UV-Vis-NIR spectroscopy and colour of bis(N-phenylsalicylaldiminato)cobalt(II) in a variety of solvents

Article abstract of DOI:10.1016/S0277-5387(03)00028-7

Cobalt(II) complex with Schiff base obtained by condensation aniline with salicylaldehyde cobalt(II) complex, was studied in variety of solvents. The product i.e. salicylidene-anilinecobalt(II) ([Co(salan)₂]) complex is a red crystalline compound easily soluble in common solvents like chloroform (CHCl₃), benzene (Bz), toluene (MBz), dioxane (DX), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and acetonitrile (ACN) that is a necessary condition to observe solvatochromism. It has been characterised by elemental analyses, molar conductivities, ultraviolet (UV) and visible (Vis) spectroscopy. The molar conductivities indicate their non-electrolytic properties in all the solvents. Electronic spectra have been used to postulate the tetrahedral geometry for the species in solutions and to determine the coordination properties of ligators and their bonding abilities (ligand-field parameters), as well as their solvatochromism. The results obtained show fine colour changes. For discrimination of colour changes we applied CIE and CIELAB colour spaces.

Full text of DOI:10.1016/S0277-5387(03)00028-7

-
Polyhedron 22 (2003) 997ꢀ1007
/
www.elsevier.com/locate/poly
UVꢀ
/
Visꢀ
/
NIR spectroscopy and colour of bis(N-
phenylsalicylaldiminato)cobalt(II) in a variety of solvents
a
Iwona Ku z´ niarska-Biernacka , Adam Bartecki , Krzysztof Kurzak *
b
a,
a
Department of Chemistry, University of Podlasie, PL 08-110 Siedlce, Poland
b
Institute of Inorganic Chemistry and Metallurgy of Rare Elements, University of Technology, PL 50-370 Wroclaw, Poland
Received 1 May 2002; accepted 15 January 2003
Abstract
Cobalt(II) complex with Schiff base obtained by condensation aniline with salicylaldehyde cobalt(II) complex, was studied in
variety of solvents. The product i.e. salicylidene-anilinecobalt(II) ([Co(salan) ]) complex is a red crystalline compound easily soluble
in common solvents like chloroform (CHCl ), benzene (Bz), toluene (MBz), dioxane (DX), dimethylformamide (DMF), dimethyl
2
3
sulfoxide (DMSO), and acetonitrile (ACN) that is a necessary condition to observe solvatochromism. It has been characterised by
elemental analyses, molar conductivities, ultraviolet (UV) and visible (Vis) spectroscopy. The molar conductivities indicate their
non-electrolytic properties in all the solvents. Electronic spectra have been used to postulate the tetrahedral geometry for the species
in solutions and to determine the coordination properties of ligators and their bonding abilities (ligand-field parameters), as well as
their solvatochromism. The results obtained show fine colour changes. For discrimination of colour changes we applied CIE and
CIELAB colour spaces.
#
2003 Elsevier Science Ltd. All rights reserved.
Keywords: Cobalt(II) complexes; Schiff base; Salicylideneaniline; Solutions; Ligand-field parameters; Electronic spectra; Chromaticity;
Solvatochromism
1
. Introduction
question: are the geometry around metal ion and its
bonding properties connected with chromaticity, we
have extended this paper including results on solvato-
chromism and chromaticity for the bis(salicylidene-
This paper is a continuation of our studies on
interpretation of the electronic spectra of the cobalt(II)
complexes with Schiff bases derived from salicylalde-
hyde and amines in various solvents [1]. It is known that,
variation of the size and nature of substituent of the
salicyclaldimine ligand can be responsible for changes in
the coordination geometry around metal ion. Because
the electronic absorption spectra of the complexes
depend on these changes, it is sensibly to calculate the
ligand-field parameters.
aniline)cobalt(II) complex ([Co(salan) ]), which was
2
investigated in a variety of solvents. It has been known
that wavenumbers for absorption maximum correlate
well with the solvent parameters such as Dimroth and
Reichardt’s ET and Kosower’s Z for charge transfer
bands in the spectra of bis(2,2?dipyridyl)bis-cyanoiro-
n(II) and analogous complexes containing Schiff base
[
2]. The position and intensity of dꢀ
been correlated with some success with different solvent
parameters [3ꢀ5]. In this paper we report similar
/
d bands also have
The main aim of this work is explanation of solvent
effect. It should be considered in two ways: (1) solvation
effect on the structure and stability of complex, (2)
/
correlation for the bis(N-phenyl-salicylaldiminato)co-
balt(II) complex. The solvent parameters considered in
this work are Kosower’s Z, Dimroth and Reichardt’s
solvatochromic effects on UVꢀ
cause we are looking for an answer for the following
/
Visꢀ/NIR spectra. Be-
E , Kamlet and Taft’s a, b, p*, dielectric constant o
T
and Gutman’s donor DN, and acceptor numbers AN.
These values are directly obtainable from literature [6ꢀ
11].
/
*
E-mail address: kkurzak@ap.siedlce.pl (K. Kurzak).
Corresponding author. Fax: ꢁ
/
48-25-644-2045.
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00028-7

998
I. Ku z´ niarska-Biernacka et al. / Polyhedron 22 (2003) 997ꢀ1007
/
The solvent effects can be the cause of both energetic
2.3. Method of calculations
shifts of absorption bands and change of solution
colour. The latter effect can be difficult to observe by
human eye. To precisely characterise the colour one
The convenient approach has been presented for the
tetragonally distorted Cr(III) complexes in work [20]. In
the present work the matrix elements of the excited
states presented in paper [20], given as a function of the
orbital energies and Racah parameters, were used for
cobalt(II) complexes, assuming hole-formalism. The
total one-electron orbital energy equations given by
Kurzak [20] were applied and reduced for complex with
O (T ) symmetry. All the band maxima reported in this
usually uses tristimuls colorimetry [12ꢀ18]. Colours of
/
solutions and solid are reported in CIE and CIELAB
colour space in our work.
2
. Experimental
h
d
2
.1. Measurements
work are determined from Gaussian analysis of the
experimental spectral contours. Absorption spectra were
fitted with Gaussian components using CFP computer
program [21] (and references herein), based on the Slavicˇ
[22] algorithm, which for the last few years has been
The molar conductances were measured using a
microcomputer pH/conductivity meter CPC-551 (Elme-
tron, Poland) and platinum dip electrode CD-2. The
ultraviolet (UV) spectra were recorded on a SPECORD
M40 (Zeiss Jena) spectrophotometer digitally (20 cm
step) after dissolving the sample for concentration c ꢀ
successfully applied by us to the resolution of dꢀd
/
ꢂ1
(ligand-field) spectra. The Lorentz (Cauchy), Gauss, and
also sum and product combination of the both may be
used to approximate the contours of the individual
unperturbated bands. The problem of the choice of the
band shapes function has been determined for some
time. In IR spectroscopy [23] (vibration spectra) the
bands are well approximated by the Lorentz function,
/
ꢂ4
5
.0ꢃ
spectra (both solutions and solid state) were carried out
digitally 1 nm step) on a Cary 5E (Varian) spectro-
photometer. The conductivities were measured for the
/
10 M. The near infrared (NIR) and visible (Vis)
(
ꢂ2
concentration c ꢀ
The NIRꢀVis and UV spectral data at selected approxi-
mately 2500 wavenumbers, i.e. 1500 over the range
5
1
/
1.0ꢃ
/
10
M at room temperature.
/
while for the bands broadened in VisꢀUV region
/
(electronic spectra) the Gauss function is a good
approximation. Theoretical treatment of the UV band
shapes [24] for the solutions systems and experimental
measurements indicated that isolated absorption bands
are of the Gaussian form. The ligand-field parameters
(CFM) were calculated using the LFP computer program
[25] (CFM/AOM). The assignment of bands is based on
fitting the resolved band maxima (from Gaussian
analysis) with the calculated transition energies (eigen-
ꢂ1
000ꢀ
8600ꢀ
/
18 900 cm
(NIR) and 1000 over the range
/
40 000 cmꢂ1 (UV), were resolved into the
Gaussian components. These spectra were used for
calculations of ligand-field (CFP/AOM) parameters (in
NIRꢀ
/
Vis region) and chromaticity coordinates (in Vis
region). The measurement conditions for the spectra in
ꢂ3
Vis region were as follows: cꢄ
.2. Chemicals
Complex [Co(salan) ] was prepared according to
/
1.0ꢃ
/
10 M, lꢄ
/
0.1 cm.
3
2
vectors) using the d quadrate energy levels with full
configuration interactions and without spinꢀ
/orbit cou-
pling. In this work the ligand-field (dꢀd) spectrum of
/
2
Sacconi et al. [19] by reaction of bis-(salicylaldehyde)co-
balt(II) dihydrate with aniline in ethanol. The solid
complex was precipitated rapidly and the pure com-
pound was obtained as red crystals. The complex is
insoluble in water but easy soluble in variety of solvents:
the non-polar with weak donor strengths like chloro-
[Co(salan) ] has been assigned by application of ligand-
field and Td symmetry. The AOM parameters, i.e.
separate values for e and e , cannot report as these
2
s
p
are linearly related to Dq in this geometry (10 Dqꢄ
/
3e ꢂe ).
/
s
p
The CIE, CIELAB, and CIELUV systems were
applied for a quantitative description of sample colour.
The chromaticity coordinates have been calculated from
form (CHCl ), benzene (Bz), toluene (MBz), and polar
3
with intermediate donor strengths like acetonitrile
(
ACN), dioxane (DX), and polar with strong donor
strengths like dimethylformamide (DMF), and dimethyl
sulfoxide (DMSO).
the absorption spectra (in region 380ꢀ780 nm) by the
/
method described in Refs. [14,26,27] for non-uniform
(CIE) and two uniform (CIELAB and CIELUV) spaces.
The calculation of these coordinates has been accom-
plished using CIEC computer program [28]. This one is
designed to calculate the colour parameters for the
solution, solid (reflectance) and simulated spectra. The
CIE tristimulus values (X, Y, Z) expressed as integrals
(or sums) [14,27] are calculated as well as chromaticity
coordinates (x, y, z) and two space parameters:
CIELAB (L*, a*, b*) and CIELUV (L*, u*, v*). The
The complex was analysed for purity by elemental
analysis. Cobalt analyses were performed by EDTA
titration using murexide as an indicator. The results
agreed with the expected composition. Analytical data
of the complex are as follows: yield 80%. Anal. Calc. for
[
Co(salan) ]ꢀC H N O Co: C, 69.18; H, 4.47; N, 6.21;
/
2
24 18 4 2
Co, 13.06. Found: C, 68.12; H, 4.52; N, 5.88; Co,
3.09%. M.p. 190 8C.
1

I. Ku z´ niarska-Biernacka et al. / Polyhedron 22 (2003) 997ꢀ
/
1007
999
Scheme 1. Cobalt(II) complex with salicylideneamine derivatives.
standard data [12,13,29] are built in the routine i.e.
colour matching functions taken every 5 (or 1 nm) in the
The cobalt(II) complexes of salicylideneamine deriva-
tives (Scheme 1), where Rꢄalkyl, aryl and cyclohexyl,
/
range 780ꢀ
/
380 (or 830ꢀ
/
360 nm), as well as standard
are red crystalline solids. They are stable on dry air,
while in solution they are easily converted into the
corresponding oxidation product [37]. Slow oxidation of
the cobalt(II) complexes causes colour change. This
process strongly depends on the solvents [38], steric
factor, temperature, and ligand-field strength [39]. It is
attained with Schiff bases predicting a stronger ligand-
field, e.g. N-alkyl-salicylideneiminates. The N-aryl-sal-
icylideneiminate presented in our studies characterises
illuminant D . Absorption spectrum is transformed
6
5
into equivalent transmission spectrum. In the case of
reflectance spectrum one can use the KubelkaꢀMunk
function [30] for preliminary data transformation.
/
3
. Results and discussion
weaker ligand-field strength, rather. Red [Co(salan) ] in
2
polar solvents is slowly oxidised in air, or more rapidly
by hydrogen peroxide, to brown. Spectrophotometric
studies exclude the oxidation of the cobalt(II) ions in all
solutions studied upon time elapsed up to 4 h (no
spectral changes were observed), similar as in our earlier
investigations on bis(5-bromosalicylidene-o-aminopyri-
dine)cobalt(II) [1].
The solutions of [Co(salan) ] were prepared by
2
dissolving a weigh amount of the complex in: CHCl3,
Bz, MBz, ACN, DX, DMF, and DMSO. The complexes
with similar bidentate Schiff bases were studied by
spectroscopy [19,31ꢀ33] previous. The electronic spectra
/
as well as magnetic moments [34,35] of cobalt(II)
complexes depend upon the geometry of the complexes.
The differences in the band positions and magnetic
moments may be regarded as diagnostic of stereochem-
istry of the cobalt(II) complexes. In fact, those are rather
straightforward way, in many cases, to determine the
geometry of a cobalt(II) complex. Typical electronic
spectrum for Co(II) with bidentate Schiff base complex
3.1. Ultraviolet spectra
The Schiff bases have been studied previously spectro-
43]. The Hsalan ligand spectra have been
46]
chemically [40ꢀ
/
presented previously in methanol solution [42,44ꢀ
/
[
36] in pyridine (octahedral) shows maxima at about
ꢂ1
and studied by us [47] in a wide variety of solvents.
Houlden et al. [47] have synthesised the Schiff bases
derived from benzalaldehyde and aniline, and quantita-
tive interpreted their electronic spectra in heptane
1
0 000, 26 000, 33 100 cm
and a shoulder at 17 000
cmꢂ1. Tetrahedral complexes show maxima at about
7
1
700, 11 200, 25 000 and 34 100 cmꢂ1, and shoulders at
7 000 and 28 000 cmꢂ1. The magnetic moments for the
solution and UV region. They resolved the spectra
ꢂ1
tetrahedral cobalt(II) complexes are in the range 4.2ꢀ
/4.7
into 13 Gaussian components in 25 000ꢀ47 000 cm
/
whereas for octahedral: 1.7ꢀ2.0 or 4.4ꢀ5.5 mB.
/
/
region. Based on the literature data [48] we have
resolved the ligand spectra into ten Gaussian component
Electronic absorption spectra of the complex studied
by us in all solutions show maxima at approximately
ꢂ1
bands in the 20 000ꢀ
/
40 000 cm
region [47]. These
have been used for analysis of complex spectra in UV
ꢂ1
7
1
700, 11 000, 25 800 and 34 000 cm
and shoulder at
7 100 cmꢂ1. Moreover, the solid-state spectrum of this
region. West [49] has compared absorption spectra of
[Co(salan) ] (in absolute EtOH and 10% aqueous EtOH)
complex is characterised by maxima at approximately
400, 10 500, 20 700, 27 600, 35 600 and 44 200 cmꢂ1
This, as well as high band intensities in the dꢀd region,
2
7
.
with ligand (in 10% aqueous EtOH). In his experiment
the electronic spectrum of [Co(salan) ] (in 10% EtOH) is
/
2
indicates the tetrahedral geometry of [Co(salan) ] com-
plex in all solutions studied.
closely related to the ligand spectrum. The author
suggests that disappearance of the band at approxi-
2

1000
I. Ku z´ niarska-Biernacka et al. / Polyhedron 22 (2003) 997ꢀ1007
/
Fig. 1. Electronic spectra of [Co(salan)
2
]: 1, cꢄ
/
4.8ꢃ
/
10ꢂ4; 2, cꢄ
/
1.0ꢃ
/
10ꢂ4 and ligand (Hsalan) 3, cꢄ
/
1.0ꢃ
10ꢂ4 M in DMSO solution.
/
Fig. 2. Electronic spectra of [Co(salan)
2
] at room temperature in solvents: 1, ACN; 2, CHCl
3
; 3, DMF; 4, DX; 5, Bz; 6, MBz and 7, DMSO, in NIRꢀ
/
Vis region (a); 1, CHCl ; 2, ACN; 3, Bz; 4, MBz; 5, DMF; 6, DMSO and 7, DX, in UV region (b).
3
mately 35 000 cmꢂ1 in 10% EtOH solution is due to
dissociation of complex. In our study we have not used
In our previous studies on bis(5-bromosalicylidene-o-
aminopyridine)cobalt(II) complex [1] we displayed that
changes in complex spectra in UV region are not
connected with coordination change. We do not observe
mixed solvents, but when the complex concentrations in
ꢂ4
‘
has been observed. Fig. 1 shows the electronic spectra of
pure’ solvents were less then cꢄ
/
5ꢃ10 M such effect
/
any changes in [Co(salan) ] spectra for concentrations
2
ꢂ4
[
Co(salan) ] in DMSO, measured for different concen-
2
ꢀ
/
5ꢃ
/
10
preting spectra were recorded as rapidly as possibly.
M in UV region. Nevertheless, the inter-
trations in comparison with Hsalan in the same solvent.
As seen, the spectrum of diluted solution of [Co(salan)2]
has similar shapes as Hsalan spectrum and the positions
of their observed bands are very close together (q.v.
spectra 2 and 3 in Fig. 1). Because of ionisation of
Fig. 2 shows the electronic absorption spectra of
[Co(salan)
region (b). All the spectra in UV region are similar and
] in various solvents in NIRꢀVis (a) and UV
/
2
ꢂ1
exhibit two bands at about 25 800 and 34 500 cm
except DX solution where latter is observed as a
shoulder, only. Additional band characterises the spec-
[
as possible were used for further studies of the spectra.
Co(salan) ] in diluted solutions highest concentrations
2

I. Ku z´ niarska-Biernacka et al. / Polyhedron 22 (2003) 997ꢀ
/
1007
1001
Table 1
Parameters of the component bands resulting from Gaussian analysis of the electronic spectrum of trans-[Co(salan)
2
] in CHCl
3
solution, and NIRꢀ
/
Vis and UV region; T
d
symmetry
o (Mꢂ1 cmꢂ1
)
n
(cmꢂ1
)
d
1/2 (cmꢂ1
)
f
Assignment
a
Band number
0
NIRꢀ
/
Vis: number of points 1471, range 5000ꢀ
/
18 868 cmꢂ1
5980
ꢂ05
ꢂ04
ꢂ05
ꢂ05
ꢂ04
ꢂ05
ꢂ05
ꢂ05
ꢂ05
ꢂ04
ꢂ03
ꢂ03
1
2
3
4
5
6
7
8
9
0
1
2
3.6
62.6
4.4
720
3250
1410
1560
2630
2160
2170
1410
1750
1370
2610
2780
1.2ꢃ
9.4ꢃ
2.9ꢃ
3.4ꢃ
4.8ꢃ
8.4ꢃ
7.1ꢃ
5.8ꢃ
5.3ꢃ
1.8ꢃ
6.7ꢃ
5.8ꢃ
/
10
10
10
10
10
10
10
10
10
10
10
10
unassigned (not dꢀd)
/
7760
8850
/
dꢀ
dꢀ
dꢀ
dꢀ
dꢀ
dꢀ
dꢀ
dꢀ
dꢀ
/
d, s-a
/
/d
4.7
10 100
11 320
13 850
15 500
16 170
16 620
17 150
20 160
21 530
/
/d
39.7
8.5
/
/d, s-a
/
/
d
d
d
d
7.1
/
/
8.8
/
/
6.6
/
/
1
1
1
29.3
558.6
453.0
/
/
d, s-a
b
/
IM
b
/
IM
RMS%
0.64
UV: number of points 1023, range 18 600ꢀ
/
39 040 (cmꢂ1
)
ꢂ03
ꢂ03
ꢂ02
ꢂ02
ꢂ02
ꢂ02
ꢂ01
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
520
540
20 150
21 350
23 330
24 330
25 580
26 880
29 060
31 260
32 380
33 420
34 170
35 790
39 030
38 010
41 470
2460
1670
2320
1930
2350
2530
3960
1240
1920
4580
4540
1910
1370
3710
4070
5.9ꢃ
4.2ꢃ
2.8ꢃ
4.0ꢃ
9.7ꢃ
4.8ꢃ
2.1ꢃ
l.0ꢃ
1.3ꢃ
2.1ꢃ
3.3ꢃ
2.1ꢃ
1.2ꢃ
2.4ꢃ
6.1ꢃ
/
10
10
10
10
10
10
10
IM
IM
IM
IM
CT
IM
IM
IM
IM
IM
CT
IM
IM
IM
IM
/
2640
/
4540
/
8930
/
4140
/
11 370
1780
/
ꢂ02
ꢂ02
/
10
1430
/
10
ꢂ01
ꢂ01
ꢂ02
ꢂ02
ꢂ01
ꢂ01
1
1
1
1
1
1
10 090
15 920
2430
/
10
10
10
10
10
10
/
/
1940
/
14 140
32 860
/
/
RMS%
0.24
a
IM, intramolecular band; CT, charge transfer band; s-a, spin-allowed transition (another dꢀd transitions are spin forbidden).
Gaussian arms of the first and second band from UV region (1, 2).
/
b
Fig. 3. Electronic spectra and the Gaussian line-shapes of [Co(salan)
b) and MBz (c).
2
] at room temperature in NIRꢀ
/
Vis region in non-polar solvents: CHCl
3
(a), Bz
(

1002
I. Ku z´ niarska-Biernacka et al. / Polyhedron 22 (2003) 997ꢀ1007
/
Fig. 4. Electronic spectra and the Gaussian line-shapes of [Co(salan)
DMF (c) and DMSO (d).
2
] at room temperature in NIRꢀVis region in polar solvents: ACN (a), DX (b),
/
cmꢂ1. No effect of higher energy UV bands (e.g. CT) on
Vis region was observed that affect the band above
Table 2
Intensities (M
ꢂ1
cmꢂ1) and positions (cmꢂ1) of CT bands resulting
from Gaussian analysis of UV region in variety of solvents
ꢂ1
19 000 cm . Usually, the observed absorption bands at
2
5 000 and 35 000 cmꢂ1 are attributed to the charge
transfer transitions [50,51]. Based on our previous
Solvent
CTCo0O
CTCo0N
max
o
max
n
max
o
n
max
studies [1] and literature data [51,52] we assigned the
ꢂ1
band at about 25 000 cm
at higher energy to MLCT (Co0
positions and intensities of both the CT bands (from
Gaussian analysis) for all the solutions studied are given
to MLCT i.e. Co0
/
O, and
CHCl
Bz
3
9830
25 580
25 570
25 560
25 630
25 630
25 580
25 640
15 920
16 030
15 470
17 300
14 520
15 470
15 250
34 170
34 350
34 390
34 230
34 320
34 280
34 240
/
N) transitions. The
11 220
10 750
10 850
8220
MBz
ACN
DX
in Table 2. Both the CT
same position in all solvent studied.
and CT
have the
Co0N
Co0O
DMF
DMSO
8850
10 700
3
.2. Visible spectra and ligand-field analysis
tra in DX and ACN solvents at 41 500 and 43 000 cmꢂ1
respectively. This band is not observed in others solvents
,
No crystallographic data of [Co(salan) ] are available.
2
ꢂ1
because of their no transmittance above 40 000 cm
.
Elerman et al. [53ꢀ
complexes: (1)
N,O)cobalt(II) and (2) bis(N-4-bromophenylsalicylaldi-
minato)cobalt(II) and presented X-ray data. In both the
complexes Co(II) ions adopt tetrahedral coordination
/
55] have synthesised two similar
bis(N-2-propyl-salicylideneamino-
All the UV spectra were resolved and the component
bands for Gaussian analysis of the complex spectra have
been assumed from the analysis of the Hsalan ligand
spectra and additional CT bands predicted for complex.
Table 1 shows, as representative example, the results of
the Gaussian analysis, parameters of the component
bands, their oscillator strength values and relative root
mean squares error (RMS%), for the full spectral range:
geometries. The Coꢀ
/
N distances are 2.00 and Coꢀ
.90 A in both the complexes. The NꢀCoꢀO angles (a
bite angle) are similar (96.48 and 96.78), and NꢀCoꢀ
OꢀCoꢀO) angles are 1208.
The spectra of bis(salicylaldehyde-aniline)cobalt(II)
/
O
˚
1
/
/
/
/N
(
/
/
the NIRꢀ/Vis and UV regions, in CHCl solution. The
3
digital spectra o ꢄ
results of all spectra (NIRꢀVis and UV) are available
from the authors on request. The background absorp-
tion from the strong IM bands was included by two the
last Gaussian arms (band 11 and 12 of first part of Table
/
f(n ) and dull Gaussian analysis
i
i
complex in Bz and pyridine solutions as well as in solid
state have been presented in literature [19,31]. Authors
[19] have reported that spectra in Bz solution and in the
/
solid state show maxima at approximately 7700, 11 200,
ꢂ1
25 000 and 34 100 cm
ꢂ1
and shoulders at about 17 000
and 28 000 cm , but in pyridine solution maxima at
1
2
, q.v. Figs. 3 and 4) that have the maxima at 20 000 and
ꢂ1
ꢂ1
1 000 cm , i.e. out of low energy part of the
10 000, 26 000, 33 100 cm
ꢂ1
and a shoulder at about
17 000 cm . The latter spectrum is very similar in shape
experimental curve. These affect the band above 15 000

I. Ku z´ niarska-Biernacka et al. / Polyhedron 22 (2003) 997ꢀ
/
1007
1003
Table 3
Assignments, transition energies and ligand-field parameters (cmꢂ1) for the [Co(salan)
2
] complex in variety of solvents; symmetry T
d
, ground term
4
A
2
Assignments
Solvent
CHCl
3
Bz
MBz
7770
ACN
7750
DX
DMF
7820
DMSO
7860
4
T
2
[F]
E[G]
7760
8850
7760
9250
7760
8740
2
2
4
2
2
2
2
4
9300
10 470
11 500
13 880
15 730
16 580
17 150
17 170
8800
9790
9340
10 420
11 360
13 800
15 420
16 310
16 700
17 150
9300
10 360
11 400
13 620
15 210
16 610
17 030
17 650
T
1
T
1
T
2
[G]
[F]
[G]
10 100
11 320
13 840
15 490
16 170
16 620
17 150
10 430
11 480
13 750
15 600
16 690
17 060
17 220
10 110
11 420
13 720
15 200
16 370
16 380
17 070
11 270
13 760
14 600
16 730
17 320
17 230
A
1
[G]
T
T
T
2
[H]
[H(1)]
[P]
1
1
RMS%
350
270
300
370
370
340
280
Dq
B
1660 (30)
410 (40)
2120 (70)
1670 (30)
420 (30)
2170 (60)
1670 (30)
420 (30)
2200 (60)
1650 (40)
440 (40)
2050 (80)
1660 (30)
420 (40)
2080 (70)
1640 (30)
430 (30)
2130 (60)
1660 (30)
460 (30)
2070 (50)
C
C/B
5.2
5.2
5.2
4.7
5.0
5.0
4.5
to the reflectance spectrum of six-coordinated adduct
Co(salan) (pyridine) ]. Kogan et al. [31] presented
magnetic moment values for [Co(salan) ] in solid state
4 show the experimental spectra in the NIRꢀ
/
Vis region
[
in all the solvents studied along with Gaussian analysis.
In general, the unique procedure (see Section 2), which
starts with Gaussian analysis, through assignment of the
bands, to calculation of the chemically useful para-
meters, is based on two assumptions: the symmetry of
compound is known, and theoretical model (e.g. ligand-
field model for the complexes) is adequate for the
calculation of the spectral parameters. Because of this,
our calculations (and Gaussian analysis of the ligand-
2
2
2
and in Bz, DX and CHCl solutions in 294 K, and
3
Sacconi et al. [19] in solid state (over the range 91ꢀ
K), and in Bz and pyridine solutions (both in 297 K).
The meff values are similar (over the range 4.2ꢀ4.4 mB)
/293
/
and a tetrahedral structure of [Co(salan) ] for solid and
non-donor solvents indicate. In pyridine solution the
value is significantly higher and equals to 4.9 m . Based
2
B
on the electronic spectra, magnetic moments and high
dipole moment values [31] (for planar complexes those
should be close to zero) authors confirm the tetrahedral
field spectra) take into account all the dꢀd transitions
that are given by ligand-field theory, even those strong
overlapped. In this region all the bands may be
/
structure of [Co(salan) ] in solid state and in non-donor
2
attributed to dꢀ
approximately 6000 cm
parameters estimation as not predicted by ligand-field
theory, i.e. not dꢀd transition. The spectra in 15 000ꢀ
region are more complicated, because of
variety of the bands (dꢀd, charge transfer, and intra-
molecular transitions) in this region, which differ
significantly in intensities. Usually, ligand-field analysis
of spectra of the transition metal complexes has been
/
d transitions, except one band at
ꢂ1
solvents.
which has been omitted in
We have confirmed lack of complex dissociation in
various solutions by conductance measurements. The
conductance values of all the [Co(salan) ] solutions are
/
/
ꢂ1
20 000 cm
2
ꢂ1
2
0.0, 0.0, 0.0, 0.1, 0.0, 0.6 and 0.9 S mol
CHCl , Bz, MBz, ACN, DX, DMF and DMSO,
cm for
/
3
respectively. They show their nonelectrolytic properties
and the predominance of an electrically neutral species
in solutions. Thus, the assumed geometrical model (Td)
is adequate for our calculations of the ligand-field
parameters for the solution systems.
made for the dꢀd isolated bands [20,21,56,57]. Transi-
/
tion energies, their assignments, values of the crystal
field (CFM) parameters, and RMS are collected in
Table 3. The best fit of the calculated and experimental
data was obtained for these results. RMS error values
are about 300 for the nine transitions fitted (q.v. Table
3). It follows that the experimental (Gaussian analysis)
and calculated energies of the parameter set optimised
are unusually close together. It can be seen that the Dq
parameter values for all studied solutions are very close
Overlapping low energetic and more intensive charge
transfer and intramolecular spectral bands complicates
the dꢀ/d spectra in Vis region. Fig. 2(a) presents the
electronic spectra of [Co(salan) ] in various solutions in
2
NIRꢀ
750ꢀ
shoulder at about 17 100 cm
/
Vis region. All the spectra exhibit two maxima at
7
/
7850 (50ꢀ
/
65) and 10 970ꢀ
/
11 150 (30ꢀ
/
45), and
Mꢂ1). As
ꢂ1
ꢂ1
(50 cm
ꢂ1
seen, the hipochromic effect is especially visible for
ꢂ1
together and are equal to 1660 cm . The similar effect
is observed for the Racah B parameter where the values
observed bands at 10 900ꢀ
/
11 100 cm . The spectra
were resolved into twelve component bands. Figs. 3 and
ꢂ1
of the B parameters are 410ꢀ460 cm . Insignificantly
/

1004
I. Ku z´ niarska-Biernacka et al. / Polyhedron 22 (2003) 997ꢀ1007
/
Fig. 6. The CIELAB plane. The colour points correspond to
Co(salan) ; k, Bz; ', MBz; j, ACN; ꢁ
] in solvents: I, CHCl
DX; m, DMF and ^, DMSO.
[
2
3
/,
Fig. 5. Correlation between wavenumbers of absorption maximum of
CTCo0N and AN in solvents: 1, MBz; 2, Bz; 3, DX; 4, DMF; 5,
3
DMSO; 6, ACN and 7, CHCl .
roughly linear correlation, with increasing hydrogen
bonding ability of solvents associated with decreasing
changes are observed for C parameter that has values in
ꢂ1
wavelength. The correlation equation has form: nmax
34 458.1910.4)ꢂ(11.90590.659) AN with correlation
coefficient rꢄ 0.992. We also compared positions of
absorption maximum of CT band with other
solvent parameters i.e. Dimroth and Reichardt’s, Gut-
man’s (donor number) and Kamlet and Taft’s. How-
ever, no other correlations between positions of
ꢄ
/
the range 2050ꢀ2200 cm . It suggests that the inter-
/
(
/
/
/
actions of donor atoms are independent on solvents
used, contrary to analogous copper(II) complexes that
are very sensitive for these type interactions [47,58,59].
/
ꢂ
/
Co0N
3
.3. Solvatochromism
CT
band and solvent parameters could be find
for solutions studied. The results show that CT
Co0N
Co0N
As mentioned above, the spectra studied display four
band position does clearly depend on AN only whereas
CT band position does not depend on any solvent
parameters.
bands. From these two bands are assigned to CT
transitions. Their intensities and wavenumbers of ab-
sorption maximum in variety of solvents are reported in
Table 2. The positions of absorption maxima of the
Co0O
CT
lower than 50 cm and they will not further discuss for
band are very similar, i.e. the band shifts are
ꢂ1
3.4. Trichromaticity colorimetry
Co0O
solvent effects. Position differences of the higher energy
CT
the solvents show solvatochromism, i.e. meant us
absorption maxima changes dependent on various
solvent parameters. All these parameters considered in
this work are directly obtainable from literature. In Fig.
All solutions of complex studied have reddishꢀ
/
orange
band are significant. As known, the most of
colour and their electronic absorption spectra display
ꢂ1
Co0N
only one maximum at approximately 25 800 cm
ꢂ1
and
26 300
shoulder at 17 100 cm
in the region 12 800ꢀ
/
ꢂ1
cm that is a range commonly employed for specifying
colours of compounds. Table 4 summarises the values of
chromaticity coordinates calculated from the absorption
5
positions of CT
absorption maximum are plotted
Co0N
against the acceptor number AN. This plot shows a
spectra of [Co(salan) ] for all the solutions studied. In
2
Table 4
The chromaticity coordinates, hab hue-angle (8), and colours of [Co(salan)
2
] in variety of solvents (c :
/
1ꢃ
/
10ꢂ2 M, lꢄ
/
0.2 cm) and solid state
b
a
Solvent
x
y
Y
L*
a*
b*
h
ab
CIE colour
CHCl
Bz
3
0.35
0.36
0.36
0.34
0.35
0.35
0.34
0.69
0.39
0.40
0.40
0.38
0.39
0.39
0.38
0.31
95.1
94.8
94.7
95.6
92.9
95.4
96.2
12.7
98.1
97.9
97.9
98.3
97.2
98.2
98.5
28.4
ꢂ
/
8.3
9.4
9.4
7.6
9.7
8.6
8.7
28.2
33.7
33.0
24.1
27.6
28.0
26.5
64.3
106.5
105.6
105.9
107.5
109.4
107.1
108.2
37.2
yellowꢀ
yellowꢀ
yellowꢀ
yellowꢀ
yellowꢀ
yellowꢀ
yellowꢀ
red
/
green
green
green
green
green
green
green
ꢂ
/
/
MBz
ACN
DX
ꢂ
/
/
ꢂ
/
/
ꢂ
/
/
DMF
DMSO
ꢂ
/
/
ꢂ
/
/
Solid (R
F
)
64.3
a
3
Colour observed for solutions in 25 cm flask: reddish-orange.

I. Ku z´ niarska-Biernacka et al. / Polyhedron 22 (2003) 997ꢀ
/
1007
1005
Table 5
Bands parameters resulting from Gaussian analysis of CoCl
2
in i-
a
propanol , and ligand-field parameters as a starting data for simula-
i
tion spectra as a function of Dq; omax, d1/2, B and C parameters are
i
constants
max (Mꢂ1 cmꢂ1
i
)
d
i
1/2 (cmꢂ1
)
n
i
max (cmꢂ1
)
Number
o
1
2
3
4
5
6
7
8
9
22.5
29.3
78.9
76.4
1950
2400
920
5540
7290
14 900
15 140
16 020
17 520
18 320
19 890
20 410
21 730
23 040
24 290
25 690
28 040
920
225.8
72.2
27.3
7.6
1900
1260
1830
1890
1950
1480
1510
1640
1930
3560
3.7
6.0
1
1
0
1
5.8
5.4
Fig. 7. Correlation between hue-angle hab and dielectric constant o in
solvents: 1, CHCl ; 2, Bz; 3, MBz; 4, ACN; 5, DX; 6, DMF and 7,
DMSO.
12
13
14
3
5.2
10.3
B
C
696
3435
1005
the case of reflectance spectra for solid sample the
KubelkaꢀMunk theory has been used for preliminary
/
Dq
data transformation (RF coefficient). Colours of solu-
tions are reported in CIE and CIELAB colour spaces.
These chromaticity parameters characterise the solu-
tions studied unambiguously and allow a comparison of
colour changes. L*, a*, b* colour space is uniform and
recommended by CIE for the colour description. The L*
is psychometric lightness and corresponds to black
a
Co2ꢁ]ꢄ
[
/
0.045 M, path lengthꢄ
/
0.1 cm; CIE chromaticity
coordinates: xꢄ
/
0.182, yꢄ0.254, Yꢄ44.7 (colour: greenish blue).
/
/
(
rꢄ0.890). The linear correlations between hue-angle
/
and other solvent parameters were not found for all the
solvents studied. The results show that the hue-angle
values mainly depend on the polarity of solvents, only.
(
L*ꢄ
/
0) and white (L*ꢄ100). The a* and b* are
/
psychometric chromaticness. Positive values of a*
correspond to red colour negative ones to green whereas
positive values of b* correspond to yellow colour
negative ones to blue. The position of colour points on
the CIELAB plane is presented in Fig. 6. The colours of
the solutions are represented by points on the chroma-
3.5. Simulation of optical spectra and colour quantitative
characteristics
In the course of our studies on optical spectra of
transition metal compounds it was shown that their
colour quantitative characteristics expressed by chro-
maticity coordinates clearly correspond to properties
and structure of the studied objects. Colour parameters
yielded by CIE, CIELAB and CIELUV colour spaces
are derived from the optical spectra and described in
detail in many sources. Our main goal was to find out
relations between the spectra and colorimetric data if
such relations do exist at all. As a result of many
ticity, positioned on the field of greenꢀyellow hues. The
/
hab values have been compared with some solvent
parameters previously [60]. In our study we compared
those values with solvent parameters, i.e. dielectric
constant, Dimroth and Reichardt’s, Kosower’s, Gut-
man’s (donor and acceptor numbers), and Kamlet and
Taft’s. The linear correlations between hue-angle (where
h ꢄarc tg (b*/a*)) and above mentioned solvent para-
/
ab
meters have been found for all the solvents except DX.
Calculated values of hue-angle against the dielectric
constant o are plotted in Fig. 7. The plot shows a
roughly linear correlation, with increasing o values
associated with increasing hab values. The data for all
investigations [14ꢀ18] it has been demonstrated that the
/
ligand-field parameter, Dq, could create a basis for
expressing such a relation with colour characteristic
parameters. This would approximately be true when the
colour of transition metal compound would be caused
studied solvents can be correlated as: h ꢄ
/
(105.89
0.008)o (correlation coefficient rꢄ
.939). We have found that the hue-angle depends on
/
ab
only by ligand-field spectra, i.e. dꢀd transitions (and not
/
0
.2)ꢁ
/
(0.0469
/
/
by e.g. CT transitions in the optical region). Hence using
the Dq parameter one should be able to simulate the
spectra and to predict the corresponding colour. Such
simulations were carried out for many systems and
0
Kosower’s Z and Kamlet and Taft’s p* parameters. The
resulting regression of the h ꢄf(Z) is: h ꢄ(98.59
0.929), the result for the
(103.690.8)ꢁ(4.46091.144)p*
/
/
/
ab
ab
1
.9)ꢁ
/
(0.1299
/
0.030)Z, (rꢄ
/
described in literature [14ꢀ/18]. The steps in using our
h ꢄf(p*) is: h ꢄ
/
/
/
/
/
model are as follows.
ab
ab

1006
I. Ku z´ niarska-Biernacka et al. / Polyhedron 22 (2003) 997ꢀ1007
/
Fig. 8. Simulation of spectra for CoCl
2
in i-propanol as a function of Dq parameter: 1ꢀ
/
100, . . . 34ꢀ
3400 cmꢂ1 (100 cmꢂ1 step), with the
/
experimental spectrum-10; all C.I. interaction is allowed and B and C parameters are constants.
1
)
The experimental optical spectrum of the proper
metal compound is chosen, in this case a solution of
anhydrous CoCl in i-propanol (cꢄ
/
0.045 M, lꢄ
/
2
0.5 cm) that characterised ‘pure’ tetrahedral sym-
metry (T ). Gaussian analysis results (component
band parameters) and ligand-field parameters are
d
being carried out. These for NIRꢀ
shown in Table 5.
The set of resulting parameters is taken as con-
/
Vis region are
2
)
)
i
i
stants: o , d , B and C (see frame in Table 5),
max
1/2
i
max
except n
The last has been calculated for variety of Dq values
set that depend on Dq values.
3
that for simulation are varied within a broad range
ꢂ1
(
energy diagram is generated using LFP program [25].
50ꢀ3400, with step 50 cm ), i.e. the transitions
/
7
Proper energy matrices are applied, here for d
electronic configuration and T symmetry accord-
d
ing to the surrounding of the Co(II) central ion in
this solvent.
4
)
For each new Dq value the overall contour of the
spectrum was calculated and the chromaticity
coordinates determined applying the CIEC computer
program [28].
The results of these simulations are demonstrated in
Fig. 8 that shows the course of the spectra for a broad
ꢂ1
ꢂ1
Dq range 100ꢀ
/
3400 cm (the step is 100 cm because
Fig. 9. The CIELAB plane. The colour points correspond to simulated
spectra for CoCl
. . 68ꢀ
3450 cmꢂ1 (50 cm
experimental spectrum.
2
in i-propanol as a function of Dq parameter: 1ꢀ
/
50,
step), the point 20 corresponds to
of graph clarity). Note that bands positions (transition
energies) in spectra simulated as well as observed
intensities are changed simultaneously. It is result that
full energy matrices were used to allow for term
interactions in our calculations (LFP program). Fig. 9
shows CIELAB colour parameters for assumed Dq
ꢂ1
.
/
Vis part only) clearly shows that colour of the CoCl
solution, for instance in the solution creating a low
ligand-field could change its hue from greenishꢀblue to
2
ꢂ1
range (the step is 50 cm ). The CIELAB data (the
/

I. Ku z´ niarska-Biernacka et al. / Polyhedron 22 (2003) 997ꢀ
/
1007
1007
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[
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