A Five-Coordinate Compound with Inverted Ligand Field: An Unprecedented Geometry for Silver(III).

By using suitable synthetic procedures, we have first isolated the square-planar organosilver(III) compounds [PPh4 ][trans-(CF3 )2 AgX2 ] [X=Cl (1 a), Br (2 a)]. The geometry and stereochemistry of the chloro-derivative 1 a 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 )2 AgX2 ]- couples (X=F, Cl, Br, I), the experimentally obtained compounds 1 a and 2 a appear to be kinetically favored stereoisomers. They display some tendency to associate an additional X- ligand affording rare five-coordinate AgIII species [(CF3 )2 AgX3 ]2- . Interestingly, compound [PPh4 ]2 [(CF3 )2 AgBr3 ] (3) has been identified by SC-XRD methods as the first AgIII derivative with trigonal symmetry in general and trigonal bipyramidal geometry in particular. This unusual five-coordinate species also exhibits inverted ligand field.