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Eu2+ was used to substitute Ca in the orthorhombic KCoO2-type layered CaTiN2 to form a Ca1−xEuxTiN2 solid solution, which showed a limited substitution around x = 0.35 with the tetragonality enhanced but the orthorhombic symmetry retained and inaccessibility for the end member EuTiN2. This was in contrast with the full solid solution Ca1−xSrxTiN2, which realized a structural transition from orthorhombic to tetragonal at x = 0.5, even though Eu2+ and Sr2+ ions have similar sizes. The Eu substitution for Ca reduced the dielectric permittivity of CaTiN2 owing to the reduced structural distortion arising from the enhanced tetragonality with the substitution. First-principle theoretical calculations on the total energies and formation energies considering the 4f electrons of Eu ions and the related magnetism were performed to understand the structural stability of the hypothetical EuTiN2. Compared with CaTiN2 and SrTiN2, EuTiN2 has much higher formation energies, making it inaccessible at high temperature. The evolutions of the experimentally observed and calculated lattice parameters of the Ca1−xEuxTiN2 solid solution showed a preference for the orthorhombic phase over the tetragonal phase for the hypothetical EuTiN2, revealing a different coordination chemistry of Eu2+–N to Eu2+–O through the comparison of the structural variations of ATiN2 and ATiO3 (A = Ca, Sr, Eu). [ABSTRACT FROM AUTHOR]

In this work, four different bis(imidazole) ligands, namely 1,4-bis(1-imidazolyl)benzene (bib), 4,4′-bis(1-imidazolyl)biphenyl (bibp), 1,4-bis (imidazol-1-ylmethylene)benzene) (bimb) and 4,4′-bis(imidazol-1-yl)diphenyl ether (bidpe), were used as the second ligand to give rise to the structural diversity of a coordination polymer based on the cobalt-miipa (H2miipa = 5-(2-methylimidazol-1-yl) isophthalic acid) system. In compound 1, miipa2− coordinates to Co(II) atoms to form the Co-miipa 3D network. On introducing linear bis(imidazole) ligands with different lengths and rigidities into the Co(II)-miipa system, the obtained compounds 2–4 form similar three-fold interpenetrating 3D MOFs constructed from the Co(II)-miipa layers pillared by bis(imidazole) ligands. While introducing the V-shaped half-flexible bis(imidazole) ligands, the obtained compound 5 exhibits a 2D double-layered network built from the Co(II)-miipa 1D quadrangular prism linked by the bis(imidazole) ligand. Each 2D double layer is further interlocked with two neighboring ones to produce an interesting 3D framework. Significantly, CoNC-5 derived from a mixture of dicyandiamide (DCD) and compound 5 with a low void volume shows a superior electrocatalytic performance for the oxygen reduction reaction. The Eonset (0.974 V) and E1/2 (0.830 V) of CoNC-5 in O2-saturated 0.1 M KOH at 1600 rpm and 5 mV s−1 are superior to those of Pt/C (0.968 and 0.799 V). The JL value of CoNC-5 (JL = 5.29 mA cm−2) is higher than that of Pt/C (5.09 mA cm−2). [ABSTRACT FROM AUTHOR]

The urothermal reactions of Co(II)/Zn(II) salts with the diverse carboxylic acid and 1,3,5,-tris(1-imidazolyl)benzene(tib) ligands afforded three novel MOFs, namely, [Co3(tib)2(abdc)2(ox)]2·6H2O (1), [Co3O(tib)(abdc)2(DMI)]·2DMI·2H2O (2) and [Zn3I2(tib)2(napdc)2]·2DMI·2H2O (3), (H2abdc = 5-amino-1,3-benzenedicarboxylate, H2napdc = 1,4-naphthalene dicarboxylic acid and DMI = 1,3-dimethyl-2-imidazolidinone). In compounds 1 and 2, the Co(II) atoms are connected by polycarboxylate ligands to form two-dimensional (2D) layers that are pillared by tib ligands leading to the formation of 3D porous frameworks. In compound 3, the Zn(II) atoms are linked by tib ligands to form one-dimensional ribbon-like chains which are further connected by polycarboxylate ligands, making a 3D framework possible. Compound 1 can selectively adsorb unsaturated hydrocarbon molecules (C2H2 and C2H4) and saturated hydrocarbon molecules (C2H6 and CH4). Specifically, compound 1 has high IAST selectivity for acetylene and methane (0.50 : 0.50, v/v) at 273 K and 1 bar. DFT calculations reveal that the π-conjugated hexagonal carbon ring may be the primary adsorption site because there are π–π interactions between the unsaturated hydrocarbon molecules (C2H2 and C2H4) and the π-conjugated hexagonal carbon ring in the framework of compound 1. [ABSTRACT FROM AUTHOR]

The urothermal reactions of Co(II)/Zn(II) salts with the diverse carboxylic acid and 1,3,5,-tris(1-imidazolyl)benzene(tib) ligands afforded three novel MOFs, namely, [Co3(tib)2(abdc)2(ox)]2·6H2O (1), [Co3O(tib)(abdc)2(DMI)]·2DMI·2H2O (2) and [Zn3I2(tib)2(napdc)2]·2DMI·2H2O (3), (H2abdc = 5-amino-1,3-benzenedicarboxylate, H2napdc = 1,4-naphthalene dicarboxylic acid and DMI = 1,3-dimethyl-2-imidazolidinone). In compounds 1 and 2, the Co(II) atoms are connected by polycarboxylate ligands to form two-dimensional (2D) layers that are pillared by tib ligands leading to the formation of 3D porous frameworks. In compound 3, the Zn(II) atoms are linked by tib ligands to form one-dimensional ribbon-like chains which are further connected by polycarboxylate ligands, making a 3D framework possible. Compound 1 can selectively adsorb unsaturated hydrocarbon molecules (C2H2 and C2H4) and saturated hydrocarbon molecules (C2H6 and CH4). Specifically, compound 1 has high IAST selectivity for acetylene and methane (0.50 : 0.50, v/v) at 273 K and 1 bar. DFT calculations reveal that the π-conjugated hexagonal carbon ring may be the primary adsorption site because there are π–π interactions between the unsaturated hydrocarbon molecules (C2H2 and C2H4) and the π-conjugated hexagonal carbon ring in the framework of compound 1. [ABSTRACT FROM AUTHOR]

A homochiral three-dimensional framework material, [Cu7(4-bpt)6(CN)(H2O)] (1) (4-bpt = 3,5-bis(4-pyridyl)-1,2,4-triazole), has been successfully synthesized by solvothermal reaction, which is generated through an unusual spontaneous asymmetrical crystallization from achiral precursors, and its photocatalytic properties in degradation of organic dyes are also investigated. [ABSTRACT FROM AUTHOR]

A 2D tri-layer compound {[Co8(tbip)6(H2O)9(OH)4]·12(H2O)}n(1) (H2tbip = 5-tert-butyl isophthalic acid) consisting of novel heptacobaltate clusters and single cobalt centers bridged by tbip2−ligands has been hydrothermally synthesized. The complex represents a rare example of a homometallic coordination polymer built up from both heptanuclear metal clusters and single metal centers simultaneously. The magnetic investigation reveals that the complex exhibits the overall predominance of antiferromagnetic coupling between magnetic centers. [ABSTRACT FROM AUTHOR]