Nine diiron(II) complexes of three bis-tetradentate pyrimidine based ligands with NCE (E = S, Se, BH3) coligands

Article abstract of DOI:10.1021/ic3012052

Three bis-tetradentate acyclic amine ligands differing only in the arm length of the pyridine pendant arms attached to the 4,6-positions of the pyrimidine ring, namely, 4,6-bis[N,N-bis(2'-pyridylethyl)aminomethyl]-2- phenylpyrimidine (L^Et), 4,6-bis[N,N-bis(2'-pyridylmethyl)aminomethyl] -2-phenylpyrimidine (L^Me), and 4,6-[(2'-pyridylmethyl)-2'- pyridylethyl)aminomethyl]-2-phenylpyrimidine (L^Mix) have been used to synthesize nine air-sensitive diiron(II) complexes: [Fe^II ₂L^Et(NCS)₄]·MeOH·³/ ₄H₂O (1·MeOH·³/₄H ₂O), [Fe^II₂L^Et(NCSe) ₄]·H₂O (2·H₂O), [Fe ^II₂L^Et(NCBH₃)₄] ·⁵/₂H₂O (3·⁵/ ₂H₂O), [Fe^II₂L^Me(NCS) ₄]·¹/₂H₂O (4·¹/₂H₂O), [Fe^II ₂L^Me(NCSe)₄] (5), [Fe^II ₂L^Me(NCBH₃)₄]·³/ ₂H₂O (6·³/₂H₂O), [Fe^II₂L^Mix(NCS)₄] ·¹/₂H₂O (7·¹/ ₂H₂O), [Fe^II₂L^Mix(NCSe) ₄]·³/₂H₂O (8·³/₂H₂O), and [Fe^II ₂L^Mix(NCBH₃)₄]·³/ ₂H₂O (9·³/₂H₂O). Complexes 3·⁵/₂H₂O, 4· ¹/₂H₂O, 5, 6·³/ ₂H₂O, and 8·³/₂H₂O were structurally characterized by X-ray crystallography, revealing, in all cases, both of the iron(II) centers in an octahedral environment with two NCE (E = S, Se, or BH₃) anions in a cis-position relative to one another. Variable temperature magnetic susceptibility measurements showed that all nine diiron(II) complexes are stabilized in the [HS-HS] state from 300 K to 4 K, and exhibit weak antiferromagnetic coupling. Mo?ssbauer spectroscopy confirmed the spin and oxidation states of eight of the nine complexes (the synthesis of air-sensitive complex 3 was not readily reproduced).

Full text of DOI:10.1021/ic3012052

Article
pubs.acs.org/IC
Nine Diiron(II) Complexes of Three Bis-tetradentate Pyrimidine Based
Ligands with NCE (E = S, Se, BH3) Coligands
Worku A. Gobeze, Victoria A. Milway, Juan Olguín, Guy N. L. Jameson, and Sally Brooker*
Department of Chemistry and the MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, P.O. Box
56, Dunedin 9054, New Zealand
S
* Supporting Information
ABSTRACT: Three bis-tetradentate acyclic amine ligands
differing only in the arm length of the pyridine pendant arms
attached to the 4,6-positions of the pyrimidine ring, namely,
4,6-bis[N,N-bis(2′-pyridylethyl)aminomethyl]-2-phenylpyri-
midine (LEt), 4,6-bis[N,N-bis(2′-pyridylmethyl)aminomethyl]-
2-phenylpyrimidine (LMe), and 4,6-[(2′-pyridylmethyl)-2′-
pyridylethyl)aminomethyl]-2-phenylpyrimidine (LMix) have
been used to synthesize nine air-sensitive diiron(II) com-
plexes: [FeII LEt(NCS)4]·MeOH·3/4H2O (1·MeOH·3/4H2O), [FeII LEt(NCSe)4]·H2O (2·H2O), [FeII LEt(NCBH3)4]·5/2H2O
2
2
2
(3·5/2H2O), [FeII LMe(NCS)4]·1/2H2O (4·1/2H2O), [FeII LMe(NCSe)4] (5), [FeII LMe(NCBH3)4]·3/2H2O (6·3/2H2O),
2
2
2
[FeII LMix(NCS)4]·1/2H2O (7·1/2H2O), [FeII LMix(NCSe)4]·3/2H2O (8·3/2H2O), and [FeII LMix(NCBH3)4]·3/2H2O
2
2
2
(9·3/2H2O). Complexes 3·5/2H2O, 4·1/2H2O, 5, 6·3/2H2O, and 8·3/2H2O were structurally characterized by X-ray
crystallography, revealing, in all cases, both of the iron(II) centers in an octahedral environment with two NCE (E = S, Se,
or BH3) anions in a cis-position relative to one another. Variable temperature magnetic susceptibility measurements showed that
all nine diiron(II) complexes are stabilized in the [HS-HS] state from 300 K to 4 K, and exhibit weak antiferromagnetic coupling.
Mossbauer spectroscopy confirmed the spin and oxidation states of eight of the nine complexes (the synthesis of air-sensitive
̈
complex 3 was not readily reproduced).
INTRODUCTION
■
The spin crossover (SCO) field is an area of contemporary
coordination chemistry that has driven an increase in reports of
the preparation and study of the magnetic properties of iron(II)
complexes. Spin crossover occurs when the electronic
configuration of the metal ion is switched between the high-
spin (HS) and low-spin (LS) states, driven by external stimuli
(temperature, pressure, light irradiation, or magnetic field).
When the SCO effect is accompanied by hysteresis it confers a
memory effect which makes these materials potential
candidates for information storage and other molecular
devices.1,2
Figure 1. Schematic representation of the literature bis-terdentate
PMAT ligand and bis-tetradentate L2 and HL3 ligands used for the
generation of dinuclear iron(II) complexes, and the ligands
synthesized in this work, LEt, LMe, and LMix, from which nine dinuclear
iron(II) complexes are made.
One of the interests of this research group is the synthesis
and design of dinucleating ligands that upon coordination to
iron(II)3,4 or cobalt(II)5 centers may lead to observation of
SCO and magnetic coupling. We have previously reported the
synthesis of the bis-terdentate-triazole based PMAT ligand6
II
of counteranion X, in [Fe2 (PMAT)2](X)4·solvents, has on the
II
SCO behavior.8
(Figure 1) and its diiron(II) complex, [Fe2 (PMAT)2]-
(BF4)4·DMF, in which two ligand strands fully encapsulate
two metal centers, with all 12 donors coming from just the two
ligand strands. The SCO properties of this complex are unique.
The localized [HS-LS] state is stable over a very wide range of
temperatures, with spin transition (ST) to the [HS-HS] form
occurring at T1/2 = 225 K3,4 and no evidence of a second ST to
the [LS-LS] form, even under 10.3 Kbar at 4 K.7 That study
was extended to include consideration of the effect the choice
More recently we have moved from bis-terdentate ligands to
various bis-tetradentate ligands, as the latter allow us to
generate diiron(II) complexes in which only one ligand strand
coordinates to the two metal centers, leaving the six-
coordination of each iron(II) ion to be completed by N-
Received: June 6, 2012
Published: July 27, 2012
© 2012 American Chemical Society
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based anions such as NCE (E = S, Se, BH3). To the best of our
knowledge, only two examples of dinucleating bis-tetradentate
ligands have been used before in the preparation of diiron(II)
complexes with N-based anions. One of them is a pyrazole-
based ligand, HL3 (Figure 1), deprotonated and used to
generate two diiron(II) complexes by this research group,9
taken to dryness by blowing nitrogen gas over it, to give C as a
pure yellow solid in a quantitative yield. Finally, nucleophilic
substitution reactions of C with either N-bis(2-pyridylmethyl)-
amine (bmpa)28,29 or N-(2-pyridylethyl)-N-(2′-pyridylmethyl)-
amine (pmpea)30,31 gave LMe and LMix, in 95 and 75% yield,
respectively (Scheme 1).
namely, the K+ salt of anionic symmetric [FeII (L3)(NCS)4]−
2
and the neutral asymmetric [FeII (L3)(py)(SeCN)(NCSe)2],
a
2
Scheme 1
both stabilized in the [HS-LS] state in the 300−2 K
temperature range. The second example is a pyrimidine-based
ligand, L2 (Figure 1), reported by Oshio and Ichida,10 which
was used to generate the neutral, symmetrical dinuclear iron(II)
complex [FeII (L2)(NCS)4]. X-ray analysis and variable
2
temperature magnetic susceptibility measurements showed
that the iron(II) centers are stabilized in the HS state at all
temperatures with a fairly weak antiferromagnetic coupling
between them (Curie and Weiss constants: C = 3.77 emu
atom−1 K and θ = −3.86 K, for data 100−270 K).
A significant number of iron(II) complexes of pyrimidine-
based ligands have shown SCO behavior.11−18 Hence we
decided to study the iron(II) coordination chemistry of three
ligands very similar to L2, but featuring a phenyl substituent,
not a hydrogen atom as in L2, at the 2-position of the
pyrimidine ring (Figure 1). The three phenyl-substituted
ligands, namely, 4,6-bis[N,N-bis(2′-pyridylethyl)-
aminomethyl]-2-phenylpyrimidine (LEt),19 4,6-bis[N,N-bis(2′-
pyridylmethyl)aminomethyl]-2-phenylpyrimidine (LMe), and
4,6-[(2′-pyridylmethyl)-2′-pyridylethyl)aminomethyl]-2-phe-
nylpyrimidine (LMix), provide differing alkyl chain lengths
between the pyridine moieties and the pyrimidine ring (Figure
1), and hence generate differing combinations of chelate ring
sizes (and variations in strain) when bound to the metal ions.
The phenyl substituent was introduced primarily because of our
well established access to the required precursor, along with the
expectation that it should enhance the solubility of both the
ligand and the resulting complexes in organic solvents, and
perhaps also the ease of crystallization. It should also be noted
that the bulky phenyl substituent inductively withdraws
electron density from the pyrimidine ring, reducing its basicity.
Hence the ligand field imposed by LMe is expected to be
different, probably somewhat lower, than that of L2, as seen in
the substituent study carried out by Lehn and co-workers on a
series of tetranuclear iron(II) pyrimidine-based grid complexes
(phenyl, SCO-active; hydrogen, fully LS).15,20 The differing
alkyl “arm” lengths offer further variations in the ligand field
strength, the general principle of which is established in the
literature.21−23 The effect of the choice of NCE (E = S, Se, and
BH3)24−27 coligands is also considered here, as this is a
particularly powerful way to control the field strength about the
iron(II) centers. Herein we report the synthesis, structural
characterization, magnetic and Mossbauer study of nine
iron(II) complexes derived from the three bis-tetradentate
a
(i) (a) PPh3, Phthalimide, DIAD, THF, rt; (b) H2N-NH2·H2O,
EtOH, rt; (ii) vinylpyridine, MeOH, ACOH, reflux, 1 week; (iii)
SOCl2, CH2Cl2, N2; (iv) bmpa28,29 (2 equiv.), Na2CO3, MeCN, KI,
reflux; (v) pmpea30,31 (2 equiv.), Na2CO3, MeCN, KI, reflux.
Complex Synthesis. All three ligands, LEt, LMe, and LMix
generate air-sensitive iron(II) complexes. Thus, all of the
complexation reactions were carried out under an inert
atmosphere (argon or nitrogen) from 1 equivalents of the
appropriate ligand and 2 equivalents of freshly prepared
[FeII(NCE)2(py)4], E = S, Se, or BH3, at reflux. The latter
starting materials32 were chosen as a source of iron(II) and
NCE coligands, and are shown here to be labile enough to
allow stoichiometry controlled formation of the desired
products.
Either methanol or acetonitrile was used as the reaction
solvent (Table 1). Methanol was used for all but four
complexes, the NCS-containing 4·1/2H2O and the NCBH3-
based 3·5/2H2O, 6·3/2H2O, and 9·H2O (MeCN used). For
those four exceptions, although inert conditions were
employed, clean product could not be obtained reproducibly
from MeOH. In most of the cases the microanalytical results
gave much lower values than expected, probably because of
ferric impurities. Oxidation of iron(II) complexes in methanol
even under an inert atmosphere has been observed before when
the iron(II) is bound to amine nitrogen donor atom rich
ligands, LEt, LMe, and LMix
.
RESULTS AND DISCUSSION
Organic Synthesis. We previously reported the synthesis
■
of bis(hydroxymethyl)-2-phenylpyrimidine (A), 4,6-bis-
(aminomethyl)-2-phenylpyrimidine (B), and LEt.19 Dialcohol
A was converted to 4,6-bis(chloromethyl)-2-phenylpyrimidine
(C) by addition of 2 equivalents of SOCl2 to a yellow
dichloromethane solution of A under an inert atmosphere (N2
or Ar; NB. This reaction does not work when done in air).
After the deep yellow suspension was stirred for 1 h, it was
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Table 1. Summary of the Percentage Yield, Color, Solvent Used, “Bulk” Product Isolation, and Crystallization Methods for
[FeII LEt(NCS)4]·MeOH·3/4H2O (1·MeOH·3/4H2O), [FeII LEt(NCSe)4]·H2O (2·H2O), [FeII LEt(NCBH3)4]·5/2H2O (3·5/2H2O),
2
2
2
[FeII LMe(NCS)4]·1/2H2O (4·1/2H2O), [FeII LMe(NCSe)4] (5), [FeII LMe(NCBH3)4]·3/2H2O (6·3/2H2O),
2
2
[FeII LMix(NCS)4]·1/2H2O (7·1/2H2O), [FeII2 LMix(NCSe)4]·3/2H2O (8·3/2H2O) and [FeII LMix(NCBH3)4]·3/2H2O (9·3/2H2O)
2
2
2
d
IR
a
b
c
ligand
LEt
complex
co-ligand
yield
color
solvent
isolation method
crystallization method
NC
B−H
1·MeOH·3/4H2O
2·H2O
3·5/2H2O
4·1/2H2O
5
6·3/2H2O
7·1/2H2O
8·3/2H2O
9·3/2H2O
NCS
80
85
91
80
82
92
58
79
90
orange
yellow
MeOH
MeOH
MeCN
MeCN
MeOH
MeCN
MeOH
MeOH
MeCN
A
A
A
B
B
A
B
B
2038
2061
2182
2068
2053
2177
2068
2064
2187
NCSe
NCBH3
NCS
yellow
VD
2334
2339
2334
LMe
brick red
brick red
orange
yellow
LLD1
LLD1
LLD1
NCSe
NCBH3
NCS
LMix
NCSe
NCBH3
yellow
LLD2
yellow
A
a
b
c
units %. A = Et2O addition to reaction solution; B = precipitated from the reaction solution. VD = vapor diffusion of Et2O into DMF:MeCN
d
(1:5) solution; LLD1 = liquid−liquid diffusion in an H-tube in MeOH; LLD2 = liquid−liquid diffusion in an H-tube in MeOH-EtOH (2:1). units
cm−1.
ligands that enhance the basic character and stabilize iron-
(III).33
and 9·H2O, was observed at 2185, 2179, and 2173 cm−1,
respectively (B−H stretch at 2342, 2347, and 2342 cm−1,
respectively), as expected for N-bound NCBH3.
Four of the complexes, 4·1/2H2O, 5, 7·1/2H2O, and
8·3/2H2O, precipitated directly from the reaction solution
(Table 1), so were simply filtered off. The other five complexes
did not precipitate, so initially the reaction solutions were vapor
diffused with diethyl ether, under Schlenk conditions. However,
this resulted in solids for which variable and poor microanalysis
data were obtained, again presumably because of partial
oxidation to ferric products. Therefore the isolation of these
five complexes, namely, 1·MeOH·3/4H2O, 2·H2O, 3·5/2H2O,
6·3/2H2O, and 9·H2O, was instead achieved by slow addition of
diethyl ether by cannula into the reaction solution (Table 1).
Only in the case of 3 was even this method found not to be
totally reliable (see later).
X-ray Crystal Structures. Single crystals of 3·5/2H2O and
6·3/2H2O were obtained as 3·DMF·MeCN·3/5Et2O (yellow)
and solvent free 6 (orange) by diethyl ether diffusion into the
MeCN:DMF (5:1) and MeCN solutions of the complexes,
respectively, while 4·1/2H2O and 8·3/2H2O were obtained as
solvent free 4 (red), and 8·7/10MeOH (orange-red), by liquid−
liquid diffusion of the ligand and the appropriate
[FeII(NCE)2(py)4] in MeOH and MeOH-EtOH (2:1) mixture
of solvents, respectively (Table 1 and Supporting Information,
Table S1). Single crystals of 5 (orange-red) were also obtained
solvent free by liquid−liquid diffusion of the ligand and
[FeII(NCBH3)2(py)4] in MeOH.
This resulted in nine complexes, in 58−92% yield. In all cases
the microanalysis and electrospray ionization mass spectrom-
etry (ESI-MS) results were consistent with those expected for
the desired dinuclear complexes. This was confirmed by X-ray
crystallography for 3·5/2H2O, 4·1/2H2O, 5, 6·3/2H2O, and
8·3/2H2O (see below). A summary of the yields, colors, reaction
solvents, “bulk” product isolation methods, crystallization
methods, and IR stretches for the coligands, is presented in
Table 1.
Complex 3·DMF·MeCN·3/5Et2O crystallized in the Pnma
space group with half of the molecule in the asymmetric unit
(Figure 2) and the other half generated by a mirror plane
through the C2 and C4 atoms of the pyrimidine ring and the
entire phenyl ring. The set of iso-structural complexes 4−6
(Figure 3, Supporting Information, Figure S2 and S4) which
crystallized in the P21/n space group, and complex
IR Study of Complexes. For complexes which contain
NCE anions, the position of the CN stretch provides useful
information with regard to the spin state of the iron(II) center.
For E = S and Se:34 2020−2080 cm−1 for HS iron(II)11,27,35 vs
∼2100 cm−1 for N-bound LS iron(II).36 Further, for NCS and
NCSe complexes the position of the CN stretch helps to
identify the binding mode of the anions: 2020−2080 cm−1
indicates N-bound while bands higher than ∼2100 cm−1
indicate S-bound or Se-bound (Table 1).37,38 For NCBH3
complexes the CN stretch always shows up higher than
∼2100 cm−1 when N-bound, and a strong B−H stretch occurs
at ∼2300 cm−1.27,39−41
The CN stretches for the six present E = S and Se
complexes, 1·MeOH·3/4H2O, 2·H2O, 4·1/2H2O, 5, 7·1/2H2O,
and 8·3/2H2O, occurred as a single band in the range 2039−
2062 cm−1, consistent with them all being N-bound, as
expected (Table 1).37 This is also indicative of all of these
complexes being [HS-HS] at room temperature. The CN
stretch for the three E = BH3 complexes, 3·5/2H2O, 6·3/2H2O,
Figure 2. View of the molecular structure of [FeII LEt(NCBH3)4] of
2
3·DMF·MeCN·3/5Et2O. Hydrogen atoms and solvent molecules have
been omitted for clarity. Symmetry operation A is x, 3/2 − y, z.
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pyrimidine bridge is 6.626(2) Å (Table 2), with the iron atoms
displaced from the pyrimidine mean plane by 0.556 Å. The
octahedral distortion parameter Σ value (Σ is defined as the
sum of the deviation of each of the 12 cis-angles associated with
the iron(II) center)44,45 is 50.1°, the smallest deviation from
ideal geometry in this family of complexes (Table 2). Because
of symmetry, the pyrimidine ring is perfectly orthogonal to the
attached phenyl ring, and almost parallel to the axially
positioned pyridine ring, intersecting at only 7.2(3)°. The
N−C−B groups are almost linear [178.4(5)−179.2(6)°] while
the Fe−N−C(B) linkage is slightly bent [167.3(4)−173.9(4)°].
In the three iso-structural complexes of the all-methylene-
armed ligand, 4, 5, and 6 (Figure 3, Supporting Information,
Figures S2 and S4, Table 2), the Fe···Fe distance across the
pyrimidine bridge is 6.563(2), 6.574(1), and 6.526(1) Å,
respectively. A shorter Fe···Fe separation [6.288(1) Å] was
Figure 3. View of the molecular structure of [FeII LMe(NCS)4] 4.
Hydrogen atoms have been omitted for clarity.
2
8·7/10MeOH (Figure 4) which crystallized in the P21/c space
group, all have the entire molecule in the asymmetric unit.
reported for [FeII (L2)(NCS)4],10 consistent with the report of
2
a shorter Fe−Npym bond (2.229 Å) than is seen in 4−6 (Table
2, 2.288−2.299 Å). The Fe(1) and Fe(2) centers in 4−6 are
significantly displaced above and below the pyrimidine mean
plane (4: 0.482, −0.531; 5: 0.491, −0.502, 6: 0.510, −0.524 Å).
The distortion parameters for 4−6 (Σ = 102.8−118.4°) are
larger than for 3·DMF·MeCN·3/5Et2O (50.1°). The N−C−S,
N−C−Se, and N−C−BH3 groups are almost linear [4:
176.7(8)−179.5(8); 5: 176.9(6)−178.3(6); 6: 177.2(7)−
179.6(7)°] while the Fe−N−C(S), Fe−N−C(Se), and Fe−
N−C(BH3) linkages are significantly bent [4: 144.7(7)−
161.9(6); 5: 149.4(5)−162.5(5); 6: 153.1(5)−168.8(5)°].
The phenyl ring is tilted out of the plane of the attached
pyrimidine ring by 53.2(2), 54.5(1), and 59.2(1)° for 4−6,
respectively.
The Fe···Fe distance across the pyrimidine bridge in the
complex of the mixed-ethylene-methylene-armed ligand,
8·7/10MeOH (Figure 4), is 6.782(1) Å, and is the longest
observed in this family (Table 2). This is consistent with this
complex also featuring the longest Fe−Npym bonds (average
2.391 Å, Table 2) and the biggest displacement of the iron
centers from the pyrimidine ring plane (1.106 and −1.325 Å).
Interestingly, the degree of deviation from octahedral geometry
(mean Σ = 80.6°) for this complex of the LMix ligand,
8·7/10MeOH, lies between the value seen for the complex of the
LEt ligand, 3·DMF·MeCN·3/5Et2O (50.1°), and those seen in
the complexes of the LMe ligand, 4−6 (102.8−118.4°). The
phenyl ring is twisted away from the pyrimidine mean plane by
33.5(3)°. As for 5, the N−C−Se groups are almost linear
[176.0(1)−179.3(8)°] while the Fe−N−C(Se) linkages are
somewhat bent [158.1(8)−171.5(7)°]. A hydrogen bond is
present between the methanol molecule in the lattice and the
coordinated selenocyanate counteranion (Supporting Informa-
tion, Table S7).
Comparisons of Structures. An interesting difference
between these structures is in the position of the pyridyl and
NCE groups relative to one another. In 3·DMF·MeCN·3/5Et2O
each pair of “cis” positioned NCE anions that are symmetry
related bind from the same side, so are considered to be “cis”
relative to one another while in 8·7/10MeOH they are “trans”
relative to one another. However, in 4−6 the pairs of NCE
anions are neither “cis” nor “trans” to one another. Rather, one
NCE on each iron(II) center is cis to an NCE on the other
iron(II) center, while the “other” NCE is trans to the other
NCE anion. The equatorial pyridine rings in 3·DMF·MeCN
·3/5Et2O are “cis” relative to one another, while in the other four
structures they are “trans” relative to one another.
Figure 4. View of the molecular structure of [FeII LMix(NCSe)4] of
2
8·7/10MeOH. Hydrogen atoms and solvent molecules have been
omitted for clarity.
In all cases the ligands are bound in a bis-tetradentate fashion
via the nitrogen atoms of the pyrimidine ring (Npym), tertiary
amine (Namine), and the two pyridine rings (2Npy). Two NCE
coligands (2NNCE) in cis positions complete the octahedral
(Oh) geometry (N6 mode) around each iron(II) ion. To give a
common reference point we define the “axial” direction in these
complexes to lie along the weak Fe−Npym bond and one of the
two Npy bonds (the one that is trans to Npym), while the
“equatorial” plane comprises the other Npy, Namine, and two cis-
positioned NCE coligands. The Fe−NNCE bonds are the
shortest, consistent with literature reports of related com-
plexes,10,18,42 while the Fe−Npym bonds are the longest,
presumably because of the weak basic nature of the phenyl-
substituted (inductively electron withdrawing) pyrimidine ring
relative to the pyridine ring and the tertiary amine. The mean
Fe−N bond distances (Table 2, 2.182−2.200 Å) are entirely
consistent with the iron(II) centers being in the HS state at
91−92 K.3,43 The individual cis−N−Fe−N [70.4(2)−
120.8(2)°] and trans−N−Fe−N [148.8(2)−176.7(2)°] bond
angles in these five dimetallic structures are widely dispersed
(Table 2), which is also consistent with HS centers.
Nevertheless, the average cis angles (89.7−90.0°) are
remarkably close to a perfect 90° as expected for ideal
octahedral geometries observed in contrast to the widely
dispersed trans angles (average trans angles 157.9−171.9°).
In the complex of the all-ethylene-armed ligand,
3·DMF·MeCN·3/5Et2O, the Fe1···Fe1A distance across the
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Table 2. Selected Bond Lengths, Angles, and M···M Separation for [FeII LEt(NCBH3)4]·DMF·MeCN·3/5Et2O
2
(3·DMF·MeCN·3/5Et2O), [FeII LMe(NCS)4] (4), [FeII LMe(NCSe)4] (5), [FeII LMe(NCBH3)4] (6),
2
2
2
[FeII LMix(NCSe)4]·7/10MeOH (8·7/10MeOH)
2
complex
[FeII2LEt(NCBH3)4]·solvents
[FeII2LMe(NCS)4]
[FeII2LMe(NCSe)4]
[FeII2LMe(NCBH3)4] [FeII2LMix(NCSe)4]·7/10MeOH
Fe−NNCE (Å)
2.112(4), 2.164(5)
(2.138)
2.025(7)−2.115(7)
2.023(6)−2.110(5)
2.053(5)−2.133(5)
2.056(7)−2.118(7)
(mean)
(2.068)
(2.070)
(2.093)
(2.087)
Fe−Npy (Å)
2.231(4), 2.170(5)
(2.201)
2.197(6)−2.216(6)
2.193(5)−2.215(5)
2.175(4)−2.201(5)
2.173(6)−2.2161(6)
(mean)
(2.205)
(2.202)
(2.192)
(2.197)
Fe−Namine (Å)
2.230(4)
(2.230)
2.254(6), 2.257(6)
(2.256)
2.246(5), 2.250(5)
(2.248)
2.239(4), 2.245(5)
(2.242)
2.233(6), 2.248(6)
(2.241)
(mean)
Fe−Npym (Å)
2.290(4)
(2.290)
2.299(6), 2.299(6)
(2.299)
2.298(5), 2.300(4)
(2.299)
2.285(4), 2.287(4)
(2.286)
2.433(6), 2.349(6)
(2.391)
(mean)
a
Fe···Fe (Å)
6.626(2)
6.563(2)
6.574(1)
6.526(1)
6.782(1)
Fe−NAll (Å)
2.112(4)−2.290(4)
2.025(7)−2.299(6)
2.023(6)−2.300(4)
2.053(5)−2.287(4)
2.056(7)−2.433(6)
(mean)
(2.200)
(2.184)
(2.182)
(2.183)
(2.200)
cis N−Fe−N
75.2(2)−102.2(2)
73.6(2)−120.8(2)
73.9(2)−120.1(2)
74.9(2)−120.0(2)
70.4(2)−104.9(2)
(mean)
(90.0)
(89.7)
(89.7)
(89.8)
(89.8)
trans N−Fe−N
164.3(1)−176.7(2)
148.8(2)−164.4(3)
149.4(2)−165.0(2)
150.0(2)−166.3(2)
156.2(2)−171.5(3)
(mean)
(171.9)
(157.9)
(158.3)
(159.2)
(165.7)
Σ (deg)
50.1
(50.1)
118.4, 118.0
(118.2)
117.8, 115.6
(116.7)
104.3, 102.8
(103.6)
79.3, 80.8
(80.1)
(mean)
Fe out of
pyrimidine plane
+0.556, +0.556
+0.482, −0.531
+0.491, −0.502
+0.510, −0.524
+1.106, −1.325
π-stacking
interactions:
centroid ··· centroid
3.841−3.914
3.613−3.829
3.825−3.944
3.621−3.774
3.872−3.912
3.593−3.812
11.5−23.4
(Å)
mean
plane···centroid (Å)
offset angle (deg)
9.7−21.6
9.4−23.1
E···E interactions
3.663
3.651
b
(Å)
a
b
Fe···Fe separation across the pyrimidine bridge. E is S or Se.
Table 3. Summary of Magnetic and Mossbauer Parameters for the Nine Diiron(II) Complexes Synthesized in This Work
̈
magnetic parameters
Mossbauer parameters
̈
a
b
f
c
c
c
c
d
ligand
co-ligand
complex
H
J
g
μeff/Fe
δ
ΔEQ
ΓL
ΓR
T
LEt
NCS
1·MeOH·3/4H2O
2·H2O
3·5/2H2O
4·1/2H2O
5
6·3/2H2O
7·1/2H2O
8·3/2H2O
9·3/2H2O
−J[S1S2]
−J[S1S2]
−J[S1S2]
−J[S1S2]
−J[S1S2]
−J[S1S2]
−J[S1S2]
−J[S1S2]
−J[S1S2]
−1.40
−1.65
−2.20
−1.43
−1.27
−1.56
−1.31
−1.54
−1.63
2.05
2.00
2.06
2.15
2.20
2.02
2.16
2.20
2.13
4.98
4.92
5.12
5.41
5.41
4.79
5.38
5.44
5.26
1.14
1.18
2.40
2.20
0.61
0.64
0.52
0.64
4.8
4.5
NCSe
NCBH3
NCS
LMe
1.12
1.13
1.15
1.13
1.14
1.16
2.72
2.69
0.23
0.22
0.25
0.24
4.8
4.7
4.6
4.8
4.5
4.7
NCSe
NCBH3
NCS
e
e
e
e
2.30
2.13
1.98
2.05
LMix
0.37
0.40
0.36
0.38
NCSe
NCBH3
a
b
c
d
e
f
Spin Hamiltonian used to fit the experimental data set. Units cm−1. Units mm s−1, Voigt line shape. Units K. raw data. Units μB.
As described earlier, the degree of distortion from the ideal
complexes of LEt are the most likely candidates to show SCO or
LS behavior compared to the complexes of LMe and LMix and
also the related ligand L2.
The Fe−Npym distances largely determine the Fe···Fe
separations across the pyrimidine bridge. These consequently
follow the order 8·7/10MeOH [av. 2.391, 6.782(1) Å] >
3·DMF·MeCN·3/5Et2O > [2.290, 6.626(2) Å] > 4 [av. 2.299,
octahedral geometry decreases in the order Fe2LMe (Σ 102.8−
118.4°) > Fe2LMix (Σ 80.6°) > Fe2LEt (Σ 50.1°), albeit this
must be taken with some caution as the anions are different.
Studies have shown that minimal values of Σ are associated
with strong crystal fields and hence stabilization of the LS
state.8,18,42,46 Thus, from the observed value it appears that
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6.563(2) Å] ≈ 5 [av. 2.299, 6.574(1) Å] > 6 [av. 2.286,
their differences in strain energy and coligands, show similar
magnetic features (Table 3, Supporting Information, Figures
S6−S13).
6.526(1) Å] (Table 2). This also explains why they are all
longer than seen in [FeII L2(NCS)4] [2.229, 6.288(1) Å].10
2
There are no intra/intermolecular π-ring stacking inter-
actions in 3·DMF·MeCN·3/5Et2O and 8·7/10MeOH. However,
in 4−6 the equatorial pyridine rings that are “trans” to each
other are tilted toward the central pyrimidine plane.
Consequently, there are offset parallel intramolecular inter-
actions between the trans positioned pyridine and pyrimidine
rings [N(14) and N(18) with N(11) pyrimidine ring, Table 2
and Supporting Information, Figures S1, S3, and S5]. There are
also offset parallel weak intermolecular interactions between the
pyridine rings [N(14) and N(17) of adjacent molecules] in 4−
6 as well as S···S and Se···Se interactions in 4 and 5
(Supporting Information, Figures S1 and S3).18,42 As no spin
transition takes place in any of the complexes no statements
can be made about the influence of these interactions on
cooperativity.
To probe the oxidation and spin states of the iron centers
further, 57Fe Mossbauer spectra were measured at low
̈
temperatures (4.4−4.8 K). Unfortunately, the samples were
air sensitive and by the time the Mossbauer data was collected
̈
the aged magnetic sample of 3·5/2H2O contained significant
ferric impurities. Then, as noted earlier, attempts to repeat the
clean preparation of that iron(II) sample failed, despite
repeated attempts. Likewise, 1·MeOH·3/4H2O contained very
small amounts of a ferric impurity (Supporting Information,
Figure S14).
The Mossbauer spectra of the eight complexes (i.e., all but
̈
3·5/2H2O) proved that the iron(II) ions are indeed present in
the [HS-HS] state, in perfect agreement with the magnetic and
X-ray results (Table 3). All spectra provided parameters
characteristic of HS iron(II), that is, δ ∼ 1.1 mm s−1 and
ΔEQ ∼2−3 mm s−1.43,49 The parameters were refined assuming
initially symmetrical quadrupole doublets (equal line widths)
with Voigt line shape. The spectra of the complexes are shown
in Figure 6 and Supporting Information, Figures S14−S15.
̈
Magnetochemistry and Mossbauer Spectroscopy.
Variable temperature magnetic susceptibility measurements
were made on powder samples of all nine complexes in the
temperature range 300 to 2 K (for 2−8) or 300 to 4 K (for 1)
(Table 3, Figure 5 and Supporting Information, Figure S6−
Figure 5. Plot of χMT versus temperature for 1·MeOH·3/4H2O. The
solid line corresponds to the best fit.
S13). Least squares regression of the data to a modified Van
Vleck equation, using MAGMUN 4.1,47,48 was performed using
the Hamiltonian H = −J[S1·S2], and corrected for intermo-
lecular effects (θ, Weiss-like correction), the fraction of
paramagnetic, Curie-like impurity (α), the temperature
independent paramagnetism (TIP), and zero field splitting
(ZFS).
Figure 6. 57Fe−Mossbauer spectra for all complexes with coligands
̈
NCS and NCSe.
In all cases the iron(II) centers were found to be stabilized in
the [HS-HS] state across the entire experimental temperature
range, and to exhibit weak antiferromagnetic coupling. For
example, the plot of experimental χMT, for 1·MeOH·3/4H2O is
Unfortunately it was not possible to fit the spectrum of
6·3/2H2O or 9·3/2H2O because of the broadness of the signal,
nonethelesss the spectra are also consistent with the complexes
being stabilized in the [HS-HS]-state.
shown in Figure 5. The χMT value at 300 K of 6.2 cm3 mol−1
K
(3.1 cm3 mol−1 K per FeII, μeff = 7.08 μB, μeff/Fe = 4.98 μB) is in
agreement with the expected spin only value of an iron(II) ion
in the HS state (spin only χMT for S = 2 is 3.0 cm3 mol−1 K).
This value remains relatively constant until reaching 50 K;
In general, only those complexes with the ligand LMe gave
sharp quadrupole doublets. The LEt samples and those with
NCBH3 as coligand are particularly broad, and this almost
certainly arises from the powdery, noncrystalline nature of the
samples caused by the use of diethyl ether to rapidly precipitate
the complexes.
below this temperature the χMT value drops to 1.5 cm3 mol−1
K
at 4 K, because of ZFS. The best fit for this data set gave the
following parameters J = −1.3988 0.0058 cm−1, g = 2.0483
0.0504, TIP = 1.5 × 10−4 cm3/mol, and α = 0.05, θ = 0.25 K
(102R = 1.65) (Table 3). The eight other complexes, despite
Some general trends in the Mossbauer parameters can be
̈
observed (Table 3). When the coligand NCS is replaced by
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Table 4. Crystal Structure Determination Details for [FeII LEt(NCBH3)4]·DMF·MeCN·3/5Et2O (3·DMF·MeCN·3/5Et2O),
2
[FeII LMe(NCS)4] (4), [FeII LMe(NCSe)4] (5), [FeII LMe(NCBH3)4] (6), [FeII LMix(NCSe)4]·7/10MeOH (8·7/10MeOH)
2
2
2
2
complex
3·DMF·MeCN·3/5Et2O
51.40H70B4Fe2N14O1.60
4
5
6
8·7/10MeOH
formula
Mr
C
C40H34Fe2N12S4
922.73
C40H34Fe2N12Se4
1110.33
monoclinic
P21/n
C40H46B4Fe2N12
849.83
C42.70H40.80Fe2N12O0.70Se4
1160.81
1064.55
orthorhombic
Pnma
crystal system
space group
a [Å]
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/c
24.399(2)
22.286(1)
11.269(9)
90
11.154(4)
19.963(5)
18.506(4)
90
11.2380(6)
20.3994(9)
18.6755(10)
90
11.1880(12)
20.594(3)
18.683(2)
90
9.3377(5)
24.7012(13)
19.9340(10)
90
b [Å]
c [Å]
α [deg]
β [deg]
γ [deg]
V [Å3]
Z
90
99.121(1)
90
100.18(1)
90
99.41(1)
90
97.35(3)
90
90
6127.6(7)
4
4068.4(2)
4
4214.0(4)
4
4246.9(8)
4
4560.0(4)
4
ρcalcd.[g/cm3]
1.154
1.506
1.750
1.329
1.691
μ [mm−1
F(000)
T [K]
]
0.520
0.966
4.19
0.728
3.877
2245
1896
2184
1768
2298
92
92
91
91
91
θ range for data collection [deg]
reflections collected
independent reflections
R(int)
2.46 to 26.45
84902
2.23 to 25.41
33031
2.28 to 23.02
46867
2.22 to 24.45
49291
2.35 to 22.08
48205
6447
7172
8621
8632
8696
0.0744
0.1293
0.0964
0.1768
0.1037
T
min/Tmax
0.757
0.005
0.713
0.829
0.583
data/restraints/parameters
Gof (F2)
6447/14/396
1.070
7172/189/523
1.132
8621/0/523
1.021
8632/0/527
1.018
8696/15/570
1.035
R1/wR2 [I > 2σ(I)]
R1/wR2 (all data)
max. peak/hole [e Å−3
0.0765/0.2107
0.1061/0.2288
1.190/−0.806
0.0988/0.1824
0.1424/0.1988
1.118/−0.588
0.0535/0.1162
0.1050/0.1362
2.785/−1.676
0.0718/0.1633
0.1612/0.2022
0.518/−0.565
0.0610/0.1401
0.1405/0.1746
1.266/−1.456
]
NCSe or NCBH3, there is an increase in the isomer shift (δ)
and decrease in the quadrupole splitting (ΔEQ). There is no
pyrimidine-based ligands used in this study impose only a weak
field on iron(II), such that even when used in combination with
NCE (E = S, Se, BH3) coligands the resulting complexes do not
undergo SCO to the LS state. Use of cyanide coligands is an
obvious way to increase the field further, but this possibility was
not explored in the present study.
The observed significant distortions of the metal centers
from an ideal octahedral geometry is a key factor that favors the
[HS-HS] state and may prevent observation of the SCO
effect.8,18,42,46 Close inspection of these parameters in the
present complexes indicates that complexes of LEt are the most
likely candidates to show SCO or LS behavior, compared to
complexes of LMe and LMix. Nevertheless, even with the strong
field coligand NCBH3, the complexes of LEt were [HS-HS]
down to 2 K.
It should also be noted that SCO depends on many factors,
including the interplay between the ligand-field strength at the
transition metal ion and the interactions between the metal
complex, the counterions, and the solvate molecules, as
governed by crystal packing. Thus, modifying the ligand by
replacing the pyridimine ring phenyl substituent by one that
facilitates strong intermolecular interactions (and preferably
also increases the field strength), or use of a different
heterocycle to increase communication across the bridge, may
generate sufficient strength and cooperativity to give the
desired SCO behavior, or at least the possibility of obtaining
systems other than [HS-HS]. These aspects are the next focus
of this research group.
obvious correlation between the Mossbauer and IR data (Table
̈
1), but the trend in isomer shift can be explained when
compared with the Fe−NCE bond distances (Table 2). The
Fe−NNCE bond distances follow the trend NCBH3 > NCSe >
NCS with an average of 2.116 > 2.079 > 2.068 Å. This relation
between bond distance and isomer shift is experimentally
known,50 and theoretical investigations51 have shown that
longer Fe−N bond distances increase the isomer shift by
relative elongation of the 3s- and 4s-iron orbitals.
The decrease in the quadrupole splitting can be related to the
octahedral distortion (Σ). As Σ increases, so does the electric
field gradient caused by the 3d crystal field and thus the
quadrupole splitting also increases. On this basis, the ΔEQ
follows the order 6·3/2H2O < 5 < 4·1/2H2O (Table 3), and this
is in good agreement with the mean distortion parameters Σ: 6
(103.6°) < 5 (116.7°) < 4 (118.2°), Table 2.
CONCLUSION
■
Nine dinuclear iron(II) complexes of three bis-tetradentate
pyrimidine-based ligands, LEt, LMe, and LMix, with three NCE
coligands (E = S, Se, BH3) have been successfully synthesized
and characterized. Five complexes were structurally charac-
terized. In all cases the iron(II) centers had distorted octahedral
geometries with the degree of distortion varying in the order
Fe2LMe > Fe2LMix > Fe2LEt.
The variable temperature magnetic and Mossbauer results
̈
show that (a) weak antiferromagnetic coupling is a feature of all
of them, with −2.20 ≤ J ≤ −0.73 cm−1, and (b) they all remain
in the [HS-HS] state down to 2 K. This shows that the
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(C13), 121.3 (C13′), 116.2 (C5), 60.7 (C7), 59.6(C9′), 54.7 (C8), 36.2
(C9). ESI-MS(+) (MeOH m/z): [LMixH]+ requires 607.3292 found
607.3265. IR (KBr, cm−1): 3061, 3007, 2928, 2822, 1638, 1588, 1568,
1542, 1473, 1432, 1374, 1251, 1146, 1047, 1027, 992, 749, 694, 613,
402. λmax/nm (ε/dm3 mol−1 cm−1) [CH3CN] = 258 (28500).
EXPERIMENTAL SECTION
General experimental information is provided in the Supporting
Information. Crystal structure data is provided in Table 4 and the
Supporting Information.
Where noted acetonitrile and methanol were refluxed over CaH2
and Mg/I2 prior to use, respectively, otherwise HPLC grade was used
as received. 4,6-Bis(hydroxymethyl)-2-phenylpyrimidine (A) and LEt
were synthesized according to our previous report.19 N-Bis(2-
pyridylmethyl)amine (bmpa)28,29 and N-(2-pyridylethyl)-N-(2′-
pyridylmethyl)amine (pmpea)30,31 were prepared according to the
literature methods. [FeII(NCE)2(py)4], E = S, Se, or BH3, were made
according to the published procedure.32 All other chemicals and
solvents were of reagent grade and were used as received.
■
[FeII LEt(NCS)4]·MeOH·3/4H2O (1·MeOH·3/4H2O). To a refluxing
2
yellow solution of LEt (0.07 g, 0.11 mmol) in MeOH (3 mL) was
added a pale yellow solution [FeII(NCS)2(Py)4] (0.11 g, 0.22 mmol)
in MeOH (10 mL), all under argon, leading to an orange solution.
After 3 h the orange solution was cooled to room temperature
followed by dropwise addition of degassed diethyl ether (∼ 60 mL),
via cannula, resulting in the precipitation of an orange solid. The
mixture was left to stand for 1 h, and then the orange solid was filtered
off and dried under vacuum (0.09 g, 80%). Found: C, 52.18; H, 4.38;
4,6-Bis(chloromethyl)-2-phenylpyrimidine (C). To a pale
yellow solution of 4,6-bis(hydroxymethyl)-2-phenylpyrimidine (A)
(1.0 g, 5.0 mmol) in CH2Cl2, under nitrogen, was added SOCl2 (0.75
mL, 10 mmol). The resulting deep yellow suspension was stirred for 1
h before the solvent was removed by blowing nitrogen over it and
further dried under vacuum to give pure 4,6-bis(chloromethyl)-2-
phenylpyrimidine as an orange solid in a quantitative yield. Found: C,
56.70; H, 4.15; N, 10.84 C12H10N2Cl2 (253.13 g mol−1) requires: C,
56.94; H, 3.98; N, 11.07. δH (300 MHz, solvent CDCl3, reference
CHCl3 @ 7.26 ppm): 8.52 (2H2′, m), 7.71 (H5, s), 7.52 (2H3′ & H4′,
m), 4.76 (4H7, s). δC (125 MHz, solvent CDCl3, reference CHCl3 @
77.3 ppm): 166.5 (C2), 164.3 (C1), 136.8 (C1′), 131.3 (C4′), 128.8
(C3′), 128.6 (C2′), 115.1 (C5), 45.7 (C7). ESI-MS(+) (CHCl3-MeOH
m/z): [C12H10N2Cl2 + H]+ requires 253.0294, found 253.0276. IR
(KBr, cm−1): 3312, 1630, 1588, 1573, 1546, 1455, 1409, 1379, 1302,
1260, 1169, 1120, 1066, 1024, 933, 739, 720, 693, 685, 640, 560.
4,6-Bis[N,N-bis(2′-pyridylmethyl)aminomethyl]-2-phenyl
pyrimidine (LMe). To a mixture of 4,6-bis(chloromethyl)-2-phenyl-
pyrimidine (0.05 g, 0.2 mmol) and excess of Na2CO3 (0.42 g, 4 mmol)
in 50 mL of acetonitrile was added a solution of bmpa (0.08 g, 0.4
mmol), and a catalytic amount of KI. The reaction mixture was
refluxed overnight. The insoluble solid was filtered off and the filtrate
taken to dryness to give a red brown oil. The brown oil was dissolved
in H2O (20 mL) and extracted with CH2Cl2 (3 × 50 mL). The
combined organic phase was dried over MgSO4, filtered, and taken to
dryness to afford LMe in 95% yield. Found: C, 74.43; H, 6.01; N, 19.31
C36H34N8 (578.71 g mol−1) requires: C, 74.72; H, 5.92; N, 19.36. δH
(500 MHz, solvent CDCl3, reference CHCl3 @ 7.26 ppm): 8.53
(4H14, ddd), 8.43 (2H2′, m), 7.89 (H5, s), 7.67 (4H11, d), 7.56 (2H12,
td), 7.43 (2H3′ & 1H4′, m), 7.14 (4H13, ddd), 3.99 (8H9, s), 3.96 (4H7,
s). δC (125 MHz, solvent CDCl3, reference CHCl3 @ 77.3 ppm):
168.41 (C4), 163.91 (C1′), 158.72 (C10), 149.02 (C14), 137.76 (C2),
136.78 (C11), 130.58 (C4′), 128.48 (C3′), 128.33 (C2′), 123.09 (C12),
122.34 (C13), 115.82 (C5), 60.2 (C9), 59.5 (C7). ESI-MS(+) (CHCl3
m/z): [LMeH]+ requires 579.2979, found 579.3026; [LMeNa]+ requires
601.2801, found 601.2842. IR (KBr, cm−1): 3068, 3007, 2916, 2816,
1588, 1569, 1542, 1470, 1436, 1379, 1249, 1146, 1043, 994, 761, 689.
λmax/nm (ε/dm3 mol−1 cm−1) [CH3CN] = 259 (27000).
N, 16.11; S, 11.96. [FeII LEt(NCS)4]·MeOH·3/4H2O (1024.89 g/mol)
2
requires C, 52.76; H, 4.67; N, 16.41; S, 12.52. ESI-MS(+) (MeOH m/
z): [LEtH]+ requires 635.3605 found 635.3698; [FeIILEt(NCS)]+
requires 748.2629 found 748.2619; [FeII2LEt(NCS)3]+ requires
920.1482 found 920.1415. IR (KBr, cm−1): 3412, 2038, 1588, 1569,
1546, 1474, 1436, 1379, 1215, 1146, 1036, 1001, 754, 693, 628, 480.
[FeII LEt(NCSe)4]·H2O (2·H2O). To a yellow solution of LEt (0.07 g,
2
0.11 mmol) in MeOH (10 mL) under reflux was added a pale yellow
solution of [FeII(NCSe)2(Py)4] (0.13 g, 0.22 mmol) in MeOH (10
mL), all under argon. The resulting yellow reaction solution was
refluxed for 1 h. After cooling to room temperature, degassed diethyl
ether (∼ 60 mL) was added dropwise using a cannula leading to a
precipitation of a yellow solid. The mixture was left to stand for 1 h
before the yellow solid was filtered off and dried under vacuum (0.11
g, 85%). Found: C, 44.87; H, 3.65; N, 13.79. [FeII LEt(NCSe)4]·H2O
2
(1184.45 g mol−1) requires: C, 44.62; H, 3.74; N, 14.19. ESI-MS(+)
(CH3CN m/z): [LEtH]+ requires 635.3605 found 635.3639;
[FeIILE t(NCSe)]+ requires 796.2077 found 796.2071;
[FeII2LEt(NCSe)3]+ requires 1063.9832 found 1063.9826;
[FeII LEt(NCSe)4K]+ requires 1208.8670 found 1208.8671. IR (KBr,
cm−12): 3435, 3061, 2916, 2847, 2061, 1600, 1565, 1542, 1478, 1436,
1382, 1314, 1154, 1104, 1059, 1028, 948, 780, 754, 697, 643, 419.
[FeII LEt(NCBH3)4]·5/2H2O (3·5/2H2O). To a refluxing suspension of
2
[FeII(NCBH3)2(Py)4] (0.14 g, 0.30 mmol) in MeCN (∼10 mL) was
added a yellow solution of LEt (0.10 g, 0.15 mmol) in MeCN (∼10
mL), all under argon. All the solids dissolved within about 10 min.
After 1 h the solution was cooled to room temperature followed by
addition of degassed diethyl ether (∼ 70 mL) using a cannula,
resulting in the precipitation of a yellow solid. The yellow solid was
filtered off and dried under vacuum (0.14 g, 91%). Found: C, 56.04; H,
6.03; N, 17.18. [FeII2LEt(NCBH3)4]·5/2H2O (950.95 g mol−1
)
requires: C, 55.57; H, 6.25; N, 17.67. ESI-MS(+) (DMF-MeOH m/
z): [LEtH]+ requires 635.3605 found 635.3639; [LEtNa]+ requires
657.3425 found 657.3383 [FeIILEt(NCBH3)]+ requires 730.3243
found 730.3196; [FeII LEt(NCBH3)3]+ requires 866.3323 found
2
866.3219. IR (KBr, cm−1): 3448, 3064, 2931, 2862, 2334, 2182,
1601, 1564, 1545, 1481, 1439, 1388, 1319, 1154, 1115, 1063, 1019,
950, 756, 697, 640, 419.
4,6-[(2′-Pyridylmethyl)-2′-pyridylethyl)aminomethyl]-2-phe-
nylpyrimidine (LMix). To a mixture of pmpea (2.89 g, 13.6 mmol)
and 4,6-bis(chloromethyl)-2-phenylpyrimidine (1.78 g, 6.78 mmol) in
150 mL of warm freshly distilled acetonitrile was added an excess of
Na2CO3 (5.75 g, 54.2 mmol) and a catalytic amount of KI. The
reaction mixture was refluxed overnight. After cooling to room
temperature, the insoluble solid was filtered off, and the filtrate was
taken to dryness under reduced pressure. The resulting brown oil was
then purified by column chromatography on alumina using ethyl
acetate as eluent to give LMix as orange brown oil in 75% yield. TLC:
RF(product) = 0.60. Found: C, 73.23; H, 6.31; N, 17.71. C38H38N8·H2O
(624.78 g mol−1) requires: C, 73.05 H, 6.45; N, 17.93. δH (400 MHz,
[FeII LMe(NCS)4]·1/2H2O (4·1/2H2O). To a refluxing yellow solution
2
of LMe (0.05 g, 0.08 mmol) in MeCN (20 mL), was added 10 mL of a
yellow solution of [FeII(NCS)2(Py)4] (0.08 g, 0.16 mmol), all under
argon, initially resulting in a red solution that turn to a suspension in a
few minutes (∼10 min). The suspension was refluxed for 2 h before it
was cooled down to room temperature. The brick red solid obtained
was then filtered off and dried under vacuum (0.06 g, 80%). Found: C,
51.40; H, 3.68; N, 18.18; S, 13.30. [Fe2LMe(NCS)4]·1/2H2O (931.74 g
mol−1) requires: C, 51.56; H, 3.79; N, 18.04; S, 13.76. ESI-MS(+)
(DMF-MeOH m/z): [LMeH]+ requires 579.2979 found 579.3026;
[LMeNa]+ requires 601.2799 found 601.2840; [FeIILMe(NCS)]+
requires 692.2002 found 692.2037; [FeII LMe(NCS)3]+ requires
solvent CDCl3, reference CHCl3 @ 7.26 ppm): 8.52−8.44 (2H14′
,
2
864.0856 found 864.0963. IR (KBr, cm−1): 3345, 3068, 2926, 2068,
1599, 1569, 1545, 1474, 1434, 1392, 1343, 1287, 1154, 1095, 1048,
1011, 908,781, 761, 702, 648.
2H2′ & 2H14, m), 7.51−7.44 (2H12, H5, 2H12′, H4′ & 2H3′, m), 7.37
(2H11′, d), 7.17−7.06 (2H11, 2H13 & 2H13′), 3.94 (4H7, s), 3.91 (4H9′,
s), 3.05 (4H8 & 4H9, m). δC (100 MHz, solvent, CDCl3, reference
CHCl3 @ 77.3 ppm): 168.9 (C4), 163.85 (C2), 160.3 (C10′), 159.7
(C10), 149.3 (C14′), 149.1 (C14), 138.0 (C1′), 136.5 (C4′), 136.3 (C12′),
130.5 (C12), 128.5 (C3′), 128.4 (C2′), 123.5 (C11), 122.8 (C11′), 122.1
[FeII LMe(NCSe)4] (5). To a refluxing yellow solution of LMe (0.07 g,
2
0.11 mmol) in MeOH (10 mL), was added 10 mL of a yellow solution
of [FeII(NCSe)2(Py)4] (0.13 g, 0.22 mmol) in MeOH, all under argon,
9063
dx.doi.org/10.1021/ic3012052 | Inorg. Chem. 2012, 51, 9056−9065

Inorganic Chemistry
Article
affording a reddish suspension in a few minutes (∼10 min). The
suspension was refluxed for 1 h before it was cooled down to room
temperature. The brick red solid was then filtered off and dried under
vacuum (0.10 g, 82%). Found: C, 43.19; H, 3.12; N, 15.03;
1604, 1569, 1542, 1481, 1444, 1390, 1301, 1154, 1115, 1016, 758, 692,
631, 417.
ASSOCIATED CONTENT
[FeII LMe(NCSe)4] (1110.31 g mol−1) requires: C, 43.27; H, 3.09;
■
2
N, 15.14. ESI-MS(+) (DMF-MeOH m/z): [LMeH]+ requires 579.2979
found 579.2817; [LMeNa]+ requires 601.2799 found 601.2647;
[FeIILMe(NCSe)]+ requires 740.1451 found 740.1240;
[FeII LMe(NCSe)3]+ requires 1007.9214 found 1007. 8961. IR (ATR,
cm−12): 2053, 1600, 1569, 1544, 1477, 1438, 1414, 1393, 1346, 1287,
1155, 1096, 1049, 1014, 946, 908.
S
* Supporting Information
Includes details on instrumentation and measurements, details
of structure determinations and disorder modeling, additional
bond length and angle information, packing interaction figures
and additional structure figures. Also additional magnetic and
[FeII LMe(NCBH3)4]·3/2H2O (6·3/2H2O). To a refluxing suspension
Mossbauer plots and a figure of bmpa and pmpea. This
̈
2
of FeII(NCBH3)2(Py)4 (0.09 g, 0.20 mmol) in MeCN (10 mL), was
added a yellow solution of LMe (0.06 g, 0.10 mmol) in MeCN (8 mL),
all under argon, resulting in a clear orange red solution after a few
minutes (∼10 min). After the reaction solution was refluxed for 3 h,
and cooled down to room temperature, degassed diethyl ether (∼ 75
mL) was slowly added using a cannula to give a yellow suspension.
The suspension was left to stand for 1 h at room temperature before
the yellow solid was filtered off and dried under vacuum (0.75 g, 92%).
material is available free of charge via the Internet at http://
pubs.acs.org. Supplementary crystallographic data can be
obtained from the CCDC using the following reference
codes: CCDC 856975−856979. This data can be obtained
free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Found: C, 54.63; H, 5.42; N, 19.69. [FeII LMe(NCBH3)4]·3/2H2O
AUTHOR INFORMATION
■
2
(833.59 g mol−1) requires: C, 54.79; H, 5.63; N, 19.17. ESI-MS(+)
(DMF-MeOH m/z): [LMeH]+ requires 579.2979 found 579.2956;
[LMeNa]+ requires 601.2799 found 601.2795; [FeIILMe(NCBH3)-
(H2O)]+ requires 692.2722 found 692.1994; [FeIILMe(NCBH3)]+
Corresponding Author
*E-mail: sbrooker@chemistry.otago.ac.nz.
Notes
requires 674.2616 found 674.2530; [FeII LMe(NCBH3)3]+ requires
2
The authors declare no competing financial interest.
810.2696 found 810.1628. IR (KBr, cm−1): 3433, 3068, 2926, 2339,
2177, 1599, 1567, 1545, 1478, 1439, 1395, 1343, 1287, 1115, 1051,
1014, 903, 761, 692, 645.
ACKNOWLEDGMENTS
■
[FeII LMix(NCS)4]·1/2H2O (7·1/2H2O). To a refluxing yellow solution
2
We are grateful to the University of Otago (Postgraduate
Scholarship and Publishing Bursary to W.A.G.), the MacDiar-
mid Institute, and the Marsden Fund for funding this research.
We thank Prof. Keith S. Murray and Dr. Boujemaa Moubaraki
(Monash University) for the magnetic measurements on
1·MeOH·3/4H2O and helpful suggestions, and Mrs. Marianne
Dick and Mr. Bob McAllister (Campbell Microanalytical
Laboratory, University of Otago) for the microanalyses.
of LMix (0.06 g, 0.09 mmol) in MeOH (10 mL), was added a yellow
solution of [FeII(NCS)2(Py)4] (0.09 g, 0.18 mmol) in MeOH (10 mL)
gradually resulting in a yellow suspension (∼ 5−10 min). The yellow
suspension was further refluxed for 2 h before it was cooled down to
room temperature. The yellow solid was then filtered off and dried
under vacuum (0.05 g, 58%). Found: C, 52.60; H, 4.12; N, 17.29; S,
12.67. [FeII LMix(NCS)4]·1/2H2O (959.79 g mol−1) requires: C, 52.56;
2
H, 4.10; N, 17.51; S, 13.36. ESI-MS(+) (DMF-MeOH m/z): [LMixH]+
requires 607.3292 found 607.3265; [FeIILMix(NCS)]+ requires
720.2316 found 720.2316; [FeII LMix(NCS)3]+ requires 892.1169
2
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[FeII LMix(NCSe)4]·3/2H2O (8·3/2H2O). To a refluxing yellow
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