Esterification of the ligand: Synthesis, characterization and crystal structure of a iron(III) 18-metallacrown-6 complex with methyl 4-(5′-chlorosalicylhydrazinocarbonyl) butyrate

Article abstract of DOI:10.1016/j.ica.2011.10.021

The multidentate ligand, 4-(5′-chlorosalicylhydrazinocarbonyl) butyric acid, has been synthesized and reacted with FeCl₃ to produce the iron(III) 18-metallacrown-6 complex [Fe^III₆(C ₁₃H₁₂N₂

Full text of DOI:10.1016/j.ica.2011.10.021

Inorganica Chimica Acta 383 (2012) 20–25
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Esterification of the ligand: Synthesis, characterization and crystal
structure of a iron(III) 18-metallacrown-6 complex with methyl
4-(50-chlorosalicylhydrazinocarbonyl) butyrate
⇑
Cheng-Zhi Jin, Shu-Xiang Wu, Long-Fei Jin , La-Mei Wu, Jian Zhang
Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, Hubei Province, South-Central University for Nationalities,
Wuhan 430074, China
a r t i c l e i n f o
a b s t r a c t
The multidentate ligand, 4-(50-chlorosalicylhydrazinocarbonyl) butyric acid, has been synthesized and
reacted with FeCl3 to produce the iron(III) 18-metallacrown-6 complex [FeIII6(C13H12N2O5Cl)6-
(CH3OH)6]ꢀ5CH3OH. In the complex the ligand 4-(50-chlorosalicylhydrazinocarbonyl) butyric acid was
esterified and transferred into methyl 4-(50-chlorosalicylhydrazinocarbonyl) butyrate. In the crystal
structure, the hexanuclear 18-membered rings of iron atoms are linked by six hydrazide N–N groups.
The deprotonated and esterified ligand acts as a trianionic pentadentate ligand, one phenolate oxygen,
one hydrazide nitrogen and one carbonyl oxygen in the ligand are bound to one Fe3+ cation, and the other
carbonyl oxygen plus the other hydrazide nitrogen in the same ligand are chelated to an adjacent Fe3+
cation. In hydrochloric acid the metallacrown [FeIII6(C13H12N2O5Cl)6(CH3OH)6]ꢀ5CH3OH can be treated
with SnCl2 to obtain purified ester methyl 4-(50-chlorosalicylhydrazinocarbonyl) butyrate.
Ó 2011 Elsevier B.V. All rights reserved.
Article history:
Received 14 May 2011
Received in revised form 23 September
2011
Accepted 6 October 2011
Available online 25 October 2011
Keywords:
Metallacrown
Iron complex
Crystal structure
Esterification
1. Introduction
process of the iron 18-MC-6 metallacrowns [FeIII6(C12H9N2O5)6-
(H2O)2(CH3OH)4] and [FeIII6(C12H8N2O5Cl)6(H2O)4(CH3OH)2] [28,29].
Metallacrowns and its analogues have attracted considerable
attention. In the structure, metallacrowns exhibit a cyclic hole
generally analogous to crown ether with transition metal ions
and nitrogen atoms replacing the methylene carbon atoms [1,2].
Metallacrowns [9-MC-3] [3], [12-MC-4] [4], [15-MC-5] [5,6],
[12-MC-6] [7], [16-MC-8] [8], [18-MC-6] [9,10], [18-MC-8] [7],
[24-MC-6] [11], [30-MC-10] [12], [36-MC-12] [13], [40-MC-10]
[14], [60-MC-20] [15], stacking metallacrowns [16,17] as well as
a variety of dimers and fused metallacrowns [18,19] have been
reported.
In this paper we report a new esterification of 4-(50-chloro-
salicylhydrazinocarbonyl) butyric acid (H4cshcba) (2) via metal-
lacrowns and the synthesis, characterization and crystal structure
of iron(III) 18-MC-6 metallacrown [FeIII6(C13H12N2O5Cl)6(CH3-
OH)6]ꢀ5CH3OH (3) (Scheme 1).
2. Experimental
2.1. Chemicals
Metallacrowns have been studied not only for their esthetic
appeal but also for their potential functions. As a result of the pres-
ence of transition metal ions in the metallacrown ring, metallacr-
owns may be used as cation, anion, and molecular recognition
agents; catalysts; building blocks for extended solids; magnetism;
biologic agents and sensors [20–23]. Several copper-pyrazolate-
based metallacrown systems show catalytic activity [24–27].
Taking the similarity between salicylhydrazides and carboxylic
acids with salicyl-bis-hydrazide into account, we have expanded
the types of precursor ligand with the intention of catalyzing ester-
ification. We have previously shown that propenoic acids with
salicyl-bis-hydrazide can be translated to esters in self-assembly
Chemicals for the synthesis of compounds were used as pur-
chased. Methanol, ethanol and chloroform were used without
any further purification. 5-Chlorosalicylic acid, sulfuric acid, hydro-
chloric acid, hydrazine hydrate, glutaric anhydride, pyridine,
FeCl3ꢀ6H2O and SnCl2ꢀ2H2O were purchased from China Sinopharm
Group Chemical Reagent Co., Ltd. All chemicals and solvents were
reagent grade. 5-Chlorosalicylhydrazide was prepared according to
literature procedures [30].
2.2. Characterization
C, H and N elemental analysis were performed on a Perkin El-
mer 2400 Series II CHNS/O Analyzer. Fe was determined by atomic
absorption spectroscopy on a Shimadzu AA-6300 Spectrophotom-
⇑
Corresponding author. Tel./fax: +86 27 67842752.
E-mail address: longfei.jin@yahoo.com (L.-F. Jin).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.10.021

C.-Z. Jin et al. / Inorganica Chimica Acta 383 (2012) 20–25
OH
21
OH
was added. The resulting dark brown solution was stirred for 2 h
at 40 °C and refluxed for 4 h, and filtered. After 7 days, black crys-
tals were deposited from the mother liquor. In the complex 3 the
ligand 2 has been esterified and transferred into methyl 4-(50-chlo-
rosalicylhydrazinocarbonyl) butyrate (H3mcshcb) (4). Yield: 41%;
Cal. For C89H116Cl6Fe6N12O41: C 41.79, H 4.57, N 6.57, Fe 13.10;
Found: C 41.62, H 4.39, N 6.62, Fe 13.22. IR (KBr pellet, cmꢁ1):
glutaric anhydride
O
O
H
H
N
N
Cl
NH2
Cl
N
H
OH
O
O
1
2
m
m
OH, 3187 versus broad;
(Fe–O)phenolic, 449%.
mC@O, 1729 s; mC@N–C@N, 1608 versus;
FeCl3
CH3OH, Pyridine
[FeIII6(C13H12N2O5Cl)6(CH3OH)6]·5CH3OH
2.5. Preparation of methyl 4-(50-chlorosalicylhydrazinocarbonyl)
butyrate (H3mcshcb) (4)
3
To obtain 4, the solution of 3 was directly concentrated under
reduced pressure. Then a solution of SnCl2ꢀ2H2O (6.77 g, 30 mmol)
in 3 molLꢁ1 HCl (50 mL) was added to the residue of 3 at 0 °C. The
resultant mixture was slowly warmed to 30 °C and stirred for 4 h,
and filtered. The resulting white precipitate was rinsed with
2 molLꢁ1 HCl, and dried under vacuum to afford white solid com-
pound 4. Yield: 47%; m.p. 207–208 °C; Cal. for C13H15ClN2O5: C
49.60, H 4.80, N 8.90; Found: C 49.51, H 4.63, N 8.81; 1H NMR
OH
SnCl2
HCl
O
O
H
N
Cl
N
H
OCH3
O
4
Scheme 1. Synthetic routes and chemical structures of the compounds.
(DMSO-d6),
d ppm: 11.94 (s, 1H; –PhOH), 10.54 (s, 1H;
–PhCONH–), 10.27 (s, 1H; –NHCO–CH2–), 7.90 (s, 1H; o-PhCH),
7.48–7.46 (d, 1H; p-PhCH), 7.01–6.99 (d, 1H; m-PhCH), 3.60 (s,
3H; –OCH3), 2.31–2.24 (m, 4H, –CH2–CH2–CH2–), 1.79–1.82 (m,
eter. Melting points were obtained using a digital melting-point
apparatus, TP Micro Printer S-X6. Infrared spectra were recorded
on a Thermo Nicolet Corporation NEXUS 470 FT-IR Spectrometer
in the 4000–400 cmꢁ1 region, using KBr pellet. UV–Vis spectra
were recorded on a Perkin Elmer Lambda 35 UV–Vis Spectrometer.
1H NMR and 13C NMR spectra measurements were performed on a
Avance III 400 MHz NMR spectrometer at 25 °C, operating at
400 MHz in 5 mm tubes. Chemical shifts were referenced to
residual solvent peak. Thermogravimetry (TG) carried out on
Perkin–Elmer Diamond DSC TG-DTA 6300 thermal analyzer. Vari-
able-temperature dc magnetic susceptibility data were collected
on the polycrystalline samples over a 2–300 K temperature range
at 1 KOe under zero field cooled conditions using a Quantum
Design SQUID MPMS XL-7 magnetometer.
2H; CH2–CH2COOH); 13C NMR (DMSO-d6),
d ppm: 174.57
(–NHCO–CH2), 170.89 (–COO–), 165.49 (–PhCO–), 157.78 (–PhC–
OH), 133.94 (p-PhC), 128.43 (o-PhC), 123.22 (m-PhC-Cl), 119.67
(–PhC–CO–), 117.03 (m-PhC), 49.05 (–OCH3), 33.25 (–NHCO–
CH2–), 32.70 (–CH2–COOCH3), 20.89 (–CH2–CH2COOH); IR (KBr
pellet, cmꢁ1):
1729 s; C@N–C@N, 1605 versus;
m
O–H, 3191 s, broad;
mN–H, 2946 s, broad; mC@O,
m
m(C–OH)phenolic, 1216 s, 1182 s.
2.6. X-ray crystal structure determination
A black crystal of the complex 3 with approximate dimensions
of 0.30 ꢂ 0.06 ꢂ 0.05 mm3 was placed on a Bruker Smart APEX
diffractometer. Intensity data were collected with a graphite
2.3. Synthesis of 4-(50-chlorosalicylhydrazinocarbonyl) butyric acid
(H4cshcba) (2)
monochromatic Mo K
a total of 37800 reflections corrected by SADABS [31,32] in the
1.93 ꢃ h ꢃ 25.50 range, 20319 were independent with Rint
0.0523, of which 13638 observed reflections with I > 2 (I) were
a radiation (k = 0.71073 Å) at 123(2) K. From
=
A solution of glutaric anhydride (2.80 g, 0.024 mol) in chloro-
form (50 mL) was slowly added to a solution of 5-chlorosalicylhyd-
razide (3.73 g, 0.02 mol) in chloroform (50 mL) at 0 °C. The reaction
mixture was warmed to boiling point and stirred for 5 h. Then the
mixture was filtered and rinsed with ethanol. Yield: 86%; m.p.
247–248 °C; Cal. for C12H13N2O5Cl: C 47.92, H 4.36, N 9.31; Found:
C 47.88, H 4.38, N 9.36; 1H NMR(DMSO-d6), d ppm: 11.94 (bs, 1H; –
PhOH), 10.54 (s, 1H; –PhCONH–), 10.26 (s, 1H; PhCONH–NH), 7.90
(s, 1H; o-PhCH), 7.49–7.46 (d, 1H; p-PhCH), 7.01–6.99 (d, 1H;
m-PhCH), 2.31–2.24 (m, 4H; –CH2–CH2–CH2–), 1.80–1.76 (m, 2H;
–CH2–CH2COOH); 13C NMR (DMSO-d6), d ppm: 174.59 (–COOH),
170.89 (–NHCO–CH2–), 165.46 (–PhCONH–), 157.75 (–PhCOH),
133.95 (p-PhC), 128.43 (o-PhC), 123.21 (m-PhC-Cl), 119.67
(–PhC–CO–), 117.04(m-PhC), 33.23 (–NHCO–CH2–), 32.68 (–CH2–
r
used in the structural analysis. The structure was solved using
direct methods and standard difference map techniques and was
refined by full-matrix least-squares procedures on F2 with SHELXTL
program package [32]. All non-hydrogen atoms were refined aniso-
tropically. Hydrogen atoms were included in calculated positions
and were refined using a riding model. The final refinement con-
verged at R1 = 0.0417, wR2 = 0.1274 (w = 1/[
r
2(Fo2)+(0.0260)2 +
0.6771P], where P = (Fo2 + 2Fc2)/3) (for 20319 unique reflections),
(D/r)max = 0.006, S = 1.161, (Dq)max = 0.855 and (Dq)min =
ꢁ0.612 e/Å3. Crystal data and refinement details are presented in
Table 1.
COOH), 20.87 (–CH2–CH2COOH); IR (KBr pellet, cmꢁ1):
3301 s, broad; O–H, 3190 versus broad; N–H, 2974 s, broad;
O–H, 2638 s, broad; C@O, 1701 versus; C@N–C@N, 1601
(C–OH)phenolic, 1218 s, 1115 s.
mOCO–H,
3. Results and discussion
m
m
m
m
m
3.1. Synthesis of iron(III) metallacrown 3
versus;
m
The metallacrown
3 was synthesized via the reaction of
2.4. Synthesis of [FeIII6(C13H12N2O5Cl)6(CH3OH)6]ꢀ5CH3OH (3)
FeCl3ꢀ6H2O with the ligand 4-(50-chlorosalicylhydrazinocarbonyl)
butyric acid which has been prepared previously by a procedure
through a direct reaction between 5-chlorosalicylhydrazide and
glutaric anhydride, in the methanol + pyridine solution (Scheme 2).
The complex 3 is black crystalline solid.
A mixture of 2 (3.00 g, 10 mmol) in methanol (100 mL) and
FeCl3ꢀ6H2O (3.24 g, 12 mmol) in methanol (20 mL) was stirred for
20 min. Then pyridine (10 mmol) dissolved in methanol (10 mL)

22
C.-Z. Jin et al. / Inorganica Chimica Acta 383 (2012) 20–25
Table 1
Crystallographic data.
OH
O
O
H
N
Cl
N
H
OCH3
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C89H116Cl6Fe6N12O41
2557.74
O
4
triclinic
ꢀ
P1
Chart 1. H3mcshcb (4).
14.482(3)
14.772(3)
27.064(5)
85.460(3)
89.074(3)
73.162(3)
5524.2(19)
2
1.538
1.002
2640
0.30 ꢂ 0.06 ꢂ 0.05
1.93–25.50
ꢁ13 ꢃ h ꢃ 17
ꢁ17 ꢃ k ꢃ 17
ꢁ32 ꢃ l ꢃ 32
37800
b (Å)
c (Å)
rate and reduced Fe3+. In the process of preparation, to obtain ester
with good-yield, the resulting dark brown solution that had been
formed by the reaction of ligand 2 with Fe3+ will be directly con-
centrated under reduced pressure to obtain the residue of 3. This
is a solid material that is formed by complete evaporation of the
solvent which was used for the reaction between 2 and iron(III)
chloride to make 3, before any attempt is made to crystallise 3.
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g/cm3)
l
(mmꢁ1
)
F(000)
Crystal size (mm)
h range (°)
Index ranges
½FeIIIðC13H12N2O5ClÞ ðCH3OHÞ ꢄ ꢀ 5CH3OH þ SnCl2 þ HCl
6
6
6
! C13H15ClN2O5 þ FeCl2 þ SnCl4 þ CH3OH
ð1Þ
Observed reflections
Independent reflections (Rint
)
20319 (0.0523)
0.0417
0.1274
a
R1
3.3. Characterization
b
wR2
Goodness-of-fit
1.161
In the IR spectra, the ligand 2 shows stretching bands attributed
to C@O, C@N, C–OH (phenolic) and N–H at 1701, 1601, 1218 and
1115, and 2974 cmꢁ1, respectively [34]. Bands at 3301, 3190 and
P
P
a
R1
=
||Fo| ꢁ |Fc||/ |Fo|.
P
P
wR2 = [ w(Fo ꢁ Fc2)2/ w(Fo2)2]1/2
.
b
2
2638 cmꢁ1 are assigned to
m
O–H vibrations which may be involv-
ing intramolecular hydrogen bonding, while bands at 1218 and
In iron(III) metallacrown 3, the ligand 4-(50-chlorosalicylhydraz-
1115 cmꢁ1 are attributed to
mO–H (phenolic) [35,36]. In addition,
a strong band found at 1601 cmꢁ1 is assigned to C@N–N@C group
[34–36].
inocarbonyl) butyric acid has been esterified and transferred into
H3mcshcb (4, Chart 1). The synthesis system play an important
role in the formation of new ligand. Through the analysis of the
reaction system [FeIII6(C13H12N2O5Cl)6(CH3OH)6]ꢀ5CH3OH, we
deduce that the esterification of carboxylic acid with salicyl-
bis-hydrazide is a new internal esterification by metallacrown it-
self, which are defined as an internal self-catalytic reaction [33].
For the 18-MC-6 iron(III) metallacrown, [FeIII6(C13H12N2O5Cl)6(CH3-
OH)6], in the internal self-catalytic reaction, the reactant is
[FeIII6(C11H9N2O3Cl–COOH)6(H2O)m(CH3OH)n] (m = 1–6, n = 1–6)
which contains the mainly ligand 4-(50-chlorosalicylhydrazinocar-
bonyl) butyric acid with a carboxylic acid group –COOH. The
carboxylic acid group can be combined with iron, then reacted with
a activity coordination of methanol to produce ester. Eventually the
product [FeIII6(C11H9N2O3Cl–COOCH3)6(CH3OH)6] was obtained by
the internal self-catalytic reaction. In the catalytic reaction the iron
can be identified as the catalytic center.
The IR spectra of the esterified ligand 4 are similar to 2. The
stretching bands attributed to C@O, C@N, C–OH (phenolic) and
N–H at 1729, 1605, 1216 and 1182, and 2946 cmꢁ1, respectively.
Band at 3191 cmꢁ1 is assigned to
mO–H vibration with intramolec-
ular hydrogen bonding. The strong band at 1605 cmꢁ1 is assigned
to C@N–N@C group.
In the complex 3, the absence of the N–H and C@O stretching
vibration bands is consistent with the deprotonation of the CONH
groups and coordination to the Fe(III) ion. The broad band at
3187 cmꢁ1 is reasonably assigned to OH stretching vibration which
is attributable to coordinated methanol molecules. The C@N–N@C
framework seen at l605 cmꢁ1 in the ligand 4 shifted to 1608 cmꢁ1
upon coordination to Fe(III) ion. The appearance of the band at
449 cmꢁ1 supports the involvement of phenolic oxygen in coordi-
nation through deprotonation (Fe–O, phenolic). The biding sites in
3 are similar to previously reports [9], which is also consistent with
the X-ray structural analysis.
3.2. Isolation of H3mcshcb
The 1H NMR of the ligand 2 presents a multiplet in the range d
1.80–1.76 for the methylene protons with a group –CH2COOH; a
multiplet in the range d 2.31–2.24 for the methylene protons with
group –NHCO– and –COOH, respectively; a doublet in the range d
7.01–6.99 for the phenyl proton 3-PhCH; a doublet in the range d
To obtain the ester methyl 4-(50-chlorosalicylhydrazinocarbon-
yl) butyrate, we have treated the metallacrown 3 with SnCl2 in
hydrochloric acid (Eq. (1)). The reduction takes place and leads to
separate into methyl 4-(50-chlorosalicylhydrazinocarbonyl) buty-
OH
O
O
6
H
+ 6 FeCl3·6H2O + 6 C5H5N + 17 CH3OH
N
Cl
N
H
OH
O
CH3OH
[FeIII6(C13H12N2O5Cl)6(CH3OH)6]·5CH3OH + 6 C5H5NH·Cl + 12 HCl + 42 H2O
Scheme 2. Synthetic route and chemical structures of the iron(III) metallacrown 3.

C.-Z. Jin et al. / Inorganica Chimica Acta 383 (2012) 20–25
23
Table 2
7.49–7.46 for the phenyl proton 4-PhCH; a singlet at d 7.90 for the
Selected bond lengths (Å) and angles (°) in 3.
phenyl proton 6-PhCH; two singlet at d 10.54 and 10.26 for the
hydrazine protons; a singlet at d 11.94 for the phenolic hydroxyl
group proton. In the 13C NMR spectra of the ligand 2, five peaks be-
tween 110 ppm and 140 ppm are possible, concluded to be the five
isolated carbon of phenyl ring, in addition to one carbon is con-
cluded in the range of 150–160 ppm. Three methylene carbons fall
into the 20–40 ppm, the three carbonyl carbons are judged in the
165–175 ppm region. All these assignments are in good agreement
with the spectra obtained.
Bond lengths
Fe1–N1
Fe1–O6
Fe2–N4
Fe2–O10
Fe3–N6
Fe3–O15
2.097(7)
2.002(6)
2.035(6)
2.043(6)
2.038(7)
2.046(6)
Fe4–N8
2.061(7)
2.078(7)
2.047(7)
2.027(7)
2.038(8)
2.043(6)
Fe4–O25
Fe5–N10
Fe5–O28
Fe6–N12
Fe6–O33
Bond angles
O1–Fe1–O6
O1–Fe1–N1
O8–Fe2–N4
O2–Fe2–O10
O9–Fe3–O15
O15–Fe3–N5
100.9(2)
93.9(3)
86.8(2)
93.7(2)
94.6(2)
87.9(2)
O19–Fe4–N7
O24–Fe4–O21
O20–Fe5–O28
N10–Fe5–O31
O32–Fe6–N12
O32–Fe6–O36
94.8(3)
91.4(2)
92.5(3)
92.6(3)
86.2(3)
91.0(2)
For the esterified ligand 4, the assignments of 1H NMR and 13C
NMR are similar to 2, except methyl group. The methyl protons of 4
present a singlet at d 3.60 in the 1H NMR spectra. Its methyl carbon
present a peak at 49.05 ppm in the 13C NMR.
3.4. Crystal structure of 3
4.882–4.920 Å. There are not any solvent molecules in the ‘host’
hole of metallcrown 3. At the same time, there are many kinds of
intermolecular hydrogen bonds in 3. These O–Hꢀ ꢀ ꢀO hydrogen
bond distances range between 2.610(8) and 2.874(8) Å. The hydro-
gen bonds in the crystal structure not only can form interesting
architectures, but also fix dexterously the solvent molecules and
carbomethoxy-group avoiding badly disorder.
The iron(III) metallacrown 3 crystallizes in the triclinic system
ꢀ
and space group P1. The molecular structure of 3 is shown in
Fig. 1. Important bond distances and angles are presented in Table
2. In ring 1 and 2, the two hexanuclear 18-membered rings of iron
atoms are linked by six hydrazide N–N groups, respectively. The
deprotonated and esterified ligand H3mcshcb acts as a trianionic
pentadentate ligand, one phenolate oxygen, one hydrazide nitro-
gen and one carbonyl oxygen in the ligand are bound to one Fe3+
cation, and the other carbonyl oxygen plus the other hydrazide
nitrogen in the same ligand are chelated to an adjacent Fe3+ cation.
The alternation of the connection that forced the cyclic ring system
of 3 to form as following trains: ring 1, –N1–Fe1–N2–N3–Fe2–N4–
N5–Fe3–N6–N1A–Fe1A–N2A–N3A–Fe2A–N4A–N5A–Fe3A–N6A–;
and ring 2, ndash;N7–Fe4–N8–N9–Fe5–N10–N11–Fe6–N12–N7A–
Fe4A–N8A–N9A–Fe5A–N10A–N11A–Fe6A–N12A–. All the iron
atoms of the rings adopt distorted octahedron coordination geom-
etry of the FeN2O4 type. The chirality of the metal centers in com-
3.5. Thermogravimetry
The TG curve of 3 exhibits four steps of weight losses with the
increasing temperature. From 30 to 134 °C, the weight loss was
9.5%, it is assigned to loss of the outside solvents and the sublima-
tion of the residue; from 134 to 420 °C, 44.4% of weight was lost,
which contributed to the loss of coordinated methanol molecules,
and the sublimation of the residue. From 420 to 608 °C, the TG
curve descended equably, and the weight loss is 29.0%. The weight
loss in this area should be deposition of the ligand mcshcb3ꢁ. From
608 to 800 °C, there was no change in the spare weight.
plex 3 are between the
K and D forms. As can clearly be seen from
the structure of 3, all ligands have been esterified and transferred
into H3mcshcb. The average iron–oxygen/nitrogen distance is Fe1
2.034, Fe2 2.030, Fe3 2.037, Fe4 2.028, Fe5 2.033, and Fe6
2.034 Å, respectively. Owing to the d5 high-spin electronic config-
uration of the iron(III) ion, there is no Jahn–Teller distortion in the
FeN2O4 octahedron. The approximate dimensions of the oval-
shaped cavity are about 10.12 Å for ring 1, and 10.07 Å for ring 2,
at largest diameter at the center of the hole. The neighboring
Feꢀ ꢀ ꢀFe interatomic distances in the 18-membered rings are
3.6. Magnetic property
The magnetic property of powder 3, obtained between 2 and
300 K using a Quantum Design SQUID MPMS XL-7 magnetometer,
is shown in Fig. 2. For the iron(III) metallacrown 3, the molar effec-
tive magnetic moment (leff) shows the presence of an antiferro-
magnetic coupling between the Fe(III) spin 5/2 centers. The
effective magnetic moment steadily decreased as the temperature
Fig. 1. Perspective view of 3 (solvent molecules and all hydrogen atoms have been omitted for clarity).

24
C.-Z. Jin et al. / Inorganica Chimica Acta 383 (2012) 20–25
ꢁ1
Fig. 2. Plots of vm (s), leff (h) vs. T and fitting line of leff (–) for the iron(III) metallacrown 3.
was lowered from 300 K (
and then abruptly to reach 2.01
l
eff = 13.22
B at 2.0 K (Fig. 2). The value of leff
at 300 K is smaller than the expected value (14.49 B) for six
noninteracting FeIII (S = 5/2). This is
characteristic of
l
B) to 65 K (
l
eff = 9.75 lB
)
trianionic pentadentate ligand, one phenolate oxygen, one hydra-
zide nitrogen and one carbonyl oxygen in the ligand are bound
to one Fe3+ cation, and the other carbonyl oxygen plus the other
hydrazide nitrogen in the same ligand are chelated to an adjacent
Fe3+ cation.
l
l
a
antiferromagnetic coupling, which is confirmed by a fitting to the
Curie–Weiss law with h = ꢁ20.5 K using the data within T > 65 K.
With the lowering temperature, the interaction among the iron
cluster becomes obvious. While the temperature cools to 2 K the
The metallacrown 3 can be further treated with SnCl2 to obtain
purified ester 4-(50-chlorosalicylhydrazinocarbonyl) butyrate. The
reduction takes place in hydrochloric acid and results in
moment leff is 2.01 lB
.
methyl 4-(50-chlorosalicylhydrazinocarbonyl) butyrate and Fe2+
.
Below about 65 K, the magnetic measurements deviate signifi-
cantly from the Curie–Weiss law suggesting that a magnetic model
considering the various internal magnetic pathways within the Fe6
cluster should be analyzed to describe the low temperature data.
The magnetic behavior of 3 might be due to a combination of the
following causes, when taking the inverse center symmetry into
account: (i) exchange interaction between the neighboring iron
ions bridged by the hydrazide N–N groups; (ii) exchange interac-
tion between the near-neighboring iron ions; (iii) exchange inter-
action between the para-neighboring iron ions; (iv) zero field
splitting (ZFS) of the ground state of FeIII. The equation describing
the temperature dependence of the magnetic susceptibility must
contain the following parameters: g, J1 (exchange interaction
between the neighboring iron ions); J2 (exchange interaction
between the near-neighboring iron ions); J3 (exchange interaction
between the para-neighboring iron ions); D (ZFS parameter for the
iron(III) ions). The modeling of the magnetic based data upon such
an equation is not reliable because overparametrization.
H3mcshcb is a special class of ester with bis-hydrazide. To our
knowledge, this class of ester can not be synthesized via a modular
acid-catalyzed approach.
Acknowledgments
This work was supported by the Key Project of Natural Science
Foundation of Hubei Province, China (2008CDA067) and the Foun-
dation of South-Central University for Nationalities.
Appendix A. Supplementary material
CCDC 774695 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.2011.
10.021.
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