Tetrahedral M4(μ4-O) Motifs Beyond Zn: Efficient One-Pot Synthesis of Oxido-Amidate Clusters via a Transmetalation/Hydrolysis Approach

While zinc μ₄-oxido-centered complexes are widely used as versatile precursors and building units of functional materials, the synthesis of their analogues based on other transition metals is highly underdeveloped. Herein, we present the first efficient systematic approach for the synthesis of homometallic [M₄(μ₄-O)L₆]-type clusters incorporating divalent transition-metal centers, coated by bridging monoanionic organic ligands. As a proof of concept, we prepared a series of charge-neutral metal-oxido benzamidates, [M₄(μ₄-O) (NHCOPh)₆] (M = Fe, Co, Zn), including iron(II) and cobalt(II) clusters not accessible before. The resulting complexes were characterized using elemental analysis, FTIR spectroscopy, magnetic measurements, and single-crystal X-ray diffraction. Detailed structural analysis showed interesting self-assembly of the tetrahedral clusters into 2D honeycomb-like supramolecular layers driven by hydrogen bonds in the proximal secondary coordination sphere. Moreover, we modeled the magnetic properties of new iron (II) and cobalt (II) clusters, which display a general tendency for antiferromagnetic coupling of the μ₄-O/μ-benzamidate-bridged metal centers. The developed synthetic procedure is potentially easily extensible to other M(II)-oxido systems, which will likely pave the way to new oxido clusters with interesting optoelectronic and self-assembly properties and, as a result, will allow for the development of new functional materials not achievable before.

Chiral superstructures from homochiral Zn2+ , Co2+ , Fe2+ -2,6-bis (aryl ethylimine)pyridine complexes

We report the hierarchical supramolecular organization of metallosupramolecular homochiral complexes 1-Λ-(S,S,S,S)-M²⁺ /1-∆-(R,R,R,R)-M²⁺ and 2- Λ-(S,S,S,S)-M²⁺ /2-∆- (R,R,R,R)-M²⁺ of M²⁺ = Co²⁺ , Fe²⁺ , Zn²⁺ metal ions with chiral pseudo-terpyridine-type ligands: 1-(S,S) or 1-(R,R) = 2,6-bis (naphthyl ethylimine)pyridine and 2-(S,S) or 2-(R,R) = 2,6-bis (phenyl-ethylimine)pyridine. Circular dichroism measurements in solution were used to confirm the enantiomeric nature of all twelve complexes. For crystal structures of 1- Λ- (S,S,S,S)-M²⁺ or 1-∆- (R,R,R,R)-M²⁺ complexes, absolute configurations {∆ (or P), Λ (or M)} were confirmed by refinement of the Flack parameter x: -0.007 ≤ x ≤ 0.11 for the single crystals of 1-Λ-(S,S,S,S)-M²⁺ /1-∆- (R,R,R,R)-M²⁺ , 2- Λ- (S,S,S,S)-Fe²⁺ , and 2-∆- (R,R,R,R)-Co²⁺ .

Estimation of conventional C-Hπ (arene), unconventional C-Hπ (chelate) and C-Hπ (thiocyanate) interactions in hetero-nuclear nickel(ii)-cadmium(ii) complexes with a compartmental Schiff base

Three new heteronuclear nickel(ii)/cadmium(ii) complexes, [(SCN)(Cl)Cd(L)Ni(DMF)₂] (1), [(SCN)(CH₃CO₂)Cd(L)Ni(CH₃OH)₂] (2) and [(SCN)(Cl)Cd(L)Ni(NH₂CH₂CH₂CH₂NH₂)]_n (3) {where H₂L = N,N'-bis(3-ethoxy-salicylidene)propane-1,3-diamine is a N₂O₄ compartmental Schiff base}, have been synthesized and characterized. The structures of the complexes have been confirmed by single crystal X-ray diffraction studies. In each complex, nickel(ii) is placed in the inner N₂O₂ environment and cadmium(ii) is placed in the outer O₄ compartment of the compartmental Schiff base. Furthermore, the importance of unconventional C-Hπ (chelate) interactions in the solid state of both complexes and C-Hπ (thiocyanate) interaction in complex 2 has been described by means of DFT and MEP calculations and characterized using NCI plots. All complexes show photoluminescence at room temperature upon irradiation by ultraviolet light. The lifetimes of excited states are in the range of 2-6 ns.

Unique trapping of paddlewheel copper(ii) carboxylate by ligand-bound {Cu2} fragments for [Cu6] assembly

Trapping of paddlewheel {Cu₂(carboxylate)₄} by ligand-bound {Cu₂(μ-H₂L)}³⁺ units resulted in dumbbell-shaped [Cu₆] complexes modulating the tetracarboxylate bridged Cu⋯Cu separations.

African Viper Poly-His Tag Peptide Fragment Efficiently Binds Metal Ions and Is Folded into an α-Helical Structure

Snake venoms are complex mixtures of toxic and often spectacularly biologically active components. Some African vipers contain polyhistidine and polyglycine peptides, which play a crucial role in the interaction with metal ions during the inhibition of snake metalloproteases. Polyhistidine peptide fragments, known as poly-His tags, play many important functions, e.g., in metal ion transport in bacterial chaperon proteins. In this paper, we report a detailed characterization of Cu(2+), Ni(2+), and Zn(2+) complexes with the EDDHHHHHHHHHG peptide fragment (pHG) derived from the venom of the rough scale bush viper (Atheris squamigera). In order to determine the thermodynamic properties, stoichiometry, binding sites, and structures of the metal-pHG complexes, we used a combination of experimental techniques (potentiometric titrations, electrospray ionization mass spectrometry, UV-vis spectroscopy, circular dichroism spectroscopy, and electron paramagnetic resonance spectroscopy) and extensive computational tools (molecular dynamics simulations and density functional theory calculations). The results showed that pHG has a high affinity toward metal ions. The numerous histidine residues located along this sequence are efficient metal ion chelators with high affinities toward Cu(2+), Ni(2+), and Zn(2+) ions. The formation of an α-helical structure induced by metal ion coordination and the occurrence of polymorphic binding states were observed. It is proposed that metal ions can "move along" the poly-His tag, which serves as a metal ion transport pathway. The coordination of Cu(2+), Ni(2+), and Zn(2+) ions to the histidine tag is very effective in comparison with other histidine-rich peptides. The stabilities of the metal-pHG complexes increase in the order Zn(2+) < Ni(2+)≪ Cu(2+).