Synthesis, structure, and properties of a binuclear Fe(III) complex with N-(1-propanol)-N,N-bis(3-tert-butyl-5-methyl-2-hydroxybenxyl)amine

Article abstract of DOI:10.1007/s11243-010-9422-6

Mannich reaction of 2-Amino propanol, 2-tert-butyl-4-methylphenol, and formaldehyde in the ratio of 1:2:2 provides a new compound, N-(1-propanol)-N,N- bis(3-tert-butyl-5-methyl-2-hydroxybenxyl)amine (H₃L), which has been characterized by X-ray crystallography and elemental analysis. In the presence of Et₃N, the reaction of H₃L and FeCl₃? 6H₂O gives a dinuclear Fe(III) complex [Fe₂L₂] 1, which has been characterized by X-ray crystallography, magnetic measurement, and cyclic voltammetry. The value of μ_eff at room temperature (5.97 μ_B) is much less than the expected spin-only value (8.37 μ_B) of two high spin (hs) Fe³⁺ (S = 5/2) ions [μ = g[?σZS(S + 1)]^1/2], indicating there are strong coupling interactions between Fe³⁺ ions. The magnetic behavior of 1 denotes the occurrence of intramolecular antiferromagnetic interactions (J = -13.35 cm^-1 ). CV of 1 reveals two reversible waves at 0.433 and 1.227 V versus AgCl/Ag, which can be ascribed to the successive redox coupling of Fe^IIFe^II/Fe^IIIFe^II and Fe ^IIIFe^II/Fe^IIIFe^III, respectively.

Full text of DOI:10.1007/s11243-010-9422-6

Transition Met Chem (2010) 35:999–1003
DOI 10.1007/s11243-010-9422-6
Synthesis, structure, and properties of a binuclear Fe(III)
complex with N-(1-propanol)-N,N-bis
(3-tert-butyl-5-methyl-2-hydroxybenxyl)amine
•
Xing-wu Tan Jin-ye Chen Xiao-hua Xie
•
•
•
Shu-zhong Zhan Yuan-fu Deng
Received: 3 August 2010 / Accepted: 2 September 2010 / Published online: 19 September 2010
Ó Springer Science+Business Media B.V. 2010
Abstract Mannich reaction of 2-Amino propanol, 2-tert-
butyl-4-methylphenol, and formaldehyde in the ratio of
1:2:2 provides a new compound, N-(1-propanol)-N,N-bis-
((3-tert-butyl-5-methyl-2-hydroxybenxyl)amine (H3L), which
has been characterized by X-ray crystallography and ele-
mental analysis. In the presence of Et3N, the reaction of H3L
and FeCl3ꢀ6H2O gives a dinuclear Fe(III) complex [Fe2L2]
1, which has been characterized by X-ray crystallography,
magnetic measurement, and cyclic voltammetry. The value
of leff at room temperature (5.97 lB) is much less than the
polynuclear complexes, and such studies have led to
essential insights into magnetostructural correlations [7–9].
It is well-known that in O-bridged systems the M–O–M
angle plays a vital role in determining the nature of
magnetic exchange between the metal ions [10, 11].
The study of magnetic exchange mechanisms between
metal centers will be useful in finding suitable building
blocks for the assembly of new magnetic materials and in
the development of new redox catalysts. An approach
toward this important goal is the design and preparation of
ligands that impart novel chemistry when incorporated into
the metal coordination sphere. The use of polydentate
ligands has afforded an impressive array of coordination
complexes with new architectures. Among them, the che-
lating phenolate groups have attracted our attention, as
these compounds have remarkable bridging ability to
afford multinuclear complexes that are potentially useful
for the development of new magnetic materials and cata-
lysts [12–17].
expected spin-only value (8.37 lB) of two high spin (hs)
P
Fe3? (S = 5/2) ions [l = g[ ZS(S ? 1)]1/2], indicating
there are strong coupling interactions between Fe3?
ions. The magnetic behavior of 1 denotes the occurrence
of intramolecular antiferromagnetic interactions (J =
-13.35 cm-1). CV of 1 reveals two reversible waves at
0.433 and 1.227 V versus AgCl/Ag, which can be ascribed
to the successive redox coupling of FeIIFeII/FeIIIFeII and
FeIIIFeII/FeIIIFeIII, respectively.
In this work, a new ligand (H3L) (Scheme 1) has been
prepared by the reaction of 2-Amino propanol, 2-tert-butyl-
4-methylphenol, and formaldehyde. In the presence of
Et3N, H3L reacts with FeCl3ꢀ6H2O to give a dinuclear
iron(III) complex 1. Here, we describe the synthesis and
characterization of H3L, and its iron complex 1, including
the crystal structures of H3L and 1, as well as the magnetic
and electrochemical properties of 1.
Introduction
Dinuclear metal (i.e. iron) complexes of chelating alkoxide
and aryl oxide ligands have attracted considerable interest
due to the structural elucidation of metalloenzymes and
redox catalysts, as well as the mechanistic understanding
of spin-coupled systems [1–6]. Particular interest has
been directed toward the exchange phenomena in di- and
Experimental
X. Tan ꢀ J. Chen ꢀ X. Xie ꢀ S. Zhan (&) ꢀ Y. Deng
College of Chemistry & Chemical Engineering,
South China University of Technology,
510640 Guangzhou, China
Magnetic susceptibility data for powder samples were
collected in the temperature range 2–300 K with a Quan-
tum Design SQUID Magnetometer MPMS XL-7. Effective
magnetic moments are calculated by the equation
e-mail: shzhzhan@scut.edu.cn
123

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Transition Met Chem (2010) 35:999–1003
t Bu
Scheme 1 Schematic
representation of the synthesis
of H3L and complex 1
t Bu
t Bu
HO
OH
OH
CH2O
+ NH2(CH2)3OH
2
H3L
N
Me
Me
Me
OH
t Bu
t Bu
Me
Me
O
O
O
Et3N
FeCl3 6H2O
N
N
Fe
Fe
O
O
O
t Bu
t Bu
Me
Me
1
leff = 2.828(vMT)1/2, where vM is the molar magnetic
susceptibility. Electrochemical experiments were carried
out with an Auto Lab instrument with a Platinum wire
working electrode, a platinum plate counter electrode, and
an AgCl/Ag electrode as the reference electrode. For the
experiments performed in CH3CN as solvent (ca. 1.2 9
10-5 mol L-1) containing 0.1 mol L-1 tetra-n-butylam-
monium perchlorate (TBAP) as supporting electrolyte, the
potential is referenced to an AgCl/Ag electrode.
X-ray crystallography
Data were collected with a Bruker SMART CCD area
detector using graphite monochromated Mo-K radiation
˚
(0.71073 A) at room temperature. All empirical absorption
corrections were applied by using the SADABS program
[18]. The structures were solved using direct methods, and
the corresponding non-hydrogen atoms refined anisotropi-
cally. All the hydrogen atoms of the ligands were placed in
calculated positions with fixed isotropic thermal parame-
ters and included in the structure factor calculations in the
final stage of full-matrix least-squares refinement. All
calculations were performed using the SHELXTL com-
puter program [19]. Table 1 lists details of the crystal
parameters, data collection, and refinement for HL and 1.
The selected bond distances and angles for HL and 1 are
listed in Tables 2 and 3.
Synthesis of H3L
A solution of 2-tert-butyl-4-methylphenol (3.28 g, 0.020 mol)
in ethanol (30 mL) was mixed with 3-amino-1-propanol
(0.75 g, 0.010 mol). 37% aqueous formaldehyde (1.80 mL,
0.020 mol) was added and the mixture was refluxed for
12 h. The reaction mixture was filtered, and the solid was
purified by crystallization at -4 °C from 9:1 dichloro-
methane/hexane to obtain yellow crystals, which were
collected and dried in vacuo (3.3 g, 75%). Found (calcd)
for C27H41NO3: C 76.0 (75.8), H 9.5 (9.6), N 3.3 (3.3).
Results and discussion
Scheme 1 shows the procedure of the synthesis of H3L and
complex 1. Mannich reaction of 2-tert-butyl-4-methyl-
phenol, 3-amino-1-propanol, and formaldehyde gave a new
compound H3L. In the presence of triethylamine, the
reaction of H3L and FeCl3ꢀ6H2O provided a dinuclear
Fe(III) complex 1.
Synthesis of 1
To a solution, containing ligand H3L (0.43 g, 1.0 mmol)
and triethylamine (0.30 g, 3.0 mmol) in THF/C2H5OH
(25 mL, 1:1), FeCl3ꢀ6H2O (0.270 g, 1.0 mmol) was added;
the color of the solution changed from yellow to deep red.
The solution was allowed to slowly evaporate to give red
crystals, which were collected and dried in vacuo (0.21 g,
44%). Anal. Found (calcd) for C27H38FeNO3: C 67.9
(67.7), H 8.0 (7.9), N 2.9 (2.9).
X-ray quality crystals of H3L were obtained by hexane
diffusion into an ethyl acetate solution of HL. An ORTEP
view of HL is displayed in Fig. 1. H3L contains a potential
[O3N] donor set and is a -3 anionic ligand (L3-) when
deprotonated. The distances between the nitrogen and
˚
carbon atoms are 1.474(3), 1.477(3), and 1.472(3) A,
respectively. C–O bond lengths are 1.367(3), 1.373(3), and
˚
1.409(3) A, respectively.
123

Transition Met Chem (2010) 35:999–1003
1001
˚
Table 1 Crystallographic data for compounds H3L and 1
Table 3 Selected bond distances (A) and angles (°) for complex 1
Parameter
H3L
1
Bond distances
Fe(1)–O(2)#1
Fe(1)–O(1)#1
Fe(1)–N(1)#1
N(1)–C(25)
1.8523(16) Fe(1)–O(3)#1
1.9594(15) Fe(1)–O(1)
1.8677(15)
2.015(2)
Empirical formula
Formula weight
C27H43NO4
445.63
C31H46FeNO4
552.54
2.184(2)
1.497(3)
1.500(3)
Fe(1)–Fe(1)#1
N(1)–C(24)
3.1433(11)
1.498(3)
˚
k(A)
0.71073
Triclinic
P - 1
0.71073
Triclinic
P - 1
Crystal system
Space group
N(1)–C(12)
Bond angles
˚
Unit cell dimension (A,°)
O(2)#1–Fe(1)–
O(3)#1
112.67(7) O(2)#1–Fe(1)–
O(1)#1
117.28(7)
a
b
c
a
b
c
10.527(2)
11.318(2)
12.379(3)
98.61(3)
10.677(2)
13.266(3)
13.335(3)
106.32(3)
105.25(3)
113.36(3)
1506.3(6)
2
O(3)#1–Fe(1)–
O(1)#1
130.02(7) O(2)#1–Fe(1)–O(1) 97.78(7)
O(3)#1–Fe(1)–O(1) 96.48(7)
O(1)#1–Fe(1)–O(1) 75.46(7)
110.32(3)
102.46(3)
1309.4(5)
2
O(2)#1–Fe(1)–
N(1)#1
91.34(7)
O(3)#1–Fe(1)–
N(1)#1
90.01(8)
3
˚
O(1)#1–Fe(1)–
N(1)#1
90.65(7)
O(1)–Fe(1)–N(1)#1 165.75(6)
V (A )
Z
Fe(1)#1–O(1)–Fe(1) 104.54(7)
Dc (Mgm-3
)
1.125
1.218
The symmetry operation: #1 x, y, z; #2 -x, -y, -z
F(000)
484
594
h range for data collection
Reflections collected/unique
Data/restraints/parameters
Goodness-of-fit on F2
3.02 to 27.47
12,858/5,915
5,915/0/285
1.088
3.06 to 25.20
11,955/5,371
5,371/0/334
1.058
Final R indices [I [ 2r(I)]
R1 = 0.0685
wR2 = 0.2096
R1 = 0.1226
wR2 = 0.2653
R1 = 0.0442
wR2 = 0.1261
R1 = 0.0502
wR2 = 0.1317
R indices(all data)
˚
Table 2 Selected bond distances (A) and angles (°) for H3L
Bond distances
O(1)–C(1)
O(3)–C(27)
N(1)–C(25)
Bond angles
1.367(3)
1.409(3)
1.477(3)
O(2)–C(13)
N(1)–C(12)
N(1)–C(24)
1.373(3)
1.474(3)
1.472(3)
Fig. 1 ORTEP plot of H3L. H2O molecule is omitted for clarity
˚
2.15 A [20]. Two iron centers are separated by
˚
3.1433(11) A, a value that is similar to those found in other
C(12)–N(1)–C(25) 110.94(17) C(12)–N(1)–C(24) 110.36(19)
C(25)–N(1)–C(24) 109.68(18)
oxygen-bridged dinuclear iron compounds [21, 22]. The
bridging plane containing Fe(1), O(1), Fe(1a), O(1a) is
planar with the torsion angle O(1a)–Fe(1)–O(1)–Fe(1a) of
0°. The angle of Fe–O(1)–Fe is 104.54(7)°.
The symmetry operation: #1 x, y, z; #2 -x, -y ? 2, -z
The ORTEP view of 1, excluding solvent molecules, is
illustrated in Fig. 2. The structure of 1 sits on a crystallo-
graphic center of symmetry and the two halves of the
molecule are symmetry related. The molecular structure of
1 is formed by two ligand (L3-) molecules, two iron atoms,
and two THF solvent molecules. The geometry at each iron
center is best described as a distorted trigonal bipyramid.
The iron atom is bonded to two phenolate oxygens [O(2),
O(3)], two hydroxy oxygens [O(1), O(1a)], and one amine
nitrogen [N(1)]. The observed Fe–O bond distances fall in
Compared with the structure of H3L, the ligand in 1
shows a little variation of the bonding on coordination. The
N–C bond distances in H3L are 1.470(3), 1.473(3), and
˚
1.477(3) A, respectively. It would be expected that the
N–C bond distances would be dissimilar as a consequence
of the different bond order between these atoms. The
corresponding bond distances are 1.497(3), 1.498(3), and
˚
1.500(3) A, respectively.
The magnetic behavior of complex 1 was studied in the
range 2–300 K and is shown in Fig. 3 in the form of vM
versus T. The value of leff at room temperature (5.95 lB) is
much less than the expected spin-only value (8.37 lB) of two
˚
the range 1.8523(16) to 2.015(2) A. The Fe–N distance
˚
[2.184(2) A] is similar to the octahedral Fe–N distance of
123

1002
Transition Met Chem (2010) 35:999–1003
Fig. 2 ORTEP plot of 1. THF
molecules are omitted for clarity
.025
.020
.015
.010
.005
0.000
-.005
FeIIIFeII → 2FeIII
20
10
0
2FeII → FeIIIFeII
-10
0
100
200
300
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
T/K
E/V
Fig. 3 Plot of the temperature dependence of the vM for 1
Fig. 4 Cyclic voltammogram of 1 in CH3CN/0.1 mol L-1 [Bu4N]ClO4
P
at 50 mV s-1 scan rate
high-spin (hs) Fe3? (S = 5/2) ions [l = g[ ZS(S ? 1)]1/2],
indicating there are strong interactions between Fe3? ions.
The effective magnetic moment (leff) decreases abruptly
with cooling to a minimum value of 0.1 lB at 2 K.
Assuming isotropic exchange, the experimental mag-
netic data are simulated for the dimeric Fe(III) system
based on the spin Hamiltonian H = -2JS1S2 with the
following equation (S1 = S2 = 5/2) [23]:
Very good agreement between the theoretical and experi-
mental data is obtained by using the following parameters:
g = 2.0, J = -13.35 cm-1, which is the normal strengths
of antiferromagnetic interaction for (l-alkoxo)diiron(III)
complexes. The coupling constant J has been reported to be
-11 to -26 cm-1 for mono- and bis(l-alkoxo)diiron(III)
complexes [24–27]. In accordance with Gorun and Lippard
[7], the magnitude of anti-ferromagnetic coupling is deter-
mined by the structural parameter P, which represents a half
of the shortest super-exchange pathway between two iron
vM ¼ ð2Nb2g2=kTÞ½ð55 þ 30 expðꢁ10J=kTÞ
þ 14 expðꢁ18J=kTÞ þ 5 expðꢁ24J=kTÞ
þ expðꢁ28J=kTÞÞ=ð11 þ 9 expðꢁ10J=kTÞ
þ 7 expðꢁ18J=kTÞ þ 5 expðꢁ24J=kTÞ
þ 3 expðꢁ28J=kTÞ þ expðꢁ30J=kTÞÞꢂ
atoms. The relation between the P parameter and J is given
by -J (cm-1) = Aexp(BP(A)), where A = 8.763 9 10
11
˚
123

Transition Met Chem (2010) 35:999–1003
1003
4. Du Bois J, Mizoguchi TJ, Lippard SJ (2000) Coord Chem Rev
200–202:443
5. Tshuva EY, Lippard SJ (2004) Chem Rev 104:987
6. Britovsek GJP, Gibson VC, Wass DF (1999) Angew Chem Int Ed
38:428
7. Gorun SM, Lippard SJ (1991) Inorg Chem 30:1625
8. Jullien J, Juhasz G, Mialane P, Dumas E, Mayer CR, Marrot J,
Riviere E, Bominaar EL, Munck E, Secheresse F (2006) Inorg
Chem 45:6922
9. Labisbal E, Rodriguez L, Souto O, Sousa-Pedrares A, Garcia-
Vazquez J, Romero J, Sousa A, Yanez M, Orallob F, Real J (2009)
Dalton Trans 8644
10. Merz L, Haase W (1980) J Chem Soc Dalton Trans 875
11. Thompson LK, Mandal SK, Tandon SS, Bridson JN, Park MK
(1996) Inorg Chem 35:3117
12. Tshuva EY, Versano M, Goldberg I, Kol M, Weitman H,
Goldschmidt Z (1999) Inorg Chem Commun 2:371
13. Rothwell LP (1988) Acc Chem Res 21:153
14. Schweiger SW, Tillison DL, Thorn MG, Fanwick PE, Rothwell IP
(2001) J Chem Soc Dalton Trans 2401
and B = -12.663. Applying the structural parameter P of
complex 1 to the Gorun–Lippard equation resulted in
J = -12.8 cm-1, which agrees with the experimental data.
The cyclic voltammograms of complex 1 measured in
CH3CN/0.1 M [Bu4N]ClO4 are shown in Fig. 4. 1 shows
two redox couples, at 0.433 and 1.227 V versus AgCl/Ag,
which can be ascribed to the successive redox coupling of
FeIIFeII/FeIIIFeII and FeIIIFeII/FeIIIFeIII, respectively.
In summary, the present study shows that the N-(1-pro-
panol)-N,N-bis(3-tert-butyl-5-methyl-2-hydroxybenxyl)amine
gives a dinuclear iron(II) complex. Currently, we are explor-
ing this further, as well as the reactions of H3L with other
metals.
Supplementary data
15. Caulfield MJ, Russo T, Solomon DH (2000) Aust J Chem 53:545
16. Castellano B, Solari E, Florian C, Re N, Chiesi-Villa A, Rizzoli C
(1999) Chem Eur J 5:722
17. Nie H, Aubin SMJ, Mashuta MS, Wu CH, Richardson JF,
Hendrickson DN, Buchanan RM (1995) Inorg Chem 34:2382
18. Sheldrick GM (1996) SADABS, program for empirical absorp-
CCDC 775011 and 757783 contain the supplementary
crystallographic data of H3L and 1, respectively. These data
can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (?44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk.
¨
tion correction of area detector data. University of Gottingen,
¨
Gottingen
19. Sheldrick GM (1997) SHELXS 97, program for crystal structure
¨
¨
refinement. University of Gottingen, Gottingen
20. Norman RE, HolzRC, Menage S, QueL Jr, ZhangJH, O0Connor CJ
(1990) Inorg Chem 29:4629
Acknowledgment This work was supported by the Research Foun-
dation for Returned Chinese Scholars Overseas of Chinese Education
Ministry (No. B7050170), the National Science Foundation of China
(No. 20971045), and the Student Research Program (SRP) of South
China University of Technology.
21. Werner R, Ostrovsky S, Griesar K, Haase W (2001) Inorg Chim
Acta 326:78
¨
22. Horn A Jr, Vencato I, Bortoluzzi AJ, Horner R, Nome Silva RA,
Spoganicz B, Drago V, Terenzi H, de Oliveira MCB, Werner R,
Haase W, Neves A (2005) Inorg Chim Acta 358:339
23. Wrobleski JT, Brown DB (1978) Inorg Chem 17:2959
24. Walker JD, Poli R (1990) Inorg Chem 29:756
25. MCnage S, Que L Jr (1990) Inorg Chem 29:4293
References
26. Krebs B, Schepers K, Bremer B, Henkel G, Althaus E, Muller-
Wannuth W, Griesar K, Haase W (1994) Inorg Chem 33:1907
27. Ming LJ, Jang HG, Que L Jr (1992) Inorg Chem 31:359
1. Kurtz DM (1990) Chem Rev 90:585
2. Wallar BJ, Lipscomb JD (1996) Chem Rev 96:2625
3. Solomon EI, Brunold TC, Davis MI, Kemsley JN, Lee SK,
Lehnert N, Neese F, Skulan AJ, Yang YS, Zhou J (2000) Chem
Rev 100:235
123