N,N′-bis(2-hydroxy-3-methoxybenzylidene)-1,3-diaminopropane dimeric 4f and 3d–4f heterodinuclear complexes: Syntheses, crystal structures and magnetic properties

Synthesis, spectroscopic findings and crystal engineering of Pb(ii)-Salen coordination polymers, and supramolecular architectures engineered by σ-hole/spodium/tetrel bonds: a combined experimental and theoretical investigation

Spontaneous self-assembly is one of the available synthetic routes to achieve structurally versatile and unique crystal complexes with selected metal-ligand combinations in the spirit of pseudohalides. In this endeavour, we designed a novel 1D coordination polymer (CP), [(Cd)(Pb)(L)(η¹-NCS)(η¹-SCN)] _n (1), using a compartmental Salen ligand (H₃L) in the presence of NaSCN. The characterization of the CP was accomplished using several spectroscopic techniques: MALDI-TOF, PXRD, SEM, EDX mapping, and single-crystal X-ray crystallography. The CP crystallizes in the monoclinic space group P2₁/c with Z = 4. SCXRD reveals Cd(ii) and Pb(ii) metal ions fulfilled distorted square pyramidal and hemi-directed coordination spheres. Cd(ii) is placed in the inner N₂O₂ and heavier Pb(ii) in the outer O₄ compartments of the de-protonated form of the ligand [L]^2-. Supramolecular interactions in the intricate crystal structure produced attractive molecular architectures of the compound. The flexible aliphatic -OH pendent group coordinates with the Pb(ii) ions. This unique binding further elevates the supramolecular crystal topographies. The supramolecular interactions were authenticated by Hirshfeld surface analysis (HSA). The observation of the recurring unconventional tetrel bonds was rationalized by DFT calculations and surface plots of molecular electrostatic potential (MEP). In the 1D polymeric chain in the complex, the O-atom of the -OH groups shows a tetrel bonding interaction with the Pb atom. We have found that the combination of QTAIM/NCI and QTAIM/ELF plots helps reveal the nature of these contacts. Moreover, the QTAIM/ELF plot determines the donor-acceptor interaction between the O-atom and the Pb atom, establishing the σ-hole. Agreeably, the σ-hole interaction also helps Pb(ii) serve as a Lewis acid in the complex. Finally, spodium and tetrel bonds are formed, possible thanks to a hemi-directional coordination sphere of the Pb atoms in the polymer described.

A theoretical insight on the anion⋯anion interactions observed in the solid state structure of a hetero-trinuclear complex

A hetero-nuclear cobalt(iii)/potassium complex has been synthesized and characterized by several analytical techniques. DFT computations indicate the existence of anion⋯anion interactions in its solid state.

Design and catalytic studies of structural and functional models of the catechol oxidase enzyme

The catechol oxidase activity of three copper/bicompartmental salen derivatives has been studied. One mononuclear, [CuL] (1), one homometallic, [Cu₂L(NO₃)₂] (2), and one heterometallic, [CuMnL(NO₃)₂] (3) complexes were obtained using the ligand H₂L = N,N'-bis(3-methoxysalicylidene)-1,3-propanediamine through different synthetic methods (electrochemical, chemical and solid state reaction). The structural data indicate that the metal ion disposition models the active site of type-3 copper enzymes, such as catechol oxidase. In this way, their ability to act as functional models of the enzyme has been spectrophotometrically determined by monitorization of the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butyl-o-benzoquinone (3,5-DTBQ). All the complexes show significant catalytic activity with ratio constants (k_obs) lying in the range (223-294) × 10^-4 min^-1. A thorough kinetic study was carried out for complexes 2 and 3, since they show structural similarities with the catechol oxidase enzyme. The greatest catalytic activity was found for the homonuclear dicopper compound (2) with a turnover value (k_cat) of (3.89 ± 0.05) × 10⁶ h^-1, which it is the higher reported to date, comparable to the enzyme itself (8.25 × 10⁶ h^-1).

Heteronuclear cobalt(iii)/sodium complexes with salen type compartmental Schiff base ligands: methylene spacer regulated variation in nuclearity

Three unique heteronuclear cobalt(iii)/sodium Schiff base complexes have been synthesized and characterized. Nuclearity of these complexes changes as a result of alteration of the steric hindrance in the ligand moiety.

A microporous Mg2+ MOF with cation exchange properties in a single-crystal-to-single-crystal fashion

A microporous Mg²⁺ MOF shows single-crystal-to-single-crystal exchange of Mg²⁺ by Cu²⁺ ions.

Thiacalix[4]arene-supported heterodinuclear NiII–LnIII complexes: slow magnetic relaxation behavior in the dysprosium analogue

Three thiacalix[4]arene-supported ferromagnetic Ni^II–Ln^III complexes have been isolated. The dysprosium analogue exhibits field-induced SMM behavior and diamagnetic dilution can efficiently influence the dipole–dipole interaction between magnetic centers.

The exceptionally rich coordination chemistry generated by Schiff-base ligands derived from o-vanillin

Recent and relevant examples of homo- and heterometallic complexes generated by Schiff base ligands derived from o-vanillin, as well as their properties, are discussed.

Two-dimensional coordination polymers constructed by [Ni(II)Ln(III)] nodes and [W(IV)(bpy)(CN)6]2- spacers: a network of [Ni(II)Dy(III)] single molecule magnets

Three isomorphous two-dimensional (2D) coordination polymers of general formula {[Ni(II)(valpn)Ln(III)(NO3)(H2O)(μ-NC)4W(IV)(bipy)(CN)2]·xH2O·yCH3CN}n have been synthesized by reacting Ph4P[W(V)(CN)6(bipy)] with the heterodinuclear [Ni(II)Ln(III)(valpn)(O2NO)3] complexes [H2valpn = 1,3-propanediyl-bis(2-iminomethylene-6-methoxyphenol), bipy = 2,2'-bipyridine, and Ln = Gd (1), Dy (2), and Tb (3) with x = 2 (1), 3.9 (2), and 3.35 (3) and y = 2.50 (1), 2 (2), and 1.8 (3)]. Their crystal structures consist of [Ni(II)Ln(III)] 3d-4f nodes which are connected by [W(IV)(bipy)(CN)6](2-) diamagnetic linkers resulting from the reduction of W(V) to W(IV) during the reaction process. The Ni(II) and Ln(III) ions occupy the inner and outer coordination sites of the dideprotonated valpn ligand, respectively, and they are doubly bridged by the phenoxo oxygen atoms of such a ligand. The value of Ni(II)···Ln(III) separation through this bridge is 3.4919(10) (1), 3.4760(10) (2), and 3.4799(9) (3) Å, and those of the angles at the bridgehead phenoxo atoms are 106.6(2) and 107.3(2) (1), 106.9(2), and 107.8(2) (2) and 106.5(2)-106.8(2)° (3). Each W(IV) is eight-coordinated with a bidentate bipy molecule and six cyanide-carbon atoms building a somewhat distorted square antiprism environment. The rare-earth cations are nine-coordinated, the donor atoms describing a monocapped square antiprism for 1 and 3 and a tricapped trigonal prism for 2. Magnetic susceptibility measurements in the temperature range 1.9-300 K show the occurrence of ferromagnetic interactions between the Ni(II) and Ln(III) ions in 1-3. Frequency-dependent alternating susceptibility signals were observed for the Dy(III) derivative below 8.0 K under an applied dc field of 2500 G indicating the presence of slow magnetic relaxation with values of the pre-exponential factor (τ0) and energy barrier (E(#)) of ca. 5.7 × 10(-8) s and 15.9 cm(-1), respectively. Complex 2 constitutes the first example of a 2D 3d-4f heterobimetallic single molecule magnet (SMM).

Structural, spectroscopic characterization and EPR spectra of nitrato-μ-[N,N'-ethylenebis(3-methoxysalicylideneimine) Cu(II)Ag(I)] complex

A novel heterodinuclear complex formed by the reaction of silver nitrate with Schiff base complex of copper(II) has been synthesized and characterized by Infrared (IR), ultraviolet-visible (UV-VIS), electron paramagnetic resonance (EPR) and X-ray diffraction methods. Preparation and crystal structure of the heterodinuclear complex, LCuAgNO3, (L=N,N'-ethylenebis(3-methoxysalicylideneimine) are reported. The crystal structure consists of ordered dinuclear units with CuII and AgI ions are bridged by two oxygen atoms of Schiff base ligand. The copper(II) ion has a distorted square-planar geometry involving the N2O2 donor set of Schiff base ligand. The g-values were calculated for title complex both in polycrystalline state at 298 K and in frozen DMF (113 K). The evaluated metal-ligand bonding parameters showed strong in-plane σ bonding.