Double-decker phthalocyanine complexes with Tb3+ or Dy3+ showed slow magnetization relaxation as a single-molecular property. The temperature ranges in which the behavior was observed were far higher than that of the transition-metal-cluster single-molecule magnets (SMMs). The significant temperature rise results from a mechanism in the relaxation process different from that in the transition-metal-cluster SMMs. The effective energy barrier for reversal of the magnetic moment is determined by the ligand field around a lanthanide ion, which gives the lowest degenerate substate a large |Jz| value and large energy separations from the rest of the substates in the ground-state multiplets.

Alternating current (ac) magnetic susceptibility and magnetization hysteresis loop measurements have been carried out for anionic bis(phthalocyaninato)terbium and bis(phthalocyaninato)dysprosium. The two mononuclear lanthanide complexes show the characteristic temperature and frequency dependence in the ac susceptibility signals, reflecting their slow magnetization relaxation. From the Arrhenius analysis of the ac susceptibility data obtained for a diluted sample in a diamagnetic matrix, it has been found that the magnetization relaxation in the Tb complex is dominated by the two-phonon Orbach process in the temperature range 25−40 K and direct or Raman process below 25 K. In the Dy complex case, the Orbach process is the main relaxation process in the range 3−12 K. The Δ values in the Orbach term, corresponding to the height of the potential energy barrier to magnetic moment reversal, are in good agreement with the energy differences between the lowest and second lowest substates of the ground multiplet in the two cases. In the magnetization−field (M − H) loop measurements at 1.7 K, clear hysteresis has been observed for both complexes. These results indicate that the two double-decker phthalocyanine−lanthanide complexes behave as magnets at the single-molecular level. They are the first lanthanide compounds as well as the first mononuclear complexes showing such behaviors. Differences in the magnetization relaxation mechanism between the new “mononuclear lanthanide magnets” and the transition-metal-cluster-based SMMs (single-molecule magnets) are discussed.

Single-molecule magnets (SMMs) are the class of high-spin molecules that exhibit magnetization hysteresis at low temperature, that is, the property of macroscopic magnets. [1][2][3][4][5] Most SMMs are composed of several transition-metal ions, whose spins are coupled by strong exchange interactions to give a large effective spin with a predominant uniaxial anisotropy. The quantum nature of SMMs is manifested by staircase hysteresis loops, [5,6] temperature-independent relaxation, [7][8][9][10][11][12] and quantum phase interference. [13] The discovery of these phenomena led to potential applications in quantum computing.

The f-electronic structures of the ground states of anionic bis(phthalocyaninato)lanthanides, [Pc(2)Ln](-) (Pc = dianion of phthalocyanine, Ln = Tb(3+), Dy(3+), Ho(3+), Er(3+), Tm(3+), or Yb(3+)), are determined. Magnetic susceptibilities of the powder samples of [Pc(2)Ln]TBA (TBA = tetra-n-butylammonium cation) in the range 1.8-300 K showed characteristic temperature dependences which resulted from splittings of the ground-state multiplets. NMR signals for the two kinds of protons on the Pc rings at room temperature were shifted to lower frequency with respect to the diamagnetic Y complex in Ln = Tb, Dy, and Ho cases, and to higher frequency in Er, Tm, and Yb cases. The ratios of the paramagnetic shifts of the two positions were near constant in the six cases. This indicates that the shifts are predominantly caused by the magnetic dipolar term, which is determined by the anisotropy of the magnetic susceptibility of the lanthanide ion. Using a multidimensional nonlinear minimization algorithm, we determined a set of ligand-field parameters that reproduces both the NMR and the magnetic susceptibility data of the six complexes simultaneously. Each ligand-field parameter was assumed to be a linear function of atomic number of the lanthanide. The energies and wave functions of the sublevels of the multiplets are presented. Temperature dependences of anisotropies in the magnetic susceptibilities are theoretically predicted for the six complexes.

Q-Chem 2.0 is a new release of an electronic structure program package, capable of performing first principles calculations on the ground and excited states of molecules using both density functional theory and wave function-based methods. A review of the technical features contained within Q-Chem 2.0 is presented. This article contains brief descriptive discussions of the key physical features of all new algorithms and theoretical models, together with sample calculations that illustrate their performance.