Modeling of Eu3+ Energy Levels in Complexes with 1,10-Phenanthroline Derivatives

Article abstract of DOI:10.1023/A:1025166522469

The experimental electronic spectra of the Eu³⁺ ion in three groups of the Eu complexes (β-diketonates, acetates, and nitrates) with the 1,10-phenanthroline derivatives were used to calculate the crystal field parameters for the model of the ne

Full text of DOI:10.1023/A:1025166522469

Russian Journal of Coordination Chemistry, Vol. 29, No. 8, 2003, pp. 574–581. Translated from Koordinatsionnaya Khimiya, Vol. 29, No. 8, 2003, pp. 617–624.
Original Russian Text Copyright © 2003 by Puntus, Zolin.
Modeling of Eu3+ Energy Levels in Complexes
with 1,10-Phenanthroline Derivatives
L. N. Puntus and V. F. Zolin
Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Moscow, Russia
Received August 22, 2002
Abstract—The experimental electronic spectra of the Eu3+ ion in three groups of the Eu complexes (β-diketo-
nates, acetates, and nitrates) with the 1,10-phenanthroline derivatives were used to calculate the crystal field
parameters for the model of the nearest environment of this ion with the C2v point group symmetry. It was
shown that these parameters can be used for estimating the coordination number of the metal cation and estab-
lishing the structural peculiarities.
The correlations between the spectra and structures butadiene were taken on the UR-20 and Nicolet Magna
of the lanthanide β-diketonates, acetates, and nitrates 750 FTIR spectrophotometers at 300 K.
with the 1,10-phenanthroline were studied in [1–4] by
IR, Raman, and optical spectroscopies (luminescence
RESULTS AND DISCUSSION
and excitation spectra). The crystal field parameters
(CFP) were not used in these studies, since the experi-
mental data on the Stark splittings of the Eu3+ levels for
each of the group under consideration were insufficient
for reliable estimation of the CFP, particularly, the
sixth-order parameters. In this work, the combined use
of the energies of the Eu3+ levels in the spectra of all
three groups of compounds, which differed in the coor-
dination numbers of the lanthanide ions, made it possi-
ble not only to calculate these parameters, but to apply
the calculation results for establishing the structure of
the nearest surrounding of the lanthanide ions and
determining their interaction with ligands.
The [Eu(DPM)3Phen] structure described in [5] is
similar to the structures of the other lanthanide β-dike-
tonates with heterocyclic diimines [6–8]. The coordina-
tion polyhedron of Eu3+ in these compounds is the dis-
torted square antiprism formed by six oxygen atoms
and two nitrogen atoms (the coordination number (CN)
of the europium ion being eight). The point group sym-
metry of the coordination polyhedron is close to C2.
The additional deformation of the antiprism caps due to
the rotation of the ligand planes can increase the poly-
hedron symmetry to C2v. This assumption agrees with
the use of the model of the complex with the distorted
coordination polyhedron.
The [Eu(CH3COO)3Phen] crystals are built of the
dimeric molecules. All the three acetate groups perform
different structural functions [9]. One of them acts as
the bidentate bridge, the second is the tridentate-bridg-
ing-cyclic group, while the third is the bidentate-cyclic
group. The coordination polyhedron of the Eu3+ ion is
formed by seven oxygen atoms of the carboxylate
anions and two nitrogen atoms of the 1,10-phenanthro-
line molecule (CN 9). The polyhedron can be repre-
sented as a distorted tetragonal one-capped antiprism or
as a three-capped trigonal prism. The symmetry of the
model coordination polyhedron will be close to C2v as
the tridentate bridging-cyclic acetate groups change
their positions.
EXPERIMENTAL
The europium compounds with the 1,10-phenan-
throline (Ph) derivatives [Eu(L)3Ph] were synthesized
as described elsewhere [2–4]. Here L is dipivaloyl-
methanate (DPM) or acetate anions; Ph are the 1,10-
phenanthroline derivatives: 3,4,7,8-tetramethyl-1,10-
phenanthroline (Tmphen), 5-methyl-1,10-phenanthro-
line (Phphen), 4,7-diphenyl-1,10-phenanthroline (Dph-
phen), 5-nitro-1,10-phenanthroline (Nphen). The
europium nitrates with Ph of the composition
[Eu(NO3)3(Ph)2] were obtained by mixing the ethanol
solutions of Eu(NO3)3 · 6H2O and of the phenanthroline
derivatives. The compositions of the compounds were
confirmed by the elemental analysis data.
The coordination polyhedron of the Eu3+ ion in the
The luminescence and excitation spectra were nitrate complexes with the phenanthroline derivatives
recorded on a SLM Aminco SPF 500 spectrometer and of the composition [Eu(NO3)3(Phen)2] [10] is a two-
DFS-12 spectrograph at 77 and 300 K. The Raman capped dodecahedron formed by six oxygen atoms of
spectra were recorded on a Nicolet Magna 860 FTIR three bidentate nitrate anions and four nitrogen atoms
spectrometer at 300 K. IR absorption spectra of the of two molecules of heterocyclic diimine (CN 10). All
compound emulsions in vaseline oil and hexachloro- the three nitrate groups lie above, while the phenanthro-
1070-3284/03/2908-0574$25.00 © 2003 åÄIä “Nauka /Interperiodica”

MODELING OF Eu3+ ENERGY LEVELS
575
of the levels of the 5D0–7F4 transition in the cubic-sym-
metry crystal field, is close to unity in the case of the β-
diketonates and acetates and is zero for nitrates (Fig. 1).
The B04/B44 and B06/B46 values have different signs,
which corresponds to an increased contribution of the
cubic components of the crystal field.
line molecules, below the equatorial plane of the com-
plex. One nitrate group is on the two-fold symmetry
axis, whereas the other two are in the general positions.
The symmetry of the model coordination polyhedron
will be close to C2v as the coordinated phenanthroline
molecules are respectively rotated.
In order to calculate the CFP, we selected the model
of the nearest environment of the lanthanide ion with
the point symmetry C2v. The CFP calculated for such a
model provide sufficiently adequate agreement
between the theoretical energies of the europium ion
levels and the experimental values (standard deviation
of the calculated values from the experimental values
being ~12 cm–1). The selected model is supported by
the effect of leveling of interaction of the charges at the
oxygen atoms and of the charges at the nitrogen atoms
(more exactly, the dipole moments of the phenanthro-
line molecules) with the lanthanide ion due to the
strong dependence of this interaction on the reverse dis-
tances between the interacting charges. As the result of
this leveling, the symmetry of the effective nearest
environment of the lanthanide ion becomes higher than
the symmetry of the real distribution of ions.
The most accurate experimental data on the Stark
7
splittings of the levels in CF are provided by the F1,
7F2, and 7F4 levels of the ground 7FJ (J = 0–6) multiplet
of the Eu3+ ion. At the same time, even in this case, one
cannot always establish all the Stark components of
these levels, for instance, the 7F4 level for the europium
β-diketonates or the 7F2 level for the europium nitrates.
That is why the positions of the Stark components of
the Eu3+ levels are determined using the linear depen-
dences of the centers of gravity of different levels on the
position of the center of gravity of the 7F1 or any other
level, for which they are reliably estimated [14]. We
used our experimental data and constructed the plots of
the linear dependence between the positions of the cen-
5
5
ters of gravity of the D0–7F1 and D0–7F2 transitions,
which are similar to the plot previously reported in [14],
and of the 5D0–7F1 and 5D0–7F4 transitions (Fig. 2). In
Table 1, the energies (Ö) of the Stark components of the
transitions determined from these plots are marked by
asterisk.
The Stark splitting of the levels of the lanthanide
ions in the lattice crystal field was described by the
Hamiltonian of a crystal field [11], which is the sum of
the products of the CFP Bkq by the Ckq operators, pro-
portional to the normalized spherical harmonics Ykq :
The plots of the center of gravity of the 5D0–7F4 tran-
sition on the center of gravity of the 5D0–7F1 transition
for the considered groups of compounds are the parallel
straight lines that cannot be laid in one line (Fig. 2). It
is known that the degeneration of the centers of gravity
of the electron levels, which differ in the full angular
momentum J, inside multiplets, whose energy is deter-
mined by the repulsion of the 4f electrons, in particular,
Hcf = Σkq[Bkq(Ckq + (–1)qCkq) + iSkq(Ckq – (–1)qCkq)],
Ckq(4π/2n + 1)1/2Ykq.
For the C2v symmetry, all Skq values are equal to zero,
and therefore only nine CFP remain.
The CFP were calculated by adjusting the theoreti-
cal values of the Stark splittings using the experimental
data. In this case, the CFP calculation is an inverse
problem that can give many solutions depending on the
conditions and restrictions of the model used, for exam-
ple, the direction of the quantization axis, etc. [12]. We
imposed the following additional conditions.
7
inside the F multiplet of the Eu3+ ion, is removed by
the spin–orbit coupling. In this case, the energies of the
centers of gravity (E ) for the levels with different J
depend linearly on the spin–orbit coupling constant.
Apparently, when constructing the plots of the energies
of the centers of gravity of some levels in a multiplet vs.
the energies of the centers of gravity of the other levels
in the same multiplet, the linear dependence will be
obtained, since the former and the latter energies
depend linearly on the spin–orbit coupling constant.
The real dependence of the centers of gravity of the lev-
els on the spin–orbit coupling constant will be linear
only with the assumption that the parameters of the
electrostatic repulsion (the Slater radial integrals [11])
are constant. This partially holds for the single-type
crystal lattices (for isomorphic crystals of compounds
with almost identical composition). This condition is
likely to be observed in each of the three groups under
study, but is violated when going from one group to the
other one.
The fixed sign of the B02 parameter, i.e., positive for
the β-diketonates (in this case, proceeding from X-ray
diffraction data, one can expect large values of the axial
component of the crystal field (CF) of a second order)
and negative sign for the europium acetates and nitrates
with Ph.
According to Lea, Leask, and Wolf [13], the value of
X
1 – X
---------------
X, which is determined by the relationship
F(4)B04
F(6)B06
=
The 5D0–7F3 transition is forbidden, and in the most
spectra of the investigated compounds, it contains only
-----------------
, where F(4) and F(6) are the numerical coef-
ficients for J = 4, and used for describing the structure 3 or 4 weak lines instead of seven possible lines. That
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 8 2003

576
PUNTUS, ZOLIN
I
a
b
c
1700
1600
1500
1400
ν, cm–1
Fig. 1. Luminescence spectra of (a) [Eu(DPM) Phen], (b) [Eu(CH COO) Phen], and (c) [Eu(NO ) (Phen) ] at 77 K.
3
3
3
3 3
2
is why the data on the Stark structure of this level were displaced by the value of the Stokes shift of the EV
not taken for the CFP calculations. The experimental bands (Fig. 3). The frequency of the respective vibra-
and calculated values of the Eu3+ energy levels in differ- tion assigned to a combined vibration including the
ent compounds with 1,10-phenanthroline are given in symmetric extension of the chelate ring of the β-diket-
Table 1. The values of the CFP for the studied three onate is equal to: 1380 in [Eu(DPM)3Mphen], 1385 in
groups are presented in Table 2.
[Eu(DPM)3Phen] and [Eu(DPM)3Nphen], 1393 in
[Eu(DPM)3Tmphen], and 1399 in
cm–1
Among the investigated compounds, [Eu(DPM)3Ph]
have the lowest symmetry of the europium coordina-
tion polyhedra. In order to establish the Stark compo-
nents of the 5D0–7F4 transition, we had to separate weak
lines of the electronic transitions and intense electron-
vibration (EV) components of the Stokes band of the
[Eu(DPM)3Phphen] and [Eu(DPM)3Dphphen]. Hence,
in the [Eu(DPM)3Ph] series, this frequency, as well as
the Stark splittings of the Eu3+ level, depends on the
size of substituents in Ph.
The variation of one ligand (phenanthroline deriva-
5D0–7F2 transition and isolate the EV bands by compar- tives), with the second ligand (dipivaloylmethanate)
ing with the phonon-free lines of the 5D0–7F2 transition remaining unchanged, mainly affects the amplitudes of
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 8 2003

MODELING OF Eu3+ ENERGY LEVELS
577
Table 1. The experimental (Eexp) and calculated (Ecalcd) energies (cm–1) of the Eu3+ levels in different Eu complexes with
Phen
[Eu(DPM)3Phen]
[Eu(CH3COO)3Phen]
[Eu(NO3)3[Phen)2]
Levels
symmetry
symmetry
symmetry
Eexp
Ecalcd
Eexp
Ecalcd
Eexp
Ecalcd
type
type
type
7F0
7F1
A1
A2
B1
B2
A1
B2
A2
B1
A1
B2
A2
A1
B1
A2
B2
B1
B2
A1
B1
A2
B1
A1
B2
A2
A1
A1
0
0
285
A1
B1
B2
A2
A2
A1
A1
B2
B1
B2
A2
B2
A1
B1
B1
A2
B2
B1
A1
A1
B2
A2
B1
A2
A1
A1
0
0
330
A1
B1
B2
A2
A2
A1
A1
B2
B1
B2
A2
B2
B1
A1
B1
A2
B2
B1
A1
A1
B2
A2
A1
B1
A2
A1
0
0
301
286
329
327
374
297
366
331
378
362
519
518
400
393
447
448
7F2
901
903
974
976
952
951
909
910
990
980
981
985
1032
1099
1267
1039
1096
1263
1812
1850
1892
1923
1943
1952
1984
2680
2728
2743
2778
2860
2968
3024
3026
3075
1027
1080
1100
1021
1085
1108
1809
1847
1885
1893
1900
1903
1943
2680
2694
2714
2761
2841
2869
2900
2942
3060
1018
1083
1193
1010
1083
1197
1781
1821
1862
1893
1876
1902
1978
2586
2595
2636
2739
2866
2873
2941
2960
3094
7F3
1845
1886
1836
1893
1808
1856
1889
1950
1925
1945
2698
2698*
2698*
2758
2817
2882
2904
2941
3068
17222
7F4
2683
2735
2584
2599
2635
2734
2869
2869*
2943
2961
3096
17215
2735*
2785
2850
2971
3026
3026*
3077
5D0
17241
The negative sign of the CFP B02 (Table 1) for the
the CF rhombic components (Table 2). These values are
likely to correlate with the sizes of substituents. They
are at minimum for the compounds with meth-
ylphenanthroline and at maximum for the compounds
with more bulky phenyl derivatives of phenanthroline.
In general, the CF changes in the series of the phenan-
throline derivatives are insignificant. The CFP for
[Eu(DPM)3Tmphen] and [Eu(DPM)3Nphen] were not
calculated, since the spectra of the nonequivalent lumi-
nescence centers were not separated in these cases. The
acetate group agrees with X-ray diffraction data and
corresponds to an increased distribution density of a
negative charge in the equatorial region. The calcula-
tions gave the increased values of the CF tetragonal
components, i.e., the large values of B04 and B44 . This
fact is likely to point to two bidentate-bridging and to
two tridentate bridging-cyclic carboxyl groups in the
equatorial region of the dimeric compound (four bridg-
ing carboxyl groups of our model with the C2v point
symmetry). When going across the Ph series in the
direction of increasing of the acceptor properties of
their radicals (except for the bulky Ph, such as Tmphen,
Dphphen), the B02 and B04 parameters gradually
increase in this group, which suggests that the bond
between the Eu3+ ion and the oxygen atoms becomes
values of the sixth-order CFP, i.e., B06–B66 , for DPM
family are minimum, which illustrates the tendency of
the sixth-order CFP to decrease with a decrease in the
coordination number of the lanthanide ion observed
when comparing these values for the three groups
under consideration.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 8 2003

578
PUNTUS, ZOLIN
Table 2. Crystal field parameters of the Eu3+ ion (cm–1) in different Eu complexes with the 1,10-phenanthroline derivatives
B02
B22
B04
B24
B44
B06
B26
B46
B66
Compound
[Eu(DPM)3Mphen]
700
701
17
–1412
959
327
385
484
393
347
299
320
314
280
285
399
740
780
415
342
376
–304
–255
191
299
334
194
536
443
489
398
456
443
491
705
736
461
549
405
–87
–288
–124
–164
–266
–237
–232
–259
–357
–279
–1227
–544
–329
–1308
–1246
–1301
86
[Eu(DPM)3Phen]
94
155
150
81
–1190 1046
–1242 976
–1050 1089
–16
62
[Eu(DPM)3Phphen]
[Eu(DPM)3Dphphen]
[Eu(CH3COO)3Tmphen]
[Eu(CH3COO)3Mphen]
[Eu(CH3COO)3Phen]
[Eu(CH3COO)3Phphen]
[Eu(CH3COO)3Dphphen]
[Eu(CH3COO)3Nphen]
[Eu(NO3)3(Tmphen)2]
[Eu(NO3)3Mphen)2]
[Eu(NO3)3(Phen)2]
685
–59
660
–289
15
–135
–171
–186
–194
–214
–252
–295
–298
–347
–418
–483
–507
–718
–720
–726
–855
–768
–802
–807
–803
–730
–762
–720
–964
59
75
–1067
–873
528
647
545
501
650
575
706
805
819
624
572
377
42
30
60
–1031
–1034
–919
85
73
73
68
57
25
–968
127
158
176
109
97
372
–49
–72
307
344
222
–1177
–1177
–1229
–1218
–1306
–1096
[Eu(NO3)3(Phphen)2]
[Eu(NO3)3(Dphphen)2]
[Eu(NO3)3(Nphen)2]
119
stronger. In this group, the B04/B44 and B06/B46 ratios are [Eu(CH3COO)3Mphen] spectra are similar (the Bqk val-
ues are close), the former compound has the higher
symmetry. Such a decrease in the symmetry, when
going from the acetate with the methyl derivative of
phenanthroline to the acetate with phenanthroline,
probably occurs due to an increase in the nonequivalent
charge distribution in the nearest environment of the
europium ions. Such nonequivalence can be explained,
for example, by a growing difference in the functions of
the bidentate-bridging and tridentate bridging-cyclic
groups resulting from the steric hindrances of the
ligands in the coordination core and increasing due to a
decrease in the total volume of the complex with the
removed CH3 radical.
very close to those typical for CF with a high, for exam-
ple, cubic, symmetry.
Judging from the CFP values, the most symmetric
charge distribution in the nearest environment of the
Eu3+ ion is observed in the europium acetate with
Mphen, which agrees with IR and Raman spectra.
Although
the
[Eu(CH3COO)3Phen]
and
–
Ö(7F4), cm–1
2950
2900
2850
2800
2750
The broadening of the lines from the Eu3+ electron
transitions in the luminescence spectra of the acetates
with the bulky substituents (such as Phphen, Dphphen)
is likely to be due to the steric hindrances arising during
crystal lattice packing. This made the assignment of the
1
5
lines in the region of the D0–7F4 transition difficult.
Therefore, we had to use the similarity of the lumines-
cence spectra when going across the Ph series.
2
*
*
The luminescence spectra of the nitrates with Ph
contain minimum number of intense lines, therefore the
nearest surrounding of the europium ion in these com-
pounds has the highest symmetry (Fig. 1). As was pre-
viously reported in [3], this group of compounds
exhibit significant value of the electron-vibration inter-
action. In the region of the overlapping of the phonon-
3
*
*
*
*
360
370
380
–
Ö(7F1), cm–1
7
5
free lines of the D0–7F2 transition with the electron-
Fig. 2. The center of gravity of the F level as a function of
4
7
vibration band of the 5D0–7F0 transition, the conditions
the center of gravity of the F level for (1) [Eu(DPM) Ph],
1
3
(2) [Eu(CH COO) Ph], and (3) [Eu(NO ) (Ph) ].
for the EV mixing of states are fulfilled and the EV res-
3
3
3 3
2
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 8 2003

MODELING OF Eu3+ ENERGY LEVELS
579
I
a
5D0–7F4
5D0–7F2 + 1380 cm–1
5D0–7F3
b
5D0–7F2 + 1385 cm–1
c
5D0–7F2 + 1396 cm–1
15500
15000
14500
14000
ν , cm–1
Fig. 3. Luminescence spectra of (a) [Eu(DPM) Mphen], (b) [Eu(DPM) Phen], and (c) [Eu(DPM) Phphen] in the region of the
3
3
3
5
7
D − F transition at 77 K.
0
4
onance is observed, which complicates the study of the pared with the data obtained from the plot of the centers
of gravity of the 7F2 level.
7
Stark structure of the F2 level. The separation of the
Stark components of this level and EV lines was per-
formed using IR and Raman spectra for estimation of
The europium nitrates with Ph have the greatest
(~530 cm–1) splitting of the 5D0–7F4 transition (for the β-
the Stokes displacements of the EV lines and was com- diketonates and acetates, it is ~395 and ~380 cm–1,
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 8 2003

580
PUNTUS, ZOLIN
respectively). Because of the increased number of the solid angles occupied by these atoms in the first coordi-
spectral lines (more than nine) in the region of the 5D0–
7F4 transition, we had to turn to the plot of the centers
nation sphere with an increase in the cation coordina-
tion number. One should note that the mutual repulsion
of the ligands also results in the averaging, weakening,
and symmetrization of the effect of the nearest sur-
rounding on the ligand ion with an increase in the coor-
dination number.
of gravity of the 5D0–7F4 transition and select the Stark
components of the transition. After the analysis of the
vibration spectra, we could separate the phonon-free
electronic and EV lines in the region of this transition.
The electron-vibration mixing of states results in an
increase in the intensity of the EV satellites of the 5D0–
The analysis of the vibration spectra and the plots of
7
7
the centers of gravity of the F2 and F4 levels vs. the
center of gravity of the Eu3+ 7F1 level made it possible
to establish some Stark components of the Eu 5D0–7F2
and 5D0–7F4 transitions in the case of the nitrates and β-
diketonates with Ph, respectively. As the result, the CFP
were calculated for the models of luminescence centers
with the C2vsymmetry for three groups of the europium
compounds with the phenanthroline derivatives: the β-
diketonates, acetates, and nitrates with different coordi-
nation numbers.
7F2 transition that lie in the region of the phonon-free
5D0–7F4 transition. The Stokes displacement of these
satellites with respect to the most intense Stark compo-
5
nent of the D0–7F2 transition is equal to 1525 and
1530 cm–1 in the case of [Eu(NO3)3(Phen)2] and
[Eu(NO3)3(Mphen)2], respectively. The satellites
observed in this region can be assigned to the stretching
vibrations ν(C=C) and ν(C=N) of the condensed aro-
matic rings in phenanthroline. A number of peculiari-
ties of the [Eu(NO3)3(Ph)2] luminescence spectra that
determine the relative values of the different-order CFP
are explained probably by the high coordination num-
ber (CN 10) of the Eu3+ ion in these compounds. The
The comparison of the obtained crystal field param-
eters for these groups shows that the relative values of
the CFP depend on the coordination number of the lan-
thanide ion. In particular, as the coordination number of
the Eu3+ ion increases, the amplitudes of harmonics of
the second-order crystal field are decreased, while the
amplitudes of harmonics of the sixth-order crystal field
increase. The discovered correlation can be useful
when studying complexes with the unknown coordina-
tion number of the metal cation.
significant changes in the CFP values, particularly, B22 ,
B24 , B26 for the europium nitrates with Ph allow one to
divide the group under consideration into two sub-
groups identified previously by the authors of [3].
The comparison of three groups of compounds in
terms of the calculated CFP reveals the correlation
between the relative values of the CFP of different
orders and the coordination number of the Eu3+ ion. The
ACKNOWLEDGMENTS
The authors are grateful to V.I. Tsaryuk for synthe-
sizing the europium acetates and nitrates with the 1,10-
phenanthroline derivatives we used in this study and for
recording the luminescence spectra and to professor
Ya. Legendziewicz and doctor R. Shostak from the
Wroclaw University for providing IR and Raman spec-
tra of the investigated compounds.
least sixth-order CFP (B06 ~ 250 cm–1) and the greatest
second-order CFP (B02 ~ 690 cm–1) are observed for
[Eu(DPM)3Ph] (CN 8). The europium acetates with Ph
(CN 9) have the intermediate sixth-order CFP values and
the minimum second-order CFP values (B06 ~ 980 cm–1,
B02 ~ 190 cm–1). The greatest CFP values of the sixth
order and the intermediate CFP values of the second
order (B06 ~ 1200 cm–1, B02 ~ 390 cm–1) are observed in
This work was supported by the Russian Foundation
for Basic Research (projects nos. 01-02-16837 and 02-
02-06316).
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