Adducts of cobalt(II) bis(salicylaldiminates) and redox-active Phenoxazin-1-one: Synthesis, structure, and magnetic properties

Article abstract of DOI:10.1007/s11172-013-0251-6

Adducts of cobalt(II) bis(salicylaldiminates) and 2,4,6,8-tetra-tert- butylphenoxazin-1-one were synthesized and their molecular and crystal structures were determined. According to the ESR and magnetochemical data, the metal atom is in the low-spin trivalent state (CoIII) due to the intramolecular electron transfer to the redox-active ligand. In the solid state, the mixed- ligand complexes are stable in air for several months, but in solution at elevated temperatures they dissociate to the starting components. Such a behavior detected by the temperature depen- dence of the effective magnetic moment is explained by the quantum chemical DFT calcula- Tions of the energy barriers of possible valence tautomeric dynamics, whose values were found to be higher than the enthalpy of dissociation.

Full text of DOI:10.1007/s11172-013-0251-6

Russian Chemical Bulletin, International Edition, Vol. 62, No. 8, pp. 1744—1751, August, 2013
1744
Adducts of cobalt(II) bis(salicylaldiminates) and redoxꢀactive
phenoxazinꢀ1ꢀone: synthesis, structure, and magnetic properties
M. Yu. Antipin,a† E. P. Ivakhnenko,b Yu. V. Koshchienko,b P. A. Knyazev,b M. S. Korobov,b
A. V. Chernyshev,b K. A. Lyssenko,a A. G. Starikov,c and V. I. Minkinb,c
aA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation
bResearch Institute of Physical and Organic Chemistry, Southern Federal University,
194/2 prosp. Stachki, 344090 RostovꢀonꢀDon, Russian Federation
cSouthern Scientific Center, Russian Academy of Sciences,
41 prosp. Chekhova, 344006 RostovꢀonꢀDon, Russian Federation.
Eꢀmail: andr@ipoc.sfedu.ru
Adducts of cobalt(II) bis(salicylaldiminates) and 2,4,6,8ꢀtetraꢀtertꢀbutylphenoxazinꢀ1ꢀone
were synthesized and their molecular and crystal structures were determined. According to the
ESR and magnetochemical data, the metal atom is in the lowꢀspin trivalent state (CoIII) due to
the intramolecular electron transfer to the redoxꢀactive ligand. In the solid state, the mixedꢀ
ligand complexes are stable in air for several months, but in solution at elevated temperatures
they dissociate to the starting components. Such a behavior detected by the temperature depenꢀ
dence of the effective magnetic moment is explained by the quantum chemical DFT calculaꢀ
tions of the energy barriers of possible valence tautomeric dynamics, whose values were found
to be higher than the enthalpy of dissociation.
Key words: complexes, phenoxazinꢀ1ꢀone, magnetic properties, valence tautomerism.
Considerable interest in studying the structures and
published in 1973.14 The authors considered the interacꢀ
tion of the CoII and FeII salicylalethylenediaminate comꢀ
plexes with pꢀ and oꢀbenzoquinones, 9,10ꢀphenanthreneꢀ
quinone, and 1,2ꢀnaphthoquinone. The adducts of other
planar CoII complexes with оꢀbenzoquinone were studied
further. These studies showed that the reaction was acꢀ
companied by the metalꢀtoꢀligand electron transfer in all
cases.15—18 The adduct formation of CoII acetylacetonate
with оꢀbenzoquinone was studied by Kabachnik and coꢀ
authors.19 In all above works, metal oxidation to the triꢀ
valent state and ligand transition to the оꢀsemiquinone
form were observed.
The mixedꢀligand complexes of bis(acetylacetonato)ꢀ
ruthenium with оꢀiminoꢀ, оꢀiminothioquinones, and
оꢀdiiminoquinones 1 were described and structurally charꢀ
acterized.20,21
The structure formed due to the electron transfer from the
Ru2+ ion to the lowest unoccupied *ꢀMO of iminoquinone
was ascribed to complex 1 (X = O) (Scheme 1) on the basis
of the values of С—О and C—N bond lengths typical of the
iminosemiquinone form of the redoxꢀactive ligand and
spectroelectrochemical data. At the same time, valence
tautomerism was reported for none of the synthesized adducts.
In this work, we showed the possibility of synthesizing
wide series of mixedꢀligand hexacoordinate cobalt comꢀ
magnetoswitchable properties of bistable transition metal
complexes with redoxꢀactive (nonꢀinnocent) ligands is
caused by the possibility to produce from them molecular
switches,1—3 molecular memory devices,4—6 displays,7—9
and holographic devices.10,11 The mechanism of thermoꢀ
or photocontrolled rearrangements of these complexes (reꢀ
dox isomerism or valence tautomerism) is determined by
the intramolecular electron transfer between the metal ion
and ligand system. This effect most frequently appears in
the complexes of hexacoordinate cobalt and manganese
with two sterically hindered oꢀquinones or their imino
derivatives in which the coordination saturation of the
central ion is provided by the addition of a neutral bidenꢀ
tate ligand with donor nitrogen atoms.12,13
The other approach to the synthesis of metal complexꢀ
es capable of exhibiting valence tautomerism is the formaꢀ
tion of a stable complex of the tetracoordinate metal with
the bidentate redoxꢀactive ligand. The intramolecular reꢀ
dox processes expected in these associates will be caused
by the transition of the redoxꢀactive ligand from the neuꢀ
tral (BQ) to radicalꢀanion (SQ) form. One of the first
reports devoted to the study of complexes of this type was
† Deceased.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1744—1751, August, 2013.
1066ꢀ5285/13/6208ꢀ1744 © 2013 Springer Science+Business Media, Inc.

Adducts of cobalt(II) bis(salicylaldiminates)
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
1745
Scheme 1
for each complex. The Сo(1)N(2)C(35)C(30)C(29)O(3)
cycle has a chair conformation with the deviation of the
cobalt atom, whereas the О(4) atom shifts from the plane
in the Сo(1)N(3)C(49)C(44)C(43)O(4) cycle. The obꢀ
served conformational differences do not result in a signifꢀ
icant variation of the bond lengths with both metal atom
and in sixꢀmembered metallocycles and are probably
caused by shortened intramolecular contacts in crystals 2а
and 2b. Indeed, in the case of the metallocycles with the
deviation of the oxygen atom, the aryl substituent at the
N(3) atom lies above the plane of the redox ligand and
forms shortened contacts С(55)...С(1) and C(50)...N(1),
which do not differ virtually for both structures and lie in
the ranges 3.077(4)—3.193(4) and 2.849(4)—2.877(4) Å.
Although the formation of these shortened contacts has,
very probably, a forced character (for steric reasons), it
cannot be excluded that similar stacking interactions can
act as a possible channel of charge transfer.
The С(2)—О(2) (1.312(3)—1.315(4) Å), N(1)—C(1)
(1.366(4)—1.375(4) Å), and C(1)—С(2) (1.417(5)—
1.429(4) Å) bond lengths in the fiveꢀmembered cycle
formed by the central cobalt atom with the donor centers
of the redox ligand are consistent with the mean values of
these bond lengths for the ligands in the iminosemiquinoꢀ
ne (ISQ) form in the complexes of the Third Period metꢀ
als.23 It should be mentioned that the matrix of rootꢀmeanꢀ
square amplitudes of shifts of the cobalt atom is fairly
isotropic in both structures, which also indirectly indiꢀ
cates the absence of a superposition of different spin states
of the metal atom.24
X = O, S
plexes 2 formed by the interaction of redoxꢀactive 2,4,6,8ꢀ
tetraꢀtertꢀbutylphenoxazinꢀ1ꢀone (3) with tetrahedral
cobalt(II) bis(salicylaldiminates) 4. Complexes 2 stable in
air are formed due to two consecutive reactions: coordinaꢀ
tion of the redoxꢀactive ligand and intramolecular oneꢀ
electron oxidation by this ligand of the tetrahedral highꢀ
spin СоII complex to form the octahedral lowꢀspin СоIII
complex (Scheme 2).
The molecular structures of complexes 2a and 2b were
determined22 by Xꢀray diffraction analysis (Fig. 1).
Both molecular and crystal structures of complexes 2а
and 2b are virtually identical (Table 1). Insignificant difꢀ
ferences are caused by different amounts of solvate acetoꢀ
nitrile molecules, namely, 1.4 and 1 in 2а and 2b, respecꢀ
tively. In turn, the variation of the number of solvate molꢀ
ecules results in different numbers of symmetrically indeꢀ
pendent molecules of the complex (one in 2а and two in 2b)
and, as a consequence, in doubling parameter с in comꢀ
plex 2b. The central cobalt atom is characterized by
a slightly distorted octahedral configuration. The fiveꢀmemꢀ
bered metallocycles Сo(1)O(2)C(2)C(1)N(1) in complexꢀ
es 2а and 2b adopt the envelope conformations with the
cobalt atom shifted from the plane, whereas the conforꢀ
mation of the sixꢀmembered rings for two ligands differs
Thus, the data obtained indicate the stabilization of
the radicalꢀanion (ISQ) structure of the redoxꢀactive ligand
in complexes 2 formed due to the intramolecular electron
transfer from the Со2+ ion (Scheme 3).
The radicalꢀion form of the redoxꢀactive ligand (ISQ)
in complexes 2a and 2b is confirmed by the data of ESR
spectroscopy. The spectrum of the crystalline sample of
complex 2b is a singlet with Н = 120 G and g = 1.9948.
Scheme 2
R = H (a), Me (b)

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Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
Antipin et al.
C(52)
C(53)
C(51)
C(50)
C(54)
C(49)
N(3)
C(45)
C(55)
C(17)
C(46)
C(34)
C(15)
C(20)
C(44)
O(3)
C(18)
C(19)
C(33)
C(47)
C(32)
C(21)
C(43)
C(16)
C(29)
Co(1)
C(25)
C(11)
O(1)
O(4)
N(1)
C(2)
C(48)
C(30)
C(6)
C(1)
C(3)
O(2)
C(5)
C(7)
C(4)
C(31)
N(2)
C(35)
C(36)
C(41)
C(37)
C(40)
C(38)
C(39)
Fig. 1. Molecular structure of complex ISQꢀ2a. The numeration of atoms in complex 2b is identical. The solvent molecules and
hydrogen atoms are omitted.
Table 1. Bond lengths (d) and bond angles () in 2a and in one of the independent ISQꢀ2b molecules
Bond
d/Å
Angle
/deg
2a
2b
2а
2b
Co(1)—O(2)
Co(1)—O(3)
Co(1)—O(4)
Co(1)—N(1)
Co(1)—N(2)
Co(1)—N(3)
O(1A)—C(6A)
O(1A)—C(20A)
O(2A)—C(2A)
O(3A)—C(29A)
O(4A)—C(43A)
C(1A)—N(1A)
N(1A)—C(15A)
N(2A)—C(35A)
N(2A)—C(36A)
N(3A)—C(49A)
N(3A)—C(50A)
1.873(2)
1.893(2)
1.886(2)
1.975(3)
1.952(3)
1.958(3)
1.396(4)
1.393(4)
1.314(4)
1.313(4)
1.321(4)
1.375(4)
1.391(4)
1.299(4)
1.444(4)
1.294(4)
1.440(4)
1.885(2)
1.885(2)
1.886(2)
1.976(3)
1.957(3)
1.950(3)
1.392(4)
1.382(4)
1.312(4)
1.313(4)
1.318(4)
1.366(4)
1.380(4)
1.295(4)
1.447(4)
1.292(4)
1.445(4)
O(2A)—Co(2)—O(4A)
O(2A)—Co(2)—O(3A)
O(4A)—Co(2)—O(3A)
O(2A)—Co(2)—N(2A)
O(4A)—Co(2)—N(2A)
O(3A)—Co(2)—N(2A)
O(2A)—Co(2)—N(3A)
O(4A)—Co(2)—N(3A)
O(3A)—Co(2)—N(3A)
N(2A)—Co(2)—N(3A)
O(2A)—Co(2)—N(1A)
O(4A)—Co(2)—N(1A)
O(3A)—Co(2)—N(1A)
N(2A)—Co(2)—N(1A)
N(3A)—Co(2)—N(1A)
86.76(9)
173.04(9)
89.06(9)
87.31(9)
172.62(10)
88.52(10)
91.25(10)
84.99(10)
94.45(10)
88.51(10)
92.88(11)
85.62(10)
177.87(12)
84.10(10)
171.19(10)
100.23(10)
93.24(11)
88.84(11)
91.55(10)
86.48(10)
93.74(10)
89.09(10)
91.98(10)
85.50(10)
178.30(11)
84.29(10)
170.86(10)
100.03(10)
91.91(11)
89.72(11)
The ESR spectra of a solution of complex 2b in toluene
(210 K) have a hyperfine structure (HFS) and contain ten
HFS lines caused by the interaction of an unpaired elecꢀ
tron with the cobalt and nitrogen nuclei (Fig. 2). An analꢀ
ysis of the structure of the spectrum makes it possible to
determine the constants of spin density distribution in the
chelate fragment of 2b: аN =15.4 G, aCo = 12.0 G. The
temperature rise results in line broadening, indicating an
equilibrium in solution shifted toward the structure that
includes penoxazinone in the neutral IQ form.

Adducts of cobalt(II) bis(salicylaldiminates)
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
1747
Scheme 3
T/К
320
300
210
20 G
H/G
Fig. 2. ESR spectra of compound ISQꢀ2b in a toluene solution at
different temperatures (aN = 15.4 G, aCo = 12.0 G, g = 1.9936)
and the simulated ESR spectrum at 210 K (dashes).
imum at 598 nm coincides with the longꢀwavelength band
of free phenoxazinone.
R = H (a), Me (b)
When the temperature of the solution varies from 283
to 328 K, the absorption intensity at 598 nm increases and
that at 900—1100 nm decreases. The observed changes are
completely reversible (Fig. 4). The presence of two isoꢀ
The structure of complex 2b is confirmed by the data
of magnetic susceptibility measurements indicating its lowꢀ
spin electron state. In the solid phase, the effective moꢀ
ment of complex 2b is 1.93 B and remains almost unꢀ
changed in the temperature range from 77 to 298 K. At the
same time, the variation of the temperature of a solution
of the complex in deuterated toluene from 263 to 333 K is
accompanied by reversible changes in the magnetic moꢀ
ment from 1.89 to 2.67 B. This behavior of the complex
can be caused by either the valenceꢀtautomeric equilibriꢀ
um in solution between the lowꢀ (S = 1/2) (ISQ) and
highꢀspin (S = 3/2) (IQ) redox isomers of complex 2b, or
its dissociation to the starting components: 2,4,6,8ꢀtetraꢀ
tertꢀbutylphenoxazinꢀ1ꢀone 3 and bis(salicylaldiminate)ꢀ
cobalt(II) 4b (R = Me), whose magnetic moment is
4.36 B (in benzene it is 4.32 B).25 In order to choose
between these two possible mechanisms, we studied
the absorption spectra of complex 2b in the above temperꢀ
ature range.
eff

•104/L mol–1 cm–1
eff

•103/L mol–1 cm–1
4
8
6
4
2
0
3
2
1
1
1
2
400 600 800 1000
/nm
2
The spectrum of complex 2b in toluene recorded at
283 K (Fig. 3) contains the lowꢀintensity broad band with
a maximum at 987 nm ( = 6.5•102 L mol–1 cm–1) and
a shoulder at 935 nm ( = 6.4•102 L mol–1 cm–1), which
can be assigned to the chargeꢀtransfer transitions,26 and
the bands at 598 and 397 nm. The absorption with a maxꢀ
400
600
800
1000
1200 /nm
Fig. 3. Absorption spectra of complex 2b (1) and phenoxazinone
3 (2) in toluene normalized to the concentration, Т = 283 K.
Inset: the amplified longꢀwavelength part of the spectra.

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Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
Antipin et al.
A (arb. units)
1.89
sbestic points indicates that two forms are involved in the
dynamic equilibrium. The dissociation products of comꢀ
plex 2b can be ascribed to one of these forms. The dissoꢀ
ciative mechanism of the observed processes is favored by
the spectral data presented in Fig. 5 showing that the conꢀ
secutive dilution of a solution of complex 2b is accompaꢀ
nied by a decrease in the absorbance at 900—1100 nm and
an increase in a range of 598 nm characteristic of the
absorption of free phenoxazinone 3. The stability constant
of ISQꢀ2b estimated from the data in Fig. 5 using the
dilution method27 is 9.6•103 L mol–1. The thermodynamic
1.68
1.47
1.26
1.05
0.84
0.63
0.42
0.21
5
1
1
5
5
1
parameters of equilibrium ISQꢀ2b
3 + 4b at 298 K
calculated from the temperature dependence of the abꢀ
sorption spectra are the following: Н = 46 1 kJ mol–1
,
400 500
600
700 800 900
/nm
S = 78 3 J mol–1 K–1, and G = 22.5 kJ mol–1. The
same parameters determined from the data of the temꢀ
perature dependence of the magnetic moment are Н =
Fig. 5. Absorption spectra of complex 2b in toluene at the conꢀ
stant product С2b•l = 1.22•10–3 mol cm L–1 at optical pathꢀ
length l = 0.1 (1), 0.5 (2), 1.0 (3), 2.0 (4), and 5.0 cm (5), Т = 293 K.
= 39 kJ mol–1, S = 77 J mol–1 K–1, and G = 16.1 kJ mol–1
.
A probable reason for the discrepancy of the values of
G obtained by different methods can be an impurity inꢀ
clusion of the redoxꢀisomeric rearrangements of complexꢀ
es 2 to the dynamic process observed in solution.
To explain the processes observed in solutions of comꢀ
plexes 2, we performed the quantum chemical study of
model compounds 2´a in which the tertꢀbutyl groups in
positions 4 and 6 of phenoxazinone 3 were replaced by
hydrogen atoms.
The calculation results for isolated ligand 3´ in the
neutral (IQ) and radicalꢀanion (ISQ) forms are given in
Fig. 6. The reduction of the ligand is accompanied by the
elongation of the C—O and C—N bonds by 0.03 and
0.05 Å, respectively. These measurements are well consisꢀ
tent with the data obtained for оꢀiminobenzoquinone
ligands in similar oxidation states.28
iminate)cobalt 4a with neutral form of ligand 3´. Spin
density localization in structure 5 on the metal atom (qsCo
=
= 2.66) is characteristic of highꢀspin divalent cobalt (see
structure 4a). Lowꢀspin isomer of adduct 2´a corresponds
to structure LSꢀ6 on the doublet PES in which the spin
density on the metal atom is absent (Table 2) and the
single unpaired electron is localized on the redoxꢀactive
ligand, indicating its radicalꢀanion form. The calculated
geometric characteristics of structure LSꢀ6 well reproduce
the Xꢀray diffraction data for complex 2a (see Table 1).
The lowꢀspin form of adduct LSꢀ6 is by 11.1 kcal mol–1
more preferable than highꢀspin form HSꢀ5, which is conꢀ
sistent with the data of magnetochemical measurements
and allows one to expect valence isomerism.
In order to establish the mechanism of a process reꢀ
sponsible for the change in the magnetic properties of
adduct 2´a, we searched for minimumꢀenergy crossing
point (MECP) between two PES. The calculations resulted
Structure 5 on the quartet potential energy surface
(PES) corresponds to the associate of bis(salicylaldꢀ
A (arb. units)
Table 2. Total energy (Еtot), stabilization energy (Est), relaꢀ
0.8
Co
tive energy (E), and spin density on the metal atom (qs
)
2
for structures 3´, 4a, and 5—7 calculated by the DFT
B3LYP*/6ꢀ311++G(d,p) method
0.6
Co
Structure
S
–Etot/au
Est
E
qs
kcal mol–1
0.4
1
SQꢀ3´
ISQꢀ3´
4a
HSꢀ5
LSꢀ6
0
980.7715572
980.8446537
2644.977701
3625.750513
3625.768162
3625.747164
—
—
—
0.8
11.9
—
—
—
11.1
0
—
—
2.67
2.66
0.04
—
1/2
3/2
3/2
1/2
—
0.2
1
2
0
MECPꢀ7
–1.3
13.2
500
600
700
800
900
/nm
Fig. 4. Absorption spectra of complex 2b in toluene in the temꢀ
perature range from 283 (1) to 328 K (2) with an increment of
Note. The stabilization energy (Est) was calculated relaꢀ
tively to isolated molecules of bis(chelate) and phenoxaziꢀ
none in the neutral form.
5 K, С4b = 8.32•10–5 mol L–1
.

Adducts of cobalt(II) bis(salicylaldiminates)
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
1749
1.225
1.477
1.438
1.382
1.229
1.255
1.528
1.453
1.467
1.415
1.352
1.365
1.371
1.367
1.407
1.486
1.423
1.375
1.383
1.417
1.395
1.354
1.364
1.374
IQꢀ3´
ISQꢀ3´
1.991
1.990
1.894
1.917
1.983
1.913
2.184
2.098
2.158
1.982
1.385
2.004
1.308
2.296
1.388
1.255
1.484
1.447
1.425
1.433
1.368
1.417
1.371
1.372
1.318
1.413
1.378
1.396
1.410
1.437
1.361
1.377
1.428
1.407
1.368
1.363
HSꢀ5
LSꢀ6
1.970
2.130
1.974
2.116
2.026
2.148
1.390
1.276
1.461
1.438
1.341
1.415
1.426
1.367
1.385
1.419
1.365
1.370
MECPꢀ7
Fig. 6. Geometric characteristics of ligands 3´ and structures 5—7 calculated by the DFT B3LYP*/6ꢀ311++G(d,p) method. Hydroꢀ
gen atoms are omitted. Interatomic distances are given in Å.
in structure MECPꢀ7 lying by 13.2 kcal mol–1 higher than
structure LSꢀ6 (see Table 2). This value somewhat exꢀ
ceeds the experimental values for the valenceꢀtautomeric
(VT) rearrangement of the cobalt complexes but is quite
attainable. The energy profile of the expected VT rearꢀ
rangement is presented in Fig. 7.

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Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
Antipin et al.
E/kcal mol–1
method for F2. All calculations were performed using the
SHELXTL program package.29 ESR spectra were obtained on
a Bruker EMX Plus 10/12 Xꢀband spectrometer. The hyperfine
coupling constants of the ESR spectra were calculated using the
Bruker WinEPR SimFonia program package. Absorption specꢀ
tra were measured on an Agilent 8453 spectrophotometer
equipped with a Peltier thermostat. The magnetic moments in
solution were measured using a published method30 on a Bruker
Avance 600 NMR spectrometer (600 MHz).
1.3
0
–0.8
MECPꢀ7
2 + 3
HSꢀ5
–11.9
Quantum chemical calculations were performed in the
framework of the density functional theory (DFT) by the Gaussꢀ
ian03 program31 using the 6ꢀ311++G(d,p) basis set and B3LYP*
modified functional32 that differs from the standard hybrid
B3LYP functional by a decrease in the Hartree—Fock contribuꢀ
tion from 0.20 to 0.15. The MECP were calculated using the
program code developed by Harvey.33
LSꢀ6
Reaction coordinate
Fig. 7. Energy profile of the intramolecular redox isomerization
of complex 2´a.
The Xꢀray diffraction studies of compounds 2а and 2b were
performed on a SMART APEX II CCD diffractometer (MoK
radiation, graphite monochromator,  scan mode). The strucꢀ
tures were solved by a direct method and refined by least squares
in the anisotropic fullꢀmatrix approximation for Fhkl 2. Positions
of hydrogen atoms were calculated and refined in the isotropic
approximation using the riding model. The main crystallographꢀ
ic data and refinement parameters are given in Table 3. All
It follows from Fig. 7 that the transition of adduct 2´a
from lowꢀspin form LSꢀ6 to highꢀspin form HSꢀ5 through
MECPꢀ7 is poorly probable. This is due to the low stabiliꢀ
zation energy of highꢀspin electromer HSꢀ5 of adduct 2´a
(0.8 kcal mol–1) and destabilization of MECPꢀ7 with reꢀ
spect to the starting components by 1.3 kcal mol–1. Thus,
it was shown by the quantum chemical calculations that
the observed dissociation of adducts 2 to the initial
bis(chelate) 4 and phenoxazinone 3 accompanied by a
change in the magnetic characteristics is caused by the
fact that this process is energetically preferred over the
valenceꢀtautomeric rearrangement.
Table 3. Main crystallographic data and refinement parameters
for structures 2а and 2b
Parameter
2a
2b
This study showed that synthesized adducts 2 are charꢀ
acterized by the lowꢀspin ground state including the trivaꢀ
lent cobalt atom and phenoxazinone in the radicalꢀ
monoanion form. The increase in the magnetic moment
of solutions of these compounds with the temperature rise
is caused by dissociation to the initial molecules rather
than by valence tautomerism. To accomplish this type of
intramolecular rearrangements, one has to obtain adducts,
all forms of which, including the MECP structures, are
energetically more favorable than isolated molecules of
the bis(chelate) and redoxꢀactive ligand. Now we are
searching for these structures.
Empirical formula
Molecular weight
T/K
Crystal system
Space group
Z (Z´)
a/Å
b/Å
c/Å
/deg
C57H63.50CoN4.50O4 C60H69CoN5O4
934.55
100
983.13
100
Monoclinic
P21/c
Monoclinic
P21/c
4 (1)
8 (2)
9.3949(2)
46.4300(10)
11.8471(3)
90.00
9.9261(11)
43.970(5)
24.063(3)
90.00
/deg
99.8410(10)
90.00
90.224(2)
90.00
/deg
3
V/Å
5091.7(2)
1.219
10502(2)
1.244
dcalc/g cm–3
/cm–1
3.87
3.79
Experimental
F(000)
1984
4184
2max/deg
Number of measured
reflections
Number of independent
reflections
Number of reflections
with I > 2(I)
Number of refined
parameters
R1
wR2
54
31987
55
106420
Complexes 2 were synthesized by reflux for 30 min of a benzꢀ
ene solution (5 mL) containing bis(salicylaldiminate)cobalt(II) 4
(0.3 mmol) and an equivalent amount of 2,4,6,8ꢀtetraꢀtertꢀbutylꢀ
phenoxazinꢀ1ꢀone 3. After the solvent was evaporated and the
residue was dried in air, compound 2 was recrystallized from
acetonitrile or dimethylformamide. The yields of the complexes
were 80—90%.
Compound 2a. M.p. 138—139 С. Found (%): C, 73.92;
H, 6.84; N, 4.82; Co, 6.75. C54H59CoN3O4. Calculated (%):
C, 74,29; H, 6.81; N, 4.81; Co, 6.75.
Compound 2b. M.p. 133—134 С. Found (%): C, 74.51;
H, 7.09; N, 4.73; Co, 6.61. C56H63CoN3O4. Calculated (%):
C, 74.65; H, 7.05; N, 4.66; Co, 6.54.
The structures of complexes 2a and ISQꢀ2b were determined
by a direct method and refined using the fullꢀmatrix leastꢀsquares
10983
6809
608
24089
13392
1293
0.0612
0.1676
0.945
0.0673
0.1490
0.996
Goodnessꢀofꢀfit
Residual electron
density
/e Å–3(min/
–0.543/1.354
–0.782/1.057
)
max

Adducts of cobalt(II) bis(salicylaldiminates)
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
1751
calculations were performed using the SHELXTL PLUS proꢀ
gram package.34 The coordinates of atoms and geometric paraꢀ
meters for compounds 2а and 2b were deposited with the Camꢀ
bridge Crystallographic Date Centre (CCDC 947030 and 947031,
respectively).
kin, Dokl. Akad. Nauk, 2011, 438, 485 [Dokl. Chem.
(Engl. Transl.), 2011, 438, 155].
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Chem., 2002, 41, 5810.
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Strizhakova, I. I. Vorontsov, A. V. Vologzhanina, K. A. Lysꢀ
senko, G. V. Romanenko, M. V. Fedin, V. I. Ovcharenko,
Yu. N. Bubnov, Eur. J. Inorg. Chem., 2010, 34, 5401.
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This work was financially supported by the Ministry of
Education and Science of the Russian Federation (agreeꢀ
ment No. 14.A18.21.0808) and the Council on Grants at
the President of the Russian Federation (Program for State
Support of Leading Scientific Schools of the Russian Fedꢀ
eration, Grant NShꢀ927.2012.3).
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Received July 5, 2013;
in revised form July 16, 2013