Isostructural mononuclear complexes of heavy lanthanides with the pentadentate Schiff-base dapsc ligand were synthesized, [Ln(H₂dapsc)(H₂O)₄](NO₃)₃ (Ln = Tb, Dy, Ho, Er), and characterized structurally and magnetically. AC magnetic susceptibility measurements revealed that complexes of Dy³⁺ and Er³⁺ Kramers ions are field-induced single-ion magnets whereas the Tb and Ho complexes show no slow magnetic relation in DC fields up to 6000 Oe. DC and AC magnetic properties of these complexes were rationalized in terms of superposition crystal-field model calculations for Ln³⁺ ions, which have resulted in good agreement between the experiment and the theory. It is shown that low single-molecule magnet characteristics of the Dy and Er complexes and the absence of slow-magnetic relaxation in the Tb and Ho complexes are primarily due to the low-symmetry coordination of Ln³⁺ ions.

A series of five new mononuclear pentagonal bipyramidal Co(II) complexes with the equatorial 2,6-diacetylpyridine bis(semicarbazone) ligand (H₂dapsc) and various axial pseudohalide ligands (SCN, SeCN, N(CN)₂, C(CN)₃, and N₃) was prepared and structurally characterizated: [Co(H₂dapsc)(SCN)₂]∙0.5C₂H₅OH (1), [Co(H₂dapsc)(SeCN)₂]∙0.5C₂H₅OH (2), [Co(H₂dapsc)(N(CN)₂)₂]∙2H₂O (3), [Co(H₂dapsc)(C(CN)₃)(H₂O)](NO₃)∙1.16H₂O (4), and {[Co(H₂dapsc)(H₂O)(N₃)][Co(H₂dapsc)(N₃)₂]}N₃∙4H₂O (5). The combined analyses of the experimental DC and AC magnetic data of the complexes (1–5) and two other earlier described those of this family [Co(H₂dapsc)(H₂O)₂)](NO₃)₂∙2H₂O (6) and [Co(H₂dapsc)(Cl)(H₂O)]Cl∙2H₂O (7), their theoretical description and the ab initio CASSCF/NEVPT2 calculations reveal large easy-plane magnetic anisotropies for all complexes (D = + 35 − 40 cm⁻¹). All complexes under consideration demonstrate slow magnetic relaxation with dominant Raman and direct spin–phonon processes at static magnetic field and so they belong to the class of field-induced single-ion magnets (SIMs).

A series of six seven-coordinate pentagonal-bipyramidal (PBP) erbium complexes, with acyclic pentadentate [N₃O₂] Schiff-base ligands, 2,6-diacetylpyridine bis-(4-methoxybenzoylhydrazone) [H₂DAPMBH], or 2,6-diacethylpyridine bis(salicylhydrazone) [H₄DAPS], and various apical ligands in different charge states were synthesized: [Er(DAPMBH)(C₂H₅OH)Cl] (1); [Er(DAPMBH)(H₂O)Cl]·2C₂H₅OH (2); [Er(DAPMBH)(CH₃OH)Cl] (3); [Er(DAPMBH)(CH₃OH)(N₃)] (4); [(Et₃H)N]⁺[Er(H₂DAPS)Cl₂]⁻ (5); and [(Et₃H)N]⁺[Y₀.₉₅Er₀.₀₅(H₂DAPS)Cl₂]⁻ (6). The physicochemical properties, crystal structures, and the DC and AC magnetic properties of 1–6 were studied. The AC magnetic measurements revealed that most of Compounds 1–6 are field-induced single-molecule magnets, with estimated magnetization energy barriers, U_eff ≈ 16–28 K. The experimental study of the magnetic properties was complemented by theoretical analysis based on ab initio and crystal field calculations. An experimental and theoretical study of the magnetism of 1–6 shows the subtle impact of the type and charge state of the axial ligands on the SMM properties of these complexes.

Four cyano-bridged bimetallic complexes, {[Mn(salpn)]₂[Fe(CN)₅NO]}_n (1), {[Mn(salpn)(CH₃OH)]₄[Mn(CN)₅NO]}[C(CN)₃]·3H₂O (2), {[Mn(dapsc)][Fe(CN)₅NO]·0.5CH₃OH·0.25H₂O}_n (3) and {[Mn(salpn)(CH₃OH)]₄[Fe(CN)₅NO]}(ClO₄)₂·4H₂O (4), where salpn²⁻ = N,N′-1,3-propylene-bis(salicylideneiminato) dianion and dapsc = 2,6-diacetylpyridine-bis(semicarbazone), have been synthesized and structurally characterized by single crystal X-ray diffraction. In 1, the nitroprusside anion [Fe(CN)₅NO]²⁻ coordinates with four [Mn(salpn)]⁺via four co-planar CN⁻ groups, whereas each [Mn(salpn)]⁺ links two [Fe(CN)₅NO]²⁻ ions, which results in a two-dimensional network. The structure of 3 contains two independent neutral infinite chains {[Mn(dapsc)][Fe(CN)₅(NO)]}_∞ consisting of alternating cationic [Mn^II(dapsc)]²⁺ and anionic [Fe^II(CN)₅(NO)]²⁻ units connected through cyanide bridges. The cation complexes 2 and 4 have a pentanuclear molecular structure in which four [Mn(salpn)(MeOH)]⁺ fragments are linked by the [Mn(CN)₅NO]³⁻ or [Fe(CN)₅(NO)]²⁻ moieties, respectively. The magnetic and photochromic properties of 1 and 3 have been studied. The thermal magnetic behaviour of the complexes indicates the presence of weak antiferromagnetic interactions between Mn³⁺ or Mn²⁺ mediated by diamagnetic [Fe(CN)₅NO]²⁻ bridges. Irradiation of 1 and 3 with light gives birth to the long-lived metastable states of nitroprusside.

We report the synthesis, crystal structure and magnetic properties of the new heptacoordinated mononuclear erbium(III) complex (Et₃NH)[Er(H₂DAPS)Cl₂] (H₄DAPS = 2,6-diacetylpyridine bis-(salicylhydrazone)) (1). The coordination polyhedron around the Er(III) ion features a slightly distorted pentagonal bipyramid formed by the pentagonal N₃O₂ chelate ring of the H₂DAPS ligand in the equatorial plane and two apical chloride ligands. Detailed high-frequency/high-field electron paramagnetic resonance (HF-EPR) studies of 1 result in the precise determination of the crystal field (CF) splitting energies (0, 290 and 460 GHz) and effective g-values of the three lowest Kramers doublets (KDs) of the Er(III) ion. The obtained HF-EPR data are in good agreement with the results from CF analysis for the Er(III) ion based on the simulation of the dc magnetic data of 1. The results from dynamic susceptibility measurements indicate that there is no slow relaxation of magnetisation behaviour. This observation is discussed in terms of the electronic structure of 1 obtained from experimental and theoretical results.