Four isostructural LnZn2 trinuclear complexes, [Ln(NO3){Zn(L)(SCN)}2] (H2L is a Schiff base ligand derived from o-vanillin and ethylenediamine), were synthesized, which include light lanthanide ions as spin carriers (Ln = Ce 1, Pr 2, Nd 3, and Sm 4). These complexes involve a linear Zn(II)–Ln(III)–Zn(II) array, which leads to an axially stressed ligand field and can also cause single-moleluce magnet (SMM) behavior in oblate-type electronic distributions of ground sublevels found in Ce(III), Pr(III), and Nd(III). Slow magnetic relaxation behavior was observed in 1 and 3 under an applied bias dc field of 1000 Oe, whereas such a slow relaxation was not observed in 2 and 4. The appearance of field-induced SMM behavior in 1 and 3 was correlated with the even-numbered Jz sublevels of Ce(III) and Nd(III) ions known as the Kramers system.

Five LnZn2 trinuclear complexes, [Ln(NO3){Zn(L)(SCN)}2] (H2L is a Schiff base ligand derived from o-vanillin and ethylenediamine; Ln = Tb 1, Dy 2, La 3, Tb0.14La0.864, and Dy0.21La0.795), were synthesised in which the ZnII–LnIII–ZnII array exhibits two slightly different arrangements: 1 and 2 exhibited slightly bent arrangements, whereas 3–5 exhibited more linear arrangements. These differences in the arrangements lead to a slightly different coordination geometry around LnIII. From the detailed studies of dynamic susceptibility, 1 and 2 were found to be paramagnetic, whereas 4 and 5 were SMMs with barriers for the flipping of magnetisation with a height of 41.2(4) K and 156(4) K, respectively.

Linear Zn(II)–Ce(III)–Zn(II) complex, which involves only one 4f electron as a spin source, behaves as an SMM. Easy-axis magnetic anisotropy for the ground 2F5/2 state of Ce(III) was achieved by a uni-axial crystal field, which is formed with four phenoxo oxygens as axial donors with the other five oxygens as equatorial donors.

An assemblage of a Tb(III) ion and two mononuclear [ZnII(L)] complexes as antenna chromophores (H2L: Schiff base ligand) afforded a luminescent single-molecule magnet. The f–f emission spectrum had partially resolved fine structure which provides detailed information on the magnetic anisotropy of the 7F6 ground multiplet of the Tb(III) ion.

Six linear trinuclear [Ln{Zn(L)(AcO)}2]BPh4 complexes (H2L denotes the Schiff-base ligand formed by a condensation reaction between ethylenediamine and two equivalents of o-vanillin), including Ln = Tb (1), Dy (2), Ho (3), Er (4), Tm (5) and Yb (6) were synthesized and were confirmed to be isostructural via X-ray crystallographic analyses. The Ln(III) ion in each complex is deca-coordinated by four equatorial oxygen donors from the methoxo groups of the Schiff-base ligands, two oxygen donors from the acetate anions and four axial oxygen donors from the phenoxo groups of the Schiff-base ligands. AC susceptibility measurements, with an oscillating frequency of 10 to 10000 Hz, revealed that 1, 2, 4 and 6 show slow magnetic relaxation under a 1000 Oe DC bias field, which occurs via a single process, as confirmed by the semi-circular Cole–Cole plots. These complexes are considered to be field-induced single-molecule magnets under these conditions. The presence or absence of the slow magnetic relaxation process is discussed by correlating the characteristic magnetic anisotropy of each Ln(III) ion with the ligand field anisotropy.

A family of single-chain magnets (SCMs), of which the SCM character originated from the spatial arrangement of high spin FeII ions with easy-plane anisotropy, was synthesized, and their magnetic properties were investigated. The chain complexes including alternating high-spin FeII ions and low-spin FeIII ions, catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4·3MeNO2 (1·3MeNO2), catena-[FeII(ClO4)(H2O){FeIII(MeL)2}](ClO4)2·2MeNO2·H2O (2·2MeNO2·H2O), catena-[FeII(ClO4)(H2O){FeIII(BuL)2}](ClO4)2·3.5MeNO2 (3·3.5MeNO2), and catena-[{FeII(ClO4)(H2O)FeII(H2O)2}0.5{FeIII(PhL)2}](ClO4)2.5·4EtNO2 (4·4EtNO2), were synthesized with the use of bridging ligand Hbpca (bis-(2-pyridylcarbonyl)amine)) and its derivatives of HMeL, HBuL, and HPhL each incorporating methyl, tert-butyl, or phenyl group on the 4-position of pyridyl ring. These complexes showed a typical ferrimagnetic behavior on direct current (dc) susceptibility data, and from an alternating current (ac) susceptibility measurements, SCM or superparamagnetic behaviors were confirmed with the Δ/kB values of 22.5(4), 21.8(18), and 28.8(3) K for 1·3MeNO2, 2·2MeNO2·H2O, and 3·3.5MeNO2, of which the easy-axis anisotropy was originated from the orthogonal arrangement of easy-planes of FeII ions. In the crystal structures, cylindrical voids were formed along the chain axis being surrounded by four chains in 1·3MeNO2, 2·2MeNO2·H2O, and 4·4EtNO2 and two chains in 3·3.5MeNO2, and solvent molecules as well as coordination-free perchlorate anions occupied these voids in a slightly different fashion depending on the complexes. 2·2MeNO2·H2O maintains its chemical composition in a dried condition, whereas 1·3MeNO2, 3·3.5MeNO2, and 4·4EtNO2 easily release solvent molecules to give 1, 3, and 4, respectively. 1 and 3 maintain the crystalline character showing slightly different X-ray diffraction (XRD) patterns from those of 1·3MeNO2 and 3·3.5MeNO2, and an enhancement of SCM character after release of the solvent molecules was observed for both. 4 lost crystalline character to become amorphous, and it lost the SCM character at the same time.

The tetramanganese(III) and hexamanganese(III) complexes, [Mn4(μ-pzbg)2(Hpzbg)2(MeO)4(MeOH)(H2O)]Cl2 (1) and [Mn6O4(Hpzbg)4(AcO)4(MeO)2] (2), were synthesized by using a monopyrazolyl biguanide derivative (H2pzbg) as a multinucleating ligand, which was newly prepared by the nucleophilic addition of pyrazole to Dicyandiamide. Single-crystal X-ray analysis revealed that 2 possesses a face-sharing double cubane structure, in which six Mn(III) ions are bridged by six MeO− with four terminal κ2N-Hpzbg−. On the other hand, 1 possesses an incomplete face-sharing double cubane structure in which four Mn(III) ions are bridged by four MeO− and two κ2N:κ2N-pzbg2− accompanied by two terminal κ2N-Hpzbg−. In 1, both ferromagnetic and antiferromagnetic interactions occur between manganese(III) ions, of which the ferromagnetic one is assigned to be the interaction via the imino nitrogen atom, while all manganese(III) ions are connected in an antiferromagnetic manner in 2.

Five LnZn2 trinuclear complexes, [Ln(NO3){Zn(L)(SCN)}2] (H2L is a Schiff base ligand derived from o-vanillin and ethylenediamine; Ln = Tb 1, Dy 2, La 3, Tb0.14La0.864, and Dy0.21La0.795), were synthesised in which the ZnII–LnIII–ZnII array exhibits two slightly different arrangements: 1 and 2 exhibited slightly bent arrangements, whereas 3–5 exhibited more linear arrangements. These differences in the arrangements lead to a slightly different coordination geometry around LnIII. From the detailed studies of dynamic susceptibility, 1 and 2 were found to be paramagnetic, whereas 4 and 5 were SMMs with barriers for the flipping of magnetisation with a height of 41.2(4) K and 156(4) K, respectively.

Six linear trinuclear [Ln{Zn(L)(AcO)}2]BPh4 complexes (H2L denotes the Schiff-base ligand formed by a condensation reaction between ethylenediamine and two equivalents of o-vanillin), including Ln = Tb (1), Dy (2), Ho (3), Er (4), Tm (5) and Yb (6) were synthesized and were confirmed to be isostructural via X-ray crystallographic analyses. The Ln(III) ion in each complex is deca-coordinated by four equatorial oxygen donors from the methoxo groups of the Schiff-base ligands, two oxygen donors from the acetate anions and four axial oxygen donors from the phenoxo groups of the Schiff-base ligands. AC susceptibility measurements, with an oscillating frequency of 10 to 10000 Hz, revealed that 1, 2, 4 and 6 show slow magnetic relaxation under a 1000 Oe DC bias field, which occurs via a single process, as confirmed by the semi-circular Cole–Cole plots. These complexes are considered to be field-induced single-molecule magnets under these conditions. The presence or absence of the slow magnetic relaxation process is discussed by correlating the characteristic magnetic anisotropy of each Ln(III) ion with the ligand field anisotropy.

An assemblage of a Tb(III) ion and two mononuclear [ZnII(L)] complexes as antenna chromophores (H2L: Schiff base ligand) afforded a luminescent single-molecule magnet. The f–f emission spectrum had partially resolved fine structure which provides detailed information on the magnetic anisotropy of the 7F6 ground multiplet of the Tb(III) ion.

Linear Zn(II)–Ce(III)–Zn(II) complex, which involves only one 4f electron as a spin source, behaves as an SMM. Easy-axis magnetic anisotropy for the ground 2F5/2 state of Ce(III) was achieved by a uni-axial crystal field, which is formed with four phenoxo oxygens as axial donors with the other five oxygens as equatorial donors.

Four isostructural LnZn2 trinuclear complexes, [Ln(NO3){Zn(L)(SCN)}2] (H2L is a Schiff base ligand derived from o-vanillin and ethylenediamine), were synthesized, which include light lanthanide ions as spin carriers (Ln = Ce 1, Pr 2, Nd 3, and Sm 4). These complexes involve a linear Zn(II)–Ln(III)–Zn(II) array, which leads to an axially stressed ligand field and can also cause single-moleluce magnet (SMM) behavior in oblate-type electronic distributions of ground sublevels found in Ce(III), Pr(III), and Nd(III). Slow magnetic relaxation behavior was observed in 1 and 3 under an applied bias dc field of 1000 Oe, whereas such a slow relaxation was not observed in 2 and 4. The appearance of field-induced SMM behavior in 1 and 3 was correlated with the even-numbered Jz sublevels of Ce(III) and Nd(III) ions known as the Kramers system.