EPR of Cu z+ in Cadmium Saccharin [Cd(sac)2(Hâ¢O)4]-2H20 ... nuclei. Saccharin is extensively used asa noncalo¡ sweetener and an antidote against.
Appl. Magn. Reson. 23, 43-49 (2002)
Applied Magnetic Resonance 9 Springer-Verlag 2002 Printed in Austria
EPR of Cu z+ in Cadmium Saccharin [Cd(sac)2(H•O)4]-2H20 and [Cd(sac)2(HydEt-en)2 ] Complexes in Single-Crystal and Powder Forms Y. Yerli l, A. K a r a d a g 2, and 17 KiiksaP t Department of Physics and ZDepartment of Chemistry, Faculty of Sciences, 0ndokuz May]s University, Samsun, Turkey Received March 15, 2002; revised June 20, 2002
Abstraet. The electron paramagnetic resonance spectra of Cu2§ in [Cd(sac)2(H20)4]. 2H20 and
[Cd(sae)2(HydEt-en)2] (HydEt-en = N-(2-hydroxyethyl)-ethylenediamine) single crystals and powder
were examined at room temperature. A detailed study of the speetra of the compounds indicates
the replacement of Cd2+ in the host compounds with Cu2+. [Cd(sae):(H20)4] 92H~O shows the presence of two sites for Cu:+ and [Cd(sac)2(HydEt-en)2] has a single site. The principal values for the g-tensor and the hyperfine tensor for Cu2+ in the two eompounds were obtained. The Cu2§ ion was found to be mostly in the 3d~2_e,orbital and the ground-state wavefunction of [Cd(sac)2(HydEten)2] was constructed.
1 Introduction The electron paramagnetic resonance (EPR) spectra o f C u 2+ (3d 9) have been studied extensively and found to be informative about the crystalline electric fields and environmental effects [1~5]. In doped compounds the Cu z+ ion mostly replaces a divalent o r a monovalent cation by fulfilling the charge compensation with some other nuclei. Saccharin is extensively used a s a noncalo¡ sweetener and an antidote against metal poisoning [7, 8]. It forms [M(sac)2(H20)4].2H20 complexes, where M i s a divalent metal ion such as Cu z+, Zn 2+ and Cd z+ [9]. Single-crystal X-ray studies on these complexes show that they are isostructural and crystallize in the monoclinic space group P21/c [10]. On the other hand, replacing the aqua ligands with N-(2hydroxyethyl)-ethylenediamine (NH2CHzCH2NHCHzCH2OH) ligand, the space group becomes triclinic P1 [11]. Therefore ir is o f interest to investigate the EPR o f Cu z+ ion in these [Cd(sac)2(H20)4].2H20 and [Cd(sac)•(HydEt-en)z ] complexes. From the single-crystal studies and powder spectra, g- and hyperfine tensors for the complexes were obtained.
44
Y. Yerli et al.
2 Experimental Single crystals o f Cu2+-doped [Cd(sac)2(H20)4].2H20 and [Cd(sac)2(HydEt-en)2 ] complexes were grown by slow evaporation o f saturated aqueous solutions admixed in stochiometric ratios o f about 0.5 percent o f CuC12. The crystal structure o f [Cd(sac)2(H20)4]-2H20 is monoclinic, the space group P21/c and the unit cell parameters a r e a = 0.8036 nm, b = 1.6145 nm, c = 0.7870 nm, ,B = 100024 '. The unit cell o f this complex contains two molecules [9, 10]. The crystal structure o f [Cd(sac)2(HydEt-en) z] is triclinic with the space group P1 and the unit cell parameters are a = 1.101 nm, b = 1.121 nm, c = 1.182 nm, a = 86~ ', y = 68~ ' , t i = 80062 '. The unit cell contains two molecules [11]. In these compounds, Cd 2+ ion has an octahedral geometry and is surrounded by four aqua molecules and two saccharinate anions, (C7H4NO3S)- , in [Cd(sac)2(H20)4]- 2H20, and in [Cd(sac)z(HydEt-en)2 ] two (sac)(HydEt-en) groups. The EPR spectra were recorded on a VarŸ E-109G EPR spectrometer with 20 m W microwave power and 100 kHz magnetic field modulation o f amplitude 1 G. The single crystals were rotated on a Lucit pillar in three mutually perpendicular planes and the spectra were recorded at 10 ~ steps at room temperature. The g factors were found by comparison with a diphenylpicrylhydrazyl sample o f g = 2.0036.
3 Results and Discussion Two typical EPR spectra for Cu2+-doped [Cd(sac)2(H20)4].2H20 are shown in Fig. 1 for two different orientations o f the magnetic field. Figure la shows the 310 toT
J
j ~
10 mT
J
i
b
Fig. 1. EPR spectra of C u 2+ in [Cd(sac)2(H20)4].2H:O. a The magnetic field is in the a'c-plane along the c-axis, b The magnetic field is in the £ 40~ from the b-axis.
EPR of Cu2+ in Cd Saecharin Complexes
45
spectrum when the magnetic field is in the a*c-plane along the c-axis. Figure lb depicts the spectrum when the magnetic field is in the bc-plane and 40 ~ from the b-axis. Figure 2 shows the powder spectrum of this complex. The values of the resonance magnetic field for the hyperfine structure components in units of ~ ~ against the orientation of the magnetic field are depicted in Fig. 3. These spectra obviously belong to the Cu 2+ ion (S = 1/2, 1 = 3/2) and can be fitted with the spin Hamiltonian
~=
P(g=~Sx + g~B~se + g~~85~) + AzzLS~ + A~~ryS~ + AjxSx.
The principal values of the g- and A-tensors and their direction cosines obtained by the diagonalization procedure are given in Table 1. From Fig. 3 it is seen that when the magnetic field is in the a*c-plane, only the spectrum of one Cu 2§ site, and in the other orientations of the magnetic field the spectrum of two Cu 2§ sites, can be distinguished. This is consistent with the monoclinic symmetry of the crystal and indicates the presence of two magnetically different sites for Cu 2+. Therefore, these results suggest that the Cu 2§ ion enters into the Cd 2§ places in this complex. The ionic radius of Cd 2+ (113 pro) is large enough for the admission of Cu 2+ (72 pm). The principal values of gand A-tensors obtained from the powder spectrum (Fig. 2), g~x = 2.131, gyy = 2.053, g= = 2.383, A~ = 2.5 mT, A~ = 5.2 mT, A= = 11.2 mT, are in good agreement with the single-crystal data (Table 1). The single-crystal and powder spectra of [Cd(sac)2(HydEt-en)2 ] are shown in Figs. 4 and 5, respectively. Since the single crystals have triclinic symmetry, there is only one site and this is seen also from the curve of the ~fr versus the orien-
I
I
I
I
t
g~ 10 mT I
I
iII
gxx' I, I I gyy Fig. 2. Powder EPR spectrum of Cu2§ in [Cd(sac)2(H20)4]. 2H20 at room temperature.
46
Y. Yerli et al. 6.50
(a*~
(a'c)
~c)
6.00
5.50
5.00
4.50
4.00
0
3"0 6"0 90 120 150 180
3"0 6"0 90 120 150 180 0
30
60 90 120 150 180
Angle (~ Fig. 3. g• for the hyperfine structure components of Cu 2+ in [Cd(sac)2(H20)4 ] 92H20 against orientation of the magnetic field at room temperature.
tation of the magnetic field in Fig. 6. The spin-Hamiltonian parameters obtained from the experimental results are shown in Table 2. The principal values o f gand A-tensor measured from the powder spectrum (Fig. 5), g.= = 2.091, gyy = 2.044, g= = 2.228, A.~, = 2.0 mT, A= = 6.4 mT, A~~ = 17.2 mT, are in agreement with the single-crystal results (Table 2). For the g-values of both complexes in Tables 1 and 2 it can be seen that g = > g = > gyy and hence R = (gx~ - g y y ) / ( g = - g.=) is smaller than unity. Therefore, a 3dx2 y2 ground state for Cu 2§ seems to be dominant in both complexes [12, 13]. Formulation of the admixture of the Ix 2 - y2) and 13z2 - r 2) orbitals in the ground-state wavefunction of the Cu 2+ in the rhombic symmetry has been
Table 1. Principal values of the spin-Hamiltonian parameters (g and A) and their direction cosines with respect to the a', b, c axes in Cu2+-doped [Cd(sac)2(H20)4].2H20 single crystal at room temperature (Ag = _+0.0005 and AA = _+0.05 toT). Direction cosines Site
ii
I
xx yy
II
xx yy
zz
zz
gii
2.1476 2.0435 2.3870 2.1317 2.0563 2.3830
a"
b
c
A , (mT)
0.6770 -0.2948 0.6742 0.6723 0.2902 0.6809
+0.4044 +0.6163 _+0.6756 _+0.4110 _+0.6185 _+0.6696
0.6148 0.7301 -0.2980 -0.6155 0.7301 0.2965
3.2 5.0 11.4 2.6 5.4 11.2
a" 0.4162 0.5519 0.7225 -0.5223 0.4503 0.7240
Direction cosines b +0.0812 _+0.7689 _+0.6341 +0.3035 +0.6953 _+0.6514
c
0.9056 -0.3237 -0.2752 0.7965 0.5601 0.2265
EPR of Cu2+ in Cd Saccharin Complexes
47
310 mT
l
J 20 mT
Fig. 4. EPR spectra of Cu2§ in [Cd(sac)2(HydEt-en)2] when the magnetic field is in the a'c*-plane along the a~
established and applied b y m a n y authors [14-18]. The ground-state w a v e f u n c t i o n , i n c l u d i n g also the c o v a l e n c y effect o f the metal ion, is written as [15, 16] ~=
(a,2)I/z[ctlxZ
_ y2) + f l l 3 z 2 _ r2)],
(1)
o~,2 is the p r o b a b i l i t y o f the u n p a i r e d electron in the d orbital o f the metal a n d is the m e a s u r e o f the covalency. The n o r m a l i z a t i o n c o n d i t i o n for m i x i n g coefficients a and fl is
where
a 2 + 132 = 1.
(2)
gzz
I
20 mT
I
g~.x I
I
I
g~
Fig. 5. Powder EPR spectrum of Cu2+ in [Cd(sac)2(HydEt-en)2] at room temperature.
48
Y. Yerli et al.
(a'c*)
(bc*)
6"041
5"581
0
3"0 60
90 IZO 110 180
30
60 90 120 150 1800 Angle (o)
30
60
90 189 150 180
Fig. 6. g• for the hyperfine structure components of Cu2+ in [Cd(sac)2(HydEt-en)z] against orientation of the magnetic field at room temperature.
Application of the equations given in ref. 15 and 16 and of the principal values of g- and A-tensors yields
(3)
= (0.963)vz[0.996]x2 _ yZ) + 0.087[ 3z2 - r2)]
for [Cd(sac)2(HydEt-en)2], since the principal axes of the g- and A-tensors seem to coincide for the compound. The average of the principal values of the hyperfine interaction tensor o f Cu 2+ in [Cd(sac)2(HydEt-en)2] (8.7 mT) is somewhat larger than that o f Cu 2+ in [Cd(sac)2(H20)4].2HzO (6.5 mT). This may be due to the covalency o f Cu 2+ in these complexes. However, as the principal axes of the g- and A-tensors for the [Cd(sac)2(H20)4] 92H20 seem not to coincide, an approximate ground-state wavefunction cannot be constructed. Table 2. Principal values of the spin-Hamiltonian parameters (g and A) and their direction cosines with respect to the a o, b, c" axes in Cu2§ [Cd(sac).,(HydEt-en)2] single crystal at room temperature (Ag = --+0.0005 and ,5,4 = +0.05 mT). Direction cosines ii
gii
a"
xx
2.0827 2.0453 2.2227
0.1097 0.2092 0.9716
yy zz
b
0.6847 -0.7245 0.0786
c*
0.7204 0.6566 -0.2228
Direction cosines b c~
A~~ (mT)
a*
2.1 6.7 17.3
0.2211 0.0985 0.9702
-0.6784 0.7302 0.0804
0.7005 0.6760 -0.2283
EPR of Cu 2+ in Cd Saccharin Complexes
49
F u r t h e r m o r e , at s o m e o r i e n t a t i o n s o f the m a g n e t i c field the s u p e r h y p e r f i n e interaction o f C u 2+ with N nuclei can be o b s e r v e d for both c o m p l e x e s . T h e largest v a l u e o f the s u p e r h y p e r f i n e interaction is 1.4 m T in [Cd(sac)z(HydEt-en)2 ]. S i n c e the effect c o u l d not be o b s e r v e d at m o s t o f the orientations o f the m a g n e t i c field, a detailed study c o u l d not be carried out.
4 Conclusions E P R o f C u z+ in [ C d ( s a c ) 2 ( H 2 0 ) 4 ] . 2 H 2 0 and [Cd(sac)2(HydEt-en)2 ] c o m p l e x e s indicates the m o n o c l i n i c and t ¡ s y m m e t r i e s o f their single crystals. T h e spinH a m i l t o n i a n parameters for Cu z+ in these two c o m p l e x e s o f different ligands w e r e obtained.
References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18,
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Authors' address: Fevzi K6ksal, Department of Physics, Faculty of Sciences, Ondokuz Mayls University, 55139 Samsun, Turkey
