Reversible Electron Transfer in a Linear {Fe2Co} Trinuclear Complex Induced by Thermal Treatment and Photoirraditaion

• DOI: 10.1002/anie.201201305
• Publication Date: 2012-03-22T22:25:46Z
• Authors: Tao Liu; Da‐Peng Dong; Shinji Kanegawa; Soonchul Kang; Osamu Sato; Yoshihito Shiota; Kazunari Yoshizawa; Shinya Hayami; Shuo Wu; Cheng He; Chun‐Ying Duan
• Keywords: Thermal Treatment

A light change: linear cyanido-bridged Fe2Co compound (see picture) exhibits a reversible, thermally induced cooperative charge transfer transition accompanying spin and polar–nonpolar transformation in the trinuclear cluster. The change magnetic properties polarity could also be by irradiation with light. Bistable materials possess two close-lying states, which can reversibly interchanged external stimuli such as temperature, light, pressure, guest molecules.1 These offer attractive opportunities for realization of energy-efficient, switchable, molecule-based data storage electronic devices.2 current topic research this field is preparation switchable multifunctional molecules more than coexist or interact synergistically.3 An important shows significant both distribution (polarization) at molecular level. Tunable molecules, spin-crossover complexes, are recording devices.4 Furthermore, an essential feature regulating nonlinear optical ferroelectric properties.5 In particular, study ferroelectricity, order without inversion symmetry responsible electric polarization, has recently attracted attention.6, 7 Thus, it to design new compounds state controlled stimuli. To end, development that consist paramagnetic donors acceptors attracting considerable interest because lattice distortion charge-transfer processes involve not only concomitant spin-state changes but their dielectric properties.8, 9 Significant susceptibility constant were observed near neutral–ionic phase temperature complexes.8 dimerization donor acceptor induces formation polar structure from nonpolar breaking center result transfer. Moreover, been reported dinuclear cobalt complex dioxolene bridging ligand between (donor/acceptor) (acceptor/donor) irradiation.9 This accompanied magnetization cluster, molecular-level representation interconversion polarization similar aforementioned complex. With rational design, various discrete multinuclear complexes have synthesized using different building blocks cyanometallates.10 However, until now, cobalt-dioxolene system show through response thermal Therefore, remains challenge. work, we aimed synthesizing bimetallic clusters centrosymmetrical structures capable metal ion on edge. process was expected induce multiplicity.11 cluster one. synthesize centrosymmetric choose [FeTp(CN)3]− (Tp=hydrotris(pyrazolyl)borate) block treat [Co(Meim)4]2+ (Meim=N-methylimidazole). One cyanide bridge unit thought coordinate CoII ion, tunes redox potential required terminal ligands form hydrogen-bonding interactions noncoordinated solvent stabilizing bistable intermolecular interactions. fact, {[FeTp(CN)3]2Co(Meim)4}⋅6 H2O (1), sandwiched iron (Scheme 1). Compound 1 exhibited induced, reversible electron hysteresis photoinduced excitation band. a) Structure [Fe(Tp)(CN)3]− block. b) [Co(N-methylimidazole)4]2+ c) Arrangement electron-transfer-induced molecule. Single-crystal X-ray diffraction (XRD) analysis revealed crystallizes space group. crystal comprises neutral {[FeTp(CN)3]2Co(Meim)4} (Figure water located b). Within three nitrogen atoms Tp carbon coordinated each center. Each N6 octahedral environment four Meim equatorial plane monodentate apical position. comprised one unique Three ions array Fe1–Co1–Fe1 (symmetry codes 1−x, 1−y, 1−z) angle 180.0°. hydrogen bonds formed (O⋅⋅⋅O distance 2.76–2.92 Å) (O⋅⋅⋅N 2.75–2.94 S1), providing strong needed stabilize state. Side view arrangement 240 K 150 K. Packing diagram along axis H omitted clarity. Fe green, Co teal, C gray, N blue, B yellow, O red. At K, elongated short CoNMeim distances 2.121–2.133 Å longer CoNcyanide 2.154 Å. FeC bond lengths 1.924–1.932 Å, FeN 1.977–1.983 Such structural characteristics indicated centers CoIIHS (HS=high spin) whereas FeIIILS (LS=low ions, forming FeIIILS(μ-CN)CoIIHS linkages.12 when crystals slowly cooled decreased 1.966–1.967 1.915 compressed coordination sphere. range CoIIILS (ca. 1.9 Å).12 1.897–1.927 1.994–1.996 temperature-dependent variations suggested intramolecular converted into CoIII parts FeIII FeII basis balance, occurred randomly sites. Additional evidence found infrared (IR) spectroscopy studies S2). 290 νCN absorptions attributed free absorption [FeIIITp(CN)3]− (2120 2141 cm−1) linkages (2150 cm−1). As decreased, stretches 2044, 2061, 2085, 2172 cm−1, [FeIITp(CN)3]2− FeIILS(μ-CN)CoIIILS FeIIILS(μ-CN)CoIIILS these temperature-induced IR spectra completely upon warming samples, consistent induction metal-to-metal (MMCT). 57Fe Mössbauer recorded 300 6.0 characterize states S3). high-temperature (HT) quadrupole doublet parameters δ (isomer shift)=−0.01 ΔEQ (quadrupole splitting)=0.86 mm s−1, characteristic LS species. additional δ=0.21 ΔEQ=0.41 corresponding species, observed. peak area ratio species 0.51/0.49 suggesting complete HT low-temperature (LT) phase. Magnetic measurements performed verify MMCT 1. room χT value 4.10 cm3 mol−1 per unit, presence orbital contribution.12 values remained nearly 2). decreasing (0.5 min−1) 160 afforded decrease values, reaching 0.70 170 contrast, heating min−1), increased returned initial small loop. confirmed involved (S=1/2) (S=3/2) LT diamagnetic FeIILS (S=0) centers. According results, all changed expressed {[FeIIITp(CN)3]2CoII(Meim)4}⋅6 H2O⇄{[FeIIITp(CN)3][FeIITp (CN)3]CoIII(Meim)4}⋅6 H2O. further down 2.0 indicating behavior isolated ions. Field-dependent 1.8 steeply 1.17 Nβ 50 kOe, agrees FeIILSFeIIILSCoIIILS S4). Because interactions, bistability respect temperature. entropy-driven process, systems.13 plays role tuning solvents Temperature-dependent susceptibilities before (•) after (▪) vs. T. Inset: α–β SCF densities phases, HS=high LS=low spin. 1, ligand-based bands UV region relatively broad band 438 nm shoulder 520 S5). assigned LMCT MLCT chromophores. FeII→CoIII intervalence band, related complexes.14 weak most components FeIIILS-CN-CoIIHS-NC-FeIIILS low FeIILS-CN-CoIIILS-NC-FeIIILS Irradiation 532 laser corresponds We investigated photo-effect determine possibility site. Under laser-diode-pumped Nd:YAG (λ=532 nm, 30 mW cm−2, 24 h) 5 rapidly reached maximum 1.5 h, thus pairs photogenerated. Photoinduced relaxed treatment up 90 2), recovered treatment. support occurrence 532-nm peaks generated S6). fact valence-state FeIILS-CoIIILS FeIIILS-CoIIHS group, molecule phase, transferred became asymmetric phase.15 Upon heating, its state, demonstrating polarity. estimate structures, carried out DFT calculations (the phase) sextet (Table S1). Calculated FeIIILS(1.0), CoIIILS(0.0), FeIILS(0.0) FeIIILS(1.1), CoIIHS(2.8), FeIIILS(1.1) B3LYP/6-311G* level theory. calculated Mulliken charges influenced valence calculations, permanent dipole moment 18.4 D, no computational results experimental observations. Note that, contrast ionic cobalt–dioxolene system,9 neutral. For depends within position counterions. polarity, crystal-packing effect should considered, difficult control. It easier control choosing linkage distribution. conclusion, obtained trinulear showing Accompanying transfer, showed future, might interesting direct solid field.7 Synthesis 1: solution Bu4N[(Tp)Fe(CN)3]16 (0.1 mmol) mL methanol placed bottom side H-shaped tube, aqueous Co(NO3)2⋅6 (0.05 N-methylimidazole introduced other side. Then, layered over solutions sides provide diffusion pathway. Crystallization several weeks gave 60 % yield Elemental analysis, C40H56N26O6B2CoFe2: 40.40, 4.75, 30.62; found: 40.74, 4.57, 30.95. information about properties, measurements, IR, XRD well methods, see Supporting Information. Detailed facts importance specialist readers published ”Supporting Information”. documents peer-reviewed, copy-edited typeset. They made available submitted authors. 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