A Thermal And Structural Study on Lanthanum Hexacyanocobaltate(III) Pentahydrate. Part II

The thermal dehydration of La[Co(CN)₆]⋅5H₂O proceeded through at least three stages from the temperature range of30~230°C, and an abrupt mass loss occurred around 350°C and the perovskite type oxide,LaCoO₃ was obtained at 1000°C. After dehydration, the color of the anhydride changed from white to pale blue around 230°C and furthermore, the color changed to blue around 290°C. These color changes were discussed on the basis of the changes of coordination structures around Co ions. In La[Co(CN)₆]⋅5H₂O, Co³⁺ ions lie at the center of the O_h crystal field consisted of six CN^– ions. However, in the pale blue specimen, Co³⁺ ions were situated in the center of D_4h crystal field which was distorted the O_h one by lengthening of the trans CN^– ions along z-axis. In the blue specimen, Co³⁺ ions were reduced to Co²⁺ ions which were situated in the T_d crystal field formed by four CN^–ions as [Co(CN)₄]^2–. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fluorescence study on a liquid‐crystalline polyester containing naphthoate mesogen units

Using fluorescence spectroscopy, we investigated intermolecular interaction between mesogenic units in a thermotropic main‐chain LC polyester, P(HBA73/HNA27), containing oxybenzoate (HBA) and oxynaphthoate (HNA) mesogenic units. It is known that P(HBA73/HNA27), which has a high molecular weight, shows second harmonic generation (SHG) activity. P(HBA73/HNA27) showed fluorescence at 410 nm and 430 nm, originating from two kinds of intermolecular interaction. Fluorescence with a peak at 410 nm comes from the ground‐state complex between partially overlapping naphthoate units or between naphthoate and oxybenzoate units whose interaction is weak. Fluorescence at 430 nm comes from the ground‐state complex between fully overlapping naphthoate units whose interaction is strong. The relative fluorescence intensity for 430 nm compared to 410 nm increases with increases in inherent viscosity, η_inh, of P(HBA73/HNA27), the composition ratio of HNA/HBA, and temperature. The fluorescence intensity ratio, I₄₃₀/I₄₁₀, of P(HBA73/HNA27) shows the same inherent‐viscosity dependence with its sudden increase at η_inh = 1.4 ∽ 2.2 dL/g as its SHG activity does, supporting the polar structure and uniformity of LC orientation of the present LC polyester. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2922–2928, 2000