Photoluminescence properties of tetrahedral zinc(ii) complexes supported by calix[4]arene-based salicylaldiminato ligands

Synthesis, Crystal Structure, Fluorescence and Theoretical Calculations of Three Zn(II)/Cd(II) Complexes with Bis-dentate N,N-Quinoline Schiff Base

Three d10 metal complexes, ZnL(OAc)2 (1), CdL(OAc)2 (2) and [CdL2(NO3)2]·CH3CN (3) were synthesized using the ligand (E)-N-(3-methoxy-4-methylphenyl)-1-(quinolin-2-yl)methanimine (L) and characterized by FT-IR spectra, NMR spectra, and CHN elemental analysis. Single-crystal X-ray diffraction analysis revealed that complexes 1 and 2 are isostructural, with the central metal adopting a hexacoordinate octahedral geometry, while complex 3 adopts a triangular dodecahedron geometry. Thermal gravimetric analysis showed that these complexes exhibit good thermal stability. Solid-state fluorescence spectroscopy measurements demonstrated that complexes 1-3 exhibit bright yellow-green fluorescence (λem = 564 nm for 1; 524 nm for 2; 542 nm for 3), suggesting their potential as photoluminescent materials. Furthermore, DFT calculations, including frontier molecular orbitals, energy levels, and surface electrostatic potential, provided insights into the structural and electronic spectral properties of complexes 1-3.

Probing a Hydrogen-π Interaction Involving a Trapped Water Molecule in the Solid State

The detection and characterization of trapped water molecules in chemical entities and biomacromolecules remains a challenging task for solid materials. We herein present proton-detected solid-state Nuclear Magnetic Resonance (NMR) experiments at 100 kHz magic-angle spinning and at high static magnetic-field strengths (28.2 T) enabling the detection of a single water molecule fixed in the calix[4]arene cavity of a lanthanide complex by a combination of three types of non-covalent interactions. The water proton resonances are detected at a chemical-shift value close to zero ppm, which we further confirm by quantum-chemical calculations. Density Functional Theory calculations pinpoint to the sensitivity of the proton chemical-shift value for hydrogen-π interactions. Our study highlights how proton-detected solid-state NMR is turning into the method-of-choice in probing weak non-covalent interactions driving a whole branch of molecular-recognition events in chemistry and biology.

A bisphenol based fluorescence chemosensor for the selective detection of Zn2+ and PPi ions and its bioluminescence imaging

A bisphenol based fluorescence "turn-on" chemosensor 4,4'-(propane-2,2-diyl)bis(2-((E)-(2-(benzo[d]thiazol-2-yl)hydrazineyldene)methyl)phenol) (BHMP) has been synthesized and its sensing behavior was tested towards various ionic species. The chemo-sensing behavior of BHMP has been established through absorption, fluorescence, NMR, and mass spectroscopic techniques. The probe BHMP selectively detects zinc ions over other metal ions and the resulting BHMP + Zn²⁺ ensemble serves as a secondary probe for the detection of pyrophosphate (PPi) anion specifically over other anions. The spectroscopic studies reveal the fluorescence enhancement of BHMP in association with Zn²⁺ ions was quenched in the presence of pyrophosphate (PPi) anions. A probable mechanism of this selective sensing behavior was described on the basis of "OFF-ON-OFF" strategy for detection of both cations and anions. Moreover, the biological applicability of the chemosensor BHMP was examined via cell imaging studies.

Dinuclear Tb and Dy complexes supported by hybrid Schiff-base/calixarene ligands: synthesis, structures and magnetic properties

The synthesis of the new lanthanide complexes [HNEt3][Dy2(HL1)(L1)] (5), and [Ln2(L2)2] (Ln = TbIII (7), DyIII (8)) supported by the hybrid Schiff-base/calix[4]arene ligands H4L1 (25-[2-((2-methylphenol)imino)ethoxy]-26,27,28-trihydroxy-calix[4]arene) and H3L2 (25-[2-((2-methylpyridine)imino)ethoxy]-26,27,28-trihydroxy-calix[4]arene) are reported. Spectroscopic data (for 5) and X-ray crystallographic analysis (for 7·4MeCN, 8·4MeCN) reveal the presence of dimeric structures, featuring doubly-bridged NO4Ln(μ-O)2LnO4N (5) or N2O3Ln(μ-O)2LnO3N2 cores (7, 8) with seven-coordinated Ln3+ ions. The magnetic properties of polycrystalline samples of 5, 7 and 8 were studied by variable temperature dc and ac magnetic susceptibility measurements. The χ''(T) vs. T plots show no maxima in zero field, but the maxima can be detected under a 3 kOe dc field. The relaxation times τ obey the Arrhenius law above 5 K. Anisotropy barriers of ∼18 cm-1 (26 K) for 5 and ∼23 cm-1 (33 K) for 8 were determined.

Light controlled oxidation by supramolecular Zn(ii) Schiff-base complexes

Application of Schiff-base ligands for the controlled zinc ion induced formation of electronic triplet states and the initialisation of photoreactivity.

Utilising an anilido-imino ligand to stabilise zinc-phosphanide complexes: reactivity and fluorescent properties

A series of zinc complexes bearing the anilido-imino ligand [(o-C6H4{N(C6H3iPr2)}{C(CH3) = NC6H3iPr2})] [(LDipp)ZnX] has been generated. This includes two amide derivatives, [(LDipp)Zn(N{SiMe3}2)] and [(LDipp)Zn(NH{Dipp})] and two phosphanide derivatives, [(LDipp)ZnPCy2] and [(LDipp)ZnPPh2]. The chemistry of the phosphanide complexes towards chalcogens was examined, with sulfur, selenium and tellurium oxidising the phosphorus centre of the dicylohexylphosphanide complex [(LDipp)ZnPCy2] to form [(LDipp)Zn(E)2PCy2] (E = S, Se, Te). Addition of tellurium to the diphenylphosphanide complex [(LDipp)ZnPPh2] results in formation of Ph2PPPh2 and [(LDipp)ZnTeZn(LDipp)]. The absorption and emission properties of these complexes was examined and the quantum yields are highly dependent upon the non-ancillary ligand X.

A self-assembled nanotube supported by halogen bonding interactions

Upper-rim halogenation of a calix[4]arene modulates the packing of self-assembled nanotubes through the formation of complementary halogen bonding interactions.

Benzothiazole integrated into a cryptand for ESIPT-based selective chemosensor for Zn2+ ions

A novel 2(2′-hydroxyphenyl) benzothiazole-based cryptand (L) exhibits high fluorescence intensity in the presence of Zn²⁺ ions by stopping the excited state intramolecular proton transfer (ESIPT) process with a detection limit of 0.20 μM.

Dinuclear lanthanide complexes supported by a hybrid salicylaldiminato/calix[4]arene-ligand: synthesis, structure, and magnetic and luminescence properties of (HNEt3)[Ln2(HL)(L)] (Ln = SmIII, EuIII, GdIII, TbIII)

Salicylaldimine/calix[4]arenes support dinuclear, triply bridged, luminescent, lanthanide complexes.