Bis-Monophospholyl Dysprosium Cation Showing Magnetic Hysteresis at 48 K

[Image: see text] 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 synthesize 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 magnetization reversal of 1760 K (1223 cm(–1)) and magnetic hysteresis up to 48 K. Ab initio calculation of the spin dynamics reveals 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 toward rationally achieving higher magnetic blocking temperatures in these systems in the future.