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

Abstract

By using suitable synthetic procedures, we have first isolated the square-planar organosilver(III) compounds [PPh4][trans-(CF3)2AgX2] [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)2AgX2]− 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)2AgX3]2−. Interestingly, compound [PPh4]2[(CF3)2AgBr3] (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.