Nuclear Spin Isomers: Engineering a Et4N[DyPc2] Spin Qudit

Two dysprosium isotopic isomers were synthesized: Et4N[(DyPc2)-Dy-163] (1) with I = 5/2 and Et4N[(DyPc2)-Dy-164] (2) with I = 0 (where Pc = phthalocyaninato). Both isotopologues are single-molecule magnets (SMMs); however, their relaxation times as well as their magnetic hystereses differ considerably. Quantum tunneling of the magnetization (QTM) at the energy level crossings is found for both systems via ac-susceptibility and m-SQUID measurements. m-SQUID studies of 1(I= 5/2) reveal several nuclear-spin-driven QTM events; hence determination of the hyperfine coupling and the nuclear quadrupole splitting is possible. Compound 2(I= 0) shows only strongly reduced QTM at zero magnetic field. 1(I= 5/2) could be used as a multilevel nuclear spin qubit, namely qudit (d = 6), for quantum information processing (QIP) schemes and provides an example of novel coordination-chemistry-discriminating nuclear spin isotopes. Our results show that the nuclear spin of the lanthanide must be included in the design principles of molecular qubits and SMMs.