Qi-Jian Pan

Crystal structure, magnetism, and dielectric properties based on the axially chiral ligand 2,2′-dinitro-4,4′-biphenyldicarboxylic acid

Six novel metal–organic-frameworks (MOFs), [Ni(nbpdc)(4,4′-bpy)(H2O)]n (1), [Ni2(nbpdc)2(4,4′-bpy)2(H2O)2]n (2), [Ni(nbpdc)(4,4′-bpy)]n (3), [Mn(nbpdc)(4,4′-bpy)]n (4), [Co(nbpdc)(4,4′-bpy)]n (5), and [Zn2(nbpdc)2(4,4′-bpy)]n (6), with different crystal structures and divalent cations (Zn(II), Ni(II), Mn(II), and Co(II)) from the same ligands nbpdc and 4,4′-bpy (H2nbpdc = 2,2′-dinitro-4,4′-biphenyldicarboxylic acid, 4,4′-bpy = 4,4′-bipyridine) have been synthesized and characterized. Complex 1 showed a new point group of 222 and a new topology structure of sqc6. Crystal structures of complexes 2–6 with the same nonpolar point group of 2/m were determined by single-crystal X-ray diffraction. Complex 2 exhibited a rare three-interlude 3D structure with (44·62)(48·66·8) topology. Complexes 3–5 featured the same topology structure of (44·610·8)(44·62). Complex 6 had a 3D framework with (10)(6·82·103·124)2(62·8)2(8)2 topology. In addition, complex 1 displayed commendable adsorption of N2 at room temperature. 4 and 5 showed antiferromagnetism. Moreover, all six MOFs displayed abnormal dielectric peaks from 225 K to 275 K, which were measured at various frequencies and temperatures.

Temperature-induced reversible structural phase transition of 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane bis(perchlorate)

1,4-Dimethyl-1,4-diazabicyclo[2.2.2]octane bis(perchlorate), C8H18N22+·2ClO4−, was synthesized and separated as colorless rodlike crystals. Differential scanning calorimetry (DSC) measurements revealed that this compound underwent a reversible phase transition at ca. 201.7 K with a hysteresis of 5.1 K width, which was also confirmed by dielectric measurements. Single crystal X-ray diffraction data suggested that there was a transition from a room temperature phase with the space group of Pnma (a = 15.5417(14) A, b = 13.3677(12) A, c = 20.7728(19) A, V = 4315.7(7) A3 and Z = 12) to a low temperature one with a space group of P21/n (a = 13.331(3) A, b = 15.185(4) A, c = 20.477(5) A, β = 90.895(3)°, V = 4144.8(17) A3 and Z = 12), and symmetry breaking occurred with an Aizu notation of mmmF2/m. The order–disorder transition of ClO4− anions and the ordering of twisting motions of the dabco ring may drive the phase transition.

Novel pure Pnma–P212121 ferroelastic phase transition of 1,4-diisopropyl-1,4-diazonia-bicyclo[2.2.2]octane tetra-chlorobromo-M(II) (M = Mn and Co)

Two novel phase transition compounds Dip-DABCO tetra-chlorobromo-M(II) (M = Mn and Co), (Dip-DABCO = 1,4-diisopropyl-1,4-diazonia-bicyclo[2.2.2]octane) C12H26N2·MnBrCl3 (1) and (C12H26N2)4·(CoBr1.25Cl2.75)4 (2) were synthesized, and their structures have been determined by means of single-crystal X-ray diffraction. The two compounds are isomorphous. Differential scanning calorimetry (DSC) measurements indicated that compounds 1 and 2 underwent a reversible phase transition at ca. 245.2 K with a hysteresis width of 4.4 K and at ca. 222.3 K with a hysteresis width of 5.5 K, respectively. The variable-temperature single-crystal X-ray diffraction data suggests that the phase transition was from high crystallographic symmetry with a space group of Pnma to a low-symmetry state with a space group of P212121. That is, Landau symmetry breaking occurred with a pure GPT (mmm–222). The ordering of twisting motions of the 1,4-diazoniabicylo[2,2,2]octane ring may have driven the phase transition.

Two novel metal–organic coordination polymers based on ligand 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide with phase transition, and ferroelectric and dielectric properties

Two novel metal–organic complexes {[Ag3(dabcodo)(NO3)3]·H2O}n (1) and [Ca(dabcodo)(H2O)4Cl2]n (2) containing metal salt and 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide (dabcodo), in which dabcodo is coordinated with two types of metal ions, were successfully synthesized. Differential scanning calorimetry, powder X-ray diffraction, variable-temperature structural analyses, dielectric measurements and rectangular polarization-electric field hysteresis loops revealed that 1 underwent phase transition from room-temperature-phase Pca21 to low-temperature-phase Cc at Tt ≈ 217 K, accompanied by remarkable dielectric relaxation. Compound 1 was a typical ferroelectric–ferroelectric phase transition material with an electric hysteresis loop showing a remnant polarization (Pr) of ca. 0.23 μC cm−2 and a coercive field (Ec) of 6.5 kV cm−1. Room-temperature and low-temperature phases of 1 featured the same topology structure of {34·46·517·616·72}. Compound 2 underwent a paraelectric–paraelectric phase transition from room-temperature-phase I4/mmm to low-temperature-phase Cmcm at Tt ≈ 177 K. Moreover, this study contributes to a deeper understanding of the structure–property relationship in emerging metal–organic ferroelectrics.

Self-assembly of 1-D and 3-D transition-metal coordination polymers based on 4-(1H-l,3-benzimidazol-2-yl)pyridine 1-oxide

Three metal-organic coordination polymers based on 4-(1H-l,3-benzimidazol-2-yl)pyridine 1-oxide (BImPyO) with the molecular structures [Cu2(C12H8N3O)2]n (1), [Cu(C12H8N3O)]n (2), and [Zn(C12H8N3O)Cl]n (3) were synthesized under hydrothermal conditions. They showed diverse coordination modes and were further characterized by elemental analysis, infrared spectroscopy, and single crystal X-ray structure analysis, respectively. In 1 and 2, BImPyO generated a 1-D chain by adopting μ2-kN : kN′ coordination to bridge two Cu(II) ions with bis-N-chelation. In 3, by adopting μ3-kN : kN′:kO coordination, BImPyO bridged three crystallographically independent Zn(II) ions to form a 3-D framework; 3 exhibits strong fluorescent emission in the solid state at room temperature. Graphical abstract

Synthesis, structures, luminescent and dielectric properties of lanthanide coordination polymers

Abstract Under hydrothermal conditions, four lanthanide coordination polymers were synthesized based on 4-(4,5-dicarboxy-1H-imidazol-2-yl)pyridine 1-oxide (H3DCImPyO), with the molecular forumulas [Eu(HDCImPyO)·(H2O)2·(CHO2)]n (1), [Sm(HDCImPyO)·(H2O)2·(HCO2)]n (2), {[La(HDCImPyO)·(H2O)·(HCO2)]·O2}n (3) and {[Y(HDCImPyO)·(C2O4)·(H2O)2]·H2O}n (4). With diverse coordination modes, they were further characterized by elemental analysis, infrared spectroscopy, dielectric measurement, and single-crystal X-ray structural analysis. Complexes 1 and 2 were isostructural and had similar structures with {44, 62} topology. Complex 1 exhibited strong fluorescent emission in the solid state at room temperature. In 3, HDCImPyO2− adopted μ4-kO, O′: kO′, O′′: O′′′: O′′′′ coordination to bridge four La(III) ions to form a 3-D framework with {4. 52}2{42. 510. 612. 7. 83} topology. In 4, both HDCImPyO2− ligands and Y3+ cations were simplified as linkers to form an interpenetrating 3-D framework with {413. 62}2{422. 66} topology.

Self-assembly of 1-D, 2-D, and 3-D transition-metal coordination polymers based on a T-shaped tripodal ligand 4-(4,5-dicarboxy-1H-imidazol-2-yl)pyridine 1-oxide

Three coordination polymers, {[Co(C10H5N3O5)(H2O)2]·H2O}n (1), {[Mn3(C10H5N3O5)2Cl2(H2O)6]·2H2O}n (2), and {[Cu3(C10H4N3O5)2(H2O)3]·4H2O}n (3), based on a T-shaped tripodal ligand 4-(4,5-dicarboxy-1H-imidazol-2-yl)pyridine 1-oxide (H3DCImPyO), were synthesized under hydrothermal conditions. The polymers showed diverse coordination modes, being characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray structure analysis. In 1, the HDCImPyO2− generated a 1-D chain by adopting a μ2-kN, O : kN′, O′ coordination mode to bridge two Co(II) ions in two bis-N,O-chelating modes. In 2, the HDCImPyO2− adopted a μ3-kN, O : kO′, O′′ : O′′′ coordination mode to bridge two crystallographically independent Mn(II) ions, forming a 2-D hcb network with {63} topology. In 3, by adopting μ4-kN, O : kO′, O′′ : kN′′, O′′′ : O′′′′ coordination, DCImPyO3− bridged three crystallographically independent Cu(II) ions to form a 3-D framework having the stb topology. Three metal-organic coordination polymers, {[Co(C10H5N3O5)(H2O)2]·H2O}n (1), {[Mn3(C10H5N3O5)2Cl2(H2O)6]·2H2O}n (2), and {[Cu3(C10H4N3O5)2(H2O)3]·4H2O}n (3), based on a T-shaped tripodal ligand 4-(4,5-dicarboxy-1H-imidazol-2-yl)pyridine 1-oxide (H3DCImPyO), were synthesized by the hydrothermal method.