Diverse metal−organic complexes (MOCs), shaped as rectangles, triangles, hexagons, prisms, and cages, can be formed by coordination between metal ions (Pt, Pd, Ru, Rh, Ir, Zn, Co, and Cd) and organic ligands, with potential applications as alternatives to conventional biomedical materials for therapeutic, sensing, and imaging purposes. MOCs have been investigated as anticancer drugs in the treatment of malignant tumors in lung, cervical, breast, colon, liver, prostate, ovarian, brain, stomach, bone, skin, mouth, thyroid, and other cancers. MOCs with one, two, and three cavities have also been investigated as drug carriers and prepared for the loading and release of different drugs. In addition, MOCs can target proteins by the shape effect and recognize sugars and DNA by electrostatic interactions, as well as estradiol by host−guest interactions, etc. This Perspective mainly covers achievements in the biomedical application of MOCs. We aim to identify some key trends in the reported MOC structures in relation to their biomedical activity and potential applications.

Herein, we report the preparation of a multifunctional metallacage-core supramolecular gel by orthogonal metal coordination and host-guest interactions. A tetragonal prismatic cage with four appended 21-crown-7 (21C7) moieties in its pillar parts was first prepared via the metal-coordination-driven self-assembly of cis-Pt(PEt)(OTf), tetraphenylethene (TPE)-based sodium benzoate ligands and linear dipyridyl ligands. Further addition of a bisammonium linker to the cage delivered a supramolecular polymer network via the host-guest interactions between the 21C7 moieties and ammonium salts, which formed a supramolecular gel at relatively higher concentrations. Due to the incorporation of a TPE derivative as the fluorophore, the gel shows emission properties. Multiple stimuli responsiveness and good self-healing properties were also observed because of the dynamic metal coordination and host-guest interactions used to stabilize the whole network structure. Moreover, the storage and loss moduli of the gel are 10-fold those of the gel without the metallacage cores, indicating that the rigid metallacage plays a significant role in enhancing the stiffness of the gel. The studies described herein not only enrich the functionalization of fluorescent metallacages via elegant ligand design but also provide a way to prepare stimuli-responsive and self-healing supramolecular gels as robust and smart materials.

Light-harvesting is one of the key steps in photosynthesis, but developing artificial light-harvesting systems (LHSs) with high energy transfer efficiencies has been a challenging task. Here we report fluorescent hexagonal Pt­(II) metalla­cycles as a new platform to fabricate artificial LHSs. The metalla­cycles (4 and 5) are easily accessible by coordination-driven self-assembly of a triphenyl­amine-based ditopic ligand 1 with di-platinum acceptors 2 and 3, respectively. They possess good fluorescence properties both in solution and in the solid state. Notably, the metalla­cycles show aggregation-induced emission enhancement (AIEE) characteristics in a DMSO–H2O solvent system. In the presence of the fluorescent dye Eosin Y (ESY), the emission intensities of the metalla­cycles decrease but the emission intensity of ESY increases. The absorption spectrum of ESY and the emission spectra of the metalla­cycles show a considerable overlap, suggesting the possibility of energy transfer from the metalla­cycles to ESY, with an energy transfer efficiency as high as 65% in the 4 a +ESY system.

Despite the widespread clinical application of chemotherapeutic anticancer drugs, their adverse side effects and inefficient performances remain ongoing issues. A drug delivery system (DDS) designed for a specific cancer may therefore overcome the drawbacks of single chemotherapeutic drugs and provide precise and synergistical cancer treatment by introducing exclusive stimulus responsiveness and combined chemotherapy properties. Herein, we report the design and synthesis of a supramolecular drug delivery assembly 1 constructed by orthogonal self-assembly technique in aqueous media specifically for application in liver cancer therapy. Complex 1 incorporates the β-cyclodextrin host molecule-functionalized organoplatinum(II) metallacycle 2 with two specific stimulus-responsive motifs to the signaling molecule nitric oxide (NO), in addition to the three-armed polyethylene glycol (PEG) functionalized ferrocene 3 with redox responsiveness. With this molecular design, the particularly low critical aggregation concentration (CAC) of assembly 1 allowed encapsulation of the commercial anticancer drug doxorubicin (DOX). Controlled drug release was also achieved by morphological transfer via a sensitive response to the endogenous redox and NO stimuli, which are specifically related to the microenvironment of liver tumor cells. Upon combination of these properties with the anticancer ability from the platinum acceptor, in vitro studies demonstrated that DOX-loaded 1 is able to codeliver anticancer drugs and exhibit therapeutic effectiveness to liver tumor sites via a synergistic effect, thereby revealing a potential DDS platform for precise liver cancer therapeutics.

Herein, we describe a novel multicomponent self-assembly approach that has the prospect of furnishing unprecedented heterometallic bicyclic architectures with a high level of constitutional control. The methodology relies on the coordination directionality, and the stoichiometry of the individual precursor units, as well as on the difference of the coordination preference of the associated metal ions. As a proof-of-concept example, two aesthetically pleasing Fe-Pt heterometallic bicyclic metallacycles 6a and 6b, consisting of nine communicative components from four unique species, were prepared in ca. 70% isolated yields and fully characterized by multinuclear NMR, 2D NMR, electrospray ionization time-of-flight mass, and UV-vis spectroscopies. Furthermore, density functional theory based computations suggest that each of these supramolecular constructs encompasses two twisted [organo-Pt(II)←pyridine] coordination based irregular hexagons that are joined via a robust [terpyridine→Fe(II)←terpyridine] hinge.

Some new symmetrical diimino tetradentate Schiff base ligands were synthesized by the reaction of 3,4-diaminobenzophenone with salicylaldehyde derivatives, such as [3,4-bis(((2-hydroxy-4-methoxyphenyl)methylene)amino)phenyl]phenylmethanone (L 1 ), [3,4-bis(((2-hydroxy-5-methoxyphenyl)methylene)amino)phenyl]phenylmethanone (L 2 ), [3,4-bis(((5-bromo-2-hydroxyphenyl)methylene)amino)phenyl]phenylmethanone (L 3 ) and [3,4-bis(((2-hydroxy--5-nitrophenyl)methylene)amino)phenyl]phenylmethanone (L 4 ). Additionally, a tetradentate Schiff base ligand [3,4-bis(((2-hydroxy-3-methoxyphenyl)methylene)amino)phenyl]phenylmethanone (L 5 ) was synthesized. All the Schiff bases and their Ni(II), Cu(II) and Zn(II) complexes were characterized using elemental analysis and infrared, electronic, mass and 1 H-NMR spectroscopy. The formation constants of the complexes were measured using UV-Vis spectroscopic titration at constant ionic strength 0.10 M (NaClO 4 ), at 25 °C in dimethylformamide (DMF) as solvent. 64ASADI, SEPEHRPOUR and MOHAMMADI veral metal chelates of the ONNO donor class of Schiff bases were studied as oxygen carrier and they were found to be useful models for bioinorganic processes. 6,7 Schiff bases are effective inhibitors and could be adsorbed on the surface of metals. 8 Symmetric tetradentate Schiff base complexes have been extensively used as macrocycle models. 9 These compounds have received considerable attention because of their potential use as catalysts, 10-14 and their antibacterial, 5,15,16 antifungal, 17 antitumour 18,19 and herbicidal activities. 20 The main goals of this study were the synthesis and characterization of some new tetradentate Schiff bases and their complexation with Ni(II), Cu(II) and Zn(II) metals. These compounds were characterized by elemental analysis, and FT-IR, 1 H-NMR, mass and UV-Vis techniques. In addition, the formation constants, K f , were determined spectrophotometrically and the free energy changes, ΔG , at 25 °C, were calculated for the complexes. The effects of the electronic and steric nature of substituents on the Schiff base type ligands on the formation constants and free energy changes resulting from complex formation were studied.

We report herein that the preparation of two novel discrete organoplatinum(II) metallacycles by means of coordination-driven self-assembly of a 90° organoplatinum(II) acceptor, cis-(PEt3)2Pt(OTf)2, with two donors, a pyridyl donor, 9,10-di(4-pyridylvinyl)anthracene (DPA), and one of two dicarboxylate ligands. The obtained two metallacycles display aggregation-induced emission (AIE) as well as solvatochromism. More interestingly, both metallacycles exhibit near-infrared fluorescent emission in the solid state, greatly different from the free ligand DPA. Furthermore, ammonia detection has been achieved by the observation of simple optical changes of the metallacycles’ thin films either in color or in fluorescence, thereby representing a promising platform for convenient biochemical analysis.

Considerable progress in platinum metalla­cycle-based supra­molecular polymerization has promoted the fabrication and application of supra­molecular materials. However, despite recent advances, supra­molecular polymers constructed through platinum metalla­cycle-based host–guest complexation remain rare because of the dynamics of platinum metalla­cycles. Here, we achieve linear supra­molecular polymerization via platinum metalla­cycle-based host–guest complexation by following the design rule of suppressing the dynamics of the metalla­cycles. The establishment of the platinum metalla­cycle-based host–guest system and the realization of this type of supra­molecular polymerization are expected to open opportunities for platinum metalla­cycle-based functional materials.