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A family of four Ln(III) complexes has been synthesized with the general formula [Ln 2 (NO 3 ) 4 (L) 2 (S)] (Ln = Gd, Tb, Er, and S = H 2 O; 1 , 2 and 4 , respectively/Ln = Dy, S = MeOH, complex 3 ), where HL is the flexible ditopic ligand N '-(1-(pyridin-2-yl)ethylidene)pyridine-2-carbohydrazide. The structures of isostructural MeOH/H 2 O solvates of these complexes were determined by single-crystal X-ray diffraction. The two Ln III ions are doubly bridged by the deprotonated oxygen atoms of two "head-to-head" 2.21011 (Harris notation) L¯ ligands, forming a central, nearly rhombic {Ln III 2 (μ-OR) 2 } 4+ core. Two bidentate chelating nitrato groups complete a sphenocoronal 10-coordination at one metal ion, while two bidentate chelating nitrato groups and one solvent molecule (H 2 O or MeOH) complete a spherical capped square antiprismatic 9-coordination at the other. The structures are critically compared with those of other, previously reported metal complexes of HL or L¯. The IR spectra of 1 - 4 are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The f-f transitions in the solid-state (diffuse reflectance) spectra of the Tb(III), Dy(III), and Er(III) complexes have been fully assigned in the UV/Vis and near-IR regions. Magnetic susceptibility studies in the 1.85-300 K range reveal the presence of weak, intramolecular Gd III ∙∙∙Gd III antiferromagnetic exchange interactions in 1 [ J / k B = -0.020(6) K based on the spin Hamiltonian Ĥ = -2 J ( Ŝ Gd1 ∙ Ŝ Gd2 )] and probably weak antiferromagnetic Ln III ∙∙∙Ln III exchange interactions in 2 - 4 . Ac susceptibility measurements in zero dc field do not show frequency dependent out-of-phase signals, and this experimental fact is discussed for 3 in terms of the magnetic anisotropy axis for each Dy III center and the oblate electron density of this metal ion. Complexes 3 and 4 are Single-Molecule Magnets (SMMs) and this behavior is optimally observed under external dc fields of 600 and 1000 Oe, respectively. The magnetization relaxation pathways are discussed and a satisfactory fit of the temperature and field dependencies of the relaxation time τ was achieved considering a model that employs Raman, direct, and Orbach relaxation mechanisms.

Reaction of the dinucleating phenol-based ligand, H3bpmp (2,6-bis-[(3-hydroxy-propylimino)-methyl]-4-methyl-phenol), with Cu(2+) ions in the presence of a hybrid base (NEt3 and NaN3) necessary for the in situ generation of required numbers of hydroxido ions, results in the formation of a novel NO3(-) capped and HO(-) supported {Cu12} coordination complex {Cu6(μ3-OH)3(μ3-Hbpmp)3(μ3-NO3)}2(NO3)2(OH)2·2H2O·2MeOH (1). When the components are combined in right proportions (metal : ligand : NEt3 : NaN3 = 2 : 1 : 3 : 2) in MeOH, twelve Cu(2+) ions assemble in a cuboctahedral geometry, containing six square and eight triangular faces around a considerable void space. Six of the eight [Cu3] triangular faces are bound by the six Hbpmp(2-) ligands with six free pendant propanol arms around the central hexagonal plane. X-ray structure determination indicates new geometrical features for the core formation and reveals the face-capping potential of the H3bpmp ligand for the growth of a cuboctahedral coordination cage with the support of anions like HO(-) and NO3(-). The experimentally observed (J/kB = -173 K) strong antiferromagnetic coupling within the Cu12 complex has been justified by the DFT calculations.

Reaction of the mononuclear Ni(II) complex [Ni{2-Py(6-NH2)NHC(S)NP(S)(OiPr)2}2] with different salicylaldehydes leads to new antiferromagnetically coupled trinuclear double-stranded helicates , where Ni(II) metal ions are coordinated by two bis-anionic thiourea ligands and two deprotonated molecules of the corresponding aldehyde.

Four dinuclear bis(μ-Cl) bridged copper(II) complexes, [Cu(2)(μ-Cl)(2)(L(X))(2)](ClO(4))(2) (L(X) = N,N-bis[(3,5-dimethylpyrazole-1-yl)-methyl]benzylamine with X = H(1), OMe(2), Me(3) and Cl(4)), have been synthesized and characterized by the single crystal X-ray diffraction method. In these complexes, each copper(II) center is penta-coordinated with square-pyramidal geometry. In addition to the tridentate L(X) ligand, a chloride ion occupies the last position of the square plane. This chloride ion is also bonded to the neighboring Cu(II) site in its axial position forming an SP-I dinuclear Cu(II) unit that exhibits small intramolecular ferromagnetic interactions and supported by DFT calculations. The complexes 1-3 exhibit methylmonooxygenase (pMMO) behaviour and oxidise 4-tert-butylcatechol (4-TBCH(2)) with molecular oxygen in MeOH or MeCN to 4-tert-butyl-benzoquinone (4-TBQ), 5-methoxy-4-tert-butyl-benzoquinone (5-MeO-4-TBQ) as the major products along with 6,6'-Bu(t)-biphenyl-3,4,3',4'-tetraol and others as minor products. These are further confirmed by ESI- and FAB-mass analyses. A tentative catalytic cycle has been framed based on the mass spectral analysis of the products and DFT calculations on individual intermediates that are energetically feasible.