Theoretical Studies on the Magnetic Switching Controlled by Stacking Patterns of Bis(maleonitriledithiolato) Nickelate(III) Dimers

Lanthanide-Sensitized Upconversion Iridium Complex via Triplet Energy Transfer

Cyclometalated iridium (Ir) complexes demonstrate impressive capabilities across a range of fields, including biology and photocatalysis, due to their tunable optical characteristics and structure flexibility. However, generating upconversion luminescence of Ir complexes under near-infrared light excitation is challenging. Herein, by employing lanthanide-doped upconversion nanoparticles (UCNPs) as the sensitizer, a new strategy is demonstrated to gain upconversion luminescence of Ir complexes via triplet energy transfer. This design relies on a rationally designed hybrid of core-shell structured NaYbF4:Tb@NaTbF4 UCNPs and new Ir phosphonate complexes, in which UCNPs can migrate upconverted energy to the surface of nanoparticles through Tb3+-mediated energy migration and then sensitize the upconversion luminescence of Ir complexes upon 980 nm excitation. Both experimental and theoretical investigations highlight the significance of triplet energy transfer from excited Tb3+ ions to the triplet state of Ir complexes in the sensitization of upconversion luminescence of Ir complexes. These findings may open exciting avenues for fabricating hybrid Ir materials with new functions and driving the development of UCNP-based nanomaterials.

Two-Dimensional Spin-Crossover Molecular Solid Solutions with Tunable Transition Temperatures across 90 K

Spin-crossover (SCO) materials exhibit remarkable potential as bistable switches in molecular devices. However, the spin transition temperatures (Tc) of known compounds are unable to cover the entire ambient temperature spectrum, largely limiting their practical utility. This study reports an exemplary two-dimensional SCO solid solution system, [FeIII(H0.5LCl)2-2x(H0.5LF)2x]·H2O (H0.5LX = 5-X-2-hydroxybenzylidene-hydrazinecarbothioamide, X = F or Cl, x = 0 to 1), in which the adjacent layers are adhered via hydrogen bonding. Notably, the Tc of this system can be fine-tuned across 90 K (227-316 K) in a linear manner by modulating the fraction x of the LF ligand. Elevating x results in strengthened hydrogen bonding between adjacent layers, which leads to enhanced intermolecular interactions between adjacent SCO molecules. Single-crystal diffraction analysis and periodic density functional theory calculations revealed that such a special kind of alteration in interlayer interactions strengthens the FeIIIN2O2S2 ligand field and corresponding SCO energy barrier, consequently resulting in increased Tc. This work provides a new pathway for tuning the Tc of SCO materials through delicate manipulation of molecular interactions, which could expand the application of bistable molecular solids to a much wider temperature regime.

[(18-Crown-6)K][Fe(1)Cl(1)4 ]0.5 [Fe(2)Cl(2)4 ]0.5 : A Multifunctional Molecular Switch of Dielectric, Conductivity and Magnetic Properties

Multifunctional materials that exhibit different physical properties in a single phase have potential for use in multifunctional devices. Herein, we reported an organic-inorganic hybrid compound [(18-crown-6)K][Fe(1)Cl(1)₄ ]_0.5 [Fe(2)Cl(2)₄ ]_0.5 (1) by incorporating KCl and FeCl₃ into a 18-crown-6 molecule, which acts as a host of the six O atoms providing a lone pair of electrons to anchor the guest potassium cation, and [FeCl₄ ]^- as a counterion for charge balance to construct a complex salt. This salt exhibited a one-step reversible structural transformation giving two separate high and low temperature phases at 373 K, which was confirmed by systematic characterizations including differential scanning calorimetry (DSC) measurements, variable-temperature structural analyses, and dielectric, impedance, variable-temperature magnetic susceptibility measurements. Interestingly, the structural transformation was coupled to both hysteretic dielectric phase transition, conductivity switch and magnetic-phase transition at 373 K. This result gives an idea for designing a new type of phase-transition materials harboring technologically important magnetic, conductivity and dielectric properties.

Temperature-dependent ESR and computational studies on antiferromagnetic electron transfer in the yeast NADH dehydrogenase Ndi1

The electron transfer mechanism of Ndi1.

Theoretical studies on oxidation-switchable second-order nonlinear optical responses of Metallosalen-Keggin polyoxometalate derivatives

The one-electron oxidation effect on the first hyperpolarizability of Metallosalen-Keggin polyoxometalate derivatives.

The origin of the antiferromagnetic behaviour of the charge-transfer compound (HMTTF)[Ni(mnt)2]

Herein we disclose the origin of the magnetic behaviour of the remarkable (HMTTF)[Ni(mnt)₂] charge-transfer compound.

Crystal structure of bis-[1-(naphthalen-1-ylmeth-yl)pyridinium] bis-(2,2-di-cyano-ethene-1,1-di-thiol-ato-κ(2) S,S')nickelate(II)

In the ion-pair complex, bis­[1-(naphthalen-1-ylmeth­yl)pyridinium] bis­(2,2-di­cyano­ethene-1,1-di­thiol­ate-κ²S,S′)nickelate(II), C—H⋯N and C—H⋯Ni hydrogen bonds as well as π–π inter­actions between the ions result in the formation of a three-dimensional network.

A new ion-pair complex, (C₁₆H₁₄N)₂[Ni(C₄N₂S₂)₂] or (1-NaMePy)₂[Ni(imnt)₂], where 1-NaMePy is 1-(4-naphthyl­methyl­ene)pyridinium and imnt is 2,2-di­cyano­ethene-1,1-di­thiol­ate, was obtained by the direct reaction of NiCl₂, K₂imnt and (1-NaMePy)⁺Br⁻ in H₂O. The asymmetric unit contains a [1-NaMePy]⁺ cation and one half of an Ni(imnt)₂²⁻ anion. The Ni^II ion lies on an inversion centre and adopts a square-planar configuration with Ni—S bond lengths of 2.200 (1) and 2.216 (1) Å. In the [1-NaMePy]⁺ cation, the naphthyl ringsystem and the pyridinium ring make a dihedral angle of 90.0 (2)°. In the crystal, C—H⋯N and C—H⋯Ni hydrogen bonds, as well as π–π inter­actions between the chelate ring and the pyridinium ring [centroid–centroid distance = 3.675 (2) Å] link the ions into a three-dimensional network.

1,1'-(Ethane-1,2-di-yl)dipyridinium bis-(1,2-di-cyano-ethene-1,2-di-thiol-ato-κ(2) S,S')cuprate(II)

In the title ion-pair complex, (C12H14N2)[Cu(C4N2S2)2], the complex anion exhibits a highly twisted coordination environment around the tetra-coordinated Cu(II) atom. The dihedral angles between the 1,2-di-cyano-ethene-1,2-di-thiol-ato ligands and between the two pyridine rings in the cation are 37.49 (3) and 29.18 (10)°, respectively. Weak C-H⋯N and C-H⋯S hydrogen bonds link the cations and anions into a three-dimensional network.

Bis[1-(eth-oxy-carbonyl-meth-yl)pyridinium] bis-(1,2-dicyano-ethene-1,2-dithiol-ato-κ(2)S,S')nickelate(II)

The asymmetric unit of the title ion-pair complex, (C(9)H(12)NO(2))(2)[Ni(C(4)N(2)S(2))(2)], contains two 1-(eth-oxy-carbonyl-meth-yl)pyridinium cations and one bis-(1,2-dicyano-ethene-1,2-dithiol-ato)nickelate(II) dianion, which exhibits a slightly distorted square-planar coordination geometry. In the crystal, the cations are linked by strong C-H⋯O hydrogen bonds into C(6) chains along [100]. The cations and anions are linked into a three-dimensional architecture by weak C-H⋯N and C-H⋯S inter-actions.

Bis(4-dimethyl-amino-1-ethyl-pyridinium) bis-(1,2-dicyano-ethene-1,2-dithiol-ato-κ(2)S,S')nickelate(II)

The asymmetric unit of the title complex, (C₉H₁₅N₂)₂[Ni(C₄N₂S₂)₂], comprises one 4-dimethyl­amino-1-ethyl­pyri­din­ium cation and one half of a [Ni(mnt)₂]²⁻ (mnt²⁻ = maleo­nitrile­dithiol­ate) anion; the complete anion is generated by the application of a centre of inversion. The Ni^II ion is coordinated by four S atoms of two mnt²⁻ ligands and exhibits a square-planar coordination geometry.

Observation of metal ion dependent packing structures and magnetic behaviors of metal-bis-1, 2-dithiolene complexes

The crystal structures and magnetic properties were investigated experimentally and theoretically for two S = ½ spin chain complexes, which consist of [M(mnt)(2)](-) (M = Pt for 1 or Pd for 2) with 1-(4'-bromo-2'-flurobenzyl)-4-aminopyridinium (1-BrFBz-4-NH(2)Py(+)). The 1-BrFBz-4-NH(2)Py(+) cations exhibit different molecular conformations and arrangements in 1 and 2; the [M(mnt)(2)](-) anions form regular stacks in 1, whereas they form irregular stacks in 2. In addition, the intermolecular interactions between the [M(mnt)(2)](-) anions and cations are also different from each other in the crystals of 1 and 2. Complex 1 shows the magnetic characteristics of a low-dimensional antiferromagnetic coupling spin system with a spin-Peierls-type transition around 7 K, and complex 2 exhibits diamagnetism over the temperature range of 5-300 K. Theoretical analyses, based on the calculations for the charge density distributions of [Pt(mnt)(2)](-) and [Pd(mnt)(2)](-) anions and the magnetic exchange constants within the anion spin chains, addressed the diverse molecular alignments in the crystals of 1 and 2 and distinct magnetic behaviors between 1 and 2.

Bis[(2-chloro-4-fluoro-benz-yl)triphenyl-phospho-nium] bis-(1,2,5-thia-diazole-3,4-dithiol-ato)nickelate(II)

The title ion-pair complex, (C₂₅H₂₀ClFP)₂[Ni(C₂N₂S₃)₂], was obtained by the direct reaction of (4-F,2-ClBzTPP)⁺·Br⁻ [4-F,2-ClBzTPP⁺ is (2-chloro-4-fluoro­benz­yl)triphenyl­phos­pho­nium], NiCl₂·6H₂O and Na₂tdas (tdas²⁻ is 1,2,5-thia­diazole-3,4-dithiol­ate) in methanol. The asymmetric unit of the title structure comprises one (4-F,2-ClBzTPP)⁺ cation and half of an [Ni(tdas)₂]²⁻ complex anion, with the Ni^II ion situated on a center of symmetry, leading to a slightly distorted square-planar coordination of the latter. In the cation, the tetra­hedral angles around the P atom are nearly undistorted. In the crystal, the cations and anions are linked by C—H⋯S, C—H⋯N and C—H⋯Cl hydrogen bonds.

1-Butyl-pyridinium bis-(1,2-dicyano-ethene-1,2-dithiol-ato)nickelate(III)

The Ni^III atom in the anion of the title complex, (C₉H₁₄N)[Ni(C₄N₂S₂)₂], is coordinated by four S atoms of two maleonitrile­dithiol­ate ligands, and exhibits a square-planar coordination geometry.

Bis(8-hy-droxy-1-methyl-quinolin-1-ium) bis-(1,2-dicyano-ethene-1,2-dithiol-ato)nickelate(II) dihydrate

In the title ion-pair complex, (C(10)H(10)NO)(2)[Ni(C(4)N(2)S(2))(2)]·2H(2)O, the anion has crystallographically imposed centre of symmetry. The Ni(II) atom exhibits a slightly distorted square-planar coordination geometry. In the crystal, the water mol-ecule links anions and cations into a three-dimensional network via O-H⋯N, O-H⋯S and O-H⋯O hydrogen bonds. The structure is further stabilized by weak S⋯π contacts [S⋯centroid = 3.8047 (9) Å] and π-π stacking inter-actions [centriod-centroid distance = 3.8653 (7) Å].

3-Butyl-1-methyl-1H-imidazol-3-ium bis-(1,2-dicyano-ethene-1,2-dithiol-ato-κS,S')nickel(III)

In the title compound, (C₈H₁₅N₂)[Ni(C₄N₂S₂)₂], the Ni^III atom is coordinated by four S atoms of two maleonitrile­dithiol­ate ligands and exhibits a distorted square-planar geometry. In the crystal, the cations and anions are connected alternately by weak inter­molecular C—H⋯N hydrogen bonds, forming a zigzag chain along [201].

Bis[1-(4-chloro-benz-yl)pyridinium] bis-(1,2,5-thia-diazole-3,4-dithiol-ato)nickelate(II)

The asymmetric unit of the salt, (C₁₂H₁₁ClN)₂[Ni(C₂N₂S₃)₂], comprises one cation and a half of Ni(tdas)₂ (tdas = 1,2,5-thia­diazole-3,4-dithiol­ate) anion. The Ni^II atom is located at a centre of inversion. The Ni^II atom has a square-planar coordination with Ni—S distances of 2.2052 (4) and 2.1970 (5) Å. In crystal, weak C—H⋯S and C—H⋯Ni contacts are observed between the anions and cations.

3,3'-Dimethyl-1,1'-(propane-1,3-di-yl)diimidazol-1-ium bis-(1,2-dicyano-ethene-1,2-dithiol-ato-κS,S')nickelate(II)

In the title compound, (C₁₁H₁₈N₄)[Ni(C₄N₂S₂)₂], the asymmetric contains one half-complex, with the cation placed on a twofold axis and the anion located on an inversion center. The Ni^II ion in the anion is coordinated by four S atoms of two maleonitrile­dithiol­ate ligands, and exhibits the expected square-planar coordination geometry.

Unsymmetrical diimine chelation to M(II) (M=Zn, Cd, Pd): atropisomerism, pi-pi stacking and photoluminescence

Three types of atropisomeric unsymmetrical diimine complexes, tetrahedral (L(R)(Φ))MX(2) (M = Zn, Cd; X = Cl, Br; R = Me, CMe(3), OH, OMe, Cl; 1a-k, type-I), tetrahedral (L(Me2)(Φ))ZnBr(2) (2, type-II) and square planar (L(OH)(ϕ))PdCl(2) (3, type-III) with different photoluminescence properties, have been reported (L(R)(Φ) = (E)-4-R-N-(pyridine-2-ylmethylene)aniline; Φ = dihedral angle between the diimine unit including the pyridine ring and the phenyl ring planes). In crystals, Φ = 0° for type-I, 90° for type-II and 63° for type-III atropisomers have been confirmed by single crystal X-ray structure determinations of 1c, 1e, 2 and 3·H(2)O isomers. Optimizations of geometries in methanol have established Φ = 28-32° for type-I, 90.83° for type-II and 43.44° for type-III isomers. In solids, type-I atropisomers with Φ = 0, behave as conjugated 14πe systems facilitating π-π stacking and are brightly luminescent at room temperature while type-II and type-III isomers in solid and type-I isomers in solutions are more like non-conjugated 8πe + 6πe systems and non-emissive. Frozen glasses of acetonitrile, methanol and dichloromethane-toluene mixture at 77 K of type-I isomers are emissive and display structured excitation and emission spectra for R = Me, CMe(3), OMe species. Excitation and emission maxima of frozen glasses (λ(ex) = 320-380 nm; λ(em) = 440-485 nm) are red shifted in the solid (λ(ex) = 390-455 nm; λ(em) = 470-550 nm). TD-DFT calculations on 1b, 1d, 1f and stacked (1b)(2) isomers and luminescence lifetime measurements have elucidated that an excited (1)ILCT state has been the origin of emission of the type-I isomers and delocalizations of the photoactive π(diimine) and π(diimine)(*) orbitals of the L(R)(Φ) over the stacked layers shift the λ(ext) and λ(em) of solids to lower energies than those in frozen glasses. The trends of diimine ligand based electron transfer events of the complexes in DMF have been investigated by cyclic voltammetry at 298 K.

Bis[1-(3-cyano-benz-yl)pyridinium] bis-(1,2-dicyano-ethene-1,2-dithiol-ato)nickelate(II)

In the ionic title complex, (C(13)H(11)N(2))(2)[Ni(C(4)N(2)S(2))(2)], the Ni(II) ion is located on an inversion centre so the asymmetric unit contains one-half [Ni(mnt)(2)](2-) dianion (mnt(2-) is maleonitrile-dithiolate) and one 1-(3-cyano-benz-yl)pyridinium cation ([CNBzPy](+)). The Ni(II) ion in the [Ni(mnt)(2)](2-) anion is coordinated by four S atoms of two mnt(2-) ligands, and exhibits square-planar coordination geometry. In the [CNBzPy](+) cation, the benzene and pyridine rings are twisted with respect to the C/C/N plane incorporating the methyl-ene C atom that links them. The crystal structure is stabilized by Coulombic inter-actions.