Herein we report the synthesis and characterization of a dinuclear Tb single-molecule magnet (SMM) with two [TbPc] units connected via a fused-phthalocyaninato ligand. The stable and robust complex [(obPc)Tb(Fused-Pc)Tb(obPc)] (1) was characterized by using synchrotron radiation measurements and other spectroscopic techniques (ESI-MS, FT-IR, UV). The magnetic couplings between the Tb ions and the two π radicals present in 1 were explored by means of density functional theory (DFT). Direct and alternating current magnetic susceptibility measurements were conducted on magnetically diluted and nondiluted samples of 1, indicating this compound to be an SMM with improved properties compared to those of the well-known [TbPc] and the axially symmetric dinuclear Tb phthalocyaninato triple-decker complex (Tb(obPc)). Assuming that the probability of quantum tunneling of the magnetization (QTM) occurring in one TbPc unit is P, the probability of QTM simultaneously occurring in 1 is P, meaning that QTM is effectively suppressed. Furthermore, nondiluted samples of 1 underwent slow magnetic relaxation times (τ ≈ 1000 s at 0.1 K), and the blocking temperature (T) was determined to be ca. 16 K with an energy barrier for spin reversal (U) of 588 cm (847 K) due to D geometry and weak inter- and intramolecular magnetic interactions as an exchange bias (H), reducing QTM. Four hyperfine steps were observed by micro-SQUID measurement. Furthermore, solution NMR measurements (one-dimensional, two-dimensional, and dynamic) were done on 1, which led to the determination of the high rotation barrier (83 ± 10 kJ/mol) of the obPc ligand. A comparison with previously reported Tb triple-decker compounds shows that ambient temperature NMR measurements can indicate improvements in the design of coordination environments for SMMs. A large U causes strong uniaxial magnetic anisotropy in 1, leading to a χ value (1.39 × 10 m) that is larger than that for Tb(obPc) (0.86 × 10 m). Controlling the coordination environment and spin arrangement is an effective technique for suppressing QTM in TbPc-based SMMs.

The phthalocyaninato double-decker complexes [M(obPc)2 ](0) (M= Y(III) , Tb(III) , Dy(III) ; obPc=2,3,9,10,16,17,23,24-octabutoxyphthalocyaninato), along with their reduced ([M(obPc)2 ](-) [P(Ph)4 ](+) ; M=Tb(III) , Dy(III) ) and oxidized ([M(obPc)2 ](+) [SbCl6 ](-) (M=Y(III) , Tb(III) ) counterparts were studied with (1) H, (13) C and 2D NMR. From the NMR data of the neutral (i.e., with one unpaired electron in the ligands) and anionic Tb(III) complexes, along with the use of dispersion corrected DFT methods, it was possible to separate the metal-centered and ligand-centered contributions to the hyperfine NMR shift. These contributions to the (1) H and (13) C hyperfine NMR shifts were further analyzed in terms of pseudocontact and Fermi contact shifts. Furthermore, from a combination of NMR data and DFT calculations, we have determined the spin multiplicity of the neutral complexes [M(obPc)2 ](0) (M=Tb(III) and Dy(III) ) at room temperature. From the NMR data of the cationic Tb(III) complex, for which actually no experimental structure determination is available, we have analyzed the structural changes induced by oxidation from its neutral/anionic species and shown that the interligand distance decreases upon oxidation. The fast electron exchange process between the neutral and anionic Tb(III) double-decker complexes was also studied.

Two dysprosium isotopic isomers were synthesized: Et N[ DyPc ] (1) with I=5/2 and Et N[ DyPc ] (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 μ-SQUID measurements. μ-SQUID studies of 1 reveal several nuclear-spin-driven QTM events; hence determination of the hyperfine coupling and the nuclear quadrupole splitting is possible. Compound 2 shows only strongly reduced QTM at zero magnetic field. 1 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.

A combined synthetic, structural, magnetic and computational study gives insight into improving the single-molecule magnet behaviour of stable high-coordinate Dy(iii) complexes.