Takuto Matsumoto

Programmable spin-state switching in a mixed-valence spin-crossover iron grid

Photo-switchable systems, such as discrete spin-crossover complexes and bulk iron-cobalt Prussian blue analogues, exhibit, at a given temperature, a bistability between low- and high-spin states, allowing the storage of binary data. Grouping different bistable chromophores in a molecular framework was postulated to generate a complex that could be site-selectively excited to access multiple electronic states under identical conditions. Here we report the synthesis and the thermal and light-induced phase transitions of a tetranuclear iron(II) grid-like complex and its two-electron oxidized equivalent. The heterovalent grid is thermally inactive but the spin states of its constituent metal ions are selectively switched using different laser stimuli, allowing the molecule to exist in three discrete phases. Site-selective photo-excitation, herein enabling one molecule to process ternary data, may have major ramifications in the development of future molecular memory storage technologies.

Undecanuclear mixed-valence 3d–4f bimetallic clusters

Two undecanuclear 3d-4f clusters with the general formula {Mn(III)(4)Mn(IV)Ln(III)(6)}, where Ln = Gd or Tb, were synthesized, with both showing large spin ground states, and the Tb species acting as a single molecule magnet.

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.

Multiredox active [3 × 3] copper grids.

A nonanuclear copper grid complex, [Cu(II)9(L)6](BF4)6·1-PrOH·5H2O (1·1-PrOH·5H2O; L = 2,6-bis[5-(2-pyridinyl)-1H-pyrazol-3-yl]pyridine), was synthesized with a [3 × 3] grid structure consisting of nine Cu(II) ions and six deprotonated ligands and displayed four-step quasi-reversible redox behavior from [Cu(II)9] to [Cu(I)4Cu(II)5]. The corresponding heterovalent complex [Cu(I)2Cu(II)7(L)6](PF6)4·3H2O (2·3H2O) was successfully isolated and had a distorted core structure that radically changed the intramolecular magnetic coupling pathways.

Studies on the Magnetic Ground State of a Spin Möbius Strip

Here we report the synthesis, structure and detailed characterisation of three n-membered oxovanadium rings, Nan [(V=O)n Nan (H2 O)n (α, β, or γ-CD)2 ]⋅m H2 O (n=6, 7, or 8), prepared by the reactions of (V=O)SO4 ⋅x H2 O with α, β, or γ-cyclodextrins (CDs) and NaOH in water. Their alternating heterometallic vanadium/sodium cyclic core structures were sandwiched between two CD moieties such that O-Na-O groups separated the neighbouring vanadyl ions. Antiferromagnetic interactions between the S=1/2 vanadyl ions led to S=0 ground states for the even-membered rings, but to two quasi-degenerate S=1/2 states for the spin-frustrated heptanuclear cluster.

Planar copper and nickel triangles with a guanidine-derived ligand

A novel guanidine-derived ligand with three tetradentate N4 coordination sites and its trinuclear copper and nickel complexes, [Cu3] and [Ni3], were synthesized. X-ray structural analyses of [Cu3] and [Ni3] reveal the complexes to have planar triangular structures with pseudo C3 symmetry. Magnetic measurements for [Cu3] and [Ni3] complexes indicate that antiferromagnetic interactions are operative in both complexes with intratriangle exchange coupling constants of g = 2.08(1), J = −130(1) cm−1 for [Cu3], and g = 2.18(1), J = −14.9(1) cm−1 for [Ni3]. [Cu3] has a doublet spin ground state at low temperature, while the magnetic susceptibility data and magnetization curve suggest that the ground state of [Ni3] is spin singlet.

A series of tetranuclear [2 × 2] grid complexes derived from an asymmetric ligand: Structural differences based on metal ion affinities

A series of tetranuclear grid-type complexes were prepared by the reaction of the asymmetric multidentate ligand HL (HL = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridine carboxylic acid ethylester) with different metal sources. The tetranuclear copper complex, [Cu4(L1)4(NO3)4(H2O)4]·Et2O·2MeOH (1, HL1 = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridine carboxylic acid methyl ester) consists of four ligands, four copper ions, four nitrate ions and four water molecules, forming a [2 × 2] grid structure, in which all four copper ions have the same coordination environment. On the other hand, the corresponding nickel and cobalt complexes, [M4(L2)4(H2O)4]·4MeOH·6H2O (M = Ni (2) and Co (3), (H2L2 = 6-[1,3-dioxo-3-(2-phenyl)propionyl]pyridine-2-carboxylic acid)), have a similar grid core structure to the copper complex with four metal ions, four ligand molecules, and four water molecules, however, in these clusters there are two kinds of coordination site for the metal ions. Temperature-dependent magnetic susceptibility measurements for all complexes demonstrated that antiferromagnetic interactions between the metal ions were in operation. The magnetic susceptibility data of the copper and nickel complexes were analyzed using a tetranuclear model based on H = –2J(S1S2+S2S3+S3S4+S4S1) to give best-fit parameters of g = 2.11(1), J = –1.39(3) cm–1 and g = 2.19(1), J = –0.44(2) cm–1, respectively.