This paper describes the synthesis, crystal structures, detailed dc and ac magnetic properties, far-infrared magnetic spectroscopy (FIRMS), and theoretical calculations of two further examples of the scarce trigonal antiprismatic CoII complexes (octahedral complexes distorted along the C3 axis). One has been prepared from the scorpionate ligand hydridotris(1,2,4-triazolyl)borate (Ttz-) and the other from the tridentate bridging ligand 1-methylimidazole-2-carboxamide oxime (HL). The first complex has the formula [CoII(Ttz)2]·5.5H2O (1), whereas the second, [Co3(L)6](NO3)2·6H2O (2), is a mixed-valence CoIII-CoII-CoIII trinuclear complex. In 1, the pseudo-C3 axis of the trigonal antiprismatic high spin CoIIN6 coordination sphere lies along the B⋯Co⋯B direction, whereas in 2 the C3 axis of the CoIIO6 unit lies along the CoIIICoIICoIII direction. Although both complexes exhibit very strong easy-axis magnetic anisotropy, they do not show slow magnetic relaxation under zero field but rather behave like field-induced single-ion magnets (SIMs). Experimental and theoretical magneto-structural correlations carried out on all the trigonal antiprismatic CoII complexes reported to date, as well as on related model complexes, confirm, on the one hand, that the axiality gxy/gz increases when the s/h ratio decreases, that is to say when the compounds are more elongated along the C3 or pseudo C3 axis, and on the other hand, that all of them exhibit easy-axis magnetic anisotropy but with significant intrinsic transversal anisotropy (gxy/gz > 0.1), which prevents SIM behaviour in a zero-field. Furthermore, the results of the theoretical studies suggest that the use of neutral ligands based on scorpionate-tris(pyrazole)methane with bulky substituents could cause sufficient elongation along the C3 axis, due to steric hindrance, to reduce the quantum tunneling of magnetization (QTM) and increase the relaxation time to such an extent that SIM behavior would be observed at zero field.
The reaction rate of small ring cycloalkane transformations is primarily governed by strain release. The present study summarises how the interplay between substrate strain release and orbital orientations from the transition metal catalyst affects overall catalytic efficiency. Density functional theory (DFT) studies on a Rh(I) metal complex in a [5 + 1] cycloaddition reaction between vinylcyclopropane and CO are summarized. The free energy barriers for oxidative addition on singlet (7.7 kcal mol-1) and triplet (25.6 kcal mol-1) surfaces highlight how optimal orbital orientation in transition metal catalysts synergizes with strain release. The distortion-interaction energy analysis of singlet and triplet states confirmed the mechanism of synergy between strain release and orbital interaction. Distinct spin states tune the kinetics by modulating strain relief and electronic arrangements and effectively lower activation energies, enabling efficient [5 + 1] metal catalysed cycloadditions.
The rising global need for sustainable energy has intensified research into environmentally friendly energy conversion technologies, such as fuel cells and electrochemical water splitting devices. The efficiency of these technologies is strongly influenced by the activity of electrocatalysts that enable the oxygen reduction (ORR) and evolution (OER) reactions. Noble metal-based electrocatalysts, including Pt, Pd, RuO2 and IrO2, are widely regarded as benchmark materials for these reactions due to their excellent electrocatalytic activity; nevertheless, their high cost, scarcity and limited long-term stability have prompted the development of alternatives. Polyoxometalates (POMs) have attracted considerable interest as a versatile class of materials, owing to their adjustable structures, redox properties and potential to serve as efficient and economically viable catalysts. In this research, we investigate two sandwich-type Dawson POM clusters containing cobalt and nickel ([CoNi3(As2W15O56)2]16- and [NiCo3(As2W15O56)2]16-) but with different spatial arrangements. The prepared electrocatalysts exhibited notable OER activity in alkaline media, achieving maximum current densities of 86.70 and 68.32 mA cm-2 with corresponding overpotential values of 0.45 and 0.49 V vs. RHE, respectively. The electrocatalysts also demonstrated promising activity towards the ORR, with diffusion-limiting current densities of -2.98 and -2.33 mA cm-2 and onset potentials of 0.82 and 0.78 V vs. RHE, respectively. This paper provides evidence suggestive of an influence of the metal centre position within the POM framework on the ORR/OER electrochemical performance and reinforces the potential of these hybrid materials as cost-effective and sustainable bifunctional electrocatalysts for next-generation energy devices.
Three new copper(I) complexes derived from N,N'-dialkyl-β-dialdiminate anions (alkyl = iso-propyl or tert-butyl) are reported. Treatment of CuBr with Li[tBuN(CH)3NtBu] affords the tetrameric copper(I) compound Cu4[tBuN(CH)3NtBu]4. In this tetramer, the β-dialdiminate ligands adopt open-chain conformations that link the copper(I) centers into a boat-shaped 24-membered ring. Interestingly, the tetramer dissociates over several hours in solution into a dimer of stoichiometry Cu2[tBuN(CH)3NtBu]2. When copper(II) chloride is treated with Li[tBuN(CH)3NtBu], or copper(II) methoxide is treated with H[iPrN(CH)3NiPr], redox reactions take place in which the metal center is reduced to copper(I) and the β-dialdiminate anion or β-dialdimine is oxidized. Two copper(I) complexes containing oxidized β-dialdiminate groups have been isolated: in both complexes, the oxidized group has been dehydrogenated and oligomerized through C-C bond formation. All three compounds have been characterized by X-ray crystallography; selected NMR, IR, EA, and UV-Vis spectra are also reported.
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