EPR spectra of Cu2+ doped [Zn(sac)2(dmen)] and [Zn(sac)2(paen)] single crystals

Article abstract of DOI:10.1016/j.saa.2006.12.008

Cu²⁺ doped single crystals of [Zn(sac)₂(dmen)] (sac: saccharinate, dmen: N,N′-dimethylethylendiamine) and [Zn(sac)₂(paen)], (paen: N,N′-bis(3-propylamine)ethylendiamine) complexes have been investigated by electron paramag

Full text of DOI:10.1016/j.saa.2006.12.008

Spectrochimica Acta Part A 68 (2007) 394–398
EPR spectra of Cu2+ doped [Zn(sac)2(dmen)] and
[Zn(sac)2(paen)] single crystals
R. Bıyıka,∗, R. Tapramazb, O.Z. Yes¸ilelc
a Tu¨rkiye Atom Energy Institution, Sarayko¨y Nuclear Research and Training Center, 06983 Kazan Ankara, Turkey
b Ondokuz Mayıs University, Faculty of Arts and Sciences, Department of Physics, 55139 Samsun, Turkey
c Eskis¸ehir Osmangazi University, Faculty of Arts and Sciences, Department of Chemistry, 26480 Eskis¸ehir, Turkey
Received 1 September 2006; received in revised form 28 November 2006; accepted 1 December 2006
Abstract
Cu2+ doped single crystals of [Zn(sac)2(dmen)] (sac: saccharinate, dmen: N,Nꢀ-dimethylethylendiamine) and [Zn(sac)2(paen)], (paen: N,Nꢀ-bis(3-
propylamine)ethylendiamine) complexes have been investigated by electron paramagnetic resonance (EPR) technique. Detailed investigations of
the EPR spectra indicate that Cu2+ ion substitute with Zn2+ ion and forms tetrahedral complex in [Zn(sac)2(dmen)] and octahedral complex in
[Zn(sac)2(paen)] hosts. Principal values of the g and hyperfine tensors are determined and the ground state wave functions of Cu2+ ions are obtained
using EPR parameters.
© 2006 Elsevier B.V. All rights reserved.
Keywords: EPR; Zinc; Saccharin; Copper; Doping
1. Introduction
In this study, two newly synthesized saccharinate complexes
[Zn(sac)2(dmen)] and [Zn(sac)2(paen)], are studied with EPR
spectroscopy by doping paramagnetic Cu2+ ion to substitute for
Zn2+ in the host to see how the complex is formed.
Studies on paramagnetic transition metal ion complexes in
diamagnetic host lattices are reported by many authors and struc-
tural properties are discussed [1–11]. When the transition metal
ions are doped in a diamagnetic host lattice as an impurity,
they form paramagnetic centers from which the structures of
the local symmetry can be obtained by means of electron para-
magnetic resonance (EPR) spectroscopy, which is one the most
efficient techniques to get information about the structure, sym-
metry, the effects of environmental structures and electric field
in complexes. These ions mostly replace a divalent or monova-
lent cation in the host by compensating the charge deficiency
with some other nuclei in the host.
Due to their importance in biological applications saccha-
rine, its derivatives and their metal complexes are being studied
widely. Various water soluble alkaline salts of saccharine are
used as low or non caloric synthetic sweeteners and as anti-
dotes against metal poisoning [12–14]. General formula of metal
complexes of saccharine is [M(sac)2(H2O)4]·2H2O, where M
is a divalent metal ion such as Zn2+, Co2+, Cd2+ and Cu2+.
2. Experimental
Water solution of dmen (0.176 g, 2.0 mmol) and paen
(0.350 g, 2.0 mmol) are added drop wise into separate
50 mL water solution of [Zn(sac)2(H2O)4]·2H2O [11] (0.548 g,
1.0 mmol) while stirring continuously at room temperature. The
solutions, then, areheatedupto80 ◦Cinatemperaturecontrolled
bath and stirred continuously for 4 h. The reaction products are
cooled to room temperature slowly. Small crystals grown in the
solution are filtered out and washed in cold distilled water and
ethanol, and dried.
2.1. Cu2+ doped [Zn(sac)2(dmen)] and [Zn(sac)2(paen)]
[Zn(sac)2(dmen)] and [Zn(sac)2(paen)] crystals obtained in
previous process are dissolved in 25 mL (1.0 mmol) of hot water
kept at60 ◦Cintemperaturecontrolledheatbath. Approximately
0.1% of CuSO4 is added to the solution to substitute some Zn2+
with Cu2+ ions. The solution then cooled very slowly to room
temperature for purification and also for the development of
∗
Corresponding author. Tel.: +90 312 8154300; fax: +90 312 8154307.
E-mail address: recep.biyik@taek.gov.tr (R. Bıyık).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.12.008

R. Bıyık et al. / Spectrochimica Acta Part A 68 (2007) 394–398
395
Fig. 1. The structures of the complexes (a) [Zn(sac)2(dmen)] and (b)
[Zn(sac)2(paen)] determined with X-ray crystallography.
well shaped single crystals. The crystals grown in the solution
are filtered out.
X-ray diffraction analysis of [Zn(sac)2(dmen)] single crys-
tals shows that crystal symmetry is monoclinic with uni◦t cell
˚
parameters: a = 8.512, b = 12.34 and c = 20.69 A; β = 101 and
Fig. 2. EPR spectra of Cu2+ doped [Zn(sac)2(dmen)] single crystal (a) in c*a
plane when magnetic field makes 45◦ from a-axis and (b) magnetic field is along
b-axis.
Z = 4. With the same analysis made on [Zn(sac)2(paen)] crystal,
the symmetry is found to be orthorhombic with unit cell param-
˚
eters: a = 10.10, b = 14.30, c = 19.25 A and Z = 4. The structures
of the complexes determined by X-ray diffraction technique are
given in Fig. 1.
The spectra can be fitted to and described by means of the
rhombic spin Hamiltonian:
EPR spectra are recorded with Varian E-109 X-band EPR
spectrometer using 100 kHz magnetic field modulation. The sin-
gle crystals are glued on a quartz rod of a goniometer graded
in degrees and rotated at 5◦ or 10◦ intervals depending on
the variation of spectra in three mutually perpendicular planes.
The spectrometer frequency is corrected using the dpph sample
(g = 2.0036). Simulations of powder spectra of both compounds
were made using Bruker’s WINEPR software.
H = βe(gxHxSx + gyHySy + gzHzSz)
+IxAxSx + IyAySy + IzAzSz
(2)
which includes only electron Zeeman and hyperfine interactions.
The nuclear Zeeman, spin-orbit and nuclear quadrupole inter-
actions are neglected [14]. In fact, these last interactions are
intrinsic in g and hyperfine variations.
3. Results and discussion
EPR spectra of Cu2+ doped [Zn(sac)2(dmen)] and
[Zn(sac)2(paen)] single crystals are taken at room temperature
for rotations in three mutually perpendicular planes between 0◦
and 180◦. Fig. 2a and b shows the EPR spectra of Cu2+ doped
[Zn(sac)2(dmen)]singlecrystalinc*aplanewhenmagneticfield
inclined by 45◦ to the a-axis and parallel to b-axis, respectively.
Fig. 3 shows the spectrum of [Zn(sac)2(paen)] single crystal in
the ab plane with the magnetic field inclined by 140◦ to the b-
axis. The spectra arise obviously from paramagnetic Cu2+ ion
with nuclear spin of I = 3/2.
There are two sets of four lines in all spectra as seen in the
plots of angular variation of line position, shown in Figs. 4 and 6.
The spectra are resolved by fitting each line to the expression:
gk2(θ) = gi2i cos2 θ + gj2j sin2 θ + 2gi2j sin θ cos θ
(1)
where i, j and k stand for x-, y- and z-axis, respectively. The
coefficients, gi2i, gj2j and gi2j for each line are used to group the
lines belonging to paramagnetic centers and then, to determine
the g and hyperfine tensors. The tensors formed in this way are
diagonalized and principal values obtained.
Fig. 3. EPR spectra of Cu2+ doped [Zn(sac)2(paen)] when magnetic field makes
140◦ from b-axis in ab plane.

396
R. Bıyık et al. / Spectrochimica Acta Part A 68 (2007) 394–398
Fig. 4. Variation of the g2 values of all lines in three planes of Cu2+ doped [Zn(sac)2(dmen)] single crystal.
3.1. Cu2+ in [Zn(sac)2(dmen)]
that Cu2+ ion substitutes with Zn2+ ion in the host lattice in pseu-
dotetrahedral (D2d) environment [3,5]. The ground state wave
functions, assuming hybridization of s, p and d orbitals of Cu2+
ion in D2d symmetry are written to second order approximation
to be [3,15]:
Angular variations of lines of Cu2+ doped [Zn(sac)2(dmen)]
single crystal taken in three mutually perpendicular planes,
shown in Fig. 4, indicate the existence of two Cu2+ sites. The
lines of two sites are separable in ab and bc* planes. The lines of
these two sites, however, coincide in c*a plane, which is consis-
tent with monoclinic symmetry. The principal g and hyperfine
values are given in Table 1. The parameters are seen to be rhom-
bic rather then being axially symmetric.
ꢀ
ꢁ
ꢀ
ψ(B1) = dx2−y2
ꢀ
ꢀ
ꢁ
ψ(B2) = α dxy + η |pzꢁ
ꢀ
ꢀ
ꢀ
ꢁ
ꢁ
(3)
ꢀ
ψ(E) = γ dxz, dyz + ξ px, py
ꢀ
ꢀ
ꢁ
ψ(A1) = δ dz2 + δ1 |sꢁ
Powder spectrum of Cu2+ doped [Zn(sac)2(dmen)] is given
in Fig. 5 together with simulated spectrum obtained with exper-
imental spin Hamiltonian values given in Table 1. The g and
hyperfine values obtained from the powder spectrum are also
given in the same table.
where α, δ, γ, η and ξ are the coefficients of related orbitals. The
relations between spin Hamiltonian and crystal field parameters
are also taken to second order approximation as:
8α2λd
E1
63Cu2+ and 65Cu2+ lines are not resolvable because of broad
line widths. Combining the results given in Table 1 with the X-
ray crystallographic structure given in Fig. 1, it can be concluded
g (= gzz) = ge −
||
2(α2γ2λd − αγξ2λp)
g
(= gxx = gyy) = ge −
⊥
E2
ꢂ
ꢃ
ꢄ
ꢅ
4
3
4
A (= Azz) = Pd −κα2 + (g|| − 2) − α2 + (g⊥ − 2) + Ppη2
− κ
||
7
7
5
2
ꢂ
ꢃ
ꢄ
ꢅ
11
14
2
A (= Axx = Ayy) = Pd −κα2 +
(g⊥ − 2) + α2 + Ppη2
−
− κ
⊥
7
5
(4)
where λd = −829 cm−1 and λp = −925 cm−1 are spin-
orbit interaction constants and Pd = 360 × 10−4 cm−1 and
Pp = 402 × 10−4 cm−1 are dipolar hyperfine parameters for 3d
and 4p orbitals of Cu2+, respectively. κ = 0.43 is Fermi contact
parameter [3,17]; E1 and E2 are the transition energies between
B2 → B1 and B2 → E states, respectively in D2d symmetry.
When Table 1 values are used in A and A expressions of
||
⊥
Eq. (4), the coefficient η2 is obtained negligibly small compared
to α2 ≈ 0.4. With the obtained value of α2, expression for g
||
gives E1 ≈ 10,800 cm−1 as expected. Similarly g expression
⊥
gives E2 ≈ 13,000 cm−1 which is in the same order as the val-
ues given in previous works provided that γ2 ≈ 1 and ξ2 ≈ 0
[3,5]. The coefficients δ and δ1 are negligibly small higher order
contributions. This is the case encountered mostly when the
spin-orbit interaction is small compared to ligand field [3]. The
results show that hybridization of 4p orbitals are too small to be
Fig. 5. Powder spectrum (a) and simulated spectrum and (b) of Cu2+ doped
[Zn(sac)2(dmen)]. x and y compenents are not resolvable because of two com-
ponents are close to each other.

R. Bıyık et al. / Spectrochimica Acta Part A 68 (2007) 394–398
397
Table 1
Principal g and hyperfine coupling tensor (A) with direction cosines and powder spectrum values of the Cu2+ doped [Zn(sac)2(dmen)] and [Zn(sac)2(paen)]
Complex
Site
g
Direction cosiness
A (mT)
Direction cosiness
a
b
c*
0.218
a
b
c*
[Zn(sac)2(dmen)]
I
gxx = 2.129
gyy = 2.028
gzz = 2.259
0.965
0.254
−0.058
−0.144
0.706
0.692
Axx = 4.75
Ayy = 2.17
Azz = 17.37
−0.181
0.135
0.974
0.573
0.819
−0.006
0.798
−0.557
0.226
−0.660
0.718
II
gxx = 2.114
gyy = 2.028
gzz = 2.248
0.995
0.022
−0.088
−0.076
0.727
−0.681
0.049
0.685
0.726
Axx = 5.00
Ayy = 3.02
Azz = 17.37
0.995
0.022
−0.088
−0.076
0.049
0.685
0.726
0.727
−0.681
Powder spectrum values
Complex
gxx ≈ gyy = 2.082, gzz = 2.255, Axx ≈ Ayy = 3.21, Azz = 17.85
Site
g
Direction cosiness
A (mT)
Direction cosiness
a
b
c
a
b
c
[Zn(sac)2(paen)]
I
gxx = 2.130
gyy = 2.054
gzz = 2.405
0.318
−0.470
0.834
0.287
−0.823
−0.532
0.198
Axx = 5.4
Ayy = 3.1
Azz = 11.4
0.241
0.743
0.663
−0.080
−0.623
0.731
0.274
−0.143
−0.154
0.937
0.958
II
gxx = 2.135
gyy = 2.052
gzz = 2.387
−0.043
0.234
−0.971
0.651
0.743
0.150
−0.757
0.626
0.184
Axx = 4.9
Ayy = 3.5
Azz = 11.2
0.160
0.089
−0.983
0.870
0.456
0.183
0.465
−0.885
−0.004
Powder spectrum values
gxx = 2.133, gyy = 2.053, gzz = 2.395, Axx = 5.0, Ayy = 3.4, Azz = 11.2
Zn2+ ion in the host lattice in an octahedral environment with
rhombic distortion, Fig. 1.
The spin-orbit and crystal field interactions are intrinsic in
g and hyperfine tensor elements. The ground state wave func-
tion of d9 ions, given below, can be written as the mixture of
considered. The unpaired electron occupies mainly the dxy(B2)
and dxz, dyz(E) orbitals of Cu2+ ion, as will be expected from
pseudotetrahedral (D2d) structures.
3.2. Cu2+ in [Zn(sac)2(paen)]
dx2−y2 and d
orbitals of the central metal ion in octahedral
3z2−y2
Angular variations of Cu2+ doped [Zn(sac)2(paen)] indicate
the existence of two Cu2+ sites as seen in the plot of angular vari-
ations of line positions in three mutually perpendicular planes
of orthorhombic crystal, Fig. 6. The principal g and hyperfine
elements are given in Table 1. The parameters are seen to be
rhombic rather than being axially symmetric. 65Cu2+ and 63Cu2+
lines are not resolvable because of broad line widths.
environment,
ꢀ
ꢀ
ꢀ
ꢀ
ꢆ
ꢁ
ꢁ
ψ = k α dx2−y2 + β d3z2−r2
(5)
where k is the covalency parameter which indicates the proba-
bility of finding the unpaired electron in d orbital of Cu2+ ion. α
and β are the mixing coefficients of dx2−y2 and d3z2−r2 orbitals
having the normalization conditions:
Fig. 7 shows the powder and simulated spectrum of Cu2+
doped [Zn(sac)2(paen)]. These components of g and hyperfine
coupling tensors are measured and given in Table 1 together with
single crystal values. It is obvious that Cu2+ ion substitutes with
α2 + β2 = 1
(6)
Fig. 6. Variation of the g2 values of all lines in three planes of Cu2+ doped [Zn(sac)2(paen)] single crystal.

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R. Bıyık et al. / Spectrochimica Acta Part A 68 (2007) 394–398
EPR parameters related with the structural parameters for
rhombic environment are given as [16,17]
ꢇ
ꢈ
ꢈ
ꢉ
ꢉ
ꢊ
ꢊ
√
√
3α + 3β
√
√
3β
k[2(α2 + β2) − 4 3αβ]
1
Ax = P −κ +
+ (gx − ge) −
(gy − ge) +
(gz − ge)
(gz − ge)
7
14
14α
α − 3β
ꢇ
√
√
3α − 3β
√
√
k[2(α2 + β2) + 4 3αβ]
1
3β
Ay = P −κ +
+ (gy − ge) −
(gx − ge) −
7
14
√
14α
α + 3β
ꢇ
ꢈ
ꢉ
ꢈ
ꢉ
ꢊ (7)
√
4k(α2 + β2)
1
3α − 3β
1
3α + 3β
√
√
Az = P −κ +
+ (gz − ge) −
(gx − ge) +
(gy − ge)
7
14
14
α + 3β
α − 3β
8k2α2λ
Δxy
√
√
2k2λ(α + 3β)2
2k2λ(α − 3β)2
gx = ge +
,
gy = ge +
,
gz = ge +
Δyz
Δxz
k, α and β are described above. κ is the polarization constant, P
is dipolar hyperfine parameter for metal ion defined as P = kP0,
where free ion value P0 for 65Cu2+ is 388 × 10−4 cm−1 and for
63Cu2+ is 416 × 10−4 cm−1 [17]; ge = 2.0023 the free electron
g value; Δxy, Δxz and Δyz are the energy splittings of |dxyꢁ,
|dxzꢁ and |dyzꢁ states with respect to ground state, and can be
obtained using optical absorption spectroscopy. And, since the
optical absorption spectrum is irresolvable, the energy values are
calculated using Eq. (7). The values change between 11,500 and
16,000 cm−1 which are in the range of the values with similar
structures [17].
The coefficients of the both sites are seen to be slightly differ-
ent indicating a small difference in the environments of both
sites. The covalency parameter k approximately has the value of
0.72 and 0.83 for sites I and II, respectively, meaning that the
unpaired electrons spend 72 and 83% of time on d orbitals of
Cu2+ ions of both sites. The rest of the times, 28 and 13% for
two sites, respectively, are spent on ligand orbitals. Similarly,
the unpaired electron on d orbitals of Cu2+ ion for both sites
spend approximately 98 and 96% of time on dx2−y2 orbitals and
the rest of approximately 1 and 3% on d3z2−r2 orbitals for both
sites.
The wave functions of sites I and II are constructed using the
calculated values as follows:
√
ꢀ
ꢀ
ꢆ
ꢁ
ꢁ
ꢀ
ꢀ
References
ΨI = 0.72 0.994 dx2−y2 + 0.105 d3z2−r2
(8a)
(8b)
√
ꢀ
ꢀ
ꢀ
ꢀ
ꢁ
ꢁ
[1] D.E. Mauro, M.S. Domiciano, Physica B 304 (2001) 398.
[2] I. Sougandi, R. Venkatesen, P.S. Rao, Spectrochim. Acta Part A 60 (2004)
2653.
[3] S.K. Hoffmann, J. Goslar, J. Solid State Chem. 44 (1982) 343.
[4] D.W. Smith, Coordin. Chem. Rev. 21 (1976) 93.
[5] V.I. Murav’ev, Russ. J. Coordin. Chem. 31 (12) (2004) 883.
[6] B. Karabulut, R. Tapramaz, A. Bulut, Z. Naturforsch. 54a (1999)
256.
ΨII = 0.83[0.982 dx2−y2 + 0.188 d3z2−r2
[7] F. Koksal, I. Kartal, B. Karabulut, Z. Naturforsch. 54a (1999) 177.
[8] S.K. Misra, X. Li, C. Wang, J. Phys. Condens. Matter. 3 (1991)
8479.
[9] P. Huang, H. Ping, M.G. Zhao, J. Phys. Chem. Solids 64 (2003) 523.
[10] R. Bıyık, R. Tapramaz, B. Karabulut, Z. Naturforsch. 58a (2003)
499.
[11] F. Koksal, B. Karabulut, Y. Yerli, Int. J. Inorg. Mater. 3 (2001) 413.
[12] L.A. Nabors, C.G. Robert, Alternative Sweeteners, second ed., Marcel
Dekker, New York, 1991.
[13] Y. Yerli, F. Koksal, A. Karadag, Solid State Sci. 5 (2003) 1319.
[14] N.M. Atherton, Electron Spin Resonance Theory and Applications, John-
Wiley and Sons, New York, 1973.
[15] F.E. Mabbs, D. Collison, Electron paramagnetic resonance of d transition
metal compounds, in: Studies in Inorganic Shemistry, vol. 16, Elsevier
Science Publishers, 1992.
[16] T.B. Rao, M. Narayana, Phys. Stat. Sol. 6 (1964) 149.
[17] A. Abragam, B. Bleaney, Electron Paramagnetic Resonance of Transition
Ions, Oxford University Press, 1970.
Fig. 7. Powder spectrum (a) and simulated spectrum and (b) of Cu2+ doped
[Zn(sac)2(paen)].