Gift Mehlana

Methanol mediated crystal transformations in a solvatochromic metal organic framework constructed from Co(II) and 4-(4-pyridyl) benzoate

The structural transformations of compound 1 {[Co(44pba)2]4·(DMF)3·(EtOH)0.25·(H2O)4}n [44pba = 4-(4-pyridyl) benzoate] were followed during the exchange of DMF and ethanol molecules by methanol at room temperature. The new phases obtained 2 {[Co(44pba)2]·(MeOH)2.5·(H2O)}n, 3 {[Co(44pba)2(MeOH)2]2·(MeOH)2.5·(H2O)2}n and 4 {[Co(44pba)2(MeOH)2]·(MeOH)0.5·(H2O)0.5}n were studied using differential scanning calorimetry, thermogravimetric analysis and X-ray diffraction methods. The final phase 4 reverts back to 1 upon soaking 4 in a dry DMF–ethanol mixture as evidenced by the powder diffraction data and infrared spectra.

Unravelling chromism in metal–organic frameworks

This paper examines chromic metal–organic frameworks, an important class of materials owing to their applications in several technological fields. These materials change their absorption spectra upon application of an external stimuli such as heat, pressure, light etc. This review explores recent advancements in photochromic, thermochromic, solvatochromic, and piezochromic metal–organic frameworks (MOFs). Emphasis is directed towards the design of chromic MOFs as well as the mechanisms associated with the colour change upon application of an external stimulus. Compared to traditional organic and inorganic materials, MOFs show exceptional chromic behavior as they can be fine-tuned to tailor the desired properties.

Recent advances in metal–organic frameworks based on pyridylbenzoate ligands: properties and applications

In this mini review, a summary of metal–organic frameworks (MOFs) assembled using 3-(4-pyridyl)benzoate (34pba) and 4-(4-pyridyl)benzoate (44pba) is presented. These materials exhibit interesting properties such as negative and positive thermal expansion, breathing behaviour, solvatochromism/vapochromism, thermochromism luminescence and exceptional iodine capture. Throughout the review we discuss the properties exhibited by MOFs constructed from the 44pba and 34pba linkers and we also highlight some of the exceptional behaviour of these materials.

The role of C–H⋯π interactions in modulating the breathing amplitude of a 2D square lattice net: alcohol sorption studies

A breathing 2D net 1 {[Zn(34pba)2]·DMF}n assembled from mononuclear zinc(II) centres and 3-(4-pyridyl) benzoate (34pba) ditopic linker is presented. 1 undergoes a displacive phase transition to give 1d, [Zn(34pba)2]n on evacuation of DMF. This is accompanied by a 37% decrease in solvent accessible void volume. Exposure of 1d to alcohol vapours shows that the saturation uptake increases with an increase in number of carbon atoms in the alcohol. The enhanced uptake of n-butanol and n-propanol is attributed to the long alkyl chain which enhances C–H⋯π interactions with the hydrophobic pyridyl and phenyl rings of the network. These interactions trigger the breathing motion of the 2D network and allow for the entry of n-propanol and n-butanol into the channels. Methanol and ethanol are unable to initiate the dynamic motion of the framework which increases the channel volume. In consequence, these solvents are absorbed to a lesser extent. Vapour phase competition studies show that the activated material is able to absorb n-butanol in the presence of a high vapour pressure of methanol. The selectivity observed may be based on factors that allow the metal organic framework inclusion compound to assume the most relaxed conformation.

Alcohol responsive 2D coordination network of 3-(4-pyridyl)benzoate and Zinc(II)

Abstract The solvothermal reaction of 3-(4-pyridyl)benzoic acid and zinc nitrate yielded a 2D network with an sql topology. Both elemental analysis and single crystal X-ray diffraction studies confirmed the formula of the compound as {[Zn(34pba)2] · (0.5 DMF) · (0.5 H2O)}n (1). At room temperature, the desolvated phase of 1, 1d, absorbs methanol, ethanol, 1-propanol and 1-butanol but not water vapour.

Co-crystals and salts of vanillic acid and vanillin with amines

Vanillin (VAN) and its oxidized form vanillic acid (VA) have successfully formed a series of co-crystals and salts. VAN formed a co-crystal with isonicotinamide (INM) and a co-crystal hydrate with theobromine (THB). Binary co-crystals of VA with isonicotinamide (INM), hexamethylenetetramine (HEXA), phenazine (PHZ) and pyrazine-N-oxide (PZO) were obtained. Interestingly, a ternary co-crystal resulted from a 1 : 1 : 1 ratio of VA, caffeine (CAF) and nicotinamide (NAM). Salt hydrates were also formed between piperazine (PPZ) and 1,4-diazabicyclo[2.2.2]octane (DABCO) with VA. All co-crystals and salts were characterized by X-ray diffraction techniques, thermal analysis and infrared spectroscopy.

Sorption properties toward environmentally important VOCs of half-sandwich Ru(II) complexes containing perylene bisimide ligands

ABSTRACT Two py-functionalized perylene bisimide ligands were synthesized and used to make bimetallic half-sandwich Ru(II) complexes. These were characterized by IR, 1H NMR, 13C CPMAS SSNMR spectroscopy, and elemental analysis. The complexes are wheel-and-axle (waa) compounds, where the axle is the divergent ligand and the wheels are the [(p-cymene)RuCl2] units. The complexes, but not the free ligands, showed absorption of volatile organic compounds such as toluene and xylenes through heterogeneous solid/gas uptakes. The reactivity is ascribable to the waa geometry, likely by an upset of the high stacking characterizing the crystalline frameworks of the free ligands. The kinetic profiles of the uptake reactions were determined.

Synthesis, thermal properties, and biological study of metal(II) nicotinamide complexes containing fumarate dianion and fumaric acid: Crystal structure of [Ni(H2O)4(nia)2](fum)·(H2fum)

ABSTRACT New divalent transition metal nicotinamide (nia) complexes containing fumarate (fum) dianion and fumaric acid (H2fum), [M(H2O)4(nia)2](fum)·(H2fum) [M = Co (1), Cu (2), and Ni (3)] have been synthesized.The compounds were characterized by elemental analyses, infrared, UV-vis, XRPD, and TGA. Structural analysis of 3 using single-crystal X-ray diffraction technique revealed that the Ni(II) ion is coordinated by four aqua and two nia ligands in an octahedral geometry. The structure of 3 is completed with fumarate (fum2−) dianion acting as a counterion while fumaric acid (H2fum) is present as a molecule of solvation. The three complexes were investigated for biological activities.