Anion-dependent spin crossover and coordination assembly based on [Fe(tpa)]2+ [tpa = tris(2-pyridylmethyl)-amine] and [N(CN) 2]-: Square, zigzag, dimeric, and [4+1]-cocrystallized complexes

Article abstract of DOI:10.1002/ejic.201200541

A series of Fe^II complexes based on [Fe(tpa)]²⁺ building units and [N(CN)₂ ]- bridging ligands with different anions for charge balance has been prepared and characterized. They have a general formula [Fe(tpa){N(CN)₂ }]x·Y·Z, where x = 4 (14+), Y = 4ClO₄ -, and Z = 2H₂O for 1·(ClO₄) ₄(H₂O)₂ ; x = n (2n+), Z = 0, and Y = nClO ₄ -, nPF₆ -, nAsF₆ -, and nBPh₄ - for 2·(ClO₄)_n, 2·(PF₆) _n, 2·(AsF₆)_n, and 2·(BPh ₄)_n, respectively; x = 2 (32+), Z = 0, and Y = 2BPh ₄ - for 3·(BPh₄)₂ ; x = 4 (44+), Y = 3SbF₆ - + [N(CN)₂ ]-, and Z = [Fe(tpa){N(CN)₂ }2] (5) + 4H₂O for (4+5). Single-crystal X-ray diffraction studies reveal that these complexes show various structures that are affected by different counteranions, i.e., square 1·(ClO₄) ₄(H₂O)₂ , zigzag polymers [2·(ClO ₄)_n, 2·(PF₆)_n, 2·(AsF₆)_n, and 2·(BPh₄) _n], dimeric 3·(BPh₄)₂ , and [4+1]-cocrystallized (4+5). Magnetic studies show that the square complex 1·(ClO₄)₄(H₂O)₂ undergoes a two-step complete spin crossover, whereas the dimer 3·(BPh ₄)₂ is high-spin in the whole temperature range, and all zigzag polymer 2·anions show spin-crossover (SCO) behavior, the transition temperature (T1/2) of which increases with increasing anion size. Interestingly, complex (4+5) displays a gradual two-step spin crossover, which is different from that of 1·(ClO₄)₄(H ₂O)₂ and originates from the cocrystallized spin-crossover tetranuclear and monomeric species. Detailed studies on the crystal structures and magnetic properties have unveiled a remarkable anion-dependent formation of different structures and SCO behavior of these complexes.

Full text of DOI:10.1002/ejic.201200541

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FULL PAPER
DOI: 10.1002/ejic.201200541
Anion-Dependent Spin Crossover and Coordination Assembly Based on
[Fe(tpa)]2+ [tpa = tris(2-pyridylmethyl)amine] and [N(CN)2]–: Square, Zigzag,
Dimeric, and [4+1]-Cocrystallized Complexes
Rong-Jia Wei,[a] Jun Tao,*[a] Rong-Bin Huang,[a] and Lan-Sun Zheng[a]
Keywords: Spin crossover / Coordination assembly / Anion dependence / Structure elucidation / Magnetic properties
A series of FeII complexes based on [Fe(tpa)]2+ building units
and [N(CN)2]– bridging ligands with different anions for
charge balance has been prepared and characterized. They
have a general formula [Fe(tpa){N(CN)2}]x·Y·Z, where x = 4
(14+), Y = 4ClO4–, and Z = 2H2O for 1·(ClO4)4(H2O)2; x = n
studies show that the square complex 1·(ClO4)4(H2O)2 un-
dergoes a two-step complete spin crossover, whereas the di-
mer 3·(BPh4)2 is high-spin in the whole temperature range,
and all zigzag polymer 2·anions show spin-crossover (SCO)
behavior, the transition temperature (T1/2) of which increases
with increasing anion size. Interestingly, complex (4+5) dis-
plays a gradual two-step spin crossover, which is different
from that of 1·(ClO4)4(H2O)2 and originates from the cocrys-
tallized spin-crossover tetranuclear and monomeric species.
Detailed studies on the crystal structures and magnetic prop-
erties have unveiled a remarkable anion-dependent forma-
tion of different structures and SCO behavior of these com-
plexes.
–
(2n+), Z = 0, and Y = nClO4–, nPF6–, nAsF6–, and nBPh4 for
2·(ClO4)n, 2·(PF6)n, 2·(AsF6)n, and 2·(BPh4)n, respectively; x =
–
2 (32+), Z = 0, and Y = 2BPh4 for 3·(BPh4)2; x = 4 (44+), Y =
–
3SbF6 + [N(CN)2]–, and Z = [Fe(tpa){N(CN)2}2] (5) + 4H2O
for (4+5). Single-crystal X-ray diffraction studies reveal that
these complexes show various structures that are affected by
different counteranions, i.e., square 1·(ClO4)4(H2O)2, zigzag
polymers [2·(ClO4)n, 2·(PF6)n, 2·(AsF6)n, and 2·(BPh4)n], di-
meric 3·(BPh4)2, and [4+1]-cocrystallized (4+5). Magnetic
communication between SCO centers in the crystal lattice,
which plays an important role in achieving bistable proper-
ties.[6] For example, some dinuclear,[7] trinuclear,[8] and tet-
ranuclear[9] as well as a number of 1D, 2D, and 3D poly-
meric[10] SCO FeII complexes have been synthesized.
On the other hand, it is well known that secondary coor-
dination sphere species such as solvent molecules[11] and
noncoordinated counterions[12] in the crystal lattice can also
significantly influence SCO behavior by communicating
with SCO entities through hydrogen bonds and/or altering
the lattice phonon distribution that affects crystal packing
modes and intermolecular interactions.[3b]
As part of our continuous interest in SCO systems,[13] we
have recently investigated a very interesting complex,
[Fe(tpa)(NCS)2], which shows successive polymorphic
transformations from polymorph II to IV that are ac-
companied with distinct changes in SCO behavior;[13d] this
complex also shows a solvent-vapor-induced single-crystal
to single-crystal (SCSC) transformation from polymorph I
to its solvated product,[13c] and more interestingly, this com-
plex can recrystallize in various solvents and forms two sol-
vated product types, yellow [Fe(tpa)(NCS)2]·X (Fe/X = 1:1,
X = nPrOH, iPrOH, CH2Cl2, CHCl3, and MeCN) and red
[Fe(tpa)(NCS)2]2·Y (Fe/Y = 2:1; Y = MeOH and EtOH),
and between them solvent-vapor-induced reversible and
irreversible guest molecule exchanges take place in the solid
state followed by dramatic transformations in color, struc-
Introduction
Spin-crossover (SCO) complexes are one of the most
spectacular examples of switchable materials.[1] By tuning
ligand-field strength, the electronic configurations of metal
ions in SCO complexes are interconvertible between the
high-spin (HS) and low-spin (LS) states in response to heat,
pressure fluctuation, and/or light irradiation.[2] The dra-
matic changes in physical properties such as color and mag-
netic moment in association with spin crossover suggest
that SCO materials are potential candidates for futuristic
applications in memory and electronic display devices.[3]
Whereas mononuclear FeII complexes were focused on
for a long time in early SCO systems,[4] the design and syn-
thesis of polynuclear and polymeric SCO FeII complexes
have been the subject of much recent research.[5] The funda-
mental reason for this change is based on the expectation
that, in polynuclear and polymeric SCO FeII complexes,
bridging the metal ions could significantly enhance the
[a] State Key Laboratory of Physical Chemistry of Solid Surfaces
and Department of Chemistry, College of Chemistry and
Chemical Engineering, Xiamen University,
Xiamen 361005, P. R. China
Fax: +86-592-2188138
E-mail: taojun@xmu.edu.cn
Homepage: http://chem.xmu.edu.cn/english/faculty/professor/
chemistry/tao_j.html
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200541.
Eur. J. Inorg. Chem. 0000, 0–0
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R.-J. Wei, J. Tao, R.-B. Huang, L.-S. Zheng
FULL PAPER
ture and SCO behavior.[13e] Inspired by these results, we
thought that the [Fe(tpa)]2+ unit with two accessible coordi-
nation sites would be a good SCO precursor as it can be
linked by a linear bridging ligand, e.g. dicyanamide
group,[14] to generate square[9] or 1D-zigzag-chain[15] SCO
complexes. A new square SCO FeII complex, [Fe(tpa)-
4
{N(CN)2}]4·(BF4)4(H2O)2 [1·(BF4)4(H2O)2], has thus been
reported, which is constructed with [Fe(tpa)]2+ and dicyan-
amide.[13f] This complex shows both thermally and light-
induced two-step SCO and undergoes a reversible SCSC
transformation between 1·(BF4)4(H2O)2 and its solvent-free
form, 1·(BF4)4, induced by water desorption and resorp-
tion.
As we already knew that guest molecules remarkably af-
fect the SCO properties of the [Fe(tpa)(NCS)2] system[13e]
and we have successfully synthesized a square SCO
[Fe(tpa){N(CN)2}]4·(BF4)4(H2O)2 complex,[13f] we antici-
pated that complexes constructed from [Fe(tpa)]2+ and di-
cyanamide with counteranions other than BF4 could also
be obtained and their SCO behavior could be affected by
various counteranions. It has been revealed that variation
Figure 1. Schematic representation of the anion-dependent as-
sembly based on [Fe(tpa)]2+ and [N(CN)2]– building units.
Results and Discussion
–
Synthesis
All complexes based on [Fe(tpa)]2+ and [N(CN)2]– build-
of counteranions can shift reaction equilibria and result in ing units were prepared by the reaction of FeSO4,
products with different structures and physicochemical NaN(CN)2, tpa, and the sodium or potassium salt of the
properties,[16] thus it is possible to attain specific products corresponding anion in equimolar ratio. The 1D zigzag
–
–
–
by changing counteranions. In principle, the assembly rep- chainlike complexes 2·Yn (Y = ClO4 , PF6 , or AsF6 ) were
resenting the lowest free-energy state is preferred for a given easily obtained as yellow crystals in a water/ethanol (5:1)
set of conditions.[17] In the past few years, counteranions solution, whereas red crystals of 2·(BPh4)n and yellow crys-
have been successfully employed to control the formation tals of dimeric complex 3·(BPh4)2 grew simultaneously in a
of specific molecules and assemblies.[18] For example, Dun- test tube and were separated manually under a microscope.
bar and co-workers[19] recently reported an anion-directed The square complex 1·(ClO4)4(H2O)2 was synthesized in the
assembly of NiII and ZnII metallacyclophanes with 3,6- same way as that of chainlike complex 2·(ClO4)n; except a
[13f]
bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) as a bridging ligand; single-crystal of 1·(BF4)4(H2O)2
was used as a seed,
–
–
tetrahedral BF4 and ClO4 ions direct the formation of around which red crystals of 1·(ClO4)4(H2O)2 crystallized
molecular squares, [{M4(bptz)4(CH3CN)8}X][X]7 (M = in several hours, and the crystal seed of 1·(BF4)4(H2O)2 was
then removed manually. Crystals of 1·(ClO4)4(H2O)2 and
induces the formation of pentagonal [{Ni5(bptz)5- 2·(ClO4)n could also be obtained simultaneously at a higher
(CH3CN)10}SbF6][SbF6]9. concentration [0.5 mmol of each component in 6 mL water/
–
–
–
ZnII, NiII; X = BF4 , ClO4 ), whereas octahedral SbF6
In order to further understand the influences of ethanol (5:1) solution] without the addition of a seed of
counteranions on the assembly and SCO properties of the 1·(BF4)4(H2O)2. Under an optical microscope, the two com-
[Fe(tpa)]2+/dicyanamide system, we have recently synthe- plexes with different color could be easily separated by
sized a series of complexes based on the building units hand. The complex (4+5) was obtained through a transfor-
[Fe(tpa)]2+ and [N(CN)2]– with the general formula mation from the kinetically favored product to the thermo-
–
[Fe(tpa){N(CN)2}]x·Y·Z, where x = 4 (14+), Y = 4ClO4 , dynamically stable one through an in situ recrystallization
and Z = 2H2O for 1·(ClO4)4(H2O)2; x = n (2n+), Z = 0, process. An aqueous solution of FeSO4, NaN(CN)2, and
–
–
–
–
and Y = nClO4 , nPF6 , nAsF6 , and nBPh4 for 2·(ClO4)n, KSbF6 mixed with an ethanol solution of tpa without stir-
2·(PF6)n, 2·(AsF6)n, and 2·(BPh4)n, respectively; x = 2 (32+), ring gave rise to a turbid red solution with a large amount
–
Z = 0, and Y = 2BPh4 for 3·(BPh4)2; x = 4 (44+), Y = of brown precipitate, which generally dissolved and red
–
3SbF6 + {N(CN)2}–, and Z = [Fe(tpa){N(CN)2}2] (5) + crystals of (4+5) simultaneously crystallized. Elemental
4H2O for (4+5). These complexes display various structural analysis showed that the brown precipitate had similar C,
geometries (Figure 1) and different SCO behaviors, i.e., N, and H percentages to those of crystalline (4+5), and
square complex 1·(ClO4)4(H2O)2 shows a well-defined two- magnetic measurements revealed that it underwent an in-
step SCO, 1D zigzag complexes 2·(ClO4)n, 2·(PF6)n, complete SCO; powder XRD (PXRD) indicated that it was
and 2·(AsF6)n display a one-step incomplete SCO, and an amorphous solid (Supporting Information). Attempts to
2·(BPh4)n undergoes almost complete SCO, dimeric com- synthesize complexes under different conditions, such as re-
plex 3·(BPh4)2 remains in high-spin state in the whole tem- placing ethanol with methanol and changing the ratios of
perature range, and the [4+1]-cocrystallized complex (4+5) Fe/tpa/dicyanamide/anion, were performed. Little influence
shows a gradual two-step SCO originating from the tetra- was observed on the formation of chains vs. dimers vs.
nuclear and mononuclear species.
squares.
2
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Anion-Dependent Spin Crossover and Coordination Assembly
Crystal Structures
Table 1. Selected bond lengths and parameters of 1·(ClO4)4(H2O)2
and 1·(ClO4)4.
Single-crystal X-ray diffraction studies were carried out
at various temperatures in order to correlate the structures
with the different SCO phases identified by magnetic mea-
surements.
1·(ClO4)4(H2O)2
150 250
1.971/59.53 2.116/88.1 2.151/95.8
1.967/55.40 1.992/55.9 2.14/91.7
1·(ClO4)4
T [K]
Ͻd
350
[a]
[a]
Ͼ
Ͼ
[Å]/Σ[b] [°]
[Å]/Σ[b] [°]
Fe1–N
Ͻd
Fe2–N
C–H···π interactions[c] [Å] 3.687(2)
3.544(2)
3.640(2)
3.599(2)
3.385(3)
3.324(3)
2.560(1)
3.139(2)
3.951(4)
3.826(3)
3.398(4)
3.321(6)
–
Complex 1·(ClO4)4(H2O)2 is isostructural to complex
[13f]
1·(BF4)4(H2O)2
and crystallizes in the monoclinic space
C–H···O interactions[d] [Å] 3.311(2)
3.152(4)
group P21/c. The asymmetric unit is composed of half a
cationic 14+ square (two crystallographically distinct Fe1
O–H···O interactions[e] [Å] 2.862(3)
3.084(3)
–
and Fe2 ions), one water molecule, and two ClO4
–
counteranions. The [Fe(tpa)]2+ units are bridged by μ1,5
-
[a] ϽdFe–NϾ is the average Fe–N bond length. [b] The distortion
parameter Σ is defined as the sum of the absolute values of the
deviations of the 12 cis N–Fe–N angles from 90°.[20] [c] Distance
between tpa carbon atom to the centroid of the pyridyl group of
N(CN)2– groups in a square-shaped arrangement and adopt
a trans-[Fe1–Fe2–Fe1–Fe2] geometric configuration, as is
shown in Figure 2.
–
adjacent tpa. [d] Distance between ClO4 ion and pyridyl carbon
–
atom. [e] Distance between ClO4 ion and water molecule.
The 3D supramolecular structure of complex 1·(ClO4)4-
(H2O)2 can be viewed as 2D layers containing cationic 14+
–
squares, ClO4 ions, and water molecules that stack along
the b axis (Figure 3). Moderate C–H···π interactions are
also found between the pyridine rings of adjacent 14+
–
squares (Table 1). The ClO4 ions (denoted as Cl1 and Cl2)
and water molecules occupy the voids formed between the
–
cationic 14+ squares. The ClO4 ions contact with the 14+
squares through C–H···O hydrogen bonds with C···O sepa-
rations of 3.311(2) and 3.152(4) Å at 150 K and 3.385(3)
and 3.324(3) Å at 250 K, for Cl1 and Cl2, respectively; the
closest O···O distances of the O–H···O hydrogen bonds be-
–
tween the ClO4 ions and water molecules vary from
2.862(3) to 2.560(1) Å and 3.084(3) to 3.139(2) Å upon tem-
perature increases from 150 to 250 K, for Cl1 and Cl2,
respectively. At 350 K, the crystal packing of dehydrated
complex 1·(BF4)4 is similar to that of 1·(BF4)4(H2O)2.
Figure 2. ORTEP drawing of the structure of 14+ in 1·(ClO4)4-
(H2O)2 with 30% thermal ellipsoid probability. Counteranions,
water molecules, and hydrogen atoms are omitted for clarity. Sym-
metry operation: –x + 1, –y + 2, –z.
The crystal data of 1·(ClO4)4(H2O)2 were collected at
150, 250, and 350 K. Selected bond lengths and parameters
showing salient features of the structure are summarized in
Table 1. At 150 K, the Fe–N bond lengths range from 1.938
to 1.987 Å with average values of 1.971 and 1.967 Å for Fe1
and Fe2, respectively, which indicate that all FeII ions in the
cationic 14+ square are in an LS state at 150 K. Upon
warming to 250 K, the average Fe1–N bond length shows
a sizeable increase to 2.116 Å, whereas that of the Fe2–N
bonds varies slightly from 1.967 to 1.992 Å, implying that
the crystal is in an intermediate configuration, [Fe1HS
–
Fe2LS–Fe1HS–Fe2LS], at this temperature. When further
heated to 350 K, the crystal of 1·(ClO4)4(H2O)2 becomes
the dehydrated form, 1·(ClO4)4, by an SCSC transformation
process. The average Fe–N bond lengths are 2.151 and
2.140 Å for Fe1 and Fe2, respectively, indicating that all
FeII ions in the cationic 14+ square at this temperature are
in an HS configuration. A two-step (FeIILS)4 ↔ [Fe1HS
–
Figure 3. Packing diagram of 1·(ClO4)4(H2O)2 viewed along the b
axis. ClO4– counteranions are shown as tetrahedra, and water mole-
cules are shown as spheres. Hydrogen atoms are omitted for clarity.
Fe2LS–Fe1HS–Fe2LS] ↔ (FeIIHS)4 spin crossover is thus sug-
gested in this temperature range.
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Complex (4+5) crystallizes in the monoclinic space group Table 2. Selected bond lengths and parameters of complex (4+5).
C2/m, and the asymmetric unit contains half a cationic 44+
square (crystallographically distinct Fe1 and Fe2 ions), half
T [K]
270
230
130
ϽdFe1–NϾ [Å]/Σ [°]
ϽdFe2–NϾ [Å]/Σ [°]
ϽdFe3–NϾ [Å]/Σ [°]
2.077/69.2 2.032/59.5 1.974/45
2.083/73.8 2.037/61.3 1.969/46.5
2.161/85.8 2.157/80.7 2.026/57.2
–
a neutral complex 5 (denoted as Fe3 site), three half SbF6
anions and half an [N(CN)2]– free anion. In addition, there
are four water molecules per formula unit, as indicated in Anion···π interaction[a] [Å] 3.273(1)
3.208(2)
3.375(2)
3.558(4)
3.754(5)
3.525(1)
3.929(1)
3.105(1)
3.299(4)
3.495(1)
3.701(2)
3.460(1)
3.837(1)
C–H···π interaction[b] [Å] 3.444(3)
the difference density map and elemental analysis (Experi-
mental Section); however, these are severely disordered and
C–H···π interactions[c] [Å] 3.525(2)
3.757(2)
are therefore removed when the structure is refined by using
the SQUEEZE[21] function. The molecular structures of the
cationic 44+ square and neutral complex 5 are shown in
Figure 4. The [Fe(tpa)]2+ units of 44+ are interlinked by
μ1,5-N(CN)2– groups to form a square structure that is sim-
ilar to that of 14+ but adopts a cis-[Fe1–Fe1–Fe2–Fe2] geo-
metric configuration (Figure 4a). In the neutral mononu-
clear complex 5, the [Fe(tpa)]2+ unit is coordinated by two
C–H···π interactions[d] [Å] 3.571(1)
3.985(1)
[a] Distance between the central N atom of [N(CN)2]– of 44+ and
the centroid of the pyridyl group of 5. [b] Distance between the
pyridyl carbon atom of 5 and the pyridyl group centroid of 44+. [c]
Distance between the pyridyl carbon atom and the pyridyl centroid
of adjacent 44+ squares in the ab plane. [d] Distance between the
pyridyl carbon atom and the pyridyl centroid of adjacent 44+
squares in the ac plane.
–
η1-N(CN)2 anions (Figure 4b).
Based on the average Fe–N distances determined from
variable-temperature X-ray diffraction studies (Table 2), we [HS]4-to-[LS]4 one-step SCO that lacks an intermediate
can conclude that the Fe1 and Fe2 ions in the cationic 44+ [HS]2[LS]2 state, which is a typical characteristic of its con-
[13f]
square have already undergone SCO at 270 K, whereas the geners 1·(BF4)4(H2O)2
and 1·(ClO4)4(H2O)2. Because
Fe3 ion in the mononuclear molecule 5 remains in the HS the two FeII ions (Fe1 and Fe2) in the cationic 44+ square
state until 230 K and, therefore, complex (4+5) is in the undergo SCO almost synchronously, as revealed by changes
{[IP]4 + HS} (IP = intermediate phase between HS and LS in the Fe–N bond lengths of Fe1 and Fe2, the desired mul-
states, which indicates a continuous change of the bond tiple SCO steps of the cationic 44+ square are not resolved
length and an averaged population of HS and LS states in crystallographically. Instead, in the cationic 14+ square the
each SCO metal ion) state in this temperature range. Upon two different FeII ions show crystallographically different
cooling to 130 K, each FeII ion in the cationic 44+ square changes in the Fe–N bond lengths, thus showing two suc-
has converted to an LS configuration, whereas the Fe3 ion cessive SCO processes.
in the mononuclear molecule 5 is in the IP state (Table 2),
As shown in Figure 5, the cationic 44+ square and the
thus the mononuclear complex 5 undergoes an incomplete neutral molecule 5 interact with each other through a
SCO below 230 K. At higher temperatures, e.g. Ͼ 300 K, strong anion···π interaction[22] [3.105(1) Å at 130 K,
complex (4+5) would properly reach the {[HS]4+HS} state Table 2] between the central N atom of the [N(CN)2]– group
and would show an {[HS]4 + HS} ↔ {[IP]4 + HS} ↔ {[LS]4 of 44+ and one of the pyridyl groups of molecule 5, and
+ IP} two-step SCO, which originates from the SCO-active through strong C–H···π interactions [3.299(4) Å at 130 K]
nonequivalent units in the cocrystallized structure.
between the pyridyl group of molecule 5 and the pyridyl
It should be mentioned that, from the structural point of group of the cationic 44+ square. Meanwhile, the cationic
view, the cationic 44+ square in complex (4+5) displays an 44+ squares form intersquare π···π interactions [3.495(1)
Figure 4. ORTEP drawings (30% thermal ellipsoid probability) of the structure of 44+ (a) and the neutral molecule 5 (b) in complex
(4+5). Counteranions, water molecules, and hydrogen atoms are omitted for clarity. Symmetry operation: x, –y, z.
4
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Anion-Dependent Spin Crossover and Coordination Assembly
and 3.701(1) Å at 130 K] to give chainlike stacks along the H···π interactions [3.621(4), 3.678(5), and 3.613(9) Å for
c axis. The resulting {44+ + 5} units are parallel stacked to 2·(ClO4)n, 2·(PF6)n, and 2·(AsF6)n at 270 K, respectively]
form 2D layers in the bc plane (Figure 5a) that are further between the pyridyl groups of adjacent chains.
antiparallel stacked along the a axis (ABAB mode) to form
Table 3. Selected bond lengths and parameters of complexes
a 3D structure (Figure 5b), both through π···π and C–H···π
2·(ClO4)n and 2·(PF6)n.
interactions between the cationic 44+ squares; the voids in
the 3D supramolecular structure are occupied by SbF6
ions, free [N(CN)2]– ligands, and disordered water mole-
cules.
–
2·(ClO4)n
2·(PF6)n
T [K]
270
2.162
92.81
110
2.067
67.7
270
2.165
93.68
110
2.066
73.51
ϽdFe1–NϾ [Å]
Σ [°]
Anion···π interactions[a] [Å] 3.306(3) 3.306(6) 3.596(4) 3.624(2)
C–H···π interactions[b] [Å]
3.621(4) 3.586(9) 3.678(5) 3.612(3)
[a] Distance between the central N atom of [N(CN)2]– and the pyr-
idyl centroid of adjacent chain. [b] Distance between two pyridyl
groups of adjacent chains.
Table 4. Selected bond lengths and parameters of 2·(AsF6)n and
LT
2·(AsF6)n
.
LT
2·(AsF6)n 2·(AsF6)n
270 173
2.161/94.3 2.166/98.7 2.170/101.96
T [K]
ϽdFe1–NϾ [Å]/Σ [°]
ϽdFe2–NϾ [Å]/Σ [°]
110
2.138/78
3.973(7)
3.724(2)
3.689(7)
3.665(9)
1.982/48.06
3.967(6)
3.717(1)
3.739(6)
3.575(6)
Anion···π interactions[a] [Å] 3.871(5)
C–H···π interactions[b] [Å]
3.613(9)
[a] Distance between the N atom of [N(CN)2]– and the pyridyl
centroid. [b] Distance between the pyridyl C atom and the pyridyl
centroid in the adjacent chain.
For 2·(ClO4)n and 2·(PF6)n, the unit-cell volumes slightly
shrink, and the space groups remain unchanged upon tem-
perature decrease to 110 K, and at this temperature the
average Fe–N bond lengths are 2.067 and 2.066 Å for
2·(ClO4)n and 2·(PF6)n, respectively, indicating that the two
complexes may undergo incomplete SCO. For 2·(AsF6)n,
the space group also remains unchanged but with an elong-
ation of the a axis (25%) and c axis (50%) and doubling of
the cell volume upon temperature decrease; the asymmetric
unit of 2(AsF6)n at 173 K [denoted as 2·(AsF6)nLT] contains
two crystallographically different FeII centers (Fe1 and Fe2
Figure 5. Perspective view of the anion···π and C–H···π interactions
between 44+ and 5 and C–H···π interactions between 44+ squares
in the bc plane (a) and the packing diagram of cocrystallized com- sites) that are alternatively linked by [N(CN)2]– spacers to
plex (4+5) (b). SbF6– counteranions are shown as octahedra, hydro-
gen atoms are omitted for clarity.
form 1D zigzag chains running along the b axis (Figure 6d).
Based on the Fe–N distances (Table 4) determined at vari-
able temperature, we can conclude that the Fe2 center in
the zigzag chain has already undergone SCO at 173 K and
Complexes 2·(ClO4)n, 2·(PF6)n, and 2·(AsF6)n crystallize reaches the LS state at 110 K, whereas the Fe1 center re-
in the monoclinic space group P21/c with asymmetric units mains in the HS state at 110 K. The crystal packing of
LT
at 270 K containing one [Fe(tpa)]2+ unit, one [N(CN)2]– 2·(AsF6)n is similar to that of 2·(AsF6)n at 270 K, except
group, and one associated counteranion. All FeII ions are for some changes in intermolecular interactions upon SCO.
in an HS state at 270 K with average Fe–N bond lengths
The crystal structure of complex 2·(BPh4)n was deter-
(Tables 3 and 4) of 2.162, 2.165, and 2.161 Å for 2·(ClO4)n, mined at 295 and 150 K. Selected bond lengths and param-
2·(PF6)n, and 2·(AsF6)n, respectively. The adjacent FeII ions eters showing the salient features of structure are summa-
–
are bridged by μ1,5-N(CN)2 groups to form 1D zigzag rized in Table 5. Compound 2·(BPh4)n crystallizes in the
chains along the b axis, as shown in Figure 6a–c. The zigzag space group P21/c in all of the temperature range and shows
chains interact with each other through strong anion···π in- no phase transition as expected for gradual SCO behavior
teractions [3.306(3), 3.596(4), and 3.871(5) Å at 270 K for (see Magnetic Properties). The structure contains two crys-
2·(ClO4)n, 2·(PF6)n, and 2·(AsF6)n, respectively, Tables 3 tallographically different chains, denoted as the {Fe1}n and
and 4] between the [N(CN)2]– groups and the pyridyl {Fe2}n chains, which both run along the b axis and stack
groups of adjacent zigzag chains, and through strong C– alternately along the a axis (Figure 6e). The chains interact
Eur. J. Inorg. Chem. 0000, 0–0
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R.-J. Wei, J. Tao, R.-B. Huang, L.-S. Zheng
FULL PAPER
LT
Figure 6. Packing diagrams of 2·(ClO4)n (a), 2·(PF6)n (b), 2·(AsF6)n (c), 2·(AsF6)n (d), 2·(BPh4)n (e), and 3·(BPh4)2 (f). Counteranions
are shown as polyhedra. For (d) and (e), Fe1 atoms are shown as black spheres, and Fe2 atoms are shown as gray spheres. Hydrogen
atoms are omitted for clarity.
with each other only through C–H···π interactions H···anion hydrogen bonds involving the N atom of an
(Table 5). At 150 K, the average Fe–N bond lengths are [N(CN)2]– group and a C atom of an adjacent tpa ligand
1.965 and 1.975 Å for Fe1 and Fe2, respectively, indicating (Table 5). No obvious π···π or C–H···π interaction is found
that the two FeII centers are in the LS state. At 298 K, the between the 32+ units. The average Fe–N bond length is
corresponding values for the Fe1 and Fe2 centers increase 2.166 Å at 200 K, which is in the range expected for an HS
to 2.055 and 2.102 Å, respectively, which shows that the FeII FeII–N bond. Specifically, the [FeN6] coordination octahe-
ions in the two independent zigzag chains have partly dron is highly distorted with an octahedral distortion pa-
undergone SCO (incomplete SCO below room tempera- rameter (Σ) of 111.92° at 200 K. The octahedral distortion
ture). Actually, 2(BPh4)n would propably reach the [Fe1HS
+
parameter is calculated as the sum of the deviation of each
Fe2HS] state at higher temperature (Ͼ 380 K, see Magnetic of the 12 cis angles from 90°.[20] A larger Σ value should
Properties).
be associated with a weaker ligand field, and, therefore, a
decrease in the transition temperature and stabilization of
the HS state of the metal ion.[23] In the present case, the Σ
value of 3·(BPh4)2 is much larger than those of the other
FeII complexes, indicating a weaker ligand field on the FeII
center in 3·(BPh4)2, and as a result 3·(BPh4)2 retains the HS
state at all temperatures.
Table 5. Selected bond lengths and parameters for 2·(BPh4)n and
3·(BPh4)2.
2·(BPh4)n
3·(BPh4)2
T [K]
295
150
200
ϽdFe1–NϾ [Å]/Σ [°]
ϽdFe2–NϾ [Å]/Σ [°]
C–H···π interactions[a] [Å]
2.055/63.68 1.965/37.43 2.166/111.92
2.102/71.61 1.975/42.18
3.742(7)
3.540(8)
3.967(7)
–
–
–
–
–
3.675(4)
3.493(5)
3.902(2)
–
Magnetic Properties
C–H···anion interaction[b] [Å]
3.312(7)
[a] Distance between pyridyl C atom and the pyridyl group centroid
of adjacent chain. [b] Distance between the pyridyl group C atom
and the N atom of [N(CN)2]– of adjacent dimer.
The magnetic susceptibilities of the seven complexes were
measured at a sweep rate of 1 Kmin–1 under a 0.5 T applied
field. The χMT vs. T plots for 1·(ClO4)4(H2O)2 (per Fe4
Complex 3·(BPh4)2 crystallizes in the monocline space unit), the 1D chain series [2·(ClO4)n, 2·(PF6)n, 2·(AsF6)n
group P21/c, and the asymmetric unit contains half of the and 2·(BPh4)n, per Fe unit], 3·(BPh4)2 (per Fe2 unit) and
–
dimer and one BPh4 anion, and the molecular dimer, (4+5)·S (per [Fe4+Fe1] unit), are shown in Figure 7a–d.
[Fe(tpa){N(CN)2}]22+ (32+), is located on a crystallographic
The magnetic measurement of 1·(ClO4)4(H2O)2 was car-
inversion center. In the solid state, the packing of ried out in a 300–100–380 K temperature cycle (Figure 7a).
3·(BPh4)2 can be described as layers with alternate 32+ and In the first cooling mode, the χMT value is
–
BPh4 chains parallel to the ab plane. Between the chains 12.02 cm3 mol–1 K at 300 K, which decreases continuously
of 32+, the complex units are connected though weak C– and reaches a declining plateau between 250 and 230 K that
6
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Anion-Dependent Spin Crossover and Coordination Assembly
Figure 7. χMT vs. T plots of 1·(ClO4)4(H2O)2 (per Fe4 unit) (a), the 1D chain series [2·(ClO4)n, 2·(PF6)n, 2·(AsF6)n and 2·(BPh4)n] (per
Fe atom) (b), 3·(BPh4)2 (per Fe2 unit) (c), and (4+5) (per [Fe4+Fe1] unit) (d).
corresponds to an [HSFe1–LSFe2–HSFe1–LSFe2] state (see tures of T1 = 209 K and T2 = 290(ȇ)/296(Ȇ) K, respec-
Crystal Structures). The χMT value then decreases smoothly tively. The dehydration of complex 1·(ClO4)4(H2O)2 does
–
and attains a constant value of 0.05 cm3 mol–1 K between not significantly change the magnetic behavior. The BF4
160 and 100 K. In the warming process, the χMT vs. T curve analogue shows a more obvious dehydration effect on SCO
is similar to that of the first cooling process and reaches a with T1/2 values of 302 (T1) and 194 (T2) K and 294 (T1)
value of 14.14 cm3 mol–1
K at 380 K, indicating that and 211 (T2) K for 1·(BF4)4(H2O)2 and 1·(BF4)4, respec-
1·(ClO4)4(H2O)2 undergoes complete SCO and is in the tively. The different dehydration effect between the two iso-
(FeIIHS)4 state above 350 K. However, the complex at this structural complexes obviously originates from the different
temperature is in fact the hydrated form 1·(ClO4)4, as re- hydrogen-bond interactions induced by different counter-
vealed by structural determination, and thermogravimetric anions.
analysis (Figure S1 in Supporting Information) also shows
Complex 2·(ClO4)n displays an abrupt, incomplete SCO
that dehydration is completed at the conclusion of this with T1/2 = 126 K (Figure 7b). The χMT value per FeII unit
warming process, so in the second cooling process magnetic is 3.07 cm3 mol–1 K at 300 K, which begins to decrease
measurements were performed by using the in situ obtained rapidly from 150 K and reaches
a
plateau of
solvent-free sample. Upon cooling, the χMT value remains 1.57 cm3 mol–1 K between 108 and 30 K that is followed by
constant until 340 K, then decreases continuously and com- a further decrease of the χMT value, because of the zero-
pletely overlays that of the first cooling process below field effect of residual HS FeII ions. Complex 2·(PF6)n dis-
300 K. Above 300 K, the SCO shows hysteretic behavior plays a continuous, incomplete SCO with T1/2 = 168 K. At
(width 6 K, Figure 7a inset) that is most probably due to 300 K, the χMT value is 3.07 cm3 mol–1 K, which is in good
the dehydration process. This small apparent hysteresis can agreement with the value expected for HS FeII ions. On
be reproduced by using a fresh sample of 1·(ClO4)4(H2O)2. cooling, the χMT value decreases sharply between 200 and
This overall profile indicates that complex 1·(ClO4)4(H2O)2 130 K and then reaches a plateau of 1.62 cm3 mol–1 K, indi-
displays a two-step complete SCO with critical tempera- cating a near “half” SCO.
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R.-J. Wei, J. Tao, R.-B. Huang, L.-S. Zheng
FULL PAPER
Complex 2·(AsF6)n shows an incomplete SCO with Counteranions with different shapes and electronegativities
slightly complicated behavior (Figure 7b). The room-tem- are expected to modify the structures and intermolecular
perature χMT value is 3.08 cm3 mol–1 K, which is similar to interactions of the assembled system, thus resulting in dif-
the expected value for an HS FeII ion. Upon temperature ferent degrees of “chemical pressure” on the SCO-active
decrease, the χMT value firstly remains constant until 240 K centers and subsequently influences their SCO behavior.
and then decreases smoothly to reach a narrow plateau of Moreover, for the 1D zigzag chain family, there is an ap-
2.67 cm3 mol–1 K between 190 and 186 K. As has been re- proximately linear relationship between anion size and the
vealed by crystallographic studies, the asymmetric unit of SCO critical temperature. All 1D complexes show similar
2·(AsF6)n undergoes a phase transition and contains two packing structures, in which different counteranions do not
crystallographically different FeII centers, one remains in an observably change interchain interactions but significantly
HS state (Fe1) and the other one (Fe2) keeps on undergoing influence the SCO properties. The transition temperatures,
SCO below 173 K. So, the appearance of a narrow plateau T1/2, of the zigzag chain complexes are 126, 168, 158, and
(width 4 K) is most probably due to the phase transition. 276 K for 2(ClO4)n, 2(PF6)n, 2(AsF6)n, and 2(BPh4)n,
This strange step is reproducible. The χMT value below this respectively, which correlates approximately with the sizes
–
–
–
plateau further decreases and reaches a wide plateau between of counteranions in the order ClO4 Ͻ PF6 Ͻ AsF6
Ͻ
–
130 and 30 K (1.65 cm3mol–1K), followed by a sudden drop BPh4 . However, the detailed mechanism of the relationship
due to the zero-field effect of the HS FeII ion (Fe1).
between the size of the counteranion and SCO T1/2 is still
Complex 2·(BPh4)n displays gradual SCO behavior over unclear.[20] Tuchagues reported a series of SCO complexes
[24]
a wide temperature range between 380 and 150 K with T1/ with formula [Fe(trim)2]X2
[trim = 4-(4-imidazolylme-
2 = 276 K (Figure 7b). The χMT value per FeII unit at 380 K thyl)-2-(2-imidazolylmethyl)imidazole, X = I–, Br–, Cl–], of
(2.98 cm3 mol–1 K) is in agreement with the expected value which the transition temperature follows the order X– = I–
for an HS FeII ion and decreases gradually upon tempera- (T1/2 = 380 K) Ͼ Br– (340 K) Ͼ Cl– (180 K). In these com-
ture lowering and reaches the minimum value of plexes, the halide counteranions interact with the complex
0.20 cm3 mol–1 K at 150 K, corresponding to an LS FeII ion. cation through hydrogen bonds and reduce the basicity of
In complete contrast to the other six complexes, neighboring ligand donor groups. As a result, strong
3·(BPh4)2 is paramagnetic in the whole temperature range cation···anion hydrogen bonds are expected to stabilize the
(Figure 7c). From the structural point of view, the high-spin state and decrease the transition temperature.
[Fe(tpa)]2+ units in 3·(BPh4)2 are doubly bridged by However, some complexes exhibit the exact opposite behav-
[N(CN)2]– groups, forming highly distorted coordination ior.[12b–12d,25] Meanwhile, counteranions may prevent SCO-
geometries (Table 5) and consequently resulting in the active species from achieving cooperative lattice interac-
weakest ligand field among these complexes.
tions, thus leading to gradual SCO (gradual and nonhyster-
Magnetic studies on complex (4+5) were performed in etic).[26] In the present case, all complexes show nonhyster-
the 2–390 K temperature range (Figure 7d). Upon tempera- etic SCO behavior, which indicates that the presence of
ture increase from 2 to 10 K, the χMT value increases counteranions remarkably eliminates interchain or inter-
slightly from 0.77 to 0.87 cm3 mol–1 K and remains constant square cooperative interactions.
until 130 K, consistent with the {[LS]4 + IP} state revealed
by crystallographic studies; after this temperature, the χMT
value increases in a multiple step manner separated at 245
Conclusions
A series of FeII complexes based on [Fe(tpa)]2+ and
[N(CN)2]– building units with various counteranions has
been synthesized. Magnetic studies have revealed that the
SCO properties of these complexes are profoundly influ-
enced by the counteranions. Complex 1·(ClO4)4(H2O)2 un-
dergoes a two-step complete SCO, 3·(BPh4)2 is in HS state
in the whole temperature range. Complex (4+5) displays a
gradual two-step SCO originated from the different SCO-
active tetranuclear and mononuclear species cocrystallized
in the lattice. The 1D chainlike complexes are inclined to
undergo an SCO with a higher transition temperature and
more gradual transition behavior with larger counteranions.
The present study may contribute a feasible route toward
exploring anion-direct synthesis and assembly of SCO com-
plexes.
and 298 K (Figure 7d inset) and finally attains a value of
16.19 cm3 mol–1 K at 390 K that corresponds to the {[HS]4
+ HS} state. The χMT value at 245 K is 9.14 cm3 mol–1 K,
which may originate from the {[IP]4 + HS} intermediate
state revealed by structural analysis (Table 2, 230 K). Ther-
mogravimetric analysis (Figure S2 in Supporting Infor-
mation) indicates that the χMT increase at 298 K is ac-
companied by desorption of guest water molecules, which
starts at room temperature and is complete at ca. 360 K.
Because the desorption is completed at the conclusion of
the heating process (390 K), magnetic studies in the cooling
process were performed by using the in situ obtained dehy-
drated sample. Upon cooling, the χMT value remains con-
stant until 370 K, then decreases continuously and overlays
completely that of heating process below 290 K.
Anion Effect on SCO
Experimental Section
It is obvious that the SCO properties of the seven com-
Materials and Physical Measurements: All starting materials were
plexes are profoundly influenced by various counteranions. obtained commercially and were used without further purification.
8
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Anion-Dependent Spin Crossover and Coordination Assembly
Elemental analyses for C, H, and N were performed with a Vario
EL III analyzer. Thermogravimetric measurements were taken with
a TG 209F1 thermogravimetric analyser. The IR spectra (KBr pel-
lets) were recorded in the range 400–4000 cm–1 with an AVA-
TAR330 FTIR spectrophotometer. PXRD studies were performed
with a Panalytical X-Pert PRO diffractometer with Cu-Kα radiation
(λ = 0.15418 Å, 40.0 kV, 30.0 mA). Magnetic susceptibility mea-
surements were performed with a Quantum Design MPMS XL7
magnetometer at a sweeping rate of 1 Kmin–1 under a magnetic
field of 5000 Oe. Magnetic data were calibrated with the sample
holder, and diamagnetic corrections were estimated from Pascal’s
constants.
group in (4+5) at 230 and 270 K was removed when the data were
refined by using SQUEEZE, and in the lattice of this complex crys-
tal there are four guest water molecules per formula unit, which
are severely disordered and were also removed when the data were
refined. Crystallographic data and structural refinement details for
the seven complexes are presented in Tables 6 and 7. CCDC-860037
[for (4+5) at 270 K], -860038 [for (4+5) at 230 K], -860039 [for
(4+5) at 130 K], -882699 [for 1·(ClO4)4(H2O)2 at 150 K], -882700
[for 1·(ClO4)4(H2O)2 at 250 K], -882701 [for 1·(ClO4)4 at 350 K], -
882702 [for 2·(ClO4)n at 270 K], -882703 [for 2·(ClO4)n at 110 K], -
882704 [for 2·(PF6)n at 270 K], -882705 [for 2·(PF6)n at 110 K], -
882706 [for 2·(BPh4)n at 295 K], -882707 [for 2·(BPh4)n at 150 K], -
882708 [for 2·(AsF6)n at 270 K], -882709 [for 2·(AsF6)n at 173 K], -
882710 [for 2·(AsF6)nLT at 110 K], -882711 [for 2·(BPh4)2 at 200 K]
contain 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_requ-
est/cif.
Crystallographic Data Collection and Structure Refinement: Diffrac-
tion data were collected with Oxford Gemini S Ultra and Bruker
Apex 2000 diffractometers by using graphite-monochromated Mo-
Kα (λ = 0.71073 Å) and Cu-Kα (λ = 0.15418 Å) radiation. Crystal
structures were solved and refined by using the SHELXTL pro-
gram suite.[27] Direct methods yielded all non-hydrogen atoms,
which were refined anisotropically, and hydrogen atoms were posi-
tioned in the riding model. The highly disordered free [N(CN)2]–
1·(ClO4)4(H2O)2: An aqueous solution (5 mL) of FeSO4·7H2O
(0.1 mmol), sodium dicyanamide (0.1 mmol) and NaClO4·xH2O
Table 6. Crystal data and refinements for 1·(ClO4)4(H2O)2, 2·(BPh4)n, and (4+5).
1·(ClO4)4(H2O)2
1·(ClO4)4
2·(BPh4)n
(4+5)
Empirical formula
Formula mass
[gmol–1]
Crystal system
Space group
T [K]
C80H76Cl4Fe4N28O18
2082.89
C80H72Cl4Fe4N28O16C88H76B2Fe2N14
C104H98F18Fe5N41O4Sb3
2972.73
2046.86
1462.95
monoclinic
monoclinic
P21/c
350
monoclinic
P21/c
295
monoclinic
P21/c
150
C2/m
270
250
150
230
130
39.4291(10)
a [Å]
b [Å]
c [Å]
17.7486(9) 18.0614(12) 18.5178(18)
14.6375(8) 14.7280(10) 15.0730(14)
17.3299(9) 17.4153(12) 17.330(2)
108.858(6) 107.134(7) 107.957(12)
25.958(3)
25.5990(9) 39.947(2)
39.777(3)
10.9101(13) 10.7891(4) 18.0746(12) 17.9767(9) 17.8352(4)
27.037(3) 26.9584(9) 17.4747(9) 17.4208(10) 17.2743(4)
102.141(3) 102.229(3) 106.042(6) 105.828(7) 106.161(3)
7485.8(16) 7276.7(4) 12125.8(12) 11984.4(12) 11667.7(5)
β [°]
V [Å3]
4260.6(4) 4427.0(5)
4601.5(8)
2
Z
2
2
4
4
4
4
4
Dcalcd. [gcm–3]
1.624
0.881
21467
0.0644
0.1612
1.563
0.848
22400
0.0792
0.1784
1.477
0.813
22879
0.0910
0.2965
1.298
0.445
40551
0.1065
0.2552
1.335
0.458
34199
0.0762
0.1569
1.628
10.694
32561
0.0935
0.2748
1.648
10.820
32992
0.0804
0.2600
1.692
11.114
30907
0.0868
0.2638
μ [mm–1]
Reflections collected
R1 [IϾ2σ(I)][a]
wR2 (all data)
[a] R1 = ||Fo| – |Fc||/|Fo|; wR2 = {[w(Fo – Fc ) ]/[w(Fo2)2]}1/2; w = 1/[σ2(Fo2) + (ap)2 + bp], where p = [max(Fo2,0) + 2Fc ]/3; and Rw =
2
2 2
2
[w(|Fo| – |Fc|)2/w|Fo|2]1/2, where w = 1/σ2(|Fo|).
Table 7. Crystal data and refinements for 2·(ClO4)n, 2·(PF6)n, 2·(AsF6)n, 3·(BPh4)2.
LT
2·(ClO4)n
2·(PF6)n
2·(AsF6)n
2·(AsF6)n
3·(BPh4)2
Empirical formula
Formula mass
[gmol–1]
Crystal system
Space group
T [K]
a [Å]
b [Å]
c [Å]
C20H18ClFeN7O4
511.71
C20H18F6FeN7P
557.23
C20H18AsF6FeN7C40H36As2F12Fe2N14
C88H76B2Fe2N14
1462.95
601.18
1202.37
monoclinic
monoclinic
monoclinic
P21/c
270
monoclinic
P21/c
173
monoclinic
P21/c
200
P21/c
270
P21/c
270
110
110
110
11.8968(7) 11.6605(9) 12.5418(9) 12.2910(7) 12.9495(12)
12.2573(7) 12.1480(10) 11.9957(7) 11.8209(6) 11.5443(8)
15.6197(10) 15.5343(12) 16.4189(13) 16.2532(9) 16.6774(15)
107.408(6) 106.593(8) 108.513(9) 108.233(6) 107.827(9)
15.7697(8) 15.6729(6) 10.7102(11)
11.5582(5) 11.4801(4) 17.4267(18)
26.7570(18) 26.5369(13) 19.836(3)
108.157(5) 108.798(4) 92.696(10)
β [°]
V [Å3]
2173.4(2)
4
1.564
0.861
2108.8(3)
4
1.612
0.887
10520
0.1350
0.2871
2342.4(3)
4
1.580
0.783
8886
0.0552
0.1319
2242.9(2) 2373.4(3)
4
1.650
0.818
8258
0.0417
0.0742
4634.1(4)
4
1.723
2.140
20802
0.0937
0.3100
4520.0(3)
4
1.767
2.194
19933
0.0616
0.1887
3698.1(7)
2
1.314
0.450
18039
0.0780
0.1455
Z
4
Dcalcd. [gcm–3]
1.682
2.089
11016
0.0754
0.2096
μ [mm–1]
Reflections collected 10400
R1 [IϾ2σ(I)][a]
wR2 (all data)
0.0516
0.1053
[a] R1 = ||Fo| – |Fc||/|Fo|; wR2 = {[w(Fo – Fc ) ]/[w(Fo2)2]}1/2; w = 1/[σ2(Fo2) + (ap)2 + bp], where p = [max(Fo2,0) + 2Fc ]/3; and Rw =
2
2 2
2
[w(|Fo| – |Fc|)2/w|Fo|2]1/2, where w = 1/σ2(|Fo|).
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/KAP1
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Pages: 12
R.-J. Wei, J. Tao, R.-B. Huang, L.-S. Zheng
FULL PAPER
(0.1 mmol) was poured without stirring into an ethanolic solution
(1 mL) of 0.1 mmol tpa. A single-crystal seed of 1·(BF4)4(H2O)2
was added to the resulting yellow solution, which was then kept
under N2; red 1·(ClO4)4(H2O)2 crystallized in a few days. The crys-
tal seed was removed manually, and red crystals of 1·(ClO4)4-
(H2O)2 were collected by filtration. Yield: ca. 30 mg (60%).
C80H76Cl4Fe4N28O18 (2082.86): calcd. C 46.13, H 3.68, N 18.83;
and the precipitate before conversion to (4+5), magnetic properties
of the precipitate before conversion to (4+5), and IR spectra of all
complexes.
Acknowledgments
found C 45.91, H 3.62, N 18.70. IR (KBr): ν = 3430 (m), 2924 (w),
˜
This work was supported by the National Natural Science Founda-
tion of China (NSF of China) (Grants 90922012, 20971106,
21021061) and the Specialized Research Fund for the Doctoral
Program of Higher Education (Grant 20110121110012).
2315 (w), 2251 (s), 2162 (s), 1603 (m), 1480 (w), 1441 (m), 1383
(w), 1090 (s), 766 (m), 626 (m), 505 (w) cm–1.
2·(ClO4)n, 2·(PF6)n, and 2·(AsF6)n: An aqueous solution of
FeSO4·7H2O (5 mL), sodium dicyanamide (0.1 mmol) and
NaClO4·xH2O (0.1 mmol) was poured without stirring into an eth-
anolic solution (1 mL) of tpa (0.1 mmol). The mixture was put
aside under N2, and yellow crystals of 2·(ClO4)n were collected by
filtration several days later. Crystals of 2·(PF6)n and 2·(AsF6)n were
prepared similarly with KPF6 and AsF6, respectively. Yield of
2·(ClO4)n: ca. 25 mg (50%). C20H18ClFeN7O4 [2·(ClO4)n] (511.71):
calcd. C 46.94, H 3.55, N 19.16; found C 47.01, H 3.68, N 19.45.
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IR (KBr): ν = 3438 (w), 2339 (w), 2247 (m), 2204 (s), 2175 (s),
˜
1604 (m), 1447 (m), 1408 (m), 1098 (s), 1017 (m), 763 (m), 621 (m),
513 (w) cm–1. Yield of 2·(PF6)n: ca. 28 mg (50%). C20H18F6FeN7P
[2·(PF6)n] (557.23): calcd. C 43.11, H 3.26, N 17.60; found C 43.33,
H 3.04, N 17.70. IR (KBr): ν = 3412 (w), 2344 (w), 2253 (m), 2207
˜
(s), 2175 (s), 1700 (w), 1605 (m), 1447 (w), 1019 (w), 838 (s), 763
(m), 557 (m) cm–1. Yield of 2·(AsF6)n: 30 mg (50%).
C20H18AsF6FeN7 [2·(AsF6)n] (601.18): calcd. C 39.96, H 3.02, N
16.31; found C 39.80, H 3.006, N 16.71. IR (KBr): ν = 3431 (m),
˜
2341 (m), 2254 (m), 2207 (s), 2174 (s), 1605 (m), 1445 (w), 1396
(w), 1019 (w), 765 (m), 701 (s) cm–1.
2·(BPh4)n and 3·(BPh4)2:
A methanolic solution (5 mL) of
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FeSO4·7H2O (0.1 mmol), sodium dicyanamide (0.1 mmol), and
NaBPh4 (0.1 mmol) was stirred for 15 min and then filtered. The
filtrate was placed in the bottom of a test tube. Above this solution,
a methanolic solution (5 mL) of tpa (0.1 mmol) was layered. Red
crystals of 2·(BPh4)n and yellow crystals of 3·(BPh4)2 crystallized
simultaneously in 3 d and were collected by filtration and separated
manually under a microscope. Yield of 2·(BPh4)n: ca. 28 mg (40%).
C88H76B2Fe2N14 (1462.95): calcd. C 72.25, H 5.24, N 13.40; found
C 72.33, H 5.09, N 13.12. IR (KBr): ν = 3417 (w), 3052 (m), 2294
˜
(w), 2247 (w), 2167 (s), 1604 (m), 1575 (m), 1479 (m), 1442 (m),
1337 (w), 1156 (w), 1098 (w), 1052 (w), 1020 (w), 764 (m), 733
(s), 704 (s), 612 (m) cm–1. Yield of 3·(BPh4)2: ca. 20 mg (30%).
C88H76B2Fe2N14 (1462.95): calcd. C 72.25, H 5.24, N 13.40; found
C 72.53, H 5.04, N 13.70. IR (KBr): ν = 3446 (w), 3049 (w), 2312
˜
(w), 2234 (w), 2187 (s), 1604 (w), 1572 (m), 1480 (w), 1439 (w),
1373 (w), 1152 (w), 1101 (w), 1052 (w), 1019 (w), 763 (w), 741 (w),
730 (w), 703 (m), 606 (m) cm–1.
(4+5): An aqueous solution (5 mL) of FeSO4·7H2O (0.5 mmol), so-
dium dicyanamide (0.5 mmol), and KSbF6 (0.5 mmol) was poured
without stirring into an ethanolic solution (1 mL) of tpa
(0.5 mmol); the resulting turbid red solution with a large amount
of precipitate was sealed in a bottle under N2. The precipitate gen-
erally transformed into red crystals of (4+5) in 2 weeks. Red crys-
tals suitable for X-ray single-crystal diffraction were collected by
filtration. Yield: ca. 18 mg (30%). C104H98F18Fe5N41O4Sb3
(2972.64): calcd. C 42.02, H 3.32, N 19.32; found C 42.32, H 3.37,
N 19.62 for crystals of (4+5); C 41.61, H 3.27, N 18.92 for the
precipitate. IR (KBr): ν = 3448 (m), 2924 (w), 2276 (w), 2191 (s),
˜
2165 (s), 1604 (m), 1440 (m), 1394 (w), 1099 (w), 1052 (w), 1020
(w), 764 (w), 683 (w), 633 (m), 514 (w) cm–1.
Supporting Information (see footnote on the first page of this arti-
cle): TGA data of 1·(ClO4)4(H2O)2 and (4+5), PXRD data of (4+5)
10
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Anion-Dependent Spin Crossover and Coordination Assembly
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Received: May 19, 2012
Published Online: ᭿
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Job/Unit: I20541
/KAP1
Date: 27-08-12 18:31:24
Pages: 12
R.-J. Wei, J. Tao, R.-B. Huang, L.-S. Zheng
FULL PAPER
Spin Crossover
R.-J. Wei, J. Tao,* R.-B. Huang,
L.-S. Zheng ..................................... 1–12
Anion-Dependent Spin Crossover and Co-
ordination Assembly Based on [Fe(tpa)]2+
[tpa
= tris(2-pyridylmethyl)amine] and
[N(CN)2]–: Square, Zigzag, Dimeric, and
[4+1]-Cocrystallized Complexes
Keywords: Spin crossover / Coordination
assembly / Anion dependence / Structure
elucidation / Magnetic properties
A
series of FeII complexes based on
prepared. The complexes show various
structures and diverse spin-crossover be-
haviors that are affected by the coun-
teranions.
[Fe(tpa)]2+ and [N(CN)2]– [tpa = tris(2-pyr-
idylmethyl)amine] building units in the
presence of various counteranions has been
12
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