A series of cyanide bridged Fe-Co molecular squares, [Co(2)Fe(2)(CN)(6)(tp*)(2)(dtbbpy)(4)](PF(6))(2)·2MeOH (1), [Co(2)Fe(2)(CN)(6)(tp*)(2)(bpy)(4)](PF(6))(2)·2MeOH (2), and [Co(2)Fe(2)(CN)(6)(tp)(2)(dtbbpy)(4)](PF(6))(2)·4H(2)O (3) (tp = hydrotris(pyrazol-1-yl)borate, tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate, bpy =2,2'-bipyridine, dtbbpy =4,4'-di-tert-butyl-2,2'-bipyridine), were prepared by the reactions of [Fe(CN)(3)(L)](-) (L = tp or tp*) with Co(2+) and bidentate ligands (bpy or dtbbpy) in MeOH. In the molecular squares, Fe and Co ions are alternately bridged by cyanide ions, forming macrocyclic tetranuclear cores. Variable temperature X-ray structural analyses and magnetic susceptibility measurements confirmed that 1 exhibits two-step charge-transfer induced spin transitions (CTIST) centered at T(1/2) = 275 and 310 K in the solid state. The Fe and Co ions in 1 are the low-spin (LS) Fe(III) and high-spin (HS) Co(II) ions, described here in the high-temperature (HT) phase ([Fe(III)(LS2)Co(II)(HS2)]) at 330 K, while a low-temperature (LT) phase ([Fe(II)(LS2)Co(III)(LS2)]) with LS Fe(II) and Co(III) ions was dominant below 260 K. X-ray structural analysis revealed that in the intermediate (IM) phase at 298 K 1 exhibits positional ordering of [Fe(III)(LS2)Co(II)(HS2)] and [Fe(II)(LS2)Co(III)(LS2)] species with the 2:2 ratio. In photomagnetic experiments on 1, light-induced CTIST from the LT to the HT phase was observed by excitation of Fe(II) → Co(III) intervalence charge transfer (IVCT) band at 5 K and the trapped HT phase thermally relaxed to the LT phase in a two-step fashion. On the other hand, 2 and 3 are in the HT and LT phases, respectively, throughout the entire temperature range measured, and no CTIST was observed. UV-vis-NIR absorption spectral measurements and cyclic voltammetry in solution revealed that the different electronic states in 1-3 are ascribable to the destabilization of iron and cobalt ion d-orbitals by the introduction of methyl and tert-butyl groups to the ligands tp and bpy, respectively. Temperature dependence of UV-vis-NIR spectra confirmed that 1 exhibited a one-step CTIST in butyronitrile, of which T(1/2) varied from 227 to 280 K upon the addition of trifluoroacetic acid.

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It is well known that scale layer on work roll forms in hot sheet rolling of steel and scale layer on work roll plays an important role for hot rolling process. The formation conditions of scale layer on work roll are slightly known qualitatively and are hardly understood quantitatively. In order to investigate quantitatively the conditions of scale formation, three steels with different Si content are used and the slip rolling is carried out at a constant roll speed changing the scale thickness of steel workpiece and the reduction. The formation conditions of scale layer on work roll are examined quantitatively by observation of work roll surface after slip rolling. The experiments are carried out at constant rolling conditions of a velocity ratio of 20, a rolling speed of 50 m/min and a furnace temperature of 800 °C, changing the rolling reductions of 0.3, 0.5 and 1.0 mm and scale thickness of workpiece. The colza oil is used as base oil. The emulsion concentration is 3.0%. The emulsion temperature is controlled at 40 °C. Scale layer on work roll forms easily with increasing rolling reduction and decreasing scale thickness of workpiece for three steels A, B and C. In order to estimate quantitatively the formation condition of scale layer on work roll, parameter α which is given by a ratio of the rolling reduction to scale thickness of workpiece is proposed. Scale layer on work roll forms when values of parameter α become same for each steels. Values of parameter α become larger in order of steels A, B and C and it can be understood that scale layer on work roll forms easily in order of steels A, B and C. When FeO layer in scale of the steel surface adheres on work roll surface, it is expected that scale layer on work roll forms easily and strongly by transformation from FeO to Fe3O4, considering that the chemical composition of scale layer on work roll is Fe3O4.

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