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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]

Different aromatic polycarboxylic acids are employed as auxiliary ligands to give rise to structural diversities in Co(II)-tpt (tpt = 2,4,6-tris(4-pyridyl)-1,3,5-triazine) frameworks. By introducing various secondary aromatic polycarboxylate anions, namely, biphenyl-3,4′,5-tricarboxylic acid (H3bpt), 1,3,5-benzenetricarboxylic acid (H3btc) and 2,6-dimethyl pyridine-3,5-dicarboxylic acid (H2dmdcpy) into the Co(II)-tpt system (tpt = 2,4,6-tris(4-pyridyl)-1,3,5-triazine), four new complexes [Co3(tpt)2(Hbpt)3]·0.5DMDP (1) (DMDP = N,N′ = dimethylpropyleneurea), [Co3(btc)2(tpt)(H2O)3]·3H2O (2), [Co2(btc)(tpt)2Cl]·DMDP·1.5H2O (3) and [Co(tpt)(dmdcpy)]·H2O (4) were obtained. Complexes 1 and 2 reveal amazing 3D networks in which the polycarboxylate ligands and Co(II) ions connect with each other to form regular 3D porous frameworks with 1D cylindrical channels partitioned by virtue of the tpt ligands. Complexes 3 and 4 exhibit unusual 3D frameworks constructed from the Co–polycarboxylate layers pillared by tpt ligands. In addition, compound 1 was chosen as a precursor to prepare Co, N-codoped porous carbon materials (denoted as CoNC) as an eletrocatalyst for oxygen reduction reactions. In particular, the effect of different nitrogen sources on the electrocatalytic performance of MOF derived carbon materials was investigated. We found that although different nitrogen-containing ligands have a certain effect on the electrocatalytic performance of the synthesized CoMOF derived carbon materials, the additional nitrogen source has a significant effect on it. CoNC-A derived from compound 1 exhibits greater limiting current density than that of a Pt/C catalyst, while CoNC-B derived from a mixture of compound 1 and dicyandiamide shows almost identical onset potential but remarkably more positive half-wave potential as well as higher limiting current density as compared to commercial Pt/C catalysts. [ABSTRACT FROM AUTHOR]