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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, H2LH (1-Dy, 3-Ho, 4-Er and 6-Tb complexes) or H2LOCH3, (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 (H2LH, [H2DAPBH]) or 1,1'-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))di-4-methoxybenzohydrazine (H2LOCH3, [H2DAPMBH]) with common lanthanide salts. The terbium complex [Tb(LH)(NO3)(H2O)2](DME)2 (5-Tb) with one ligand H2LH 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 Ueff = 29 K at 800 Oe in 1-Dy and Ueff = 70 K at 300 Oe in 2-Dy) and erbium complex (Ueff = 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. [ABSTRACT FROM AUTHOR]

A series of three mononuclear pentagonal-bipyramidal V(III) complexes with the equatorial pentadentate N3O2 ligand (2,6-diacethylpyridinebis(benzoylhydrazone), H2DAPBH) in the different charge states (H2DAPBH0, HDAPBH1−, DAPBH2−) and various apical ligands (Cl−, CH3OH, SCN−) were synthesized and characterized structurally and magnetically: [V(H2DAPBH)Cl2]Cl·C2H5OH (1), [V(HDAPBH)(NCS)2]·0.5CH3CN·0.5CH3OH (2) and [V(DAPBH)(CH3OH)2]Cl·CH3OH (3). All three complexes reveal paramagnetic behavior, resulting from isolated S = 1 spins with positive zero-field splitting energy expected for the high-spin ground state of the V3+ (3d2) ion in a PBP coordination. Detailed high-field EPR measurements for compound 3 show that its magnetic properties are best described by using the spin Hamiltonian with the positive ZFS energy (D = +4.1 cm−1) and pronounced dimer-like antiferromagnetic spin coupling (J = −1.1 cm−1). Theoretical analysis based on superexchange calculations reveals that the long-range spin coupling between distant V3+ ions (8.65 Å) is mediated through π-stacking contacts between the planar DAPBH2− ligands of two neighboring [V(DAPBH)(CH3OH)2]+ complexes. [ABSTRACT FROM AUTHOR]

The influence of the solution total alkalinity and the base cation and anion types on the structure and properties of molybdenum oxo-methoxides formed in reaction of MoCl5 in methanol as following: MoCl5 +CH3OH+M+A−, where M+ =K+ or Na+, and A− =OCH3 − or OH− was studied. The investigation has shown that hetero-bimetallic oxo-methoxides containing Na or K ions – [NaMo2O2(OCH3)7(CH3OH)] (1), [KMo2O2(OCH3)7(CH3OH)2] (2) – are formed in alkaline media with sodium or potassium methoxides taken as a base. Single crystal X-ray structure determination (XRD) of the complexes 1 and 2 revealed that their crystal structures can be considered as consisting of anionic [Mo2O2(OCH3)7]− and cationic [Na(CH3OH)]+ or [K(CH3OH)2]+ fragments assembled into different supramolecular aggregates. When Na, K or Mg methoxides are used as a base, while the medium remains to be acidic, regardless the cation type the same compounds are formed, namely, [Mo2Cl2(OCH3)8] (3) or [Mo2Cl4(OCH3)6] (4) (in the absence of alkali). When KOH or NaOH are used instead of respective methoxides it has been shown that at weakly acidic (close to neutral) media the octanuclear molybdenum cluster [Mo8O8(μ3-O)4(μ2-O)4(μ3-OCH3)2(μ2-OCH3)4Cl2(CH3OH)4]·6CH3OH (5·6CH3OH) is formed as a main product. The DFT calculations of the mechanism of complex 5 formation were carried out. The process of octanuclear Mo(V) cluster formation from initially formed binuclear ones was shown to be a thermodynamically favorable. The detailed analysis within QTAIM theory of an electron density distribution function ρ(r) in the crystal of 2 obtained directly from its X-ray diffraction data has been performed. This analysis has provided the direct and convincing experimental evidence of the Mo–Mo bond presence in a dimolybdenum clusters and, in addition, allowed to estimate the energy of some important interatomic interactions in 2 and related clusters. [ABSTRACT FROM AUTHOR]

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, Ueff ≈ 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. [ABSTRACT FROM AUTHOR]

The molecular and electronic structures and the vibrational spectra of the mixed-valence Mg–Mo cluster [Mg2(MeOH)4−Mo4 VIMo4 VO22(OMe)6]2− were calculated to locate two pairs of MoV centers with strong Mo–Mo bonding. [Copyright &y& Elsevier]

A series of three mononuclear pentagonal-bipyramidal V(iii) complexes with the equatorial pentadentate N3O2 ligand (2,6-diacethylpyridinebis(benzoylhydrazone), H2DAPBH) in the different charge states (H2DAPBH0, HDAPBH1-, DAPBH2-) and various apical ligands (Cl-, CH3OH, SCN-) were synthesized and characterized structurally and magnetically: [V(H2DAPBH)Cl2]Cl·C2H5OH (1), [V(HDAPBH)(NCS)2]·0.5CH3CN·0.5CH3OH (2) and [V(DAPBH)(CH3OH)2]Cl·CH3OH (3). All three complexes reveal paramagnetic behavior, resulting from isolated S = 1 spins with positive zero-field splitting energy expected for the high-spin ground state of the V3+ (3d2) ion in a PBP coordination. Detailed high-field EPR measurements for compound 3 show that its magnetic properties are best described by using the spin Hamiltonian with the positive ZFS energy (D = +4.1 cm-1) and pronounced dimer-like antiferromagnetic spin coupling (J = -1.1 cm-1). Theoretical analysis based on superexchange calculations reveals that the long-range spin coupling between distant V3+ ions (8.65 Å) is mediated through π-stacking contacts between the planar DAPBH2- ligands of two neighboring [V(DAPBH)(CH3OH)2]+ complexes.

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln(DAPMBH)(N 3 )C 2 H 5 OH]C 2 H 5 OH} n where H 2 DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)-a new pentadentate pyridine-base [N 3 O 2 ] ligand and Ln = Dy ( 1 ), Y 0.930 Dy 0.070 ( 2 ), Er ( 3 ), Y 0.923 Er 0.077 ( 4 ), and Gd ( 5 ). X-ray diffraction analysis of 1 - 5 show that the central lanthanide atoms are eight-coordinated with the N 5 O 3 donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N 3 - bridges connecting the metal centers into infinite chain. The [LnN 5 ] coordination polyhedron can be regarded as a distorted dodecahedron ( 3 ] coordination polyhedron can be regarded as a distorted dodecahedron ( D 2 d ). AC magnetic measurements revealed that compounds 1 - 4 show field-induced single-molecule magnet behavior, with estimated energy barriers U eff ≈ 47-17 K. The experimental study of magnetic properties was complemented by theoretical analysis based on crystal-field calculations. Direct current magnetic susceptibility studies revealed marginally weak intrachain exchange interaction between Ln 3+ ions mediated by the end-to-end azide bridging groups ( J ≈ -0.015 cm -1 for 5 ). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated ( 1 , 3 ) and diluted ( 2 , 4 ) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds 1 and 3 are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln 3+ ions.