ELECTRONIC SPECTRAL CHARACTERIZATION OF Tm (III) SYSTEMS INVOLVING N, S & O ENVIRONMENT IN DMSO MEDIUM

Abstract

Electronic spectral parameters, viz. Judd-Ofelt (T λ = T 2 , T 4 , T 6 , T 4 /T 6 and T 4 /T 2), and bonding parameters (β, δ% 1/2 and η have been evaluated for saturated solutions of eight ligands having N, S & O donor atoms, doped with Tm (III) ion. The change in symmetry around Tm (III) and covalency in M-L interaction has been observed.

Full text

Int. J. Chem. Sci.: 8(4), 2010, 2756-2762
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*Author for correspondence; E-mail: mkvyas2007@rediffmail.com
ELECTRONIC SPECTRAL CHARACTERIZATION OF
Tm (III) SYSTEMS INVOLVING N, S & O ENVIRONMENT IN
DMSO MEDIUM
MAHENDRA VYAS*, GOURAV CHAWLAa and H. K. PANDEYa
Department of Chemistry, Govt. Engineering College, BIKANER (Raj.) INDIA
aP. G. Department of Chemistry, Govt. Dungar College, BIKANER (Raj.) INDIA
ABSTRACT
Electronic spectral parameters, viz. Judd-Ofelt (Tλ = T2, T4, T6, T4/T6 and T4/T2), and bonding
parameters (β, δ%1/2 and η have been evaluated for saturated solutions of eight ligands having N, S & O
donor atoms, doped with Tm (III) ion. The change in symmetry around Tm (III) and covalency in M-L
interaction has been observed.
Key words: Thulium (III), f-f Transition, Electronic spectral parameters, Ligands, N, S & O Donor atoms.
INTRDUCTION
Since the publication of Judd – Ofelt theory1-3 for the lanthanide complexes, a great
deal of work has been reported on the measurement of f-f transitions for free and aquo/solvent
ions of lanthanide in different chemical environment by several workers4-8. The Schiff base
complexes9,10 of lanthanide (III) ions [Pr (III) & Nd (III)] have been studied extensively
through various electronic spectral parameters. Similarly, sulphonanilide complexes of Ln (III)
have also been studied and characterized through absorption spectra.11-17
In the present investigation, ligands having N, S & O as donor atoms viz. urea (L1),
thiourea (L2), DMG (L3), semicarbazide (L4), thiosemicarbzide (L5), acetaldehyde-
semicarbazone (L6), N,N-DPTU (L7) and DPG (L8) have been chosen for complexation with
Tm (III) ion and complexes were characterized through various electronic spectral
parameters like Judd-Ofelt parameters (Tλ = T2, T4, T6, T4/T6 and T4/T2), Oscillator strength
(P), nephelauxetic ratio (β) ,bonding parameter (b1/2), Sinha covalency parameter (δ%) and

Int. J. Chem. Sci.: 8(4), 2010 2757
covalency angular overlap parameter (η), to have a comparative study of complexation with
different ligands.
In the present investigation of Tm (III) complexes, the solution spectra yields four
bands viz.
3H6 → 1G4, 3H6 → 3F2, 3H6 → 3F3 and 3H6 → 3H4
Bonding in complexes have been derived by using partial and multiple regression
method involving theories given by Slater-Condon & Lande and Judd-Ofelt. The study gives
valuable information regarding M-L bonding, spin-orbit interaction and inter electronic
repulsion.
EXPERIMENTAL
It is difficult to explore the spectra of Ln ions in different systems, particularly in
hypersensitive region. In order to get better spectra, one should go for better ligating system
or for dilution. In the present work, former aspect has been taken into consideration by
selecting various ligands having N, S & O donor atoms and doped model technique has been
used. In this technique, a saturated solution of ligand is prepared in a suitable solvent and
during solubilization phenomenon, stoichiometric amount of metal ion is added. In the
present work, eight systems of Tm (III) ion, doped in saturated solution of ligand have been
prepared by adding 0.0802 g.
TmCl3.6H2O (Supplied by Across Limited, USA) per 25 mL of ligand solution was
used. The solution spectrum of each system has been recorded in the range 400-850 nm by
using standard spectrophotometer. All the systems were characterized by various parameters.
Different parameters were calculated by using partial and multiple regression
method by using following formulae -
Intensity parameter
(a) Oscillator strength (P)
P = 4.315 x 10-9 ∫ ∈ dν …(1)
(where ∈ = molar absorptivity ν = frequency in wave number)
≈ 4.6 X 10-9 x ∈max ∆ ν 1/2

M. Vyas et al.: Electronic Spectral Characterization of….
2758
(b) Judd-Ofelt parameters (T2, T4 and T6):
Pobs = T2 ν [U(2)]2 + T4 ν [U(4)]2 + T6 ν [U(6)]2 …(2)
(where [U(2)]2, [U(4)]2, [U(6)]2 are matrix elements)
(c) R.M.S. Deviation (σ)
σ = [ ∑(Pcal – Pobs)2 / N ]1/2 …(3)
(where N = Number of levels taken)
Bonding parameters
(a) Nephelauxetic ratio (β)
β = νc / νf …(4)
where νc and νf = wave numbers of f-f transition in spectra of metal complex and
free metal ion in solvent, respectively.
(b) Bonding parameter (b1/2)
b1/2 = [ ½ (1-β)]1/2 …(5)
(c) Sinha’s covalency parameter (δ%):
δ = [1-β / β ] X 100 …(6)
(d) Covalency angular overlap parameter (η):
η = [1 - β1/2 / β1/2] …(7)
Metal-ligand interaction was evaluated on the basis of these parameters
Oscillator strength (P): Hypersensitive transitions show greater change in the value
of oscillator strength than non-hypersensitive transitions. For hypersensitive transitions,
value of oscillator strength (P) was found directly proportional to υT6. Peacock7,8 proposed
this linear correlation for oscillator-strength.
Judd-Ofelt parameters: These are indicative of the degree of metal-ligand (M-L)
interactions (T2), the refractive index of medium (T4) and the change in symmetry around
the cation (T6).

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R.M.S. deviation (σ): From the calculated and observed values of oscillator strength
(P), the value of r.m.s deviation (σ) for all the eight systems were computed by using the
equation (3).
Low values of r.m.s deviation for all the systems proved Judd-Ofelt theory.
Bonding parameters: The positive value of (b ) infers covalency in (M-L) bond.
The change (low & high) in the value of other bonding parameters (β, δ%, η) depict weak
and strong metal-ligand covalent bond character, respectively.
Symmetry parameter (T4/T6): The value of this parameter is found to be similar, if
‘Ln’ ion is surrounded by ligand environment of similar symmetry. The change in the value
of this ratio reflects the change in ‘Ln’ environment i.e. the change in symmetry.
Coordination parameter (T4/T2): This parameter reflect the coordination behavior
around metal ion. If its value is found similar for various systems, it shows same co-
ordination environment around metal ion. The change in value of this ratio reflects the
change in ‘Ln’ environment i.e. different coordination behavior around metal ion.
Thus, these two parameters give valuable information about symmetry and co-
ordination behavior in all the systems.
Table 1: Observed and calculated values of oscillator strength (P) of the four bands
recorded for Tm (III) ion systems involving ligand environment in DMSO
solvent
1G4
O.S[P] x 106
3F2
O.S[P] x 106
3F3
O.S[P] x 106
3H4
O.S[P] x 106
Bands →
Tm (III) system
↓ Exp. Cal. Exp. Cal. Exp. Cal. Exp. Cal.
Tm (III) + L1 3.62 4.05 0.56 0.86 6.02 6.31 10.40 10.65
Tm (III) + L2 3.62 4.06 0.56 0.86 6.02 6.32 10.40 10.65
Tm (III) + L3 3.79 4.01 0.49 0.64 4.96 5.11 10.42 10.55
Tm (III) + L4 3.60 4.06 0.55 0.87 5.98 6.28 10.42 10.69
Tm (III) + L 5 3.54 3.99 0.62 0.94 6.07 6.38 10.42 10.69
Tm (III) + L 6 3.65 4.05 0.57 0.85 5.98 6.24 10.40 10.63
Tm (III) + L 7 3.45 3.92 0.64 0.97 6.17 6.49 10.42 10.70
Tm (III) + L 8 3.74 4.08 0.56 0.80 5.98 6.21 10.40 10.60

M. Vyas et al.: Electronic Spectral Characterization of….
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Table 2: Computed values of tλ parameters for Tm (III) systems involving ligand
environment in DMSO solvent
Tm (III) system T2 x 109 T
4 x 109 T6 x 109 T4/T6 r.m.s deviation
(σ)±1.0 x 10-9
Tm (III) + L1 2.66 0.79 0.22 3.55 3.28
Tm (III) + L2 2.66 0.78 0.22 3.52 3.30
Tm (III) + L3 2.82 0.68 0.16 4.08 1.64
Tm (III) + L4 2.68 0.77 0.22 3.46 3.45
Tm (III) + L5 2.64 0.75 0.24 3.10 3.44
Tm (III) + L6 2.67 0.78 0.21 3.59 3.02
Tm (III) + L7 2.58 0.75 0.25 2.99 3.59
Tm (III) + L8 2.67 0.81 0.20 3.93 2.59
Table 3: Computed values of b1/2, β, η and δ For Tm (III) systems
Tm (III) system β b
1/2 δ η
Tm (III) + L 1 0.9836 0.0903 1.6582 0.0082
Tm (III) + L 2 0.9836 0.0903 1.6582 0.0082
Tm (III) + L 3 0.9830 0.0919 1.7218 0.0085
Tm (III) + L 4 0.9838 0.0899 1.6455 0.0081
Tm (III) + L 5 0.9839 0.0896 1.6328 0.0081
Tm (III) + L 6 0.9833 0.0913 1.6964 0.0084
Tm (III) + L 7 0.9970 0.0384 0.2972 0.0014
Tm (III) + L 8 0.9833 0.0913 1.6963 0.0084
RESULTS AND DISCUSSION
The values of various spectral parameters including oscillator strength (P),
nephelauxetic ratio (β), bonding parameter (b1/2), Sinha covalency parameter (δ%) and
Covalency angular overlap parameter (η) etc. have been reported in Tables 1-3.

Int. J. Chem. Sci.: 8(4), 2010 2761
The observed change in the various intensity parameters show that the f ↔ f
transition resulting from spin-orbit interaction in Tm (III) ion is due to the interaction of f-
orbital with the ligand present in the saturated solution.
The calculation of various parameters involve Slater-Condon & Lande and Judd-
Ofelt theories as reported by earlier workers.4,5 Red-shift has been observed in all energy
bands as compared to the free ion; thereby, establishing the validity of Stater-Condon and
Lande theory.
The R.M.S. deviation varies from 1.64 x 10-9 to 3.59 x 10-9 in all the systems. The
R.M.S. deviation is very small, suggesting the validity of Judd-Ofelt theory for f-f transition.
The T4/T6 ratio varies 2.99 to 4.08, which indicates variation in symmetry around
doped Tm (III) ion in saturated lignd solution.
The values of nephelaxetic ratio (β) and bonding parameter (b1/2) as well as little
variation in their values, suggest that the 4f orbitals are very slightly involved in the bonding
in saturated solutions doped with Tm (III) ion.
ACKNOWLEDGEMENT
The authors are grateful to Principal, Dungar College, Bikaner for providing
necessary facilities.
The authors are also highly thankful to Prof. M. P. Poonia, Principal, Govt.
Engineering College, Bikaner, Mrs. Chanchal Kachhawa, Head, Deptt. of Chemistry, Dr.
Praveen Purohit and Mr. R. C. Beniwal, Govt. Engineering College, Bikaner for their whole
hearted cooperation.
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Revised : 26.11.2010 Accepted : 27.11.10