Spin crossover FeII complexes as templates for bimetallic oxalate-based 3D magnets

We present the synthesis and structural characterization of the salt [Fe(bpp)₂][MnCr(ox)₃]₂ · bpp · CH₃OH. It crystallizes in the monoclinic space group. This material contains an anionic [MnCr(ox)₃]⁻ 3D 10-gon ferromagnetic network, that orders below 3.0 K. The channels created by this architecture are filled by the spin crossover cations [Fe(bpp)₂]²⁺ (bpp = 2,6(bispyrazol-3-yl)pyridine), free ligand and solvent molecules. No spin transition has been observed at ambient pressure.     

Synthesis,structural characterizations,spectroscopic and magnetic properties of MnII and MnIII complexes with an unprecedented bridging coordination mode of 2-salicylichydrazono-1,3-dithiolane ligand

Two new complexes [Mn^III(HL)₂(acac)] and [Mn^II(HL)₂]_n have been obtained by reacting manganese(III) acetylacetonate monohydrate or manganese(II) chloride monohydrate with 2-salicylichydrazono-1,3-dithiolane ligand (H₂L). Both compounds have been fully characterized by spectroscopic methods and single crystal X-ray diffraction. In the solid state, the molecular packing are described and discussed in term of weak H-bonds and short contacts. The unprecedented bridging coordination mode of this ligand lead to the first 2-salicylichydrazono-1,3-dithiolane-bridged coordination polymer [Mn^II(HL)₂]_n. The EPR spectrum of this compound was obtained with g ≈ 2.07, corresponding to a manganese ion (+II) in octahedral high-spin coordination sphere. The Mn^II complex exhibit paramagnetic behavior corresponding to quasi-isolated metal centers.     

A convenient MnIII starting material for the synthesis of homo- and heterometallic manganese carboxylate clusters: Mn9 and Mn10−xFex complexes

The use of a convenient source of Mn^III ions, namely the [Mn(OR)(O₂CR′)₂]_n (R = H, Me, and R′ = Me, Bu^t) family of 1-D coordination polymers, afforded two new enneanuclear and decanuclear molecular clusters, homometallic [Mn₉O₇(O₂CBu^t)₁₃(MeCN)₂] (3) and heterometallic [Mn_10?xFe_x(OMe)₂₀(O₂CMe)₁₀] (x < 10) (4), respectively. Compound 3 was synthesized by a solvent-induced structural transformation, whereas complex 4 resulted from the reaction of [Mn(OH)(O₂CMe)₂]_n with an Fe^III source. The core of 3 comprises two [Mn₄O₂]⁸⁺ butterfly units and a [Mn₃O]⁷⁺ triangular unit fused together by sharing one Mn atom. Magnetic susceptibility measurements of 3 revealed dominant antiferromagnetic interactions within the molecule, and a ground state of S = 1 with many low-lying excited states. Complex 4 is a mixed Fe^III/Mn^III single-strand molecular wheel, which forms 3D nanotubular stacks arranged in a zig–zag fashion. The described work suggests that the [Mn(OR)(O₂CR′)₂]_n compounds represent excellent starting materials for Mn^III carboxylate cluster chemistry.     

New derivatives of an enneanuclear Mn SMM

The reaction of the neutral triangular species [Mn₃O(O₂CR)₆L₃] (R = Me, Ph, CMe₃; L = py) with the tripodal ligands H₃tmp (1, 1, 1-tris(hydroxymethyl)propane) and H₄peol (pentaerythritol) affords the enneanuclear complexes [Mn₉O₇(O₂CMe)₁₁(tmp)(py)₃(H₂O)₂] (2); [Mn₉O₇(O₂CMe)₁₁(Hpeol)(py)₃(H₂O)₂] (3); [Mn₉O₇(O₂CCMe₃)₁₁(Hpeol)(py)₃(H₂O)₂] (4); and [Mn₉O₇(O₂CPh)₁₁(Hpeol)(py)₃(H₂O)₂] (5). Complexes 2–5 are characterized by spin ground states of S = 17/2 with axial zero-field splitting parameters in the range D = −0.26–0.30 cm⁻¹. Sweep-rate and temperature dependent hysteresis loops diagnostic of SMM behaviour are observed below 1.2 K featuring steps at regular intervals of field.     

A mixed-valence Mn6 cluster capped by nitronyl nitroxide units

A mixed-valence Mn₆ cluster, [Mn₆O₂(t-BuCO₂)₁₀(H₂O)(NNPy)₂] (2), has been synthesized by the assembly of [Mn₆O₂(t-BuCO₂)₁₀(THF)₄] · THF (1) with a nitronyl nitroxide radical molecule, 2-(p-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NNPy). Complex 2 consists of [Mn₆O₂]¹⁰⁺ core and two NNPy radical attachments, where the [Mn₆O₂]¹⁰⁺ core is composed of two Mn^III ions (i.e., the inner Mn ions) bridged by two μ₄-O²⁻ and four Mn^II ions (i.e., the outer Mn ions) surrounding the inner Mn^III ions via the two μ₄-O²⁻, forming an edge-shared double-tetrahedral polygon (vertices: Mn ions, centers: μ₄-O²⁻). Bridges by pivalate groups in μ₂- and μ₃-modes assist the coordination spheres around these Mn ions. Two of the outer Mn^II ions in trans position are, to the sixth coordination site, occupied by NNPy molecule (pyridine-N coordination). One of the outer Mn^II ions is occupied by a water molecule to complete octahedral geometry, but the rest of them is vacancy taking a square-pyramidal geometry. The variable-temperature direct current (DC) magnetic susceptibility was collected in the temperature range of 1.81 to 300 K at a 1 kOe appled field. The molar magnetic susceptibility (χ_M) steadily increases from 0.053 emu mol⁻¹ at 300 K to 0.29 emu mol⁻¹ at 20 K, showing a kink (peak), and then increases rapidly to 0.70 emu mol⁻¹ at 1.81 K. The profile of this magnetic behavior indicates that the intracluster spin cancellation takes place bellow 20 K to derive an S_Mn6 = 0 by strong antiferromagnetic interaction between Mn ions. This is consequently leading to paramagnetic isolation of only the two nitronyl nitroxide units as if remaining as exchange-uncorrelated spin carriers. The variable-temperature ESR spectra show a sharp signal below 30 K with g = 2.00, proving the presence of free nitronyl nitroxide radical, in which double integral of such signal obeys the Curie–Weiss law that follows the susceptibility result in the low-temperature region.     

Spin crossover behavior in two-dimensional bimetallic coordination polymer FeII(3-bromo-4-picoline)2[AuI(CN)2]2: Synthesis,crystal structures,and magnetic properties

A new novel 2D network bimetallic Fe^IIAu^I spin crossover coordination compound based on 3-bromo-4-picoline and bridged cyano ligands, {Fe^II(3-bromo-4-picoline)₂[Au^I(CN)₂]₂}_n (1), has been synthesized and characterized by elemental analyses and IR, using single-crystal X-ray analysis at 293 K and at 90 K and magnetic measurements. The Fe^II ions in 1 have octahedral FeN₆ coordination geometries, which are linked by a [Au^I(CN)₂]^? unit at the equatorial plane to form a polymeric 2D sheet architecture. The two pyridine rings coordinate at the axial positions. The structure of 1 comprises parallel 2D arrays and the layers interact by pairs, defining bilayers with strong binuclear aurophilic Au?Au interactions. Furthermore, intermolecular Au?Br and Br?Br distances in 1 are significantly smaller than the sums of the van der Waals radii. Variable-temperature (2–300 K) magnetic susceptibility measurements of 1 have been performed to determine behaviors of spin transition. The susceptibility data of 1 indicates that about 50% of the HS states are changed to LS states at 75 K. The Fe–N bond distances at 90 K show that ratio of high spin states agree with the SQUID data.     

Ferromagnetic interaction between [Ni(bdt)2]− anions in [Mn2(Saloph)2(μ-OH)][Ni(bdt)2](CH3CN)2

A new molecule-based magnetic material [Mn₂(Saloph)₂(μ-OH)][Ni(bdt)₂](CH₃CN)₂ was prepared by the metathesis of [Mn(Saloph)(H₂O)(ClO₄)] (S = 2) and TBA[Ni(bdt)₂] (S = 1/2). In the crystal, [Ni(bdt)₂]^? anions form square lattices which are separated from each other by the layers of antiferromagnetically coupled binuclear cations [Mn₂(Saloph)₂(μ-OH)]⁺. The magnetic susceptibility of the material coincides with the sum of the S = 2 van Vleck dimer model and S = 1/2 Heisenberg ferromagnetic square lattice model with 2J = ?92.4 and +4.5 K, respectively. The origin of the ferromagnetic interaction can be explained by the T-shaped intermolecular overlap mode of SOMOs which spreads to the ends of [Ni(bdt)₂]^? molecules.     

Synthesis,structures and magnetic properties of two hexanuclear complexes

The reaction of salicylaldoxime (H₂salox) with Mn(ClO₄)₂ · 6H₂O, NaN(CN)₂ and NEt₃ in MeOH affords a Mn^III₆ hexanuclear complex of [Mn₆O₂(salox)₆(MeOH)₆(NCNCONH₂)₂] (1), while reaction of H₂salox with MnCl₂ · 4H₂O and NEt₄OH in EtOH affords a Mn^III₆ hexanuclear complex of [Mn₆O₂(salox)₆(EtOH)₄(H₂O)₂Cl₂] (2). Both complexes 1 and 2 contain a [Mn^III₆(μ₃-O)₂]¹⁴⁺ core, which is a known structural type in the family of Mn₆ complexes. Variable temperature magnetic susceptibilities and magnetization measurement of complexes 1 and 2 have been carried out. Exchange interactions of metal centers for complexes 1 and 2 are fitted by a full diagonalization matrix method. The fitting results indicate that both complexes 1 and 2 have the ground-state spin value of S = 4, and the ground state of complex 1 has the much closer energy to low-lying spin states than that of complex 2. Magnetization measurements at 2.0–4.0 K and 10–70 kG confirm that the ground state is S = 4, with significant magnetoanisotropy as gauged by the D value of ?0.82 cm^?1 and ?1.18 cm^?1, for 1 and 2, respectively. The frequency dependence of the out-of-phase component in alternating current magnetic susceptibilities for both complexes 1 and 2 indicates the slow magnetic relaxation of superparamagnetic behaviour with a U_eff of 27.0(1) K and τ₀ = 3.8(2) × 10^?9 s for complex 1, and U_eff of 25.1(6) K and τ₀ = 4.6(1) × 10^?8 s for complex 2.     

Spectral and physico-chemical investigations of novel homo-dinuclear di-μ2-alkoxo bridged Schiff base complexes: 57Fe Mössbauer parameters of the Fe(III) complex

Spectral and molecular model computations on homo-dinuclear complexes [M₂L₂(H₂O)₂Cl₂] [L = 1-(salicylaldeneamino)-3-hydroxypropane, M = Cr³⁺, Mn³⁺, Fe³⁺, Co³⁺, Ni³⁺ or Cu³⁺] are consistent with a distorted hexa-coordinate geometry. X-band EPR spectral data indicated a rhombic distortion around Cu(II) ion. Magnetic moment and ⁵⁷Fe Mössbauer data confirmed a high-spin state electronic configuration (t_2g³e_g², S = 5/2) and asymmetric ligand environment around Fe(III) with nuclear transitions Fe(±3/2 → 1/2) exhibiting Kramer's double degeneracy. The neighboring Fe(III) nuclei in the homo-dinuclear species are antiferromagnetically coupled.     

Syntheses,crystal structures and magnetic properties of coordination polymers Ni(NO2)2 and Ni(4,4′-bipy)(NO2)2

Two new coordination polymer frameworks Ni(NO₂)₂ (1) and Ni(4,4′-bipy)(NO₂)₂ (2) (4,4′-bipy = 4,4′-bipyridine) were synthesized by solvothermal reaction in formamide, and were characterized by elemental analysis, IR spectroscopy, single crystal X-ray diffraction, and magnetic measurement. In compound 1, each Ni²⁺ ion is linked with four neighboring Ni²⁺ ions through μ_1,3-nitrito bridges forming 2D layered structure. In compound 2, each Ni²⁺ ion is bridged with six neighboring Ni²⁺ ions through four μ_1,3-nitrito groups and two 4,4′-bipy ligands forming 3D structure. Magnetic measurements show weak ferromagnetism within framework of the two compounds with T_N = 19 K (1) and 21 K (2).     

Synthesis,structure and magnetic properties of 2-D and 3-D [cation]{M[Au(CN)2]3} (M = Ni, Co) coordination polymers

In order to study the templating effect of the cation and the resulting impact on the magnetic properties, reactions of M(II) salts with [cation][Au(CN)₂] were conducted, yielding a series of coordination polymers of the form [cation]{M[Au(CN)₂]₃} (cation = ⁿBu₄N⁺, PPN⁺ (bis(triphenylphosphoranylidene)ammonium); M = Ni(II) and Co(II)). The structures of ⁿBu₄N{M[Au(CN)₂]₃} and PPN{M[Au(CN)₂]₃} (M = Ni and Co) contain two distinct 3-D anionic frameworks of {M[Au(CN)₂]₃}⁻, hence the framework was sensitive to the cation, but not to the identity of the metal center. In ⁿBu₄N{M[Au(CN)₂]₃}, the metal centers are connected by [Au(CN)₂] units to form six 2-D (4, 4) rectangular grids that are fused through the M centers to yield a complex three-dimensional framework which accommodates the ⁿBu₄N⁺ cations. In PPN{M[Au(CN)₂]₃}, the framework adopts a simpler non-interpenetrated Prussian-blue-type pseudo-cubic array, with the PPN⁺ cations occupying each cavity; no reduction in dimensionality occurs despite the large cation size. In the presence of water, {Co(H₂O)₂[Au(CN)₂]₂} · ⁿBu₄N[Au(CN)₂] was obtained, a 2-D layered polymer that contains neutral sheets of {Co(H₂O)₂[Au(CN)₂]₂} which are separated by ⁿBu₄N[Au(CN)₂] layers; aurophilic interactions of 3.4250(13) Å and hydrogen-bonding connect the layers. The magnetic properties of all compounds were investigated by SQUID magnetometry. The Ni(II) polymers have similar magnetic behaviour, which are dominated by zero-field splitting with very weak antiferromagnetic interactions at low temperature (D ∼ 2–3 cm⁻¹, zJ < 1 cm⁻¹). The magnetic behaviour of all of the Co(II) polymers were found to be very similar, and dominated by single-ion effects (i.e. a large first-order orbital contribution). No significant magnetic coupling is observed in any of these coordination polymers, suggesting that the [Au(CN)₂] bridging unit behaves as a poor mediator of magnetic exchange in these high-dimensionality systems.     

Lithium–manganese–nickel-oxide electrodes with integrated layered–spinel structures for lithium batteries

A series of lithium–manganese–nickel-oxide compositions that can be represented in three-component notation, xLi[Mn_1.5Ni_0.5]O₄ · (1 − x){Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂}, in which a spinel component, Li[Mn_1.5Ni_0.5]O₄, and two layered components, Li₂MnO₃ and Li(Mn_0.5Ni_0.5)O₂, are structurally integrated in a highly complex manner, have been evaluated as electrodes in lithium cells for x = 1, 0.75, 0.50, 0.25 and 0. In this series of compounds, which is defined by the Li[Mn_1.5Ni_0.5]O₄–{Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂} tie-line in the Li[Mn_1.5Ni_0.5]O₄–Li₂MnO₃–Li(Mn_0.5Ni_0.5)O₂ phase diagram, the Mn:Ni ratio in the spinel and the combined layered Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ components is always 3:1. Powder X-ray diffraction patterns of the end members and the electrochemical profiles of cells with these electrodes are consistent with those expected for the spinel Li[Mn_1.5Ni_0.5]O₄ (x = 1) and for ‘composite’ Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ layered electrode structures (x = 0). Electrodes with intermediate values of x exhibit both spinel and layered character and yield extremely high capacities, reaching more than 250 mA h/g with good cycling stability between 2.0 V and 4.95 V vs. Li° at a current rate of 0.1 mA/cm².     

Tetranuclear azido-bridged copper(II) complex [Cu4(μ-salpn)2(μ1,1-N3)2(N3)2(H2O)2]: Synthesis,characterization and crystal structure

The reaction of salpnH₂ Schiff-base ligand (salpnH₂ = N,N′-bis(salicylidene)-1,3-propylenediamine) with Cu(NO₃)₂·3H₂O and a large excess of NaN₃ (1:2:8 molar ration), lead to the formation of [Cu₄(μ-salpn)₂(μ_1,1-N₃)₂(N₃)₂(H₂O)₂] (1), which has been successfully obtained and characterized by elemental analyses, IR spectroscopy and single-crystal X-ray diffraction. The strong absorption band at about 2000–2100 cm^?1 and at 1597 cm^?1 regions of the IR spectrum of 1 clearly proves the presence of the both end-on (EO) bridging and terminal azido ions and CN (azomethine) groups, respectively. Single-crystal X-ray analyses revealed that the copper atoms are bridged alternately by end-to-on (EO) azido and phenoxo-salpn ligands in the prepared tetranuclear copper(II) complex [Cu₄(μ-salpn)₂(μ_1,1-N₃)₂(N₃)₂(H₂O)₂] (1).     

Synthesis,characterization and fluorescence properties of hexanuclear zinc(II) complexes

Two hexanuclear zinc(II) complexes, [Zn₆(L¹)₂(μ₂-OH)₂(μ₂-CH₃COO)₈] · CH₃CN (1 · CH₃CN) and [Zn₆(L²)₂(μ₂-OH)₂(μ₂-CH₃COO)₈] · 4CH₃CN (2 · 4CH₃CN), where HL¹ = 4-methyl-2,6-bis(cyclohexylmethyliminomethyl)-phenol and HL² = 4-methyl-2,6-bis(1-naphthalylmethyliminomethyl)-phenol, have been synthesized and characterized by elemental analysis, FT-IR and fluorescence spectroscopic methods, and by X-ray diffraction analysis. In the asymmetric unit of complex 1, two of the three zinc atoms have pentacoordinate geometries and the other is tetrahedrally coordinated, whereas the three distinct Zn atoms in complex 2 adopt three different coordination environments, namely distorted octahedral, trigonal bipyramidal and tetrahedral. The fluorescence properties of the ligands and complexes have been investigated.     

Synthesis,structural characterization and magnetic properties of a novel metallacrown [Fe6(amshz)6(C3H7NO)6]·6CH3OH

The novel 18-metallacrown-6 metallamacrocycle, with the formula of [Fe₆(amshz)₆(C₃H₇NO)₆]·6CH₃OH (1), has been synthesized by the self-assembly reaction of iron ions with N-substituted salicylhydrazide ligands. Six Fe(III) ions and six deprotonated N-acetyl-3-methylsalicylhydrazide (amshz^3?) ligands construct a planar 18-membered ring based on Fe–N–N–Fe linkage. Due to the coordination, the ligand enforces the stereochemistry of the Fe³⁺ ions as a propeller shape with alternating …ΔΛΔΛ… configurations. There exists a strong antiferromagnetic exchange interaction with μ_eff = 12.54 μ_B at 300 K between the Fe(III) spin 5/2 centers.     

Dinuclear triple helical Mn(III), Fe(III) and Co(III) complexes

Synthesis, characterization and physical properties of the dinuclear triple helical complexes [Mn₂(μ-L)₃] (1), [Fe₂(μ-L)₃] (2) and [Co₂(μ-L)₃] (3) with the tetradentate Schiff base (H₂L) derived from 1 mol equiv. of hydrazine and 2 mole equiv. of 2-hydroxy-1-naphthaldehyde are described. Triple helical molecular structures of 2 and 3 have been confirmed by X-ray crystallography. Magnetic susceptibility measurements reveal complex 3 is diamagnetic while a weak antiferromagnetic interaction is operative between the metal centres in both 1 and 2.     

3D pillar-layered coordination polymers based on 4d–4f heterometallic assembly

By control of mixed ligands with particular coordination sites, heterometallic coordination polymers, [Ln₂(H₂O)₂Ag(C₂O₄)₂(ina)₃]_n (Ln = Eu (1), Dy (2), Hina = isonicotinic acid) and {[LnAg(C₂O₄)(na)₂]·2H₂O}_n (Ln = La (3), Tb (4), Hna = nicotinic acid), have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, thermogravimetric analysis (TGA), and single-crystal X-ray diffraction. These coordination polymers feature 3D pillar-layered coordination frameworks constructed from two-dimensional (2D) lanthanide–carboxylate layers and Ag(ina) or Ag(na) pillars. It is interesting that the in situ decarboxylation of pyridine-2,3-dicarboxylic acid into nicotinic acid was observed. The luminescent properties of 1 and 4 were also studied.     

Spectroscopy,thermal and structural studies of new ZnII coordination polymer, [Zn3(μ-bpa)4.5(AcO)3](ClO4)3·4.26H2O

Three Zn^II coordination polymers with acetate and perchlorate anions, [Zn₃(μ-bpa)_4.5(AcO)₃](ClO₄)₃·4.26H₂O (1), [Zn₂(μ-bpe)₃(AcO)₂](ClO₄)₂ (2) and [Zn₂(bpe)(AcO)₄] (3), bpa = 1,2-bis(4-pyridyl)ethane and bpe = 1,2-bis(4-pyridyl)ethene, have been synthesized and characterized by elemental analysis, IR, ¹H NMR, and ¹³C NMR spectroscopies, and the structure of compound 1 was determined by single-crystal X-ray diffraction. The thermal stabilities of compounds 1–3 were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The structural studies of compound 1 show that the structure may be considered as a three-dimensional coordination polymer of zinc(II) with large voids filled with disordered water molecules. The stability of the porous networks after removal of the guest water molecules is confirmed by X-ray powder diffraction.     

Assembly of two novel Lindqvist polyoxoanion-templated coordination polymers with standard honeycomb cavities

Two novel polyoxometalate(POM)-templated coordination polymers: [Cu₂(phnz)₃][M₆O₁₉] (M = Mo for 1, W for 2; phnz = phenazine), have been hydrothermally synthesized and characterized by routine physical methods and single crystal X-ray diffraction. In the compounds, Lindqvist POMs as templates induce the [Cu₂(phnz)₃] complexes to 2D hexagonal metal-organic framework (MOF), which represents 6³ topologies of dimensions ca. 13.515 × 13.515 × 13.515 Å. Furthermore, the 2D sheets are held together by Lindqvist POMs into 3D supramolecular networks with 1D channel, and Lindqvist POMs site in the channels. The successful syntheses and isolation of two compounds provide a novel example of the utility of POM clusters as templates for self-assembly extended framework with cavities.     

A ruthenium(II) complex with the propionate ion: Synthesis,characterization and cytotoxic activity

The complex [Ru(η²-O₂CCH₂CH₃)(dppe)₂]PF₆ (dppe = 1,2-bis(diphenylphosphino)ethane) was prepared and characterized by elemental analysis, spectroscopic techniques, X-ray crystallography, HRESIMS and HRESIMS/MS. The characterization data are consistent with a cis arrangement for the dppe ligands and a bidentate coordination of the propionate ligand through carboxylate oxygens. Cytotoxicity assays were carried out on human and murine cancer and normal cell lines. In general, the [Ru(η²-O₂CCH₂CH₃)(dppe)₂]PF₆ complex was more cytotoxic than both its precursor cis–[RuCl₂(dppe)₂] and the reference metallodrug cisplatin. The best results against the HepG2 human tumour cell line and S180 murine tumour cell line were found with IC₅₀ values of 6.5 ± 0.2 and 0.18 ± 0.03 μM, respectively.