) 19 323
cm-1; µeff ) 2.2 µB. Anal. Calcd. for C30H60Cl4Cu2N12O4: C, 39.08;
H, 6.51; N, 18.24; Cu, 13.78. Found: C, 40.01; H, 6.60; N, 18.44;
Cu, 13.61.
(iii) [Cu(II)(1-phenylamidino-O-i-butylurea)tn]2(H2O)2(Cl2)2 (3).
Color, violet; yield ) 80%; mp )128 °C; λmax(DMF) ) 19 455
cm-1, µeff ) 2.42 µB. Anal. Calcd. for C30H60Cl4Cu2N12O4: C,
39.08; H, 6.51; N, 18.24; Cu, 13.78. Found: C, 39.21; H, 6.48; N
,18.30; Cu, 13.76.
(iv) [Cu(II)(1-phenylamidino-O-i-butylurea)en]2(H2O)2(Cl2)2 (4).
Color, violet; yield ) 70%; mp ) 132 °C; λmax(DMF) ) 19 120
cm-1; µeff ) 2.61 µB. Anal. Calcd. For C28H56Cl4Cu2N12O4: C,
37.62; H, 6.27; N, 18.81; Cu, 14.22. Found: C, 38.10; H, 6.32; N,
19.11; Cu, 14.30.
(v) [Cu(II)(1-phenylamidino-O-methylurea)tn]Cl2 (5). Color, pale
pink; yield ) 65%; mp ) 132 °C; λmax (DMF) ) 19 065 cm-1
;
µeff ) 1.82 µB. Anal. Calcd. for C12H22Cl CuN6O: C, 35.95; H,
2
5.49; N, 20.97; Cu, 15.85. Found: C, 35.81; H, 5.60; N, 21.22; Cu,
15.81.
Experimental Section
Methods and Materials. Phenyldicyandiamide (PD) was pre-
pared by following a published procedure.9
Preparation of Complexes. (A) Dichloro-mono-(1-phenylami-
(vi) [Cu(II)(1-phenylamidino-O-ethylurea)tn]Cl2. H2O (6). Color,
pale pink; yield ) 60%; mp ) 133 °C; λmax(DMF) ) 19 055 cm-1
;
µeff ) 1.88 µB. Anal. Calcd. for C13H26Cl2CuN6O2: C, 36.06; H,
6.01; N, 19.42; Cu, 14.68. Found: C, 35.91; H, 6.30; N, 19.81;
Cu, 14.44.
n
dino-O-alkylurea)copper(II) (where alkyl ) CH3, C2H5, C3 H7,
n
C4 H9) was prepared using our published procedure.10
(B) Dichloro-mono-(1-phenylamidino-O-i-butylurea)copper(II)
was prepared by refluxing cupric chloride (0.85 g) and phenyldi-
cyandiamide (0.80 g) in isobutanol on a steam bath for 2 h. The
intense blue complex was filtered off immediately, washed several
times with acetone ,and dried in air. Yield ) 80%; mp ) 195 °C;
Physical Measurements. Microanalyses were performed on a
carbon, hydrogen, nitrogen analyzer Perkin-Elmer 240C model; IR
spectra were recorded on KBr disks on a Shimadzu FT-IR-8400S.
The X-ray powder patterns of complexes were obtained on a Philips
X-ray diffractometer Model PW 1710 with Ni-filtered Cu KR
radiation in the 2θ range of 10-40°. Photo acoustic spectra (PAS)
on solid samples were recorded using a homemade spectrometer
in the 350-800 nm range using a Tungsten halogen lamp as the
source,11 whereas solution spectra were recorded on a Beckmann
DU-640 spectrophotometer. EPR experiments were conducted using
a BRUKER ESP-300 spectrometer operated at X-band frequency
(9.5 GHz) with 100 kHz field modulation. DPPH was used as a
field marker. Temperature was varied in the range 100-400 K using
a Eurotherm BVT 2000 variable temperature accessory with liquid
nitrogen as the coolant in a flow system. The room-temperature
magnetic moments (µeff) were measured using a PAR vibrating
sample magnetometer (VSM) model 155. Molar conductance in
MeOH was measured at room temperature on an Elico conductivity
bridge type CM-82T. Thermal studies of the compounds were
carried out in an air atmosphere with a Shimadzu thermal analyzer
DT-30.
λ
max(DMF) ) 13 927 cm-1; µeff ) 1.88 µB. Anal. Calcd. for C12H18-
Cl2CuN4O: C, 39.07; H, 4.88; N, 15.19; Cu, 17.23. Found: C, 38.92;
H, 4.81; N, 15.20; Cu, 17.31.
(C) For the complexes [Cu(II)(1-phenylamidino-O-alkylurea)-
n
tn]Cl2, where alkyl ) CH3, C2H5, C3 H7, C4n,iH9; tn ) 1,3-
diaminopropane and en ) 1,2-diaminoethane, the respective blue
dichloromono-(1-phenylamidino-O-alkylurea)copper(II) complexes
(0.1 mol) were dissolved in hot ethanol. Tn or en (1.0 mol) was
added with constant stirring in a beaker on a steam bath for 30-
45 min. After being kept overnight in a refrigerator, the complexes
were obtained. They were washed repeatedly with ethanol and dried
in air.
(6) (a) Unchulee, S.; Blake, A. J.; Peter, H.; Wilson, C. CrystEngComm.
2004, 6 (15), 70 and references therein. (b) Begley, M. J.; Hubberstey,
P.; Moore, C. H. M. J. Chem. Res., Synop. 1991, 334. (c) Begley, M.
J.; Hubberstey, P.; Moore, C. H. M. J. Chem. Res., Synop. 1986, 172.
(d) Black, A. J.; Hubberstey, P.; Suksangpanya, U.; Wilson, C. J.
Chem. Soc., Dalton Trans. 2000, 3873. (e) Suksangpanya, U.; Blake,
A. J.; Hubberstey, P.; Parker, D. J.; Teat, S. J.; Wilson, C. CrystEng-
Comm. 2003, 5, 23.
(7) Ajitkumar, L. S.; Ibopishak, O. S.; Manihar, A. S.; Hemakumar, R.
K. S.; Kadam, R. M.; Bhide, M. K.; Dhobale, A. R.; Sastry, M. D.
Spectrochim. Acta, Part A 2004, 60, 1593.
(8) Ibopishak, O. S.; Damayenti, M.; Rajen, N. S.; Hemakumar, R. K.
S.; Manoj, M.; Kadam, R. M. Polyhedron 2005, 24, 909.
(9) Curd, F. H. S.; Rose, F. L. J. Chem. Soc. 1946, 729.
(10) Ajitkumar, L. S.; Ibopishak, O. S.; Manihar, A. S.; Hemakumar, R.
S.; Kadam, R. M.; Bhide, M. K.; Sastry, M. D. Transition Met. Chem.
2001, 26, 532.
X - Ray Powder Diffraction Studies. Because single crystals
of these compounds could not be obtained despite our repeated
attempts, the exact crystal structure determination could not be done.
To give a typical idea about the single phasic nature of the
compounds, we have carried out powder XRD studies on these
compounds. The binuclear complexes 3 and 4 crystallize in
(11) Dhobale, A. R.; Chaturvedy, T. P.; Venkiteswarn, S.; Sastry, M. D.
Bhabha Atomic Research Centre External Report No. E-019; Bhabha
Atomic Research Centre: Trombay, India, 1996.
2194 Inorganic Chemistry, Vol. 45, No. 5, 2006

Copper(II) Binuclear Complexes of 1-Phenylamidino-O-alkylurea
the range 3637-3648 cm-1 and at ca. 1630 cm-1 may be
assigned to νO-H and νH-O-H, respectively, for lattice water
present in the complexes.22,23 Two bands at ca. 1062 and ca.
1392 cm-1 are due to the νC-C and νC-N bands of 1,2-
diaminoethane and 1,3-diaminopropane.24 An interesting
observation in the IR spectra of complex 3, recorded carefully
after heating the complex and KBr at 100 °C, is the
substantial decrease in the band assigned for νOH, suggesting
the loss of water molecules in this temperature range.
EPR Spectra. The room-temperature EPR spectrum of a
powdered sample of dichloromono(1-phenylamidino-O-i-
butyurea)copper(II) complex, which was used as a starting
compound for the preparation of binuclear copper complexes,
showed an axially symmetric signal with g| ) 2.2075 and
g ) 2.0450. EPR spectra were also recorded on polycrys-
talline samples of a number of copper(II) complexes of
monoclinic structures with unit cell dimensions a ) 15.252(17) Å,
b ) 14.682(10) Å, c ) 13.606(13) Å, and â ) 111.2(1)° and a )
15.278(35) Å, b ) 14.665(21), Å, c ) 13.603(27) Å, and â )
111.1(1)°, respectively. Most of the prominent diffraction lines
could be satisfactorily indexed on the basis of a monoclinic unit
cell using Powder X program.12 The typical fit parameters of these
phases are given in the Supporting Information.
Results and Discussion
Electronic Spectra. The complexes of copper(II) with
1-phenylamidino-O-alkylurea (alkyl ) CH3, C2H5, C3H7,
C4n,iH9) with 1,2-diaminoethane (en) or 1,3-diaminopropane
(tn) and bis(1-phenylamidino-O-methylurea)copper(II) chlo-
ride are violet/light pink in color. The unusual pink coloration
arises from the strong ligand field in the [CuN4] chromophore
group. The photoacoustic (PA) spectra of the solid complexes
showed a broad band at ca. 19 000 cm-1 attributable to high
energy d-d electronic transitions. This absorption band is
almost similar to that observed in square planar copper(II)
complexes with succinimidato copper(II) complexes,13 cop-
per(II)-O-alkyl-1-amidinourea complexes,14 and closely re-
lated biguanide compounds.15 In addition, a weak absorption
band at ca. 26 400 cm-1 was observed in the spectra of
complexes 1, 2, 3, and 4, which may be attributable to weak
metal-metal bonding.7,16 When the electronic spectra of the
binuclear complexes were recorded in DMF solvent, the
broad absorption band arising from the d f d transitions
was shifted in the range 18 382-19 455 cm-1. The shift may
be due to axial ligation of solvent molecules. An intense
absorption band at ca. 25 906 cm-1 in the solution spectra
is due to the charge-transfer band.14
n
1-phenylamidino-O-alkylurea (alkyl ) CH3, C2H5, C3 H7,
n
i
C4 H9, C4 H9) with 1,3-diaminopropane (tn) and 1-phenyla-
midino-O-i-butylurea with 1,2-diaminoethane (en). The EPR
spectra of solid complexes 5 (Figure 2a) and 6 showed a
single broad-band resonance at ca. g ) 2.0550. However,
well-resolved spectra with a quartet hyperfine structure (Cu,
I ) 3/2) on parallel components were obtained when EPR
spectra of dilute solutions of these complexes in MeOH or
DMF were recorded at 77 K.
Interesting results were obtained in the case of copper
complexes 1, 2, 3, and 4, for which the EPR spectra were
recorded in the solid state (shown in Figures 1c, 1d, 2a, and
1b, respectively). The EPR spectra of these complexes
consisted of two intense bands, separated by ca. 500 G, with
features of perpendicular components (D). On either side of
these intense perpendicular components, a signal consisting
of several narrow lines with nearly double the separation as
that of perpendicular separation were observed (2D). The
seven-line hyperfine structure on the low-field parallel
component with the relative intensity ratio 1:2:3:4:3:2:1 is
due to interaction of unpaired spins with two equivalent Cu2+
nuclei (I ) 3/2). The hyperfine coupling observed on the
parallel components (A| ) 100 G) is nearly half of that
observed for the corresponding mononuclear complexes in
DMF/MeOH. In addition, a weak signal at 1600 G corre-
sponding to the forbidden transition ∆Ms ) (2 and exhibit-
ing a seven-line hyperfine structure was observed, confirming
the formation of the binuclear complex. Similar spectra have
been reported for binuclear complexes of copper DL-tartrate1
and copper dimers stabilized in a CeO2 matrix.25 It may be
noted that EPR spectra of binuclear complexes in MeOH
and DMF at 77 K mainly consist of mononuclear complexes,
indicating dissociation of these complexes to their monomers,
which is supported by the conductance value in MeOH (ΛM
) 154-168 Ω-1 cm2 mol-1 for a bi-univalence electrolyte).
Ir Spectra. The Ir spectrum of phenyldicyandiamide
shows a νCtN band at 2167 cm-1 and a νCdN7,17 band at 1656
cm-1. In all the complexes, the presence of the νCdN band
in the range 1571-1596 cm-1 indicates coordination through
the C)N group of the phenylamidine part. The N)C-O-C
fragment of 1-phenylamidino-O-alkylurea is more delocal-
ized, and the bond order of the )C-O- group is raised,
which gives a new νCdN in the range 1680-1690 cm-1 after
coordination.8,10,18,19 Bands in the 470-480 cm-1 range and
at ca. 315 cm-1 have been assigned to the νCu-N and νCu-Cl
bands of the dichloro-mono(1-phenylamidino-O-i-butylurea)-
copper(II) complex, respectively. In the IR spectra of
complexes 1, 2, 3, and 4, a broad and strong band in the
range 3255-3266 cm-1 is assigned to the νN-H band of the
primary amine,20,21 and the appearance of medium bands in
(12) Jakkal, V. S. Bhabha Atomic Research Centre, Mumbay, India.
PowderX, a Fortran program for indexing and refining the unit cell
parameter; private communication, 2005.
(13) Yamada, S.; Miki, S. Bull. Chem. Soc. Jpn. 1963, 36, 680.
(14) Wasson, J. R.; Trapp, C. J. Phys. Chem. 1969, 73, 3763.
(15) (a) Ray, P.; Bagghi, P. N. J. Indian Chem. Soc. 1939, 6, 617. (b) Ray,
P. J. Indian Chem. Soc. 1941, 18, 217.
(16) Krishna, K. N.; Vinod, P. S. Transition Met. Chem. 1996, 21, 507.
(17) Das, A.; Bagchi, A.; Saha, S. R. Indian J. Chem., Sect. A 1990, 29,
361.
(22) Deltcheff, C. R.; Thouvenot, R.; Franck, R. Spectrochim. Acta, Part
A 1976, 32, 587.
(23) Indira, V.; Joy, P. A.; Alekar, N. A.; Gopinathan, S.; Gopinathan, C.
Indian J. Chem., Sect. A 1997, 36, 687.
(18) Barnard, P. F. B. J. Chem. Soc. A 1969, 2140.
(19) Jamnicky, M.; Segla, P.; Koman, M. Polyhedron 1995, 14, 1837.
(20) Silverstein, R.; Bassler, G.C. Spectrometric Identification of Organic
Compounds, 2nd ed.; Wiley: New York, 1967; p 86.
(21) Ponticelli, G. Inorg. Chim. Acta 1971, 5 (3), 461.
(24) Jan, G. H.; Preez, D. B. J. A. M.; Brecht, V. J. Chem. Soc., Dalton
Trans. 1989, 253.
(25) Abou kais, A.; Bennani, A.; Aissl, C. F.; Wrobel, G.; Guelton, M. J.
Chem. Soc., Faraday Trans. 1992, 88 (4), 615.
Inorganic Chemistry, Vol. 45, No. 5, 2006 2195

Pramodini Devi et al.
Figure 1. EPR spectra of different Cu(II) dimers and monomers at 300 K
(a) complex 5, (b) complex 4, (c) complex 1, and (d) complex 2.
The most accurate values of g|, g , A|Cu, A Cu, and D for
binuclear complexes were deduced by computer simulation
assuming axial symmetry and are given in Table 1.
Figure 2. EPR spectra of complex 3 in the solid state at (a) 300, (b) 365,
(c) 368, (d) 375, and (e) 390 K.
EPR Spectra at Low Temperatures (77-300 K). The
isotropic exchange-interaction constant J, or the separation
between the singlet and triplet, was calculated from the
temperature dependence of the intensity of the half-field
signal7,25 ∆Ms ) (2 for complexes 1, 2, 3, and 4. The
increase in the intensity of the EPR signal (∆Ms ) (2) with
decreaing temperature is much more than that expected from
the Boltzmann population difference within the triplet
manifold. It appears that the isotropic exchange interaction
between the interacting spins of the binuclear complex is
ferromagnetic in nature. In addition to an increase in the
intensity of allowed and forbidden transitions, there was also
an increase in the zero-field splitting as the temperature was
lowered in the range 350-77 K (complex 4, D ) 0.0493
cm-1 at 300 K and D ) 0.0530 cm-1 at 77 K). The increase
in the D value is significant and may occur because of lattice
contraction at lower temperatures.29
at g )2.0555, which was attributed to the formation of
mononuclear complex. The triplet-state EPR signal com-
pletely disappeared at about 380 K. The changes in the EPR
spectra were found to be irreversible and were associated
with the loss of water molecules in binuclear complexes.
Thermal gravimetric (TG) experiments of complex 3 showed
weight loss in the 360-380 K range, which corresponds to
the loss of two water molecules. The coordinated water in
hydrated complexes is usually lost at higher temperatures
(550-600 K). The loss of water molecules at relatively low
temperatures suggests that water is weakly bound by
hydrogen bonds to the ligands in all binuclear complexes 1,
2, 3, and 4. Comparison of the IR spectra of the virgin
complex 3 with the one recorded after heating the complex
at 380 K indicates a substantial decrease in the intensity of
band at 3637 cm-1 without any noticeable changes in other
band positions, which is attributed to the loss of water
molecules. Also, the absence of the IR bands at ca. 650, 740,
and 950 cm-1, which are characteristic of coordinated water,
further confirmed that water is not coordinated to the
complex but is instead weakly bound by hydrogen bonds to
the ligands.
EPR Spectra at High Temperatures (300-400 K). The
temperature dependence of the EPR spectra was studied in
the high-temperature range 300-400 K for complex 3
(Figure 2). Above 360 K, the intensity of the triplet-state
signal decreases abruptly with the appearance of a new signal
The values of g|, g , A|Cu, and A Cu measured for a number
of mononuclear 5, 6, and binuclear Cu(II) complexes 1, 2,
3, and 4 are typical of those values for Cu(II) atoms
coordinated to nitrogen ligands with a square planar coor-
dination around a metal ion. The measured EPR (g and A)
(26) Williamson, W. B.; Lunsford. J. H. J. Phys. Chem. 1976, 80, 2664.
(27) (a) Fritz, H. P.; Keller, H. J.; Teil, B. Z. Naturforsch. 1965, 206, 1145.
(b) Raynor, J. B.; Teil, B. Z. Naturforsch. 1969, 241, 775.
(28) Chao, C. C.; Lunsford, J. H. J. Chem. Phys. 1972, 57 (7), 2890.
(29) Sreehari, N.; Varghese, B.; Manoharan, P. T. Inorg. Chem. 1990, 29,
4011.
2196 Inorganic Chemistry, Vol. 45, No. 5, 2006

Copper(II) Binuclear Complexes of 1-Phenylamidino-O-alkylurea
Table 1. EPR Parameters of Cu(II) Mononuclear (M) and Binuclear (B) Complexes with Different Ligands
matrix
g|
g
giso
A| (G)
A
(G)
Aiso (G)
D (cm-1
)
J (cm-1
)
r (Å)
ref
14
[Cu(1-phABiUH)Cl2] (M)
complex 5 (M)
complex 6 (M)
2.2075
2.1774
2.1779
2.24a
2.0450
2.0400
2.0405
2.06a
2.0992
2.0858
2.0863
2.1200
2.0973
2.0947
2.1063
2.0897
2.0833
2.0823
210
212
218
30
32
25
90
92
89
[Cu(1-AAUH)2]Cl2 (M)
2.176b
2.216
2.058b
2.034
[Cu(NH3)4]2+ (M)
[Cu(NH3)4][PtCl4] (M)
complex 4 (B)
160
211
100
26
27
2.217
2.051
28
89
2.1640
2.1650
2.1599
2.0525
2.0425
2.0435
0.0493c
0.0530b
0.0510
.0520b
0.0495
0.0505
0.0525b
0.0525
0.0225
0.0057
0.066
+55
+50
3.99
3.84
complex 1 (B)
100
complex 2 (B)
complex 3 (B)
2.1595
2.1730
2.0430
2.0485
2.0818
2.0900
100
100
3.88
3.96
[Cu(1-PhABUH)en(H2O)]Cl2 (B)
[Cu(1-PhAMUH)SO4]2 (B)
(Cu2v)2i,n(DL)-(tart)4-2 (B)
2.1200
2.2383
2.224
2.2079
2.3450
2.0525
2.1773
2.0860
2.0403
2.0660
2.0750
2.1976
2.1320
2.0962
2.1590
90
+57
+27
-18
-52
4.00
4.70
3.85
4.50
6
6
1
25
28
82
85
81
(Cu2+
(Cu2+
)
)
i,nCeO2 (B)
13.5
37.5
2
i,nY zeolite (B)
0.048
2
a At room temperature. b At 77 K. c At 300 K.
parameters for mononuclear complexes ([Cu(1-phABiUH)-
coordinates Cu(II) to give square planar [CuL2]2+complex
cations, which, because of their versatile hydrogen-bonding
capacity, form diverse hydrogen-bonded supramolecular
architectures with anions. In [CuL2]Cl2‚2H2O, alternating
cations and chloride anions are hydrogen bonded to form a
one-dimensional chain. These one-dimensional chains are
further linked by complex hydrogen-bonding contacts in-
volving anions and water molecules, forming two-dimen-
sional sheets.34 In our present study, we have synthesized a
series of binuclear complexes [Cu(II)(1-phenylamidino-O-
alkyllurea)en/tn(H2O)]Cl2 (alkyl ) C3H7 and C4H9) using the
bidentate ligand 1-phenylamidino-O-alkyl urea (4 N-H
donor sites) and bidentate ligands en (ethylenediamine) or
tn (1,3-diaminopropane). There are four N-H donors avail-
able in the ligand 1-phenylamidino-O-alkylurea. Two N-H
groups from this ligand and two from either 1,2-diamino-
ethane or 1,3-diaminopropane occupy the equatorial posi-
tions around the copper(II), giving a nearly square planar
geometry. The loss of water on heating the binuclear
complexes at relatively low temperatures (380 K) and
dissociation of all binuclear complexes in MeOH and DMF,
as evident from EPR and conductivity studies, clearly sug-
gest that two monomers are held together by weak hydro-
gen bonding to form a ferromagnetic interaction between
two copper atoms. In our complexes, there is also room for
possible interaction between the chloride and NH group of
the ligands in the solid state.34 The structure of the binuclear
complexes will consist of monomers involving interac-
tion of the ligands, anions, and water molecules; how-
ever, proposing the structure without single-crystal X-ray data
will be highly speculative. Our study will attract further
research for structure determination of these binuclear
complexes.
Cl2], 5, and 6) are close to those values for [Cu(amidino-
26
O-alkylurea)2]Cl2,14 Cu(NH3)4, and [Cu(NH3)4][PtCl4]27
complexes having square planar geometry. We have evalu-
2
ated the angle x (28°) using the equation g2 ) g|2cos2(x) +
g sin2(x),30where g| (2.1943) and g (2.0530) represent g
2
values for the mononuclear complex, and x is the angle
between the Cu-Cu direction and the parallel direction; g|
is replaced by g2 (2.1640), as g| and the Cu-Cu direction
for binuclear complex 4 do not coincide. The average
distance between two unpaired electrons was calculated by
using the equation D ) 3g2â2/(2r3) ) 1.39 × 104 g r-3.31
The average distance r between the two unpaired electrons
estimated for different binuclear complexes is given in Table
1.
Recently, it has been shown that, in solid state, chromium
complexes32 with the general formula cis-[CrA4(OH)2(OH)]2
(where A4 represents four nitrogen ligators from an appropri-
ate number of monodentate and polydentate ligands) have a
dimeric structure, in which two molecules are bound together
by powerful hydrogen bonds such that it can transmit an
antiferromagnetic interaction between the two chromium
centers, even though they are separated by a distance of 5
Å. Similarly, in cyano-bridged Cu(II)-Ni(II) heterobimetallic
complexes,33 a weak long-range (9.75 Å) ferromagnetic
interaction between two copper ions through hydrogen
bonding was observed.
A series of coordination complexes containing a poly-
methylene-linked bis(N-alkylamidino-O-alkylurea)copper(II)
cation, e.g., [CuL2]2+, with nitrate, halides, and tetrafluo-
roborate anions, has been synthesized because of the poly-
dentate nature of the ligand (eight N-H donor centers and
two oxygen acceptor centers). The tetradentate ligand
On the basis of our experimental evidence, we suggest
the most probable structure of the monomer (Figure 3) in
forming binuclear complex 3.
(30) Chikira, M.; Kon, H. J. Chem. Soc. Dalton Trans. 1979, 245.
(31) Eaton, S. S.; More, K. M.; Sawant, B. M.; Eaton, G. R. J. Am. Chem.
Soc. 1983, 105, 6560.
(32) Goodson, P. A.; Glerup, J.; Hodgson, D. J.; Michelsen, K.; Ry-
chlewska, U. Inorg. Chem. 1994, 33, 359.
(33) Ali, M.; Ray, A.; Sheldrick, W. S.; Mayer-Figge, H.; Gao, S.; Sahmes,
M. New J. Chem. 2004, 28, 412.
(34) Suksangpanya, U.; Blake, A. J.; Hubberstey, P.; Wilson, C. Crys-
tEngComm. 2002, 4 (92), 552.
Inorganic Chemistry, Vol. 45, No. 5, 2006 2197

Pramodini Devi et al.
with a decrease in the temperature clearly indicate ferro-
magnetic coupling between two interacting Cu(II) ions. EPR
studies on solid complexes in the temperature range 300-
400 K suggested irreversible dissociation of the binuclear
complex into the mononuclear complex by the loss of weakly
bonded water. This was confirmed independently by IR and
thermal studies. Our present investigations clearly indicate
that hydrogen-bonding interactions involving ligands, water,
and anions play an important role in forming ferromagnetic
coupling between two Cu atoms.
Acknowledgment. Authors express their gratitude to Dr.
V. K. Manchanda Head, Radiochemistry Division, BARC,
for his keen interest in this work. We thank Dr. S. N. Achari,
Applied Chemistry Division, BARC, for X-ray measurements
and useful discussions. R.K.H.S. is grateful to Manipur
University for a leave grant.
Figure 3. Proposed structure of [Cu(II)(1-phenylamidino-O-i-butylurea)-
tn]2+ in forming complex 3.
Conclusions
EPR studies on newly synthesized copper(II) mixed-ligand
complexes of 1,2-diaminoethane or 1,3-diaminopropane with
1-phenylamidino-O-alkylurea (alkyl ) CH3, C2H5, C3H7, and
C4n,iH9) have shown that some of them (1, 2, 3, and 4) exist
as binuclear complexes (S ) 1). The high magnetic-moment
values of these complexes and an increase in EPR intensity
Supporting Information Available: The IR spectra of complex
4 and crystallographic data for complexes 3 and 4. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC051037T
2198 Inorganic Chemistry, Vol. 45, No. 5, 2006