Systematic investigation of an array of TCNQ lanthanide complexes: synthesis, structure and magnetic properties

An array of TCNQ (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) lanthanide complexes, namely, [Ln₂(TCNQ)₄(H₂O)₁₀(EtOH)₂][2TCNQ]·xH₂O [Ln = La (1, x = 5), Pr (2, x = 3)], [Ln₂(TCNQ)₄(H₂O)₁₀][2TCNQ]·yH₂O [Ln = Gd (3, y = 6), Dy (4, y = 5)] and [Ln(TCNQ)₂(H₂O)₆][TCNQ]·H₂O·MeOH [Ln = Er (5), Lu (6)], have been synthesized by salt-elimination reactions. X-ray crystallographic analysis indicates that 1–6 are discrete ion complexes. Cations of 1–4 adopt a dimer structure, while cations of 5 and 6 display a monomer structure. The magnetic study proposes that an antiferromagnetic interaction between TCNQ radicals exists in 1–6. The depopulation of the Stark levels for 2 and 5 leads to a continuous decrease in χ_mT when the samples are cooled from 300 K to 2 K. The desolvated 3, namely, 3a exhibits a unique magnetic conversion from the magnetic disordering to the magnetic ordering at 4 K. 4 shows a ferromagnetic coupling between paramagnetic centers.