Two-dimensional (2D) metal–organic frameworks (MOFs) have been a worldwide research interest due to their potential application in supercapacitors. Herein, a cobalt-based layered MOF ([Co2(μ-SO4)(Hppza)2(H2O)3]n, namely, SEU-1; H2ppza = 3-(pyridin-4-yl)-1H-pyrazole-5-carboxylic acid) has been synthesized via a one-step solvothermal method. Single X-ray diffraction analysis shows that the SEU-1 exhibits a (3,3,4)-connected 2D structure with a Schläfli symbol of (62·8)(63)(64·8·10). Variable-temperature magnetic susceptibility data display that antiferromagnetic interactions between two CoII ions exist in SEU-1. The supercapacitive performance has been evaluated in the three-electrode system. Its maximum specific capacitance is 145.5 F g−1 at 1 A g−1, along with the specific capacitance retention of 92.7% at the current density of 5 A g−1 after 6000 cycles in 3 M KOH solution. These results demonstrate that SEU-1 is a good candidate for electrode material for electrochemical energy storage.

This study explores the synthesis and diverse properties of newly synthesised water-soluble cobalt (II) complexes (1-3). Analysis of the complexes through various methods, including Hirshfeld surface analysis, reveals distinctive intermolecular interactions, particularly robust H-bonding contributions to crystal packing. 2D fingerprint plots provide quantitative insights into supramolecular interactions, while TGA-DSC analysis elucidates multi-step decomposition processes, mainly involving organic moieties. FT-IR and SCXRD confirm the structures of the complexes. Magnetic susceptibility measurements show paramagnetic behaviour in all complexes. FMO calculations expose HOMO-LUMO gaps and charge transfer processes, with NBO analysis emphasizing the significance of chloride, nitrogen, and oxygen atoms in coordination. In addition, pkCSM profile was carried out. The biological properties of the complexes reveal potent antibacterial activity for 2 and 3 against Gram-positive and Gram-negative bacteria. Despite lower antibacterial efficacy compared to standard antibiotics, their water solubility suggests potential human pharmacological applications. In terms of anti-inflammatory activity, all three complexes exhibit concentration-dependent prevention of ovalbumin denaturation, with 2 being the most effective. Compound 3, despite having seven carboxyl groups, exhibits the weakest anti-inflammatory effect, potentially attributed to complex formation obscuring these groups. Furthermore, all complexes display antioxidant activities; 1 and 2 are greater than BHT in the ferric thiocyanate assay.

New metastable SmSi3-x (x = 0-0.05) is obtained by high-pressure high-temperature synthesis (9.5 GPa, 870-1270 K). Powder diffraction data refinements reveal that the crystal structure of SmSi3 is isotypic to that of YbSi3 (space group I4/mmm, a = 7.23634(5) Å, c = 11.0854(1) Å). In the crystal structure, two types of Si2 dumbbells agglomerate into layers, which embed the samarium atoms. At ambient pressure, SmSi3 decomposes exothermally upon heating into Si and SmSi2-x. Single-crystal structure refinements of a specimen SmSi3-x (x=0.05) reveal considerable electron density, which is not accounted for by the YbSi3 model. The additional maxima can be assigned to disorder which affects the samarium positions and induces silicon vacancies. Scanning transmission electron microscopy experiments evidence that the disorder can be attributed to extended defects.  Magnetic measurements on SmSi3-x reveal van Vleck paramagnetic behavior and antiferromagnetic ordering at low temperatures. Computations within the local spin density approximation (LSDA and LSDA+U) on the crystal structure of SmSi3 reproduce the anti­ferro­magnetic coupling as the favored long-range order. Quantum chemical analysis of the chemical bonding in SmSi3 reveals two-center two-electron bonds within the Si2 dumbbells plus a total of a little less than four electrons in lone pairs at each silicon atom.

The substituents in 2,6-bis(2-R-2H-tetrazol-5-yl)pyridyl neutral ligands R2btp (R = Me, tBu) revealed a prominent effect when reacting with iron(II) salts, in combination with the nature of the anion. According to metal:ligand molar ratio, reaction of R2btp with FeCl2 led to isolate [FeII(R2btp-k3N,N’,N”)2](FeIIICl4)2, R = Me (1a) and tBu (2a), where the octahedral iron(II) centres bring two tridentate ligands in mer coordination mode, but also [FeII(tBu2btp-k3N,N’,N”)(tBu2btp-kN)2(H2O-kO)](FeIIICl4)2 (2b), where one ligand is tridentate, while the other two coordinate the iron(II) through one tetrazolyl nitrogen atom, and the octahedral sphere is completed by one water molecule. In all cases, half of the iron ions are oxidised to iron(III) forming the paramagnetic tetrachloroferrato counterions. Reaction of tBu2btp with Fe(ClO4)2×6H2O led to the octahedral [FeII(tBu2btp-k3N,N’,N”)2](ClO4)2∙4DCM (4a∙4DCM), which shows solvent-dependent spin crossover behaviour: while 4a∙4DCM is blocked in the high spin state, its unsolvated form, 4a, undergoes spin transition to low spin in two subsequent steps at 206 K, with opening of a 23-K hysteresis (T1/2¯ = 194 K, T1/2­ = 217 K), and at 136 K (T1/2¯ = 135 K, T1/2­ = 137 K). The magnetic profile changes to an incomplete spin transition when the sample absorbs water molecules yielding 4a×1.5H2O.

The Front Cover shows the course of a stream in which 2-naphthol is converted to a quinone intermediate by a bis(μ-oxido) complex. Subsequent condensation with 1,2-phenylendiamine results in benzo[a]phenazine working as an antimicrobial protective shield for the contaminated lake the stream is crossing on its way to the sea. Thanks to the antimicrobial function of the phenazine, the lower stream is protected from the contamination of plant diseases carrying soil bacteria flowing into the lake from a crop field. More information can be found in the Research Article by S. Herres-Pawlis and co-workers.