Oluseun Akintola

Recent studies have highlighted the biological significance of 8-hydroxyquinoline-2-carboxylic acid (8-HQA) as a metal chelator. In this work, several techniques were applied for the study of the interaction of 8-HQA with vanadium(IV/V) oxidometal ions at a temperature of T = 298.2 K and an ionic strength of I = 0.20 mol dm^-3 in KCl_(aq). The redox behavior of the chemical system was defined, and the stability constants of the formed complexes were determined by H⁺-ion selective electrode potentiometry and UV-vis spectrophotometric titrations, while nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopies and mass spectrometry provided stoichiometric and structural information. The formation of both oxidovanadium(IV) and dioxidovanadium(V) ML complexes with 8-HQA was observed in aqueous solution, with both complexes being particularly stable in acidic conditions. The dioxidovanadium(V) compound is stable even at neutral pH, but dimeric or tetrameric hydrolytic species are predominant under alkaline conditions. In contrast, oxidovanadium(IV) complexes undergo oxidation as the pH increases. Nevertheless, under strictly anaerobic conditions, the complexation of oxidovanadium(IV) by 8-HQA can also occur at pH > 6.0. The nature of the oxidovanadium(IV) and dioxidovanadium(V) ML complexes, representing the major species formed in solution, was further investigated by DFT calculations.

We report two chemically very similar non-oxido V(IV) complexes that feature distorted octahedral and distorted trigonal prismatic coordination geometries, as elucidated by single-crystal X-ray diffraction. Both compounds are thermally stable and show no degradation in the presence of air or water. An in-depth echo-detected field-sweep (EDFS) ESR spectroscopic study in frozen solution at temperatures below 10 K revealed resolved hyperfine interactions with the spin-bearing ⁵¹V nucleus, along with additional couplings to neighboring ¹⁴N and ¹H nuclei detected in ESEEM experiments. Investigation of the spin dynamics, and of the potential influence of the distinct coordination geometries, yielded long spin-lattice relaxation times (T₁) exceeding 100 ms at 5 K, which decreased to about 40 µs at 50 K. These long T₁ times therefore do not limit the spin coherence, and consequently the phase-memory times (T_m), at very low temperatures. The latter ranged from 5 to 8 µs and exhibited negligible temperature dependence within the investigated range. However, the use of a deuterated solvent increased T_m by approximately one order of magnitude to 52 µs at 5 K, though it also resulted in a more pronounced temperature dependence. Coherent spin manipulation was demonstrated by echo-detected transient nutation experiments, revealing well-defined Rabi oscillations with frequencies in the range of 13 MHz at an attenuation level of 9 dB and figures of merit exceeding 10³ in deuterated solvent. Cluster correlation expansion (CCE) simulations reproduce the experimentally observed trends and identify the surrounding nuclear spin bath as the dominant decoherence source under dilution-limit conditions. No significant differences attributable to the distinct coordination geometries or structural variations in the ligand backbone were observed. These findings establish the present vanadium(IV) complexes as competitive candidates for molecular spin qubits and promising targets for future surface-deposition studies

In this work, the coordination properties of 8-hydroxyquinoline-2-carboxylic acid (8-HQA, LH₂) toward Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ are discussed. Stability constants for Mn²⁺, Co²⁺, and Ni²⁺/8-HQA systems were determined by ISE-H⁺ (glass electrode) potentiometry, and those of Cu²⁺ and Zn²⁺/8-HQA by ultraviolet–visible (UV–vis) spectrophotometry, in KCl_(aq) at I = 0.2 mol dm^–3 and T = 298.2 K. For all systems, three species are formed: MLH⁺, ML, and ML₂ ^2–. 8-HQA proved a good sequestering agent of M²⁺ over a wide pH range, as also shown by the calculated pL_0.5 values. The stability of the formed metal complexes follows the expected Irving–Williams trend, especially concerning the ML₂ ^2– species, with log β₁₂₀: 12.45 ± 0.01 (Mn²⁺) < 13.45 (Fe²⁺) < 15.90 ± 0.04 (Co²⁺) < 17.17 ± 0.05 (Ni²⁺) < 20.64 ± 0.03 (Cu²⁺) > 18.78 ± 0.02 (Zn²⁺). This trend is inversely correlated to the M–N bond length determined by quantum mechanical calculations. These studies, together with voltammetry and electron paramagnetic resonance spectroscopy, allowed us to derive information about the coordination modes, structure, and nature of the formed species. Results support the formation of ML₂ ^2– complexes over possible ML­(OH)⁻, with 8-HQA acting as tridentate in all formed species, including the protonated MLH⁺.

Synthesis of a hybrid material based on the immobilization of the aliphatic nickel–PNP pincer complex on the Fe ₃ O ₄ @TiO ₂ core–shell significantly affects the sensing of glucose and antibacterial activity.

The reduction of the iron(II) half-sandwich precursors [Cp'FeN(R)(SiMe₃)] (R = SiMe₃, 2,6-di-iso-propylphenyl (dipp)) with KC₈ yields the one-dimensional polymeric iron(I) complexes {[Cp'Fe(N(SiMe₃)₃)]K}_n (4) and {[Cp'Fe(N(dipp)(SiMe₃))]K}_n (5). Addition of 18-crown-6 breaks up these chains and affords the monomeric salts [Cp'Fe(N(SiMe₃)₂)][K(18-crown-6)(thf)₂] (6) and [Cp'Fe(N(dipp)(SiMe₃))][K(18-crown-6)(thf)₂] (7). All four compounds were structurally characterized by single-crystal X-ray diffraction analysis and adopt an S = 3/2 spin ground state. Zero-field ⁵⁷Fe Mössbauer spectra uncover slow magnetic relaxation at low temperatures in each complex. Complementary CASSCF/NEVPT2 calculations reveal an S = 3/2 ground-state Kramers doublet that is ca. 100 cm^-1 below the first excited state. These findings are confirmed by results from DC susceptibility and magnetization experiments. The slow relaxation of magnetization is further characterized via AC susceptibility measurements, unveiling detectable slow relaxation of magnetization at zero external field for 4-6. Complex 4 exhibits an unusual field dependence of the quantum tunneling of magnetization, akin to exchange-bias effects, which are commonly observed in lanthanide dimers.

Dinuclear Mn^III(μ-NC)Fe^III molecular Prussian blue analogue reported here exhibits field-induced SMM behavior with U_eff of 15.09 K and protonation induced metal to metal electron transfer in solution.

Four new cobalt(II) coordination networks based on the nitrilotribenzoic acid ligand (H₃ntb) with the formula {[Co₃(ntb)₂(solv)2]}_n (where solv = dmf, def, dma, and EtOH), denoted as JUMP-4(solv), are reported. The trinuclear cobalt(II) clusters that constitute the three-dimensional network are coordinated by the six carboxylate groups of two bridging, deprotonated ntb^3- ligands. These clusters have two flexible coordination sites on the two terminal cobalt ions, which are partially saturated by the condensation of these clusters, leading to unprecedented inverted Figaro chains. Three of the frameworks were synthesized by combining cobalt(II) chloride and the ligand in a mixture of acetonitrile and the corresponding amide (dmf, def, and dma) in a 9:1 ratio, while the ethanol analogue could only be obtained by single-crystal-to-single-crystal transformation starting from the dmf and dma derivatives. The difference in the size of the solvents coordinated to the terminal cobalt(II) ions results in a pore-partitioning effect, as reflected in the argon sorption behavior of the networks. Magnetic measurements reveal antiferromagnetic interactions between the anisotropic cobalt(II) ions along the alternating inverted Figaro chains.

A simple and controllable synthesis led to both amorphous and crystalline porous TiO₂with remarkably high surface area and pore volume. Their distinctive characteristics influenced their effectiveness in photocatalytic and catalytic processes.

A surface-modified TiO ₂ hybrid material with a copper( ii )-NNN pincer complex exhibits efficient catalytic activity in click chemistry with alkyl halide precursors.

Potassium-based energy storage devices are attracting increasing attention as an alternative to lithium and sodium systems.