Deng-Deng Huang

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.

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

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.