Crown-containing naphtho- and anthraquinones: Synthesis and complexation with alkali and alkaline-earth metal cations

Article abstract of DOI:10.1007/s11172-012-0323-z

Novel naphtho- and anthraquinones conjugated with benzo- and dibenzo-18-crown-6 ethers were obtained. Their complexation reactions with Groups Ia and IIa metal perchlorates in acetonitrile were studied by spectrophotometric titration. In most cases, the complexation involves the crown ether moiety; the stability constant of the resulting complex decreases in the following order: Ba²⁺ > Sr²⁺ > Ca²⁺ > Na⁺. For crown-containing anthraquinone imines characterized by prototropic imine-enamine tautomerism, the complexation shifts the equilibrium toward the imine species, which allow these compounds to be classified among a rarely occurring type of tautomeric chromoionophores. Unlike other cations, the magnesium ions preferably interact with the heteroatoms of the anthraquinone moiety (the imine N atom, the OH group, and the carbonyl O atom of the benzamido group); the logK value reaches 4.4. The chelation to the Mg²⁺ cations and the effect of the complexation on the tautomeric equilibrium was confirmed by quantum chemical calculations.

Full text of DOI:10.1007/s11172-012-0323-z

Russian Chemical Bulletin, International Edition, Vol. 61, No. 12, pp. 2282—2294, December, 2012
2282
Crownꢀcontaining naphthoꢀ and anthraquinones:
synthesis and complexation with alkali and alkalineꢀearth metal cations
T. P. Martyanov,a E. N. Ushakov,a V. A. Savelyev,b and L. S. Klimenkoc
aInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation.
Eꢀmail: martyanov89@yandex.ru; enꢀushakov@mail.ru
bN. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences,
9 prosp. Akad. Lavrent´eva, 630090 Novosibirsk, Russian Federation.
Eꢀmail: vicsav@nioch.nsc.ru
cYugra State University,
16 ul. Chekhova, 628012 KhantyꢀMansiysk, Russian Federation.
Eꢀmail: l_klimenko@ugrasu.ru
Novel naphthoꢀ and anthraquinones conjugated with benzoꢀ and dibenzoꢀ18ꢀcrownꢀ6 ethers
were obtained. Their complexation reactions with Groups Ia and IIa metal perchlorates in
acetonitrile were studied by spectrophotometric titration. In most cases, the complexation
involves the crown ether moiety; the stability constant of the resulting complex decreases in the
following order: Ba2+ > Sr2+ > Ca2+ > Na+. For crownꢀcontaining anthraquinone imines
characterized by prototropic "imine—enamine" tautomerism, the complexation shifts the equiꢀ
librium toward the imine species, which allow these compounds to be classified among a rarely
occurring type of tautomeric chromoionophores. Unlike other cations, the magnesium ions
preferably interact with the heteroatoms of the anthraquinone moiety (the imine N atom, the
OH group, and the carbonyl O atom of the benzamido group); the logK value reaches 4.4. The
chelation to the Mg2+ cations and the effect of the complexation on the tautomeric equilibrium
was confirmed by quantum chemical calculations.
Key words: naphthoquinone, anthraquinone, crown ether, chromoionophore, prototropic
tautomerism, complexation, parameterized matrix modeling, spectrophotometric titration.
The quest for highly selective analogs of natural ionoꢀ
phores such as shuttling proteins in the Na+/K+ channel,
enzyme cofactors, Mg2+—ATP, etc. resulted in the synꢀ
thesis of a great number of macrocyclic compounds.1
Crown ethers were among the first selective ionophores
obtained.2,3 Later, they have been used to synthesize a wide
range of compounds with additional (apart from ion transꢀ
fer) functions including chromophoric, luminophoric,
photochromic, electrochromic/electrochemical, and other
properties.4,5 Polyfunctionalized crown compounds can
be employed as the basis for design of optical or electroꢀ
chemical sensors capable of detecting metal cations and
some organic ions, controlled molecular devices and maꢀ
chines, biometric probes, and models of biological systems.
Among chromogenic crown compounds, quinone deꢀ
rivatives are of particular interest. They feature an addiꢀ
tional electrochromic/electrochemical function (i.e., the
tendency toward the reversible redox quinoneꢀhydroquinoꢀ
ne transition6). For this reason, the synthesis of novel
crownꢀcontaining quinones and a quantitative study of
their complexing properties are of considerable theoretiꢀ
cal and practical interest. Quantitative investigations of
the ionophoric characteristics of such compounds are curꢀ
rently represented by only a few examples.7,8
Earlier,9—12 it has been demonstrated that quinones
are convenient chromophores for the design of optical
molecular sensors (donorꢀacceptor chromoionophores4).
In the present work, we describe the synthesis of novel
crownꢀcontaining chemosensors having one or two chromoꢀ
phoric naphthoꢀ or anthraquinone moieties in their strucꢀ
tures and report the results of their complexation
with Group Ia and IIa metal perchlorates in acetonitrile
solution.
Results and Discussion
Crownꢀcontaining naphthoquinone 1 was obtained by
nucleophilic substitution of the Cl atom in 2,3ꢀdichloroꢀ
1,4ꢀnaphthoquinone (2) by the arylamino group of
4ꢀaminobenzoꢀ18ꢀcrownꢀ6 (3) (Scheme 1).13 Heating of
an ethanolic solution of the starting compound 2 and
crown ether 3 in the presence of a base followed by workup
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2261—2273, December, 2012.
1066ꢀ5285/12/6112ꢀ2282 © 2012 Springer Science+Business Media, Inc.

Crownꢀcontaining naphthoꢀ and anthraquinones
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
2283
and separation of the reaction mixture by column chroꢀ
matography afforded 4ꢀ(2ꢀchloroꢀ1,4ꢀnaphthoquinonꢀ3ꢀ
yl)aminobenzoꢀ18ꢀcrownꢀ6 (1) as the major reaction
product (55% yield).
forming 9ꢀaryloxyꢀ1,10ꢀanthraquinone (7a). 1,10ꢀAnꢀ
thraquinone derivatives are highly reactive toward nucleoꢀ
philic agents and hence the aryloxy group can easily (at
~20 C) be replaced by an arylamino group.16 The target
product 4´ꢀ(2ꢀbenzoylaminoꢀ1ꢀhydroxyꢀ9,10ꢀanthraquinꢀ
onꢀ9ꢀimino)benzoꢀ18ꢀcrownꢀ6 (8) was obtained in 70%
yield (see Scheme 3).
Scheme 1
Crown ethers with two chromogenic groups were synꢀ
thesized using the same procedure. Photocondensation of
1ꢀaryloxyꢀ9,10ꢀanthraquinones 6 with 4,4´ꢀ and 4,5´ꢀdiꢀ
aminodibenzoꢀ18ꢀcrownꢀ6 ethers (4a,b) gave isomeric
4´,4ꢀ and 4´,5ꢀbis(2ꢀbenzoylaminoꢀ1ꢀhydroxyꢀ9,10ꢀ
anthraquinonꢀ9ꢀimino)dibenzoꢀ18ꢀcrownꢀ6 ethers (9a,b)
in high yields and 4´,5ꢀbis(4ꢀbenzoylaminoꢀ1ꢀhydroxyꢀ
9,10ꢀanthraquinonꢀ9ꢀimino)dibenzoꢀ18ꢀcrownꢀ6 (9c)
(Scheme 4).
Complexation of 1,4ꢀnaphthoquinonylaminobenzocrown
ethers. Complexation of crownꢀcontaining naphthoquinoꢀ
nes 1 and 5a,b with alkali and alkalineꢀearth metal cations
in acetonitrile was studied by spectrophotometric titration
(SPT). The concentration of metal perchlorate in solution
was varied from 0 to ~0.001 mol L–1. The concentration
of the ligand was kept constant during SPT. The SPT data
obtained for the system 1—Ca(ClO4)2 are shown in Fig. 1.
The electronic absorption spectra of naphthoquinoꢀ
nes 1 and 5a,b show a wide longꢀwavelength band (LB)
with a maximum at 494—496 nm. Addition of alkali and
alkalineꢀearth metal perchlorates to solutions of these
compounds (C = (1—5)•10–5 mol L–1) shifts the LB to
the shorter wavelengths, thus indicating complexation at
the crown ether moiety.3—5
A similar procedure with dibenzocrown ethers 4a,b gave
crown derivatives 5a,b containing two naphthoquinone
moieties (Scheme 2).
Macrocyclic 9ꢀimino derivatives of 9,10ꢀanthraquinoꢀ
ne were obtained photochemically as proposed earlier.14,15
This method involves irradiation of a mixture of photoꢀ
chromic 1ꢀaryloxyꢀ9,10ꢀanthraquinone (6a) and amiꢀ
nobenzocrown ether 3 in benzene (Scheme 3).
The stability constants and electronic absorption specꢀ
tra of the complexes were calculated using parameterized
matrix modeling of SPT data.17 In all cases, experimental
When compound 6a is exposed to light, the aryl subꢀ
stituent migrates to the O atom in the periꢀposition, thus
Scheme 2
4: X = H, Y = NH2 (a); X = NH2, Y = H (b)
5: R1 = H, R2 = Nq (a); R1 = Nq, R2 = H (b)
Nq =

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Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
Mart´yanov et al.
Scheme 3
7a
Scheme 4
4: X = H, Y = NH2 (a); X = NH2, Y = H (b)
6: R1 = NHCOPh, R2 = H (a); R1 = H, R2 = NHCOPh (b)
7: R1 = NHCOPh (a, b), H (c); R2 = H (a, b), NHCOPh (c)
9: R1 = NHCOPh (a, b), H (c); R2 = H (a, b), NHCOPh (c); R3 = H (a), Aq (b, c); R4 = Aq (a), H (b, c)
Aq =
data were approximated well by an equilibrium reaction
leading to a 1 : 1 complex
where L is the ligand molecule, Mn+ is the metal cation,
and K1:1 is the stability constant of the complex. The
logK1:1 values and the spectral characteristics of the comꢀ
plexes are given in Table 1.
L + Mn+
L•Mn+
,
(1)

Crownꢀcontaining naphthoꢀ and anthraquinones
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
2285
D
Benzocrownꢀcontaining naphthoquinone 1 has a lowꢀ
er cationꢀinduced hypsochromic effect  compared to
a phenylazacrown analog10 but the stability constants of
its complexes are substantially higher.
Figure 2 allows one to compare the plots of logK vs.
the metal cation radius (rM) for the complexes of crownꢀ
containing naphthoquinone 1 and its bischromophoric
analog 5a with alkali and alkalineꢀearth metal cations.
The stability of the complexes of compounds 1 and 5a,b
with alkalineꢀearth metal cations increases with an inꢀ
crease in rM, which is typical of benzoꢀ and dibenzoꢀ18ꢀ
crownꢀ6 derivatives.18 A similar trend is observed in the
plot of logK vs. rM for complexes 1 with alkali metal catꢀ
ions, which agrees with the literature data for benzoꢀ18ꢀ
0.3
1
2
0.1
500
600
/nm
crownꢀ6 ethers.19 The stability constants of the Ca2+, Sr2+
,
Fig. 1. Electronic absorption spectra of compound 1 in MeCN
(CL = 4.4•10–5 mol L–1) at different concentrations of Ca(ClO4)2
(CM = (0—1.3)•10–4 mol L–1): (1) free ligand and (2) comꢀ
plex 3•Ca2+
and Ba2+ complexes with naphthoquinone 1 are much
higher than those of the complexes derived from isomeric
bisnaphthoquinones 5a,b. At the same time, the logK valꢀ
ues of complex 1•Mg2+ are slightly lower than those of
complexes 5a,b•Mg2+. It is worth noting that the Na+/K+
selectivity is inverted when moving from naphthoquinone
to bisnaphthoquinone. The appreciable differences beꢀ
tween compounds 1 and 5a,b in complexing ability and
.
Table 1. Stability constants of the complexes of compounds 1
and 5a,b with alkali and alkalineꢀearth metal cations and the
spectrophotometric characteristics of these compounds and their
complexes*
selectivity are due to replacement of the single Csp3—Csp
3
bond in benzocrown ether 1 by an aromatic Csp2—Csp
2
bond, which reduces the electron density on two O atoms
and makes the macrocycle conformationally less flexible
and slightly contracted.
Complexation of 9,10ꢀanthraquinonꢀ9ꢀiminobenzoꢀ
crown ethers. 1ꢀHydroxyꢀ9,10ꢀanthraquinone 9ꢀimines are
known to exist as mixtures of two tautomers (imine and
enamine species).21 The position of tautomeric equilibriꢀ
um depends on a variety of factors such as the substituent
Complex
logK

max/nm

•10–3
–/nm
max
/L mol–1 cm–1
1
494
486
488
486
481
478
477
480
496
486
488
477
479
480
480
494
488
490
477
479
480
480
6.0
6.20
6.06
6.11
6.32
6.23
6.25
6.04
10.0
10.6
10.8
11.1
11.1
10.9
11.0
6.7
—
8
6
1•Li+
2.16
4.78
5.06
2.36
8.16
8.07
8.92
1•Na+
1•K+
8
1•Mg2+
1•Ca2+
1•Sr2+
1•Ba2+
5a
13
15
15
15
—
10
8
19
17
16
16
—
6
logK
5a•Na+
5a•K+
5a•Mg2+
5a•Ca2+
5a•Sr2+
5a•Ba2+
5b
5b•Na+
5b•K+
5b•Mg2+
5b•Ca2+
5b•Sr2+
5b•Ba2+
4.78
4.60
2.74
6.18
7.01
7.18
9
8
7
6
5
4
3
2
1´
2´
4.82
4.62
2.80
6.26
7.11
7.29
6.83
6.88
7.13
7.00
6.97
7.07
1
2
4
17
15
14
14
Li+ Mg2+
0.06
Na+ Ca2+
0.10
Sr2+
0.12
K+ Ba2+
* In MeCN (water content < 0.03 vol.%) at 25 C, CL
=
= (1—5)•10–5 mol L–1, CM = 0—0.001 mol L–1, K = [L•Mn+]/
([L][Mn+]), the total measurement error of K is within 20%
(the standard error for K in the modeling of the SPT data does
not exceed 1%), max is the position of the LB maximum, max is
the molar absorption coefficient at max,  = max(complex) –
– max(dye).
0.08
rM/nm
Fig. 2. Plots of logK vs. the metal cation radius rM for the comꢀ
plexes of compounds 1 (1) and 5a (2) with alkali and alkalineꢀ
earth metal cations in MeCN. The rM values are taken from
Ref. 20.

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Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
Mart´yanov et al.
•103/L mol–1 cm–1
nature, the polarity of the solvent, and the phase state.
Earlier,16 we have proved that 9ꢀaryliminoꢀ1ꢀhydroxyꢀ
9,10ꢀanthraquinones predominantly exist in the imine
form: the imine/enamine ratio in deuterated acetonitrile
is ~4 : 1 (15N NMR data).
The electronic absorption spectrum of crown comꢀ
pound 8 in acetonitrile is shown in Fig. 3. The spectral
pattern suggests the presence of two unresolved bands in
the visible region. To position the maxima of these bands
(max), we approximated the spectral curves with two logꢀ
normal22 functions (see Fig. 3). The band with max = 435 nm
was assigned to the imine tautomer of compound 8, while
the less intense band with max = 545 nm was assigned to
the enamine tautomer (Scheme 5). Crown compounds
9a,b have similar absorption characteristics.
8
1
6
3
2
4
2
4
0
400
500
600
/nm
Fig. 3. Experimental electronic absorption spectrum of crown
compound 8 in acetonitrile (1) and its approximation (2) by the
sum of two functions lognormal (3, 4).
Scheme 5
shifts the prototropic equilibrium "imine—enamine" toꢀ
ward the imine tautomer. This conclusion agrees with the
results of quantum chemical calculations (see next secꢀ
tion). In addition, complexation is accompanied by small
hypsochromic shifts of the absorption bands due to both
tautomers. The observed hypochromic and hypsochromic
changes are due to the electronꢀwithdrawing effect of the
cation present in the crown cavity on the chromophoric
fragment.
Imine (435 nm)
For most of the ligand—metal salt systems studied, the
SPT patterns were similar to that observed for the system
8—Ba(ClO4)2 (except for the system 9a—Mg(ClO4)2, see
below).
Using parameterized matrix modeling,17 we found that
SPT data are always (except for titration with the magneꢀ
sium salt) approximated well by an equilibrium reaction
D
0.6
Enamine (545 nm)
Complexation of crownꢀcontaining imines 8 and 9a,b
with alkali and alkalineꢀearth metal cations in acetonitrile
was studied by spectrophotometric titration. The concenꢀ
tration of metal perchlorate in solution was varied from 0
to ~0.01 mol L–1. The concentration of the ligand was
kept constant during SPT. The SPT data obtained for the
system 8—Ba(ClO4)2 are shown in Fig. 4.
0.4
2
1
0.2
With an increase in the concentration of the metal salt,
the absorption by the enamine tautomer of compound 8
(~540 nm) becomes substantially less intense, while the
absorption band of the imine tautomer (~430 nm) inꢀ
creases. Similar spectral changes have been noted earlier
for 1ꢀhydroxyꢀ9,10ꢀanthraquinone 9ꢀarylimines as the solꢀ
vent polarity decreases.16 Most likely, an interaction of
a metal cation with the crown ether moiety of compound 8
400
500
600
/nm
Fig. 4. Electronic absorption spectra of crown compound 8 in
MeCN (CL = 1.2•10–5 mol L–1) at different concentrations of
Ba(ClO4)2 (CM = (0—3)•10–5 mol L–1): (1) free ligand and (2)
complex 8•Ba2+
.

Crownꢀcontaining naphthoꢀ and anthraquinones
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
2287
Table 2. Equilibrium constants for the complexation reactions of
compounds 8 and 9a,b with alkali and alkalineꢀearth metal catꢀ
ions and the spectrophotometric characteristics of these comꢀ
pounds and their complexesa
leading to a 1 : 1 complex. When treating the matter riꢀ
gorously, these ligand—metal cation systems contain
four lightꢀabsorbing components whose concentrations
are determined by the equilibrium reactions shown in
Scheme 6.
im
im
im
en c
Complex
logKb


•10–3


max
max
/nm
/L mol–1 cm–1
/nm
Scheme 6
8
—
435
432
432
436
432
8.9
—
.—
8•Na+
8•К+
8•Mg2+
4.48
4.73
4.13
1.64
9.70
9.77
9.06
9.73
–3
–3
+1
–3
0.187
0.237
0.162
0.335
.
0.465
0.488
0.470
.—
8•Mg2+
+ Mg2+
8•Ca2+
8•Sr2+
8•Ba2+
9a
9a•Na+
9a•Mg2+
9a•Mg2+
+ Mg2+
9a•Ca2+
9a•Sr2+
9a•Ba2+
9b
+
7.52
7.84
8.18
—
3.97
4.41
1.40
427
427
427
435
432
440
432
9.98
10.0
9.95
16.0
16.8
15.5
17.3
–8
–8
–8
—
Here, Im and En are the imine and enamine tautomers
of crownꢀcontaining anthraquinones, respectively, and
K1—K4 are the equilibrium constants.
Obviously, the ratios of the concentrations [Im]/[En]
and [Im•Mn+]/[En•Mn+] do not vary with the concenꢀ
tration of the metal cation; so such systems can formally
be described by two lightꢀabsorbing components [L] =
= [Im] + [En] and [L•Mn+] = [Im•Mn+] + [En•Mn+
and complexation in these systems, by an equilibrium of
the type (1).
–3
0.278
+5 –0.139
–3
+
0.415
5.19
5.88
6.03
—
4.08
4.94
6.06
6.25
429
427
429
432
428
428
428
429
17.6
17.8
17.6
16.0
16.7
17.4
17.7
17.7
–6
–8
–6
—
–4
–4
–4
–3
0.349
0.511
0.479
.—
0.259
0.425
0.497
0.459
]
9b•Na+
9b•Ca2+
9b•Sr2+
9b•Ba2+
It can easily be demonstrated that the apparent stabilꢀ
ity constant K1:1 is related to the constants K1, K3, and K4
by the following equation:
a In MeCN (water content < 0.03 vol.%) at 25 C, CL = (3—12)•
im
•10–6 mol L–1, CM = (0.3—1400)•10–5 mol L–1; 
position of the LB maximum of the imine species, 
is the
max
K1:1 = K1[(K4 + 1)/(K3 + 1)].
im
is the
max
im
,
molar absorption coefficient of the the imine species at 
max
Since experimental data provide K3 > K4, the apparent
constant K1:1 is somewhat lower than the stability conꢀ
stant of the complex of imine tautomer K1.
For the systems 8—Mg(ClO4)2 and 9a—Mg(ClO4)2,
an acceptable error in the approximation of SPT data was
achieved with two equilibrium reactions:
im =  im(complex) –  im(dye).
max
max
b K = [L•Mn+]/([L][Mn+]) for the complexes L : Mn+ (1 : 1),
K = [L•(Mn+)2]/([L•Mn+][Mn+]) for the complexes L : Mn+
(1 : 2); the total measurement error of K is within 20% (the
standard error for K in the modeling of the SPT data does not
exceed 1%).
c
en = [en(dye) – en(complex)]/en(dye), where en is the moꢀ
lar absorption coefficient of the enamine species at 545 (8),
558 (9a), and 548 nm (9b).
L + Mg2+
L•Mg2+
,
L•Mg2+ + Mg2+
L•(Mg2+)2.
The plots of logK1:1 vs. rM (Fig. 5) allow convenient
comparison of anthraquinone 8, bisanthraquinone 9a, and
naphthoquinone 1 in complexing ability. In the case of
crownꢀcontaining anthraquinones, moving from a monoꢀ
chromophore to a bischromophore changes the complexꢀ
ing ability and selectivity, generally in the same way as
noted above for crownꢀcontaining naphthoquinones (see
Fig. 2). The causes of these changes were discussed in the
preceding section.
The complexes of anthraquinone 8 are mostly less staꢀ
ble than the corresponding complexes of naphthoquinone
1. A striking exception is provided by Mg2+ complexes.
Analogous conclusions can be made when comparing data
for crownꢀcontaining bisanthraꢀ and bisnaphthoquinones
9a,b and 5a,b, respectively.
The equilibrium constants of the complexation reacꢀ
tions of compounds 8 and 9a,b with alkali and alkalineꢀ
earth metal cations and the spectrophotometric characꢀ
teristics of these compounds and their complexes are givꢀ
en in Table 2. To characterize the extent of cationꢀinꢀ
duced spectral changes, we employed two parameters: the
shift of the longꢀwavelength maximum (im) in the elecꢀ
tronic absorption spectrum and the relative hypochromic
effect en at the absorption maximum of the enamine
tautomer (see Table 2). The en values for alkali and
alkalineꢀearth metal cations amount to 0.28 and 0.51, reꢀ
spectively. The maximum hypochromic effects are obꢀ
served for the complexation with Sr2+ (en = 0.49—0.51).

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Mart´yanov et al.
logK
Scheme 7
9
8
7
6
5
4
3
2
1
2
3
1
2
Li+ Mg2+
0.06 0.08
Na+ Ca2+
0.10
Sr2+
0.12
K+ Ba2+
rM/nm
Fig. 5. Plots of logK1:1 vs. the metal cation radius rM for the
complexes of naphthoquinone 1 (1) and anthraquinones 8 (2)
and 9a (3) with alkali and alkalineꢀearth metal cations in MeCN.
Let us consider distinctive features in the complexꢀ
ation of crownꢀcontaining anthraquinones with Mg2+
.
First, according to SPT data, the systems 8—Mg2+ and
9a—Mg2+ produce two types of complexes: L•Mg2+ and
L•(Mg2+)2. Second, the logK1:1 values with Mg2+ for comꢀ
pounds 8 and 9a are higher by ~1.5 orders of magnitude
than those of the corresponding naphthoquinones 1 and 5a,
while they are noticeably lower with other cations. These
facts can be explained rationally if one assumes that crownꢀ
containing anthraquinones contain, apart from the crown
ether moiety, an additional, more efficient site for coordiꢀ
nation to Mg2+. Three heteroatoms of the chromophore
moiety can serve as such a site (Scheme 7).
Mg(ClO4)2, we detected only two equilibrium complexꢀ
ation reactions.
The electronic absorption spectra of compounds 8 and
9a, as well as those of their Mg2+ complexes, are shown in
Figs 6 and 7, respectively.
For bischromophoric molecules 9a,b, the presence
of three coordinative sites could reasonably be asꢀ
sumed; however, in the concentration range studied for
Different changes observed in the electronic absorpꢀ
tion spectra upon the formation of complexes 8•Mg2+
•103/L mol–1 cm–1
•103/L mol–1 cm–1
16
10
8
2
1
12
2
6
8
3
1
4
4
3
2
400
500
600
/nm
400
500
600
/nm
Fig. 6. Electronic absorption spectra of crown compound 8 (1)
and complexes 8•Mg2+ (2) and 8•(Mg2+)2 (3) in acetonitrile.
Fig. 7. Electronic absorption spectra of compound 9a (1) and
complexes 9a•Mg2+ (2) and 9a•(Mg2+)2 (3) in acetonitrile.

Crownꢀcontaining naphthoꢀ and anthraquinones
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
2289
Table 3. Total energies E and bond lengths d in the tautomers of compound 8 and complex 8•Ca2+, calculated by the M06ꢀ2X/
6ꢀ31G(d)/COSMO(MeCN) method
Compound
E/au
d/Å
C(9)—N
C(1)O—H
C(9)N—H
C(4´)—N
C(1´)O—Ca C(2´)O—Ca
Imine 8
–2217.25201
–2217.25120
–2417.19611
1.007
1.667
1.002
1.682
1.657
1.039
1.686
1.038
1.409
1.422
1.407
1.420
1.290
1.327
1.290
1.331
—
—
2.462
2.467
—
—
2.444
2.451
Enamine 8
Imine 8•Ca2+
Enamine 8•Ca2+ –2417.19340
(en = 0.162) and 9a•Mg2+ (en = –0.139) suggest
a structural difference between these complexes. Most likeꢀ
ly, the metal cation in complex 9a•Mg2+ interacts with
the heteroatoms of both chromophoric moieties (i.e., this
complex has a pseudocyclic structure). This assumption
agrees with the fact that complex 9a•Mg2+ is superior to
complex 8•Mg2+ in thermodynamic stability (see Table 2).
The formation of binuclear complex 9a•(Mg2+)2 probaꢀ
bly does not affect the pseudocyclic structure, and the
magnesium cation is coordinated by the crown ether moiꢀ
ety. The possibility of formation of pseudocyclic complex
9a•Mg2+ was demonstrated by quantum chemical calcuꢀ
lations (see below).
thraquinone moiety with participation of two MeCN molꢀ
ecules (Scheme 8).
The geometries of structures 8A and 8B and the MeCN
molecule in the gas phase were completely optimized by
the DFT method with the functional M06ꢀ2X and the
basis set 6ꢀ31G(d). The calculated models of the comꢀ
a
Mg
O
N
Quantum chemical modeling. The effect of the comꢀ
plexation of crownꢀcontaining imines on the tautomeric
equilibrium imine—enamine in acetonitrile was studied
using a DFT approach. We used the hybrid functional
M06ꢀ2X,23 which is more efficient than "standard" funcꢀ
tionals in the description of noncovalent interactions, and
the basis set 6ꢀ31G(d). The solvent effect was included in
the model with the COSMO method.24 The calculated
geometries of the tautomers of complex 8•Ca2+ are shown
in Fig. 8. The total energies and bond lengths in the tauꢀ
tomers of compounds 8 and 8•Ca2+ are given in Table 3.
The tautomers of compound 8 are very close in energy;
i.e., the calculated data suggest the coexistence of both
structures in solution. The imine tautomer of compound 8
is slightly more preferable (E(enamine) – E(imine) =
= 2.1 kJ mol–1), in agreement with experimental data (see
Fig. 3). Upon complexation, the difference between the
total energies of the enamine and imine tautomers inꢀ
creases (E(enamine) – E(imine) = 5.9 kJ mol–1); i.e.,
the equilibrium is shifted toward the imine tautomer,
which agrees with the experiment as well (see Fig. 4). The
cationꢀinduced shifts of the tautomeric equilibrium imiꢀ
ne—enamine, which are observed for anthraquinones 8
and 9a,b, allow these compounds to be classified among
a rarely occurring type of crownꢀcontaining tautomeric
chromoionophores.25,26
C
C(1´)
H
C(2´)
C(4´)
C(9)
C(1)
b
C(1´)
C(2´)
C(4´)
C(9)
C(1)
To estimate the efficiency of two different coordinaꢀ
tive sites in crown compound 8 with respect to Mg2+, we
calculated the energy of a hypothetical transfer of the magꢀ
nesium cation from the crown ether cavity to the anꢀ
Fig. 8. 3D models of the tautomers of complex 8•Ca2+ calculatꢀ
ed by the M06ꢀ2X/6ꢀ31G(d)/COSMO(MeCN) method.*
* Figs 8—10 are available in full color in the onꢀline version of the journal (http://www.springerlink.com/issn/1573ꢀ9171/current).

2290
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
Mart´yanov et al.
Scheme 8
8•Mg2+
(8A)
8•Mg2+ •(CN—Me)2 (8B)
antr
crown
plexes are shown in Fig. 9. The DFT energy for the reacꢀ
Unfortunately, the COSMO method precludes reliable esꢀ
timation of the solvation energy difference between the
complexes of the types 8A and 8B.27 That is why we estiꢀ
mated the energy of Mg2+ transfer in acetonitrile while
considering only the solvation energy for two MeCN molꢀ
ecules (–53.9 kJ mol–1) and ignoring the solvation energy
difference between the complexes. In this approximation,
the transfer energy is –14.7 kJ mol–1, which is qualitativeꢀ
ly consistent with the experimentally substantiated asꢀ
sumption that Mg2+ preferentially interacts with the
heteroatoms of the anthraquinone moiety of compound 8.
We also theoretically studied the structure of the preꢀ
sumed pseudocyclic complex 9a•Mg2+. Two structures of
complex 9a•Mg2+ (pseudocyclic and open) are shown in
Fig. 10. Both are optimized in the gas phase by the DFT
method with the functional PBE28 and the basis set 3z. In
structure closed(9a•Mg2+)•MeCN (see Fig. 10, a), the
magnesium cation coordinates to a solvent molecule, three
heteroatoms of one chromophoric moiety, and one heteroꢀ
atom of the other. In structure open(9a•Mg2+)•2MeCN
(see Fig. 10, b), the metal cation coordinates to two solꢀ
vent molecules and three heteroatoms of one chromoꢀ
phoric moiety. The coordination bond lengths in these
complexes are 1.95—2.22 Å.
tion in the gas phase (see Scheme 8) is –68.6 kJ mol–1
.
a
Mg
O
N
C
H
8A
b
To estimate the relative stability of the pseudocyclic
complex 9a•Mg2+, we considered a ring opening reaction
involving a solvent molecule
closed(9a•Mg2+)•MeCN + MeCN
open(9a•Mg2+)•2MeCN.
The energy of this reaction was calculated with allowꢀ
ance for the energy of MeCN solvation (~–27 kJ mol–1
,
8B
see above) while ignoring the solvation energy difference
between the complexes closed(9a•Mg2+)•MeCN and
open(9a•Mg2+)•2MeCN. In this approximation, the DFT
Fig. 9. 3D models of two complexes of compound 8 with Mg2+
calculated by the DFT/M06ꢀ2X method: (a) the Mg2+ cation in
the crown ether cavity and (b) the Mg2+ cation coordinated to
the heteroatoms of the anthraquinone moiety and two MeCN
molecules. The DFT energies of structures 8A and 8B (see
Scheme 8) in the gas phase are –2416.9330 and –2682.3439 au,
respectively.
energy for the opening of the pseudoꢀring is ~19.7 kJ mol–1
,
which suggests higher stability of the pseudocyclic
complex. Detailed quantum chemical analysis of strucꢀ
ture 9a•Mg2+ in a solvent is very laborious. Our calculaꢀ

Crownꢀcontaining naphthoꢀ and anthraquinones
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
2291
a
Mg
O
N
C
closed(9a•Mg2+)•MeCN
b
open(9a•Mg2+)•2MeCN
Fig. 10. PBE/3zꢀoptimized pseudocyclic (a) and open (b) structures of complex 9a•Mg2+ in the gas phase; the hydrogen atoms are
omitted. The calculated DFT energies of closed(9a•Mg2+)•MeCN and open(9a•Mg2+)•2MeCN in the gas phase are –3842.6088
and –3975.2471 au, respectively.
tion only shows the fundamental possibility of formation
of a pseudocyclic Mg2+ complex with crownꢀcontaining
bisanthraquinone 9a.
magnesium cations, as well as the shift of the tautomeric
equilibrium upon the complexation, were confirmed by
quantum chemical calculations. The results obtained can
be used in the design of novel optical chemosensors from
accessible derivatives of naphthoꢀ and anthraquinone and
crown ethers.
We synthesized novel crownꢀcontaining naphthoꢀ and
anthraquinones, which act as photometric indicators for
alkali and alkalineꢀearth metal cations. 1,4ꢀNaphthoꢀ
quinone derivatives bind metal cations by the crown ether
moiety, which results in a hypsochromic shift of the longꢀ
wavelength absorption band. The cationꢀinduced changes
in the electronic absorption spectra of crownꢀcontaining
1ꢀhydroxyꢀ9,10ꢀanthraquinone 9ꢀimines are mainly due
to the shift of the tautomeric equilibrium imineꢀenamine
to the imine tautomer. We demonstrated that these comꢀ
pounds contain, apart from the crown ether moiety, an
Experimental
Acetonitrile (special purity grade, class 0, water content
<0.03 vol.%, Criochrom) was used as purchased. Benzene and
ethanol were dried with precalcined (220 C) CaCl2 and CuSO4,
respectively, followed by distillation in vacuo;29,30 Mg(ClO4)2,
Ca(ClO4)2, Sr(ClO4)2, and Ba(ClO4)2 were dried in vacuo at
230 C before use; LiClO4, NaClO4, and KClO4 were dried at
170 C. Isomeric diaminodibenzoꢀ18ꢀcrownꢀ6 ethers 4a,b were
prepared by reduction of 4,4´ꢀ and 4,5´ꢀdinitrodibenzoꢀ18ꢀ
additional, more efficient site for coordination to Mg2+
.
This site is represented by three heteroatoms of the anꢀ
thraquinone moiety. The structures of the complexes with

2292
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
Mart´yanov et al.
crownꢀ6 ethers with hydrazine hydrate in diethylene glycol dimꢀ
ethyl ether in the presence of Pd/C as a catalyst. The isomers of
dinitrodibenzocrown ethers were synthesized by nitration of
dibenzoꢀ18ꢀcrownꢀ6 according to a known procedure31 and
additionally purified by crystallization from N,Nꢀdimethylꢀ
formamide.
Electronic absorption spectra were recorded on a Specordꢀ
M40 spectrophotometer in quartz cells (l = 4.75 cm) with tightly
fitted groundꢀglass stoppers.
IR spectra (KBr pellets) were recorded on Vectorꢀ22 spectroꢀ
photometers (Bruker).
1H NMR spectra were recorded on a Bruker WPꢀ200SY inꢀ
strument in CDCl3 and DMSOꢀd6. Chemical shifts  are referꢀ
enced to SiMe4 as the internal standard.
Mass spectra (EI, 70 eV) were measured on a Finnigan MATꢀ
8200 instrument (injector temperature 100—220 C).
Column chromatography was carried out on silica gel
(5—140 m); for TLC, Silufol UVꢀ254 standard plates were emꢀ
ployed. Melting points were determined on a Kofler hot stage.
Synthesis of compounds 1 and 5a,b (general procedure).
A mixture of compound 2 (0.1 g, 0.44 mmol), 3 (0.138 g,
0.44 mmol), or 4a (4b) (0.343 g, 0.88 mmol) and sodium acetate
(0.009 g, 0.10 mmol) was stirred in ethanol (40 mL) at 60 C for
3 h. The course of the reaction was monitored by TLC. The
reaction mixture was poured into water (50 mL) and kept at
~20 C for 24 h. The precipitate that formed was filtered off,
dried, and purified by column chromatography on SiO2 with
benzene and ethanol—benzene (1 : 2) as eluents. The unreacted
starting naphthoquinone was recovered from a first, light yellow
fraction of the eluate. By increasing the polarity of the eluent,
the main redꢀviolet fraction containing the target product was
isolated.
3ꢀChloroꢀ2ꢀ[(2,3,5,6,8,9,11,12,14,15ꢀdecahydrobenzo[b]ꢀ
[1,4,7,10,13,16]hexaoxacyclooctadecinꢀ18ꢀyl)amino]naphthoꢀ
quinone (1). Yield 0.125 g (55%). 1H NMR (DMSOꢀd6),
: 3.54—4.09 (m, 16 H, OCH2CH2); 6.70 (dd, 1 H, H(5´),
J = 8.5 Hz, J = 2.2 Hz); 6.80 (d, 1 H, H(3´), J = 2.2 Hz); 6.90
(d, 1 H, H(6´), J = 8.5 Hz); 7.80 (m, 1 H, H(6)); 7.85 (m, 1 H,
H(7)); 8.01 (m, 1 H, H(5)); 8.03 (m, 1 H, H(8)); 9.20 (br.s, 1 H,
NH). IR (/cm—1): 3437 (N—H); 3325 (C—Harom); 2920, 2875
(CH2); 1672, 1643 (C=O); 1597 (C=C); 1570 (C=Carom).
Found (%): C, 60.45; H, 5.36; N, 2.61. C26H28ClNO8. Calcuꢀ
lated (%): C, 60.29; H, 5.45; N, 2.70.
(N—H); 3134, 3107 (C—Harom); 2927, 2876 (CH2); 1676, 1644
(C=O); 1595 (C=Carom). Found (%): C, 62.49; H, 4.07; N, 3.53.
C40H32Cl2N2O10. Calculated (%): C, 62.26; H, 4.18; N, 3.63.
Synthesis of compounds 8 and 9a—c (general procedure).
A solution of 2ꢀ (6a) or 4ꢀbenzoylaminoꢀ1ꢀ(4ꢀtertꢀbutylphenꢀ
oxy)ꢀ9,10ꢀanthraquinone (6b) (0.1 g, 0.2 mmol) and 4ꢀaminoꢀ
benzoꢀ18ꢀcrownꢀ6 (2) (0.08 g, 0.25 mmol) or 4,4´(4,5´)ꢀdiꢀ
aminodibenzoꢀ18ꢀcrownꢀ6 (4a,b) (0.06 g, 0.15 mmol) in dry
benzene (100 mL) was exposed to the full light of an SVDꢀ125A
mercury lamp (1.5—2 h) or to sunlight (4—5 h). Photolysis was
carried out at ~20 C until the starting compound was completeꢀ
ly consumed (monitoring by TLC). The solvent was removed
in vacuo at 40 C and the residue was washed with hexane, filꢀ
tered off, and dried at ~20 C. Then the residue was dissolved in
benzene (10—15 mL) and purified by column chromatography
on SiO2 with benzene and ethanol—benzene (1 : 3) as eluents.
A first, yellow fraction eluted with benzene contained 2ꢀbenzoylꢀ
aminoꢀ1ꢀhydroxyꢀ9,10ꢀanthraquinone as a byꢀproduct. Subseꢀ
quent gradient elution with increasing polarity of the eluent
(through addition of ethanol) afforded a brown fraction containꢀ
ing the target product.
Nꢀ{9ꢀ[(2,3,5,6,8,9,11,12,14,15ꢀDecahydrobenzo[b][1,4,7,
10,13,16]hexaoxacyclooctadecinꢀ18ꢀyl)imino]ꢀ1ꢀhydroxyꢀ10ꢀ
oxoꢀ9,10ꢀdihydroanthracenꢀ2ꢀyl}benzamide (8). Yield 0.091 g
1
(70%), m.p. 187—189 C. H NMR (DMSOꢀd6), : 3.66—4.12
(m, 16 H, OCH2CH2); 6.84 (dd, 1 H, H(5´), J = 9.0 Hz,
J = 2.2 Hz); 6.99 (d, 1 H, H(3´), J = 2.2 Hz); 7.07 (d, 1 H,
H(6´), J = 9.0 Hz); 7.54—7.68 (m, 7 H, H(6), H(7), Ph); 7.72
(d, 1 H, H(3), J = 8.5 Hz); 7.99 (m, 1 H, H(8)); 8.20 (m, 1 H,
H(5)); 8.48 (d, 1 H, H(4), J = 8.5 Hz); 9.70 (s, 1 H, NH); 16.97
(s, 1 H, OH). IR (/cm–1): 3388 (N—H); 3071 (C—Harom);
2933, 2874 (CH2); 1671, 1660 (C=O, C=N); 1590 (C=Carom).
Found (%): C, 67.88; H, 5.62; N, 4.21. C37H36N2O9. Calculatꢀ
ed (%): C, 68.09; H, 5.56; N, 4.29.
N,N´ꢀ{9,9´ꢀ[(6,7,9,10,17,18,20,21ꢀOctahydrodibenzo[b,k]ꢀ
[1,4,7,10,13,16]hexaoxacyclooctadecineꢀ2,14ꢀdiyl)diimino]bisꢀ
(1ꢀhydroxyꢀ10ꢀoxoꢀ9,10ꢀdihydroanthracenꢀ2ꢀyl)}dibenzamide
(9a). Yield 0.156 g (75%), m.p. 173—176 C. 1H NMR (CDCl3),
: 4.05—4.21 (m, 16 H, OCH2CH2); 6.50—7.00 (m, 6 H, H(3´),
H(3), H(5´), H(5), H(6´), H(6)); 7.00—7.40 (m, 4 H, H(6),
H(7)); 7.51 (m, 10 H, 2 Ph); 7.86 (d, 1 H, H(3), J = 8.5 Hz); 7.94
(m, 2 H, H(8)); 8.31 (m, 2 H, H(5)); 8.77 (d, 2 H, H(4),
J = 8.5 Hz); 9.25 (br.s, 2 H, NH); 17.13 (s, 2 H, OH). IR (/cm–1):
3356 (N—H); 3069, 3036 (C—Harom); 2962, 2928 (CH2); 1682,
1662 (C=O, C=N); 1591 (C=Carom). MS (EI, 70 eV), m/z: 1040
2,2´ꢀ[(6,7,9,10,17,18,20,21ꢀOctahydrodibenzo[b,k][1,4,7,
10,13,16]hexaoxacyclooctadecineꢀ2,14ꢀdiyl)diamino]bis(3ꢀchloroꢀ
naphthoquinone) (5a). Yield 0.085
g
(25%). 1H NMR
[M+]. Found (%): C, 71.37; H, 4.73; N, 5.09. C62H48N4O12
Calculated (%): C, 71.53; H, 4.64; N, 5.38.
.
(CDCl3—DMSOꢀd6), : 3.83—4.04 (m, 16 H, OCH2CH2); 6.68
(dd, 2 H, H(5´,5), J = 8.5 Hz; J = 2.2 Hz); 6.81 (d, 2 H,
H(3´,3), J = 2.2 Hz); 6.89 (d, 2 H, H(6´,6), J = 8.5 Hz); 7.78
(m, 2 H, H(6)); 7.85 (m, 2 H, H(7)); 8.02 (m, 4 H, H(5,8));
8.62 (br.s, 2 H, NH). IR (/cm ): 3437 (N—H); 3325
(C—Harom); 2920, 2875 (CH2); 1672, 1643 (C=O); 1597, 1570
(C=Carom); 1132 (C—O). Found (%): C, 62.54; H, 4.04; N, 3.51.
C40H32Cl2N2O10. Calculated (%): C, 62.26; H, 4.18; N, 3.63.
2,2´ꢀ[(6,7,9,10,17,18,20,21ꢀOctahydrodibenzo[b,k]
[1,4,7,10,13,16]hexaoxacyclooctadecineꢀ2,13ꢀdiyl)diamino]
bis(3ꢀchloronaphthoquinone) (5b). Yield 0.078 g (23%). 1H NMR
(CDCl3—DMSOꢀd6), : 3.88—4.09 (m, 16 H, OCH2CH2);
6.63—6.66 (m, 4 H, H(5´), H(3´), H(4), H(6)); 6.76 (d, 2 H,
H(6´), H(3), J = 8.5 Hz); 7.63—7.75 (m, 4 H, H(6), H(7)); 8.02
(m, 4 H, H(5), H(8)); 8.62 (br.s, 2 H, NH). IR (/cm–1): 3202
N,N´ꢀ{9,9´ꢀ[(6,7,9,10,17,18,20,21ꢀOctahydrodibenzo[b,k]ꢀ
[1,4,7,10,13,16]hexaoxacyclooctadecineꢀ2,13ꢀdiyl)diimino]ꢀ
bis(1ꢀhydroxyꢀ10ꢀoxoꢀ9,10ꢀdihydroanthracenꢀ2ꢀyl)}dibenzamide
(9b). Yield 0.162 g (78%), m.p. 165—169 C. 1H NMR (CDCl3),
: 3.88—4.25 (m, 16 H, OCH2CH2); 6.18 (dd, 2 H, H(5´), H(4),
J = 8.5 Hz, J = 2.5 Hz); 6.25 (d, 2 H, H(3´), H(6), J = 2.5 Hz);
6.68 (d, 2 H, H(6´), H(3), J = 8.5 Hz); 7.20—7.65 (m, 14 H,
H(6), H(7), 2 Ph); 7.86 (d, 2 H, H(3), J = 8.5 Hz); 7.95 (m, 2 H,
H(8)); 8.31 (m, 2 H, H(5)); 8.81 (d, 2 H, H(4), J = 8.5 Hz); 9.29
(br.s, 2 H, NH); 17.19 (s, 2 H, OH). IR (/cm–1): 3386 (N—H);
3073 (C—Harom); 2962, 2930 (CH2); 1673, 1657 (C=O, C=N);
1591 (C=Carom). MS (EI, 70 eV), m/z: 1040 [M+]. Found (%):
C, 71.14; H, 4.98; N, 5.45. C62H48N4O12. Calculated (%):
C, 71.53; H, 4.64; N, 5.38.

Crownꢀcontaining naphthoꢀ and anthraquinones
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
2293
N,N´ꢀ{10,10´ꢀ[(6,7,9,10,17,18,20,21ꢀOctahydrodibenzoꢀ
[b,k][1,4,7,10,13,16]hexaoxacyclooctadecineꢀ2,13ꢀdiyl)diꢀ
imino]bis(4ꢀhydroxyꢀ9ꢀoxoꢀ9,10ꢀdihydroanthracenꢀ1ꢀyl)}dibenzꢀ
amide (9c). Yield 0.15 g (72%), m.p. 137—140 C. 1H NMR
(CDCl3), : 3.90—4.18 (m, 16 H, OCH2CH2); 6.52 (dd, 2 H,
H(5´), H(4), J = 8.5 Hz, J = 2.2 Hz); 6.56 (d, 2 H, H(3´),
H(6), J = 2.2 Hz); 6.84 (d, 2 H, H(6´), H(3), J = 8.5 Hz); 7.40
(d, 2 H, H(2), J = 8.5 Hz); 7.51—7.63 (m, 10 H, 2 Ph); 7.82
(m, 2 H, H(8)); 8.12 (m, 4 H, H(6), H(7)); 8.32 (m, 2 H, H(8));
9.12 (d, 2 H, H(3), J = 9.0 Hz); 13.20 (s, 2 H, NH); 15.60
(s, 2 H, OH). IR (/cm–1): 3446 (O—H, N—H), 3181, 3063
(C—Harom), 2982, 2941 (CH2), 1671, 1633 (C=O, C=N), 1590
Parameterized modeling of the data from competitive SPT
was carried out using two equilibrium reactions:
L + M2+
L + Na+
L•M2+
,
L•Na+,
where M2+ = Ca2+, Sr2+, or Ba2+
.
The stability constants KNa for the complexes L•Na+ were
determined beforehand from direct titration data.
Quantum chemical calculations. First, conformational screenꢀ
ing for a model aminobenzocrown ether and its Mg2+ complex
was carried out using molecular mechanics (MMFF94s force
field33). In both cases, up to 10 000 conformers were found from
which 25 conformers with relative energies of 0—3 kcal mol–1
were selected. Then these conformers were optimized (DFT,
functional PBE,28 basis set 3z) with the Priroda program34 to
select lowestꢀenergy structures. A similar procedure was applied
to the anthraquinone moiety and its magnesium complex. Subꢀ
sequently, the anthraquinone moiety was combined with the
benzocrown ether moiety and the resulting structure 8 was optiꢀ
mized (DFT, hybrid functional M06ꢀ2X,23 basis set 6ꢀ31G(d))
with the Gaussian 09 program.35 Likewise, the structures of Mg2+
complexes were calculated.
The geometries of the tautomers of compound 8 and comꢀ
plex 8•Ca2+ (coordination to the crown ether moiety) were calꢀ
culated as described above. The functional M06ꢀ2X was used
because of its higher efficiency compared to "standard" funcꢀ
tionals in the description of noncovalent interactions. The solꢀ
vation effects were included in the model with the COSMO
method.24 This method can be applied to the tautomers of comꢀ
plex 8•Ca2+ because the structure of the crown ether moiety
with the coordinated cation remains virtually unchanged when
moving from one tautomer to the other, so the errors arising
from the presence of a localized charge cancel out when calcuꢀ
lating the energy difference between the tautomers.
(C=C). Found (%): C, 72.03; H, 4.65; N, 5.61. C62H48N4O12
Calculated (%): C, 71.53; H, 4.65; N, 5.38.
.
Spectrophotometric titration (SPT) was carried out at a fixed
concentration of the ligand: CL = 4.4•10–5 (3), 1.8•10–5 (5a,b),
1.2•10–5 (8), and 3.0•10–6 mol L–1 (9a,b). The concentration
of the metal salt was varied from 0 to 0.02 mol L–1
.
For titration of highly stable complexes with alkalineꢀearth
metal cations (logK > 7), competitive titration was used: soluꢀ
tions to be mixed contained NaClO4 (C = 0.01 mol L–1) and the
concentration of alkalineꢀearth metal perchlorate was varied in
a range of (0—1)•10–3 mol L–1
.
The stoichiometry of the complexation, the stability conꢀ
stants of the complexes, and the electronic absorption spectra
of the components were determined by parameterized matrix
modeling of SPT data.17 In all cases, except for the systems
8—Mg(ClO4)2 and 9a—Mg(ClO4)2, the SPT data were well apꢀ
proximated with an equilibrium reaction leading to a 1 : 1 comꢀ
plex. For the systems 8—Mg(ClO4)2 and 9a—Mg(ClO4)2, the
acceptable error of approximation was achieved when using two
equilibrium reactions (1) and (2):
L•Mn+ + Mn+
L•(Mn+)2,
(2)
where L is the ligand molecule, Mn+ is the metal cation, and K1:1
and K1:2 are the equilibrium constants.
Since reaction (2) occurs between charged species, the equiꢀ
librium constant K1:2 depends on the ionic strength of solution.
For this reason, parameterized modeling of SPT data for the
systems 8—Mg(ClO4)2 and 9a—Mg(ClO4)2 was performed with
allowance for the activity coefficients of charged species in soluꢀ
tion according to the Debye—Hückel equation in the second
approximation:
The conventional diameters of the solvate complex
Mg2+•6MeCN and the complex 8•Mg2+ were calculated with
the Gaussian 09 program (key word "Volume").
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 11ꢀ03ꢀ00447).
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log
,
A = 1.824•106(T)–1.5, B = 50.29(T)–0.5
,
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Received July 23, 2012;
in revised form November 21, 2012