Four coordination polymers, [Co2(Hnbpdc)2(nbpdc)(bipy)2]n (1), [Co3(nbpdc)3(bipy)3(H2O)2]n·2nH2O (2), [Co4(nbpdc)4(bipy)(H2O)4]n (3), and [Co2(nbpdc)2(bpee)(3/2)]n·0.25nH2O (4) [H2nbpdc = 2-nitrobiphenyl-4,4′-dicarboxylic acid, bipy = 4,4′-bipyridine and bpee = 1,2-di(4-pyridyl)ethane] have been synthesized by hydrothermal methods and studied by means of X-ray crystallography, topological analyses and magnetic analyses. Compounds 1–3 were synthesized from the same reactants under controlled conditions (pH and ligand ratio). Compounds 1, 2 and 4 contain bis(carboxylate)-bridged dinuclear motifs as secondary building units (SBUs). In 1 and 2 the SBUs are connected into 44 layers by bis(chelating) nbpdc and pairwise bipy linkers. In 1, the layers are pillared into a 3D framework with the pcu topology by Hnbpdc, which is coordinated to one layer and hydrogen-bonded to another layer. In 2, the layers and the linear [Co(bipy)]n chains intercalated between the layers are connected by nbpdc to produce a 3D framework exhibiting a rarely observed 4,6-connected topology. In 4 the SBUs are connected by nbpdc [bis(chelating) and bis(bridging)] and bpee (single and pairwise) to yield a 3D framework, which defines a new 6-connected net with point symbol (4(10)·5(2)·6(3)). Notably, this new net and the known hex-6-P6(2)22 net represent the first examples of topologically different nets having the same coordination sequences, point and vertex symbols. Compound 3 contains carboxylate- and aqua-bridged tetranuclear motifs as SBUs, which are connected by covalent linkers (nbpdc and bipy) and sextuple O–H···O hydrogen bonds to generate a 3D framework, which defines a new 10-connected net with point symbol (4(24)·5(12)·6(8)·7) (considering only covalent linkers) and a new 12-connected net with point symbol (3(12)·4(36)·5(17)·6) (including also the hydrogen bonds as linkers). Magnetic studies on 1 and 2 demonstrated that the bis(syn–skew-carboxylate) bridges between octahedral Co(II) ions induce ferromagnetic coupling; 4 is peculiar in that octahedral and tetrahedral Co(II) ions are linked by mixed syn–syn and syn–skew carboxylate bridges, which give rise to antiferromagnetic coupling.

Two Cd(ii) metal-organic frameworks were synthesized from the NH-functionalized dicarboxylate ligand 9H-carbazole-2,7-dicarboxylic acid (2,7-H2CDC). Compound , [Cd4(CDC)4(DMF)4]·4DMF·4H2O, displays 2D square grid networks based on novel tetranuclear [Cd4(COO)8] secondary building units (SBUs) and pairwise CDC(2-) linkers. Compound , (H3O)2[Cd3(2,7-CDC)4]·3DMF·4H2O, is also based on 4-connected SBUs and pairwise CDC linkers, but the unusual trinuclear [Cd3(COO)8] SBUs lead to 2-fold interpenetrated 3D diamond-type frameworks with guest accessible voids. Both compounds display strong blue fluorescence in the solid state, and compound shows high catalytic activity for Knoevenagel condensation.

An azido-functionalized Zr(II) metal-organic framework (MOF), UiO-67-N 3 , was synthesized from 2-azidobiphenyl-4,4 0 -dicarboxylic acid. During the synthesis, the ligand can undergo in situ thermocyclization to give 9H-carbazole-2,7-dicarboxylic acid. It proved that UiO-67-N 3 can be obtained at relatively low temperature without ligand transformation. Post-synthetic modification of UiO-67-N 3 was successfully performed via the click reactions between the azido group and different alkyne compounds to produce new MOFs with different functionalities, UiO-67-Tz-X with X ¼ COOCH 3 , OH and NH 2 . These clicked MOFs, especially UiO-67-Tz-NH 2 , exhibit better stability than the mother material UiO-67-N 3 . The catalytic properties of the clicked MOFs were studied using the Knoevenagel condensation reactions between benzaldehyde and different methylene compounds. Only the NH 2 -functionalized MOF is active, suggesting that the amino group, rather than the triazole group or any other component of the framework, is the crucial active site. The catalysis is heterogeneous. The MOF is recyclable for the reaction with malononitrile but not for the reaction with ethyl cyanoacetate. The deactivation in the latter case is proposed to be because the amino site reacts with the ester group of ethyl cyanoacetate to form amide.

The flexible zwitterionic dicarboxylate ligand 1,4-bis(4-carboxylato-1-pyridinium)butane (bcpb) assumes different conformations to collaborate with pseudohalides in various coordination modes to produce coordination polymers in which distinct anionic motifs with mixed carboxylate and pseudohalide bridges are interlinked by the cationic butylenebis(pyridinium) tethers. The Cu(II) compound, [Cu2(bcpb)(N3)4]n·nH2O (1), is a 1D coordination polymer based on the defective dicubane-like [Cu4(μ3-1,1,1-N3)2(μ-1,1-N3)2(μ-1,1-OCO)2] cluster. With Mn(II), four distinct 3D coordination polymers, [Mn4(bcpb)4(N3)(H2O)4]n(ClO4)7n·nCH3OH·3nH2O (2), [Mn2.5(bcpb)(N3)5(H2O)2]n (3), [Mn2(bcpb)(N3)4]n·nH2O (4), and [Mn2(bcpb)(NCO)4]n·nH2O (5), were characterized. 2 is the first Mn(II) compound with the rare μ4-1,1,3,3 azide bridge and exhibits an unusual 3D framework based on the [Mn4(μ4-1,1,3,3-N3)(μ-1,3-OCO)6] cluster. In 3, the unique undulated honeycomb-like [Mn2(μ-1,3-N3)3]n layers are interlinked into a 3D framework by disordered [Mn(μ-1,1-N3)4(μ-1,3-OCO)2] and [(O(aqua)-H)2···OCO]2 moieties, and the bcpb ligands serve as additional interlayer linkers to lead to the rare self-catenated 6(6) net. 4 and 5 show 3-fold interpenetrated 3D frameworks based on the chains with (μ-1,1-N3)2(μ-1,3-OCO) and (μ-N,N-NCO)2(μ-1,3-OCO) bridges, respectively. Magnetic studies indicated that 1 shows competing ferromagnetic and antiferromagnetic interactions. Compounds 2-5 all show antiferromagnetic coupling between Mn(ii) ions, while 3 shows 3D ordering. Analyses of magneto-structural data suggest a general trend that the antiferromagnetic interaction through (μ-1,1-N3)2(μ-1,3-OCO) or (μ-N,N-NCO)2(μ-1,3-OCO) increases with a decrease of the Mn···Mn distance.