By using suitable synthetic procedures, we have first isolated the square-planar organosilver(III) compounds [PPh₄][trans-(CF₃)₂AgX₂] [X = Cl (1a), Br (2a)]. The geometry and stereochemistry of the chloro-derivative 1a have been unambiguously established by single-crystal X-ray diffraction (SC-XRD) methods. Following our calculations on the relative stability of the cis-trans-[(CF₃)₂AgX₂]⁻ couples (X = F, Cl, Br, I), the experimentally obtained compounds 1a and 2a appear to be kinetically favoured stereoisomers. They display some tendency to associate an additional X⁻ ligand affording rare five-coordinate Ag(III) species [(CF₃)₂AgX₃]²⁻. Interestingly, compound [PPh₄]₂[(CF₃)₂AgBr₃] (3) has been identified by SC-XRD methods as the first Ag(III) derivative with trigonal symmetry in general and trigonal bipyramidal geometry in particular. It is also identified as the first five-coordinate species with inverted ligand field.