Synthesis and characterization of new ketooximes and their complexes

Article abstract of DOI:10.1134/S0036023606090105

The starting point of the research was the reaction of chloroacetyl chloride with biphenyl in the presence of aluminum chloride. 4-Biphenylhydroximoyl chloride (HL) was obtained by reacting synthesized 4-(chloroacetyl)biphenyl with alkyl nitride. Four new substituted 4-(alkylaminoisonitrosoacetyl)biphenyles (ketooximes) were prepared by reacting 4-biphenylhydroximoyl chloride with corresponding amines in EtOH. The following amines were used for ligands: p-toluidine, p-chloroaniline, pyrrolidine, and 4-aminoacetophenone. Mononuclear complexes with a metal-ligand ratio of 1: 2 were prepared using cadmium(II), cobalt(II), copper(II), nickel(II), lead(II), and zinc(II) salts. These compounds have been characterized by elemental analyses, AAS, infrared spectra and magnetic susceptibility measurements. The ligands have been further characterized by ¹H NMR. The results suggest that the ketooximes act as bidentate ligands which bond metal ions through the oxime and carbonyl oxygen. Nauka/Interperiodica 2006.

Full text of DOI:10.1134/S0036023606090105

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2006, Vol. 51, No. 9, pp. 1467–1472. © Pleiades Publishing, Inc., 2006.
COORDINATION
COMPOUNDS
Synthesis and Characterization of New Ketooximes
1
and Their Complexes
F. Karipcin and F. Arabali
Faculty of Science and Arts, Department of Chemistry,University of Süleyman Demirel, Isparta, Turkey
e-mail: fkaripcin@hotmail.com
Received 07.12.2005
Abstract—The starting point of the research was the reaction of chloroacetyl chloride with biphenyl in the
presence of aluminum chloride. 4-Biphenylhydroximoyl chloride (HL) was obtained by reacting synthesized
4-(chloroacetyl)biphenyl with alkyl nitride. Four new substituted 4-(alkylaminoisonitrosoacetyl)biphenyles
(ketooximes) were prepared by reacting 4-biphenylhydroximoyl chloride with corresponding amines in EtOH.
The following amines were used for ligands: p-toluidine, p-chloroaniline, pyrrolidine, and 4-aminoacetophe-
none. Mononuclear complexes with a metal-ligand ratio of 1 : 2 were prepared using cadmium(II), cobalt(II),
copper(II), nickel(II), lead(II), and zinc(II) salts. These compounds have been characterized by elemental anal-
yses, AAS, infrared spectra and magnetic susceptibility measurements. The ligands have been further charac-
1
terized by H NMR. The results suggest that the ketooximes act as bidentate ligands which bond metal ions
through the oxime and carbonyl oxygen.
DOI: 10.1134/S0036023606090105
INTRODUCTION
commercially purchased and were used without further
purification.
The chemistry of transition metal complexes with
α-dioxime ligands has been well studied and is the sub-
ject of several reviews and many papers [1–5]. How-
ever, little information concerning the ketooxime metal
complexes is available [6, 7]. Several similar com-
pounds were synthesized by Karipcin et al. [8, 9].
Karipcin et al. have synthesized the ketooxime of
4,4'-bis(chloroacetyl)biphenylmethane and some of
their amine derivatives and complexes [8]. In the
present study, cadmium(II), cobalt(II), copper(II),
nickel(II), lead(II), and zinc(II) complexes with four
new ketooxime-derived 4-biphenylhydroximoyl chlo-
rides and corresponding amines were synthesized. In
the studies mentioned above, similar complexation
characteristics were observed as the ligand with same
amine derivatives formed mononuclear complexes with
metal–ligand ratio of 1 : 2.
IR spectra (4000–400 cm–1) were recorded on a Per-
kin Elmer BX FT-IR spectrophotometer as KBr pellets.
1H NMR spectra of the ligands were recorded from
DMSO solutions with TMS as an internal standard at
the Laboratories of the Scientific and Technical
1
Research Council of Turkey (TUBITAK). H NMR
spectra of the complexes could not be determined, since
these compounds are not totally soluble in organic sol-
vents. C, H, and N contents were determined microan-
alytically on a LECO 932 CHNS analyzer, and metal
contents were estimated spectrophotometrically on a
Perkin Elmer 800 AA spectrometer. Room temperature
magnetic susceptibility measurements were deter-
mined on a Sherwood Scientific Magnetic Susceptibil-
ity Balance (Model MX1). Melting points were mea-
sured on an IA 9100 Electrothermal apparatus and are
uncorrected.
EXPERIMENTAL
Preparation of the Ligands
All ligands were prepared by a similar method. A
solution of amines (16.5 mmol p-toluidine, p-chloroa-
niline, pyrrolidine, and 4-aminoacetophenone) in abso-
lute ethanol (20 cm3) was added dropwise with contin-
uous stirring to a solution of 4-biphenylhydroximoyl
chloride (3.893 g, 15 mmol) in ethanol (50 cm3) in the
presence of Et3N (15 mmol) for 30 min. at 0°C. Precip-
itation and color change were observed in the reaction
medium immediately. After that period, the reaction
4-(Chloroacetyl)biphenyl [10] and 4-biphenylhy-
droximoyl chloride [10] were synthesized as previously
described. All solvents, amines and metal salts
(Co(NO3)2 · 6H2O, Ni(AcO)2 · 4H2O, Cu(AcO)2 · H2O,
Zn(AcO)2 · 2H2O, Cd(NO3)2 · 4H2O, Pb(AcO)2 · 3H2O)
used for the synthesis and physical measurements were
1
The text was submitted by the authors in English.
1467

1468
KARIPCIN, ARABALI
mixture was stirred for 2 h more at the same tempera- presence of aluminum chloride according to Friedel-
Crafts acylation [10]. 4-Biphenylhydroximoyl chlo-
ride (HL) was obtained by reacting 4-(chloro-
acetyl)biphenyl with alkyl nitride in the presence of dry
HCl gas [10]. 4-(alkylaminoisonitrosoacetyl)biphenyls
(HL1–HL4) were prepared by reaction of HL with p-tolu-
idine, p-chloroaniline, pyrrolidine, and 4-aminoace-
tophenone, respectively. 4-(4-methylphenylaminoisoni-
trosoacetyl)biphenyl(HL1), 4-(4-chlorophenylaminoi-
sonitrosoacetyl)biphenyl(HL2), 4-[pyrrolidylisonitro-
soacetyl]biphenyl (HL3) and 4-(4-acetylphenylaminoi-
sonitrosoacetyl)biphenyl (HL4) were prepared. The
structural formula (Fig. 1) of ketooxime ligands were
verified by elemental analyses, 1H NMR, and IR spectral
data, presented in Tables 1–3.
ture. Then it was allowed to stir at ambient temperature
for 2 h. The powder resulting from the reaction is insol-
uble in ethanol and this was filtered off; washed with
aqueous sodium bicarbonate (1%), distilled water, and
ethanol; and dried in air.
Preparation of the Complex
A solution of an equivalent amount of metal salt in
ethanol (20 cm3) was added to a hot solution of ligand
(HL1–HL4) [1 mmol, 0.284 g HL1, 0.346 g HL2, 0.331 g
HL3, 0.358g HL4] in ethanol (50 cm3) and was continu-
ously stirred. A distinct change in color and decrease in
pH (pH 3.0–3.5) was observed, an equivalent amount of
ethanolic solution of KOH (0.1 M) was added dropwise
to adjust to a pH value of about 5–6, and the solid prod-
uct was precipitated. The complex precipitated was
On interaction with cadmium(II), cobalt(II), cop-
per(II), nickel(II), lead(II), and zinc(II) salts,
ketooxime ligands yielded complexes corresponding to
kept on a water bath at 80°C for one hour in order to the general formula [M(Lx)2(H2O)2]. For the structural
complete the precipitation. The mixture was cooled to
ambient temperature and the solid product was filtered
off. Then it was washed with hot water and ethanol and
dried in air.
The colors, yield, melting points, elemental analy-
ses, and IR data of the complexes and ligands are given
in Tables 1 and 2. 1H NMR data of ligands are given in
Table 3.
characterization of metal complexes, elemental analy-
ses, AAS, FT-IR and magnetic susceptibility measure-
ments were used and spectral-analytical data for all
these complexes are presented in Tables 1 and 2. The
metal-to-ligand ratio of the all complexes was found to
be 1 : 2 and they have two additional coordinated H2O
molecules.
1
The H NMR spectrum of 4-biphenylhydroximoyl
chloride exhibits a singlet peak for the OH protons of
oxime group at 13.69 ppm. In all ligands, a singlet peak
in the 11.15–11.78 ppm. range is also attributed to the
OH proton of the oxime group. The higher shift of the
RESULTS AND DISCUSSION
The reaction steps for the synthesis of 4-(alkylami-
noisonitrosoacetyl)biphenyl ligands (HL1–HL4) are OH protons of the oxime group is typical of condensa-
given in Scheme 1. 4-(Chloroacetyl)biphenyl was pre- tion reaction with 4-biphenylhydroximoyl chloride and
pared from chloroacetyl chloride and biphenyl in the corresponding amines. The other singlet peak observed
O
O
AlCl
3
+ ClH2C
C
C
CH2Cl
CH2Cl
RONO/HCl
O
C NOH
Cl
R-H
O
C
C NOH
R
O
R:
NH
CH3 NH
Cl
N
NH
,
C CH3
,
,
1
4
Scheme 1. Synthesis of 4-(Alkylaminoisonitrosoacetyl)biphenyls (HL –HL ).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 9 2006

SYNTHESIS AND CHARACTERIZATION OF NEW KETOOXIMES
Table 1. Analytical and physical data for the ligands and their complexes
1469
Calcd. (Found), %
Compound
Colour
Mp, °C Yield, %
C
H
N
Metal
HL
Light yellow
Yellow
169
54
85
76
73
96
69
67
56
85
95
89
74
62
55
58
61
84
73
69
50
63
70
68
75
72
62
58
69
74
64.79 (64.72)
76.40 (76.31)
62.52 (62.57)
63.54 (66.98)
66.55 (66.15)
66.98 (66.68)
55.95 (56.30)
66.39 (66.54)
68.50 (68.31)
56.68 (56.74)
60.49 (60.12)
60.15 (59.72)
60.51 (60.57)
50.98 (50.99)
60.01 (59.85)
73.49 (73.48)
58.85 (58.69)
63.47 (63.32)
63.04 (62.99)
63.49 (63.81)
52.12 (52.41)
62.87 (62.76)
73.77 (73.91)
61.25 (61.21)
65.29 (65.67)
64.92 (65.02)
65.31 (65.09)
55.19 (55.38)
64.78 (64.75)
3.88 (4.05)
5.49 (5.70)
5.25 (4.96)
5.62 (5.72)
5.59 (5.10)
5.62 (5.32)
4.69 (4.74)
5.57 (5.91)
4.31 (4.31)
4.28 (4.19)
4.57 (5.02)
4.54 (4.06)
4.57 (4.75)
3.85 (3.94)
4.53 (4.87)
6.17 (6.31)
5.76 (6.16)
6.21 (6.19)
6.17 (6.48)
6.22 (6.25)
5.10 (4.73)
6.16 (6.08)
5.07 (5.48)
4.91 (5.08)
5.23 (4.95)
5.20 (4.76)
5.23 (4.96)
4.42 (3.97)
5.19 (5.54)
5.39 (4.96)
8.48 (8.29)
–
–
HL1
144
[Cd(L1)2(H2O)2]
[Co(L1)2(H2O)2]
[Cu(L1)2(H2O)2]
[Ni(L1)2(H2O)2]
[Pb(L1)2(H2O)2]
[Zn(L1)2(H2O)2]
HL2
Light brown
Dark brown
Dark brown
Brown
240
6.94 (6.73) 13.94 (13.60)
240
7.44 (7.81)
7.39 (7.48)
7.44 (7.91)
7.82 (8.27)
8.38 (8.54)
7.79 (7.81)
220
270*
200
Yellow
6.21 (6.61) 22.97 (23.14)
Light brown
Yellow
205*
168
7.37 (7.67)
7.99 (7.59)
8.60 (8.82)
–
[Cd(L2)2(H2O)2]
[Co(L2)2(H2O)2]
[Cu(L2)2(H2O)2]
[Ni(L2)2(H2O)2]
[Pb(L2)2(H2O)2]
[Zn(L2)2(H2O)2]
HL3
Orange
285*
270*
208
6.61 (6.28) 13.27 (13.42)
Dark brown
Brown
7.06 (6.79)
7.01 (6.86)
7.06 (7.84)
7.43 (7.56)
7.95 (8.21)
7.39 (7.06)
Light brown >300
Yellow
205
5.95 (5.96) 21.98 (22.33)
Light brown
Yellow
241
6.99 (6.46)
9.52 (9.74)
8.18 (8.49)
–
131
[Cd(L3)2(H2O)2]
[Co(L3)2(H2O)2]
[Cu(L3)2(H2O)2]
[Ni(L3)2(H2O)2]
[Pb(L3)2(H2O)2]
[Zn(L3)2(H2O)2]
HL4
Yellow
297*
184.5
190
7.63 (7.19) 15.30 (15.73)
Dark brown
Green
8.22 (8.29)
8.17 (7.91)
8.23 (7.88)
8.65 (9.02)
9.26 (9.20)
8.61 (8.40)
Dark brown >300
Yellow
185
>300
144
6.75 (6.46) 24.98 (25.16)
Yellow
8.15 (7.97)
7.82 (7.56)
9.51 (9.81)
–
Cream
[Cd(L4)2(H2O)2]
[Co(L4)2(H2O)2]
[Cu(L4)2(H2O)2]
[Ni(L4)2(H2O)2]
[Pb(L4)2(H2O)2]
[Zn(L4)2(H2O)2]
* Decomposition point.
Orange
240
6.49 (6.04) 13.03 (13.40)
Brown
230*
244*
270*
250
6.92 (7.29)
6.88 (7.21)
6.92 (6.82)
7.28 (7.39)
7.80 (8.12)
7.26 (7.06)
Dark brown
Light brown
Yellow
5.85 (5.47) 21.64 (21.85)
6.87 (7.08) 8.01 (8.29)
Yellow
>300
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 9 2006

1470
KARIPCIN, ARABALI
Table 2. Magnetic measurements and IR spectral data for the ligands and their metal complexes (cm–1)
µ
eff (µB)
Compound
N–H
ν(OH)
ν(CH)aliph
C=O
ν(C=N)
ν(NO)
per M(II)
HL
HL1
–
–
3256 b
2824 w
2919 w
2922 w
2920 w
2920 w
2920 w
2924 w
2922 w
2915 w
2925 w
2921 w
2926 w
2928 w
2915 w
2931 w
2918 m
2923 w
2969 w
2971 w
2971 w
2969 w
2920 m
2920 w
2922 w
2922 w
2925 w
2926 w
2926 w
2929 w
1655 s
1671 s
1671 w
1668 w
1674 w
1670 w
1654 w
–
1602 s
1600 s
1600 s
1601 s
1601 s
1600 s
1600 s
1576 s
1599 s
1599 s
1600 s
1600 s
1599 s
1599 s
1599 s
1602 s
1601 m
1600 s
1600 s
1599 s
1600 m
1575 s
1601 s
1599 s
1599 s
1599 s
1599 s
1598 s
1574 s
1029 s
946 s
–
3379 m
3395 m
3392 b
3391 b
3391 b
3401 b
3392 b
3428 s
3427 b
3448 b
3415 b
3416 b
3425 b
3414 b
–
3233 b
[Cd(L1)2(H2O)2]
[Co(L1)2(H2O)2]
[Cu(L1)2(H2O)2]
[Ni(L1)2(H2O)2]
[Pb(L1)2(H2O)2]
[Zn(L1)2(H2O)2]
HL2
[Cd(L2)2(H2O)2]
[Co(L2)2(H2O)2]
[Cu(L2)2(H2O)2]
[Ni(L2)2(H2O)2]
[Pb(L2)2(H2O)2]
[Zn(L2)2(H2O)2]
HL3
[Cd(L3)2(H2O)2]
[Co(L3)2(H2O)2]
[Cu(L3)2(H2O)2]
[Ni(L3)2(H2O)2]
[Pb(L3)2(H2O)2]
[Zn(L3)2(H2O)2]
HL4
[Cd(L4)2(H2O)2]
[Co(L4)2(H2O)2]
[Cu(L4)2(H2O)2]
[Ni(L4)2(H2O)2]
[Pb(L4)2(H2O)2]
[Zn(L4)2(H2O)2]
Dia.
3.90
2.09
3.56
Dia.
Dia.
–
–
985 m
–
1006 m
1006 m
1005 m
967 m
–
–
–
–
991 m
3368 s
1650 s
1654 w
1669 w
1671 s
1669 w
1654 w
1660 s
1675 m
–
963 s
Dia.
3.95
1.51
3.76
Dia.
Dia.
–
–
984 m
–
1007 m
1007 m
1007 m
973 m
–
–
–
–
1006 m
1006 m
1006 m
1007 m
1006 m
1007 m
1007 m
1021 m
963 s
3413 m
3469 b
3400 b
3385 b
3401 b
3415 b
3400 b
3357 s
–
Dia.
2.12
2.39
3.57
Dia.
Dia.
–
–
–
–
–
–
–
–
–
–
–
–
3429 s
3430 b
3432 b
3447 b
3452 b
3436 b
3401 b
1672 s
1668 s
1673 s
1674 s
1669 m
1671 m
1673 s
Dia.
4.70
2.50
3.64
Dia.
Dia.
987 m
–
1006 m
1006 m
999 m
–
–
–
1006 m
1021 m
–
Note: s—strong, m—medium, w—weak, b—broad.
Table 3. The 1H NMR data ( as ppm.) for the ligands
Compound
O–H
N–H
C–Harom
C–Haliph
C–Hring
HL
13.69 (s, 1H)
11.15 (s, 1H)
11.45 (s, 1H)
–
–
7.31–8.08 (m, 9H)
6.70–8.08(m, 13H)
6.80–8.09 (m, 13H)
6.60–8.14(m, 9H)
7.42–8.07(m, 13H)
–
–
HL1
HL2
HL3
HL4
8.57 (s, 1H)
8.85 (s, 1H)
–
3.44 (s, 3H)
–
–
–
–
3.13–4.11(m, 8H)
–
11.78 (s, 1H)
9.238 (s, 1H)
2.46 (s, 1H)
Note: s—singlet, d—dublet, t—triplet, m—multiplet.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 9 2006

SYNTHESIS AND CHARACTERIZATION OF NEW KETOOXIMES
1471
O
NOH
C
C
HN
CH3
4-(4-metylphenylaminoisonitrosoacetil)biphenyl, C21H18N2O2
O
NOH
C
C
HN
Cl
4-(4-clorophenylaminoisonitrosoacetil)biphenyl, C20H15N2O2Cl
O
NOH
C
C
N
4-(pyrrolidilisonitrosoacetil)biphenyl, C18H18N2O2
O
NOH
O
C
C
C
HN
CH3
4-(4-acetophenylaminoisonitrosoacetil)biphenyl, C22H18N2O3
Fig. 1. The Structure of 4-(Alkylaminoisonitrosoacetyl)biphenyls.
in the δ = 8.57–9.24 ppm. range can be assigned to the stretching vibrations. In the IR spectra of metal com-
NH signal; it appeared after the condensation reaction.
The aromatic C–H protons of the ligands measured
6.60–8.14 ppm., aliphatic C–H protons 2.46–4.11 ppm.
The spectral data of a DMSO solution of the ligands
support the proposed structure and indicate the forma-
tion of 4-(alkylaminoisonitrosoacetyl)biphenyl ligands.
These values are also in good agreement with those of
known oximes [11, 12].
In the FT-IR spectra of keto oxime ligands (as KBr
pellets), bands at 3379–3429, 3233–3413, 1650–1675,
1599–1602, and 946–1006 cm–1 were assigned to NH,
OH, C=O, C=N, and N=O stretching vibrations,
respectively. Stretching C=N vibrations appearing at
about 1600 cm–1 in the ligands appeared at the same
place in the metal complexes of these ligands, indicating
coordination through the O atom of oxime groups.
Stretching ϑC=O vibrations are affected upon complexation
and became weaker or dissappeared completely. This indi-
cated coordination through the C=O group. The OH
vibrations of oxime appearing at 3233–3413 cm–1 in the
spectra of ligands dissappeared completely in the spec-
tra of metal complexes. Howewer, the OH vibration of
the coordinated H2O appeared in the ketooxime-pyr-
rolidyne (HL3) ligand and its complexes. Furthermore,
the OH stretching vibrations of coordinated H2O in the
complexes are probably shown in same range as NH
plexes, bands at 3448–3401, 1675–1654, 1601–1574,
and 1007–967 cm–1 belong to N–H, C=O, C=N and
N−O stretching vibrations, respectively. These absorp-
tion data are in agreement with those previously
reported for substituted ketooximes [13, 14].
In order to prepare complexes, we used a standard
procedure through the reaction of ligands with metal
salts. A mixture of ligand, metal salts, and an equivalent
amount of KOH (0.1 M) in ethanol gave the desired
complexes in 50–96% yields. According to the IR data,
elemental analyses and magnetic susceptibility mea-
surements, the mononuclear complexes have a metal :
ligand ratio of 1 : 2 and an octahedral structure (Fig. 2).
The room temperature magnetic moment measure-
ments show that all Zn(II), Cd(II), and Pb(II) com-
plexes are diamagnetic. The nickel(II) complexes are
paramagnetic with magnetic susceptibility values of
3.56–3.76 µB, which fits the two-spin value, 2.83 µB.
The results of the Ni(II) complexes fit the d8 metal ion
in an octahedral structure [15, 16]. The copper(II) and
cobalt(II) complexes are paramagnetic with magnetic
susceptibilities 1.51–2.50 and 2.12–4.70 µB, respec-
tively. The Cu(II) complexes fit spin values 1.73 µB. and
the Co(II) complexes fit tri-spin values, 3.36 µB.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 9 2006

1472
KARIPCIN, ARABALI
OH
R
2
N C
O C
C O
C N
O
M
O
OH
R
2
M: Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II)
O
C
,
,
Cl
,
NH
R: NH
CH3 NH
CH3
N
Fig. 2. The Structure of metal complexes of 4-(Alkylaminoisonitrosoacetyl)biphenyls.
7. P. S. Reddy and K. H. Reddy, Polyhedron 19, 1687
ACKNOWLEDGMENTS
(2000).
The study was supported by the Research Fund of
Suleyman Demirel University (Isparta-Turkey). We are
indebted to Prof. Dr. Güleren Alsancak for assistance
related to infrared, AA spectra and elemental analyses
data.
8. F. Karipcin, H. I. Ucan, and I. Karatas, Trans. Met.
Chem. 27, 813 (2002).
9. F. Karipcin, I. Karatas, and H. I. Ucan, Turk. J. Chem.
27, 453 (2003).
10. N. Levin and W. H. Hartung, J. Org. Chem. 7, 408
(1942).
11. H. E. Ungnade, B. Fritz, and L. W. Kissinger, Tetrahe-
REFERENCES
dron 19, 235 (1963).
1. L. Tschugaeff, Ber. 40, 3498 (1907).
12. H. E. Ungnade, L. W. Kissinger, A. Narath, and
D. C. Barham, J. Org. Chem. 28, 134 (1963).
2. J. V. Burakevich, A. M. Lore, and G. P. Volpp, J. Org.
13. J. E. Caton and C. V. Banks, Inorg. Chem. 6, 1670
Chem. 36, 1 (1971).
(1967).
3. I. Karatas and H. I. Ucan, Synth. React. Inorg. Met.-Org.
14. A. Nakamura, A. Konishi, and S. Otsuka, J. Chem. Soc.,
Dalton Trans., 488 (1979).
15. F. A. Cotton and G. Wilkinson, Advanced Inorganic
Chemistry (Wiley, New York, 1988).
Chem. 28, 383 (1998).
4. F. Karipcin and I. Karatas, Synth. React. Inorg. Met.-Org.
Chem. 31, 1817 (2001).
5. A. Coskun and I. Karatas, Turk. J. Chem. 28, 173 (2004).
6. A. Chakravorty, Coord. Chem. Rev. 13, 3 (1974).
16. M. A. Deveci and G. Irez, Synth. React. Inorg. Met.-Org.
Chem. 26, 871 (1996).
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