Influence of supramolecular bonding contacts on the spin crossover behaviour of iron(ii) complexes from 2,2′-dipyridylamino/s-triazine ligands

Article abstract of DOI:10.1039/c3dt50326g

Reactions of the related ligands 2-(N,N-bis(2-pyridyl)amino)-4,6- bis(phenoxy)-(1,3,5)triazine (L1) and 2-(N,N-bis(2-pyridyl)amino)-4,6- bis(pentafluorophenoxy)-(1,3,5)triazine (L1^F) with iron(ii) thiocyanate produced two spin-crossover coordination compounds with distinct cooperative behaviours. trans-[Fe(L1)₂(NCS)₂] ·2CH₂Cl₂ (1) displays a very gradual transition centred at T = 233 K, characterized by a ΔT₈₀ (namely the temperature range within which 80% of the transition considered occurs) of 90 K, while that of fluorinated trans-[Fe(L1^F)₂(NCS) ₂]·2CH₃CN (3) is significantly more abrupt (and centred at T = 238 K), with a ΔT₈₀ of 50 K, resulting from supramolecular contacts induced by the fluorinated phenol groups. The coordination compound equivalent to 1 with selenocyanate anions, namely trans-[Fe(L1)₂(NCSe)₂]·4CH₂Cl ₂·4CH₃OH (2), also exhibits SCO properties centred at T = 238 K, but the transition is very gradual (ΔT₈₀ = 150 K). Light-induced excited spin-state trapping (LIESST) is effective although incomplete for 2 and 3, while it is complete with a T_LIESST of 58 K for 1. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3dt50326g

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Influence of supramolecular bonding contacts on the
spin crossover behaviour of iron(II) complexes from
2,2’-dipyridylamino/s-triazine ligands†
Cite this: Dalton Trans., 2013, 42, 7120
Nanthawat Wannarit,a,c Olivier Roubeau,*b Sujittra Youngme,*c Simon J. Teatd and
Patrick Gamez*a,e
Reactions of the related ligands 2-(N,N-bis(2-pyridyl)amino)-4,6-bis(phenoxy)-(1,3,5)triazine (L1) and
2-(N,N-bis(2-pyridyl)amino)-4,6-bis(pentafluorophenoxy)-(1,3,5)triazine (L1F) with iron(II) thiocyanate pro-
duced two spin-crossover coordination compounds with distinct cooperative behaviours. trans-[Fe-
(L1)2(NCS)2]·2CH2Cl2 (1) displays a very gradual transition centred at T12 = 233 K, characterized by a ΔT80
(namely the temperature range within which 80% of the transition considered occurs) of 90 K, while that
of fluorinated trans-[Fe(L1F)2(NCS)2]·2CH3CN (3) is significantly more abrupt (and centred at T12 = 238 K),
with a ΔT80 of 50 K, resulting from supramolecular contacts induced by the fluorinated phenol
groups. The coordination compound equivalent to 1 with selenocyanate anions, namely trans-[Fe-
(L1)2(NCSe)2]·4CH2Cl2·4CH3OH (2), also exhibits SCO properties centred at T12 = 238 K, but the transition is
very gradual (ΔT80 = 150 K). Light-induced excited spin-state trapping (LIESST) is effective although
incomplete for 2 and 3, while it is complete with a TLIESST of 58 K for 1.
Received 31st January 2013,
Accepted 27th February 2013
DOI: 10.1039/c3dt50326g
www.rsc.org/dalton
temperature, pressure or light.4–7 Such behaviour is obviously
very attractive, especially with d6 Fe(II) ions for which the LS
Introduction
The spin-crossover (SCO) phenomenon is a particularly inter- state is diamagnetic and sharp differences in optical properties
esting manifestation of the ligand-field theory.1,2 Hence, for are often associated with the SCO; therefore, SCO compounds
octahedral d4–d7 transition-metal complexes that may be may find applications in molecular switches,8 data-storage
either low spin (LS) or high spin (HS), the occurrence of SCO is devices9,10 and optical displays.11–13 Consequently, SCO has
associated with intermediate ligand-field strength,3 for which attracted a great deal of attention from the scientific commu-
the transition-metal compound may present HS ↔ LS bistabi- nity during decades, and this area of research has been experi-
lity through the application of an external stimulus like encing a tremendous development since the past 5 years.14–20
Thus, many SCO iron(II) complexes have been reported, typi-
cally exhibiting an octahedral [FeN6] core obtained from
ligands containing aromatic nitrogen-donor groups, such as
pyridine or azole rings.21–24
aDepartament de Química Inorgànica, QBI, Universitat de Barcelona, Martí i
Franquès 1-11, 08028, Barcelona, Spain. E-mail: patrick.gamez@qi.ub.es;
http://www.bio-inorganic-chemistry-icrea-ub.com; Fax: +34 934907725
bInstituto de Ciencia de Materiales de Aragón (ICMA), CSIC and Universidad de
Zaragoza, Plaza San Francisco s/n, 50009 Zaragoza, Spain
cMaterials Chemistry Research Unit, Department of Chemistry and Centre of
Excellence for Innovation in Chemistry, Faculty of Science, Khon Kaen University,
Khon Kaen 40002, Thailand
Since 2006, we have been involved in the design and prep-
aration of various types of pyridine-containing ligands for the
generation of SCO compounds.25–29 In particular, one of the
families of ligands developed is based on the 1,3,5-triazine (or
s-triazine) ring.30 For instance, the ligand 2,4,6-tris(dipyridin-
2-ylamino)-1,3,5-triazine (dpyatriz),31 including three 2,2′-
dipyridylamine units on a s-triazine ring, has allowed us to
synthesize iron(II) coordination compounds with interesting
SCO properties.25,30,32,33 Then, Murray and co-workers
have described various dipyridylamino-substituted-triazine
ligands, which have produced a number of SCO compounds
with distinct transition behaviours,34–38 thus illustrating the
potential of this category of ligands to create molecular
switches.
dAdvanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road,
Berkeley, CA 94720, USA
eInstitució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys
23, 08010 Barcelona, Spain
†Electronic supplementary information (ESI) available: Tables S1–S3 summar-
izing crystallographic and refinement parameters for 1–3; Fig. S1–S4 illustrating
particular features of the solid-state structures of 1–3; ΔH and ΔS for 3 (Fig. S5);
a d(χT)/dT vs. T plot for 3 (Fig. S6); Fig. S7 depicting the single-crystal X-ray struc-
ture of L1; Table S4 summarizing crystallographic and refinement parameters
for L1. CCDC 921061–921067 and 922570. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c3dt50326g
7120 | Dalton Trans., 2013, 42, 7120–7130
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Scheme 1 Preparation
of
ligands
2-(N,N-bis(2-pyridyl)amino)-4,6-bis
(phenoxy)-(1,3,5)triazine (L1) and 2-(N,N-bis(2-pyridyl)amino)-4,6-bis(penta-
fluorophenoxy)-(1,3,5)triazine (L1F).
Fig. 1 Representation of the molecular structure of compound 1 (LS state,
In the present study, two new members of this family of
determined at 100 K) with a partial atom-numbering scheme. The hydrogen
2,2′-dipyridylamino/s-triazine ligands have been prepared. The atoms and the lattice dichloromethane molecules are not shown for clarity. Sym-
metry operation: a, 1 − x, 1 − y, 1 − z.
straightforward and selective substitutions of the three chlor-
ide atoms of 2,4,6-trichloro-1,3,5-triazine by phenolic reagents
and 2,2′-dipyridylamine yield the related ligands 2-(N,N-bis(2-
pyridyl)amino)-4,6-bis(phenoxy)-(1,3,5)triazine (L1,
R = H;
Table 1 Coordination bond lengths (Å) and angles (°), and supramolecular
interactions for compound 1 at three different temperatures
Scheme 1) and 2-(N,N-bis(2-pyridyl)amino)-4,6-bis(pentafluoro-
phenoxy)-(1,3,5)triazine (L1F, R = F; Scheme 1). These two
ligands, which differ by the replacement of the hydrogen
atoms of the phenoxyl groups of L1 by fluorides (L1F), have
been designed to investigate the role played by supramolecular
interactions (i.e. π⋯π interactions, halogen bonding) induced
by the distinct aryl groups in the SCO properties of the corre-
sponding trans-[FeL2(NCS)2] complexes.
Bond
100 K (LS)
1.943(2)
1.992(2)
1.981(2)
10.138(2)
240 K
300 K (HS)
2.075(4)
2.216(3)
2.203(3)
10.301(4)
Fe1–N1
Fe1–N2
Fe1–N3
Fe1⋯Fe1inter
2.051(2)
2.163(2)
2.149(2)
10.239(2)
a
Angleb
N2–Fe1–N3
N2–Fe1–N3a
N1–Fe1–N1a
100 K
86.8(6)
93.3(6)
180
240 K
83.5(8)
96.5(8)
180
300 K
82.4(1)
97.6(1)
180
ΣFec
31
37
40
58
46
67
Φd
Results and discussion
H-bonding contacts
C11–H11A⋯O2
100 K
3.559(3)
3.415(3)
240 K
3.609(4)
3.508(4)
300 K
3.642(8)
3.526(7)
Synthesis and crystal structures
The ligands 2-(N,N-bis(2-pyridyl)amino)-4,6-bis(phenoxy)-
(1,3,5)triazine (L1) and 2-(N,N-bis(2-pyridyl)amino)-4,6-bis-
(pentafluorophenoxy)-(1,3,5)triazine (L1F) are readily prepared
via a two-step reaction in THF from 2,4,6-trichloro-1,3,5-
C27–H27A⋯C13
Lone pair⋯π interactions
Cg5⋯S1
100 K
3.459(1)
240 K
3.561(1)
300 K
3.598(2)
a Closest inter-monomer Fe⋯Fe distance. b Symmetry operation: a, 1 −
x, 1 − y, 1 − z. c Σ = the sum of |90 − θ| for the 12 N–Fe–N angles in the
octahedron.43,44 d Φ = the sum of |60 − θ| for the 24 N–Fe–N angles
describing the trigonal twist angle.15,41
triazine, following
a straightforward synthetic procedure
(Scheme 1 and the Experimental section).39,40
Compound 1, trans-[Fe(L1)2(NCS)2]·2CH2Cl2, is obtained
with a yield of 70% by direct addition of a freshly prepared
water/methanol solution of iron(II) thiocyanate (1 equiv.) to a
dichloromethane solution containing 2 equiv. of L1. 1, which
exhibits SCO properties (see section Magnetic studies), crystal-
for Fe–Npyridine and ca. 0.13 Å for Fe–NNCS when the tempera-
ture is raised to 300 K (Table 1), which describe a full spin
transition that has been observed as well by variable-tempera-
ture magnetic susceptibility measurements (see below). At
240 K, the distances found, i.e. 2.149(2)–2.163(2) Å for Fe–Npyri-
ˉ
lizes in the triclinic space group P1, at 100, 240 and 300 K
(Table S1†). A representation of the molecular structure of 1 at
100 K (low-spin state) is depicted in Fig. 1. Selected bond
lengths and angles are listed in Table 1.
and 2.051(2) Å for Fe–NNCS, correspond to an HS–LS
dine
mixture of about 78/22, in agreement with bulk magnetic
studies.
The distortion parameters Σ and Φ gauge the magnitude of
the deformation of the coordination geometry relative to a
perfect octahedron (for which Σ = Φ = 0).15,41,42 For LS 1, Σ =
31 and Φ = 37 and these values increase to respectively 46 and
The iron(II) centre in 1 displays the expected octahedral
coordination environment, typically observed for iron(II)
thiocyanate complexes with this family of dipyridylamino-sub-
stituted-triazine ligands.25,33–38 The metal ion is coordinated
by two L1 ligands in the equatorial plane of the octahedron,
the apical positions being occupied by two trans thiocyanate
anions (Fig. 1). At 100 K, the Fe–Npyridine distances in the range
1.981(2)–1.992(2) Å are characteristic of an LS iron(II) ion. The
Fe–NNCS bond lengths of 1.943(2) Å are also indicative of an LS
state. These coordination bond lengths increase by ca. 0.22 Å
67 for the HS state (Table 1). ΔΣ (ΣHS − ΣLS) and ΔΦ (ΦHS
−
ΦLS) thus illustrate the extent of the structural changes that
take place during the spin transition. For 1, ΔΣ = 15 and ΔΦ =
30. The high ΔΦ value indicates a severe distortion of the
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original octahedral geometry towards a trigonal prismatic
structure, a feature that is commonly noticed upon LS → HS
transition.15 Such a structural distortion may affect the degree
of interaction between the spin active species, resulting in
cooperativity between the switching centres that is normally
reflected by an abrupt LS ↔ HS crossover phenomenon.
Actually, the magnetic studies (see below) reveal a weakly co-
operative behaviour since a complete HS-to-LS conversion is
realized within a temperature range of ca. 90 K (see section
Magnetic studies).
The crystal packing of 1 shows that the iron(II) centres
weakly interact along the crystallographic c axis through
C–H⋯O and C–H⋯π contacts (which are affected by the tran-
sition; see Table 1), producing a supramolecular 1D chain
(Fig. 2A). These chains do not significantly interact with each
other (Fig. 2B), which may explain the moderate cooperativity
of the SCO behaviour observed by magnetic measurements
(see below).
In addition, the molecules of 1 display intramolecular lone
pair⋯π interactions45 between the thiocyanate sulfur atoms
and the triazine rings (Cg5⋯S1 = 3.459(1) Å; Fig. S1†).
Compound 2, trans-[Fe(L1)2(NCSe)2]·4CH2Cl2·4CH3OH, is
obtained with a yield of 63%, applying the same synthetic pro-
cedure as that used to prepare 1, replacing iron(II) thiocyanate
by iron(II) selenocyanate. As anticipated, 2 is an SCO com-
pound (see section Magnetic studies), which crystallizes in the
monoclinic space group P21/c in its LS state (Table S2†). A view
of the molecular structure of 2 is shown in Fig. 3.
Fig. 3 Representation of the molecular structure of compound 2 (LS state,
determined at 100 K) with a partial atom-numbering scheme. The hydrogen
atoms and the lattice dichloromethane molecules are not shown for clarity. Sym-
metry operation: a, 1 − x, 1 − y, 1 − z.
Table 2 Coordination bond lengths (Å) and angles (°), and supramolecular
interactions for compound 2 (low-spin state)a
Bond
100 K (LS)
1.940(4)
1.992(4)
2.009(4)
8.642(4)
Fe1–N1
Fe1–N2
Fe1–N3
Fe1⋯Fe1inter
b
Angle
100 K (LS)
86.5(2)
93.6(2)
180
N2–Fe1–N3
N2–Fe1–N3a
N1–Fe1–N1a
ΣFec
25
32
Φd
Unsurprisingly, the coordination environment of the iron(II)
ion in 2 is similar to that of 1 (see Fig. 1 and 3). The observed
octahedral geometry is formed by four pyridine donors in the
equatorial plane (belonging to two L1 ligands) and two axial
NCSe− anions. The Fe–Npyridine bond lengths ranging from
1.992(4) to 2.009(4) Å and the Fe–NNCSe distances of 1.940(4) Å
π⋯π interactions
Cg7⋯Cg7j
100 K (LS)
3.717(4)
3.234(9)
3.208(8)
3.796(8)
C22⋯C24j
C22⋯C23j
C8⋯C10d
C–H⋯π contacts
C4–H4A⋯C17g
C5–H5A⋯C18g
100 K (LS)
3.607(7)
3.552(7)
Lone pair⋯π interactions
Cg5⋯Se1
3.501(2)
Hydrogen bond
O1s–H1s⋯O2s
O1s–H1s–O2s
O2s–H2s⋯N5
O2s–H2s–N5
2.828(12)
150(8)
3.074(9)
155(7)
a Symmetry operation: a, 1 − x, 1 − y, 1 − z; d, −x, 1 − y, 1 − z; g, x, 1/2
− y, 1/2 + z; j, −x, 1 − y, −z. b Closest inter-monomer Fe⋯Fe distance.
c Σ
= the sum of |90 − θ| for the 12 N–Fe–N angles in the
octahedron.43,44 d Φ = the sum of |60 − θ| for the 24 N–Fe–N angles
describing the trigonal twist angle.15,41
(Table 2) are typical for an LS iron(II) system, and are compar-
able to those found for 1 (Tables 1 and 2). Unfortunately, crys-
tallographic data for HS 2 could not be obtained. Actually,
single crystals of 2 did not diffract enough at room tempera-
ture, most likely as a result of solvent evaporation (and particu-
larly dichloromethane).
Fig. 2 Views of the crystal packing of LS 1 showing (A) the formation of a
supramolecular 1D chain along the crystallographic c axis by means of weak
C–H⋯O and C–H⋯π contacts (respectively C11–H11A⋯O2 = 3.559(3) Å, green
dotted lines and C27–H27A⋯C13 = 3.415(3) Å, red dotted lines); (B) the
arrangement of the chains in the ab plane illustrating the lack of significant
interactions between them.
The crystal packing of LS 2 reveals the formation of a 1D
chain of iron(II) complexes that are connected by parallel-
7122 | Dalton Trans., 2013, 42, 7120–7130
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displaced π⋯π interactions involving the phenyl ring (C21, selenium atoms and the triazine rings (Cg5⋯Se1 = 3.501(2) Å;
C22, C23, C24, C25, C26), with a centroid-to-centroid distance Fig. S3†).
of 3.717(4) Å (Cg7⋯Cg7j; see Table 2 and Fig. 4A). These π
Compound 3, trans-[Fe(L1F)2(NCS)2]·2CH3CN, is prepared
stacks are characterized by short C⋯C contact distances of with a yield of 65% by direct addition of a freshly prepared
3.208(8) Å (C22⋯C23j) and 3.234(9) Å (C22⋯C24j). It has to be water–acetonitrile solution of iron(II) thiocyanate (1 equiv.) to
noted that these π⋯π stacking interactions (which are not an acetonitrile solution containing 2 equiv. of L1F. As the pre-
occurring in 1) give rise to a different orientation of the corre- vious two complexes, 3 exhibits spin-transition properties (see
ˉ
sponding phenyl rings in compounds 1 and 2 (see phenyl section Magnetic studies). 3 crystallizes in the triclinic P1
rings of the oxygen atom O2 in Fig. 1 and 3). These chains are space group at 100, 190 and 280 K (Table S3†). Selected coordi-
weakly interacting with each other via π⋯π (C8⋯C10d) and C– nation bond distances and angles are listed in Table 3. A view
H⋯π (C4–H4A⋯C17g and C5–H5A⋯C18g) long contacts (see of the molecular structure of 3 is depicted in Fig. 5.
Table 2 and Fig. 4B).
Surprisingly, although the iron(II) complexes appear to
better interact with each other compared to those in 1, the
SCO behaviour of 2 is clearly much less cooperative; actually,
the transition is very gradual as the HS state is fully converted
into the LS state within a temperature range of over 150 K (see
section Magnetic studies). This feature may be explained by
the presence of numerous solvent molecules in the crystal
lattice of 2. Indeed, compound 2 is surrounded by 8 solvent
molecules, i.e. 4CH3OH and 4CH2Cl2, while only 2CH2Cl2 are
found for 1. Therefore, all these solvent molecules in 2 (which
are interacting with each other and with the complex; see
hydrogen bonds in Table 2) most likely affect the propagation
of the spin transition; hence, the behaviour of 2 resembles
that of a diluted system (see Fig. S2†), in which the metal
centres within the solid are transiting independently, thus
resulting in a non-cooperative conversion following Boltzmann
population of states.
Table 3 Coordination bond lengths (Å) and angles (°), and supramolecular
interactions for compound 3 at three different temperatures
Bond
100 K (LS)
1.937(1)
1.979(1)
1.988(1)
8.350(1)
190 K
280 K (HS)
2.056(3)
2.194(2)
2.207(2)
8.643(2)
Fe1–N1
Fe1–N2
Fe1–N3
Fe1⋯Fe1inter
1.943(1)
1.985(2)
1.989(1)
8.412(1)
a
Angleb
N2–Fe1–N3
N2–Fe1–N3a
N1–Fe1–N1a
100 K
190 K
280 K
86.16(5)
93.85(5)
180
86.19(6)
93.81(6)
180
81.83(9)
98.17(9)
180
ΣFec
30
36
30
36
41
72
Φd
π⋯π interactionsb
O1⋯C16c
100 K
190 K
280 K
3.112(2)
3.255(2)
3.387(2)
3.757(1)
3.118(3)
3.247(3)
3.378(3)
3.747(1)
3.092(4)
3.238(4)
3.385(5)
3.787(2)
O1⋯C17c
C15⋯C16c
Cg3⋯Cg3b
Finally, similarly to 1, the molecules of 2 display intramole-
cular lone pair⋯π interactions between the selenocyanate
Halogen⋯halogen contactsb
F8⋯F9l
100 K
2.781(2)
190 K
2.803(2)
280 K
2.815(4)
Lone pair⋯π interactions
Cg5⋯S1
100 K
3.457(1)
190 K
3.489(1)
280 K
3.579(2)
a Closest inter-monomer Fe⋯Fe distance. b Symmetry operation: a, 1 −
x, 1 − y, 1 − z; b, −1 + x, y, z; c, 1 − x, 1 − y, 2 − z; l, 2 − x, 2 − y, 1 − z.
c Σ
= the sum of |90 − θ| for the 12 N–Fe–N angles in the
octahedron.43,44 d Φ = the sum of |60 − θ| for the 24 N–Fe–N angles
describing the trigonal twist angle.15,41
Fig. 4 Views of the crystal packing of LS 2 showing (A) the formation of a
supramolecular 1D chain via parallel-displaced π⋯π interactions (Cg7⋯Cg7j =
3.717(4) Å (the inset illustrates a parallel-displaced π⋯π stack); (B) the feeble
interactions of the chains (one chain is shown in green) by means of weak π⋯π
(C8⋯C10d = 3.796(8) Å) and C–H⋯π (C4–H4A⋯C17g = 3.607(7) Å and C5–
H5A⋯C18g = 3.552(7) Å) contacts. Symmetry operations: d, −x, 1 − y, 1 − z; g,
x, 1/2 − y, 1/2 + z; j, −x, 1 − y, −z.
Fig. 5 Representation of the molecular structure of compound 3 (LS state,
determined at 100 K) with a partial atom-numbering scheme. The hydrogen
atoms and the lattice acetonitrile molecules are not shown for clarity. Symmetry
operation: a, 1 − x, 1 − y, 1 − z.
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The coordination environment of the iron(II) ion in 3 is ana-
Dalton Transactions
logous to those of compounds 1 and 2. The equatorial plane of
the octahedron contains four pyridine donors belonging to
two L1F ligands, and the axial positions are occupied by two
thiocyanate anions. At 100 K, the Fe–Npyridine and Fe–NNCS
coordination bond lengths are typical for an LS FeN6 (Table 3),
and are comparable to those of 1 and 2. For HS 3 at 280 K,
these bond distances increase by respectively ca. 0.22 and
0.12 Å (Table 3), thus giving characteristic values for this spin
state. This full LS → HS transition is corroborated by magnetic
measurements (see below). At 190 K, the Fe–Npyridine and Fe–
N
NCS distances are indicative of an LS–HS mixture of about 95/
5, in agreement with the data obtained by magnetic-suscepti-
bility measurements (see below).
The distortion parameters Σ and Φ amount to respectively
30 and 36 for LS 3, and to 41 and 72 for HS 3. Hence, the corre-
sponding ΔΣ and ΔΦ values of respectively 11 and 36 again
reflect a strong distortion of the octahedral geometry upon LS
→ HS transition. As mentioned above, such a distortion is
often associated with cooperativity between the transiting
centres. In the present case, ΔΦ = 36 is higher than that found
for the related complex 1 (ΔΦ = 30). Therefore, a greater coop-
erative behaviour is expected for 3 in comparison to 1; in fact,
a clearly more abrupt transition (see the corresponding χT vs.
T plots below) is observed for 3, which may be rationalized by
specific crystal-packing features induced (at least in part) by
the fluorinated ligand L1F.
Fig. 6 Views of the crystal packing of LS 3 showing (A) the formation of a
Actually, the crystal packing of LS 3 reveals an intricate supramolecular 1D chain via parallel-displaced pentafluorophenyl⋯pentafluoro-
phenyl interactions (O1⋯C16c 3.112(2) Å, O1⋯C17c 3.255(2) and
=
=
Å
network of strong supramolecular bonds (Fig. 6). First, mole-
cules of 3 are connected via strong lone pair⋯π (O1⋯C16c
and O1⋯C17c; see Table 3 and Fig. 6A) and π⋯π (C15⋯C16c;
see Table 3 and Fig. 6A) interactions. It has to be noted that
the O1⋯C16c contact distance of 3.112(2) Å is below the sum
of the van der Waals radii of O and C (i.e. 3.22 Å), thus indicat-
ing a very strong interaction between the fluorinated aromatic
rings (through lone pair⋯π interactions46–48). These supra-
molecular bonds generate a 1D chain that runs along the
crystallographic c axis. Next, the 1D chains are associated by
means of nearly face-to-face π⋯π interactions between co-
ordinated pyridine moieties characterized by a centroid-to-
centroid distance of 3.757(1) Å (see Table 3 and Fig. 6B). This
spatial arrangement produces a 2D supramolecular sheet in
the ac plane (Fig. 6B). Finally, the 2D sheets are connected to
each other by double strong F⋯F bonds (indeed, the F8⋯F9l
distance of 2.781(2) Å is well below the sum of the van der
C15⋯C16c = 3.387(2) Å) (the inset illustrates the occurrence of a parallel-dis-
placed stack between two pentafluorophenyl rings); (B) the formation of 2D
sheets by means of π⋯π interactions between coordinated pyridine rings
(Cg3⋯Cg3b = 3.757(1) Å). One supramolecular chain is shown in green; (C) the
formation of a 3D supramolecular framework through the connection of the 2D
sheets by strong F⋯F bonding contacts (F8⋯F9l = 2.781(2) Å) (the inset illus-
trates the bonding interaction of pentafluorophenyl rings via double halogen⋯
halogen contacts), a 2D supramolecular sheet is shown in green. Symmetry
operations: b, −1 + x, y, z; c, 1 − x, 1 − y, 2 − z; l, 2 − x, 2 − y, 1 − z.
ca. 50 K (while it is about 90 K for 1 and 150 K for 2; see
below).
As for 1 and 2, lone pair⋯π interactions are realized
between the thiocyanate sulfur atoms and the triazine rings
(Cg5⋯S1 = 3.457(1) Å; Fig. S4†).
Magnetic, photomagnetic and thermal studies
Waals radii of two F atoms, namely 2.94 Å),49 giving rise to a Confirmation of the process of thermal SCO indicated by the
3D framework (Fig. 6C). structural observations on single crystals of 1–3 was obtained
In summary, the transiting iron(II) centres are very well through magnetization measurements on bulk samples in the
linked to each other (within all the crystal lattice, in contrast temperature range 5–300 K. The resulting temperature depen-
to 1 and 2). Moreover, the solid-state structure of 3 includes dencies of the χT product (Fig. 7), χ being the molar paramag-
less lattice solvent molecules than 2 (which contains 8 mole- netic susceptibility, evidence for all three compounds a
cules of the solvent per iron(II) complex); hence 3 is clearly the complete and gradual thermal SCO. For compound 1, the χT
most compact of the three systems. Therefore, an efficient product is 3.19 cm3 mol−1 K at 300 K, a value typical for an
cooperative behaviour may be expected for 3. As a matter of Fe(II) ion in an HS S = 2 state. χT starts to decrease already
fact, the magnetic studies show the steepest HS ↔ LS tran- from 300 K to reach values of ca. 0.11–0.07 cm3 mol−1 K below
sition for 3, which is completed within a temperature range of 160, which are now indicative of a fully populated LS S = 0
7124 | Dalton Trans., 2013, 42, 7120–7130
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Fig. 7 χT vs. T plot for 1 (empty circles), 1’ (full circles), 2 (empty rhomboids)
and 3 (full squares) showing the complete and gradual SCO. Lines are only
guides to the eye.
Fig. 8 Molar heat capacities of 3 showing a broad hump associated with the
SCO. The dashed line is the estimated lattice component. Inset: excess heat
capacities associated with the SCO in 3. The full line is a fit to the domain model
of Sorai (see the text and ref. 57) with n = 6.2.
state. The corresponding transition is centred at T12 = 233 K.
The selenocyanate derivative 2 exhibits a more gradual SCO
centred at T12 = 228 K, with a χT value of only 2.95 cm3 mol−1
K at 300 K (thus suggesting that the transition process has
already started to take place at this temperature), and
<0.10 cm3 mol−1 K below 130 K. In contrast, the SCO process,
centred at T12 = 238 K, is more abrupt for 3 (as a result of a
better cooperativity; see above), with a decrease of χT from
3.10 cm3 mol−1 K at 280 K down to 0.2–0.1 below 200 K. This
comparatively more cooperative character is illustrated by a
smaller ΔT80 value of 50 K (80% of the transition occurs
within about 50 K) for 3, compared to those observed for 1 and
2, respectively, at 90 and 150 K. These observations are repro-
duced upon warming, thus without detectable hysteresis, and
over various cycles and batches, although only for fresh crystal-
line material in the case of 1. Indeed, a more gradual, though
complete, SCO centred at ca. 173 K is detected for the poorly
crystalline powder 1′ obtained upon air exposure of 1, which is
ascribed to the loss of lattice solvent molecules (as indicated
by Elemental Analysis; see the Experimental section). The
observation of a similar T12 for the thiocyanate and selenocya-
nate derivatives 1 and 3 agrees with our previous report with
the related complexes obtained with the ligand 6-chloro-N-
phenyl-N,N-di(pyridin-2-yl)-1,3,5-triazine-2,4-diamine.33 It thus
seems that the replacement of S by Se in this family of trans-
[FeIIL2(NCX)2] compounds has only little influence on the SCO
temperature, in contrast to other NCX-based SCO
compounds.50–54
Fig. 9 χT vs. T plot for 1’ (left), 2 (middle) and 3 (right), showing the process of
SCO (grey empty circles), the (partial) LS to HS photo-induced trapping at 10 K
(full circles) and the relaxation back to the LS ground state and normal behav-
iour upon warming (black empty circles).
of a cooperative character of the SCO.55,56 In particular, the
excess entropy is well above the purely electronic component,
RLn5; it thus encloses a significant content arising from the
coupling of the electronic transition with lattice phonons.
Fitting the excess heat capacity of 3 to Sorai’s domain model57
results in a number of interacting molecules per domain of n =
6.2 (red line in the inset of Fig. 8), which is characteristic of a
relatively cooperative SCO, in agreement with the magnetic
studies (Fig. 9).
Preliminary photomagnetic studies on thin samples of 1′, 2
and 3 indicate that an HS metastable state can be trapped for
all three compounds at low temperatures through the so-called
LIESST effect,58 although with distinct efficacies. Indeed, while
an increase of χT is detected upon irradiation in the
500–650 nm range at 10 K, the initial rate of increase is
highest for 1′, and smallest for 3, for a similar sample thick-
ness. In addition, the rate of increase drops more rapidly for 2
and 3, with stable values, corresponding to incomplete trap-
ping of at most 40 and 20% HS respectively, reached at longer
Confirmation of the relatively cooperative character of the
SCO for 3 was obtained from Differential-Scanning Calorimetry
(DSC). Indeed, while only very broad poorly energetic humps
are detected for 1′ and 2, the molar heat capacity of 3 at con-
stant pressure, Cp, exhibits a strong anomaly between 200 and
280 K, culminating at ca. 237 K (see Fig. 8), which can be
attributed to the SCO phenomenon in 3. Both the associated
excess enthalpy and entropy are relatively large, respectively, at
11.70 kJ mol−1 and 49.6 J mol−1 K−1 (see the Experimental
section and Fig. S5†), which is usually seen as a consequence
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1
irradiation times. On the other hand, a full HS state can be with an LS band (possibly A1→3T1), giving rise to competitive
trapped in the case of 1′. Upon warming, an increase of χT is LIESST and reverse-LIESST processes.58,60,61
first observed, which corresponds to the Zero-Field Splitting
effect of trapped HS species. Subsequently, a decrease gradu-
ally sets in, which is due to the thermally-activated relaxation
SCO systems based on 2,2′-dipyridylamino-substituted triazine
ligands and Fe(NCS)2
back to the LS state that is reached at ca. 85 K. A characteristic
TLIESST temperature of 58 K can be defined,59 through the first
As mentioned earlier, iron(II) complexes of the type trans-
[FeIIL2(NCS)2], where L is a 2,2′-dipyridylamino-substituted
derivative of χT (Fig. S6†). For the other two compounds, χT
triazine ligand (Scheme 2), usually display SCO properties, and
the two new members of this family of compounds, namely 1
and 3, verify this characteristic. Since the first report of such
an SCO system by some of us,25 we and Murray and co-workers
have reported a number of 2,2′-dipyridylamino/triazine-based
complexes.33–35,37,38 Relevant structural features and SCO prop-
erties of these coordination compounds are described in
Table 4. To date, 14 different trans[FeIIL2(NCS)2] complexes
have been obtained from 13 distinct ligands. Out of them, two
do not show SCO properties; in fact, the simplest member of
decreases already from 10 K to reach values similar to those
of the normal LS state at ca. 70 K. Thus, even with a partial
trapping, relaxation of the trapped HS species back to the LS
ground state is not as fast at low temperatures as in the pre-
viously reported compound trans-[Fe(Cladpat)2(NCS)2].33
Therefore, considering that the three samples had a similar
thickness, the most likely origin of the lack of efficiency of the
LIESST effect in 2 and 3 is an overlap of the 5T2→5E (HS) band
this family of ligands, namely when
=
= Cl, does not
generate an iron(II) SCO compound.33 Surprisingly, the trans-
[FeIIL2(NCS)2] complex whose ligand L contains two diphenyla-
mine substituents is also a non-SCO material. All other com-
pounds exhibit SCO properties (complete or incomplete
transitions), with T12 values (T12 corresponds to the temperature
at which half of the transiting iron(II) centres have changed
their spin state) ranging from 110 up to 260 K, indicating that
the transition can be fine-tuned through selection of the R
Scheme 2 Representation of the trans-[FeIIL2(NCS)2] complexes whose struc-
tural and SCO properties are described in Table 4.
substituents on the triazine ring (see Table 4).
and
symbolize different
Table 4 Structural and SCO properties of crystallographically characterized trans-[FeIIL2(NCS)2] compounds with 2,2’-dipyridylamino-substituted triazine ligands L
(Scheme 2)
SCO
SCO
behaviour
Lattice
solvent(s)
Nuclearity character
Hysteresis T12
ΔΣ
ΔΦ
Ref.
Chlorine
Chlorine
Chlorine
Aniline
Monomer
Monomer Gradual;
—
No
Complete
—
No
—
178 K
—
15
—
27
H2O
No
33
33
ΔT80 a = 50 K
Very gradual;
ΔT80 ≈ 50 K
Chlorine
Dipyridylamine
Dipyridylamine
Polymer
Incomplete No
(half SCO)b
Complete
Complete
Complete
∼205 K 13/9c 26/0c CH3OH
38
25
37
Dipyridylamine
Dipyridylamine
Dipyridylamine
Dipyridylamine
Dipyridylamine
Dipyridylamine
Dibenzylamine
Monomer Gradual;
No
No
No
200 K
175 K
200 K
190 K
260 K
110 K
12
31
No
ΔT80 = 40 K
Very gradual;
ΔT80 = 77 K
Gradual;
ΔT80 = 55 K
Gradual;
ΔT80 = 39 K
Gradual;
ΔT80 = 50 K
Very gradual;
ΔT80 = 80 K
Pyridine-4(1H)one Polymer
Pyridine-4(1H)one Polymer
12/13c 22/24c CH2Cl2
12/11c 21/6c CHCl3–CH3OH 37
Phenol
Polymer
Polymer
Polymer
Incomplete No
Incomplete No
8/1c
4/3c
20/6c H2O–CH3OH
37
37
35
34
Hydroquinone
Aza-15-crown-5
Dibenzylamine
9/8c
CH2Cl2
CH3OH
No
d
d
Complete
Complete
No
No
—
—
Monomer Gradual;
ΔT80 = 50 K
Monomer
Monomer Very gradual;
ΔT80 ≈ 80 K
Monomer Very gradual;
ΔT80 = 90 K
∼170 Ke 13
27
Diphenylamine
Aza-15-crown-5
Diphenylamine
Aza-15-crown-5
—
No
Complete
—
No
—
—
—
31
CH2Cl2
n-C3H7OH
34
35
∼240 K 14
Phenol
Phenol
Complete
Complete
No
No
233 K
238 K
15
11
30
36
CH2Cl2
CH3CN
This work
This work
Pentafluorophenol Pentafluorophenol Monomer Gradual;
ΔT80 = 50 K
a ΔT80 is the temperature range within which 80% of the transition considered occurs. b The full LS state is not reached as only half of the iron(II)
centres are transiting.38 c The compound exhibits two crystallographically distinct iron(II) centres. d Only the X-ray structure of the LS compound
has been reported.35 e A different polymorphic form of this compound exhibits a very gradual spin transition (ΔT80 ≈ 85 K) centred at 300 K.34
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groups (and the possibilities are limitless). All compounds represents the next logical step of investigation. Actually, these
display very gradual to gradual spin transitions, the more studies have been initiated by our group and the outcome will
abrupt one (ΔT80 = 39 K) being obtained when
lamine and
= dipyridy- be reported in a future paper.
= phenol. It is actually a 1D polymeric chain37
wherein the cooperativity between the iron(II) ions appears to
be relatively efficient. By comparison, when dipyridylamine is
Experimental section
Physical measurements
replaced by a phenol, i.e. when
=
= phenol, a significantly
more gradual behaviour (ΔT80 = 90 K) is observed for the corre-
sponding monomeric species. No hysteretic behaviours have
been observed for all these systems; however, it is assumed
that careful design of a 2,2′-dipyridylamino-substituted tria-
zine ligand(s) L with well-chosen R substituents will allow us
to enhance cooperativity between the iron(II) centres that may
favour the occurrence of hysteresis.
It can be noted once again that lattice solvent molecules
have a great effect on the SCO properties of a coordination
compound. Indeed, for the trans-[FeIIL2(NCS)2] complex with
Infra-red spectra (as KBr pellets) were recorded with a Nicolet
5700 FT-IR spectrometer. Elemental analyses were performed
by the Servei de Microanalisi, Consejo Superior de Investiga-
ciones Cientifícas (CSIC) of Barcelona. 1H NMR spectra were
recorded at room temperature with a Varian Unity 300 MHz
spectrometer; chemical shifts are reported in ppm relative to
the residual solvent signal of CDCl3 (δ = 7.26 ppm).
Variable-temperature magnetic-susceptibility data were col-
lected on microcrystalline samples of 1–3 with Quantum
Design SQUID magnetometers housed at either the SAI Physi-
cal Measurements of the University of Zaragoza or the Serveis
Cientificotècnics of the Universitat de Barcelona. Pascal’s con-
stants were used to estimate diamagnetic corrections to the
molar paramagnetic susceptibility, and a correction was
applied for the sample holder. Warming and cooling rates
were of the order of 0.3 K min−1. Irradiation experiments were
performed using the Quantum Design fibre optics setup
(FOSH) on thin pellets (<0.5 mm). The applied field was 1 T
throughout the whole study. The light source was a Xenon arc
lamp equipped with sets of short-pass and long-pass filters
(SPF or LPF). Specifically for the present study, an SPF 650 nm
and an LPF at 500 nm were used. Data were corrected for the
empty FOSH signal, determined beforehand.
= dipyridylamine and
= pyridine-4(1H)one, distinct SCO
behaviours have been obtained in dichloromethane and in
chloroform/methanol. In dichloromethane, the compound
exhibits a very gradual transition (ΔT80 = 77 K) centred at T21
=
175 K, while a more abrupt transition (ΔT80 = 55 K) is observed
in CHCl3–CH3OH, at a higher temperature (T12 = 200 K). This
clearly illustrates the sensitivity of the SCO phenomenon,
where not only the coordination sphere of the metal ion is
important but also the interactions between the complexes in
the solid-state and the involvement of lattice solvent molecules
(as observed for instance in the present study with compounds
1 and 1′).
Differential Scanning Calorimetry (DSC) experiments were
performed with a Q1000 calorimeter with the LNCS accessory
from TA Instruments. The temperature and enthalpy scales
were calibrated with a standard sample of indium, using its
melting transition (156.6 °C, 3296 J mol−1). Measurements
were carried out using aluminium pans with a mechanical
crimp, with an empty pan as a reference. The zero-heat flow
procedure described by TA Instruments was followed to derive
heat capacities, using a synthetic sapphire as a reference com-
pound. An overall accuracy of ca. 0.2 K for the temperature and
up to 5 to 10% for the heat capacity was estimated over the
whole temperature range, by comparison with the synthetic
sapphire. A lattice heat capacity was estimated from the data
below and above the anomaly associated with the SCO process
(dashed line in Fig. 8). Excess enthalpy and entropy were
derived by integration of the excess heat capacity with respect
to T and LnT, respectively.
Conclusions
In the present study, three new members of the still small (but
increasing) family of SCO compounds based on the 2,2′-dipyri-
dylamino/s-triazine moiety have been obtained and fully
characterized. The investigation carried out clearly shows the
importance of supramolecular contacts in the cooperativity of
the spin-transition process. Indeed, the triazine ligand con-
taining the fluorinated phenolic groups generates a Fe(II)–NCS
complex (i.e. 3) whose SCO is significantly more abrupt (ΔT80
= 50 K) than that of the equivalent coordination compound
(i.e. 1) with the ligand bearing simple phenolic substituents
(ΔT80 = 90 K). These distinct behaviours are obviously due to
the fluoride atoms; actually, the F atoms give a π-acidic charac-
ter to the phenyl rings, hence favouring the occurrence of
strong intermolecular π⋯π interactions (which do not take
place in the solid-state structure of compound 1, which lacks
the F atoms). In addition, the F atoms are involved in strong
intermolecular halogen⋯halogen bonding contacts (with F⋯F
Materials and syntheses
contact distances well below the sum of the vdW radii), All reactions were performed under aerobic conditions and all
improving further the cooperative character of the SCO. reagents and solvents were used as purchased. TLC was per-
The exploration of the physical properties of the iron(II) formed on Alugram® SIL G/UV/254 silica gel precoated sheets
complexes (with NCS or NCSe anions) obtained from the (Macherey–Nagel, Germany). Purification of the organic
mixed ligand, namely the 2,2′-dipyridylamino/s-triazine ligand ligands was carried out by column chromatography using
containing both phenol and pentafluorophenol groups, silica gel SDS 60 ACC (0.035–0.070 mm).
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2-(N,N-Bis(2-pyridyl)amino)-4,6-bis(phenoxy)-(1,3,5)triazine
(L1)
Preparation of 2-chloro-4,6-bis(pentafluorophenoxy)-(1,3,5)-
triazine. 5.0 g (27.11 mmol) of 2,4,6-trichloro-1,3,5-triazine
were dissolved in 100 mL of dry THF. Two equivalents (7.01 g,
54.22 mmol) of DIPEA were then added under stirring. The
resulting yellow solution was cooled down to 0 °C and two
equivalents (9.98 g, 54.22 mmol) of pentafluorophenol were
added portionwise. After 15 minutes, the white crystalline pre-
cipitate of DIPEA·HCl was separated by filtration and the fil-
trate was evaporated under reduced pressure. The consequent
solid material was dissolved in diethyl ether and the second
crop of insoluble DIPEA·HCl was removed by filtration. After
evaporation under reduced pressure, pure 2-chloro-4,6-bis
(pentafluorophenoxy)-(1,3,5)triazine was obtained as a white
powder with a yield of 45% (5.83 g, 11.22 mmol). IR (KBr): ν =
3431(w), 2991(w), 2674(w), 2465(w), 1655(m), 1609(s), 1577(s),
1522(br,s), 1475(s), 1437(m), 1372(s), 1306(s), 1224(w), 1169(m),
The synthesis of ligand L1 was performed in two straight-
forward steps.
Preparation of 2-chloro-4,6-bis(phenoxy)-(1,3,5)triazine.
5.0 g (27.11 mmol) of 2,4,6-trichloro-(1,3,5)triazine were dis-
solved in 100 mL of dry THF. Two equivalents (7.01 g,
54.22 mmol) of N,N-diisopropylethylamine (DIPEA) were
added subsequently under stirring. The resulting yellow solu-
tion was cooled down to 0 °C, and two equivalents (5.10 g,
54.22 mmol) of phenol were added portionwise. After com-
pletion of the addition, the ice bath was removed and the reac-
tion mixture was stirred for 15 min. The white precipitate
obtained (identified as a first crop of the chlorhydrate salt of
DIPEA) was removed by filtration. The remaining solid was dis-
solved in diethyl ether and the undissolved white powder cor-
responding to a second crop of DIPEA·HCl was separated by
filtration. Removal of the solvent under reduced pressure pro-
duced pure 2-chloro-4,6-bis(phenoxy)-(1,3,5)triazine as a white
powder with a yield of 45% (6.08 g, 12.16 mmol). IR (KBr): ν =
3420(w), 3058(w), 1578(m), 1531(s), 1485(m), 1455(m),
1421(m), 1383(s), 1293(s), 1253(m), 1193(m), 1162(w), 1068(w),
985(w), 948(s), 867(w), 842(w), 802(w), 767(m), 693(m), 657(w),
1155(m), 1078(s), 998(s), 805(m), 640(w) cm−1
.
Preparation of 2-(N,N-bis(2-pyridyl)amino)-4,6-bis(penta-
fluorophenoxy)-(1,3,5)triazine (L1F). One equivalent of (1.10 g,
8.80 mmol) of DIPEA was added to a solution of 2-chloro-4,6-
bis(pentafluorophenoxy)-(1,3,5)triazine (4.20 g, 8.80 mmol) in
50 mL of dry THF. Next, one equivalent (1.50 g, 8.80 mmol) of
2-dipyridylamine was added and the resulting reaction mixture
was refluxed for two hours. The solution was then cooled
down to room temperature, and the solvent was evaporated
under reduced pressure. The remaining solid material was dis-
solved in diethyl ether and the insoluble white powder, i.e.
DIPEA·HCl, was removed by filtration. The solvent was evapor-
ated under reduced pressure and the crude compound was
purified by column chromatography, using the solvent mixture
EtOAc–n-hexane (50 : 50) as an eluent. Pure ligand L1F (Rf =
0.63) was obtained with a yield of 55% (2.96 g, 4.82 mmol).
Elemental analyses calculated (found) (%) for C25H8F10N6O2:
C: 48.88 (50.16), H: 1.31 (1.10), N: 13.68 (13.64). It has to be
noted that higher experimental values for C may be obtained
with triazine-based compounds.40 1H NMR (300 MHz, CDCl3,
room temp.): δ = 8.40 (ddd, J = 4.9, 1.9, 0.8 Hz, 2H), 7.73 (ddd,
J = 8.0, 7.5, 2.0 Hz, 2H), 7.47 (dt, J = 8.1, 0.9 Hz, 2H), 7.20 (ddd,
J = 7.5, 4.9, 1.0 Hz, 2H) ppm. IR (KBr): ν = 3428(w), 1596(s),
1562(s), 1519(s), 1417(s), 1435(m), 1375(s), 1309(m), 1305(m),
1254(m), 1234(m), 1166(m), 1076(s), 997(s), 812(w), 774(w),
485(5) cm−1
.
Preparation of 2-(N,N-bis(2-pyridyl)amino)-4,6-bis(phenoxy)-
(1,3,5)triazine (L1). One equivalent (1.10 g, 8.80 mmol) of
DIPEA was added to a solution of 4.20 g (8.80 mmol) of
2-chloro-4,6-bis(phenoxyl)-(1,3,5)triazine in 50 mL of dry THF.
Next, one equivalent (1.50 g, 8.80 mmol) of 2-dipyridylamine
was added and the reaction mixture was refluxed for two
hours. Subsequently, the solution was cooled down to room
temperature, and the solvent was evaporated under reduced
pressure. The solid obtained was dissolved in diethyl ether
and the remaining DIPEA·HCl salt was removed by filtration.
The resulting crude compound was purified by column chrom-
atography using the solvent mixture CH2Cl2–MeOH (99 : 1) as
an eluent. Pure ligand L1 (Rf = 0.42) was obtained as a white
crystalline powder with a yield of 55% (2.86 g, 6.58 mmol).
Elemental analyses calculated (found) (%) for C25H18N6O2: C:
69.11 (69.01), H: 4.18 (4.24), N: 19.34 (19.47). 1H NMR
(300 MHz, CDCl3, room temp.): δ = 8.38–8.33 (m, 2H), 7.62
(ddd, J = 8.1, 7.5, 2.0 Hz, 2H), 7.47 (d, J = 8.1 Hz, 2H),
7.33–7.23 (m, 4H), 7.19–7.05 (m, 8H) ppm. IR (KBr): ν = 3427
(w), 3056(w), 2974(w), 2857(w), 1565(m), 1488(m), 1432(m),
1374(s), 1303(m), 1238(m), 1200(m), 1080(w), 995(w), 807(w),
770(m), 690(m) cm−1. The molecular structure of L1 was deter-
mined by single-crystal X-ray diffraction. A representation of
the crystal structure of L1 is depicted in Fig. S7.† The corre-
sponding crystallographic and refinement parameters are sum-
marized in Table S4.†
697(w), 662(w) cm−1
.
trans-[Fe(L1)2(NCS)2]·2CH2Cl2 (1)
A methanolic solution (5 mL) of KNCS (0.019 g, 0.2 mmol) was
added to an aqueous solution (2 mL) of FeSO4·7H2O (0.028 g,
0.1 mmol). After 15 minutes of stirring, the precipitate of
K2SO4 was removed by filtration. Ascorbic acid (in small quan-
tities) was added to the filtrate to prevent oxidation to iron(III).
Subsequently, a solution of L1 (0.086 g, 0.2 mmol) in dichloro-
methane was added to the iron(II) solution. The resulting
yellow reaction mixture was filtered and the filtrate was left
unperturbed for the slow evaporation of the solvent. After
three days, small yellow single crystals of 1, suitable for X-ray
2-(N,N-Bis(2-pyridyl)amino)-4,6-bis(pentafluorophenoxy)-
(1,3,5)triazine (L1F)
Ligand L1F was synthesized in a similar manner using penta- diffraction studies, were obtained with a yield of 70% (85 mg,
fluorophenol instead of phenol.
0.07 mmol, based on iron). Elemental analyses calculated
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(found) (%) for C53H38FeN14O4S2Cl2 (1 – CH2Cl2): C: 56.54 the Royal Golden Jubilee Program (RGJ, Grant no. PHD/0234/
(55.71), H: 3.40 (3.30), N: 17.42 (17.59). IR (KBr): ν = 3435(w), 2550) and Khon Kaen University for research grant.
a
2067(m), 1604(m), 1556(m), 1488(m), 1376(s), 1309(m), SY acknowledges The Thailand Research Fund, the National
1245(m), 1201(m), 1016(w), 809(w), 772(w), 688(w) cm−1
.
Research University Project of Thailand, Office of the Higher
Education Commission, through the Advanced Functional
Materials Cluster of Khon Kaen University and the Center of
Excellence for Innovation in Chemistry (PERCH-CIC), Office
of the Higher Education Commission, Ministry of Education.
The Advanced Light Source is supported by the Director,
Office of Science, Office of Basic Energy Sciences of the
U. S. Department of Energy under contract no. DE-AC02-
05CH11231. OR acknowledges funding from the Ministerio de
Economía y Competitividad of Spain (Project MAT2011-24284).
trans-[Fe(L1)2(NCSe)2]·4CH2Cl2·4MeOH (2)
Compound 2 was obtained using the synthetic procedure
applied to prepare 1, but using KNCSe (0.029 g, 0.2 mmol)
instead of KNCS. Single crystals of 2, suitable for X-ray diffrac-
tion studies, were obtained after three days with a yield of 63%
(101 mg, 0.063 mmol, based on iron). Elemental analyses cal-
culated (found) (%) for C55H46FeN14O6Se2Cl2 (2 – 4CH2Cl2–
4MeOH + 3H2O): C: 52.54 (52.03), H: 3.56 (3.08), N: 16.50
(17.04). IR (KBr): ν = 3425(w), 3066(w), 2074(s), 1602(m),
1559(m), 1487(m), 1435(m), 1373(s), 1311(m), 1249(m),
1194(m), 1077(w), 1018(w), 906(w), 808(w), 767(w), 687(w)
Notes and references
cm−1
.
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Acknowledgements
PG acknowledges ICREA (Institució Catalana de Recerca i
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vidad of Spain (Project CTQ2011-27929-C02-01). NW thanks
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This journal is © The Royal Society of Chemistry 2013
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7130 | Dalton Trans., 2013, 42, 7120–7130
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