Trivalent Lanthanide Compounds with Fluorinated Thiolate Ligands: Ln−F Dative Interactions Vary with Ln and Solvent

The fluorinated tris-thiolate compounds Ln(SC6F5)3 can be isolated as THF, pyridine, or DME coordination complexes.
In THF, the larger Ce forms dimeric [(THF)3Ce(SC6F5)3]2 (1) with bridging thiolate ligands, while the smaller lanthanides
(Ln = Ho (2), Er (3)) form monometallic (THF)3Ln(SC6F5)3 compounds. There is a tendency for fluoride to coordinate
to Ln throughout the lanthanide series (Ce−Er). The cerium compound 1 contains a pair of bridging thiolates
connecting two eight-coordinate Ce(III) ions. Of the two terminal thiolates, only one exhibits a distinct Ce−F bond.
In contrast, the Ho derivative (THF)3Ho(SC6F5)3 is a molecular compound in the solid state, with two monodentate
thiolates and one thiolate that again coordinates through both S and F atoms. Incorporation of a stronger Lewis
base reduces but does not necessarily eliminate the tendency to form Ln−F bonds. Structural characterization of
the eight-coordinate (pyridine)4Sm(SC6F5)3 (4) reveals a single, clearly defined Ln−F interaction, while in (pyridine)4Yb(SC6F5)3 (5) there are no Yb−F bonds. In the structure of (DME)2Er(SC6F5)3 (6) the DME ligands completely displace
F from the Er coordination sphere.