A series of three mononuclear pentagonal-bipyramidal V(iii) complexes with the equatorial pentadentate N₃O₂-ligand were synthesized and characterized structurally and magnetically.

A series of five neutral mononuclear lanthanide complexes [Ln(HL)(L)] (Ln = Dy³⁺, Ho³⁺ Er³⁺ and Tb³⁺) with rigid pentadentate N₃O₂-type Schiff base ligands, H₂L^H (1-Dy, 3-Ho, 4-Er and 6-Tb complexes) or H₂L^OCH3, (2-Dy complex) has been synthesized by reaction of two equivalents of 1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))dibenzohydrazine (H₂L^H, [H₂DAPBH]) or 1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))di-4-methoxybenzohydrazine (H₂L^OCH3, [H₂DAPMBH]) with common lanthanide salts. The terbium complex [Tb(L^H)(NO₃)(H₂O)₂](DME)₂ (5-Tb) with one ligand H₂L^H was also obtained and characterized. Single crystal X-ray analysis shows that complexes 1–4 have the composition {[Ln³⁺(HL)⁻(L)²⁻] solv} and similar molecular structures. In all the compounds, the central Ln³⁺ ion is chelated by two interlocked pentadentate ligands resulting in the coordination number of ten. Each lanthanide ion is coordinated by six nitrogen atoms and four oxygen atoms of the two N₃O₂ chelating groups forming together a distorted bicapped square antiprismatic polyhedron N₆O₄ with two capping pyridyl N atoms in the apical positions. The ac magnetic measurements reveal field-induced single-molecule magnet (SMM) behavior of the two dysprosium complexes (with barriers of U_eff = 29 K at 800 Oe in 1-Dy and U_eff = 70 K at 300 Oe in 2-Dy) and erbium complex (U_eff = 87 K at 1500 Oe in 4-Er); complex 3-Ho with a non-Kramers Ho³⁺ ion is SMM-silent. Although 2-Dy differs from 1-Dy only by a distant methoxy-group in the phenyl ring of the ligand, their dynamic magnetic properties are markedly different. This feature can be due to the difference in long-range contributions (beyond the first coordination sphere) to the crystal-field (CF) potential of 4f electrons of Dy³⁺ ion that affects magnetic characteristics of the ground and excited CF states. Magnetic behavior and the electronic structure of Ln³⁺ ions of 1–4 complexes are analyzed in terms of CF calculations.

A facile synthetic strategy based on a retrosynthetic philosophy was developed and employed for the preparation of the polynuclear Mo–Mg oxomethoxides – high valence precursors of N₂ fixing catalysts.