Lanthanum and Gadolinium Complexes with Neutral Tertiary Phosphine Ligands: Synthesis, Structures, Magnetism and Bonding

The coordination chemistry of lanthanoids with neutral tertiary phosphine ligands is still largely underdeveloped, with only few examples and none for some of the lanthanoids, such as gadolinium. Therefore, the formation of organometallic lanthanum and gadolinium phosphine complexes was investigated. Solvent-free precursors [Ln(COT)I] and [LnCp3] (Ln = La, Gd) were reacted with the bisphosphines 1,2-bis(dimethylphosphino)ethane (dmpe) and 1,2- bis(dimethylphosphino)methane (dmpm). The resulting complexes [Gd(COT)I(dmpe)], [{Gd(COT)(μ-I)}2(μ-dmpm)], [{LnCp3}2(μ-dmpe)] (Ln = La, Gd) and the precursor [Gd(COT)I(thf)2] could be isolated and were characterized by single crystal x-ray diffraction. Depending on the ancillary ligands and bisphosphines backbone, chelating and bridging coordination modes were observed for the bisphosphine ligands. The magnetism of the dimeric gadolinium complexes was investigated via SQUID magnetometry. A weak antiferromagnetic coupling was found between the Gd3+ ions in [{Gd(COT)(μ-I)}2(μ-dmpm)]. A DFT study was performed on the isolated complexes to study the nature of the Ln-P bonds. Quantum theory of atoms in molecules analysis showed a correlation between the (overall small) bond covalency and the Ln-P bond length.