Synthesis, acid hydrolysis, and Visible spectra of some bromopentakis(alkylamine)cobalt(III) complexes

Abstract

Complexes of the [Co(RNH2)5Br]2+ type with R = Me, Et, n‐Pr and n‐Bu have been synthesized. The acid hydrolysis of these complexes have been studied in aqueous solution except for the butylamine complex, in which case the acid hydrolysis has been done in diocane‐water medium because the complex is only slightly soluble in water. The acid hydrolysis of these complexes follow a pseudo‐first‐order reaction rate law and an SN2 mechanism with an octahedral wedge transition state has been assigned. The visible spectra of these complexes, together with [Co(NH3)5Br]2+, have been recorded and the overlapped bands have been resolved into Gaussian curves by least squares. Values of crystal field parameters Dq(RNH2), Dq(Br) and Dt in the complexes have been determined with a method originally devised by Wentworth and Piper. The calculated results agree well with those reported by other workers and a linear relationship previously observed by Mitzner et al. between Dq(RNH2) and ΔH° of proton ionization of RNH3+ ions is also found.