Charge-Transfer Salts of Biferrocene Derivatives with F2- and F4

Article pubs.acs.org/crystal

Charge-Transfer Salts of Biferrocene Derivatives with F2- and F4‑Tetracyanoquinodimethane: Correlation Between Donor− Acceptor Ratios and Cation Valence States Tomoyuki Mochida,*,†,‡ Yusuke Funasako,† Eri Nagabuchi,‡ and Hatsumi Mori§ †

Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Hyogo 657-8501, Japan Department of Chemistry, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274-8510, Japan § Institute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581, Japan ‡

S Supporting Information *

ABSTRACT: Charge-transfer salts of biferrocene derivatives bearing branched-alkyl substituents [1′-R1-1‴-R2-1,1″-biferrocene; R1 = R2 = isopropylthio (D1), isopropyl (D2), isobutyl (D3), neopentyl (D4), and R1 = isobutyl and R2 = neopentyl (D5)] were prepared and crystallographically characterized. F2- and F4-tetracyanoquinodimethane (TCNQ) produced salts with D/A ratios of 1:3 ([D1][F2TCNQ]3, [D2][F2TCNQ]3), 1:2 ([D2][F 4TCNQ]2, [D3][F4TCNQ]2), 2:3 ([D1]2[F4TCNQ]3), and 1:1 ([D2][F4TCNQ], [D4][F2TCNQ], [D4][F4TCNQ], [D5][F4TCNQ]). [Ni(mnt)2] produced a 1:1 salt [D3][Ni(mnt)2]. Although the biferrocenium salts reported to date contain only monocations, the cation valence in these salts decreases as the donor/acceptor ratio increases; the 1:3 and 1:2 salts contain biferrocenium dications, the 1:1 salts contain mixed-valence biferrocenium monocations, and the intermediate 2:3 salt contains both the dication and monocation. The packing structures of the salts differ significantly despite being composed of donors and acceptors with very similar shapes. The salts are paramagnetic, and their magnetic susceptibility values are consistent with the valence state of the cations. The cations in the 1:1 salts exhibited valence-trapped states because of the local electrostatic interactions between the cation and anion.

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INTRODUCTION The crystal engineering of supramolecular organometallic materials including metallocene-based salts has become an important area of research in recent years.1 Many chargetransfer salts of ferrocene derivatives have been synthesized to date, from the viewpoint of magnetism and electrical conductivity.2−4 Among ferrocene-related organometallics, biferrocene is one of the most well-known electron donors and exhibits three redox states (Figure 1): neutral, monocation,

Recently, we have investigated the preparation and properties of biferrocenium salts with FnTCNQ (n = 0, 1, 4; TCNQ = tetracyanoquinodimethane) and [M(mnt)2] anions (mnt = maleonitriledithiolate; M = Ni, Co), which contain mixedvalence monocations.6 These salts exhibit intriguing physical properties such as magnetism, dielectric properties,6c electrical conduction,6a and phase transition phenomena.6b,c Several Mössbauer spectroscopy studies on biferrocene−TCNQ salts have been reported in the literature.7 The correlation between the valence states and the assembled structures of biferrocenium salts are especially interesting from the viewpoint of crystal engineering. In this study, we have prepared charge-transfer salts of a series of biferrocene derivatives bearing branched-alkyl substituents [1′-R1-1‴-R2-1,1″-biferrocene; R1 = R2 = isopropylthio (D1), isopropyl (D2), isobutyl (D3), neopentyl (D4), and R1 = isobutyl and R2 = neopentyl (D5)] (Figure 2a). D5 is an unsymmetrical donor having an intermediate molecular volume between that of D3 and D4. Ten salts with F2TCNQ, F4TCNQ, and [Ni(mnt)2] were obtained and

Figure 1. Three redox states of biferrocene.

and dication. Electron transfer in mixed-valence monocation salts has attracted considerable attention. The investigation of these salts by Mössbauer spectroscopy and other methods has revealed that their valence states are affected by molecular symmetry and the crystalline environment.5 © 2014 American Chemical Society

Received: January 2, 2014 Revised: February 1, 2014 Published: February 13, 2014 1459

dx.doi.org/10.1021/cg500006e | Cryst. Growth Des. 2014, 14, 1459−1466

Crystal Growth & Design

Article

Table 1. Summary of the Biferrocenium Salts Derived from D1−D5 compound 1 2 3 4

5

6 7 8 9

10 11a

Figure 2. (a) Donors and (b) acceptors used in this study.

12a 13b a

crystallographically characterized. Although the biferrocenium salts reported to date almost exclusively contain monocations, these salts were found to contain dications, monocations, or both. The structures and valence states of related salts, [D1]2[Ni(mnt)2]3, [D2][Ni(mnt)2], and [D4][Ni(mnt)2], were reported previously.6c,8

D/A ratio

structure type

valence state

FnTCNQ Salts with Dications [D1][F2TCNQ]3 1:3 1:3 mixed[D]2+[A3]2− stack [D2][F2TCNQ]3 1:3 (anion [D]2+[A3]2− column) [D2][F4TCNQ]2 1:2 c [D]2+[A2]2− [D3][F4TCNQ]2 1:2 segregated[D]2+[A2]2− stack FnTCNQ Salt with Dication and Monocation [D1]2[F4TCNQ]3 2:3 segregated[D]2+[D]+[A3]3− stack FnTCNQ Salts with Monocations [D3][F4TCNQ] 1:1 2:2 mixed[D]+[A]− stack [D4][F2TCNQ] 1:1 c [D]+[A]− [D4][F4TCNQ] 1:1 2:2 mixed[D]+[A]− stack [D5][F4TCNQ] 1:1 2:2 mixed[D]+[A]− stack [Ni(mnt)2] Salts [D3][Ni(mnt)2] 1:1 c [D]+[A]− [D2][Ni(mnt)2] 1:1 segregated[D]+[A]− stack [D4][Ni(mnt)2] 1:1 c [D]+[A]− [D1]2[Ni(mnt)2]3 2:3 segregated[D]2+[D]+[A3]3− stack

Ref 6c. bRef 8. cNo stacking structures.

appears similar to D4 because of the disorder of the substituents. Valence States. Biferrocene derivatives can be monocationic (D+) or dicationic (D2+) (Figure 1), and intramolecular Fe−Cp(centroid) and Fe−C(Cp) distances are reliable criteria for the determination of their valence state (Cp = cyclopentadienyl ring). The investigation of the cation geometries revealed that their valence states depend on the D/ A stoichiometry; the 1:3 and 1:2 salts (1−4) contain dications (D2+), the 1:1 salts (6−10) contain monocations (D+), and the intermediate 3:2 salt (5) contains both a dication and monocation (average D1.5+). The Fe−Cp(centroid) distances in 1−10 are shown in Figure 4 and are also listed in Table 2 along with the Fe−C(Cp) distances. The average Fe− Cp(centroid) distance for D2+ is 1.705 Å (1.704−1.706 Å, in 1−4), while that for D+ is 1.675 Å (1.670−1.679 Å, in 6−10). The distance in 5 (1.690 Å) is intermediate between those of D2+ and D+, indicating that this salt contains a 1:1 mixture of D2+ and D+ in the cation site. These are consistent with the anion charge and magnetic susceptibilities, as shown below. In the monocations in 6−10, the Fe−Cp(centroid) distances in the Fe1 and Fe2 sites differ, indicating a valence-trapped state, where Fe1 and Fe2 sites are cationic and neutral, respectively. The differences for 7 and 10 are large (∼0.05 Å), indicating complete valence trapping, whereas those for 6, 8, and 9 are smaller (∼0.02 Å), suggesting incomplete valence trapping.6c The tendencies of the Fe−C(Cp) distances are consistent with those of the Fe−Cp(centroid) distances, although there is some scattering in the individual Fe−C(Cp) distances. The valence-trapping tendency of the monocation salts is attributed to local Fe···NC electronic interactions between the cations and anions.6c,d In 6−9, the cationic sites (Fe1) are surrounded by three or four cyano groups, whereas the neutral

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RESULTS AND DISCUSSION General Structural Features. Compositions and structure types of the salts prepared in this study (1−10) and related salts (11−13)6c,8 are summarized in Table 1. Three F2TCNQ salts and six F4TCNQ salts were obtained, which exhibited various D/A ratios of 1:3 (1 and 2), 1:2 (3 and 4), 2:3 (5), and 1:1 (6−9). The reaction of D3 and F4TCNQ produced both the 1:2 and the 1:1 salt (4 and 6), depending on the crystallization conditions. Because FnTCNQ (n = 0, 1) afforded only 1:3 salts,6a,b such variation in the D/A ratio was unexpected. Most of the salts exhibit either segregated-stacklike or mixed-stack-like assembled structures, though several salts have no stacking structures and belong to neither category. Biferrocenium−TCNQ salts having similar substituents often exhibit similar crystal structures, partly because the cations are bulky.6a,e However, the packing structures of these salts differs significantly, despite being composed of similar donors and acceptors. There were no π−π contacts between the donors except for in 5 because of the steric hindrance of the donor substituents. However, there were some π−π contacts between the cation and anion in the mixed-stack salts. The acceptors in all the salts exhibit π−π interactions to form dimers or trimers. The molecular structures of the cations in each salt are shown in Figure 3. The cations in 1 and 3 are located on the crystallographic inversion center and are centrosymmetric, whereas the other cations are unsymmetrical. One of the substituents of the cations in 2 and 10 and both substituents in 6 exhibit 2-fold disorder. The unsymmetrical cation D5 in 9 1460



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Table 2. Intramolecular Distances around Fe in 1−10 salts

site

Fe−Cpa/Å

1 2

Fe1 Fe1 Fe2 Fe1 Fe1 Fe2 Fe1 Fe2 Fe1 Fe2 Fe1 Fe2 Fe1 Fe2 Fe1 Fe2 Fe1 Fe2

1.706 1.704 1.705 1.704 1.705 1.706 1.695 1.685 1.685 1.662 1.702 1.655 1.688 1.663 1.681 1.659 1.702 1.650

3 4 5 6 7 8 9 10 a

Fe−C(Cp)/Å 2.089 2.082 2.083 2.091 2.085 2.087 2.082 2.070 2.064 2.042 2.084 2.048 2.072 2.051 2.066 2.049 2.081 2.040

(2.151(6)−2.047(6)) (2.150(8)−2.03(10)) (2.123(8)−2.038(9)) (2.132(2)−2.064(2)) (2.124(3)−2.058(4)) (2.111(4)−2.056(4)) (2.144(5)−2.045(4)) (2.136(5)−2.036(6)) (2.11(10)−2.011(9)) (2.056(6)−2.02(10)) (2.132(3)−2.054(3)) (2.072(3)−2.036(4)) (2.130(4)−2.031(5)) (2.063(4)−2.039(6)) (2.132(4)−2.033(5)) (2.082(5)−2.035(5)) (2.138(3)−2.053(3)) (2.061(4)−2.026(3))

Distance between Fe and the centroid of the Cp ring.

complete valence trapping. The ferrocenium sites in 1−4 are surrounded by three or four cyano groups. The charges on the acceptors, estimated from the intramolecular bond lengths,9 are consistent with the cation charges. In 1−2, three acceptor molecules accommodate two electrons, and their charge distribution is described below. The acceptors in 3−9 are monoanions, which form diamagnetic dimers in the crystals, except in the case of 5. [Ni(mnt)2] in 10 is a monoanion having virtually the same molecular geometry (average Ni−S distance: 2.14 Å) as that in [nBu4N][Ni(mnt)2].10 This anion also forms diamagnetic dimers. Structures of the 1:3 Salts. [D1][F2TCNQ]3 (1) and [D2][F2TCNQ]3 (2) are 1:3 salts containing biferrocenium dications. Their assembled structures are shown in Figure 4, panels a and b, respectively, and differ significantly from one another. In the crystal structure of 1, the acceptors form centrosymmetric trimers, and the trimers and donors are stacked alternately, forming a 1:3 mixed-stack structure (Figure 5a). The distance between the centroids of adjacent acceptors in the trimer is 3.37 Å and that between the neighboring donor and acceptor is 3.81 Å. The charges on the central and outer acceptors in the trimer, as estimated from the bond lengths, are −1 and −0.5, respectively,9 and therefore the total charge of the trimer is −2. In the crystal structure of 2, the acceptor molecules form a twisted stacking structure, and the cations are located between the acceptor columns (Figure 5b). There are three crystallographically independent acceptors (I, II, and III) in the column. The short distance between the centroids of I and II (3.31 Å), which is much shorter than those of II−III (4.00 Å) and I−III (4.29 Å), indicates the formation of a diamagnetic dimer. This feature suggests that I and II are essentially monoanions, while III is neutral. The charge distribution, estimated from the bond lengths, for these acceptors are −0.4, −1.2, and −0.1, respectively. The negative charges on I and II seem to be under- and overestimated, respectively, likely because of estimation errors. The higher negative charge on the central molecule II in the trimer unit of I, II, and III may result from its interactions with I and III. The overlap integral between the SOMO of the acceptors in the dimer (23.2 × 10−3) is much

Figure 3. ORTEP drawing of the cations in 1−10. One of the disordered moieties is displayed in gray. Hydrogen atoms have been omitted for clarity.

Figure 4. Fe−Cp(centroid) distances of the cations in 1−10 (a and b denote the Fe1 and Fe2 sites, respectively). The average distances for D2+, D1.5+, and D+ are indicated by dotted lines.

sites (Fe2) are surrounded by one or two cyano groups and the alkyl substituents of the donors. The Fe···CN distances are between 4.2−4.7 Å in most cases. In 10, two cyano groups are close to Fe1 only, which is consistent with the valence-trapping tendency. In particular, 7 and 10 have very short Fe···NC distances (7: 4.210(3), 10: 4.073(4) Å), which account for their 1461



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Figure 6. Packing diagrams of 1:2 salts: (a) [D2][F4TCNQ]2 (3) and (b) [D3][F4TCNQ]2 (4). Only the molecules near the (001) plane are shown for clarity. Figure 5. Packing diagrams of 1:3 salts: (a) [D1][F2TCNQ]3 (1) and (b) [D2][F2TCNQ]3 (2). Dotted lines indicate the formation of trimers of the acceptors.

larger than those of II−III (5.8 × 10−3) and I−III (0.46 × 10−3). The assembled structures and valence states of 1 and 2 are very different from those of previously reported [D]+[A3]− salts [R 2 Bifc][TCNQ] 3 (R = butyl-, propyl-) 6a and [D4][FnTCNQ]3 (n = 0, 1).6b These salts have simple segregatedstack and 1:3 mixed-stack structures, respectively. The valence state of [D]2+[A3]2− in the present salts is ascribed to the stronger electron affinity of F2TCNQ. Structures of the 1:2 Salts. [D2][F4TCNQ]2 (3) and [D3][F4TCNQ]2 (4) are 1:2 salts containing biferrocenium dications. Their packing diagrams are shown in Figure 6, panels a and b, respectively. The F4TCNQ anions form diamagnetic dimers in both salts, but the assembled structures are very different from one another. In 3, the anion dimers are surrounded by eight cations, and no stacking structure is formed. The distance between the centroids of the acceptors in the dimer is 3.260 Å. Salt 4 exhibits a segregated-stack structure with a highly twisted dimer arrangement of the acceptors in the column. Structure of the 2:3 Salt. The packing diagram of the 2:3 salt [D1]2[F4TCNQ]3 (5) is shown in Figure 7. This salt exhibits a segregated-stack structure. The F4TCNQ mono-

Figure 7. Packing diagram of the 2:3 salt: [D1]2[F4TCNQ]3 (5). Dotted lines indicate the formation of trimers of the acceptors.

anions form a centrosymmetric trimer, which further constitutes one-dimensional stacking columns along the a1462



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Figure 8. Packing diagram of 1:1 salts: (a) [D3][F4TCNQ] (6), (b) [D4][F2TCNQ] (8), and (c) [D5][F4TCNQ] (9).

axis. The distance between the centroids of F4TCNQ in the trimer is 3.40 Å, and that between the trimers is 5.69 Å. The Fe−Cp distance indicates that the Fe1 and Fe2 sites contain Fc+ and Fc+0.5, respectively. This indicates that the cation site accommodates D+ and D2+ in a 1:1 ratio and that the cationic site of D+ is localized on the Fe1 site. No superlattice reflections were observed by X-ray diffraction measurements, indicating the random inclusion of D+ and D2+. The charge localization in D+ is ascribed to the stronger electrostatic interaction of the Fe1 site with the acceptors. The Fe···NC distances for Fe1 (4.205(5) and 4.308(5) Å) were shorter than that for Fe2 (4.320(5) Å). The valence state of this salt is similar to that of [D1] 2 [Ni(mnt) 2 ] 3 (13), 8 which is represented as [D]+[D]2+[A3]2−, but the D2+ and D+ occupy different sites in 13, as determined by crystallographic measurements. Structures of the 1:1 Salts. [D3][F4TCNQ] (6), [D4][F 2 TCNQ] (7), [D4][F 4 TCNQ] (8), and [D5][F4TCNQ] (9) are 1:1 salts, and their structures closely resemble each other, although none are isomorphous. The packing diagrams of 6, 8, and 9 are shown in Figure 8, panels a, b, and c, respectively. The structures resemble that of [diethylbiferrocene][F4TCNQ].6a These salts contain biferrocenium monocations with valence-trapped states, and the charge localization on Fe1 is due to the Fe···CN-local electrostatic interactions. The acceptors form diamagnetic dimers (centroid−centroid distances: 3.24−3.28 Å). Their assembled structures are composed of a unit of two biferrocenium cations bridged by the acceptor dimer via the Fe···NC interactions. When viewed perpendicular to the acceptor plane, 6, 8, and 9 are regarded as 2:2 mixed-stack structures (...[D][D][A][A]...) because of the π−π contacts between the acceptor and the Cp ring of the adjacent donor (centroid−centroid distances: 4.05−4.41 Å), while 7 has no such donor−acceptor π−π contacts. The substituents in 6 and 9 exhibit extensive disorder, which accompanies a 2-fold disorder of the adjacent acceptor around the molecular long axis. The packing diagram of [D3][Ni(mnt)3] (10) is shown in Figure 9. This salt has no stacking structure and resembles [D4][Ni(mnt)2].6c The Fe1···NC distance between the anion and cation is short (4.073(4) Å), which causes charge localization. The [Ni(mnt)2] anion forms centrosymmetric dimers with intermolecular S···S contacts (3.547(2) Å).

Figure 9. Packing diagram of [D3]2[Ni(mnt)3]2. Dotted lines indicate short Fe···NC distances.

Magnetic Susceptibilities. Magnetic susceptibilities of 1, 2, 3, 5, and 8 are shown in Figure 10 in the form of χT vs T plots. The χT value at room temperature for 5 is 1.81 emu K mol−1, those for 1−3 are 1.22−1.33 emu K mol−1, and that for

Figure 10. The temperature dependence of the magnetic susceptibilities of 1−3, 5, and 8, represented in the form of χmT vs T. 1463



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8 is 0.54 emu K mol−1. The χT values for the ferrocenium cations are 0.5−0.7 emu K mol−1.4,6c Therefore, these values consistently correspond to three spins from [D]2+[D]+, two spins from [D]2+, and one spin from [D]+, respectively. The contribution of the anion spins is small because they form singlets in the dimer, or trimer units in the salts. In the case of 5, the spins are antiferromagnetically coupled in the columnar structure. The temperature independent behaviors in 2, 3, and 8 are typical of biferrocenium salts. In contrast, the χT values of 1 and 5, which contain D1, decrease with decreasing temperature. This is ascribed to the temperature-dependent loss of orbital contribution or intramolecular antiferromagnetic interactions in D2+ caused by the effects of the sulfur substituents, as also observed for [D1]2[Ni(mnt)2]3.8 Salt 1 becomes almost diamagnetic at 2 K likely because of singlet formation in the dication; 5 exhibits a value corresponding to one spin even at 2 K, which is probably because of the contribution of the monocation, while the contribution of the dication is lost.

of Celite. The solvent was evaporated, and the residue was purified by column chromatography (silica gel, eluent: ethyl acetate/hexane 1:26). The first and second bands contained 1-bromo-1′-neopentylferrocene and 1′,1‴-diisobutylbiferrocene, respectively. The third band contained 1-isobutyl-1‴-(1-hydroxyneopentyl)biferrocene, which was purified by recrystallization from hexane (orange crystals, 121 mg, 13.9% yield). Under a dinitrogen atmosphere, lithium aluminum hydride (35 mg, 0.93 mmol) and AlCl3 (31 mg, 0.23 mmol) were successively added in small portions to a diethyl ether solution (10 mL) of the obtained 1′-isobutyl-1‴-(1-hydroxyneopentyl)biferrocene (121 mg, 0.232 mmol). After overnight stirring, the reaction was quenched with a small amount of methanol and water, and the solution was extracted with diethyl ether. The organic layer was washed twice with water and saturated aqueous NaCl solution and dried over magnesium sulfate, and the solvent was removed by evaporation. The crude product was further purified by column chromatography (silica gel, eluent: hexane). Orange crystals, 51 mg (yield 44%). 1H NMR (CDCl3, ppm): 4.22 (t, 4H), 4.10 (t, 4H), 3.86 (t, 4H), 3.80 (t, 4H), 2.02 (m, 4H), 1.51 (m, 1H), 0.76 (d, 6H), 0.73 (s, 9H). Charge-Transfer Salts. [D1][F2TCNQ]3 (1), [D2][F2TCNQ]3 (2), [D2][F4TCNQ]2 (3), and [D3][F4TCNQ]3 (4) were obtained as dark violet crystals by the vapor diffusion of pentane into a dichloromethane solution of the donor and acceptor. The salts were obtained in ∼10−40% yields, depending on the amount of the solvents used, with the exception of 4, which was obtained in very low yield. 1: Anal. Calcd for C62H36 N12F6Fe2S2: C, 60.11; H, 2.93; N, 13.57. Found: C, 58.95; H, 2.99; N, 13.38. IR (cm−1): 3115, 3105, 3055, 2187 (CN), 2166, 1611, 1541, 1520, 1481, 1464, 1458, 1414, 1395, 1371, 1348, 1310, 1242, 1206, 1146, 1070, 891, 883, 849. 2: Anal. Calcd for C62H36 N12F6Fe2: C, 63.39; H, 3.09; N, 14.31. Found: C, 63.10; H, 3.18; N, 14.28. IR (cm−1): 3119, 3103, 3086, 3061, 3047, 2187 (CN), 2166, 1611, 1574, 1526, 1485, 1377, 1348, 1300, 1252, 1207, 1182, 1153, 1138, 1067, 1028, 1013, 889, 864. 3: Anal. Calcd for C50H30N8F8Fe2: C, 59.66; H, 3.00; N, 11.14. Found: C, 59.41; H, 3.23; N, 11.03. IR (cm−1): 3114, 2194 (CN), 1637, 1541, 1501, 1400, 1352, 1337, 1265, 1197, 1145, 1060, 968, 859. 4: IR (cm−1): 3115, 3098, 2955, 2901, 2870, 2195 (CN), 2176, 1531, 1393, 1348. Microanalysis was not possible because of the very low yield. [D1]2[F4TCNQ]3 (5) was obtained as dark green crystals by the slow diffusion of a solution of the acceptor in ethyl acetate into a solution of the donor. Anal. Calcd for C88H60N12F12Fe4S4: C, 56.67; H, 3.24; N, 9.01. Found: C, 56.47; H, 3.33; N, 8.81. IR (cm−1): 3098, 2357, 2347, 2332, 2195 (CN), 2176, 1636, 1533, 1497, 1418, 1391, 1369, 1346, 1339, 1242, 1198, 1153, 1144, 1111, 1059, 968, 885, 849, 841, 822. [D3][F4TCNQ] (6), [D4][F2TCNQ] (7), [D4][F4TCNQ] (8), and [D5][F4TCNQ] (9) were obtained as dark violet crystals by slow cooling a dichloromethane solution of the donor and acceptor to −30 °C. 6: Anal. Calcd for C40H34N4Fe2F4: C, 63.35; H, 4.52; N, 7.39. Found: C, 62.46; H, 4.54; N, 7.27. IR (cm−1): 3096, 2957, 2195(CN), 2176(CN), 1533, 1508, 1499, 1393, 1341, 970. 7: Anal. Calcd for C42H40N4F2Fe2: C, 67.22; H, 5.37; N, 7.47. Found: C, 67.43; H, 5.51; N, 7.58. IR (cm−1): 3340, 2956, 2216, 2193 (CN), 1610, 1517, 1475, 1361, 1346, 1251, 1220, 1197, 1163, 1111, 1058, 1028, 869. 8: Anal. Calcd for C42H38N4F4Fe2: C, 64.14; H, 4.87; N, 7.13. Found: C, 64.16; H, 5.04; N, 7.17. IR (cm−1): 3461, 3097, 2958, 2194 (CN), 2177, 1631, 1529, 1498, 1390, 1361, 1340, 1236, 1197, 1143, 970, 819. 9: Anal. Calcd for C41H36N4Fe2F4: C, 63.75; H, 4.70; N, 7.25. Found: C, 63.52; H, 4.75; N, 7.22. [D3]2[Ni(mnt)3]2 (10) was obtained as black plate crystals by the vapor diffusion of pentane into a dichloromethane solution of equimolar amounts of the donor and [Fe(C5H5)2][Ni(mnt)2]. Anal. Calcd for C62H36 N12F6Fe2S2: C, 60.11; H, 2.93; N, 13.57. Found: C, 58.95; H, 2.99; N, 13.38. IR (cm−1): 3109, 2961, 2949, 2870, 2372, 2359, 2353, 2342, 2334, 2226, 2205 (CN), 1526, 1506, 1464, 1435, 1385, 1368, 1329, 1260, 1202, 1159, 1111, 1034, 1022, 1001, 918, 899, 876, 845, 829. X-ray Crystallography. X-ray data for were collected on a Bruker SMART APEX CCD and Rigaku Mercury diffractometers using Mo(Kα) radiation (λ = 0.71069 Å). Crystallographic parameters are listed in Tables 3 and 4. The structures were solved by the direct

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CONCLUSION Charge-transfer salts of biferrocene derivatives bearing branched-alkyl substituents were prepared. F2- and F4TCNQ produced salts with varying D/A ratios of 1:3−1:1. Although the biferrocenium salts reported to date almost exclusively contain monocations, the salts reported herein contain biferrocenium monocation in the 1:1 salts, dication in the 1:2 and 1:3 salts, and both in the intermediate 2:3 salt. The donor/ acceptor ratios seem to determine the cation valence. Although biferrocenium−TCNQ salts having similar substituents often exhibit similar crystal structures, the packing structures of the salts differed significantly despite using donors and acceptors with very similar shapes. The salts are paramagnetic, and their magnetic susceptibility values are consistent with the valence state of the cations. The cations in the 1:1 salts exhibited valence-trapped states, resulting from the local Fe···NC electrostatic interactions between the cation and anion. The dependence of the cation valence states in the biferrocenium salts of FnTCNQ (n = 0−4) has been reported in this and in related studies.6 On the basis of these relationships, the preparation of salts whose valence state is controllable by external stimuli is currently under progress in our laboratories.

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EXPERIMENTAL SECTION

General. 1H NMR spectra were measured on a JEOL ECP-400 Fourier transform spectrometer. Infrared spectra were recorded on a SHIMADZU Prestige-21 FTIR-8400S spectrometer attached to an AIM-8800 microscope in the 4000−400 cm−1 range. The temperature dependence of the magnetic susceptibilities was measured from 300 to 2 K using a Quantum Design MPMS-XL SQUID magnetometer under a magnetic field of 5000 G. The core diamagnetic components were corrected by calculation using Pascal’s constants. Intermolecular overlap integrals were calculated by the extended Hückel molecular orbital method.13 Materials. F4TCNQ was purchased from TCI. 1′,1‴-Bis(isobutylthio)-1,1″-biferrocene (D1),8 1′,1‴-diisopropyl-1,1″-biferrocene (D2),6c 1′,1‴-diisobutyl-1,1″-biferrocene (D3),11 1′,1‴-dineopentyl-1,1″-biferrocene (D4),6c F2TCNQ,12 and [Fe(C5H5)2][Ni(mnt)2]14 were prepared using literature methods. 1-Isobutyl-1‴neopentyl-1′,1″-biferrocene (D5) was prepared as follows: activated copper (527 mg, 8.3 mmol), was added to a mixture of 1-bromo-1′-(1hydroxyneopentyl)ferrocene (300 mg, 0.83 mmol) and 1-isobutyl-1′bromoferrocene (267 mg, 0.83 mmol),6c and the mixture was heated at 135 °C for 2 days under a nitrogen atmosphere. The resultant solid was extracted with dichloromethane and filtered through a short plug 1464



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Table 3. Crystallographic Parameters for 1−5 formula formula weight T [K] crystal system space group a [Å] b [Å] c [Å] α [°] β [°] γ [°] V [Å3] Z dcalcd [g cm−3] μ [cm−1] F(000) reflection collected independent reflection parameters refl/parameter ratio R1a, wR2b (I > 2σ(I)) R1a, wR2b (all data) goodness of fit completeness (%) a

1

2

3

4

5

C62H36N12Fe2S2F6 1238.85 173 triclinic P1̅ 8.8461(13) 10.3280(15) 15.349(2) 107.093(3) 103.143(3) 94.373(3) 1289.8(3) 1 1.595 7.23 630 9568 6373 381 16.73 0.0766; 0.2108 0.1244; 0.2385 1.038 98.5

C62H36N12Fe2F6 1174.73 298 monoclinic P21 8.9102(11) 19.302(2) 15.1245(18)

C50H30N8Fe2F8 1006.52 100 triclinic P1̅ 8.618(3) 10.569(5) 11.615(5) 102.884(6) 90.817(6) 94.545(6) 1027.5(7) 1 1.627 7.92 510 8525 4130 309 13.37 0.0415; 0.1135 0.0427; 0.1147 1.024 98.2

C52H34N8Fe2F8 1034.57 298 orthorhombic Pbca 23.7236(9) 13.0622(5) 29.5079(12)

C44H30N6Fe2F6S2 932.56 173 triclinic P1̅ 11.373(2) 12.066(2) 15.327(3) 79.997(4) 72.885(4) 73.854(4) 1921.0(7) 2 1.612 9.37 948 12351 7803 545 14.32 0.0597; 0.1504 0.1017; 0.1702 1.035 99.3

94.102(2) 2594.5(5) 2 1.504 6.37 1196 15600 5891 769 7.66 0.0526; 0.0885 0.1339; 0.1084 1.02 99.9

9144.0(6) 8 1.503 7.15 4208 57265 9349 632 14.78 0.0498; 0.1124 0.0888; 0.1306 1.012 99.9

R1 = Σ||Fo| − |Fc||/Σ|Fo|. bRw = [Σw(Fo2 − Fc2)2/Σw(Fo2)2]1/2.

Table 4. Crystallographic Parameters for 6−10 formula formula weight T [K] crystal system space group a [Å] b [Å] c [Å] α [°] β [°] γ [°] V [Å3] Z dcalcd [g cm−3] μ [cm−1] F(000) reflection collected independent reflection parameters refl/parameter ratio R1a, wR2b (I > 2σ(I)) R1a, wR2b (all data) goodness of fit completeness (%) a

6

7

8

9

10

C40H34N4Fe2F4 758.41 298 monoclinic C2/m 20.898(4) 12.177(2) 15.722(3)



C41H36N4Fe2F4 772.44 298 monoclinic C2/c 29.4296(19) 12.2475(7) 21.0413(11)

C36H34N4Fe2NiS4 821.32 298 monoclinic P21/c 8.226(3) 21.294(7) 20.955(6)

103.236(2)

95.088(6)

7382.6(7) 8 1.390 8.41 3184 21680 6760 512 13.20 0.0557; 0.1608 0.0984; 0.1885 1.046 99.9

3656.1(19) 4 1.492 15.53 1688 22924 7472 454 16.46 0.0522; 0.1363 0.0629; 0.1476 1.042 99.8

114.889(3) 3629.5(11) 4 1.388 8.54 1560 11218 3881 296 13.11 0.0852; 0.2637 0.1200; 0.2949 1.078 99.8

R1 = Σ∥Fo| − |Fc∥/Σ|Fo| bRw = [Σw(Fo2 − Fc2)2/Σw(Fo2)2]1/2.

methods (SHELXS-9715), and the non-hydrogen atoms were refined anisotropically. The hydrogen atoms were placed at idealized positions and allowed to ride on the relevant heavier atoms. Empirical absorption corrections were applied. Molecular structures and packing diagrams were drawn using ORTEP-3 for windows16 and Mercury 3.1,17 respectively.

Crystallographic data for the structures in this paper were deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC 263336 (1), 977134 (2), 978733 (3), 978734 (4), 263335 (5), 978735 (6), 978736 (7), 978737 (8), 978738 (9), and 977135 (10). 1465



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Inorg. Chem. 2005, 44, 8628−8641. (d) Mochida, T.; Kobayashi, T.; Akasaka, T. J. Organomet. Chem. 2013, 741−742, 72−77. (e) Mochida, T.; Funasako, Y.; Yamazaki, S.; Mori, H., submitted. (7) (a) Iijima, S.; Mizutani, F. Mol. Cryst. Liq. Cryst. 1998, 322, 79− 84. (b) Nakashima, S.; Iijima, S.; Motoyama, I.; Katada, M.; Sano, H. Hyperfine Interact. 1988, 40, 315−318. (c) Iijima, S.; Saida, R.; Motoyama, I.; Sano, H. Bull. Chem. Soc. Jpn. 1981, 54, 1375−1379. (8) Mochida, T.; Nagabuchi, E.; Takahashi, M.; Mori, H. Chem. Commun. 2014, 50, 2481−2483. (9) (a) Kistenmacher, T. J.; Emage, T. J.; Bloch, A. N.; Cowan, D. O. Acta Crystallogr. 1982, B38, 1193−1199. (b) Stang, S. L.; Conan, F.; Pala, J. S.; Mest, Y. L.; Garland, M-. T.; Baggio, R.; Faulquest, E.; Leblanc, A.; Molinie, P.; Toupet, L. J. Chem. Soc., Dalton Trans. 1998, 489−496. (c) Wiygul, F. M.; Ferraris, J. P.; Emge, T. J.; Kistenmacher, T. J. Mol. Cryst. Liq. Cryst. 1981, 78, 279−293. (10) Mochida, T.; Suzuki, S.; Moriyama, H.; Terao, H.; Sugawara, T. Acta Crystallogr. 2000, C56, 1183−1184. (11) Nakashima, S.; Masuda, Y.; Motoyama, I.; Sano, H. Bull. Chem. Soc. Jpn. 1987, 60, 1673−1680. (12) Mochida, T.; Hasegawa, T.; Kagoshima, S.; Sugiura, S.; Iwasa, Y. Synth. Met. 1997, 86, 1797−1798. (13) Mori, T.; Kobayashi, A.; Sasaki, Y.; Kobayashi, H.; Saito, G.; Inokuchi, H. Bull. Chem. Soc. Jpn. 1984, 57, 627−633. (14) Hobi, M.; Zürcher, S.; Gramlich, V.; Burckhardt, U.; Mensing, C.; Spahr, M.; Togni, A. Organometallics 1996, 15, 5342−5346. (15) Sheldrick, G. M. Acta Crystallogr. 2008, D64, 112−122. (16) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−838. (17) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; van de Streek, J.; Wood, P. A. J. Appl. Crystallogr. 2008, 41, 466−470.

ASSOCIATED CONTENT

S Supporting Information *

X-ray crystallographic information files are available for 1−10. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel/Fax: +81-78803-5679. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported financially by KAKENHI Grant Number 23110719 from MEXT. We thank K. Takazawa, R. Kiso, and M. Saito (Toho University) for sample preparation. This work was performed using facilities of the Institute for Solid State Physics, the University of Tokyo.

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REFERENCES

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Charge-Transfer Salts of Biferrocene Derivatives with F2- and F4

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