Synthesis, structure and catalytic activity of an oxo-bridged dinuclear oxovanadium complex of an isonicotinohydrazide ligand

Salicylidene-based dual-responsive 'turn on' fluorometric chemosensors for the selective detection of Zn2+, Al3+ and F- ions: theoretical investigation and applications in the live cell imaging of zebrafish larvae and molecular logic gate operation

Four salicylidene-based dual-responsive chemosensors 1,5-bis(5-bromosalicylaldehyde)carbohydrazone (R1), 1,5-bis(5-bromosalicylaldehyde)thiocarbohydrazone (R2), 1,5-bis(3-ethoxysalicylaldehyde)carbohydrazone (R3) and 1,5-bis(3-ethoxysalicylaldehyde)thiocarbohydrazone (R4) were synthesized and characterized. The molecular structures of R1 and R3 were confirmed by single crystal X-ray diffraction technique, which crystallized in the orthorhombic Pbcn and monoclinic P21/n space groups, respectively. The chemosensor molecules were investigated for their recognition properties against the selected cations (K+, Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Fe3+ and Al3+) and anions (F-, Cl-, Br-, I-, HSO4-, H2PO4-, ClO4-, N3- and NO3-) by colorimetry, absorption spectroscopy, fluorescence spectroscopy, 1H NMR spectroscopy and theoretical studies. The sensor molecules showed colorimetric responses for the Co2+, Ni2+, Cu2+ and Fe3+ cations and the F- anion. Interestingly, the Zn2+ and Al3+ cations showed only the 'turn on' fluorometric response, whereas the F- anion showed both colorimetric and fluorometric responses. The binding constants were determined using the Benesi-Hildebrand (B-H) equation from the fluorescence titrations and found to be higher for R3 towards the Al3+ cation (2.03 × 106 M-1) with a low limit of detection (1.79 μM) and for R4 towards the F- anion (5.13 × 105 M-1) with a low limit of detection (5.23 μM). The chemosensors established 1 : 2 and 1 : 1 binding stoichiometries with the sensed cations and anion, respectively, as confirmed by Job's plots. The computational studies show a lower band gap of HOMO-LUMO when the chemosensors bind with the sensed inorganic ions compared to the free chemosensors. Furthermore, the observed fluorescent behaviour of the Zn2+ and Al3+ cations have motivated us to investigate the practical applications in the live cell-imaging of zebrafish larvae as well as in the development of a molecular logic gate.

Systematic Development of Vanadium Catalysts for Sustainable Epoxidation of Small Alkenes and Allylic Alcohols

The catalytic epoxidation of small alkenes and allylic alcohols includes a wide range of valuable chemical applications, with many works describing vanadium complexes as suitable catalysts towards sustainable process chemistry. But, given the complexity of these mechanisms, it is not always easy to sort out efficient examples for streamlining sustainable processes and tuning product optimization. In this review, we provide an update on major works of tunable vanadium-catalyzed epoxidations, with a focus on sustainable optimization routes. After presenting the current mechanistic view on vanadium catalysts for small alkenes and allylic alcohols' epoxidation, we argue the key challenges in green process development by highlighting the value of updated kinetic and mechanistic studies, along with essential computational studies.

Cytotoxic oxidovanadium(IV) complexes of tridentate halogen-substituted Schiff bases: First dinuclear V(IV) complexes with O → VIV = O → VIV = O core

The reaction of potentially N,N,O-tridentate Schiff base ligands, Cl-LH, Br-LH, BrCl-LH and H-LH, with [V^IVO(acac)₂] in 2:1 ratio in methanol gave the corresponding mononuclear and dinuclear oxidovanadium(IV) complexes, VO(Cl-L)₂ (1), VO(Br-L)₂ (2), [(BrCl-L)₂(H₂O)V(μ-O)VO(BrCl-L)₂] (3) and [(H-L)₂(H₂O)V(μ -O)VO(H-L)₂] (4), in good yields. The ligands and complexes were fully characterized by elemental analysis and FT-IR spectroscopy. The ligands were also characterized by ¹H NMR spectroscopy. The oxidation state of V(IV)O with d¹ configuration in all synthesized complexes was confirmed by EPR. Moreover, the structures of 2 and 3 were determined by X-ray diffraction (XRD) analysis which revealed them as mono- and dinuclear vanadium(IV) complexes, respectively, with the ligands coordinated as bidentate chelates. The structure of 3 represents the first example of dinuclear V(IV) complex with O → V^IV = O → V^IV = O core (Cambridge Structural Database (CSD)​, version 5.42, update of May 2021). The cytotoxicity of ligands and complexes was evaluated towards ovarian (A2780), breast (MCF7) and prostate (PC3) cancer cells at 48 h. While ligands showed modest IC₅₀ values (>42 μM), all complexes turned out to be effective in the range 3.9-17.2 μM. In particular, A2780 and MCF7 cell lines were the most sensitive to the newly synthesized V(IV)O complexes.

The crystal structures and Hirshfeld surface analysis of N',N'''-((1E,1'E)-{[methyl-enebis(-oxy)]bis-(6-bromo-3,1-phenyl-ene)}bis-(methan-ylyl-idene))bis-(isonicotinohydrazide) dihydrate and N',N'''-((1E,1'E)-{[butane-1,4-diylbis(-oxy)]bis-(2,1-phenyl-ene)}bis-(methan-ylyl-idene))bis-(isonicotino-hydrazide) [+ solvent]

The title compounds, C27H20Br2N6O4·2H2O, (I), and C30H28N6O4·[+ solvent], (II), both crystallize with one half-mol-ecule in the asymmetric unit. The whole mol-ecule of (I) is generated by twofold rotation symmetry, with the twofold rotation axis bis-ecting the C atom of the -O-CH2-O- bridge. This results in a folded or U-shaped conformation of the mol-ecule. The whole mol-ecule of (II) is generated by inversion symmetry, with the central CH2-CH2 bond of the -O-(CH2)4-O- bridge being located about a center of inversion. This results in a step-like conformation of the mol-ecule. The central C(=O)N-N=C regions of the isonicotinohydrazide moieties in both compounds are planar and the configuration about the imine C=N bonds is E. In compound (I), the benzene and pyridine rings are inclined to each other by 37.60 (6)°. The two symmetry-related pyridine rings are inclined to each other by 74.24 (6)°, and the two symmetry-related benzene rings by 7.69 (6)°. In compound (II), the benzene and pyridine rings are inclined to each other by 25.56 (11)°. The symmetry-related pyridine rings are parallel, as are the two symmetry-related benzene rings. In the crystal of (I), a pair of water mol-ecules link the organic mol-ecules via Owater-H⋯O and Owater-H⋯N hydrogen bonds, forming chains along [001], and enclosing an R 4 2(8) and two R 1 2(5) ring motifs. The chains are linked by N-H⋯Npyridine hydrogen bonds, forming a supra-molecular framework. There are also a number of C-H⋯O hydrogen bonds, and C-H⋯π and offset π-π inter-actions [inter-planar distance = 3.294 (1) Å] present reinforcing the framework. In the crystal of (II), mol-ecules are linked by N-H⋯Npyridine hydrogen bonds, forming a supra-molecular framework. Here too there are also a number of C-H⋯O hydrogen bonds present, and a C-H⋯π inter-action, reinforcing the framework. For compound (II), a region of disordered electron density was corrected for using the SQUEEZE [Spek (2015 ▸). Acta Cryst. C71, 9-18] routine in PLATON. Their formula mass and unit-cell characteristics were not taken into account during refinement.

Catalytic Applications of Vanadium: A Mechanistic Perspective

The chemistry of vanadium has seen remarkable activity in the past 50 years. In the present review, reactions catalyzed by homogeneous and supported vanadium complexes from 2008 to 2018 are summarized and discussed. Particular attention is given to mechanistic and kinetics studies of vanadium-catalyzed reactions including oxidations of alkanes, alkenes, arenes, alcohols, aldehydes, ketones, and sulfur species, as well as oxidative C-C and C-O bond cleavage, carbon-carbon bond formation, deoxydehydration, haloperoxidase, cyanation, hydrogenation, dehydrogenation, ring-opening metathesis polymerization, and oxo/imido heterometathesis. Additionally, insights into heterogeneous vanadium catalysis are provided when parallels can be drawn from the homogeneous literature.

Crystal structure of (E)-N'-(5-bromo-2-hy-droxy-benzyl-idene)nicotinohydrazide monohydrate

In the title compound, C13H10BrN3O2·H2O, the conformation about the azomethine double bond is E. The mol-ecule exists in the amido form with a C=O bond length of 1.229 (2) Å. There is an intra-molecular O-H⋯N hydrogen bond forming an S(6) ring motif. The whole mol-ecule is almost planar, with an r.m.s. deviation of 0.021 Å for all non-H atoms, and the dihedral angle between the planes of the pyridine and benzene rings is 0.74 (12)°. In the crystal, the water mol-ecule of crystallization links the organic mol-ecules via Ow-H⋯O, Ow-H⋯N and N-H⋯Ow hydrogen bonds and short C-H⋯Ow contacts, forming sheets lying parallel to (100). Within the sheets there is a weak π-π inter-action involving the pyridine and benzene rings [centroid-to-centroid distance = 3.8473 (15) Å]. The sheets are linked via C-H⋯Br inter-actions, forming a three-dimensional network.