Photochemistry of Ru(II) Triazole Complexes with 6-Membered Chelate Ligands: Detection and Reactivity of Ligand-Loss Intermediates.

Photochemical ligand release from metal complexes may be exploited in the development of novel photoactivated chemotherapy agents for the treatment of cancer and other diseases. Highly intriguing photochemical behavior is reported for two ruthenium(II) complexes bearing conformationally flexible 1,2,3-triazole-based ligands incorporating a methylene spacer to form 6-membered chelate rings. [Ru(bpy)2(pictz)]2+ (1) and [Ru(bpy)2(btzm)]2+ (2) (bpy = 2,2'-bipyridyl; pictz = 1-(picolyl)-4-phenyl-1,2,3-triazole; btzm = bis(4-phenyl-1,2,3-triazol-4-yl)methane) exhibit coordination by the triazole ring through the less basic N2 atom as a consequence of chelation and readily undergo photochemical release of the pictz and btzm ligands (ϕ = 0.079 and 0.091, respectively) in acetonitrile solution to form cis-[Ru(bpy)2(NCMe)2]2+ (3) in both cases. Ligand-loss intermediates of the form [Ru(bpy)2(κ1-pictz or κ1-btzm)(NCCD3)]2+ are detected by 1H NMR spectroscopy and mass spectrometry. Photolysis of 1 yields three ligand-loss intermediates with monodentate pictz ligands, two of which form through simple decoordination of either the pyridine or triazole donor with subsequent solvent coordination (4-tz(N2) and 4-py, respectively). The third intermediate, shown to be able to form photochemically directly from 1, arises through linkage isomerism in which the monodentate pictz ligand is coordinated by the triazole N3 atom (4-tz(N3)) with a comparable ligand-loss intermediate with an N3-bound κ1-btzm ligand also observed for 2.

Hierarchical Spin-Crossover Cooperativity in Hybrid 1D Chains of FeII -1,2,4-Triazole Trimers Linked by [Au(CN)2 ]- Bridges.

Foremost, practical applications of spin-crossover (SCO) materials require control of the nature of the spin-state coupling. In existing SCO materials, there is a single, well-defined dimensionality relevant to the switching behavior. A new material, consisting of 1,2,4-triazole-based trimers coordinated into 1D chains by [Au(CN)2 ]- and spaced by anions and exchangeable guests, underwent SCO defined by elastic coupling across multiple dimensional hierarchies. Detailed structural, vibrational, and theoretical studies conclusively confirmed that intra-trimer coupling was an order of magnitude greater than the intramolecular coupling, which was an order of magnitude greater than intermolecular coupling. As such, a clear hierarchy on the nature of elastic coupling in SCO materials was ascertained for the first time, which is a necessary step for the technological development of molecular switching materials.

Dinuclear acetylide-bridged ruthenium(ii) complexes with rigid non-aromatic spacers.

Rigid dinuclear ruthenium complexes containing non-aromatic caged and polycyclic spacer groups were synthesised and characterised. The complexes, [trans,trans-{Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)}2(µ-C[triple bond, length as m-dash]C-X-C[triple bond, length as m-dash]C)], where X = 1,4-bicyclo[2.2.2]octane (C8H12) or 1,12-p-carborane (p-C2B10H10), were formed via the metathesis of terminal organic bisacetylenes with the methylruthenium complex, [trans-Ru(dmpe)2(CH3)(C[triple bond, length as m-dash]CtBu)], under mild conditions. Electrochemical studies demonstrated electronic interactions across the non-aromatic caged and polycyclic spacers was less than in the analogous complex with an aromatic spacer group, [trans,trans-{Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)}2(µ-C[triple bond, length as m-dash]C-p-C6H4-C[triple bond, length as m-dash]C)]. Mononuclear complexes, [trans-Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)(C[triple bond, length as m-dash]C-X-C[triple bond, length as m-dash]CH)], were also synthesised. [trans-Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)(C[triple bond, length as m-dash]C-C8H12-C[triple bond, length as m-dash]CH)] and [trans,trans-{Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)}2(µ-C[triple bond, length as m-dash]C-p-C2B10H10-C[triple bond, length as m-dash]C)] were structurally characterised by X-ray crystallography.

Long-lived MLCT states for Ru(ii) complexes of ferrocene-appended 2,2'-bipyridines.

In this study, we present two ruthenium(ii) diimine complexes appended with ferrocene which show metal to ligand charge transfer 3MLCT emission lifetimes around 630 ns. We also present a similar complex with two ferrocene units which has decreased emission. These complexes have been studied by electrochemical, electronic absorption, and Raman, resonance Raman and transient resonance Raman means, coupled with density functional theoretical approaches. For these systems, the optical spectra are dominated by a low energy ruthenium(ii) MLCT transition; which can be modulated by the presence of pendant ferrocene units and the extent of conjugation of the ferrocenyl bipyridine backbone. Tuning of the lowest energy transition in terms of intensity (4 to 18 × 10-3 M-1 cm-1) and energy (535 to 563 nm) was achieved by these means.

A ferrocene based switchable molecular folding ruler.

A 2,2'-bipyridine-appended bis(ferrocene) three tiered molecular folding ruler, can be switched from a folded conformation to an extended conformation by the addition of [Cu(CH3CN)4](PF6) and 6,6'-dimesityl-2,2'-bipyridine. This extension and contraction process could be triggered either chemically or electrochemically and was reversible.

Oxidatively Locked [Co2L3]6+ Cylinders Derived from Bis(bidentate) 2-Pyridyl-1,2,3-triazole "Click" Ligands: Synthesis, Stability, and Antimicrobial Studies.

A small family of [Co2(Lpytrz)3]6+ cylinders was synthesised from bis(bidentate) 2-pyridyl-1,2,3-triazole "click" ligands (Lpytrz) through an "assembly-followed-by-oxidation" method. The cylinders were characterised using ¹H, 13C, and DOSY NMR, IR, and UV-Vis spectroscopies, along with electrospray ionisation mass spectrometry (ESMS). Stability studies were conducted in dimethyl sulfoxide (DMSO) and D2O. In contrast to similar, previously studied, [Fe2(Lpytrz)3]4+ helicates the more kinetically inert [Co2(Lpytrz)3]6+ systems proved stable (over a period of days) when exposed to DMSO and were even more stable in D2O. The triply stranded [Co2(Lpytrz)3]6+ systems and the corresponding "free" ligands were tested for antimicrobial activity in vitro against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) microorganisms. Agar-based disk diffusion and Mueller-Hinton broth micro-dilution assays showed that the [Co2(Lpytrz)3]6+ cylinders were not active against either strain of bacteria. It is presumed that a high charge of the [Co2(Lpytrz)3]6+ cylinders is preventing them from crossing the bacterial cell membranes, rendering the compounds biologically inactive.

Antimicrobial Properties of Tris(homoleptic) Ruthenium(II) 2-Pyridyl-1,2,3-triazole "Click" Complexes against Pathogenic Bacteria, Including Methicillin-Resistant Staphylococcus aureus (MRSA).

A series of tris(homoleptic) ruthenium(II) complexes of 2-(1-R-1H-1,2,3-triazol-4-yl)pyridine "click" ligands (R-pytri) with various aliphatic (R = butyl, hexyl, octyl, dodecyl, and hexdecyl) and aromatic (R = phenyl and benzyl) substituents was synthesized in good yields (52%-66%). The [Ru(R-pytri)3]2+(X-)2 complexes (where X- = PF6- or Cl-) were characterized by elemental analysis, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), 1H and 13C nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies, and the molecular structures of six of the compounds confirmed by X-ray crystallography. 1H NMR analysis showed that the as-synthesized materials were a statistical mixture of the mer- and fac-[Ru(R-pytri)3]2+ complexes. These diastereomers were separated using column chromatography. The electronic structures of the mer- and fac-[Ru(R-pytri)3]2+ complexes were examined using ultraviolet-visible (UV-Vis) spectroscopy and cyclic and differential pulse voltammetry. The family of R-pytri ligands and the corresponding mer- and fac-[Ru(R-pytri)3]2+ complexes were tested for antimicrobial activity in vitro against both Staphylococcus aureus and Escherichia coli bacteria. Agar-based disk diffusion assays indicated that two of the [Ru(R-pytri)3](X)2 complexes (where X = PF6- and R = hexyl or octyl) displayed good antimicrobial activity against Gram-positive S. aureus and no activity against Gram-negative E. coli at the concentrations tested. The most active [Ru(R-pytri)3]2+ complexes ([Ru(hexpytri)3]2+ and Ru(octpytri)3]2+) were converted to the water-soluble chloride salts and screened for their activity against a wider range of pathogenic bacteria. As with the preliminary screen, the complexes showed good activity against a variety of Gram-positive strains (minimum inhibitory concentration (MIC) = 1-8 µg/mL) but were less effective against Gram-negative bacteria (MIC = 16-128 µg/mL). Most interestingly, in some cases, the ruthenium(II) "click" complexes proved more active (MIC = 4-8 µg/mL) than the gentamicin control (MIC = 16 µg/mL) against two strains of methicillin-resistant S. aureus (MRSA) (MR 4393 and MR 4549). Transmission electron microscopy (TEM) experiments and propidium iodide assays suggested that the main mode of action for the ruthenium(II) R-pytri complexes was cell wall/cytoplasmic membrane disruption. Cytotoxicity experiments on human dermal keratinocyte and Vero (African green monkey kidney epithelial) cell lines suggested that the complexes were only modestly cytotoxic at concentrations well above the MIC values.

Structural, Electronic, and Computational Studies of Heteroleptic Cu(I) Complexes of 6,6'-Dimesityl-2,2'-bipyridine with Ferrocene-Appended Ethynyl-2,2'-bipyridine Ligands.

Optical characterization and computational modeling of three ferrocene-appended ethynyl-2,2'-bipyridine ligands and the associated heteroleptic copper(I) complexes of 6,6'-dimesityl-2,2'-bipyridine are reported. These dyes have been studied using electrochemical analysis, electronic absorption, and Raman and resonance Raman spectroscopies, coupled with density functional theoretical approaches. For the complexes, optical spectra are dominated by a low energy copper(I) centered metal to ligand charge transfer (MLCT) transition; this is modulated by the presence of pendant ferrocene units and the extent of conjugation of the ferrocenyl bipyridine backbone. Electronic tuning due to ferrocene is shown to result in a redshift of the MCLT transition of up to ∼0.2 eV, while an elongation of conjugation appears to result in an increased MLCT intensity of around 50%.

Ferrocene-containing non-interlocked molecular machines.

Ferrocene is the prototypical organometallic sandwich complex and despite over 60 years passing since the discovery and elucidation of ferrocene's structure, research into ferrocene-containing compounds continues to grow as potential new applications in catalysis, biology and the material sciences are found. Ferrocene is chemically robust and readily functionalized which enables its facile incorporation into more complex molecular systems. This coupled with ferrocene's reversible redox properties and ability function as a "molecular ball bearing" has led to the use of ferrocene as a component in wide range of interlocked and non-interlocked synthetic molecular machine systems. This review will focus on the exploitation of ferrocene (and related sandwich complexes) for the development of non-interlocked synthetic molecular machines.

Chemically and electrochemically induced expansion and contraction of a ferrocene rotor.

A 2,2'-bipyridine-appended ferrocene rotor, 1,1'-di(5-yl-ethynyl-2,2'-bipyridine)ferrocene, can be switched from a folded/stacked (syn) conformation to an extended/unstacked (anti) conformation by the addition of [Cu(CH3CN)4](PF6) and 6,6'-dimesityl-2,2'-bipyridine. This extension and contraction process was completely reversible and could be triggered either chemically or electrochemically.