Self-assembly of discrete metallamacrocycles employing half-sandwich octahedral diruthenium(II) building units and imidazole-based ligands

Redox-Induced Hydrogen Bond Reorientation Mimicking Electronic Coupling in Mixed-Valent Diruthenium and Macrocyclic Tetraruthenium Complexes

We present the coordination-driven self-assembly of three tetranuclear metallacycles containing intracyclic NH₂, OH, or OMe functionalities through the combination of various isophthalic acid building blocks with a divinylphenylene diruthenium complex. All new complexes of this study were characterized by means of nuclear magnetic resonance spectroscopy, ultrahigh-resolution ESI mass spectrometry, cyclic and square wave voltammetry and, in two cases, X-ray diffraction. The hydroxy functionalized macrocycle 4-BOH and the corresponding half-cycle 2-OH stand out, as their intracyclic OH···O hydrogen bonds stabilize their mixed-valent one- (2-OH, 4-BOH) and three-electron-oxidized states (4-BOH). Despite sizable redox splittings between all one-electron waves, the mixed-valent monocations and trications do not exhibit any intervalence charge-transfer band, assignable to through-bond electronic coupling, but nevertheless display distinct IR band shifts of their charge-sensitive Ru(CO) tags. We ascribe these seemingly contradicting observations to a redox-induced shuffling of the OH···O hydrogen bond(s) to the remaining, more electron-rich, reduced redox site.

Key Strategy for the Rational Incorporation of Long-Lived NIR Emissive Cr(III) Chromophores into Polymetallic Architectures

The Cr^IIIN₆ chromophores are particularly appealing for low-energy sensitization via energy transfer processes since they show extremely long excited state lifetimes reaching the millisecond range in the technologically crucial near-infrared domain. However, their properties were barely harnessed in multimetallic structures because of the lack of both monitoring methods and accessible synthetic pathways. We herein report a remedy to monitor and control the formation of Cr^III-containing assemblies in solution via the design of a Cr^IIIN₆ inert "complex-as-ligand" that can be included into polymetallic architectures. As a proof of concept, these CrN₆ building blocks were reacted in solution with Zn^II or Fe^II to give extended trinuclear linear Cr-M-Cr assemblies, the structure of which could be addressed by NMR spectroscopy despite the presence of two slowly relaxing Cr^III paramagnetic centers. In addition to long Cr^III excited state lifetimes and weak sensitivity to oxygen quenching, these polymetallic assemblies display controlled Cr^III to M^II energy transfers, which pave the way for use of the "complex-as-ligand" strategy for introducing photophysically active Cr^III probes into light-converting polymetallic devices.

Self-assembled ruthenium (II) metallacycles and metallacages with imidazole-based ligands and their in vitro anticancer activity

Six tetranuclear rectangular metallacycles were synthesized via the [2+2] coordination-driven self-assembly of imidazole-based ditopic donor 1,4-bis(imidazole-1-yl)benzene and 1,3-bis(imidazol-1-yl)benzene, with dinuclear half-sandwich p-cymene ruthenium(II) acceptors [Ru₂(µ-η⁴-oxalato)(η⁶-p-cymene)₂](SO₃CF₃)₂, [Ru₂(µ-η⁴-2,5-dioxido-1,4-benzoquinonato)(η⁶-p-cymene)₂](SO₃CF₃)₂ and [Ru₂(µ-η⁴-5,8-dioxido-1,4-naphtoquinonato)(η⁶-p-cymene)₂](SO₃CF₃)₂, respectively. Likewise, three hexanuclear trigonal prismatic metallacages were prepared via the [2+3] self-assembly of tritopic donor of 1,3,5-tri(1H-imidazol-1-yl)benzene with these ruthenium(II) acceptors respectively. Self-selection of the single symmetrical and stable metallacycle and cage was observed although there is the possibility of forming different conformational isomeric products due to different binding modes of these imidazole-based donors. The self-assembled macrocycles and cage containing the 5,8-dioxido-1,4-naphtoquinonato (donq) spacer exhibited good anticancer activity on all tested cancer cell lines (HCT-116, MDA-MB-231, MCF-7, HeLa, A549, and HepG-2), and showed decreased cytotoxicities in HBE and THLE-2 normal cells. The effect of Ru and imidazole moiety of these assemblies on the anticancer activity was discussed. The study of binding ability of these donq-based Ru assemblies with ctDNA indicated that the complex 9 with 180° linear 1 ligand has the highest bonding constant K _b to ctDNA.

Coordination-driven self-assembly of ruthenium(ii) architectures: synthesis, characterization and cytotoxicity studies

Coordination-driven self-assembly of organometallic η6-arene ruthenium(ii) supramolecular architectures (MA1-MA4) was carried out by employing dinuclear ruthenium acceptors [Ru2(μ-η4-C2O4)(CH3OH)2(η6-p-cymene)2](CF3SO3)2 (Rua), [Ru2(μ-η4-C6H2O4)(CH3OH)2(η6-p-cymene)2](CF3SO3)2 (Rub), [Ru2(dhnq)(H2O)2(η6-p-cymene)2](CF3SO3)2 (Ruc) and [Ru2(dhtq)(H2O)2(η6-p-cymene)2](CF3SO3)2 (Rud) separately with a new tetratopic donor (TD) in methanol at room temperature [TD = N,N,N',N'-tetra(pyridin-4-yl)-[1,1'-biphenyl]-4,4'-diamine]. All the coordination architectures were characterized by using spectroscopic techniques. The potency of these self-assembled architectures against human cervical cancer HeLa and human lung adenocarcinoma A549 cell lines is explored in vitro using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), annexin V-FITC/PI and 2',7'-dichlorofluorescein-diacetate assays.

Coordination-driven self-assembly of discrete Ru6-Pt6 prismatic cages

The coordination-driven self-assembly of two new Ru6-Pt6 hexanuclear trigonal prismatic cages comprising arene-ruthenium(II) clips (1a(NO3)2 and 1b(NO3)2 ) and a tritopic platinum(II) metalloligand 2 has been performed in methanol at room temperature. The [3 + 2] hexanuclear cages 3a and 3b were isolated in good yields and characterized by well-known spectroscopic techniques including multinuclear NMR, mass spectrometry, UV-vis and infrared studies. Geometry optimization revealed the shapes and sizes of these hexanuclear prismatic cages. The combination of ruthenium and platinum metal center in a one-pot self-assembly reaction showcases the construction of aesthetically elegant heterometallic structures in supramolecular chemistry leading to the formation of a single major product.

Self-Assembly of Discrete RuII8 Molecular Cages and Their in Vitro Anticancer Activity

Four new octanuclear Ru(II) cages (OC-1-OC-4) were synthesized from dinuclear p-cymene ruthenium(II) acceptors [Ru₂(μ-η⁴-C₂O₄)(CH₃OH)₂(η⁶-p-cymene)₂](O₃SCF₃)₂ (A₁), [Ru₂(μ-η⁴-C₆H₂O₄)(CH₃OH)₂(η⁶-p-cymene)₂](O₃SCF₃)₂ (A₂), [Ru₂(dhnq)(H₂O)₂(η⁶-p-cymene)₂](O₃SCF₃)₂ (A₃), and [Ru₂(dhtq)(H₂O)₂(η⁶-p-cymene)₂](O₃SCF₃)₂ (A₄) separately with a tetradentate pyridyl ligand (L₁) in methanol using coordination-driven self-assembly [L₁= N,N,N',N'-tetra(pyridin-4-yl)benzene-1,4-diamine]. The octanuclear cages are fully characterized by various spectroscopic techniques including single-crystal X-ray diffraction analysis of OC-4. The self-assembled cages show strong in vitro anticancer activity against human lung adenocarcinoma A549 and human cervical cancer HeLa cell lines as observed from the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Of all the octanuclear cages, OC-3 exhibits remarkable anticancer activity against both cancer cell lines and is more active than that reported for cisplatin. The excellent anticancer activity of OC-3 and OC-4 highlights the importance of the synergistic effects of the spacer component of the dinuclear p-cymene Ru(II) acceptor clips.

Self-assembled discrete molecules for sensing nitroaromatics

Efficient sensing of trace amount nitroaromatic (NAC) explosives has become a major research focus in recent time due to concerns over national security as well as their role as environment pollutants. NO2 -containing electron-deficient aromatic compounds, such as picric acid (PA), trinitrotoluene (TNT), and dinitrotoluene (DNT), are the common constituents of many commercially available chemical explosives. In this article, we have summarized our recent developments on the rational design of electron-rich self-assembled discrete molecular sensors and their efficacy in sensing nitroaromatics both in solution as well as in vapor phase. Several π-electron-rich fluorescent metallacycles (squares, rectangles, and tweezers/pincers) and metallacages (trigonal and tetragonal prisms) have been synthesized by means of metal-ligand coordination-bonding interactions, with enough internal space to accommodate electron-deficient nitroaromatics at the molecular level by multiple supramolecular interactions. Such interactions subsequently result in the detectable fluorescence quenching of sensors even in the presence of trace quantities of nitroaromatics. The fascinating sensing characteristics of molecular architectures discussed in this article may enable future development of improved sensors for nitroaromatic explosives.

Metal-driven self-assembly: the case of redox-active discrete architectures

The growing family of redox-active rings and cages prepared using the coordination-driven self-assembly strategy is reviewed.