Lanthanum and gadolinium complexes with neutral tertiary phosphine ligands: synthesis, structures, magnetism and bonding

Lanthanum and gadolinium complexes with neutral bidentate phosphine ligands and cyclopentadienyl (Cp-) or dianionic cyclooctatetraene (COT2-) ligands were investigated. Solvent-free precursors [Ln(COT)I] and LnCp3 (Ln = La, Gd) were reacted with the bisphosphines 1,2-bis(dimethylphosphino)ethane (dmpe) and bis(dimethylphosphino)methane (dmpm). The resulting complexes [Gd(COT)I(dmpe)], [{Gd(COT)(mu-I)}2(mu-dmpm)], [{LnCp3}2(mu-dmpe)] (Ln = La, Gd) and the precursor [Gd(COT)I(thf)2] were crystallographically characterised. Depending on the ancillary ligands and bisphosphine 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)(mu-I)}2(mu-dmpm)]. Quantum chemical bonding analysis using Quantum Theory of Atoms in Molecules showed a correlation between the (overall small) bond covalency and the Ln-P bond length.