Synthesis of Planar Metal Complexes and the Stacking Abilities of Naphthalenediol-Based Acyclic and Macrocyclic Salen-Type Ligands

Enhancement of Alkali Metal Ion Recognition by Metalation of a Tris(saloph) Cryptand Having Benzene Rings at the Bridgeheads

A cryptand derivative, H₆L, which has three H₂saloph arms connected by two benzene ring bridgeheads, was synthesized and converted into the trinuclear metallocryptand, LNi₃. The nonmetalated host, H₆L, was found to bind to alkali metal ions (Na⁺, K⁺, Rb⁺, Cs⁺; logK_a = 3.37-6.67) in its well-defined cavity in DMSO/chloroform (1:9). The binding affinity was enhanced by 1-2 orders of magnitude upon the conversion into the metallocryptand, LNi₃, which can be explained by the more polarized phenoxo groups in the [Ni(saloph)] arms. The guest binding affinity of Na⁺ < K⁺ < Rb⁺ ≈ Cs⁺ was clearly demonstrated by the ¹H NMR competition experiments. The DFT calculations suggested that the Rb⁺ ion most suitably fit into the benzene-benzene spacing with a cation-π interaction and that only the largest Cs⁺ ion can almost equally interact with all six phenoxo oxygen donor atoms. The metallocryptand, LNi₃, also showed a strong binding affinity to Ag⁺ by taking advantage of cation-π interactions, which was confirmed by spectroscopic titrations and crystallographic analysis as well as DFT calculations. Thus, the well-defined three-dimensional cavity of LNi₃ was found to be suitable for strong binding with alkali metal ions as well as Ag⁺.

Unprecedented Dinuclear CuII N,O-Donor Complex: Synthesis, Structural Characterization, Fluorescence Property, and Hirshfeld Analysis

An unprecedented dinuclear CuII complex, [Cu2(L2)2], derived from a salamo-like chelating ligand H2L2, was produced by the cleavage of a newly synthesized, half-salamo-like ligand HL1 (2-[O-(1-ethyloxyamide)]oxime-3,5-dichloro-phenol). This was synthesized and characterized by elemental analyses, IR, UV–Vis and fluorescent spectra, single crystal X-ray diffraction analysis, and Hirshfeld surface analysis. X-ray crystallographic analysis indicated that the two CuII (Cu1 and Cu2) ions bore different (N2O3 and N2O2) coordination environments, the penta-coordinated Cu1 ion possessed a slightly twisted tetragonal pyramid geometry with the τ value τ = 0.004, and the tetra-coordinated Cu2 ion showed a slightly twisted square planar geometry. Interestingly, one oxime oxygen atom participated in the coordination reported previously. Moreover, an infinite two-dimensional layered supramolecular network was formed. Compared with HL1, the CuII complex possessed the characteristic of fluorescence quenching.

A Newly Synthesized Heterobimetallic NiII-GdIII Salamo-BDC-Based Coordination Polymer: Structural Characterization, DFT Calculation, Fluorescent and Antibacterial Properties

A unprecedented hetero-bimetallic 3d-4f BDC-salamo-based coordination polymer, [(L)Ni(BDC)Gd(NO3)(DMF)] was prepared and validated via elemental analyses, IR and UV–Visible absorption spectra, DFT calculation, and X-ray crystallography. The six-coordinated Ni1 ion lies at the N2O2 donor site of the L2− moiety, and one DMF O atom and carboxylate O atom occupy, collectively, the axial positions, and form a twisted octahedron. The nine-coordinated Gd1 ion consists of three oxygen atoms (O12, O13, and O14) of two carboxylate groups, two oxygen atoms (O8 and O9) derived from one bidentate nitrate group, and an O2O2 coordination site (O1, O2, O6, and O5) of the L2− unit, forming a twisted three-capped triangular prism coordination geometry. Compared to the ligand (H2L), the fluorescence intensity decreases due to the coordination of metal ions. Meanwhile, the antibacterial activities are researched.

An Unexpected Trinuclear Cobalt(II) Complex Based on a Half-Salamo-Like Ligand: Synthesis, Crystal Structure, Hirshfeld Surface Analysis, Antimicrobial and Fluorescent Properties

An unexpected trinuclear Co(II) complex, [Co3(L2)2(μ-OAc)2(CH3OH)2]·2CH3OH (H2L2 = 4,4′-dibromo-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) constructed from a half-Salamo-based ligand (HL1 = 2-[O-(1-ethyloxyamide)]oxime-4-bromophenol) and Co(OAc)2·4H2O, has been synthesized and characterized by elemental analyses, infrared spectra (IR), UV-Vis spectra, X-ray crystallography and Hirshfeld surface analysis. The Co(II) complex contains three Co(II) atoms, two completely deprotonated (L2)2− units, two bridged acetate molecules, two coordinated methanol molecules and two crystalline methanol molecules, and finally, a three-dimensional supramolecular structure with infinite extension was formed. Interestingly, during the formation of the Co(II) complex, the ligand changed from half-Salamo-like to a symmetrical single Salamo-like ligand due to the bonding interactions of the molecules. In addition, the antimicrobial activities of HL1 and its Co(II) complex were also investigated.

Synthesis and Fluorescence Properties of a Structurally Characterized Hetero-Hexanuclear Zn(II)-La(III) Salamo-Like Coordination Compound Containing Auxiliary Ligands

A hetero-hexanuclear Zn(II)-La(III) coordination compound, [{(ZnL)2La}2(bdc)2](NO3)2 (H2bdc = terephthalic acid) has been synthesized with a symmetric Salamo-like bisoxime, and characterized by elemental analyses, IR, UV-Vis, fluorescent spectroscopy, and single-crystal X-ray diffraction analysis. All of the Zn(II) ions are pentacoordinated by N2O2 donator atoms from the (L)2− unit and one oxygen atom from one terephthalate anion. The Zn(II) ions adopt trigonal bipyramidal geometries (τZn1 = 0.61, τZn2 = 0.56). The La(III) ions are decacoordinated in the Zn(II)-La(III) coordination compound and has a distorted bicapped square antiprism geometry. Meanwhile, the photophysical property of the Zn(II)-La(III) coordination compound was also measured and discussed.

A Self-Assembled ZnII-NdIII Heterohexanuclear Dimer Based on a Hexadentate N2O4-Type Ligand and Terephthalic Acid: Synthesis, Structure, and Fluorescence Properties

A self-assembled Zn^II-Nd^III heterohexanuclear coordination compound [Zn₄Nd₂(L)₄(bdc)₂]·2NO₃ based on a hexadentate Salamo-like chelating ligand (H₂L = 1,2-bis(3-methoxysalicylideneaminooxy)ethane]) and H₂bdc (H₂bdc = terephthalic acid) has been synthesized and characterized by elemental analyses, IR and UV/Vis spectra, and X-ray crystallography. Two crystallographically equivalent [Zn₂Nd(L)₂] moieties lie in the inversion center linked by two (bdc)²⁻ ligands leading to a heterohexanuclear dimer in which the carboxylato group bridges the Zn^II and Nd^III atoms. The heteropolynuclear 3d-4f coordination compound includes four Zn^II atoms, two Nd^III atoms, four completely deprotonated (L)²⁻ units, two fully deprotonated (bdc)²⁻ units, and two crystalling nitrate ions. All of the Zn^II atoms in the Zn^II-Nd^III coordination compound possess trigonal bipyramidal geometries and the Nd^III atoms possess distorted bicapped square antiprism coordination arrangements. In addition, the fluorescence properties of the ligand and the Zn^II-Nd^III coordination compound were investigated.

Effect of temperature and ligand protonation on the electronic ground state in Cu(ii) polymers having unusual secondary interactions: a magnetic and catechol oxidase study

Two new polymeric Cu(ii) compounds with significant catecholase activity are described.

Thermally Stable Zinc Disalphen Macrocycles Showing Solid-State and Aggregation-Induced Enhanced Emission

In order to investigate the solid-state light emission of zinc salphen macrocycle complexes, 7 dinuclear zinc salphen macrocycle complexes (1-7), with acetate or hexanoate coligands, are synthesized. The complexes are stable in air up to 300 °C, as shown via thermogravimetric analysis (TGA), and exhibit green to orange-red emission in solution (λ_em = 550-600 nm, PLQE ≤ 1%) and slightly enhanced yellow to orange-red emission in the solid state (λ_em = 570-625 nm, PLQE = 1-5%). Complexes 1, 2, 4, 5, and 7 also display aggregation-induced enhanced emission (AIEE) when hexane (a nonsolvent) is added to a chloroform solution of the complexes, with complex 4 displaying a 75-fold increase in peak emission intensity upon aggregation (in 0.25:0.75 chloroform:hexane mixture).

The stacking interactions of bipyridine complexes: the influence of the metal ion type on the strength of interactions

The strength of the stacking interactions in the bipy complexes of nickel, palladium, and platinum, [M(CN)2 bipy]2 (M = Ni, Pd, Pt), was calculated using the ωB97xD/def2-TZVP method. The results show that for all considered geometries, interactions are the strongest for platinum, and weakest for nickel complexes, as a result of higher dispersion contributions of platinum over the palladium and nickel complexes. It was also shown that strength of interactions considerably rises with an increase of the stacking overlap area. As a consequence of the favorable electrostatic term, the strength of interactions also rises when metal atom and cyano ligands are involved in the overlap with bipy ligand. The strongest interaction was calculated in the platinum complex, for the geometry that has overlap of metal and cyano ligands with bipy ligand with an energy of -39.80 kcal mol(-1). The energies for similar geometries of palladium and nickel complexes are -34.60 and -32.45 kcal mol(-1). These energies, remarkably, exceed the strength of the stacking interactions between organic aromatic molecules. These results can be of importance in all systems with stacking interactions, from materials to biomolecules.