Synthesis and Structure of a Series of Lanthanide(III) Thiocyanate Derivatives with THF, [Ln(NCS)3(THF)4]

The thiocyanate complexes Ln(NCS)3.(THF)4 (Ln = Nd, Eu and Er) have been prepared and their structure was studied in the solid state by X-ray diffractometric methods. They crystallize in the monoclinic space group P2(1)/a with a ranging from 19.279(9) for Nd to 18.980(9) angstrom for Er; b, c and beta have almost constant values: b = 8.11 +/- 0.01 angstrom, c = 17.68 +/- 0.05 angstrom and beta = 111.0 +/- 0.03-degrees. A peculiar feature of these complexes is the octacoordination, the dimeric nature and the fact that in the molecule the NCS groups are coordinated as mono (Ln-NCS) and bidentate (Ln-NCS-LN) ligands. The structural units assume an almost undistorted square antiprismatic coordination geometry; they are linked through bridges of NCS groups. The Ln...S distances range from 3.10 (Nd) to 3.26 angstrom (Er); these values correspond to rather weak bond interactions, but are unambiguously recognized as coordinating values in geometrical terms.