Kinetics of __-PcCu_ú__-PcCu Isothermal Conversion in Air and Thermal Behavior of __-PcCu from in Situ Real-Time Laboratory Parallel-Beam X-ray Powder Diffraction

摘要

The kinetics of the __-PcCu _ú__-PcCu conversion in air has been followed, under isothermal conditions, in situ real-time in the 423-443 K temperature range. Data have been fitted following the JMAK model. The reaction order of the kinetics at 423 K is consistent with a diffusion controlled, deceleratory nucleation rate process for 2D laminar particles, whereas at higher temperatures it is consistent with a phase boundary controlled, deceleratory nucleation rate process for 2D laminar particles. At 423 K, the overall transformation mechanism implies three steps: growth of the a-PcCu phase, disordering of adjacent columns of molecules of phthalocyanine, and nucleation and growth of the __-PcCu phase. The calculated empirical activation energy is of 187 kJ/mol significantly greater than that for the __-PcCo_ú__-PcCo conversion. This fact seems to support the reported different structures of __-PcCo and __-PcCu. Investigation of the thermal behavior of __-PcCo indicates a strongly anisotropic thermal expansion that follows the ___c_ ___a_____b trend. Moreover, the __ angle decreases with increasing temperature. Such anisotropy is consistent with the geometry of the very weak N3 ___H3 hydrogen bond which acts mainly along the c axis.