Complexes of some metal bromides with 1,4-dioxan

Abstract

The thermal decomposition reactions of MBr₂,2dx (where M = Mn, Co, or Ni; and dx = 1,4-dioxan) and MBr₂,dx (M = Co, Ni) have been investigated by thermogravimetry, differential enthalpic analyses, and dynamic reflectance spectroscopy. The 1 : 1 complexes decompose in a single step to MBr₂. The 1 : 2 complexes also decompose to MBr₂ but each by a different route. Temperatures and enthalpies of decomposition are reported.

Crystalline MBr₂,2dx,4H₂O are formed by NiBr₂ and CoBr₂ but not by MnBr₂. The visible spectra suggest that the chromophore is trans-M(2Br,4H₂O) with the dioxan molecules on lattice sites. Thermal decomposition converts these compounds into MBr₂,2dx,3H₂O, MBr₂,dx and finally MBr₂. The d–d spectrum of CoBr₂,2dx,3H₂O suggests the presence of two environments for Co²⁺, one identical with that in CoBr₂,2dx,4H₂O and the other possibly tetrahedral.