Mixed-Valent Trinuclear CoIII-CoII-CoIII Complex with 1,3-Bis(5-chlorosalicylideneamino)-2-propanol

A mixed-valent trinuclear complex with 1,3-bis(5-chlorosalicylideneamino)-2-propanol (H₃clsalpr) was synthesized, and the crystal structure was determined by the single-crystal X-ray diffraction method at 90 K. The molecule is a trinuclear Co^III-Co^II-Co^III complex with octahedral geometries, having a tetradentate chelate of the Schiff-base ligand, bridging acetate, monodentate acetate coordination to each terminal Co³⁺ ion and four bridging phenoxido-oxygen of two Schiff-base ligands, and two bridging acetate-oxygen atoms for the central Co²⁺ ion. The electronic spectral feature is consistent with the mixed valent Co^III-Co^II-Co^III. Variable-temperature magnetic susceptibility data could be analyzed by consideration of the axial distortion of the central Co²⁺ ion with the parameters Δ = –254 cm⁻¹, λ = –58 cm⁻¹, κ = 0.93, tip = 0.00436 cm³ mol⁻¹, θ = –0.469 K, g_z = 6.90, and g_x = 2.64, in accordance with a large anisotropy. The cyclic voltammogram showed an irreversible reduction wave at approximately −1.2 V·vs. Fc/Fc⁺, assignable to the reduction of the terminal Co³⁺ ions.

Polynuclear Iron(II) Pyridonates: Synthesis and Reactivity of Fe4 and Fe5 Clusters

The combination of pyridonate ligands with transition metal ions enables the synthesis of an especially rich set of diverse coordination compounds involving various κ- and μ-bonding modes and higher nuclearities. With iron(II) ions, this chemical space is rather poorly explored beyond some biomimetic models of the pyridone iron-containing hydrogenase. Here, the topologically new Fe₅ and Fe₄ clusters, Fe₅(L^H)₆[N(SiMe₃)₂]₄ (1) and Fe₄(L^Me)₆[N(SiMe₃)₂]₂ (2), were synthesized (L^H = 2-pyridonate; L^Me = 6-methyl-2-pyridonate). Complex 1 contained an unprecedented diamondoid Fe@Fe₄ tetrahedron with a central-to-peripheral Fe-Fe distance of ∼3.1 Å. The crystal structure of complex 2 displayed an Fe₄O₆ butterfly motif containing a planar Fe₄ arrangement. Mössbauer spectroscopy confirmed the high-spin ferrous character of all iron ions. SQUID magnetometry reveals that the Fe(II) ions are involved in weak magnetic exchange coupling across the pyridonate bridges that results in antiferromagnetic interactions. The Fe₄ cluster exhibits slow relaxation of magnetization under an applied magnetic field with an effective energy barrier of 38.5 K, rarely observed among the very rare examples of Fe(II) cluster-based single-molecule magnets. Studies of protolytic substitution of the amido ligands demonstrated the lability of the diamondoid Fe₅ core in 1 and the stability of the Fe₄ rhomboid in 2.

Templated synthesis of Ni(ii) complexes of unsymmetrical Schiff base ligands derived from 1,3-diamino-2-propanol: structural diversity and magnetic properties

A Ferromagnetically coupled tetranuclear, an antiferromagnetically coupled hexanuclear and a mononuclear Ni(II) complex of new unsymmetrical Schiff base ligands derived from 1,3-diamino-2-propanol have been obtained with a slight change in the carbonyl compounds.

Heterometallic ZnII⁻LnIII⁻ZnII Schiff Base Complexes with Linear or Bent Conformation-Synthesis, Crystal Structures, Luminescent and Magnetic Characterization

A series of racemic, heteronuclear complexes [Zn₂Nd(ac)₂(HL)₂]NO₃·3H₂O (1), [Zn₂Sm(ac)₂(HL)₂]NO₃·3CH₃OH·0.3H₂O (2), [Zn₂Ln(ac)₂(HL)₂]NO₃·5.33H₂O (3–5) (where HL is the dideprotonated form of N,N′-bis(5-bromo-3-methoxysalicylidene)-1,3-diamino-2-propanol, ac = acetate ion, and Ln = Eu (3), Tb (4), Dy (5), respectively) with an achiral multisite coordination Schiff base ligand (H₃L) were synthesized and characterized. The X-ray crystallography revealed that the chirality in complexes is centered at lanthanide(III) ions due to two vicinally located μ-acetato-bridging ligands. The presented crystals have isoskeletal coordination units but they crystallize in monoclinic (1, 2) or trigonal crystal systems (3–5) with slightly different conformation. In 1 and 2 the Zn^II–Ln^III–Zn^II coordination core is linear, whereas in isostructural crystals 3–5 the chiral coordination cores are bent and lie on a two-fold axis. The complexes 1, 3–5 show a blue emission attributed to the emission of the ligand. For Zn^II₂Sm^III complex (2) the characteristic emission bands of f-f* transitions were observed. The magnetic properties for compounds 1, 4 and 5 are characteristic for the paramagnetism of the corresponding lanthanide(III) ions.

A newly developed highly selective Zn2+-AcO- ion-pair sensor through partner preference: equal efficiency under solitary and colonial situation

Unusual self-sorting of an ion-pair under highly crowded conditions driven by a synthesized intelligent molecule 2-((E)-(3-((E)-2-hydroxy-3-methoxybenzylideneamino)-2-hydroxypropyl imino)methyl)-6-methoxyphenol, hereafter HBP, is described. When a mixture of various metal salts was allowed to react with HBP, only a specific ion-pair Zn^II/AcO^- in the solution simultaneously reacted, resulting in high-fidelity ion-pair recognition of HBP. This phenomenon was evidenced by significant changes in the absorption spectra and huge enhancement in emission intensity of HBP. The property that one molecule preferring one particular cation-anion pair over others is a rare but interesting phenomenon. Thus, the potential to interact selectively with the targeted ion-pair resulting in the formation of a specific complex recognized HBP as a new class of molecule that might find future applications in real time and on-site monitoring and separation of new molecules.

Transition metal complexes of a versatile polyalkoxy oxazolidine-based ligand derived from in situ cyclization

One-pot reaction between 8-hydroxyquinoline-2-carboxaldehyde (HQC) and tris(hydroxymethyl)aminomethane (TRIS) followed by in situ cyclization yielded an oxazolidine based ligand which produced four mononuclear complexes of MnII(1), CoII(2), NiII(3), ZnII(4), a tetranuclear iron (FeIII4) complex (5) and a trinuclear cobalt (CoIICoIII2) complex (6). Magnetic studies show dominant antiferromagnetic interaction in tetranuclear iron (FeIII4) complex 5 and presence of the slow relaxation of magnetisation in 6. The compounds were also studied for their antibacterial properties. The oxazolidine ligand (H3L2) of this study showed good antimicrobial activity not only against Gram-positive bacteria but against Gram-negative bacteria too. The antimicrobial efficacy of the metal complexes (1-6) is also reported.

Structure and magnetism of two chair-shaped hexanuclear dysprosium(iii) complexes exhibiting slow magnetic relaxation

Two novel hexanuclear Dy^III complexes with polyhydroxy Schiff-base ligands, [Dy₆(L¹)₄(μ₃-OH)₄(MeOH)₄]Cl₂·2MeOH·2MeCN (1) and [Dy₆(HL²)₂(μ₃-OH)₂(μ₃-OCH₃)₂(piv)₁₀(MeOH)₂] (2) (H₃L¹ = N,N′-bis(3-methoxysalicylidene)(propylene-2-ol)-1,3-diamine, H₃L² = 2,3-dihydroxypropylimino)methyl)-6-methoxyphenol, piv = pivalate), have been prepared under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction, elemental analyses, thermal analyses, and IR spectroscopy. Each of the hexanuclear complexes is constructed with Dy₃ triangular motifs as building blocks, and the six Dy^III ions are arranged in a chair-shaped conformation. Variable-temperature magnetic susceptibility measurements in the temperature range of 2–300 K indicate dominant ferromagnetic exchange interactions between the Dy^III ions in the complexes. Both complexes exhibit slow magnetic relaxation behavior.

We report two novel chair-shaped hexanuclear Dy^III complexes with different polyhydroxy Schiff-base ligands. Both complexes are constructed with Dy₃ triangular motifs as building blocks and exhibit slow magnetic relaxation behavior at low temperature.

Effect of ligand substitution on the SMM properties of three isostructural families of double-cubane Mn4Ln2 coordination clusters

Three isostructural Mn–Ln families consists of 22 complexes have been presented. Only 7, 15, and 22 for Tb, 8 and 16 for Dy, and 20 for Sm displayed slow magnetization relaxation.

Three series of heterometallic NiII–LnIII Schiff base complexes: synthesis, crystal structures and magnetic characterization

Three series of Ni^II–Ln^III complexes were synthesized using compartmental Schiff base ligands in conjunction with auxiliary ligands. Their magnetic properties have been well studied.

Crystal structure of {6,6'-dihy-droxy-2,2'-[imino-bis-(propane-1,3-diyl-nitrilo-methanylyl-idene)]diphenolato-κ(5) O (1),N,N',N'',O (1')}copper(II)

The title compound, [Cu(C20H23N3O4)], crystallizes in the space group Cc with two independent mol-ecules in the asymmetric unit. The Cu(II) atoms are each coordinated by the penta-dentate Schiff base ligand in a distorted trigonal bipyramidal N3O2 geometry. The equatorial plane is formed by the two phenolic O atoms and the amine N atom, while the axial positions are occupied by the two imine N atoms. In the crystal, the two independent mol-ecules are each connected into a column along the b axis through inter-molecular O-H⋯O hydrogen bonds. The two independent columns are further linked through an N-H⋯O hydrogen bond, forming a double-column structure.

Ligand centered radical pathway in catechol oxidase activity with a trinuclear zinc-based model: synthesis, structural characterization and luminescence properties

A new trinuclear zinc(II) complex, [Zn3(L)(NCS)2](NO3)2·CH3OH·H2O (1), of a (N,O)-donor compartmental Schiff base ligand (H2L=N,N'-bis(3-methoxysalicylidene)-1,3-diamino-2-propanol), has been synthesized in crystalline phase. The zinc(II) complex has been characterized by elemental analysis, IR spectroscopy, UV-Vis spectroscopy, powder X-ray diffraction study (PXRD), (1)H NMR, EI mass spectrometry and thermogravimetric analysis. PXRD revealed that 1 crystallizes in P-1 space group with a=9.218 Å, b=10.849 Å, c=18.339 Å, with unit cell volume is 2179.713(Å)(3). Fluorescence spectra in methanolic solution reflect that intensity of emission for 1 is much higher compared to H2L and both the compounds exhibit good fluorescence properties. The complex 1 exhibits significant catalytic activities of biological relevance, viz. catechol oxidase. In methanol, it efficiently catalyzes the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to corresponding quinone via formation of a dinuclear species as [Zn2(L)(3,5-DTBC)]. Electron Paramagnetic Resonance (EPR) experiment suggests generation of radicals in the presence of 3,5-DTBC and it may be proposed that the radical pathway is probably responsible for conversion of 3,5-DTBC to 3,5-DTBQ promoted by complex of redox-innocent Zn(II) ion.

Characterization of a meso-chiral isomer of a hexanuclear Cu(ii) cage from racemization of the l-alanine Schiff base

Revising well studied Schiff base racemization led to isolation of a new chiral architecture exhibiting relatively rare ferromagnetic properties.

Versatile chemical transformations of benzoxazole based ligands on complexation with 3d-metal ions

Two benzoxazoles derivative ligands were synthesized from the condensation of 3,5-di-tert-butyl-o-benzoquinone (DTBBQ) with ethanolamine or 1,3-diamino-2-hydroxypropane in methanol. Condensation of DTBBQ with ethanolamine gives the expected 5,7-di-tert-butyl-2-methylenhydroxylbenzoxazole (HL1) while with 1,3-diamino-2-hydroxypropane it gives (2-hydroxyethyl-2-{2,4-bis(1,1-dimethylethyl)-1-phenol-6 amino}-2{5,7-di-tert-butyl-benzoxazole}) (H(2)L2) with only one benzoxazole ring instead of the symmetric bis-benzoxazole derivative. The structure of HL1 and H(2)L2 were confirmed by NMR-spectroscopy and X-ray diffraction on a single crystal for HL1. The reaction of HL1 with CuCl(2) gives a mononuclear [Cu(II)(HL1)(2)Cl(2)] (1) complex for which the crystal structure shows that HL1 is preserved. In contrast, upon reaction with nickel(II), cobalt(II), and manganese(II) H(2)L2 is further oxidized and transformed in new ligands HL3 in mononuclear complexes [M(II)(L3)(2)] (M = Ni(II) (2); M = Co(II) (3)) and H(2)L4 in tetranuclear complex [Mn(II)(4)(HL4)(4)Cl(4)] (4) as found from the crystal structures of complexes 2-4. Electrochemical studies for complexes 2 and 3 evidence complicated redox properties. [Mn(II)(4)(HL4)(4)Cl(4)] (4) has a cubane-like structure with a "4 + 2" fashion The magnetic susceptibility of 4 is well fitted considering one Mn---Mn interaction J(a)(Mn(II)-Mn(II)) = -0.50(1) cm(-1) with g = 2.00(7).