Syntheses, crystal structures of two Fe(III) Schiff base complexes with chelating o-vanillin aroylhydrazone and exploration of their bio-relevant activities

Two novel Fe(III) complexes, Fe(HL¹)₂Cl·1.25H₂O (1) and Fe(HL²)₂·Et₃NH·H₂O (2) (H₂L¹ = o-vanillin benzoylhydrazone, H₃L² = o-vanillin salicylhydrazone) are prepared. X-ray single crystal diffraction confirms that the hydrazone ligands can be chelated to iron centre resulting in a six-coordinate octahedral configuration. Both complexes show major intercalation effect to the herring sperm deoxyribonucleic acid (HS-DNA) with high binding constants of 2.01 × 10⁴ M^-1 and 2.24 × 10⁴ M^-1, respectively. Molecular docking studies reveal both complexes can intercalate at the gap of DC5-DG2 and DG6-DC1 base pairs of DNA hexamer (1Z3F). The interaction of the complex 1 with plasmid pBR322 DNA induces distinguishable alterations of the DNA morphology. Further, the structure of plasmid pBR322 DNA treated with complex 1 in the presence of ascorbic acid has been damaged probably due to the reactive oxygen species (ROS) generation. What's more, both complexes show high affinity with bovine serum albumin (BSA), the binding constants measured by fluorescence techniques are 5.75 × 10⁶ M^-1 and 4.39 × 10⁷ M^-1, respectively. Molecular docking demonstrates that the complexes prefer the binding pocket of site III (subdomain IIB) of BSA (PDB ID: 4F5S). Similarly, dynamic light scattering (DLS) reveals that the complexes not only bind to BSA but also induce bigger size aggregates as the concentration increases.

Metal-Metal (MM) Bond Distances and Bond Orders in Binuclear Metal Complexes of the First Row Transition Metals Titanium Through Zinc

This survey of metal-metal (MM) bond distances in binuclear complexes of the first row 3d-block elements reviews experimental and computational research on a wide range of such systems. The metals surveyed are titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, representing the only comprehensive presentation of such results to date. Factors impacting MM bond lengths that are discussed here include (a) the formal MM bond order, (b) size of the metal ion present in the bimetallic core (M₂) ⁿ⁺, (c) the metal oxidation state, (d) effects of ligand basicity, coordination mode and number, and (e) steric effects of bulky ligands. Correlations between experimental and computational findings are examined wherever possible, often yielding good agreement for MM bond lengths. The formal bond order provides a key basis for assessing experimental and computationally derived MM bond lengths. The effects of change in the metal upon MM bond length ranges in binuclear complexes suggest trends for single, double, triple, and quadruple MM bonds which are related to the available information on metal atomic radii. It emerges that while specific factors for a limited range of complexes are found to have their expected impact in many cases, the assessment of the net effect of these factors is challenging. The combination of experimental and computational results leads us to propose for the first time the ranges and "best" estimates for MM bond distances of all types (Ti-Ti through Zn-Zn, single through quintuple).

Iron catalyzed oxidation of benzylic alcohols to benzoic acids

The bidentate N,O-ligands phenol-pyrazole (HL1), naphthol-pyrazole (HL2) and the commercially available ligand 5-methylphenol-benzotriazole (HL3) were used for the synthesis of novel iron(iii) complexes. The mononuclear iron complexes [FeCl(L1)2] (1), [FeCl(L2)2] (2) and [FeCl(L3)2] (3) are stable to air and moisture, both in the solid state as well as in solution, while the dinuclear, μ-oxido bridged complex [{Fe(L1)2}2(μ-O)] (1a) is air sensitive. All four complexes 1, 2, 3 and 1a were investigated for their catalytic activity in the direct one-pot oxidation of primary alcohols to carbonic acids with 30% aq. hydrogen peroxide (H2O2) as the oxidation agent. The activity in oxidation reactions of the isolated, mononuclear complexes 1-3 was further compared to their in situ prepared analogues IS1-3. Experimentally obtained results indicate a tendency of higher activity for the oxidation of primary alcohols for the in situ prepared complexes. In conclusion, the oxidation of aromatic primary alcohols to carboxylic acids using isolated iron(iii) complexes and in situ generated complexes in the presence of H2O2 results in good to high yields. The reaction is straight-forward, clean and generates water as the only by-product.

Isolation and characterization of a tetranuclear Pt-FeFe-Pt intermediate en route to the trinuclear Pt-Fe-Pt cluster

An intermediate compound, [{PtFe(piam)₂(NH₃)₂(OCH₃)}₂(μ-OCH₃)₂](ClO₄)₂ (1, piam = pivalamidate), in the synthetic process to form [Pt₂Fe(piam)₄(NH₃)₄](ClO₄)₃ (2) by mixing cis-[Pt(piam)₂(NH₃)₂]·2H₂O and iron sources was successfully isolated and characterized by single-crystal X-ray analysis. In 1, the platinum and iron atoms are bridged by two piam ligands to afford a dinuclear Pt-Fe structure and are further linked to each other by methoxide bridges at the equatorial positions of iron atoms to form a tetranuclear Pt-FeFe-Pt complex. The Pt-Fe distances in 1 are 3.0010(16) and 2.9883(17) Å, which are significantly longer than those in 2 (2.5566(15) and 2.5718(15) Å). X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and magnetic susceptibility measurements revealed that the oxidation states are Pt(+2)-Fe(+3)Fe(+3)-Pt(+2) (1) and Pt(+2)-Fe(+3)-Pt(+2) (2) with high-spin (S = 5/2) configurations in iron atoms. The magnetic susceptibility of 1 has a χT value of 5.83 cm³ mol^-1 K per Pt(+2)-Fe(+3)Fe(+3)-Pt(+2) unit at 300 K, which decreases down to 0.04 cm³ mol^-1 K at 7 K due to antiferromagnetic coupling (J = -28 cm^-1) of the two Fe(+3) centers. Compound 2 maintains its trinuclear structure in MeCN, exhibiting reversible one-electron reduction and oxidation, Pt(+2)-Fe(+2)-Pt(+2) ↔ Pt(+2)-Fe(+3)-Pt(+2), at E_1/2 = -0.19 V (vs. Fc/Fc⁺). However, in MeOH, compound 2 is decomposed into a dinuclear structure of Pt-Fe involving an equilibrium between 1 and 2.