This work presents the fabrication of 3D printed composite objects based on copper(II) one-dimensional coordination polymer (CP1) decorated with thymine along its chains with potential utility as an environmental humidity sensor and as a water sensor in organic solvents. This new composite object has a remarkable sensitivity, ranging from 0.3 to 4% of water in organic solvents. The sensing capacity is related to the structural transformation due to the loss of water molecules that CP1 undergoes with temperature or by solvent molecules competition, which induces significant change in color simultaneously. The CP1 and 3D printed materials are stable in air over one year and also at biological pHs (5-7), therefore suggesting potential applications as robust colorimetric sensor. These results open the door to generate a family of new 3D printed materials based on the integration of multifunctional coordination polymers with organic polymers.

This perspective article shows new advances in the synthesis of colloids, gels, and aerogels generated by combining metal ions and ligands of biological interest, such as nucleobases, nucleotides, peptides, or amino acids, among other derivatives. The characteristic dynamism of coordination bonds between metal center and biocompatible-type ligands, together with molecular recognition capability of these ligands, are crucial to form colloids and gels. These supramolecular structures are generated by forming weak van der Waals bonds such as hydrogen bonds or π–π stacking between the aromatic rings. Most gels are made up of nano-sized fibrillar networks, although their morphologies can be tuned depending on the synthetic conditions. These new materials respond to different stimuli such as pH, stirring, pressure, temperature, the presence of solvents, among others. For these reasons, they can trap and release molecules or metal ions in a controlled way allowing their application in drug delivery as antimicrobial and self-healable materials or sensors. In addition, the correct selection of the metal ion enables to build catalytic or luminescent metal–organic gels. Even recently, the use of these colloids as 3D-dimensional printable inks has been published. The elimination of the solvent trapped in the gels allows the transformation of these into metal–organic aerogels (MOAs) and metal–organic xerogels (MOXs), increasing the number of possible applications by generating new porous materials and composites useful in adsorption, conversion, and energy storage. The examples shown in this work allow us to visualize the current interest in this new type of material and their perspectives in the short-medium term. Furthermore, these investigations show that there is still a lot of work to be done, opening the door to new and interesting applications.

Coordination compounds as antiviral substances: from their use as antiviral drugs to novel approaches such as their use as nanocarriers of antiviral drugs, for wrapping viruses, or to release antiviral agents.

No abstract

This review focuses on the usefulness of coordination bonds to create 3D printable inks and shows how the union of chemistry and 3D technology contributes to new scientific advances, by allowing amorphous or polycrystalline solids to be transformed into objects with the desired shape for successful applications. The review clearly shows how there has been considerable increase in the manufacture of objects based on the combination of organic matrices and coordination compounds. These coordination compounds are usually homogeneously dispersed within the matrix, anchored onto a proper support or coating the printed object, without destroying their unique properties. Advances are so rapid that today it is already possible to 3D print objects made exclusively from coordination compounds without additives. The new printable inks are made mainly with nanoscale nonporous coordination polymers, metal–organic gels, or metal–organic frameworks. The highly dynamic coordination bond allows the creation of objects, which respond to stimuli, that can act as sensors and be used for drug delivery. In addition, the combination of metal–organic frameworks with 3D printing allows the adsorption or selective capacity of the object to be increased, relative to that of the original compound, which is useful in energy storage, gas separation, or water pollutant elimination. Furthermore, the presence of the metal ion can give them new properties, such as luminescence, that are useful for application in sensors or anticounterfeiting. Technological advances, the combination of various printing techniques, and the properties of coordination bonds lead to the creation of surprising, new, printable inks and objects with highly complex shapes that will close the gap between academia and industry for research into coordination compounds.

This paper describes the synthesis and characterization of several copper­(II)-uracil-1-propionic acid (UPrOH) coordination compounds, including a theoretical and experimental study of their crystalline transformations, from paddlewheel structures ([Cu2(UPrO)4(MeOH)­(OH2)]·2H2O (1), [Cu2(UPrO)4­(MeOH) 2 ]­·2MeOH (2), [Cu2(UPrO)4(OH2)2]­·6H2O (3a), [Cu2(UPrO)4­(OH2)2]­·4H2O·2MeOH (3b)), to two-dimensional coordination polymer ([KCu2(UPrO)5(OH2)2] n (4)), or to dimeric compound ([Cu2(UPrO)4(OH2)4]­·4H2O (5)), due to slight modifications in the water–methanol solvent ratio used in their synthetic processes and thanks to the formation of supramolecular structures by hydrogen bonds. The theoretical study analyzes the thermodynamic stability of the phases, finding that, if we do not consider the supramolecular interactions, paddlewheel structures are more stable than the dimeric one, regardless of the medium in which they exist. However, the cohesive energy calculations can explain the final stabilization of the dimeric structure as a result of the subsequent supramolecular interactions. These transformations also involve color changes, rendering these compounds water and methanol sensors. In addition, the magnetic study confirms the paddlewheel environments with the presence of strong antiferromagnetic Cu–Cu coupling and weak antiferromagnetic intradimer Cu–Cu interactions with metamagnetic behavior in the case of dimeric species.

This work contributes to enlightening the opportunities of the anisotropic scheme of non-covalent interactions present in supramolecular materials. It provides a top-down approach based on their selective disruption that herein has been employed to process a conventional microcrystalline material to a nanofibrillar porous material. The developed bulk microcrystalline material contains uracil-1-propionic acid (UPrOH) nucleobase as a molecular recognition capable building block. Its crystal structure consists of discrete [Cu(UPrO)2 (4,4′-bipy)2 (H2 O)] (4,4′-bipy=4,4′-bipyridine) entities held together through a highly anisotropic scheme of non-covalent interactions in which strong hydrogen bonds involving coordinated water molecules provide 1D supramolecular chains interacting between them by weaker interactions. The sonication of this microcrystalline material and heating at 45 °C in acetic acid–methanol allows partial reversible solubilization/recrystallization processes that promote the cross-linking of particles into an interlocked platelet-like micro-particles metal–organic gel, but during CO2 supercritical drying, the microcrystalline particles undergo a complete morphological change towards highly anisotropic nanofibers. This unprecedented top-down microstructural conversion provides a nanofibrillar material bearing the same crystal structure but with a highly increased surface area. Its usefulness has been tested for HPLC separation purposes observing the expected nucleobase complementarity-based separation.

Multidisciplinary applications of 3D printing inks based on metal–organic compounds are described in the Review by N. Maldonado and P. Amo‐Ochoa on page 2887.