Features of the Formation of Halide Complexes of Platinum Metals with Cobalt(III) Ammines

Reaction of solutions containing [Co(NH₃)₆]³⁺ cations and [MHal₄]^2– anions (M = Pt(II), Pd(II); Hal = Cl^–, Br^–) led to the isolation of crystalline powders of double complex salts with varying compositions. In the system with chloride anions, complexes were formed with metal molar ratios depending on the nature of the platinum metal (Co : Pt = 2 : 3, Co : Pd = 1 : 1). It was found that replacing chloride ions in the Co–Pd system with bromide ions leads to the formation of a complex with a Co : Pd ratio of 2 : 3. In the presence of sulfuric acid, compound {[Co(NH₃)₆](SO₄)₂[Co(NH₃)₆]}[PdBr₄] was formed. This compound is reported for the first time and characterized by elemental analysis, X-ray powder diffraction, IR spectroscopy, and single-crystal X-ray diffraction (CCDC no. 2355175). The structures were studied using DFT/PBE0 calculations with the def2tzvp basis set. Topological analysis of the electron density was performed, and molecular graphs of the compounds were constructed, revealing indicators of non-covalent interactions. Their energies and the total effect, which could have a significant electrostatic and inductive influence on the formation of crystal structures, were approximately estimated.