Heterogeneous reactions of solid nickel(II) complexes, VI

Abstract

The kinetics of the thermal decomposition of square-planar complexes of the type Ni(NCS)2L~ (L = ~-picoline; 2,6-1utidine and quinoline) was studied by following the loss of weight and using the isothermal method, in the temperature range of 72-147 ~ The reaction order found was n = 2/'3; this together with macroscopic observations indicates that it is the proper chemical process which is the controlling factor of the total decomposition rate. The values of the activation energies decrease in the following order: Ni(NCS)2 Q2 > Ni(NCS)2(2,6-1ut)z > Ni(NCS)2(~-pic)2; this points to the reaction course accGrding to the associative activation. Except for Ni(NCS)~Q 2, AH was found to be > E a. This experimental result may be explained by a multi-step mechanism. Possible intermediates are discussed.

Kinetics and enthalpy change in decomposition of Ni(NCS)2(3-R-pyridine)4 complexes (R=ethyl, Cl, Br, CN, NH2)

“…The activation energies (E) found for the interface advance (nucleus growth) decrease in the sequence (Table 1): 3-Clpy > 3-NH2py > 3-Brpy > 3-CNpy > 3-Etpy If the thermal decomposition of the complexes is considered to be a heterogeneous substitution reaction (dissociative or associative mechanism [6]), then the above sequence of activation energies can be explained in terms of the steric properties of the ligands [7,8]. The increasing steric density around the central atom (the increase in bulk of the ligands or the substituents on the ligands, respectively) will increase the activation energy in the formation of the bonds (associative activation), or decrease (E) in breaking bonds during the decomposition reaction (dissociative activation [6]).…”