Beata Cristóvão

This review provides a comprehensive overview of recent advances in the synthesis, structural characterization, and applications of Ru(II), Ru(III), and Ru(VI) complexes, which bear tetradentate Schiff bases of salen type. Ruthenium complexes exhibit catalytic, electrochemical, and biological properties, serving as multifunctional platforms that integrate fundamental aspects of coordination chemistry with potential practical applications.

Arylpiperazines are considered a “privileged scaffold” in medical chemistry due to their versatility and modular structure, enabling modifications towards diverse molecular targets with desired potency, selectivity, and pharmacokinetic properties. In particular, arylpiperazines are aminergic G protein-coupled receptor (GPCR) ligands and neurotransmitter transporter inhibitors, making this group of compounds attractive in central nervous system (CNS) drug discovery for treating schizophrenia, depression, sleep disorders, and Parkinson’s disease (PD). Furthermore, arylpiperazines may possess anticancer properties and can modulate some molecular targets involved in this disease. This review focuses on the structural aspects of arylpiperazines as aminergic GPCR ligands. The review centers on biologically active arylpiperazines with known X-ray structures, providing a detailed discussion of the conformations in the solid state. Next, their interactions with the aminergic GPCRs, based on experimental and molecular modelling studies, are addressed, making this review a comprehensive resource for medicinal and structural chemists working on arylpiperazines.

This review provides an overview of the synthesis, characterization and application of coordination polymers based on N,O-donor Schiff base ligands. The coordination polymers (CPs) represent a novel class of inorganic–organic hybrid materials with tunable compositions and fascinating structures. They are composed of metal ions and organic ligands. Therefore, the nature of the metal ion and type of organic ligand is the most significant factor in constructing targeted coordination polymers with the desired properties. Due to the versatile coordination modes, N,O-donor Schiff base ligands are also used to construct various CPs.

Three new cationic complexes, [Cu₄Tb₂(H₂L)₄(NO₃)₄(H₂O)₃](NO₃)₂·5.5H₂O·2MeOH (1), [Cu₄Ho₂(H₂L)₄(NO₃)₄(H₂O)₃](NO₃)₂·7.5H₂O (2), and [Cu₄Er₂(H₂ L)₄(NO₃)₄(H₂O)₃](NO₃)₂·7H₂O·3MeOH (3), were synthesized and studied using elemental and TG/DTG/DSC analyses, single-crystal X-ray diffraction, and magnetic measurements. The structure analysis showed that 1–3 crystallize as (NO₃)-bridged compounds and that the lanthanide(III) ion acts as a joint connecting two [CuH₂L] coordination units. In each heterotrinuclear unit, an asymmetry in the degree of planarity of the bridging CuO₂Ln fragments is observed. The Cu^II ions are five- and six-coordinate, with distorted square pyramidal and octahedral geometry, respectively, whereas the Ln^III ions are nine-coordinate. The solvates 1–3 are stable at room temperature, and their desolvation process is consistent with the loss of water and/or methanol molecules. The temperature dependence of the magnetic susceptibility and the field-dependent magnetization indicate the weak ferromagnetic interaction between the paramagnetic centers Cu^II and Tb^III/Ho^III 1 and 2.

A new cobalt(III) complex with a pentadentate Schiff base was synthesized using a reaction of 2,2′-{(2-hydroxypropane-1,3-diyl)bis(nitriloeth-1-yl-1-ylidene)}diphenol (H₃L) and cobalt(II) acetate in a methanolic solution. This synthesis resulted in the isolation of dinuclear compound [Co^III₂L₂] (1), which was characterized using elemental analyses and XRF, FTIR, and TG/DSC techniques. The molecular structure of the complex was confirmed using single-crystal X-ray diffraction. The structure of 1 consists of a centrosymmetric dimer in which two crystallographically equivalent cobalt(III) ions are bridged by two alkoxido oxygen atoms. In addition, each metal center is coordinated by two Schiff bases.

New heterotrinuclear complexes with the general formula [Cu₂Ln(H₂L)(HL)(NO₃)₂]·MeOH (Ln = Ho (1), Er (2), H₄L = N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane) were synthesized using compartmental Schiff base ligand in conjugation with auxiliary ligands. The compounds were characterized by elemental analysis, ATR-FTIR spectroscopy, X-ray diffraction, TG, DSC, TG-FTIR and XRD analysis. The N₂O₄ salen-type ligand coordinates 3d and 4f metal centers via azomethine nitrogen and phenoxo oxygen atoms, respectively, to form heteropolynuclear complexes having CuO₂Ln cores. In the crystals 1 and 2, two terminal Cu(II) ions are penta-coordinated with a distorted square-pyramidal geometry and a Ln^III ion with trigonal dodecahedral geometry is coordinated by eight oxygen atoms from [Cu^II(H₂L)(NO₃)]⁻ and [Cu^II(HL)(NO₃)]²⁻ units. Compounds 1 and 2 are stable at room temperature. During heating, they decompose in a similar way. In the first decomposition step, they lose solvent molecules. The exothermic decomposition of ligands is connected with emission large amounts of gaseous products e.g., water, nitric oxides, carbon dioxide, carbon monoxide. The final solid products of decomposition 1 and 2 in air are mixtures of CuO and Ho₂O₃/Er₂O₃. The measurements of magnetic susceptibilities and field dependent magnetization indicate the ferromagnetic interaction between Cu^II and Ho^III ions 1.

The paper presents the synthesis of a hydroxyapatite/iron oxide composite utilizing the wet chemical method, as well as the comparison of several selected material characteristics. As follows from the literature reports, hydroxyapatite is a common mineral possessing numerous significant properties. Nowadays, there is an increase in the amount of research on possible modifications of this compound. The promising way to improve hydroxyapatite features is its combination with iron oxide. Particularly, there can be two forms that are distinguished, namely Fe₃O₄ and γ-Fe₂O₃. These oxides exhibit valuable properties, particularly magnetism. A combination of the mentioned materials leads to multifunctional composite formation with many potential applications, as follows from several studies. However, this area of science is not fully developed. There are still many aspects to be examined. The synthesized composite and its components were analyzed by employing the following methods. The X-ray diffraction analysis revealed formation of hydroxyapatite and Fe₂O₃ crystalline phases. Moreover, porosimetry proved a larger specific area for the composite sample in comparison with other materials. The results obtained using the SEM method confirmed an external layer of hydroxyapatite and spherical shapes of internal Fe₂O₃ particles. Furthermore, the X-ray photoelectron spectroscopy data presented characteristic peaks of Fe, Ca, P, and O atoms in all samples. The Fourier Transform Infrared spectra displayed all the specific vibrations typical of the analyzed materials. What is more, the Vibrating Sample Magnetometer method confirmed the paramagnetic nature of the samples. It could be concluded that the synthesized composite has intermediate properties between the components used in the formation process. The results suggest that these composites are superparamagnetic. This type of material architecture would be well suited for biomedical applications.

In recent decades, coordination compounds have been of great interest, thanks to their fascinating structures and functional properties