Sobre a aplicabilidade da termogravimetria para a estimativa de parâmetros termoquímicos de compostos de coordenação: os elementos lantanídicos

Robson Fernandes de Farias
2000 Química Nova  
Recebido em 2/2/99; aceito em 22/2/00 ABOUT THE USE OF THERMOGRAVIMETRIC DATA TO ESTIMATE THERMOCHEMICAL PARAMETERS FOR COORDINATION COMPOUNDS: THE LANTHANIDE ELEMENTS. By using thermochemical data reported for a series of chelates of the type [Ln(thd) 3 ], thd = 2, 2, 6, 6 -tetramethyl-3,5-heptanedione and Ln = La, Pr, Nd, Sm, Gd, Tb, Ho, Er, Tm and Yb, empirical correlations were found involving thermochemical parameters (e.g. dissociation enthalpy) and the thermodynamic temperatures of the
more » ... mperatures of the beginning of thermal degradation of the chelates, t i . It is shown that t i values are of capital importance in the study of this all class of coordination compounds. Among others, the empirical equation is obtained: r 3+ = (-0,013.Z + 1,36)/0,005, that relates the lanthanide cation radius (pm) with the atomic number of the element. The remarkable fact is that this equation is achieved by using thermogravimetric and calorimetric parameters. Is also shown that t i values are related with the P(M) function values, which are very close related with the energy difference, ∆E, between the lowest electronic energy level of the f n s 2 d 1 configuration and the lowest energy level of the f n+1 s 2 configuration in the neutral gaseous atoms.
doi:10.1590/s0100-40422000000500002 fatcat:4wtia3wa3rcujmfzojigbij5t4