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Endor investigationon Cu2+-doped TGS and DTGS single crystals
Volume 49, number1
CHEMICAL PHYSICS LETTERS
ENDOR INVESTIGATION R. BOTTCHER,
I July 1977
ON Cu2+-DOPED TGS AND DTGS SINGLE CRYSTALS
D. HEINHOLD
and W. WINDSCH
Sektion Physik der Karl-Marx- Universitat, DDR- 701 Leipzig, German Democratic
Republic
Received 18 February 1977 Revised manuscript received 19 April 1977
Proton ENDOR spectw of the Cu@i)--gIycinate cheiate in ferroelectric trigIycine suIphate single crystals are reported. Magnetic hy~er~me coupling constants of the ligand protons of the amino and methylene groups are given and discussed. The ENDOK investigations confIrm the correctness of the assumed structure of the copper chefate and show that its point gzoup is only Cl in the ferroelectric phase of TGS.
fn (TGS)
single crystals of ferroelectric the copper
triglycine sulphate
ions form a chelate
with two gly-
cin& yielding the compound Cu(II)-glycinate chelate (NH2CH,COO),Cu (fig. 1) [l, 21. Both glycine molecules denoted as glycine II and III, appear in the undoped crystals in the ferroelectric phase (T, = 49°C) with different structure parameters [3]. The EPR spectra of this copper chelate complex have been studied in detail by Windsch and Welter [l] and Stankowski et al. [2] and are explained on the assumption that both gIycines own the same structure. Therefore, the point symmetry of this compound is C,,. However, EPR could not provide any exact information about the ligand hyperfine structure due to the hydrogen atoms of the NH, amine and CH, methylene groups. The ENDOR investigations have been performed with an X-band superheterodyn~ spectrometer of the
type JES3BQ at 4.2 K. A rectangular cavity (type HI&I with the rf-coif inside was used. Copper-doped TGS single crystals were grown below the Curie temperature from a saturated aqueous solution with 0.1 mass percent CuS04 by sIow evaporation. Partially deuterated crystak were obtained from a heavy-water solution. The angular dependence of the spectra has been recorded by rotating the crystal about the orthogonal a’, b and c axes, where a’ = a sin fl and fl is the angle between the a and the c axis. Strong ENDOR signals of hydrogen and nitrogen ligands of the copper ion showed up in the frequency range ‘7-20 MHz. Fig. 2 represents a typical ENDOR spectrum. Fig. 3 shows its angular
dependence,
the magnetic
field being
parallel to the bc plane. Each transition was split into a doublet with a maximum separation of 60 kHz for the protons. For the explanation of the EPR and ENDOR spectra the following spin-hamiltonian is used: *
(1) Fig. 1. Structure of the bisglycinate-Cu{II) ~~~~c~~coo~zCu-
148
complex
The exact diagonalization
of the first part of this rela-
Volume 49, number 1
nftrogen
Nt&protons
125 720 I vEffJ,j$~~
CHEMICAL PHYSICS LETTERS
16.5
16.6.3
15.5
NH,protons
15.0
CH,-
protons
1 July 1977
CH,-
profons
14.5
1z.o
Fig. 2. Proton ENDOR spectrum of (NHaCHaCOOjaCu
13.5
in TGS.
T=
13.0
12.5
4.2 K, H1[OO1]. a = (H[OlO])
12.0
= So.
analysis of the proton ENDOR transitions with the largest angular dependence. Again we diagonalized the nuclear spin hamiltouian matrix *n~c = seff * AH’~iH
-gnPHH.jiH
(2)
with the aid of a computer program. We examined four protons with different shf interactions (for the interaction data see table 1). For the purpose of learning of whether the ENDOR lines are produced either by the hydrogens of the NH, or the CH2 groups, we studied the spectra of Cu2’doped DTGS crystals with partially deuterated glycines +ND3CH2COO- _ However, the ENDOR signals identified in the TGS crystals could not be detected. The absence of the lines proves the hydrogens of the NH2
Table 1 Shf constants of the hydrogens of the amino groups A a) (MHz)
Fig. 3. Angular dependence of the amino proton ENDOR signal of (NHaCHaCOO)aCu in TGS. H la'.
tion yields the expectation value of the electron spin Se, and the deviation of the electron spin quantization direction from the external fielci direction caused by the anisotropic g and A tensor. The first step in our experiments consisted in the
-6.30 6.15 11.30 -6.60 6.50 12.15 8.80 13.50 -5.00 8.95 13.80 -5.50
Aiso a) (MHz)
3.75
4.05
Direction cosines b) -0.026 0.837 -0.547 -0.015 0.847 -0.532
5.75
5.70
-0.547 0.823 O.i63 -0.530 0.834 0.153
-0.341 0.507 0.792 -0.337 0.496
0.939 0.208 0.272 0.541 0.192
0.800
0.260
0.262 -0.005 0.965 0.261 -0.020 0.965
0.800 0.568 0.213 0.807 OS52 0.211
a] Error of the shf constants: 2 50 k&z.. b) Refer to the crystal axes a’, b and c.
149
CHEMICAL PHYSICS LETTERS
Volume 49, number 1
groups of the copper chelate to be responsible for this type of signals. Due to the simple structure of the ENDOR spectra and the higher resolution in the vicinity of the free proton frequency it was possible in the DTGS sample to investigate ENDOR signals of CH, protons with small shf splittings. The analysis of their angular dependence yields the shf constants collected in table 2. To relate the ENDOR signals observed in the DTGS crystals with the methylene protons of the copper complex we calculated the dipolar part B of the shf tensors applying the general expression for the point dipole-dipole interaction: B = A - Ai,
= Ijna~~ (3
COS’e
-
l)lr3
(3)
_
The distances r between the methylene protons and the copper ion have been evaluated from the crystallographic data [4] of the undoped crystal on the assumption that the latter is placed in the centre of the line N(II)N(III) (notation after ref. [4])_ The deviation of the experimental B values from the theoretical ones is small. The ENDOR of the assumed
investigations structure
confirm
of the copper
the correctness chelate
in TGS.
Because the principal values of the shf tensors and their direction cosines of the amino protons of the Cu(II)-chelate are different, this complex possesses triclinic symmetry C, , which explains also the angular
1 July 1977
dependence of the ENDOR spectra of the methylene protons and nitrogen nuclei. Therefore, the difference in the bonding parameters of glycine IL and III is detectable in the ferroelectric phase. Since there exists only a slight difference in the shf tensors of two aminoprotons, the deviation of the C, symmetry from the Ci symmetry is small_ Owing to the fact that the distance between the hydrogens of the NH, groups and the copper ion is smaller than 2.6 A, it is not possible to determine their positions from the anisotropic part of the shf tcnSOTS.At present we are not able to explain the parameters and the direction cosines of the latter. The orthorhombic symmetry of the shf tensors of NH, protons and the number of the ENDOR lines show that the N _ group does not rotate in TGS at T = 4.2 K. Becau in the EPR spectra no temperature dependence of th3 shf splitting has been observed, the rotation of the amino groups of the metal chelate can be excluded at room temperature. At present any explanation of ihe doublet structure of the ENDOR lines must be deferred. We suppose the line splitting to be related with the multidomain structure of our TGS crystals. The investigatidns have been performed in the Research group EF/R an_Fstkorpern der Sektion Physik der Karl-Marx-Universitat Leipzig. We wish to thank
Table 2 Shf constants of the hydrogens of the methylene groups Proton a)
A b) (MHz)
H8
-1.80
4.35
Aiso b, (MHZ)
0.07
150
’
0.119 -0.010 0.993
-0.581
0.811 0.078
6.93 2.08 1.79
3.65
0.786 0.484 -0.385
0.517 -0.173 0.838
-6.339 0.858 0.386
H13
4.44 -1.86 -2.36
0.08
0.765 0.600 0.236
0.076 -0.447 0.891
-0.640 0.663 0.388
H14
7.27 2.10 1.73
3.75
0.782 0.499 -0.374
0.499 -0.141 0.855
-0.374 0.855 0.359
H9
b) c)
0.805
0.586 -0.091
-2.30
a) Notation
Direction cosines c)
after ref. [4]. Error of the shf constants: c 30 kHz. Refer to the crystal axes a’, b and c.
a
Volume 49, number 1
CHEMKAL
&i~SICS
Dr, S. Wariewig for heIpful discussions and Mrs. R.
Winter and Miss Rehnert for growing the crystals.
References [I] W. Windsch and M-Welter, 2. Naturforsclt. 22a (1967) I.
XXI-Z-ERS
1 July 1977
[2j 3. Stankowski, A. Weckowski and S. Hedewy, J. hfagn.
Reson. 15 (i976) 498. (3 I K. Itoh and T. Mitsui, Ferroelectrics 5 (1973) 235. 14: M-L iCay and R. Kleinberg, Ferroelectrics 5 (19’73) 45.
CHEMICAL PHYSICS LETTERS
ENDOR INVESTIGATION R. BOTTCHER,
I July 1977
ON Cu2+-DOPED TGS AND DTGS SINGLE CRYSTALS
D. HEINHOLD
and W. WINDSCH
Sektion Physik der Karl-Marx- Universitat, DDR- 701 Leipzig, German Democratic
Republic
Received 18 February 1977 Revised manuscript received 19 April 1977
Proton ENDOR spectw of the Cu@i)--gIycinate cheiate in ferroelectric trigIycine suIphate single crystals are reported. Magnetic hy~er~me coupling constants of the ligand protons of the amino and methylene groups are given and discussed. The ENDOK investigations confIrm the correctness of the assumed structure of the copper chefate and show that its point gzoup is only Cl in the ferroelectric phase of TGS.
fn (TGS)
single crystals of ferroelectric the copper
triglycine sulphate
ions form a chelate
with two gly-
cin& yielding the compound Cu(II)-glycinate chelate (NH2CH,COO),Cu (fig. 1) [l, 21. Both glycine molecules denoted as glycine II and III, appear in the undoped crystals in the ferroelectric phase (T, = 49°C) with different structure parameters [3]. The EPR spectra of this copper chelate complex have been studied in detail by Windsch and Welter [l] and Stankowski et al. [2] and are explained on the assumption that both gIycines own the same structure. Therefore, the point symmetry of this compound is C,,. However, EPR could not provide any exact information about the ligand hyperfine structure due to the hydrogen atoms of the NH, amine and CH, methylene groups. The ENDOR investigations have been performed with an X-band superheterodyn~ spectrometer of the
type JES3BQ at 4.2 K. A rectangular cavity (type HI&I with the rf-coif inside was used. Copper-doped TGS single crystals were grown below the Curie temperature from a saturated aqueous solution with 0.1 mass percent CuS04 by sIow evaporation. Partially deuterated crystak were obtained from a heavy-water solution. The angular dependence of the spectra has been recorded by rotating the crystal about the orthogonal a’, b and c axes, where a’ = a sin fl and fl is the angle between the a and the c axis. Strong ENDOR signals of hydrogen and nitrogen ligands of the copper ion showed up in the frequency range ‘7-20 MHz. Fig. 2 represents a typical ENDOR spectrum. Fig. 3 shows its angular
dependence,
the magnetic
field being
parallel to the bc plane. Each transition was split into a doublet with a maximum separation of 60 kHz for the protons. For the explanation of the EPR and ENDOR spectra the following spin-hamiltonian is used: *
(1) Fig. 1. Structure of the bisglycinate-Cu{II) ~~~~c~~coo~zCu-
148
complex
The exact diagonalization
of the first part of this rela-
Volume 49, number 1
nftrogen
Nt&protons
125 720 I vEffJ,j$~~
CHEMICAL PHYSICS LETTERS
16.5
16.6.3
15.5
NH,protons
15.0
CH,-
protons
1 July 1977
CH,-
profons
14.5
1z.o
Fig. 2. Proton ENDOR spectrum of (NHaCHaCOOjaCu
13.5
in TGS.
T=
13.0
12.5
4.2 K, H1[OO1]. a = (H[OlO])
12.0
= So.
analysis of the proton ENDOR transitions with the largest angular dependence. Again we diagonalized the nuclear spin hamiltouian matrix *n~c = seff * AH’~iH
-gnPHH.jiH
(2)
with the aid of a computer program. We examined four protons with different shf interactions (for the interaction data see table 1). For the purpose of learning of whether the ENDOR lines are produced either by the hydrogens of the NH, or the CH2 groups, we studied the spectra of Cu2’doped DTGS crystals with partially deuterated glycines +ND3CH2COO- _ However, the ENDOR signals identified in the TGS crystals could not be detected. The absence of the lines proves the hydrogens of the NH2
Table 1 Shf constants of the hydrogens of the amino groups A a) (MHz)
Fig. 3. Angular dependence of the amino proton ENDOR signal of (NHaCHaCOO)aCu in TGS. H la'.
tion yields the expectation value of the electron spin Se, and the deviation of the electron spin quantization direction from the external fielci direction caused by the anisotropic g and A tensor. The first step in our experiments consisted in the
-6.30 6.15 11.30 -6.60 6.50 12.15 8.80 13.50 -5.00 8.95 13.80 -5.50
Aiso a) (MHz)
3.75
4.05
Direction cosines b) -0.026 0.837 -0.547 -0.015 0.847 -0.532
5.75
5.70
-0.547 0.823 O.i63 -0.530 0.834 0.153
-0.341 0.507 0.792 -0.337 0.496
0.939 0.208 0.272 0.541 0.192
0.800
0.260
0.262 -0.005 0.965 0.261 -0.020 0.965
0.800 0.568 0.213 0.807 OS52 0.211
a] Error of the shf constants: 2 50 k&z.. b) Refer to the crystal axes a’, b and c.
149
CHEMICAL PHYSICS LETTERS
Volume 49, number 1
groups of the copper chelate to be responsible for this type of signals. Due to the simple structure of the ENDOR spectra and the higher resolution in the vicinity of the free proton frequency it was possible in the DTGS sample to investigate ENDOR signals of CH, protons with small shf splittings. The analysis of their angular dependence yields the shf constants collected in table 2. To relate the ENDOR signals observed in the DTGS crystals with the methylene protons of the copper complex we calculated the dipolar part B of the shf tensors applying the general expression for the point dipole-dipole interaction: B = A - Ai,
= Ijna~~ (3
COS’e
-
l)lr3
(3)
_
The distances r between the methylene protons and the copper ion have been evaluated from the crystallographic data [4] of the undoped crystal on the assumption that the latter is placed in the centre of the line N(II)N(III) (notation after ref. [4])_ The deviation of the experimental B values from the theoretical ones is small. The ENDOR of the assumed
investigations structure
confirm
of the copper
the correctness chelate
in TGS.
Because the principal values of the shf tensors and their direction cosines of the amino protons of the Cu(II)-chelate are different, this complex possesses triclinic symmetry C, , which explains also the angular
1 July 1977
dependence of the ENDOR spectra of the methylene protons and nitrogen nuclei. Therefore, the difference in the bonding parameters of glycine IL and III is detectable in the ferroelectric phase. Since there exists only a slight difference in the shf tensors of two aminoprotons, the deviation of the C, symmetry from the Ci symmetry is small_ Owing to the fact that the distance between the hydrogens of the NH, groups and the copper ion is smaller than 2.6 A, it is not possible to determine their positions from the anisotropic part of the shf tcnSOTS.At present we are not able to explain the parameters and the direction cosines of the latter. The orthorhombic symmetry of the shf tensors of NH, protons and the number of the ENDOR lines show that the N _ group does not rotate in TGS at T = 4.2 K. Becau in the EPR spectra no temperature dependence of th3 shf splitting has been observed, the rotation of the amino groups of the metal chelate can be excluded at room temperature. At present any explanation of ihe doublet structure of the ENDOR lines must be deferred. We suppose the line splitting to be related with the multidomain structure of our TGS crystals. The investigatidns have been performed in the Research group EF/R an_Fstkorpern der Sektion Physik der Karl-Marx-Universitat Leipzig. We wish to thank
Table 2 Shf constants of the hydrogens of the methylene groups Proton a)
A b) (MHz)
H8
-1.80
4.35
Aiso b, (MHZ)
0.07
150
’
0.119 -0.010 0.993
-0.581
0.811 0.078
6.93 2.08 1.79
3.65
0.786 0.484 -0.385
0.517 -0.173 0.838
-6.339 0.858 0.386
H13
4.44 -1.86 -2.36
0.08
0.765 0.600 0.236
0.076 -0.447 0.891
-0.640 0.663 0.388
H14
7.27 2.10 1.73
3.75
0.782 0.499 -0.374
0.499 -0.141 0.855
-0.374 0.855 0.359
H9
b) c)
0.805
0.586 -0.091
-2.30
a) Notation
Direction cosines c)
after ref. [4]. Error of the shf constants: c 30 kHz. Refer to the crystal axes a’, b and c.
a
Volume 49, number 1
CHEMKAL
&i~SICS
Dr, S. Wariewig for heIpful discussions and Mrs. R.
Winter and Miss Rehnert for growing the crystals.
References [I] W. Windsch and M-Welter, 2. Naturforsclt. 22a (1967) I.
XXI-Z-ERS
1 July 1977
[2j 3. Stankowski, A. Weckowski and S. Hedewy, J. hfagn.
Reson. 15 (i976) 498. (3 I K. Itoh and T. Mitsui, Ferroelectrics 5 (1973) 235. 14: M-L iCay and R. Kleinberg, Ferroelectrics 5 (19’73) 45.