Complexes with Aromatic Counteranions - ACS Publications

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Intermolecular Interaction Tuning of Spin-Crossover Iron(III) Complexes with Aromatic Counteranions Asami Tsukiashi,† Manabu Nakaya,† Fumiya Kobayashi,† Ryo Ohtani,† Masaaki Nakamura,† Jack M. Harrowfield,‡ Yang Kim,† and Shinya Hayami*,†,§ †

Department of Chemistry, Faculty of Advanced Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan ‡ ISIS, Université de Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France § Institute of Pulsed Power Science (IPPS), Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan S Supporting Information *

ABSTRACT: Iron(III) spin-crossover (SCO) complexes [Fe(qsal)2]BS·MeOH· H2O (1), [Fe(qsal)2](NS)·MeOH (2), [Fe(qnal)2](NS) (3), and [Fe(qnal)2]PS· MeOH·CH2Cl2 (4) (Hqsal, N-(8-quinolinyl)salicylaldimine; Hqnal, N-(8quinolinyl)-2-hydroxy-1-naphthaldimine; BS, benzenesulfonate; NS, 1-naphthalenesulfonate; PS, 1-pyrenesulfonate) have been synthesized and characterized by Xray structure determinations and temperature-dependent magnetic susceptibility measurements. The aromatic counteranions BS, NS, and PS can be used for the tuning of intermolecular coupling through a variety of weak interactions. All of the complexes show temperature-dependent SCO behavior. but the light-induced excited spin-state trapping (LIESST) effect was observed only for 1, 3, and 4 when the samples were illuminated (λ 808 nm) for 1 h at 5 K. In particular, 59% of the LS form of 1 was converted to the metastable HS state by illumination, equal to the highest degree of conversion yet known for LIESST in [Fe(qsal)2]+ derivatives. The lack of a LIESST effect for 2 may be due to the relatively limited degree of interaction between the cations and anions in the lattice, reflected in a much longer minimum Fe···Fe separation in this complex in comparison to the others.

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INTRODUCTION Spin state changes between the high-spin (HS) and low-spin (LS) forms of metal complexes of transition-metal ions with dn (n = 4−7) configurations have been extensively investigated.1−8 Such spin state changes can be controlled by external stimuli (heat, pressure, magnetic field, light irradiation). Thus, spincrossover (SCO) complexes can be utilized in storage media, sensors, and other switchable equipment.1−8 Several lines of evidence indicate that, in the solid state, a strong cooperativity in structural changes induces abrupt spin transitions1−11 and the effect of lattice interactions on spin transitions; therefore, this cooperativity has been extensively studied and has been a particular interest of our own group.12−19 Cooperativity in structural changes associated with spin state changes appears to be strongly influenced by secondary interactions, including those associated with aromatic unit stacking, hydrogen bonding, halogen bonding, charge (cation−anion) interactions, and magnetic coupling between adjacent metal ions.1−11 It is possible to induce abrupt spin changes in cases where this cooperativity is strong, as in some striking recent examples,20 and this is of particular importance in relation to the possible use of the light-induced excited spin-state trapping (LIESST) effect.20,21 The LIESST effect is best known to occur in iron(II) compounds, and instances of the LIESST effect in iron(III) compounds are relatively rare.4,7,21 This is because the energy © XXXX American Chemical Society

levels of HS and LS states overlap in iron(III) compounds, leading to facile HS → LS relaxation. Since the first report by Hayami et al.13 of LIESST in a mononuclear Fe(III) complex, [Fe(pap)2]ClO4·H2O (Hpap = 2-(2′-pyridylimino)phenol), further reports2 have been largely limited to other derivatives of [Fe(pap)2]+ or of the related cations [Fe(qsal)2]+ and [Fe(qnal)2]+ (Hqsal = N-8-(quinolinyl)salicylaldimine; Hqnal = N-(8-quinolinyl)-2-hydroxynaphthaldimine), also having cisN4O2 coordination spheres provided by large heteroaromatic ligands, although the range of known systems is expanding.2 In the solid state, lattice interactions in crystals containing such cations increase the energy difference between the HS and LS states and prevent rapid HS → LS relaxation. In the case of [Fe(pap)2]ClO4·H2O, excitation in the near-IR (1000 nm) for 1 h at 5 K led to a LS → HS conversion corresponding to approximately 65% of the initially 100% LS species present.13 Similar treatment of [Fe(qnal-OMe)2]PF6·acetone and [Fe(qnal-OMe)2]BPh4·2MeOH (qnal-OMe = 7-methoxy-1-[(8quinolinylimino)methyl]-2-naphthalenol) again produced substantial conversions to the HS forms, with the greater degree of the former corresponding to 85% of the LS form.19 However, the maximum value of conversion in [Fe(qsal)2]+ is just 18%,17 Received: December 24, 2017

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DOI: 10.1021/acs.inorgchem.7b03126 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

K, through an optical fiber to the cavity of the SQUID magnetometer. Thermogravimetric analysis (TGA) was carried out with TG-DTA (Rigaku Thermo plus EVO). The heating rate was 10 K/min. Each time, the sample was measured in an aluminum crucible under a nitrogen atmosphere from room temperature to 700 K. Phase transition temperatures of compounds 1−4 were measured with a differential scanning calorimeter (NETZSCH, DSC3500). The scanning rate was set at 10.0 K/min to obtain clear DSC thermograms. The full DSC results are shown in the Supporting Information. The electronic absorption spectra of compounds 1−4 in methanol solution (10−5 M) and in the solid state were recorded on a SHIMADZU UV3600 instrument to complete characterization of the complexes. The data are shown in the Supporting Information. Fluorescence measurements showed the solid complexes to be nonemissive. The Mössbauer spectra (isomer shift vs metallic iron at room temperature) was performed with a Wissel MVT-1000 Mössbauer spectrometer with a 57Co/Ph source in transmission mode. All isomer shifts are given relative to α-Fe at room temperature. Measurements at low temperature were performed with a closed-cycle helium refrigerator cryostat (Iwatani Co., Ltd.). Crystal Structure Determinations. X-ray diffraction data for the single crystals were collected with a Rigaku R-AXIS RAPID II diffractometer for 1 and Rigaku Saturn70 diffractometer for 2−4 with graphite-monochromated Mo Kα radiation. The structures were solved with the SIR2004 structure solution program22 for 1−3 and SHELXT version 2014/523 for 4 and refined with ShelXL-9724 for 1 and SHELXL version 2014/724 for 2−4. Crystal parameters for 1−4 are shown in Table 1, with full structural data available from the CCDC. CCDC files 1580419 (1), 1580418 (2), 1580420 (3), and 1581653 (4) contain supplementary crystallographic data for this paper.

even though qsal constitutes a larger π-conjugated system in comparison to pap. This means that interactions within and between the stacked arrays of cations found in the lattices of all these complexes considered to provide a barrier to HS → LS return2,12−19 cannot be simply determined by the size of the πconjugated ligand entities. What the present work has shown, however, is that LIESST behavior of both qsal and qnal complexes of Fe(III) can be enhanced by the presence of planar aromatic counteranions that may be involved in various interactions, including extension of the stacking arrays. Thus, we report herein the properties of the complexes [Fe(qsal)2]BS·MeOH·H2O (1; BS = benzenesulfonate), [Fe(qsal)2](NS)· MeOH (2; NS = naphthalene-1-sulfonate), [Fe(qnal)2](NS) (3), and [Fe(qnal)2]PS·MeOH·CH2Cl2 (4; PS = pyrene-1sulfonate). The LIESST effect has been observed in complexes 1, 3, and 4.

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EXPERIMENTAL SECTION

Preparation of [Fe(qsal)2]Cl·2H2O. A solution of 8-aminoquinoline (1.44 g, 10 mmol) and salicylaldehyde (1.22 g, 10 mmol) in methanol (50 mL) was heated at reflux for 3 h. The obtained orange solution was cooled, and FeCl3·6H2O (1.35 g, 5 mmol) in methanol (50 mL) was added with vigorous stirring. Finally, a solution of triethylamine (1.01 g, 10 mmol) in methanol (10 mL) was added slowly at room temperature over 3 h, causing formation of a black precipitate, which was then recrystallized from methanol. Anal. Calcd for C32H26O4N4ClFe: C, 61.80; H, 4.21; N, 9.01. Found: C, 61.51; H, 4.22; N, 8.97. Preparation of [Fe(qsal)2]C6H5SO3·MeOH·H2O (1). A solution of [Fe(qsal)2]Cl·2H2O (0.31 mg, 0.5 mmol) in methanol (50 mL) and a solution of sodium benzenesulfonate (180 mg, 1 mmol) in methanol (50 mL) were mixed and stirred at room temperature for 3 h. The black precipitate that formed was collected by filtration and recrystallized from methanol to give blocklike black crystals. Anal. Calcd for C39H33FeN4O7S: C, 61.83; H, 4.39; N, 7.40. Found: C, 61.35; H, 4.24; N, 7.81. Preparation of [Fe(qsal)2]C10H7SO3·MeOH (2). A solution of [Fe(qsal)2]Cl·2H2O (0.31 mg, 0.5 mmol) in methanol (50 mL) and a solution of sodium 1-naphthalenesulfonate (230 mg, 1 mmol) in methanol (50 mL) were mixed and stirred at room temperature for 3 h. The black precipitate that formed was collected by filtration and recrystallized from methanol to again give blocklike black crystals. Anal. Calcd for C43H33FeN4O6S: C, 65.40; H, 4.21; N, 7.06. Found: C, 65.30; H, 4.14; N, 6.81. Preparation of [Fe(qnal)2]C10H7SO3·MeOH (3). A solution of Hqnal17 (288 mg, 1 mmol) in methanol (10 mL) and CH2Cl2 (40 mL), a solution of FeCl3·6H2O (135 mg, 0.5 mmol) in methanol (20 mL), and a solution of sodium 1-naphthalenesulfonate (230 mg, 1 mmol) in methanol (30 mL) were mixed and stirred at room temperature for 3 h to give a black precipitate. This was collected by filtration and recrystallized from methanol to once again give blocklike black crystals. Anal. Calcd for C51H37FeN4O6S: C, 68.84; H, 4.19; N, 6.30. Found: C, 68.96; H, 4.46; N, 6.21. Preparation of [Fe(qnal)2]C16H9SO3·MeOH (4). A solution of Hqnal (288 mg, 1 mmol) in a mixture of methanol (10 mL) and CH2Cl2 (40 mL), a solution of FeCl3·6H2O (135 mg, 0.5 mmol) in methanol (20 mL), and a solution of sodium 1-pyrenesulfonate (230 mg, 1 mmol) in methanol (30 mL) were mixed and stirred at room temperature for 3 h to give a black precipitate. This was collected by filtration and recrystallized from methanol to once again give blocklike black crystals. Anal. Calcd for C56H42FeN4O8.5S: C, 67.61; H, 4.26; N, 5.63. Found: C, 67.48; H, 4.01; N, 5.83. Physical Measurements. The temperature-dependent magnetic susceptibilities χmT for the compound were measured between 5 and 400 K with a superconducting quantum interference device (SQUID) magnetometer (Quantum Design MPMS-5S) in an external field of 0.5 T. LIESST experiments were carried out using a semiconductor laser emitting at 808 nm, and the samples were irradiated for 1 h at 5

Table 1. Fe−O and Fe−N Bond Lengths (Å) in Complexes 1−4 Fe−O1 Fe−O2 Fe−N1 Fe−N2 Fe−N3 Fe−N4

1

2

3

4

1.886(3) 1.883(3) 1.940(2) 1.970(2) 1.935(2) 1.980(2)

1.872(1) 1.874(1) 1.977(2) 1.940(2) 1.982(2) 1.944(2)

1.872(2) 1.879(3) 1.976(4) 1.928(4) 1.979(3) 1.933(4)

1.880(2) 1.877(2) 1.968(2) 1.931(2) 1.969(2) 1.930(2)

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RESULTS AND DISCUSSION Synthesis. All [Fe(qsal)2]X compounds were prepared according to the literature.17 The compositions of all compounds were determined by microanalysis and crystal structure analyses described below. The nonsolvated compounds were obtained by heating the solvated compounds to 127 °C followed by cooling to room temperature. Thermogravimetric analysis was performed for 1−4, showing the thermal stability of the nonsolvated complex up to approximately 550 °C for complex 1, 2, and 4 and 660 °C for 3 (Figures S1−S4). Crystal Structures and Their Analysis. Crystal structures of [Fe(qsal)2]BS·MeOH·H2O (1), [Fe(qsal)2](NS)·MeOH (2), [Fe(qnal)2](NS) (3), and [Fe(qnal)2]PS·MeOH·CH2Cl2 (4) were determined at 100 K for 1 and 2, 103 K for 3, and 296 K for 4 by single-crystal X-ray diffraction measurements (Table S1). In all complexes, the iron(III) centers are approximately octahedrally coordinated by four nitrogen atoms and two oxygen atoms from two qsal or qnal ligands in a cis-N4O2 donor set. The Fe−O and Fe−N distances (Table 1) are consistent with the iron(III) LS state. In the typical case of 1 (Figure 1a), the Fe−O bonds (1.89 Å) are significantly shorter than the Fe− N bonds (1.96 Å), inducing a pronounced distortion of the B


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Inorganic Chemistry

Figure 1. (a) Stoichiometric unit (stick representation) of 1. (b) Chain of stacked cations running parallel to the c axis with C···C interactions exceeding dispersion shown as dashed black and white lines. (c) H-bond polymer strand running parallel to the c axis formed by the anion and solvent molecules. (d) CH···O interactions (dashed lines) of a single cation with an anion and solvent molecules.

between Fe centers in separate chains being considerably longer at 10.246 Å. The Hirshfeld surface for the cation (Figure S5a) shows that indeed there are interactions beyond dispersion involving C atoms within the parallel ligand planes, specifically involving C9···C22i (and C22···C9i) at 3.219(3) Å and C6··· C25i (and C25···C6i) at 3.281(3) Å (Figure 1b). However, it also shows that accompanying these C···C interactions are CH···O interactions involving the coordinated O atoms (O1··· H7i 2.451 Å; O2···H23i 2.507 Å) and that these are part of the same chain structure as that involving the C···C interactions, so that “stacking” must be considered to be associated with interpenetration of the coordination spheres. A lattice is a three-dimensional structure as well, so that 1D chains alone cannot explain its formation. In fact, there is a stacked array of cations alternating with anions running parallel to the b axis and the Hirshfeld surfaces for both the cation and the anion show that this stacking is associated with C···C interactions beyond dispersion involving C35···C27 of 3.334(3) Å and C38···C14i (symmetry operation i: x, 1 − y, z + 0.5) of 3.320(3) Å. Consistent with the longer C···C distances here, the Hirshfeld surfaces show a lesser perurbation in comparison to that seen with the cation···cation contacts. More importantly, the Hirshfeld surfaces show not only that the anion and solvent molecules form infinite H-bonded chains running parallel to the c axis (Figure 1c) but also that the oxygen atoms of this chain are involved in CH···O interactions with the cations (Figure 1d) and that the network of OH···O and CH···O interactions alone is three-dimensional. The lattice of 2 shows some similarities to that of 1 in that undulating sheets of cations and anions alternate in parallel to

Fe−N4O2 octahedron. As is commonly the case in lattices containing complexes of large, functionalized aromatic species,25,26 stacking of the cation units is apparent, involving in the present cases both 1D and 2D arrays. Such stacked arrays, however, do not necessarily signify interactions beyond dispersion27 or even, in general, the presence of a delocalized π system28 and are certainly not indicative of the absence of stronger interactions as there must be between the oppositely charged species of an ionic lattice.29 Various tools are available for the analysis of solid-state interactions which exceed dispersion,30−32 and the Hirshfeld surfaces,33 as calculated using CrystalExplorer,33c for both the cations and anions of the present complexes (Figure S5) show that, while indeed there are specific interactions beyond dispersion involving both the stacked ligand units of separate cations and their stacked anions, a number of other interactions are also apparent. Thus, in the lattice of 1, there is an apparent segregation into alternating sheets parallel to the ac plane of cations alone in one sheet and anions plus solvent in the other. This is artificial, since the lattice can also be considered to be made up from sheets of cations + anions lying parallel to the bc plane and cross-linked by the solvent molecules, but it is useful to regard the sheet as being parallel to the ac plane, since it is obviously composed of side-by-side strands of “stacked” cations: i.e., chains where the nearly planar ligands on adjacent complex units lie close to parallel. The separation of these close ligand planes is ∼3.0 Å, and there is a significant overlap in projection, a situation typical26 of one where “π−π interactions” might be proposed. The Fe···Fei (symmetry operation i: x, 1 − y, z − 0.5) separation in the chains is 6.729 Å, the shortest distance C


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Inorganic Chemistry

Figure 2. (a) CH···C interactions within the stacked chain of cations running parallel to the b axis in the crystal of 2. (b) Interactions (dashed lines) of anions parallel to the c axis. (c) Interactions of a single anion (naphthyl group outlined in black) with one other anion, two cations through direct contacts, and a third cation via common interaction with a methanol molecule.

the bc plane (Figure 2a). The cation sheets can be considered to be made up from orthogonal zigzag chains of cations in which the Fe···Fe distances are 8.7602(5) Å in the chain parallel to c and 9.7605(6) Å in the chain parallel to b. Each chain consists of a stacked array of cations, but the distances between nearly parallel ligand planes of these stacks are relatively long, being ∼3.4 Å in the c chain and ∼4.0 Å in the b chain, and the Hirshfeld surface for the cation provides no evidence for any C···C interactions beyond dispersion in both cases. In fact, for both cations and anions, most interactions involve the periphery and not the face of the aromatic units and the only interactions beyond dispersion between the cations are of the edge to face CH···C (or CH···π) type: that is, they involve ligand units which are nearly orthogonal rather than parallel. They involve the contacts H19···C30i of 2.743(2) Å and H19···C31i of 2.709(2) Å and link cations with a separation of 9.7605(6) Å. The anions in the lattice of 2 do not form stacks with either themselves or the cations, and the only interactions beyond dispersion perpendicular to the naphthyl unit plane are two barely discernible CH···C contacts involving CH groups of cations (Fe···Fe 11.2936(6) Å) to either side of the naphthyl plane. Much more obvious are interactions of the O···C, O···HC, and CH···O types, one consequence of the last

of these being that the anions themselves form a chain parallel to the c axis (Figure 2b), while for a single anion the combination of these interactions results in the anion bridging the two cations also linked to it by the CH···C interactions, as well as a third cation through the intermediary of the methanol molecule (Figure 2c). The CH···O interactions discerned in the Hirshfeld surfaces are sufficient alone to provide threedimensional linking in the lattice. In the lattice of unsolvated 3, it is possible to discern 1D arrays of cations running parallel to a and largely separated from one another by intervening anions.34,35 The 1D chains are not regular in the sense that they consist of columns of close pairs (Fe···Fei 6.780(5) Å) where two (slightly bent) ligand units on separate Fe centers lie approximately 3 Å apart and overlap significantly in projection, while the next-nearest Fe centers (Fe···Fej 8.804(8) Å) have nearly parallel ligands ∼3.5 Å apart which have only a minor overlap in projection. These chains can also be considered to lie side by side in sheets parallel to the bc plane, and a view of such a sheet (Figure 3a) shows that there are ligands on separate Fe centers which appear to be in a stacked arrangement. However, it is only for the pairs of cations for which Fe···Fe is 6.780(5) Å that any interactions beyond dispersion perpendicular to the parallel D


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Inorganic Chemistry

Figure 3. (a) Partial view of a sheet of cations (intervening anions not shown) in the lattice of 3 showing the chains of apparently stacked close and remote pairs. (b) C···C and CH···O interactions (dashed lines) between the close-stacked pair. (c) CH···C interactions within the stacked pair. (d) CH···C and CH···O interactions of a single anion (naphthyl unit outlined in black) with surrounding cations.

ligand planes are apparent and they are accompanied by CH··· O interactions, indicating once again that interpenetration may be as important as stacking (Figure 3b). Interpenetration appears to be the more important factor in the case of the Fe··· Fe 8.804(8) Å pair, as only edge to face CH···C interactions exceed dispersion (Figure 3c). Overall, the three-dimensional structure of the lattice is a consequence of CH···C and CH···O interactions, as seen for a single anion in Figure 3d. The lattice of the solvated complex 4 is one where stacking of cations with cations and cations with anions is apparent and where again chains of stacked cations can be seen as lying side by side in sheets, here parallel to the ab plane, alternating with sheets of the anions plus methanol molecules. Even here, however, C···C interactions beyond dispersion between the stacked species lead only to a 1D chain (Figure 4a) and it is further interactions of the anion (Figure 4b) of O···C, O···HC, OH···O, and C···HC types as well as O···HC and Cl···HC interactions of methanol and dichloromethane, respectively, that generate the three-dimensional form of the lattice.25 Magnetic Behavior. The variable-temperature magnetic behavior of desolvated 1 is shown in Figure 5a. χmT values at 10 and 300 K were 0.50 and 4.39 cm3 K mol−1, respectively. These values correspond to those expected for LS and HS iron(III). Spin crossover (SCO) occurred abruptly but with negligible hysteresis, giving a cooperativity parameter value of C = 1.00, and involved two distinct steps with T1/2 = 195 and 205 K, respectively (Figure 5a). The thermodynamic parameters have been deduced from the expression obtained from the regular solution model.36 Both temperatures are well below those at which solvent loss from the solid occurs (Figure S1), and the two steps must therefore be assigned to two structural rearrangements, visible also by DSC (Figure S6). Although the structure of the HS form of the complex is unknown, it is likely, on the basis of comparisons that can be made with closely related species, that these structural rearrangements

Figure 4. (a) Partial view of a chain of stacked cations within the lattice of 4, showing C···C and CH···O interactions (dashed lines) betwee the stacked ligand units. (b) C···C, CH···C, and CH···O interactions of a single anion (pyrene unit outlined in black) with its surrounding cations (and methanol).

could be quite subtle and that their characterization would require rather detailed analysis of interactions within the lattices. Thus, when the structure of HS [Fe(qsal)2]NCSe17 is E


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Inorganic Chemistry

Figure 5. χmT vs T plot for (a) 1, (b) 2, (c) 3 and (d) 4: (black) heating measurement; (red) heating after removal of solvent; (blue) cooling after removal of solvent; (green) heating after LIESST effect.

showing a gradual and imcomplete SCO and reaching a χmT value of 1.2 cm3 K mol−1 at 5 K. The Mössbauer spectra were measured for desolvated 2 at 300 and 50 K to obtain a more detailed insight into SCO (Figure S10). At 300 K, doublet absorption with QS = 0.68 mm s−1 and IS = 0.45 mm s−1 was observed, indicating that complex 2 takes the moderate HS state. On the other hand, at 50 K, doublet absorption appeared with QS = 0.80 mm s−1 and IS = 0.52 mm s−1. Mössbauer data were also supported the magnetic behavior of 2. In contrast, unsolvated 3 exhibited an abrupt SCO with thermal hysteresis (Figure 5c), the extreme χmT values being 0.53 and 3.97 cm3 K mol−1 at 5 and 300 K, respectively, the latter value being that expected for HS Fe(III). For the heating and cooling cycles the T1/2↑ and T1/2↓ values were 219 and 188 K (ΔT = 31 K), respectively, corresponding to a cooperativity factor C of 1.53. Gradual spin transition behavior was observed with solvated [Fe(qnal)2]PS·MeOH·CH2Cl2 (200−300 K). Solvent removal occurred by increasing the temperature to 400 K. Again in contrast to desolvated 2, desolvated 4 obtained by heating at 300 K prior to the measurements (Figure 5d) showed an abrupt SCO without thermal hysteresis (cooperativity C = 1.00), the χmT value at 5 K being 1.24 cm3 K mol−1. The phase transition temperatures of compounds 1, 3, and 4 were measured by differential scannning calorimetry (Figures S6− S9) and were compared with the spin transition temperatures estimated from the δχmT/δT plots (Figures S11−S13). The DSC analysis showed that the phase transitions occurred at essentially the same temperatures as those of the spin transitions. The LIESST effect was observed for desolvated forms of the complexes 1, 2, and 4 on irradiating samples for 1 h at 5 K,

compared with that of LS [Fe(qsal)2]NCSe·CH2Cl2,14 it appears at first sight that both lattices contain sheets composed of chains of stacked cations and that the decreased minimum separation between Fe centers (7.06(1) Å in the LS form vs 7.306(1) Å in the HS) could be largely ascribed simply to the shrinkage due to bond length changes in the LS form. However, it is only in the LS form that C···C interactions between stacked ligand units can be detected and even here they result only in the formation of cation pairs and not chains extending throughout the lattice.37 The interactions beyond dispersion which appear in both lattices involve not just the faces but the peripheries of the aromatic units and are mostly of the CH···C and CH···N types, creating far more extensive links than the stacking interactions, although the full variety of interactions is not the same due to the fact that the materials differ in composition. Problems of a difference in composition and anion disorder in one form complicate any comparison of LS [Fe(qsal)2]NCS·CH2Cl2 (minimum Fe···Fe 6.88(1) Å)17 with HS [Fe(qsal)2]NCS (minimum Fe···Fe 7.24(2) Å),17 but again the formation of the HS species is associated with the loss of any interactions beyond dispersion between stacked ligand units. After the temperature was raised to 400 K, the samples showed the same magnetic behavior even though solvents were removed. Variable-temperature magnetic measurements on 2 are shown in Figure 5b. The complex showed LS states below 300 K, and the χmT value was 0.42 cm3 K mol−1 at 5 K. Then, the complex was desolvated by raising the temperature to 400 K. In a cooling experiment, the desolvated complex showed a gradual SCO and reached χmT values of 1.24 and 3.81 cm3 K mol−1 at 5 and 400 K, respectivly. The complex was desolvated by heating at 300 K prior to cooling, resulting in a material F


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CONCLUSIONS That a change in a counterion can have important effects on the behavior of a spin-active species is a well-known aspect of the chemistry of SCO complexes in general,1−11,20,35 and the presently studied materials provide further examples. What is apparent from the present structure determinations is that the influence of the counteranion in lattices containing cationic Fe(III) complexes susceptible to undergoing spin crossover may involve a number of different interactions beyond the range of dispersion forces and specifically that the obvious stacking of aromatic ligand entities does not necessarily indicate that this must control structural changes accompanying SCO, although it appears to have some role in stabilizing LS species. Aromatic···aromatic interactions beyond dispersion of the “face to face” type even appear to be entirely absent in certain cases and in general are of limited extent. In relation to LIESST behavior, one feature of the structure of 2 that may explain the absence of this effect in this particular case is that the cation··· anion interactions result in a minimum Fe···Fe separation nearly 2 Å greater than the separations in the other three complexes. This indicates that the LS/HS relaxation rates in these solids may depend upon direct magnetic interaction between the Fe(III) centers.

using a semiconductor laser (λ 808 nm) connected through an optical fiber to the cavity of the SQUID magnetometer. After irradiation, the χmT value for 1 became 2.60 cm3 K mol−1 at 5 K, indicating 59% conversion of the LS state into the photoinduced metastable HS state. The photoinduced HS species began to transform into LS species at temperatures above 41 K. In the case of 3, the χmT value after illumination at 5 K was 1.0 cm3 K mol−1, indicating approximately 23% conversion to the HS species. For 4, the χmT value reached 1.9 cm3 K mol−1 at 5 K after illumination, consistent with 44% conversion of LS to HS species. No response to irradiation was observed for 2. Full data for these LIESST experiments are given in Figure 5. The relationship between the LIESST effect and spin transition is vital to understanding the LIESST effect. Létard et al. determined the correlation between thermal spin transition T1/2 and T(LIESST).21 They proposed the general equation T(LIESST) = T0 − 0.3T1/2 for LIESST compounds and suggested that the different T0 values depend on the chemical nature of the ligand. [Fe(qsal)2]X and [Fe(qnal)2]X systems have tridentate ligands qsal and qnal, and the T(LIESST) vs T1/2 plots for 1, 3, and 4 were fitted by the T(LIESST) = T0(150 K) − 0.3T1/2 line. Although some conditions of measurements are different, the plots for for 1, 3, and 4 deviated from the T0 = 150 K line (Figure 6). It is thought that the plots deviated from the T0 = 150 K line because of the small LIESST effects.17

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b03126. Crystallographic data, intermolecular distances, TGA curves, DSC curves, temperature dependence of Mössbauer spectra, and absorption (in MeOH) and reflectance (in solid) spectra (PDF) Accession Codes

CCDC 1580418−1580420 and 1581653 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/ cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Figure 6. T(LIESST) vs T1/2 plots for 1, 3 and 4.

AUTHOR INFORMATION

Corresponding Author

*E-mail for S.H.: [email protected].

The photinduced formation of 59% of the HS form of 1 at 5 K equals the highest value of such a conversion of an [Fe(qsal) 2 ] + complex as found in [Fe(qsal) 2 ]I·(1,3,5C6I3F3).20a The latter is a particularly interesting species in that its crystal structure at 100 K, consistent with measurements of its magnetism, shows the presence of equal numbers of HS and LS cations. Consideration of the Hirshfeld surfaces of the two cations defines a variety of weak interactions (Figure S14) involving C, CH, and O centers of the cations as well as C and F centers of the 1,3,5-trifluoro-2,4,6-triiodobenzene present in the lattice, with the differences in the environments of the two cations being quite subtle. As with [Fe(qsal)2]BS·MeOH·H2O, interactions perpendicular to stacked ligand units are accompanied by CH···O interactions along the ligand plane, so that it can again be said that there is an interpenetration of the coordination spheres. In neither is it obvious what factors may limit the photostationary state at 5 K to one with 59% HS species.20a

ORCID

Manabu Nakaya: 0000-0001-8483-8131 Ryo Ohtani: 0000-0003-4840-3338 Shinya Hayami: 0000-0001-8392-2382 Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS This work was supported by a KAKENHI Grant-in-Aid for Scientific Research (A), JP17H01200. REFERENCES

(1) Takahashi, K., Ed. Inorganics 2017, 5, (3) (special issue on “Spin Crossover Complexes”). (2) Banerjee, H.; Chakraborty, S.; Saha-Dasgupta, T. Design and Control of Cooperativity in Spin-Crossover in Metal−Organic Complexes: A Theoretical Overview. Inorganics 2017, 5, 47. G


Article

Inorganic Chemistry (3) Kreutzburg, L.; Hübner, C. G.; Paulsen, H. Cooperativity of Spin Crossover Complexes: Combining Periodic Density Functional Calculations and Monte Carlo Simulation. Materials 2017, 10, 172. (4) Harding, D. J.; Harding, P.; Phonsri, P. Spin crossover in iron(III) complexes. Coord. Chem. Rev. 2016, 313, 38−61. (5) (a) Spin-crossover Materials: Properties and Applications; Halcrow, M. A., Ed.; Wiley: Chichester, U.K., 2013. (b) Halcrow, M. A. Structure:function relationships in molecular spin-crossover complexes. Chem. Soc. Rev. 2011, 40, 4119−4142. (6) Kitchen, J. A.; Brooker, S. Spin crossover in iron(II) complexes of 3,5-di(2-pyridyl)-1,2,4-triazoles and 3,5-di(2-pyridyl)-1,2,4-triazolates. Coord. Chem. Rev. 2008, 252, 2072−2092. (7) Nihei, M.; Shiga, T.; Maeda, Y.; Oshio, H. Spin Crossover Iron(III) Complexes. Coord. Chem. Rev. 2007, 251, 2606−2621. (8) Hauser, A.; Enachescu, C.; Daku, M. L.; Vargas, A.; Amstutz, N. Low-temperature lifetimes of metastable high-spin states in spincrossover and in low-spin iron(II) compounds: The rule and exceptions to the rule. Coord. Chem. Rev. 2006, 250, 1642−1652. (9) Gütlich, P., Goodwin, H. A., Eds. Top. Curr. Chem. 2004, 233 and 234. For an overview, see: Gütlich, P.; Goodwin, H. A. Spin Crossover - An Overall Perspective. Top. Curr. Chem. 2004, 233, 1−47. (10) Ogawa, Y.; Koshihara, S.; Koshino, K.; Ogawa, T.; Urano, C.; Takagi, H. Dynamical Aspects of the Photoinduced Phase Transition in Spin-Crossover Complexes. Phys. Rev. Lett. 2000, 84, 3181−3184. (11) Sato, O.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Photoinduced Magnetization of a Cobalt-Iron Cyanide. Science 1996, 272, 704−705. (12) Hayami, S.; Maeda, Y. Time-dependence of the magnetism of [Fe(pap)2]ClO4 and its solvent adducts; unexpected solid state effect in high-spin⇔low-spin state transition. Inorg. Chim. Acta 1997, 255, 181−184. (13) Hayami, S.; Gu, Z. Z.; Shiro, M.; Einaga, Y.; Fujishima, A.; Sato, O. First Observation of Light-Induced Excited Spin State Trapping for an Iron(III) Complex. J. Am. Chem. Soc. 2000, 122, 7126−7127; Minor erratum. J. Am. Chem. Soc. 2000, 122, 11569. (14) Hayami, S.; Gu, Z.; Yoshiki, H.; Fujishima, A.; Sato, O. Iron(III) Spin-Crossover Compounds with a Wide Apparent Thermal Hysteresis around Room Temperature. J. Am. Chem. Soc. 2001, 123, 11644−11650. (15) Juhasz, G.; Hayami, S.; Sato, O.; Maeda, Y. Photo-induced spin transition for iron(III) compounds with π-π interactions. Chem. Phys. Lett. 2002, 364, 164−170. (16) Hayami, S.; Shigeyoshi, Y.; Akita, M.; Inoue, K.; Kato, K.; Osaka, K.; Takata, M.; Kawajiri, R.; Mitani, T.; Maeda, Y. Reverse Spin Transition Triggered by a Structural Phase Transition. Angew. Chem., Int. Ed. 2005, 44, 4899. (17) Hayami, S.; Hiki, K.; Kawahara, T.; Maeda, Y.; Urakami, D.; Inoue, K.; Ohama, M.; Kawata, S.; Sato, O. Photo-Induced Spin Transition of Iron(III) Compounds with π-π intermolecular interactions. Chem. - Eur. J. 2009, 15, 3497−3508. (18) Komatsu, Y.; Kato, K.; Yamamoto, Y.; Kamihata, H.; Lee, Y. H.; Fuyuhiro, A.; Kawata, S.; Hayami, S. Spin-Crossover Behavior Based on Intermolecular Interactions for Cobalt(II) complexes with Long Alkyl Chains. Eur. J. Inorg. Chem. 2012, 2012, 2769−2775. (19) Nakaya, M.; Shimayama, K.; Takami, K.; Hirata, K.; Alao, A. S.; Nakamura, M.; Lindoy, L. F.; Hayami, S. Spin-crossover and LIESST Effect for Iron(III) Complex Based on π-π Stacking by Coordination Programming. Chem. Lett. 2014, 43, 1058−1060. (20) (a) Jeon, I.-R.; Mathonière, C.; Clérac, R.; Rouzières, M.; Jeannin, O.; Trzop, E.; Collet, E.; Fourmigué, M. Photoinduced reversible spin-state switching of an Fe(III) complex assisted by a halogen-bonded supramolecular network. Chem. Commun. 2017, 53, 10283−10286. (b) Phukkaphan, N.; Cruickshank, D. L.; Murray, K. S.; Phonsri, W.; Harding, P.; Harding, D. J. Hysteretic spin crossover driven by anion conformational change. Chem. Commun. 2017, 53, 9801−9804. (c) Phonsri, W.; Harding, P.; Liu, L.; Telfer, S. G.; Murray, K. S.; Moubaraki, B.; Ross, T. M.; Jameson, G. N. L.; Harding, D. J. Solvent modified spin crossover in an iron(III) complex: phase changes and an exceptionally wide hysteresis. Chem. Sci. 2017, 8, 3949−3959.

(21) Létard, J.-F.; Guionneau, P.; Nguyen, O.; Costa, J. F.; Marsén, S.; Chastanet, G.; Marchivie, M.; Goux-Capes, L. A Guideline to the Design of Molecular-Based Materials with Long-Lived Photomagnetic Lifetimes. Chem. - Eur. J. 2005, 11, 4582−4589. (22) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.; De Caro, L.; Giacovazzo, C.; Polidori, G.; Spagna, R. SIR2004: an improved tool for crystal structure determination and refinement. J. Appl. Crystallogr. 2005, 38, 381−388. (23) Sheldrick, G. M. SHELXT: Integration space group determination and structure solution. Acta Crystallogr., Sect. A: Found. Adv. 2014, 70, C1437. (24) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (25) (a) Scudder, M.; Goodwin, H. A.; Dance, I. G. Crystal supramolecular motifs: two-dimensional grids of terpy embraces in [ML2]z complexes (L = terpy or aromatic N3-tridentate ligand). New J. Chem. 1999, 23, 695−705. (b) Scudder, M.; Dance, I. G. Dimorphic Intra- and Intermolecular Aryl Motifs in Symmetrical Hexafaceted Molecules (ArnX)3Y-Z-Y(XArn)3. Chem. - Eur. J. 2002, 8, 5456−5468. (c) McMurtrie, J.; Dance, I. Engineering grids of metal complexes: development of the 2D M(terpy)2 embrace motif in crystals. CrystEngComm 2005, 7, 216−229. (d) Dance, I. G.; Scudder, M. Molecules embracing in crystals. CrystEngComm 2009, 11, 2233− 2247. (e) McMurtrie, J.; Dance, I. Alternative metal grid structures formed by [M(terpy)2]2+ and [M(terpyOH)2]2+ complexes with small and large tetrahedral dianions, and by [Ru(terpy)2]0. CrystEngComm 2010, 12, 2700−2710. (26) Janiak, C. A critical account on π-π stacking in metal complexes with aromatic nitrogen-containing ligands. J. Chem. Soc., Dalton Trans. 2000, 3885−3896. (27) Ehrlich, E.; Moellmann, J.; Grimme, S. Dispersion-Corrected Density Functional Theory for Aromatic Interactions in Complex Systems. Acc. Chem. Res. 2013, 46, 916−926. (28) Bloom, J. W. G.; Wheeler, S. E. Taking the Aromaticity out of Aromatic Interactions. Angew. Chem., Int. Ed. 2011, 50, 7847−7849. (29) Gavezzotti, A. The ″sceptical chymist″: intermolecular doubts and paradoxes. CrystEngComm 2013, 15, 4027−4035. (30) (a) Gavezzotti, A. Calculation of Intermolecular interaction Energies by Direct Numerical Integration over Electron Densities. I. Electrostatic and Polarization Energies in Molecular Crystals. J. Phys. Chem. B 2002, 106, 4145−4154. (b) Dunitz, J. D.; Gavezzotti, A. Molecular Recognition in Organic Crystals: Directed Intermolecular Bonds or Nonlocalized Bonding ? Angew. Chem., Int. Ed. 2005, 44, 1766−1787. (c) Maloney, A. G. P.; Wood, P. A.; Parsons, S. Use of the PIXEL methods to investigate gas adsorption in metal-organic frameworks. CrystEngComm 2016, 18, 3273−3281. (31) Henry, M. Nonempirical Quantification of Molecular Interactions in Supermolecular Assemblies. ChemPhysChem 2002, 3, 561−569. (32) (a) Serezhkin, V. N.; Serezhkina, L. B.; Vologzhanina, A. V. Voronoi-Dirichelet tesselation as a tool for investigation of polymorphism in molecular crystals with CwHxNyOz composition and photochromic properties. Acta Crystallogr., Sect. B: Struct. Sci. 2012, 68, 305−312. (b) Serezhkin, V. N.; Savchenko, A. V. Application of the Method of Molecular Voronoi-Dirichlet Polyhedra for Analysis of Noncovalent Interactions in Crystal Structures of Flufenamic Acid The Current Record-Holder of the Number of Structurally Studied Polymorphs. Cryst. Growth Des. 2015, 15, 2878−2882. (33) (a) Spackman, M. A.; Jayatilaka, D. Hirshfeld surface analysis. CrystEngComm 2009, 11, 19. (b) Spackman, M. A. Molecules in crystals. Phys. Scr. 2013, 87, 048103. (c) Wolff, S. K.; Grimwood, D. J.; McKinnon, J. J.; Turner, M. J.; Jayatilaka, D.; Spackman, M. A. CrystalExplorer 3.1; University of Western Australia, 2012. (34) Russell, V.; Scudder, M.; Dance, I. The crystal supramolecularity of metal phenanthroline complexes. J. Chem. Soc., Dalton Trans. 2001, 789−799. (35) Nishio, M.; Umezawa, Y.; Honda, K.; Tsuboyama, S.; Suezawa, H. CH/π hydrogen bonds in organic and organoetallic chemistry. CrystEngComm 2009, 11, 1757−1788. H


Article

Inorganic Chemistry (36) Slichter, C. P.; Drickamer, H. G. Pressure-Induced Electronic Changes in Compounds of Iron. J. Chem. Phys. 1972, 56, 2142. (37) (a) Harding, D.; Phonsri, W.; Harding, P.; Murray, K. S.; Moubaraki, B.; Jameson, G. N. L. Abrupt two-step and symmetry breaking spin crossover in an iron(III) complex: an exceptionally wide [LS-HS] plateau. Dalton Trans. 2015, 44, 15079−15082. (b) Vieira, B. J. C.; Coutinho, J. T.; Dias, J. C.; Nunes, J. C.; Santos, I. C.; Pereira, L. C. J.; Gama, V. d.; Waerenborgh, J. C. Crystal structure and spin crossover behaviour of the [Fe(5-Cl-qsal)2] [Ni(dmit)2]·2CH3CN complex. Polyhedron 2015, 85, 643−651. (c) Vieira, B. J. C.; Dias, J. C.; Santos, I. C.; Pereira, L. C. J.; Gama, V. d.; Waerenborgh, J. C. Thermal Hysteresis in a Spin-Crossover FeIII Quinolylsalicylaldimine Complex, FeIII(5-Br-qsal)2Ni(dmit)2·solv: Solvent Effects. Inorg. Chem. 2015, 54, 1354−1362.

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