Kiyotaka Mitsumoto

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.

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.

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.

Lability-controlled syntheses of heterometallic clusters.

A bulky bidentate ligand was used to stabilize a macrocyclic [Fe(III)8Co(II)6] cluster. Tuning the basicity of the ligand by derivatization with one or two methoxy groups led to the isolation of a homologous [Fe(III)8Co(II)6] species and a [Fe(III)6Fe(II)2Co(III)2Co(II)2] complex, respectively. Lowering the reaction temperatures allowed isolation of [Fe(III)6Fe(II)2Co(III)2Co(II)2] clusters with all three ligands. Temperature-dependent absorption data and corresponding experiments with iron/nickel systems indicated that the iron/cobalt self-assembly process was directed by the occurrence of solution-state electron-transfer-coupled spin transition (ETCST) and its influence on reaction intermediate lability.