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Electronic spectra of VO2+ and Co2+ in zinc hydrogen maleate tetrahydrate
Solid State Communications, Printed in Great Britain.
JO,
vol.
No.
7,
pp.
709-712,
0038-1098/89$3.00+.00
1989.
Pergamon
Press
plr
ELECTRONIC SPECTRA OF VO*+ AND Co*+ IN ZINC HYDROGEN MALEATE TETRAHYDRATE S.N. Rao, K. Ramesh and Y.P. Reddy Department of Physics, S.V. University, Tirupati - 517 502, India ( Received
10 Novenber
1988,
form 3 February
in revised
of transition The optical absorption spectra maleate tetrahydrate crystals are investigated. the results
and analysis
of the
of VO*+, EPR spectrum The results indicate that
metal doped The present
co*+:
chemical
ma1 is maleate
formula
Ds = -2700 cm-’
gir = 1.930
gl
= 1.981
Dq = 910 cm-’
B
=
H2 M(ma&l
4H20
In the case
powder is also investigated. symmetry is tetragonally
Dq = 1613 cm-’
in the
case
of Co 2+
Dt I 1176 cm-’ A,, = 193C
A1 = 76G
C = 3780 cm-’
900 cm-’
zinc hydroxide is precipitated using sulphate, By treating the freshly ammonium hydroxide. precipitated zinc hydroxide with hot maleic acid and allowing the resulting solution to evaporate slowly at the laboratory temperature, good colourless crystals of ZMTH are grown in about ten To grow the vanadyl and cobalt doped days. cystals, 0.1 Mole weight of the corresponding sulphate is added at the starting point. Optical absorption spectra of the samples in UV-VIS region are recorded with 2 mm thick crystals on a Hitachi U3400 spectrophotometer, both at laboratory and liquid nitrogen temperatures. The IR spectra are recorded at laboratory-temperature with ootassium bromide bellets on a SP3-300 Pye Unicam IR spectrophotometer. The EPR sepectra of the polycrystalline powders are recorded at both laboratory and liquid nitrogen temperatures on Varian and Jeol X-band spectrometers.
1. INTRODUCTION ZINC HYDROGEN MALEATE TETRAHYDRATE hereafter referred to as ZMTH belongs to a group of isomorphous series of compounds with the general
zinc hydrogen paper presents
VO*+ and Co*+ doped crystals.
of the polycrystalline the octahedral site
ftiorted in the case of VO*+ and trigonally distorted . The following are some of the parameters evaluated. vo*+:
1989 by P.Burlet)
where
ion (C4H2O41 and M is a divalent
cation such as Zn, Cu, Co and Ni. The crystal structure studies of ZMTH [I,21 reveal-that this compound is triclinic with space group Pl with one molecule per unit cell. There is a slight difference in the unit cell dimensions published by the two groups. The two sets of values are as follows: a = 0.729 nm. b = 0.973 nm. c = 0.536 nm a = 110.8’, ’ p = 63.3’, ’ f q 103.6’ [I] c = 0.528 nm a = 0.730 nm, b = 0.982 nm, a = 11o.*o, p = 77.10, f = 117.00 (21 The metal ions Zn are octahedrally coordinated by four water oxygen atoms and two oxygen atoms from two monodentate hydrogen maleate ligands. From the studies of EPR Spectrum of copper doped ZMTH at laboratory temperature
3 RESULTS AND ANALYSIS VO*+: ZMTH :In the optical absorption spectrum of VO*+: ZMTH, three bands are observed at laboratory
[31 it has been concluded that Cu*+ replaces Zn*+. No invesitgations on the optical absorption of ZMTH doped with transition metal ions seem to have been reported in the literature. Therefore the investigation of the optical absorption spectra of transition metal doped ZMTH is undertaken with a view to ascertain the site symmetry of the transition metal ions and to study the effect of distortions on the optical absorption spectra. EPR spectra of the polycrystalline samples are also studied to supplement the optical absorption data.
temperature at 13982, 16125 and 21047 cm-‘. At liquid nitrogen temperature all three bands have become
sharp.
exhibit any shift bands are shifted
The band at !6125 cm-’ does not in position whereas the other two towards shorter wavelengths. An
additional band at 19796 cm -’ is also recorded. The spectra are shown in Fig. 1. The EPR spectra recorded at laboratory and liquid nitrogen temperatures are similar and exhibit two sets of eight lines. The EPR spectrum at laboratory temperature is shown in Fig. 2. The IR spectrum exhibits vibrational modes characteristic of carboxylate ion and water and is shown in Fig. 3.
A brief report on the results of the VO*+ doped ZMTH has been presented at the Solid State The detailed results and Physics Symposium [41 . analysis of the investigations on vanadyl and cobalt doped ZMTH are presented in this paper. 2. EXPERIMENTAL The single crystals of pure ZMTH are grown 131. From zinc as reported in the literature
In octahedral
709
(Oh)
VO*+ ion occupies
the
rise
state
to the ground
crystal
lowest *T*g*
field
t2g orbital
the
d1 of
and gives
In the excited
state
ZINC HYDROGEN MALEATE TETRAHYDRATE symmetry
vol.
is generally
lowered
to C4v
7o;no.
f
or C2v
due to nonsymmetrical alignment of the V-O bond along the symmetry axis. The EPR spectrum of the d’ electron gives rise to the hyperfine coupling
to eight of the
electron,
spin (I = 7/i)
with the
Cov symmetry
nuclear
two sets
of ei$t
line pattern due single unpaired
lines
of 5’V.
In
are expected
whereas in C2v symmetry three sets of eight lines are expected. In the present investigation since two sets of eight lines are observed, the site symmetry of
I
I
I
I
500
600
700
600
WAVELENGTH
vo2+ ion is ascribed to C peak positions of the EP ff spin Hamiltonian parameters g,, = 1.930 A,, g1 = 1.981
A,_=
76C
(nm)
Accordingly Fig.1
symmetry. From the spectrum the following are evaluated: = 193 G
Optical absorption spectra (RT: Room Temperature; nitrogen temperature).
of
V02+: ZMTH LNT: Liquid
13982,
16125
temperature --->
the and
are
three
21047
attributed
2E, 2B2 --->2B1
bands cm-’
to
observed at
the
at
laboratory
transitions
and 2B2 --->
2Al.
2B2 The band
peak data and assignments are given in Table Based on these assignments the following cyrstal field parameters Dq, Ds and Dt are evaluated. Dq = 1613 cm-’ Ds = -2700 cm-’ In the low temperature additional energy
that
band seperation
assigned
I
I
I
I
3250
3650
4050
EPR spectrum
of V02+: ZMTH
the
of
this
agrees
mode of the water
fractional
p;’
cm-‘. band,
well with molecule.
The from the
The
*2 15-81. They represent err
and
contributions
of the
d xz (and /or dyz) in antibonding
I
I 1500
I 1000
19796
spin orbit coupling constant A = 170 cm-‘, the dipolar hyperfine splitting constant p = -127 G and the Fermi contact term K = 0.87 are evaluated from the formula given by Kivelson et al 151. EPR and optical absorption data are correlated to evaluate the molecular orbital coefficients
I 500
Dt c 1176 cm-’ spectrum an
fundamental frequency (1655 cm-‘) of H-O-H bending vibration observed in IR spectrum supports this assignment. The assignments of the observed IR bands are given in Table 2. Using the values g,, , gl , A,,, Al obtained from EPR spectrum and the free ion value of the
H (G) Fig.2
at
(1657 cm-‘)
to 2B2--->2Al
H-O-H bendig
2850
is observed
1.
orbitals
,molecular
dx2_y2, orbitals
are *2 = 0.86 2b and 2e. The values evaluated Pl *2 = 0.87. These values suggest that the inplane err bonding and out of plane bonding are covalent.
WAVENUMBERkm-‘)
Fig.3
IR spectrum
of V02’:
Co2+: ZMTH :The absorption laboratory temperature
ZMTH
spectrum recorded at exhibits, four bands at 8181,
8785. 19602 and 21316 cm-‘. At liquid temperature the band at 21316 cm-’ splits it
occupies
2E g
state.
corresponding ble.
However
the
orbital 6 Therefore e
and only
gives a
rise single
to the band
is possi2T2g --->2Eg transition in the case of V02+, the site
to
components
(21181 and
8181 and 19602 cm-’ wavelengths whereas shift towards longer
21499 cm-l).
show
shifts
the band wavelength
at
nitrogen into two
The bands
towards
at
shorter
8785 cm-’ shows side. The spectra
vi+.
711
ZlNC HYDROGEN MALEATE TETRAHYDRATE
70, No. 7
Table 1. Assignments
those expected environment.
for the bands of V02+: ZMTH
for a Co2+ ion in octahedral For divalent cobalt ion in octahedral
Band positions 4T, ,(F)---> symmetry, three spin allowed transitions ____________~_______~-~~~~~-~--~~~~~~ ‘Tlg(F) ---> 4A2g(F) and ‘TJgiF) ---> 300K SOK Assignments ____________________~~~~~~~~~~~~~~~~~ ‘Tlg(P) are expected. But the transition ?lg(F)---> (nm) (cm-‘) (nm) (cm-l) 4 A2g(F) involves the promotion of two electrons ______________________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ and is therefore expected to be very weak[91. 14021 13982 Therefore the two intense broad bands at 8181 and 2B2 ---> 2E 715 713
IfTZg(F),
2B2 ---> H-O-H
2B2 ---->
Table
2Bl
(Bend) 2Al
2. Infrared
620 475
16125 21047
Band Assignments
620
16125
19602 cm-’
505
19796
‘Tlg(F)
466
21453
assignments are supported by their shift towards higher energy as expected positive slopes of these energy levels
for VO’+:ZMTH
are assigned
--->
Sugano
(T-S)
which
shows
‘T,g(P)
diagram. shift
to ‘Tlg(F)--->
transitions
The
towards
4T2g(F)
respectively.
band
lower
at
energy
and
These
temperature from the in Tanabe8785
cm-’
is
attributed to 4Tlg(F) ---> 2Eg(G) and this in Assignment Band (cm-‘) accordance with the negative slope of the term in ____________________~~~~~~-_~_~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ the T-S diagram. With the aid of the T-S diagram 1655 C = C stretch, H-O-H bend the band at 21316 cm-’ is attributed to the 1530 CO; asymmetric stretch transition ‘Tlg(F) ---> 2Tlg(H). Based on these 1365 CO, symmetric stretch assignments the energy matrices for d7 1200 O-H bend in plane configuration [IOlare solved and the values B = 850 C-H bend out of plane 900 cm-‘, C = 3780cm-’ and Dq = 910 cm-’ give a 850-500 OH and CH deformations good fit to the observed band positions (Table 3). 350 Zn-0 stretch Table 3. Assignments for the bands of c02+: ZMTH
are given in Fig. 4. No EPR signal is observed even at liquid nitrogen temperature and therefore EPR spectrum is not recorded. The general features of the spectrum at laboratory temperature are in accordance with
1
Band positions _________________________^____________ 300K 80K ____________________----_____________
Assignments 4Tlg(F)
to
(cm -1 1 (cm-‘) (nm) (nm) ____________________~~~~~~~~________________________________
1
1222
8181
1220
8194
2Eg(G) ‘TZg(F)
1138
8785
1140
8770
4Tlg(P)
510
19602
501
19955
472
21181
2Tlg(H)
469
21316
465
21499
In the present
investigation
the band at
21316 cm-’ ascribed to 4Tl (F) ----> 2Tlg(H) is at liquid found to split into two %omponents nitrogen temperature. The splitting might be due to lowering of symmetry or spin-orbit interaction. The separation between the two components is 318
J WAVELENGlH(n”7)
Fig.4
Optical absorption spectra of Co2+: ZMTH (RT: Room temperature; LNT: Liquid nitrogen temperature).
cm -‘. If spin-orbit interaction is assumed and claculations are made, the splitting of the band Therefore spincomes to the order of 100 cm-‘. orbit interaction is ruled out. In case of the lowering of the symmetry the probable trigonal
symmetries (C,,,)
might
or rhombic
(C,,).
be
tetragonal The 2T level
(C,,,), splits
ZINC HYDROGEN MALEATE TETRAHYDRATE
712
4. CONCLUSION
into two, two and three components in tetrgonal, trigonal and rhombic symmetries respectively. Since in the
present
two, the site
investigation symmtery
the
is either
2T level tetragonal
splits
into
or
trigonal. However the 2E level splits into two in tetragonal symmetry whereas it does not split in trigonal symmetry in the absence of spin-orbit interaction [Ill . Since 2E does not split in present investigation, the site symmetry can in all probability be ascribed to a trigonal distortion. The IR soectrum is similar to that observed in V02+ reproduced.
doped
ZMTH
and
therefore
is
not
Vol. 70, No: 7
From the results
and analysis
of the present
investigation, it is evident that the V02+ and Co 2+ ions in ZMTH are octahedrally co-ordinated. The splittings of the energy levels indicate tetragonal distortion
in the case
of V02+ and trigonal
distortion in the case of Co2+ ions. The bands observed in the IR region are successfully ascribed to carboxylate ion and water molecule. Acknowledgements - The authors wish to express their thanks to CSIR (New Delhi) for financial assistance.
REFERENCES 1. 2.
3. 4. 5.
K.Saroja & S.V. Raman, Current Sci. 41, 599 (1972). A.S. Antsyshkina, M.A.Porai-Koshits & M.G. Guseinov, Izv. Akad. Nauk. SSSR, Ser. Khim. 287 (1974). M.Vithal, R.Jagannathan & C.S.Sunandana, Spectrochemica Acta, 41A, 861 (1985). S:N.Rao, K.Ramesh & Y.P.Reddy, Proc. Solid State Physics Symposium, 3OC, 124 (1987). D.Kivelson & S.K.Lee, J.Chem.Phys. 41, 1896 ( 1964).
6. 7. 8. 9. 10. 11.
A. Kasiviswanath, J.Chem.Phys. 67, 3744 (1977). & S.Ikoma, J-Inorg-NuclT.Sato, K.Nakamura _\ Chem. 41, 223 (1979). V.K. Jain, J.Phys.Soc.Japan, 46, 1250 (1979). S.Koide, PhiLMag. 4, 243 (1959). Y.Tanabe & S.Sugano, J.Phys.Soc.Jpn. 9, 766 (1954). . A.H.Pismis & S.Sugano, A.L.Schawlow, Phy.Rev. 122, 1469 (1961).
JO,
vol.
No.
7,
pp.
709-712,
0038-1098/89$3.00+.00
1989.
Pergamon
Press
plr
ELECTRONIC SPECTRA OF VO*+ AND Co*+ IN ZINC HYDROGEN MALEATE TETRAHYDRATE S.N. Rao, K. Ramesh and Y.P. Reddy Department of Physics, S.V. University, Tirupati - 517 502, India ( Received
10 Novenber
1988,
form 3 February
in revised
of transition The optical absorption spectra maleate tetrahydrate crystals are investigated. the results
and analysis
of the
of VO*+, EPR spectrum The results indicate that
metal doped The present
co*+:
chemical
ma1 is maleate
formula
Ds = -2700 cm-’
gir = 1.930
gl
= 1.981
Dq = 910 cm-’
B
=
H2 M(ma&l
4H20
In the case
powder is also investigated. symmetry is tetragonally
Dq = 1613 cm-’
in the
case
of Co 2+
Dt I 1176 cm-’ A,, = 193C
A1 = 76G
C = 3780 cm-’
900 cm-’
zinc hydroxide is precipitated using sulphate, By treating the freshly ammonium hydroxide. precipitated zinc hydroxide with hot maleic acid and allowing the resulting solution to evaporate slowly at the laboratory temperature, good colourless crystals of ZMTH are grown in about ten To grow the vanadyl and cobalt doped days. cystals, 0.1 Mole weight of the corresponding sulphate is added at the starting point. Optical absorption spectra of the samples in UV-VIS region are recorded with 2 mm thick crystals on a Hitachi U3400 spectrophotometer, both at laboratory and liquid nitrogen temperatures. The IR spectra are recorded at laboratory-temperature with ootassium bromide bellets on a SP3-300 Pye Unicam IR spectrophotometer. The EPR sepectra of the polycrystalline powders are recorded at both laboratory and liquid nitrogen temperatures on Varian and Jeol X-band spectrometers.
1. INTRODUCTION ZINC HYDROGEN MALEATE TETRAHYDRATE hereafter referred to as ZMTH belongs to a group of isomorphous series of compounds with the general
zinc hydrogen paper presents
VO*+ and Co*+ doped crystals.
of the polycrystalline the octahedral site
ftiorted in the case of VO*+ and trigonally distorted . The following are some of the parameters evaluated. vo*+:
1989 by P.Burlet)
where
ion (C4H2O41 and M is a divalent
cation such as Zn, Cu, Co and Ni. The crystal structure studies of ZMTH [I,21 reveal-that this compound is triclinic with space group Pl with one molecule per unit cell. There is a slight difference in the unit cell dimensions published by the two groups. The two sets of values are as follows: a = 0.729 nm. b = 0.973 nm. c = 0.536 nm a = 110.8’, ’ p = 63.3’, ’ f q 103.6’ [I] c = 0.528 nm a = 0.730 nm, b = 0.982 nm, a = 11o.*o, p = 77.10, f = 117.00 (21 The metal ions Zn are octahedrally coordinated by four water oxygen atoms and two oxygen atoms from two monodentate hydrogen maleate ligands. From the studies of EPR Spectrum of copper doped ZMTH at laboratory temperature
3 RESULTS AND ANALYSIS VO*+: ZMTH :In the optical absorption spectrum of VO*+: ZMTH, three bands are observed at laboratory
[31 it has been concluded that Cu*+ replaces Zn*+. No invesitgations on the optical absorption of ZMTH doped with transition metal ions seem to have been reported in the literature. Therefore the investigation of the optical absorption spectra of transition metal doped ZMTH is undertaken with a view to ascertain the site symmetry of the transition metal ions and to study the effect of distortions on the optical absorption spectra. EPR spectra of the polycrystalline samples are also studied to supplement the optical absorption data.
temperature at 13982, 16125 and 21047 cm-‘. At liquid nitrogen temperature all three bands have become
sharp.
exhibit any shift bands are shifted
The band at !6125 cm-’ does not in position whereas the other two towards shorter wavelengths. An
additional band at 19796 cm -’ is also recorded. The spectra are shown in Fig. 1. The EPR spectra recorded at laboratory and liquid nitrogen temperatures are similar and exhibit two sets of eight lines. The EPR spectrum at laboratory temperature is shown in Fig. 2. The IR spectrum exhibits vibrational modes characteristic of carboxylate ion and water and is shown in Fig. 3.
A brief report on the results of the VO*+ doped ZMTH has been presented at the Solid State The detailed results and Physics Symposium [41 . analysis of the investigations on vanadyl and cobalt doped ZMTH are presented in this paper. 2. EXPERIMENTAL The single crystals of pure ZMTH are grown 131. From zinc as reported in the literature
In octahedral
709
(Oh)
VO*+ ion occupies
the
rise
state
to the ground
crystal
lowest *T*g*
field
t2g orbital
the
d1 of
and gives
In the excited
state
ZINC HYDROGEN MALEATE TETRAHYDRATE symmetry
vol.
is generally
lowered
to C4v
7o;no.
f
or C2v
due to nonsymmetrical alignment of the V-O bond along the symmetry axis. The EPR spectrum of the d’ electron gives rise to the hyperfine coupling
to eight of the
electron,
spin (I = 7/i)
with the
Cov symmetry
nuclear
two sets
of ei$t
line pattern due single unpaired
lines
of 5’V.
In
are expected
whereas in C2v symmetry three sets of eight lines are expected. In the present investigation since two sets of eight lines are observed, the site symmetry of
I
I
I
I
500
600
700
600
WAVELENGTH
vo2+ ion is ascribed to C peak positions of the EP ff spin Hamiltonian parameters g,, = 1.930 A,, g1 = 1.981
A,_=
76C
(nm)
Accordingly Fig.1
symmetry. From the spectrum the following are evaluated: = 193 G
Optical absorption spectra (RT: Room Temperature; nitrogen temperature).
of
V02+: ZMTH LNT: Liquid
13982,
16125
temperature --->
the and
are
three
21047
attributed
2E, 2B2 --->2B1
bands cm-’
to
observed at
the
at
laboratory
transitions
and 2B2 --->
2Al.
2B2 The band
peak data and assignments are given in Table Based on these assignments the following cyrstal field parameters Dq, Ds and Dt are evaluated. Dq = 1613 cm-’ Ds = -2700 cm-’ In the low temperature additional energy
that
band seperation
assigned
I
I
I
I
3250
3650
4050
EPR spectrum
of V02+: ZMTH
the
of
this
agrees
mode of the water
fractional
p;’
cm-‘. band,
well with molecule.
The from the
The
*2 15-81. They represent err
and
contributions
of the
d xz (and /or dyz) in antibonding
I
I 1500
I 1000
19796
spin orbit coupling constant A = 170 cm-‘, the dipolar hyperfine splitting constant p = -127 G and the Fermi contact term K = 0.87 are evaluated from the formula given by Kivelson et al 151. EPR and optical absorption data are correlated to evaluate the molecular orbital coefficients
I 500
Dt c 1176 cm-’ spectrum an
fundamental frequency (1655 cm-‘) of H-O-H bending vibration observed in IR spectrum supports this assignment. The assignments of the observed IR bands are given in Table 2. Using the values g,, , gl , A,,, Al obtained from EPR spectrum and the free ion value of the
H (G) Fig.2
at
(1657 cm-‘)
to 2B2--->2Al
H-O-H bendig
2850
is observed
1.
orbitals
,molecular
dx2_y2, orbitals
are *2 = 0.86 2b and 2e. The values evaluated Pl *2 = 0.87. These values suggest that the inplane err bonding and out of plane bonding are covalent.
WAVENUMBERkm-‘)
Fig.3
IR spectrum
of V02’:
Co2+: ZMTH :The absorption laboratory temperature
ZMTH
spectrum recorded at exhibits, four bands at 8181,
8785. 19602 and 21316 cm-‘. At liquid temperature the band at 21316 cm-’ splits it
occupies
2E g
state.
corresponding ble.
However
the
orbital 6 Therefore e
and only
gives a
rise single
to the band
is possi2T2g --->2Eg transition in the case of V02+, the site
to
components
(21181 and
8181 and 19602 cm-’ wavelengths whereas shift towards longer
21499 cm-l).
show
shifts
the band wavelength
at
nitrogen into two
The bands
towards
at
shorter
8785 cm-’ shows side. The spectra
vi+.
711
ZlNC HYDROGEN MALEATE TETRAHYDRATE
70, No. 7
Table 1. Assignments
those expected environment.
for the bands of V02+: ZMTH
for a Co2+ ion in octahedral For divalent cobalt ion in octahedral
Band positions 4T, ,(F)---> symmetry, three spin allowed transitions ____________~_______~-~~~~~-~--~~~~~~ ‘Tlg(F) ---> 4A2g(F) and ‘TJgiF) ---> 300K SOK Assignments ____________________~~~~~~~~~~~~~~~~~ ‘Tlg(P) are expected. But the transition ?lg(F)---> (nm) (cm-‘) (nm) (cm-l) 4 A2g(F) involves the promotion of two electrons ______________________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ and is therefore expected to be very weak[91. 14021 13982 Therefore the two intense broad bands at 8181 and 2B2 ---> 2E 715 713
IfTZg(F),
2B2 ---> H-O-H
2B2 ---->
Table
2Bl
(Bend) 2Al
2. Infrared
620 475
16125 21047
Band Assignments
620
16125
19602 cm-’
505
19796
‘Tlg(F)
466
21453
assignments are supported by their shift towards higher energy as expected positive slopes of these energy levels
for VO’+:ZMTH
are assigned
--->
Sugano
(T-S)
which
shows
‘T,g(P)
diagram. shift
to ‘Tlg(F)--->
transitions
The
towards
4T2g(F)
respectively.
band
lower
at
energy
and
These
temperature from the in Tanabe8785
cm-’
is
attributed to 4Tlg(F) ---> 2Eg(G) and this in Assignment Band (cm-‘) accordance with the negative slope of the term in ____________________~~~~~~-_~_~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ the T-S diagram. With the aid of the T-S diagram 1655 C = C stretch, H-O-H bend the band at 21316 cm-’ is attributed to the 1530 CO; asymmetric stretch transition ‘Tlg(F) ---> 2Tlg(H). Based on these 1365 CO, symmetric stretch assignments the energy matrices for d7 1200 O-H bend in plane configuration [IOlare solved and the values B = 850 C-H bend out of plane 900 cm-‘, C = 3780cm-’ and Dq = 910 cm-’ give a 850-500 OH and CH deformations good fit to the observed band positions (Table 3). 350 Zn-0 stretch Table 3. Assignments for the bands of c02+: ZMTH
are given in Fig. 4. No EPR signal is observed even at liquid nitrogen temperature and therefore EPR spectrum is not recorded. The general features of the spectrum at laboratory temperature are in accordance with
1
Band positions _________________________^____________ 300K 80K ____________________----_____________
Assignments 4Tlg(F)
to
(cm -1 1 (cm-‘) (nm) (nm) ____________________~~~~~~~~________________________________
1
1222
8181
1220
8194
2Eg(G) ‘TZg(F)
1138
8785
1140
8770
4Tlg(P)
510
19602
501
19955
472
21181
2Tlg(H)
469
21316
465
21499
In the present
investigation
the band at
21316 cm-’ ascribed to 4Tl (F) ----> 2Tlg(H) is at liquid found to split into two %omponents nitrogen temperature. The splitting might be due to lowering of symmetry or spin-orbit interaction. The separation between the two components is 318
J WAVELENGlH(n”7)
Fig.4
Optical absorption spectra of Co2+: ZMTH (RT: Room temperature; LNT: Liquid nitrogen temperature).
cm -‘. If spin-orbit interaction is assumed and claculations are made, the splitting of the band Therefore spincomes to the order of 100 cm-‘. orbit interaction is ruled out. In case of the lowering of the symmetry the probable trigonal
symmetries (C,,,)
might
or rhombic
(C,,).
be
tetragonal The 2T level
(C,,,), splits
ZINC HYDROGEN MALEATE TETRAHYDRATE
712
4. CONCLUSION
into two, two and three components in tetrgonal, trigonal and rhombic symmetries respectively. Since in the
present
two, the site
investigation symmtery
the
is either
2T level tetragonal
splits
into
or
trigonal. However the 2E level splits into two in tetragonal symmetry whereas it does not split in trigonal symmetry in the absence of spin-orbit interaction [Ill . Since 2E does not split in present investigation, the site symmetry can in all probability be ascribed to a trigonal distortion. The IR soectrum is similar to that observed in V02+ reproduced.
doped
ZMTH
and
therefore
is
not
Vol. 70, No: 7
From the results
and analysis
of the present
investigation, it is evident that the V02+ and Co 2+ ions in ZMTH are octahedrally co-ordinated. The splittings of the energy levels indicate tetragonal distortion
in the case
of V02+ and trigonal
distortion in the case of Co2+ ions. The bands observed in the IR region are successfully ascribed to carboxylate ion and water molecule. Acknowledgements - The authors wish to express their thanks to CSIR (New Delhi) for financial assistance.
REFERENCES 1. 2.
3. 4. 5.
K.Saroja & S.V. Raman, Current Sci. 41, 599 (1972). A.S. Antsyshkina, M.A.Porai-Koshits & M.G. Guseinov, Izv. Akad. Nauk. SSSR, Ser. Khim. 287 (1974). M.Vithal, R.Jagannathan & C.S.Sunandana, Spectrochemica Acta, 41A, 861 (1985). S:N.Rao, K.Ramesh & Y.P.Reddy, Proc. Solid State Physics Symposium, 3OC, 124 (1987). D.Kivelson & S.K.Lee, J.Chem.Phys. 41, 1896 ( 1964).
6. 7. 8. 9. 10. 11.
A. Kasiviswanath, J.Chem.Phys. 67, 3744 (1977). & S.Ikoma, J-Inorg-NuclT.Sato, K.Nakamura _\ Chem. 41, 223 (1979). V.K. Jain, J.Phys.Soc.Japan, 46, 1250 (1979). S.Koide, PhiLMag. 4, 243 (1959). Y.Tanabe & S.Sugano, J.Phys.Soc.Jpn. 9, 766 (1954). . A.H.Pismis & S.Sugano, A.L.Schawlow, Phy.Rev. 122, 1469 (1961).