A Bis-Monophospholyl Dysprosium Cation Showing Magnetic Hysteresis at 48 Kelvin

Single-molecule magnets (SMMs) have potential applications in high-density data storage, but magnetic relaxation times at elevated temperatures must be increased to make them practically useful. Bis -cyclopentadienyl lanthanide sandwich complexes have emerged as the leading candidates for SMMs that show magnetic memory at liquid nitrogen temperatures, but the relaxation mechanisms mediated by aromatic C 5 rings have not been fully established. Here we synthesise a bis -monophospholyl dysprosium SMM [Dy(Dtp) 2 ][Al{OC(CF 3 ) 3 } 4 ] ( 1 , Dtp = {P(C t BuCMe) 2 }) by the treatment of in situ -prepared “[Dy(Dtp) 2 (C 3 H 5 )]” with [HNEt 3 ][Al{OC(CF 3 ) 3 } 4 ]. SQUID magnetometry reveals that 1 has an effective barrier to magnetisation reversal of 1,760 K (1,223 cm –1 ) and magnetic hysteresis up to 48 K. Ab initio calculation of the spin dynamics reveal that transitions out of the ground state are slower in 1 than in the first reported dysprosocenium SMM, [Dy(Cp ttt ) 2 ][B(C 6 F 5 ) 4 ] (Cp ttt = C 5 H 2 t Bu 3 -1,2,4), however relaxation is faster in 1 overall due to the compression of electronic energies and to vibrational modes being brought on-resonance by the chemical and structural changes introduced by the bis -Dtp framework. With the preparation and analysis of 1 we are thus able to further refine our understanding of relaxation processes operating in bis -C 5 /C 4 P sandwich lanthanide SMMs, which is the necessary first step towards rationally achieving higher magnetic blocking temperatures in these systems in future.