Hiroki Oshio

Tuning the Spin States of Two Apical Iron(II) Ions in the Trigonal‐Bipyramidal [{FeII(μ‐bpt)3}2FeII3(μ3‐O)]2+ Cations Through the Choice of Anions

When located in octahedral environment, the iron(II) ion with a d electronic configuration may adopt two different stable electronic states, namely, a diamagnetic low-spin (LS) state and a paramagnetic high-spin (HS) state, which both give rise to different magnetic, optical and electronic properties. So tuning the spin state of the iron(II) ion is significant and contributes to the development of amazing materials that can be used as molecular switches, sensors and display devices. As is well established, the spin state depends on relative strength of spin paring energy (P) and splitting energy (D0). If the former is much stronger than the latter, the HS state will be stabilised, and if D0 is stronger then the LS state will be the ground state. If P and D0 are comparable a spin crossover (SCO) may occur between the HS and LS state by external perturbations such as temperature, pressure or light irradiation. So the main task is to make a judicious choice of ligand, which can impose a proper ligand-field strength. However, in reality, the spin state of the iron(II) ion is quite sensitive to even more subtle changes such as solvent molecules, polymorphism and counterions. As one of the best representatives of switchable molecules, SCO materials have attracted considerable interest in the chemistry and materials fields. Current work mainly focuses on the enhancement of cooperativity, which results in an abrupt transition and a wider thermal hysteresis. Another promising research area, but with few examples, is the combination of magnetic-exchange and spin-transition (ST) phenomena in the same molecule or polymeric network, which could eventually afford new switching materials with considerable amplification of the response signal. Much more work should be done to expand our knowledge of spin electronics. To induce a ST, the most common method is by varying the temperature. However, light-and pressure-induced SCOs play an increasingly important role owing to their potential applications as optical and pressure switches, for example. Moreover, the latter two methods are not restricted to thermal SCO compounds: LIESST (light-induced excited spinstate trapping) may also be observed in LS compounds, whereas HS compounds may experience STs with the application of external hydrostatic pressure. Although there are many examples that exhibit thermal STs, rare spin-crossover clusters of iron(II) have been found to exhibit a mixed-spin structure and synergy between ST and magnetic interaction. Fortunately, by introducing counterions, we have successfully tuned the spin states of two apical iron(II) ions in the pentanuclear [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3-O)]2+ (Hbpt=3,5-bis(pyridin-2-yl)-1,2,4-triazole) cations through anions. Both apical ions are of LS states in [{Fe ACHTUNGTRENNUNG(mbpt)3}2Fe II 3ACHTUNGTRENNUNG(m3-O)] ACHTUNGTRENNUNG(NCS)2·10H2O (1), [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3O)] ACHTUNGTRENNUNG(ClO4)2·3H2O (2) and [{FeIIACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3-O)]I2· 4MeCN (3), and are of HS states in [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3O)] ACHTUNGTRENNUNG[FeIII2ACHTUNGTRENNUNG(m-O)Cl6]·1/2H2O (4). In this new {Fe5} family, two new developments have been achieved: 1) The ligand 4amino-3,5-bis(pyridine-2-yl)-1,2,4-triazole (abpt) has been, for the first time, used to produce the oxo-centred polynuACHTUNGTRENNUNGcle ACHTUNGTRENNUNGar iron(II) complexes; 2) Two types of spin topology have been trapped in the [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3-O)]2+ cluster that are controlled by counterions. Note that only one [a] X. Bao, J.-D. Leng, Z.-S. Meng, Dr. Z.-J. Lin, Prof. Dr. M.-L. Tong Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education State Key Laboratory of Optoelectronic Materials and Technologies School of Chemistry & Chemical Engineering Sun Yat-Sen University, Guangzhou 510275 (P.R. China) Fax: (+86) 20-8411-2245 E-mail : tongml@mail.sysu.edu.cn [b] Dr. M. Nihei, Prof. Dr. H. Oshio Graduate School of Pure and Applied Sciences University of Tsukuba, Tennodai 1-1-1, Tsukuba 305-8571 (Japan) Fax: (+81) 29-853-4238 E-mail : oshio@chem.tsukuba.ac.jp Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201000526.

Cyanide‐Bridged [Fe8M6] Clusters Displaying Single‐Molecule Magnetism (M=Ni) and Electron‐Transfer‐Coupled Spin Transitions (M=Co)

Cyanide-bridged metal complexes of [Fe(8)M(6)(μ-CN)(14)(CN)(10)(tp)(8)(HL)(10)(CH(3)CN)(2)][PF(6)](4)⋅n CH(3)CN⋅m H(2)O (HL=3-(2-pyridyl)-5-[4-(diphenylamino)phenyl]-1H-pyrazole), tp(-) =hydrotris(pyrazolylborate), 1: M=Ni with n=11 and m=7, and 2: M=Co with n=14 and m=5) were prepared. Complexes 1 and 2 are isomorphous, and crystallized in the monoclinic space group P2(1)/n. They have tetradecanuclear cores composed of eight low-spin (LS) Fe(III) and six high-spin (HS) M(II) ions (M=Ni and Co), all of which are bridged by cyanide ions, to form a crown-like core structure. Magnetic susceptibility measurements revealed that intramolecular ferro- and antiferromagnetic interactions are operative in 1 and in a fresh sample of 2, respectively. Ac magnetic susceptibility measurements of 1 showed frequency-dependent in- and out-of-phase signals, characteristic of single-molecule magnetism (SMM), while desolvated samples of 2 showed thermal- and photoinduced intramolecular electron-transfer-coupled spin transition (ETCST) between the [(LS-Fe(II))(3) (LS-Fe(III))(5)(HS-Co(II))(3)(LS-Co(III))(3)] and the [(LS-Fe(III))(8)(HS-Co(II))(6)] states.

Spin Crossover versus Low‐Spin Behaviour Exhibited in 2D and 3D Supramolecular Isomers of [FeII(2,4‐bpt)2]⋅Guest

The bistable properties (magnetic, structure and colour) of spin crossover (SCO) materials have resulted in a bright future for their applications as molecular memory, molecular switches, molecular sensors, data storage and display devices. Spin transitions (STs) between high(HS) and lowspin (LS) states can be achieved by external stimuli, such as temperature, pressure, light, magnetic or electrical switching. From practical aspects, the design and the synthesis of SCO compounds with high transition temperatures, wide thermal hysteresis and thermochroism are of crucial importance. Two strategies have been universally acknowledged to improve the cooperatives: 1) to construct covalently bridged coordination polymers; 2) to enrich intermolecular interactions, such as hydrogen bonding and p–p stacking. However, in reality, it is hard to predict theoretically the SCO property of a material until it has been characterised. The sensitivity of the SCO property to subtle changes does cause problems, but from another perspective, it may also be viewed as an opportunity to deepen our knowledge of the nature of SCO. To this end, the rich structural diversity of supramolecular isomers provided us a useful and unique perspective to understand structure–property relationships. As a branch of isomerism, polymorphism-dependent SCO compounds are not uncommon, however, most of which are mononuclear. To the best of our knowledge, only two examples focus on structural isomerism and another shows catenane isomerism-dependent SCO properties. Herein, we report the crystal structures and physical properties of four supramolecular isomers based on [FeACHTUNGTRENNUNG(2,4bpt)2]·guest (2,4-Hbpt= 3-(2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole): a 2D SCO polymer [FeACHTUNGTRENNUNG(2,4-bpt)2] (1·Fe), two LS twofold interpenetrated 3D coordination polymers with NbO topology, [Fe ACHTUNGTRENNUNG(2,4-bpt)2]·2.17 H2O (2 a) and [Fe ACHTUNGTRENNUNG(2,4bpt)2]·2.5 H2O (2 b) and a LS non-interpenetrated 3D coordination polymer with NbO topology, [FeACHTUNGTRENNUNG(2,4bpt)2]·4 dioxane·4 H2O (3). It should be mentioned that these complexes include all kinds of isomers except for optical isomers, that is, structural, conformational and catenane supramolecular isomerism. Moreover, a cobalt analogue and a Fe Co solid solution species: [Co ACHTUNGTRENNUNG(2,4-bpt)2]·0.5 H2O (1·Co) and [FexCo1 x ACHTUNGTRENNUNG(2,4-bpt)2] (x=0.93) (1·Fe–Co) have also been synthesised and characterised. The latter compound allows us to investigate SCO properties in a doped system. Our work provides a good example to study magneto–structural relationships. We choose the 2,4-Hbpt ligand mainly for the following reasons: 1) as a variant of the well-studied ligand 2,2-Rbpt (2,2-Rbpt= 4-substituted 3,5-di(2-pyridyl)-1,2,4-triazole), it should also provide an appropriate ligand field favouring the occurrence of SCO; 2) it is a good candidate to construct a coordination polymer by using the 4-position N atom, thus enhancing cooperation between SCO sites; 3) the ligand can take on abundant conformations due to its rotatable feature, thus resulting in a variety of isomers and fits our need to study structure-dependent SCO properties. All products are synthesised in solvothermal conditions at 160 8C for 3 days. However, different solvent media have an important influence on the final products. By hydrothermal treatment, five products are captured, namely, two mononuclear polymorphs based on [FeACHTUNGTRENNUNG(2,4-bpt)2ACHTUNGTRENNUNG(H2O)2],[10] 1·Fe, 2 a and 2 b. However, there are problems with low yields for all products and also poor reproducibility. So it was laborious work to collect pure 1·Fe to study its magnetic behaviour. [a] X. Bao, J.-L. Liu, J.-D. Leng, Dr. Z. Lin, Prof. Dr. M.-L. Tong Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education State Key Laboratory of Optoelectronic Materials and Technologies School of Chemistry & Chemical Engineering Sun Yat-Sen University Guangzhou 510275 (P.R.China) Fax: (+86) 20-8411-2245 E-mail : tongml@mail.sysu.edu.cn [b] Dr. M. Nihei, Prof. Dr. H. Oshio Graduate School of Pure and Applied Sciences University of Tsukuba, Tennodai 1-1-1, Tsukuba 305-8571 (Japan) [**] 2,4-Hbpt=3-(2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201001179.

Assembly of imino nitroxides with Ag(I) and Cu(I) ions

Abstract Magnetic interactions between coordinated imino nitroxides through the diamagnetic Cu(I) and Ag(I) ions, and radical assemblies by means of coordination to Ag(I) and Cu(I) ions are discussed.

Syntheses, structures and magnetic properties of multinuculear manganese complexes with Schiff base ligands

Abstract Multinulear manganese complexes with Schiff base ligands, [{MnIII4(μ3-O)(sae)4(μ-N3)(CH3OH)}2(μ-N3)]N3 ([1]N3), [MnIII6(μ3-O)2(sae)6(NCS)2] (2) and [MnII4MnIII2(sae)6(CH3OH)2Cl2] (3) (H2sae=2-salicylideneaminoethanol), were prepared and the crystal structures and magnetic properties were studied.

Synthesis, structure, and spectral and magnetic properties of trinuclear copper(II) complexes bridged by glyoximate groups

Copper(II) complexes of composition Cu3L2L′2(ClO4)2 or Cu3L2L′2(CH3OH)2(NO3)2 were obtained where L = dimethylglyoximate (dmg), diphenylglyoximate (dpg), or o-benzoquinone dioximate (bqd) dianion, L′= 2,2′-bipyridyl (bipy) or 1,10-phenanthroline (phen). The crystal structures of Cu3(dmg)2(bipy)2(CH3OH)2(NO3)2 and Cu3(dpg)2(bipy)2(CH3OH)2(NO3)2 were solved by the single-crystal X-ray method. Both have an essentially similar trinuclear structure where the [CuL2]2– dianion functions as a bridge between two copper(II) ions through its deprotonated oximate oxygens. The configuration around the central copper (with two L2– ions) is an elongated octahedron with two NO3– ions above and below the [CuL2]2–. The configuration around the terminal copper is a square pyramid with two nitrogens of bipy and two oxygens of oximate groups in the basal plane and the methanol oxygen at the apical site. Cryomagnetic investigations (80–300 K) revealed the operation of a very strong antiferromagnetic spin exchange through the oximate bridges, causing complete or nearly complete spin coupling even at room temperature. Exchange integrals (–J) larger than 300 cm–1 were evaluated for all the complexes. Based on e.s.r. spectra in methanol, it is suggested that the unpaired electron is localized on the terminal copper atom. The complexes dimerized in dimethylformamide, especially at a low temperature, and their frozen solutions each showed an e.s.r. spectrum typical of the spin-triplet state.

Unusual heat capacity of the ferric spin-crossover complex, [Fe(acpa)2]PF6, showing a gradual but complete spin-state interconversion at the fast spin-flipping rate†

Abstract The heat capacity of the iron(III) spin-crossover complex [Fe(acpa)2]PF6[Hacpa = N−(1-acetyl-2-propylidene)(2-pyridylmethyl)amine], which shows fast electronic relaxation between S = 1 2 ( 2 T 2g ) and S = 5 2 ( 6 A 1g ) in comparison with the 57Fe Mossbauer lifetime (10−7s), was measured with an adiabatic calorimeter in the 15–320 K range. Variable temperature IR and Raman spectra were recorded between 84 and 300 K. An unusually broad heat-capacity peak starting from ∼ 120K, culminating at ∼ 190K, and terminating at ∼ 280 K was observed. A normal heat capacity curve which separates the excess heat capacity from the observed values was determined. The enthalpy and entropy arising from the spin-crossover phenomenon were 7025 J mol−1 and 36.19 J K−1 mol−1, respectively. The entropy gain was well accounted for in terms of the sum (37.69 J K−1mol−1) of the contribution from a change in the spin-manifold R 1n( 6 2 ) (= 9.13 J K −1 mol −1 ) and from a change in the skeletal normal modes of vibration detected by IR and Raman spectra (28.56 J K−1 mol−1). To elucidate the question, Why does the spin-crossover occur so gradually for the complexes of the fast electronic relaxation type?, the Frenkel theory of heterophase fluctuation in liquids was applied. As a result, the number of molecules in a domain was proved to be as small as five. This makes a large fluctuation possible between the low and high spin states, eventually leading to the spin-equilibrium type transition taking place over a wide temperature range.

Structures and magnetic properties of metal cubes

Abstract Structures and magnetic properties of copper(II), nickel(II) and manganese(II) cubes are presented. In the cubes, four metal ions are assembled into the cubes by tridentate Schiff base ligands. Magnetic succeptibility measurements revealed the copper and nickel cubes have high-spin ground state, while the manganese cube has a S =0 spin ground state.

Contrasting Magnetism of [MnIII4] and [MnII2MnIII2] Squares

Two tetranuclear manganese distorted square-shaped clusters, [Mn(III)(4)(L1)(4)(mu(2)-OMe)(4)].2.5H(2)O (1) and [Mn(II)(2)Mn(III)(2)(L2)(4)(H(2)O)(2)](PF(6))(2).CHCl(3).CH(3)OH.1.5H(2)O (2) (H(2)L1 = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridinecarboxylic acid methyl ester; H(2)L2 = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridinecarboxylic acid ethyl ester), exhibit antiferromagnetic and ferromagnetic interactions between neighboring manganese ions, respectively.

Single chain magnet of a cyanide bridged FeII/FeIII complex

A 1D compound composed of cyanide bridged iron(II,III) ions was prepared and magnetic measurements revealed it to be a single chain magnet.