Programmable self-assembly of water-soluble organo-heterometallic cages [M12M'4L12] using 3-(3,5-dimethyl-1H-pyrazol-4-yl)pentane-2,4-dione (H2L)

Reversible and Turn-On Fluorescence Detection of Phosphate in Aqueous Solution and Living Cell Imaging by Supramolecular Metallacycles with AIE-Active Ligands

Luminescent supramolecular metallacycles have attracted great interest as a new promising class of sensing substrates. In this work, two tetraphenylethene (TPE)-based diimidazole and dipyrazole ligands with the aggregation-induced emission (AIE) feature were designed for the construction of supramolecular tetragonal metallacycles 1-4 with two 90° mononuclear [(bpy)M]2+ or dinuclear [(bpy)2M2]4+ acceptors (bpy = 2,2'-dipyridine; M = Pd, Pt), in which the fluorescence can be quenched to an "off" state due to the ligand-to-metal charge transfer (LMCT). Metallacycle 1 was utilized as a fluorescence sensor for phosphate (PO43-) detection in aqueous solution by means of disassembly, leading to the release of the ligand. Additionally, the metallacycle can be regenerated through self-assembly via the introduction of Pd(II) acceptors. PO43- was detected using TPE-based metallacycles over a wide concentration range, with a detection limit as low as 2.1 × 10-8 M. Furthermore, sensor 1 also presented the semiquantitative visual detection ability for PO43- in the test paper mode via fluorescence changes. The aforementioned studies not only enhance the current research on fluorescent materials but also offer a strategy for the creation of stimuli-responsive supramolecular coordination complexes.

Synthesis and coordination to the coinage metals of a trimethylpyrazolyl substituted 3-arylacetylacetone

The ligand 3-(4-(1,3,5-trimethyl-1H-pyrazol-4-yl)phenyl)acetylacetone (1) combines a Pearson hard O,O′ chelating acetylacetone donor with a softer pyrazole N donor bridged by a phenylene spacer. Deprotonation and coordination to CuII leads to a square planar bis-acetylacetonato complex; interpreting the close proximity of an adjacent complex’s pyrazole moiety as an η 2 ${{\eta}}^{2}$ coordination to the axial CuII position leads to a two dimensional extended structure. The N donor capabilities are proven by coordination to AgPF6 and AuCl; for AgI a cationic linear bis-pyrazole complex as a toluene solvate is obtained with toluene-pyrazole π-interactions and an essentially uncoordinated PF 6 - ${{\mathrm{PF}}_{6}}^{-}$ anion. In the case of AuCl a neutral linear coordination compound with one chlorido and one pyrazole ligand 1 is obtained. Comparing the dihedral angles with a closely related but shorter ligand reveals a larger rotational degree of freedom in 1, allowing for richer architectures in emerging coordination polymers.

Programmable Synthesis of Silver Wheels

The synthesis of sandwich-shaped multinuclear silver complexes with planar penta- and tetranuclear wheel-shaped silver units and a central anion, [Ag_n(2-HPB)₂(A^-)](OTf^-)_n-1, nAg^A, n = 4 or 5 and A^- = OH^- or F^- or Cl^-, is reported, along with complete spectroscopic and structural characterization. An NMR mechanistic study reveals that silver complexes were formed in the following order: 2Ag → 3Ag^H₂O → 5Ag^OH → 4Ag^OH. The central hydroxides in 4Ag^OH and 5Ag^OH exhibit exotic physical properties due to the confined environment inside the complex. The size of these silver wheels can be tuned by changing the central anion or extracting/adding one silver atom. This study provides the facile way to synthesize discrete wheel-shaped multinuclear silver complexes and provides valuable insights into the dynamics of the self-assembly process.

Designing a highly stable coordination-driven metallacycle for imaging-guided photodynamic cancer theranostics

Coordination-driven self-assembly features good predictability and directionality in the construction of discrete metallacycles and metallacages with well-defined sizes and shapes, but their medicinal application has been limited by their low stability and solubility. Herein, we have designed and synthesized a highly stable coordination-driven metallacycle with desired functionality derived from a perylene-diimide ligand via a spontaneous deprotonation self-assembly process. Brilliant chemical stability and singlet oxygen production ability of this emissive octanuclear organopalladium macrocycle make it a good candidate toward biological studies. After cellular uptake by endocytosis, the metallacycle exhibits potent fluorescence cell imaging properties and cancer photodynamic therapeutic ability through enhancing ROS production, with high biocompatibility and safety. This study not only provides a rational design strategy for highly stable luminescent organopalladium metallacycles, but also sheds light on their application in imaging-guided photodynamic cancer therapy.

A highly-luminescent metallacycle with chemical stability and singlet oxygen production ability were obtained by a spontaneous deprotonation self-assembly process, which exhibits application potential in imaging-guided photodynamic cancer therapy.

Design and programmable self-assembly of an eight-coordinate Cu(ii) heterometallic structure via a dipalladium corner as a building block

An eight-coordinate (8C) [Cu(ii)O₈] heteromultimetallic complex displaying a distorted dodecahedral structure has been synthesized via the coordination-driven programmable self-assembly of dipalladium metalloligands containing heteroditopic ligands.

N Donor substituted acetylacetones – versatile ditopic ligands

Acetylacetone (2,4-pentanedione) derivatives with N donor substituents represent ditopic ligands with coordination sites of distinctly different Pearson hardness. Deprotonation of the acetylacetone (Hacac) moiety leads to O,O′ chelating monoanionic (acac) ligands suitable for coordination to hard cations. The softer N donor site(s) preferably act as nucleophiles towards softer partners. When the organic molecules are employed as linkers and coordinate via either site, they are often selective and allow to synthesize well-ordered heterometallic solids. This review addresses the derivatives of 17 pentanediones with nitrile, pyridyl and pyrazolyl moieties as N donor substituents, with an emphasis on structurally characterized compounds. Depending on the N donor substituents and the cations, O,O′ or N coordination will dominate. The nitrile-substituted compounds essentially behave as acetylacetones; they may easily O,O′ coordinate to a wide range of cations whereas N coordination is limited to AgI, CuI or, in the case of less soft cations, to longer and presumably weaker contacts, e.g. to the more distant sites in Jahn–Teller distorted CuII. In contrast, pyridyl-substituted pentanediones act as N donor ligands, regardless whether their (H)acac site is chelating a cation or not. The still scarcely explored pyrazolyl derivative shows the most complex coordination pattern: it may be deprotonated both at the acetylacetone and the pyrazol site, the latter affording N,N′ bridging ligands. In addition to N donor nucleophilicity, the distance between the alternative coordination sites and their mutual orientation are relevant for crystal engineering applications.

Manganese(II), lead(II) and cadmium(II) coordination complexes containing a tetrazole-based acylamide ligand: synthesis and the influence of the metal ions on the structures

Three new manganese(II), lead(II) and cadmium(II) coordination complexes have been prepared by reaction of N-(1H-tetrazol-5-yl)cinnamamide (HNTCA) with divalent metal salts (MnCl2, PbCl2 and CdCl2) in a mixed-solvent system, affording mononuclear to trinuclear structures namely, bis(methanol-κO)bis[5-(3-phenylprop-2-enamido)-1H-1,2,3,4-tetrazol-1-ido-κ2 N 1,O]manganese(II), [Mn(C10H8N5O)2(CH3OH)2], (1), bis[μ-5-(3-phenylprop-2-enamido)-1H-1,2,3,4-tetrazol-1-ido]-κ3 N 1,O:N 2;κ3 N 2:N 1,O-bis{aqua[5-(3-phenylprop-2-enamido)-1H-1,2,3,4-tetrazol-1-ido-κ2 N 1,O]lead(II)}, [Pb2(C10H8N5O)4(H2O)2], (2), and hexakis[μ2-5-(3-phenylprop-2-enamido)-1H-1,2,3,4-tetrazol-1-ido-κ3 N 1,O:N 2]tricadmium(II), [Cd3(C10H8N5O)6], (3). The structures of these three compounds reveal that the nature of the metal ions and the side groups of the organic building blocks have a significant effect on the structures of the coordination compounds formed. Intermolecular hydrogen bonds link the molecules into two-dimensional [complex (1)] and three-dimensional hydrogen-bonded networks. Complexes (2) and (3) show significant fluorescence, while complex (1) displays no fluorescence.