Huge Dielectric Response and Molecular Motions in Paddle-Wheel [CuII2(Adamantylcarboxylate)4(DMF)2]⋅(DMF)2

Supramolecular crystals of Mn(15-crown-5)(MnCl4)(DMF) with dielectric phase transition, high quantum yield and phase transition-induced luminescence enhancement behavior

The supramolecular crystals, Mn(15-crown-5)(MnCl4)(DMF), (1; 15-crown-5 = 1,4,7,10,13-pentaoxacyclopentadecane), were synthesized via a self-assembly strategy under ambient conditions. Comprehensive characterization of the crystals involved microanalysis for C, H, and N elements, thermogravimetric (TG) analysis, differential scanning calorimetry (DSC) and single-crystal X-ray diffraction techniques. The results reveal that 1 undergoes a two-step thermotropic and isostructural phase transition at around 217 K and 351 K upon heating. All three phases belong to the same space group (P212121) with analogous cell parameters. These two phase transitions primarily involve the thermally activated ring rotational dynamics of the 15-crown-5 molecule, with only the transition at ca. 351 K being associated with a dielectric anomaly. 1 exhibits intense luminescence with a peak at ∼600 nm and a high quantum yield of 68%. The mechanisms underlying this intense luminescence are likely linked to low-symmetry ligand fields. Additionally, 1 displays phase transition-induced luminescence enhancement behavior, and the possible mechanism is further discussed.

Structural, Optical, Magnetic, and Dielectric Properties in Hybrid Solid Solutions of ZnαNi1-α(en)3Ag2I4 (0 < α < 1) by Varying the Relative Zn/Ni Content

The hybrids of M(en)₃Ag₂I₄ (M = Zn or Ni) are isostructural to each other and crystallize in space group P6₃22 with quite similar lattice parameters. The hybrid solid solutions Zn_αNi_1-α(en)₃Ag₂I₄ (0 < α < 1) have been prepared via self-assembly in the mixed N,N-dimethylformamide solution of AgNO₃, KI, and ethylenediamine, meanwhile, with certain relative amount of [Zn(en)₃]²⁺ and [Ni(en)₃]²⁺ ions at ambient condition. All hybrid solid solutions are isostructural to the parent hybrids M(en)₃Ag₂I₄ (M = Zn or Ni). The UV-vis-near IR diffuse reflection spectra in solid state, thermogravimetric analysis, variable-temperature magnetic susceptibility, and dielectrics have been investigated for Zn_αNi_1-α(en)₃Ag₂I₄ (0 < α < 1). The intensity of bands centered at 540 and 860 nm in UV-vis-near IR spectra, arising from the d-d electron transition in Ni²⁺ ion, as well as the Curie constant decreases linearly with the molar fraction of Zn (α)/Ni (1 - α), whereas the c-axis length, the C-N and C-C bond lengths in the ethylenediamine, the frequency-independent dielectric permittivity and the onset temperature of dielectric relaxation, and so forth show nonmonotonical alternation with the fraction of Zn (α)/Ni (1 - α) in the solid solution, and the origin for these differences is further discussed.

Crystal structures, CO₂ adsorption, and dielectric properties of [Cu(II)₂(R-benzoate)₄(pyrazine)]∞ polymers (R = m-F, 2,3-F₂, m-Cl, and m-CH₃)

m-Fluorobenzoate (m-FBA), 2,3-difluorobenzoate (2,3-F2BA), m-methylbenzoate (m-MBA), and m-chlorobenzoate (m-ClBA) were introduced into the Cu(II) binuclear unit as bridging ligands between two Cu(II) sites, which were further connected by an axial pyrazine (pz) ligand to form one-dimensional coordination polymers of [Cu(II)2(m-FBA)4(pz)]∞ (1), [Cu(II)2(2,3-F2BA)4(pz)]∞ (2), [Cu(II)2(m-MBA)4(pz)]∞ (3), and [Cu(II)2(m-ClBA)4(pz)]∞ (4), respectively. The parallel arrangements of one-dimensional (1D) polymers result in 1D channels between the polymers that crystallization CH3CN molecules can occupy to form single crystals of 1·4CH3CN, 2·4CH3CN, 3·2CH3CN, and 4·2CH3CN. Both π-dimer and dipole-dipole interactions were simultaneously observed in the interchain interactions of m-FBA and/or 2,3-F2BA ligands in crystals 1 and 2. The sizes of the one-dimensional channels between the polymers are thus modulated according to the interchain interactions between the polar BA ligands. CH3CN molecules within the channels were easily replaced by H2O under ambient conditions. CO2 adsorption-desorption isotherms of crystals 1, 2, and 3 at 195 K indicated gate-adsorption with a hysteresis, whereas two-step gate-adsorption behavior was observed for CO2 in crystal 4. Temperature- and frequency-dependent dielectric responses were not observed in crystals 1-4 under vacuum conditions, whereas dielectric anomalies were observed around 290 K for crystals 1 and 2 with adsorbed CO2. CO2 desorption from the channels in crystals 1 and 2 activated the molecular motions of polar BA ligands and dielectric responses around 290 K, which were confirmed from CO2 adsorption-desorption isotherms around 290 K and differential scanning calorimetries under CO2 conditions.