Spectral and thermal studies of solid-phase thermochromism of Co(II) double metal complexes

Article abstract of DOI:10.1016/j.saa.2006.11.015

Tetrahedral solid state structures of the blue potassium tris(aryloxo)cobaltate(II)-tetrahydrofurane complexes of the formula KCo(OAr)₃·2thf (OAr = o-chloro-, o-bromo-, m-chloro-, p-bromo, 2,6-dichloro-, 2,4-dichloro- or 2,4-dimethylphenoxide) undergo solid-phase thermal tetrahedral to octahedral transformation accompanied by change in their colours from blue to rose (one-step thermochromism). Magnetic moments, electronic and infrared spectral studies supported these results. Thermal treatment of theses complexes leads to the loss of the crystallized thf molecule yielding also blue tetrahedral complexes. However, further heating leads to the loss of the coordinated thf molecule and the formation of rose octahedral trimeric products. TG-DTA results showed that the, two solvated thf molecules were eliminated in two steps. Mass spectral studies and IR intensity measurements confirmed the trimeric behaviour of the rose octahedral geometry of thermal products. Conductance measurements of solutions of these complexes in thf indicated that they behave as non-electrolytes.

Full text of DOI:10.1016/j.saa.2006.11.015

Spectrochimica Acta Part A 68 (2007) 204–210
Spectral and thermal studies of solid-phase thermochromism
of Co(II) double metal complexes
Noura H. AL-Sha’alan∗
Department of Chemistry, Education College for Girls, Riyadh, KSA, Saudi Arabia
Received 2 October 2006; received in revised form 2 November 2006; accepted 17 November 2006
Abstract
Tetrahedral solid state structures of the blue potassium tris(aryloxo)cobaltate(II)-tetrahydrofurane complexes of the formula KCo(OAr)3·2thf
(OAr = o-chloro-, o-bromo-, m-chloro-, p-bromo, 2,6-dichloro-, 2,4-dichloro- or 2,4-dimethylphenoxide) undergo solid-phase thermal tetrahedral
to octahedral transformation accompanied by change in their colours from blue to rose (one-step thermochromism). Magnetic moments, electronic
and infrared spectral studies supported these results. Thermal treatment of theses complexes leads to the loss of the crystallized thf molecule
yielding also blue tetrahedral complexes. However, further heating leads to the loss of the coordinated thf molecule and the formation of rose
octahedral trimeric products. TG-DTA results showed that the, two solvated thf molecules were eliminated in two steps. Mass spectral studies and
IR intensity measurements confirmed the trimeric behaviour of the rose octahedral geometry of thermal products. Conductance measurements of
solutions of these complexes in thf indicated that they behave as non-electrolytes.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Thermochromism; Td to Oh transformation
1. Introduction
in this work the synthesis and thermal reactions of potassium
tris(aryloxo)cobaltate·tetrahydrofurane complexes of the for-
mula KCo(OAr)3·2thf.
The alkyloxo (–OR) and the aryloxo (–OAr) groups have
been of considerable interest to the coordination chemist due
to their ability to form strong covalent bonds with almost all
metals. Also, their tendency to act as bridges between similar
as well as different metal atoms [1]. A considerable amount of
work has been done on metal alkyloxides due to their use in
many organic synthesis and their industrial applications [1–3].
Also, much work has been done on double alkyloxides involv-
ing more than one metal atom within the molecular species
[1–3]. Thus, alkali metal alkyloxonickolate(II) have been used
as a new catalyst of higher activity in nickel-catalyst system
[4]. In addition, alkyloxocobaltate(II) complexes of the for-
mula MM’(OR)4(MBr)m·nthf, M = Li, Na or K, M’ = Ni or Co,
R = ethyl, isopropyl, isobutyl, sec-butyl, pent-3-yl, menth-3-yl,
allyl, or benzyl (m = zero; M = Na or K, m = 1–2; M = Li and
n = 1–6, have been prepared and characterized [5–8]. On the
other hand, very little work has been reported on the corre-
sponding aryloxo derivatives especially for cobalt(II). We report
2. Results and discussion
2.1. Synthetic, electronic and magnetic studies of the
original complexes 1–7
Under anaerobic conditions anhydrous CoBr2 or CoBr2·2thf
reacts with a solution of the potassium salt of o-chloro-,
o-bromo-, m-chloro-, p-bromo-, 2,6- dichloro-, 2,4-dichloro-,
or 2,4-dimethylphenol (abbreviated as KOAr) in thf; molar
ratio KOAr/Co(II) ≥4, where air-sensitive potassium
tris(aryloxo)cobaltate(II) complexes·2thf are obtained as
blue or blue violet solids. In contrast to K2Co(Oph)4·thf
complex previously reported [7], the obtained complexes,
1–7, Table 1, contain only three aryloxide moieties per each
molecular unit in spite of the presence of excess KOAr in
the reaction mixtures. This could be attributed to the bulk of
the OAr moieties beside the bridged potassium ion, which
may hindered the coordination of the fourth OAr moiety. The
structure of the complexes is indicated as follows.
∗
Tel.: +966 503167512.
E-mail address: nor hamady@yahoo.com.
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.11.015

N.H. AL-Sha’alan / Spectrochimica Acta Part A 68 (2007) 204–210
205
Table 1
The amount of the reactants used, the colour, the conditions followed to isolate the solid complexes 1–7
No.
Complex
Amount of the reactants
used (g) mmol
Colour of the
solution
Conditions of
the isolation
Yield (g) %
Analysis (cald.) found
*
CoBr2 or
CoBr2 2thf
KOAr
K
Co
OAr
1
2
3
4
5
6
7
KCo(o-ClC6H4O)3·2thf
KCo(o-BrC6H4O)3·2thf
KCo(m-ClC6H4O)3·2thf
KCo(p-BrC6H4O)3·2thf
KCo(2,4-Cl2C6H3O)3·2thf
KCo(2,6-Cl2C6H3O)3·2thf
KCo(2,6-(Me)2C6H3O)3·2thf
(7.00) 19.3
(5.90) 27.0*
(7.90) 21.8
(6.50) 29.7*
(8.80) 24.2
(8.20) 22.6
(4.85) 22.2*
(12.9) 77.0
(22.8) 108
(14.4) 86.0
(25.0) 119
(19.5) 97.0
(18.2) 91.0
(14.0) 90.0
Blue violet
Blue violet
Blue violet
Deep blue
Deep blue
Deep blue
Blue
a
a
b
a
b
c
c
(7.3) 61.0
(12.5) 57.0
(7.5) 55.0
(14.7) 65.9
(9.5) 54.0
(8.2) 49.0
(8.3) 62.9
(6.3) 6020
(5.2) 5.0
(9.4) 9.2
(7.8) 7.5
(9.4) 9.7
(7.8) 7.5
(8.1) 8.3
(8.1) 8.4
(9.7) 9.9
(61.2) 61.7
(68.1) 67.4
(61.2) 61.5
(68.1) 76.7
(66.8) 67.0
(66.8) 67.1
(60.0) 60.5
(6.3) 6.40
(5.2) 5.30
(5.4) 5.50
(5.4) 5.20
(6.5) 6.30
(a) The concentrated solution was left for 7 days at −78 ◦C, after which the precipitated crystals were isolated, (b) 5 ml n-hexane was added to the concentrated
solution previously cooled at −78 ◦C for 10 days, (c) the concentrated solution was left for 15 days at −78 ◦C, after which, 20 ml cooled n-hexane was, (d) added
and then the mixture was left for further 4 days at −78 ◦C after which the precipitated solid complex was isolated.
The prepared complexes were highly air-sensitive as the pre-
viously reported alkyloxo complexes of Co(II) and Ni(II) of the
formula KCo(OR)3·thf and KNi(OR)3·thf [5–7]. The complexes
decomposed immediately by addition of water. They react with
compounds containing acidic-H of pKH-values smaller than that
of the appropriate phenol. Thus, through the reaction of 2,4-
dichlorophenol with 7, we have obtained 5. Electronic spectral
data and magnetic moments measurements are given in Table 2.
As shown in Table 2, all the prepared solid complexes 1–7
have magnetic moments in the range 4.48–4.62 B.M. and absorb
strongly in the range 16,400–17,300 cm−1. A main absorption
band appeared at ∼16,500 cm−1 which have high values of
extinction coefficients (Table 2 and Fig. 1). These properties
are characteristic of spin-free tetrahedral cobalt(II) complexes
[9]. The tetrahedral structure would be accomplished through
the attachment of three aryloxide groups and one thf molecule
to the cobalt(II) cation.
Fig. 1. Electronic spectra of the di-solvated complex, 3(—) and its thermal
products 3a(- - -) and 3b(-·-·-).
one-step thermochromism from blue to the rose, non-solvated,
products lb–7b. The colour changes are reversible. The reverse
changes proceed on cooling the rose products to room temper-
ature and introducing dry thf-vapour into the system. The rose
product absorb thf molecules gradually and revert to the orig-
inal di-solvated complexes 1–7 in several hours or days. The
time taken in the reversible reactions as well as the temper-
ature ranges at which the rose products are formed seems to
be affected by the group(s) present in the phenoxide ring [10].
All the rose non-solvated thermal products lb–7b are stable and
could be isolated and identified. Analytical data of the com-
2.2. Thermochromism of the original complexes 1–7
Fig. 2 shows the results of visual observations on the solid-
phase thermochromism of complexes 1–7. All complexes show
Fig. 2. Results of visual observations of the thermochromic changes of the complexes, b: blue or blue violet, R: rose. The rose colour appears at the spots shown;
the right-hand ends of the lines corresponded to the decomposition points.

206
N.H. AL-Sha’alan / Spectrochimica Acta Part A 68 (2007) 204–210
Table 2
Electronic spectral data, magnetic moments and IR-vibrationa frequencies, of the original complexes, 1–7, and the corresponding thermal products, 1a–7a and 1b–7b
4
No.
Complex
Absorption maxima
μeff. (B.M.)
ν(Co–O) (cm−1
)
ν(C–O–C) (cm−1
)
4A2(F) → T2(F)
ν 10−3 (cm−1
)
10Dq (cm−1
3580
)
1
KCo(o-ClC6H4O)3·2thf
KCo(o-ClC6H4O)3·thf
KCo(o-ClC6H4O)3
16.525
16.550
16.665
16.750
19.960
20.700
4.48
4.19
5.15
665
690
450
1055
1050
–
1a
1b
3490
–
2
KCo(o-BrC6H4O)3·2thf
KCo(o-BrC6H4O)3thf
KCo(o-BrC6H4O)3
16.500
16.650
16.660
16.750
19.900
20.500
4.60
4.55
5.25
575
625
440
1070
1055
–
3585
3590
–
2a
2b
3
KCo(m-ClC6H4O)3·2thf
KCo(m-ClC6H4O)3·thf
KCo(m-ClC6H4O)3
16.650
17.450
16.600
16.750
19.800
20.900
4.61
4.56
5.22
620
630
450
1060
1045
–
3590
3580
–
3a
3b
4
KCo(p-BrC6H4O)3·2thf
KCo(p-BrC6H4O)3·thf
KCo(p-BrC6H4O)3
16.700
17.450
16.680
17.750
19.870
20.600
4.58
4.49
5.23
675
620
450
1070
1055
-
3585
3575
-
4a
4b
5
KCo(2,4-Cl2C6H3O)3·2thf
KCo(2,4-Cl2C6H3O)3·thf
KCo(2,4-Cl2C6H3O)3
16.600
17.350
16.770
17.555
19.980
20.400
4.61
4.55
5.15
620
620
470
1055
1050
–
3580
3575
–
5a
5b
6
KCo(2,6-Cl2C6H3O)3·2thf
KCo(2,6-Cl2C6H3O)3·thf
KCo(2,6-Cl2C6H3O)3
16.800
17.500
16.770
17.300
19.980
20.650
4.62
4.50
5.17
695
615
420
1055
1050
–
3590
3585
–
6a
6b
7
KCo(2,6-(Me)2C6H3O)3·2thf
KCo(2,6-(Me)2C6H3O)3·thf
KCo(2,6-(Me)2C6H3O)3
16.500
16.800
16.900
19.900
20.550
4.58
4.60
5.23
630
620
455
1070
1055
–
3575
3585
–
7a
7b
a
ν(Co-Cl) 780, ν(Co-Br) 755 cm−1
.
plexes lb–7b is summarized in Table 3 correspond to the formula
KCo(OAr)3.
weight loss at 125–181 ◦C and the corresponding endothermic
DTA peaks are due to the splitting of the second coordinated
thf molecule, at this stage the complexes change their colour
to rose. After that, the plateau, in the TG curves remain flat
until the decomposition of the complexes. The differences in
the temperature ranges, at which these rose products were
formed attributed to the differences in the electronic prop-
erties and the steric requirements of the ligand used. The
thermal treatment led us to isolate the intermediate mono-
solvated complexes, KCo(OAr)3·thf, 1a–7a (Table 3) formed
during the thermal reactions of the original complexes 1–7.
The enthalpy changes, Table 4, for the reactions of the type
blue, mono-solvated, to the rose non-solvated products were
2.3. Thermal analyses
The results of TG-DTA for the complexes 1–7 are shown
in Figs. 3 and 4 and Table 4. All the complexes liberate
the thf molecules in two steps. The first abrupt weight loss
observed in the TG-curves before 95 ◦C and the correspond-
ing endothermic DTA peaks, are due to the liberation of the
crystallized (non-coordinated) thf molecule. At this stage, the
blue colours of the complexes were unchanged as deduced from
the visual thermal observations (Fig. 2). The second abrupt

N.H. AL-Sha’alan / Spectrochimica Acta Part A 68 (2007) 204–210
207
Table 3
Analytical data of the blue mono-solvated 1a–7a and the rose non-solvated
1b–7b complexes
No.
Complex
Analysis (cald.) found
K
Co
OAr
1a
1b
KCo(o-ClC6H4O)3·thf
KCo(o-ClC6H4O)
(7.1) 7.0
(8.1) 7.9
(10.7) 11.0
(12.3) 12.5
(69.2) 70.1
(79.6) 80.1
2a
2b
KCo(o-BrC6H4O)3·thf
KCo(o-BrC6H4O)3
(5.7) 8.9
(6.4) 6.2
(8.6) 8.9
(9.6) 9.3
(75.2) 74.6
(84.0) 83.6
3a
3b
KCo(m-ClC6H4O)3·thf
KCo(m-ClC6H4O)3
(7.1) 7.3
(8.1) 7.8
(10.7) 11.0
(12.3) 12.8
(69.6) 6.8.9
(79.6) 79.3
4a
4b
KCo(p-BrC6H4O)3·thf
KCo(p-BrC6H4O)3
(5.7) 6.2
(6.4) 6.8
(8.6) 8.9
(9.6) 9.9
(75.2) 75.7
(84.0) 83.8
5a
5b
KCo(2,4-Cl2C6H3O)3·thf
(6.0) 6.4
(7.0) 6.3
(9.0) 8.7
(10.1) 10.5
(74.1) 74.6
(83.2) 82.8
KCo(2,4-Cl2C6H3O)3
6a
6b
KCo(2,6-Cl2C6H3O)3·thf
(6.0) 5.6
(7.0) 6.6
(9.0) 8.3
(10.1) 9.7
(74.1) 74.6
(83.2) 82.8
KCo(2,6-Cl2C6H3O)3
Fig. 3. TG-DTA of 1(—), 2(. . .), 3(-·-·-), 4(- - -) complexes. Heating rate
20 ◦C min−1; DTA sensitivity ␮V; amount of sample of 1–4 complexes are:
26.5, 22.9, 19.9 and 17.6 mg, respectively.
7a
7b
KCo(2,6-(Me)2C6H3O)3·thf
(7.3) 7.0
(8.5) 8.2
(11.0) 10.7
(12.8) 13.1
(68.1) 68.6
(78.8) 80.0
KCo(2,6-(Me)2C6H3O)3
solvated complex, 3a, remains nearly unchanged after liberation
of one molecule thf from the original complex 3, indicating that
the tetrahedral configuration is retained [9]. On the other hand,
the spectrum of the non-solvated rose product, 3b, show spectral
changes where broad bands of lower intensities, characteristic of
octahedral Co(II) appear [9,10]. The following equation could
be such equilibrium (Fig. 5).
estimated from the DSC measurements carried out separately.
(Fig. 4).
2.4. Spectral and magnetic changes on heating the solid
original complexes 1–7
Spectral and magnetic moment data for the original di-
solvated complexes 1–7 and the isolated thermal products la–7a
and lb–7b are collected in Table 1. Fig. 1 gives a comparison of
the visible spectra of the thermal products 3a and 3b with the
spectrum of the original blue di-solvated complex, 3, as an exam-
ple of the spectral changes on heating these types of complexes.
As shown in figure, it is clear that the spectrum of the blue mono-
The visible spectra of complexes of “a” type generally show
a main absorption band at ∼16,500 cm−1 and a shoulder at
∼172,500 cm−1. Their magnetic moments are in the range
4.19–4.56 B.M. which are somewhat lower than the values of the
Table 4
Results of TG-DAT and DSC thermal analysis of the solid complexes 1–7
No.
Complex
Desolvation
Decomposition
Temperature (◦C)
ꢀH (kJmol−1)Td to
Oh transformation
Temperature (◦C)
Weight loos
(calcd.) found (%)
1
2
3
4
5
6
7
KCo(o-ClC6H4O)3.2thf
KCo(o-BrC6H4O)3.2thf
KCo(m-ClC6H4O)3.2thf
KCo(p-BrC6H4O)3.2thf
KCo(2,4-Cl2C6H3O)3.2thf
KCo(2,6-Cl2C6H3O)3.2thf
KCo(2,6-(Me)2C6H3O)3.2thf
66–91
135–157
(11.5) 11.1
(23.1) 22.7
245
245
250
250
235
237
240
–
13.7
66–95
128–155
(9.5) 9.2
(19.0) 18.4
–
11.50
60–85
130–163
(11.5) 11.0
(23.1) 22.6
–
–
68–90
144–168
(9.5) 9.2
(19.0) 18.6
–
10.70
70–86
136–181
(9.9) 10.4
(19.8) 19.1
–
12.76
70–95
140–171
(9.9) 9.4
(19.8) 19.3
–
–
71–92
145–178
(11.9) 11.4
(23.8) 23.3
–
–

208
N.H. AL-Sha’alan / Spectrochimica Acta Part A 68 (2007) 204–210
at >1050 cm−1 which is assigned to vas(C–O–C) of the thf
molecules confirming its presence in these complexes. On the
other hand, the spectra of the rose products lb–7b are devoid
of this absorption band, besides the v(Co–O) is observed at
lower frequencies (>450 cm−1). This is taken as an indication
of the polymeric structure of these rose complexes [10,13].
Buchmann [3] has reported stretching frequencies of 718 and
555 cm−1 for M–O of the monomeric Cr(OCHBu2t )4 and the
dimeric LiCr(OCHBut2)4 · thf, respectively. Also, Komiya [14]
reported stretching frequencies of 1290 cm−1 for (C–O)Fe
in Fe(OPh)2(bpy)2. In addition, the spectra of the original
complexes show a very broad band at 3580 cm−1 which is
4
assigned to spin allowed transition [4A2– T2(F)], ν1(10 Dq)
of cobalt(II) ion in tetrahedral configuration [9]. The dis-
appearance of these broad bands in the IR spectra of the
thermal rose products, 1b–7b confirms the Td to Oh trans-
formations accompanied by colour changes from blue to rose
complexes. Furthermore, intensity measurements [15] of the
bridging Co–O bands (in both the original and the rose com-
plexes) is used to estimate the number of polymerization in the
rose complexes. The result is >1:3 for (Co–O)original: (Co–O)rose
which is in harmony with the trimeric structure
thermal products
Fig. 4. TG-DTA of 5(—), 2(. . .), 6(- - -), 7(-·-·-) complexes. Heating rate
20 ◦C min−1; DTA sensitivity ␮V; amount of sample of 5–7 complexes are:
18.50, 21.2, and 23.6 mg, respectively.
of the rose thermal products. Moreover, only one stretch-
ing band of the Co–O bond is observed in the IR spectra
of the original rose complexes which reflected the symme-
try of the coordinate bond skeleton in these complexes [16]
being D4h.
original complexes. Thus, the decrease in the number of crys-
tallized thf molecules leads to the decrease of their magnetic
moments. This may be attributed to the increase of antifer-
romagnetic interactions between adjacent Co(II) cations. On
the other hand, the visible spectra of complexes of “b” type
show a main absorption bands at −19,100 cm−1 and a shoul-
der at 20,700 cm−1. Their magnetic moments are in the range
5.15–5.23 B.M. The change in the colour of the complexes
(blue to rose) upon heating coupled with the change in spec-
tral and magnetic moments data are attributed to the formation
of octahedral trimeric products comprising bridging OAr group
[1–3,11].
2.6. Mass spectra
The polymeric behaviour of the rose complexes is confirmed
by the mass spectral study of the rose product of the o-chloro-
derivative as an example of this type of complexes. The mass
spectrum shows that the highest mass fragments corresponded
to [KCo3(o-ClC6H4O)6]+, (m/e 981; 8%), which losses K(o-
ClC6H4O) to give the fragment [Co3(o-ClC6H4O)5]+, (m/e
645.5; 11%). The mass fragmentation pattertern indicates the
presence of some dimeric species with lower abundance that
arises from the fragmentation of trimeric species. Also, the spec-
trumshowsthatthelargestnumberofmassionpeaksispresentin
the trimeric region in the spectrum, which is ascribed to form of
this complex. On the other hand, the mass spectrum of the cor-
responding original blue complex, K[(Co(o-ClC6H4O)3]·2thf,
shows a [Co(o-ClC6H4O)2]+ fragment with higher abundance.
In both mass spectra, no parent molecular ion peaks are
observed.
2.5. I.R. Spectra
All complexes show the characteristic frequency of
v(C = C)ring (>1600 cm−1). The original complexes also show
a band at >500 cm−1 attributed to v(Co–O) [12,13]. The spec-
tra of the thermal products la–7a show the presence of a band
2.7. Electrical conductance
Electrical conductance of the complexes 1–7 which
were measured in thf solutions, are ranged between
1.2–1.4 Ohm−1 cm2 mol−1 indicating that all complexes behave
as non-electrolytes in their thf solutions. These results suggest
the presence of tight ion pairs in thf. Mehrotra [1,17] attributed
the non-electrolytic nature of Na2Zr2(OPri)9 (in isopropanol)
and of alkyloxo complexes CoCl2·2BusOH, CoCl2·2BuiOH and
Fig. 5. Thermal reaction scheme of the complexes: reaction (a) Td to Td, reaction
(b) Td to Oh.

N.H. AL-Sha’alan / Spectrochimica Acta Part A 68 (2007) 204–210
209
CoCl2·2ButOH (in their parent alcohols) to the relatively low
3.3. Visual observation of thermochromic changes of the
complexes 1-7
dielectric constants of the solvents.
In order to study the thermal reactions of the original com-
plexes 1–7 and the mode of their thermochromic change of each
complex, which usually occurs within a temperature range of
several degrees, a sample of a given complex is heated slowly
to determine, firstly, the temperature at which a distinct colour
change will be observed. A new sample is then, heated to the
temperature at which this colour change took place, in order to
obtain the non-solvated complex.
3. Experimental
All glass apparatus with standard joints were used through-
out the experiments. Stringent precautions were taken to avoid
moisture and atmospheric oxygen. All preparation and subse-
quent handling of materials were carried out under dry argon.
Also, alloperationsforisolationandcharacterizationofthecom-
plexes were carried out under absolute water-free conditions
(anaerobic conditions) in an argon atmosphere using Schlenk-
techniques [18]. Chemicals used were of AR grade. Solvents
were dried over sodium metal and benzophenone and distilled
under argon immediately prior to use. Anhydrous cobalt bro-
mide was prepared by a literature method [19]. For weighing,
anaerobic sample tube-technique was used.
3.4. Isolation of the blue mono-solvated complexes 1a-7a
The mono-solvated complexes la–7a were obtained by heat-
ing a small amount of the finely powdered sample of the
corresponding original di-solvated complexes 1–7 putted in a
two-neck Schlenk tube provided with a thermometer and in-
and outlet device for argon gas in a silicon oil bath. The heating
rate did not exceed 5 ◦C min−1. The heating was continued until
the corresponding elevated temperature, deduced from the DTA
curves, at which the mono-solvated complexes are expected to
form. At this temperature the sample was left to stand for fur-
ther 1/2 h to ensure the removal of all liberated thf and to avoid
the occurrence of the backward reaction towards the original di-
solvated complexes. The product was then allowed to cool under
argon atmosphere to room temperature and then identified and
finally stored under argon.
3.1. Preparation of potassium aryloxide ligauds
All potassium aryloxide ligands were prepared by the follow-
ing general procedure: A solution of 0.1 mole of the appropriate
phenol in 50 ml dry thf was added drop wise, over a period of
2 h to 5.58 g (0.15 mol) clean potassium metal (in small pieces)
in 60 ml thf. After complete addition of the phenol and com-
plete removal of the evolved hydrogen gas, the mixture was
maintained under reflux for 2 h. The reaction mixture was then
continuously stirred at room temperature for an additional hour
and then allowed to cool and left overnight. The residual potas-
sium metal was carefully filtered in a G4 filtration unit. The
filtrate was then stored under argon. The amount of the resultant
potassium aryloxide salt in the filtrate was determined analyt-
ically by diluting 1 ml of the filtrate in 10 ml distilled water
and the resulted KOH was titrated against 0.1 M HC1. The con-
centrations of the thf solutions of the KOAr ranged between
3.5. Isolation of the non-solvated complexes 1b–7b
A new sample was treated as above, in all cases, the heating
was continued to the temperature at which the rose products
were formed as deduced from the visual observations and DTA
curves.
0.75–0.9 mol dm−3
.
3.6. Formation of the original complexes 1–7 from the
non-solvated complexes 1b–7b
3.2. Preparation of the original solid complexes 1–7
Under the presence of thf-vapour (anaerobic conditions) and
in several hours or days, the rose non-solvated complexes lb–7b
absorbed 2 mols of thf and reverted to the original blue di-
solvated complexes. The following is the analytical data of a
sample (3 and 3b) as an example of these reversible reactions.
Potassium tris(aryloxo)cobaltate(II)·2thf were prepared by
the following procedure: CoBr2 or CoBr2·2thf was reacted with
such volume of a solution of KOAr of known concentration in
thf in a molar ratio of KOAr/Co(II) ≥4. The reaction mixture
was stirred at room temperature for 1/2-2 h and then allowed to
stand for 24 h. The white, KBr, precipitate was separated under
argon atmosphere in a G4-filtrate unit. The clear filtrate was
then, concentrated in vacuo at room temperature or at a tem-
perature of maximum 40 ◦C. The solution was cooled for 5–15
days at −78 ◦C. The obtained blue solid complexes were fil-
tered under argon atmosphere in a G3-filtrate unit, washed 2
times with 5 ml dry thf, dried under vacuum and finally stored
under argon. In Table 1, the amounts of the reactants used, colour
of the resulted solutions, colour of the isolated solid complexes,
conditions of their isolation and their analytical data, are given.
The obtained complexes are bromide-free products. They are
soluble in toluene, dioxane, CHCl3 and DMF.
Complx (colour)
Elemental analysis %(calcd.) found
Co(II)
OAr−
K
3 (blue)
3b (rose)
3 (blue)
(9.4) 9.6
(12.3) 12.6
(9.4) 9.8
(61.2) 61.7
(79.6) 80.0
(61.2) 61.9
(6.3) 6.7
(6.3) 6.7
(6.3) 6.7
3.7. Analysis and measurements
Cobalt was determined using a complexometric titration
method [20]. Aryloxide groups were determined by acid-
base titration [17]. Potassium was analyzed using a PEP-7

210
N.H. AL-Sha’alan / Spectrochimica Acta Part A 68 (2007) 204–210
flame photometer. Electronic spectra were recorded as Nujol
mulls using Carry 14-spectrophotometer. Infrared spectra were
recorded as Nujol mulls or Csl pellets using a Perkin-Elmer
598 spectrometer. Mass spectra were recorded at 70 eV and
300 ◦C on an MS 5988 Hewlett-Packard mass spectrometer.
Magnetic measurements were carried out using a Gouy bal-
ance, Johnson Matthey, Alfa products, UK, model MKI. The
calibrant were Mohr’s salt and HgCo(NCS)4. The measured
molar susceptibility (χmol) was corrected for diamagnetism
and the μexp/μB was calculated from the equation μ = 2.84
[mol T]1/2. TG-DTA and DSC measurements were carried
out using a Perkin-Elmer high temperature differential ther-
mal analyzer, Delta series TGA7, coupled with 3700 data
station. The conditions of the runs are given in the caption of
Figs. 2 and 3.
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