Biomimetic iron(iii) complexes of N3O and N3O 2 donor ligands: Protonation of coordinated ethanolate donor enhances dioxygenase activity

Article abstract of DOI:10.1039/c1dt10495k

A series of iron(iii) complexes 1-4 of the tripodal tetradentate ligands N,N-bis(pyrid-2-ylmethyl)-N-(2-hydroxyethyl)amine H(L1), N,N-bis(pyrid-2- ylmethyl)-N-(2-hydroxy- propyl)amine H(L2), N,N-bis(pyrid-2-ylmethyl)-N- ethoxyethanolamine H(L3), and N-((pyrid-2-ylmethyl)(1-methylimidazol-2-ylmethyl) )-N-(2-hydroxyethyl)amine H(L4), have been isolated, characterized and studied as functional models for intradiol-cleaving catechol dioxygenases. In the X-ray crystal structure of [Fe(L1)Cl₂] 1, the tertiary amine nitrogen and two pyridine nitrogen atoms of H(L1) are coordinated meridionally to iron(iii) and the deprotonated ethanolate oxygen is coordinated axially. In contrast, [Fe(HL3)Cl₃] 3 contains the tertiary amine nitrogen and two pyridine nitrogen atoms coordinated facially to iron(iii) with the ligand ethoxyethanol moiety remaining uncoordinated. The X-ray structure of the bis(μ-alkoxo) dimer [{Fe(L5)Cl}₂](ClO₄)₂5, where HL is the tetradentate N₃O donor ligand N,N-bis(1-methylimidazol-2-ylmethyl)-N- (2-hydroxyethyl)amine H(L5), contains the ethanolate oxygen donors coordinated to iron(iii). Interestingly, the [Fe(HL)(DBC)]⁺ and [Fe(HL3)(HDBC)X] adducts, generated by adding ～1 equivalent of piperidine to solutions containing equimolar quantities of iron(iii) complexes 1-5 and H₂DBC (3,5-di-tert-butylcatechol), display two DBC^2- → iron(iii) LMCT bands (λ_max: 1, 577, 905; 2, 575,915; 3, 586, 920; 4, 563, 870; 5, 557, 856 nm; Δλ_max, 299-340 nm); however, the bands are blue-shifted (λ_max: 1, 443, 700; 2, 425, 702; 3, 424, 684; 4, 431, 687; 5, 434, 685 nm; Δλ_max, 251-277 nm) on adding 1 more equivalent of piperidine to form the adducts [Fe(L)(DBC)] and [Fe(HL3)(HDBC)X]. Electronic spectral and pH-metric titration studies in methanol disclose that the ligand in [Fe(HL)(DBC)]⁺ is protonated. The [Fe(L)(DBC)] adducts of iron(iii) complexes of bis(pyridyl)-based ligands (1,2) afford higher amounts of intradiol-cleavage products, whereas those of mono/bis(imidazole)-based ligands (4,5) yield mainly the auto-oxidation product benzoquinone. It is remarkable that the adducts [Fe(HL)(DBC)] ⁺/[Fe(HL3)(DBC)X] exhibit higher rates of oxygenation affording larger amounts of intradiol-cleavage products and lower amounts of benzoquinone. The Royal Society of Chemistry 2011.

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PAPER
Biomimetic iron(III) complexes of N3O and N3O2 donor ligands: protonation
of coordinated ethanolate donor enhances dioxygenase activity†‡
Karuppasamy Sundaravel,a Muniyandi Sankaralingam,a Eringathodi Sureshb and Mallayan Palaniandavar*a
Received 23rd March 2011, Accepted 13th June 2011
DOI: 10.1039/c1dt10495k
A series of iron(III) complexes 1–4 of the tripodal tetradentate ligands N,N-bis(pyrid-2-ylmethyl)-N-(2-
hydroxyethyl)amine H(L1), N,N-bis(pyrid-2-ylmethyl)-N-(2-hydroxy- propyl)amine H(L2),
N,N-bis(pyrid-2-ylmethyl)-N-ethoxyethanolamine H(L3), and N-((pyrid-2-ylmethyl)(1-
methylimidazol-2-ylmethyl))-N-(2-hydroxyethyl)amine H(L4), have been isolated, characterized and
studied as functional models for intradiol-cleaving catechol dioxygenases. In the X-ray crystal structure
of [Fe(L1)Cl2] 1, the tertiary amine nitrogen and two pyridine nitrogen atoms of H(L1) are coordinated
meridionally to iron(III) and the deprotonated ethanolate oxygen is coordinated axially. In contrast,
[Fe(HL3)Cl3] 3 contains the tertiary amine nitrogen and two pyridine nitrogen atoms coordinated
facially to iron(III) with the ligand ethoxyethanol moiety remaining uncoordinated. The X-ray structure
of the bis(m-alkoxo) dimer [{Fe(L5)Cl}2](ClO4)2 5, where HL is the tetradentate N3O donor ligand
N,N-bis(1-methylimidazol-2-ylmethyl)-N-(2-hydroxyethyl)amine H(L5), contains the ethanolate
oxygen donors coordinated to iron(III). Interestingly, the [Fe(HL)(DBC)]+ and [Fe(HL3)(HDBC)X]
adducts, generated by adding ~1 equivalent of piperidine to solutions containing equimolar quantities
of iron(III) complexes 1–5 and H2DBC (3,5-di-tert-butylcatechol), display two DBC2- → iron(III)
LMCT bands (lmax: 1, 577, 905; 2, 575,915; 3, 586, 920; 4, 563, 870; 5, 557, 856 nm; Dlmax, 299–340 nm);
however, the bands are blue-shifted (lmax: 1, 443, 700; 2, 425, 702; 3, 424, 684; 4, 431, 687; 5, 434, 685 nm;
Dlmax, 251–277 nm) on adding 1 more equivalent of piperidine to form the adducts [Fe(L)(DBC)] and
[Fe(HL3)(HDBC)X]. Electronic spectral and pH-metric titration studies in methanol disclose that the
ligand in [Fe(HL)(DBC)]+ is protonated. The [Fe(L)(DBC)] adducts of iron(III) complexes of
bis(pyridyl)-based ligands (1,2) afford higher amounts of intradiol-cleavage products, whereas those of
mono/bis(imidazole)-based ligands (4,5) yield mainly the auto-oxidation product benzoquinone. It is
remarkable that the adducts [Fe(HL)(DBC)]+/[Fe(HL3)(DBC)X] exhibit higher rates of oxygenation
affording larger amounts of intradiol-cleavage products and lower amounts of benzoquinone.
essential for the global carbon cycle, and have potential utilities in
Introduction
bioremediation efforts. It is catalyzed by the catechol dioxygenase
Nature typically employs metal centers within enzymes to
enzymes which can be split into two families: intradiol dioxyge-
activate dioxygen and carry out crucial transformations in-
nases and extradiol dioxygenases. While the former cleave carbon–
volved in metabolism, mammalian physiology and biodegradation
carbon bonds between the two catechol oxygens to give muconic
processes.1–5 The oxidative ring cleavage of catechol and other
dihydroxy aromatics is a key step in the biodegradation of
naturally occurring aromatic pollutants1–3 by soil bacteria, which is
anhydride,6–10 the latter cleave the carbon–carbon bond adjacent
to the catechol oxygens to yield 2-hydroxymuconic semialdehyde
as the product11–15 (Scheme 1). The isolated state of the extradiol-
cleaving enzymes is characterized by a non-heme iron(II) active
site coordinated by the so-called 2-His-1-carboxylate facial triad,
consisting of two histidines and one glutamate–aspartate protein
residue. The X-ray crystal structure of the isolated intradiol-
cleaving protocatechuate 3,4-dioxygenase (3,4-PCD) from Pseu-
domonas putida reveals a trigonal-bipyramidal iron(III) center
coordinated to four endogenous protein ligands, namely, H460,
H462, Tyr408 and Tyr447.3,7–9 The fifth coordination position is
occupied by a solvent-derived hydroxide ligand. In the substrate
activation mechanism16 proposed already, the hydroxide and the
aCentre for Bioinorganic Chemistry, School of Chemistry, Bharathi-
dasan University, Tiruchirappalli, 620 024, India. E-mail: palanim51@
yahoo.com, palaniandavarm@gmail.com; Tel: +91-431-2407053, 2407125
bAnalytical Science Discipline, Central Salt and Marine Chemicals Research
Institute, Bhavnagar, 364 002, India
† Dedicated to Professor C. Natarajan on the occasion of his 80th birthday.
‡ Electronic supplementary information (ESI) available. The results of
spectrophotometric titration using triethylamine as a base and pH-metric
titration graphs. CCDC reference numbers 819033–819035. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c1dt10495k
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Scheme 1 Mode of cleavage of extradiol and intradiol dioxygenases.
Scheme 3 Ligands employed in this study.
(hydroxyethyl)amine38 (H(L1)) by 1-methylimidazolylmethyl arms
(H(L4), H(L5)), and by replacing the ethanol moiety in H(L1)
by a propanol (H(L2)) or ethoxyethanol (H(L3)) moiety. The
imidazolyl and pyridyl donor atoms mimic the histidine imidazole
nitrogen donor function of Tyr447 in the 3,4-PCD enzyme. The
ability of the coordinated ethanolate moiety to act as an internal
base by abstracting a proton from the catechol substrate makes
the iron(III) complexes excellent functional models for the function
of axially coordinated Tyr447 in the enzyme. Thus, interestingly,
upon protonation of the ethanolate moiety in the catecholate
adducts, both the rate of dioxygenation and the yield of intradiol
cleavage product increase.
axial Tyr447 unit act as Lewis bases to accept two protons of
the catechol substrate and detach from the iron(III) center to
form an enzyme–substrate adduct (Scheme 2).4 Consequently,
the coordinated substrate with semiquinone radical character is
attacked by dioxygen to form an alkylperoxo intermediate, which
is converted into muconic anhydride.6–10
Enormous efforts17–38 have been directed towards the synthesis
and characterization of iron(III) complexes of tetradentate linear
and tripodal and tetraaza macrocyclic ligands as structural and
functional models for the catecholate-iron(III) form of catechol
dioxygenases and all these complexes yield mainly intradiol-
cleavage products. In our laboratory we have previously investi-
gated many series of iron(III) complexes of tri- and tetradentate
ligands with pyridine, (benz)imidazole, phenolate and carboxylate
donors, N2O,17,27 N3,21,28 N3O,18,20,29,30 N2O219,31 and N4,32 to closely
mimic the structure and function of intra- and extradiol-cleaving
catechol dioxygenase enzymes and correlated their reaction rate as
well as cleavage yields with the ligand environment. Very recently,
we have reported30 iron(III) complexes of tripodal tetraden-
tate monophenolate and nitrogen donor ligands as models for
extradiol-cleaving enzymes and showed that the extradiol cleavage
products are obtained in good yields upon adding an equivalent
amount of base to the iron(III)-catecholate adduct. Also, the
highest extradiol-to-intradiol product selectivity is achieved32 by
using iron(III) complexes of linear tetradentate N4 ligands in
the presence of triethylamine (1.0 equivalent). In our continuous
search for more relevant and efficient biomimetic models we have
now isolated and characterized a series of iron(III) complexes of
systematically varied tripodal tetradentate N3O (H(L1), H(L2),
H(L4) and H(L5)) and pentadentate N3O2 (H(L3)) donor ligands
(Scheme 3). We wish to understand the role of ligand steric and
electronic factors on iron(III) coordination geometry by replac-
ing one or two pyridylmethyl arms in bis(pyrid-2-ylmethyl)-N-
Experimental section
Materials
Pyridine-2-carboxaldehyde,
hyde, iron(III) perchlorate hydrate, sodium borohydride, sodium
triacetoxyborohydride, 3,5-di-tert-butylcatechol (H2DBC),
1-methylimidazole-2-carboxalde-
3-methylcatechol (3-MeH2CAT), 3-amino-1-propanol, 2(2-
aminoethoxy)ethanol (Aldrich), 3,4,5,6-tetrachlorocatechol
(H2TCC) (Lancaster), 2-amino-1-ethanol (Merck, India),
catechol (H2CAT) (Loba, India), iron(III) chloride (anhydrous)
(Merck, India) were used as received. The supporting electrolyte
tetra-N-butylammonium perchlorate (Aldrich) was prepared by
the procedure reported previously.39
Synthesis of ligands
The following general procedure40 was followed to prepare the
ligands H(L1), H(L2), H(L3) and H(L5), whereas the ligand H(L4)
was prepared in two steps.41
Scheme 2 The proposed substrate-binding process in protocatechuate 3,4-dioxygenase.
The Royal Society of Chemistry 2011 Dalton Trans., 2011, 40, 8444–8458 | 8445
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N,N-Bis(pyrid-2-ylmethyl)-N-(2-hydroxyethyl)amine
H(L1).
hydroxyethyl)amine (0.30 g, 2 mmol) and 1-methylimidazole-2-
carboxaldehyde (0.22 g, 2 mmol) were mixed in dry THF (20 mL).
Sodium triacetoxyborohydride (1.27 g, 6 mmol) was added to the
reaction mixture, followed by glacial acetic acid (0.25 g, 4 mmol).
The mixture was then stirred at room temperature for 48 h under
nitrogen atmosphere. The solvent was removed and the residue
was dissolved in dichloromethane and neutralized with saturated
sodium bicarbonate solution. The dichloromethane extract was
dried (anhydrous Na2SO4) and the solvent was evaporated to
give a yellow oil (0.33 g, 67%). The product obtained was used
without further purification for the complex preparation. 1H
NMR (400 MHz, CDCl3): d = 8.65–7.40 (m, 4H), 6.75 (d, J =
2.2 Hz, 1H), 6.70 (d, J = 2.2 Hz, 1H), 3.67 (s, 3H), 4.20 (s, 2H),
3.60 (s, 2H) 2.58 (t, J = 4.4 Hz, 2H), 3.63 (t, J = 5.0 Hz, 2H), 2.25
(br s, 1H) ppm. EI-MS m/z = 246 (C13H18N4O+).
To a mixture of 2-amino-1-ethanol (0.12 g, 2 mmol) and pyridine-
2-carboxaldehyde (0.43 g, 4 mmol) in dry tetrahydrofuran
(30 mL), sodium triacetoxyborohydride (1.69 g, 8 mmol) followed
by glacial acetic acid (0.34 mL, 6 mmol) was added under a N2
atmosphere. The reaction mixture was stirred for 72 h under a
N2 atmosphere. The solvent was removed by rotary evaporation
and the residue was dissolved in dichloromethane and then
neutralized by the addition of saturated sodium bicarbonate
solution (2 ¥ 30 mL). The organic fractions were combined,
dried with Na2SO4, and the solvent was removed under reduced
pressure to obtain the product as a yellow oil (0.41 g, 85%) which
was used without further purification for isolation of the complex.
1H NMR (400 MHz, CDCl3): d = 8.54–8.53 (m, J = 2.8 Hz, 2H),
7.62–7.58 (m, J = 8.6 Hz, 2H), 7.32–7.31 (d, J = 3.8 Hz, 2H),
7.16–7.13 (m, J = 6.2 Hz, 2H), 4.10 (s, 4H), 2.58 (t, J = 5.0 Hz,
2H), 3.65 (t, J = 5.0 Hz, 2H), 2.10 (br s, 1H), ppm. EI-MS m/z =
243 (C14H17N3O+).
N,N -Bis(1-methylimidazol-2-ylmethyl)-N -(2-hydroxyethyl)-
amine H(L5). The ligand H(L5) was prepared by the pro-
cedure adopted for the preparation of H(L1) except that 1-
methylimidazole-2-carboxaldehyde was (0.44 g, 4 mmol) was used
instead of pyridine-2-carboxaldehyde to obtain H(L5) as a creamy
yellow solid (0.36 g, 72%), which is pure enough for the preparation
N,N-Bis(pyrid-2-ylmethyl)-N-(2-hydroxypropyl)amine H(L2).
The ligand H(L2) (0.42 g, 82%) was synthesized by the procedure
described above for the preparation of H(L1) except that 3-amino-
1-propanol (0.15 g, 2 mmol) was used instead of 2-amino-1-
1
of the iron(III) complex. H NMR (400 MHz, CDCl3): d = 6.80
1
ethanol. H NMR (400 MHz, CDCl3): d = 8.54–8.53 (m, J =
(d, J = 2.6 Hz, 2H), 6.68 (d, J = 2.2 Hz, 2H), 3.64 (s, 6H), 3.60 (s,
4H), 2.55 (t, J = 3.8 Hz, 2H), 3.67 (t, J = 4.4 Hz, 2H), 2.0 (b s, 1H)
ppm. EI-MS m/z = 249 (C12H19N5O+).
2.0 Hz, 2H), 7.70–7.61 (m, J = 17.4 Hz, 2H), 7.41–7.39 (d, J =
4.0 Hz, 1H), 7.29–7.27 (d, J = 3.6 Hz, 1H), 7.21–7.14 (m, J =
14.6 Hz, 2H), 3.97 (s, 4H), 2.41 (t, J = 6.0 Hz, 2H), 3.58 (t, J =
5.2 Hz, 2H), 1.60 (m, J = 20.2 Hz, 2H), 2.12 (br s, 1H) ppm. EI-MS
m/z = 257 (C15H19N3O+).
Synthesis of iron(III) complexes
Caution: Perchlorate salts of metal complexes with organic ligands
are potentially explosive and should be handled with great care.
N,N-Bis(pyrid-2-ylmethyl)-N-ethoxyethanolamine
H(L3).
The ligand H(L3) (0.44 g, 77%) was prepared by the same method
as that used for H(L1) except that 2(2-aminoethoxy)ethanol
(0.21 g, 2 mmol) was used instead of 2-amino-1-ethanol. 1H
NMR (400 MHz, CDCl3): d = 8.54–8.50 (dd, J = 2.4, 2.4 Hz,
2H), 7.70–7.63 (m, J = 12.6 Hz, 2H), 7.54–7.52 (d, J = 4.0 Hz,
2H), 7.21–7.14 (m, J = 14.4 Hz, 2H), 3.94 (s, 4H), 3.73 (t, J =
4.4 Hz, 2H), 3.52 (t, J = 5.0 Hz, 2H), 3.49 (t, J = 4.4 Hz, 2H),
2.59 (t, J = 5.0 Hz, 2H), 2.25 (br s, 1H) ppm. EI-MS m/z = 287
[Fe(L1)Cl2] 1. FeCl3 (0.16 g, 1 mmol) in methanol (10 mL)
was added to a solution of H(L1) (0.24 g, 1 mmol) in methanol
(10 mL), stirred well and then cooled. The yellow complex
(0.30 g, 82%) was filtered off, washed with small amounts of cold
methanol and dried under vacuum. Yellow crystals of [Fe(L1)Cl2]
1 suitable for X-ray diffraction was obtained by slow evaporation
of acetonitrile : methanol (1 : 1, v/v) solution. Anal. Calcd for
C14H16N3FeCl2O (369): C, 45.56; H, 4.37; N, 11.39. Found: C,
45.58; H, 4.41; N, 11.42. ESI-MS m/z = 333 (C14H16N3OFeCl+).
+
(C16H21N3O2 ).
N -((Pyrid-2-ylmethyl)(1-methylimidazol-2-ylmethyl)-N -(2-
hydroxyethyl)amine H(L4). The ligand H(L4) was prepared in
two steps.
[Fe(L2)Cl2] 2. The complex 2 (0.31 g, 79%) was prepared by
using the procedure employed for isolating 1. Anal. Calcd for
C15H18N3FeCl2O (383): C, 47.03; H, 4.74; N, 10.97. Found: C,
47.05; H, 4.79; N, 11.01. ESI-MS m/z = 347 (C15H18N3OFeCl+).
Step 1: Synthesis of N-pyrid-2-ylmethyl-N-(2-hydroxyethyl)-
amine42. Pyridine-2-carboxaldehyde (0.54 g,
5 mmol) in
[Fe(HL3)Cl3] 3. A procedure analogous to that used to prepare
1 was adopted, using anhydrous FeCl3 (0.16 g, 1 mmol) and H(L3)
(0.28 g, 1 mmol) instead of H(L1). The solution was stirred which
resulted in the formation of yellow colored precipitate (0. 31 g
70%) after one hour and it was filtered off. Anal. Calcd. for
C16H21N3O2FeCl3 (449.56): C, 42.75; H, 4.71; N, 9.35. Found:
C, 42.77; H, 4.72; N, 9.39. X-Ray diffraction quality crystals
of 3 were obtained by the vapour diffusion of diethylether into
the complex dissolved in methanol : acetonitrile (2 : 1, v/v) solvent
methanol was added dropwise to 2-amino-1-ethanol (0.31 g,
5 mmol) in methanol (20 mL). The reaction mixture was stirred
overnight to get a bright yellow oil. NaBH4 (0.29 g, 7.5 mmol) was
◦
then added at 0 C, the solution was stirred overnight and then
rotary evaporated to dryness. The residue was dissolved in water
and extracted with dichloromethane and dried with Na2SO4. The
combined organic layer was rotary evaporated to get N-pryidy-2-
ylmethyl-N-(2-hydroxyethyl)amine as a yellow oil (0.30 g, 40%).
1H NMR (400 MHz, CDCl3): d = 8.60–7.40 (m, 4H), 4.15 (s, 2H),
2.77 (t, J = 4.2 Hz, 2H), 3.65 (t, J = 5.0 Hz, 2H), 2.20 (br s, 1H),
2.50 (br s, 1H) ppm. EI-MS m/z = 152 (C8H12N2O+).
+
mixture. ESI-MS m/z = 414 (C16H21N3O2FeCl2 ).
[Fe(L4)Cl2] 4. The complex 4 (0.23 g, 63%) was also pre-
pared by using the procedure employed for isolating [Fe(L1)Cl2].
Anal. Calcd for C13H17N4FeCl2O (372): C, 41.97; H, 4.61; N,
Step 2: Synthesis of N-pyrid-2-ylmethyl-N-(1-methylimidazol-2-
ylmethyl)-N-(2-hydroxyethyl)amine. N-Pyrid-2-ylmethyl-N-(2-
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15.06. Found: C, 41.99; H, 4.64; N, 15.08. ESI-MS m/z = 337
under identical conditions for various scan rates. The instruments
utilized included an EG & G PAR 273 Potentiostat/Galvanostat
and Pentium IV computer along with EG & G M270 software
(C13H17N4OFeCl+).
1
[{Fe(L5)Cl}2](ClO4)2 5. H(L5) (0.25 g, 1 mmol) in ethanol
(5 mL) was added to a solution of FeCl3 (0.11 g, 0.66 mmol) and
Fe(ClO4)3 (0.12 g, 0.33 mmol) in ethanol/methanol (5 + 5 mL),
stirred well and then cooled. The yellow complex (0.33 g, 75%) was
filtered off, washed with small amounts of cold methanol and dried
under vacuum. Anal. Calcd for C24H36Cl4Fe2N10O10 (878.11): C,
32.83; H, 4.13; N, 15.95. Found: C, 32.85; H, 4.17; N, 15.99. Red-
orange crystal of [{Fe(L5)Cl}2](ClO4)2 5 suitable for X-ray diffrac-
tion was obtained by slow evaporation of acetonitrile : methanol
(2 : 1, v/v) solution layered with diethylether.
to carry out the experiments and to acquire the data. H NMR
spectra were recorded on a Bruker 400 MHz spectrometer. The
cleavage products were analyzed using Hewlett Packard (HP)
6890 Gas Chromatograph (GC) series equipped with a Flame
Ionization Detector (FID) and a HP-5 capillary column (30 m ¥
0.32 mm ¥ 2.5 mm). GC-MS analysis was performed on a
Agilent 7890A GC System and 5975C inert MSD with Triple-
Axis Detector GC-MS (Electron Ionization) instrument using a
HP-5 capillary column.
Physical measurements
Data collection and structure refinement
Elemental analyses were performed on a Perkin Elmer Series II
CHNS/O analyzer 2400. The electronic spectra were recorded on
a Agilent 8453 diode array spectrophotometer (wavelength range
1100–190 nm). The pH titration was monitored using a Toshniwal
(CL 54) pH meter equipped with a combination pH electrode.
Cyclic voltammetry (CV) and differential pulse voltammetry
(DPV) were performed using a three-electrode cell configuration.
A platinum sphere, platinum plate and Ag(s)/AgNO3 were used
as working, auxiliary and reference electrodes respectively. The
supporting electrolyte used was NBu4ClO4. The platinum sphere
electrode was sonicated for two minutes in dilute nitric acid, dilute
hydrazine hydrate and then in double distilled water to remove
the impurities. The temperature of the electrochemical cell was
maintained at 25.0 0.2 ◦C by a cryocirculator (HAAKE D8
G). The solutions were deoxygenated by bubbling research grade
nitrogen and an atmosphere of nitrogen was maintained over
the solution during measurements. The E1/2 values were observed
Suitable single crystals were grown by slow evaporation of the
acetonitrile/methanol solution of complexes at 4 ◦C. A crystal
of suitable size selected from the mother liquor was immersed in
paraffin oil, then mounted on the tip of a glass fiber and cemented
using epoxy resin. Intensity data for the crystal were collected using
˚
Mo-Ka (l = 0.71073 A) radiation on a Bruker SMART APEX
diffractometer equipped with a CCD area detector at 100 K. The
crystallographic data are listed in Table 1. The SMART43 program
was used for collecting frames of data, indexing the reflections,
and determination of lattice parameters; SAINT43 program for
integration of the intensity of reflections and scaling; SADABS44
program for absorption correction, and the SHELXTL45 program
for space group and structure determination, and least-squares
refinements on F2. The structure was solved by heavy atom
method. Other non-hydrogen atoms were located in successive
difference Fourier syntheses. The final refinement was performed
by full-matrix least-squares analysis. Hydrogen atoms of the ligand
Table 1 Crystal data and structure refinement details for [Fe(L1)Cl2] 1, [Fe(H(L3))Cl3] 3 and [{Fe(L5)Cl}2](ClO4)2 5
1
3
5
Empirical Formula
Formula Weight
Crystal System
Crystal Size (mm)
Space group
C28H32Cl4Fe2N6O5
786.10
Monoclinic
C16H21Cl3FeN3O2
449.56
Monoclinic
C24H36Cl4Fe2N10O10
878.13
Monoclinic
0.31 ¥ 0.18 ¥ 0.12
0.34 ¥ 0.18 ¥ 0.08
0.52 ¥ 0.27 ¥ 0.04
P21
P21/c
P21/c
˚
a, (A)
7.0402(6)
7.358(8)
8.1513(7)
˚
b, (A)
15.9083(14)
17.0698(15)
90
94.596(2)
90
1905.6(3)
2
100
1.370
0.71073
1.117
11498
7510
406
0.0303
19.495(19)
13.953(15)
90
103.352(17)
90
1947(4)
4
100
1.533
0.71073
1.16
9901
3817
227
0.0882
12.0527(10)
17.3786(15)
90
90.6750(10)
90
1707.2(3)
2
100
1.708
0.71073
1.09
10085
3939
228
0.029
˚
c, (A)
a, (◦)
b, (◦)
g , (◦)
3
˚
V (A )
Z
Temperature, (K)
r (calc), (g cm-3)
˚
Radiation Mo-Ka (l/A)
Goodness of fit on F2
Number of reflections measured
Number of reflections used
Number of refined parameters
R(int)
Final R indices [I > 2s(I)]
R indices (all data)
R1 = 0.0627; wR2 = 0.1532
R1 = 0.0665; wR2 = 0.1558
R1 = 0.0813; wR2 = 0.1674
R1 = 0.1141; wR2 = 0.1837
R1 = 0.0606; wR2 = 0.1552
R1 = 0.0686; wR2 = 0.1600
aR1 = [R(ꢀFo|-|Fcꢀ)/R|Fo|], bwR2 = {[R(w(Fo2-Fc2)2)/R(wFo4)]1/2
}
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 8444–8458 | 8447
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