Antonio J. Calahorro

Luminescence and magnetic properties of three metal–organic frameworks based on the 5-(1H-tetrazol-5-yl)isophthalic acid ligand

Three new metal–organic frameworks based on 5-(1H-tetrazol-5-yl)isophthalic acid complexes {[Cd4(TZI)2(OH)2(H2O)4](H2O)6}n (1), {[Zn2(TZI)(OH)(H2O)2](H2O)}n (2) and {[Co8(TZI)3(OH)5((N3)2(H2O)8](H2O)8}n (3) have been synthesized in situ by hydrothermal reactions of the 5-cyano-1,3-benzenedicarboxylic acid ligand with cadmium, zinc and cobalt metallic(II) salts in the presence of sodium azide in water. Compounds 1 and 2 display intense photoluminescence properties in the solid state at room temperature, while 3 exhibits an antiferromagnetic interaction between cobalt(II) ions with a J value of −3.8 cm−1. The in situ hydrothermal syntheses reveal new possibilities for the formation of new MOFs to construct new materials with fascinating structures and potential applications.

In vivo potential antidiabetic activity of a novel zinc coordination compound based on 3-carboxy-pyrazole

A novel Zn mononuclear complex with 3-carboxy-pyrazole ligand has been prepared using conventional routes and characterized by X-ray diffraction. The structure consists of discrete neutral [Zn(C6H3N2O2)2(H2O)2] molecules held together by hydrogen interactions. This compound exhibits a potential in vivo antidiabetic activity and the in vitro toxicity can be considered negligible.

Controlling interpenetration for tuning porosity and luminescence properties of flexible MOFs based on biphenyl-4,4′-dicarboxylic acid

Four new compounds based on zinc(II) or cadmium(II) metal ions and elongated dicarboxylate and bipyridine ligands, namely, {[Cd3(μ4-bpdc)3(H2O)2]·DMF}n (1), {[Zn3(μ4-bpdc)3(μ-bpdb)]·5DMF}n (2), {[Zn2(μ4-bpdc)2(μ-bpdb)]·7DMF}n (3), and {[Zn4(μ4-bpdc)3(DMF)(μ4-O)(H2O)]·7DMF·3H2O}n (4), (where bpdc = biphenyl-4,4′-dicarboxylate, bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, DMF = dimethylformamide) have been synthesised under solvothermal conditions and structurally characterised by single crystal X-ray diffraction. The crystal structures range from 2D (in 1) to 3D (2, 3, and 4) systems according to the coordination mode acquired by the bpdc ligand and the presence of an ancillary linker. Compound 1 consists of stacked Cd-bpdc neutral layers containing isolated small voids. The coordination of the bpdb ligand (2 and 3) or the formation of a tetrahedral Zn4O cluster (in 4) generates highly open 3D architectures that share the structural feature of being doubly interpenetrated. A careful computational analysis on the crystal structures permits unravelling their void systems. Moreover, characterising the photoluminescence emission of the compounds at variable excitation wavelengths provides an opportunity to couple the luminescence response with their porosity, which could signify the potential utility of these materials as photofluorescent sensors for small adsorbates.

Slow relaxation of magnetization in 3D-MOFs based on dysprosium dinuclear entities bridged by dicarboxylic linkers

Three novel metal–organic-frameworks (MOFs) based on dysprosium as the metal and dicarboxylic ligands have been solvothermally synthesized with the aim of studying and modulating their magnetic properties according to the variation of the distances between metal centers. These materials display intense photoluminescence properties in the solid state at room temperature. In addition, a very interesting property of compound 1 is that it exhibits slow relaxation of magnetization with an activation energy barrier of 32 K. Magneto-structural correlations have been analyzed.

Effect of π–π stacking interactions on the emission properties of cadmium metal–organic frameworks based on 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene

Five multidimensional cadmium metal–organic frameworks based on the luminescent 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene linker and flexible dicarboxylate ligands have been synthesized by conventional routes. These MOFs show fascinating structures and display, in the solid state and at room temperature, intense and hypsochromic photoluminescence properties when packed as a 3D network and bathochromic photoluminescence properties when arranged as 2D networks, as compared to the emission properties of the free luminescent 4-bpdb ligand. DFT calculations have revealed the establishment of destabilizing π–π stacking interactions between pyridyl rings of neighbouring 4-bpdb aromatic linkers on the 3D networks synthesized, responsible for the unexpected hypsochromic emission. The absence of π–π stacking interactions in the 2D MOFs yields the expected bathochromic photoluminescence arising from metal coordination with the aromatic ligand.

Novel metal–organic frameworks based on 5-bromonicotinic acid: Multifunctional materials with H2 purification capabilities

Two new metal–organic frameworks based on 5-bromonicotinic acid complexes [Cd(5-BrNic)2]n (1) and [Co(5-BrNic)2(H2O)]n (2) have been synthesized by hydrothermal reactions of this ligand with cadmium and cobalt metallic(II) salts in the presence of water. Compound 1 displays intense photoluminescence properties in the solid state at room temperature, while 2 exhibits an antiferromagnetic interaction between Co(II) ions with a J value of −4.1 cm−1. Experimental studies, backed up by Monte Carlo simulations about adsorption, pore size distribution and accessible surface area reveal the capability of 2 for H2 purification applications.

Tuning the porosity through interpenetration of azobenzene-4,4′-dicarboxylate-based metal–organic frameworks

A series of zinc(II) or cadmium(II)-based compounds with elongated dicarboxylate and bipyridine ligands, namely {dma[Cd(μ-azdc)(μ-ac)]·xDMF}n (1), {[Cd2(μ4-azdc)(μ-azdc)(DMSO)4]·DMSO}n (2), [Cd3(μ4-azdc)3(DMF)2]n (3), {[Zn2(μ3-azdc)2(μ-pbptz)]·xDMF}n (4), and {[Zn3(μ4-azdc)3(μ-pbptz)2]·xDMF·yH2O}n (5) (where dma = dimethylammonium, azdc = azobenzene-4,4′-dicarboxylate, ac = acetate, DMF = dimethylformamide, DMSO = dimethylsulfoxide, pbptz = 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine), have been synthesized under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction. Crystal structures range from 2D to 3D systems according to the presence of the pbptz co-ligand, which aids the layers established by azdc ligands to increase their dimensionality. The structural diversity found in each system is the result of three factors that govern the assembling process by modulating the coordination mode of the azdc ligands: the employed solvent, counterion and metal : ligand stoichiometry. A common structural feature of these compounds is the highly open architectures achieved due to the length of the employed ligands, which favours the resulting frameworks to be interpenetrated by different degrees depending on the network topology. A careful computational analysis of the void systems of the compounds permits establishing a relationship of this phenomenon with the pore size. The photoluminescence properties of all compounds have been also investigated.

Towards a potential 4,4′-(1,2,4,5-tetrazine-3,6-diyl) dibenzoic spacer to construct metal–organic frameworks

The ligand 4,4′-(1,2,4,5-tetrazine-3,6-diyl)dibenzoic acid has been designed and explored with the aim of using it as a linker to construct three-dimensional metal–organic frameworks (MOFs). We have been successful in the formation of a potassium 3D-MOF using this novel linker. This compound has a three-dimensional structure, wherein the layers formed by potassium ions and carboxylate groups are separated by this organic ligand. Luminescence and cytotoxicity studies have been performed. We used molecular simulations to predict the porous properties of an isoreticular compared to IRMOF-16 based on this linker due to the similarity of the newly designed ligand with p-terphenyl-4,4′′-dicarboxylate present in IRMOF-16.

Luminescence and Magnetic Properties of Two Three-Dimensional Terbium and Dysprosium MOFs Based on Azobenzene-4,4′-Dicarboxylic Linker

We report the in situ formation of two novel metal-organic frameworks based on terbium and dysprosium ions using azobenzene-4,4′-dicarboxylic acid (H2abd) as ligand, synthesized by soft hydrothermal routes. Both materials show isostructural three-dimensional networks with channels along a axis and display intense photoluminescence properties in the solid state at room temperature. Textural properties of the metal-organic frameworks (MOFs) have been fully characterized although no appreciable porosity was obtained. Magnetic properties of these materials were studied, highlighting the dysprosium material displays slightly frequency-dependent out of phase signals when measured under zero external field and under an applied field of 1000 Oe.

Experimental and theoretical study of photoluminescence and magnetic properties of metal–organic polymers based on squarate and tetrazolate moieties containing linkers

We report on the synthetic, luminescence and magnetic properties of three new isostructural Zn-, Cd- and Co-based 1D coordination polymers with the novel 3-(1H-tetrazol-5-ylamino)-4-hydroxycyclobut-3-ene-1,2-dione spacer, consisting of a squarate and a tetrazolate moiety linked by a NH group. These compounds exhibit an intense blue-green photoluminescence emission at room temperature in the solid state (Cd- and Zn-based structures) and antiferromagnetic exchange interactions (Co-based materials).