Ruthenium(II) bis(2,2'-bipyridine)(4'-methyl-4-butanoate-2,2'-bipyridine) hexafluorophosphate
[CAS# 115239-59-3]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic ruthenium
• Name: Ruthenium(II) bis(2,2'-bipyridine)(4'-methyl-4-butanoate-2,2'-bipyridine) hexafluorophosphate
• Synonyms: Ruthenium(1+), bis(2,2'-bipyridine-kappaN1,kappaN1')(4'-methyl[2,2'-bipyridine]-4-butanoato-kappaN1,kappaN1')-, (OC-6-33)-, hydrogen hexafluorophosphate(1-)
• Molecular Formula: C₃₅H₃₂F₆N₆O₂PRu
• Molecular Weight: 814.70
• CAS Registry Number: 115239-59-3
• EC Number: 853-379-7
• SMILES: CC1=CC(=NC=C1)C2=NC=CC(=C2)CCCC(=O)O.C1=CC=NC(=C1)C2=CC=CC=N2.C1=CC=NC(=C1)C2=CC=CC=N2.F[P-](F)(F)(F)(F)F.[Ru+]

Safety Data

• Hazard Symbols: GHS07 Warning
• Hazard Statements: H315-H319
• Precautionary Statements: P264-P280-P302+P352-P337+P313-P305+P351+P338-P362+P364-P332+P313

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	3	H311
Acute toxicity	Acute Tox.	3	H331
Acute toxicity	Acute Tox.	3	H301

Discovory and Applicatios

Ruthenium(II) bis(2,2'-bipyridine)(4'-methyl-4-butanoate-2,2'-bipyridine) hexafluorophosphate is a luminescent coordination complex widely studied in the field of photochemistry, electrochemistry, and molecular imaging. The compound consists of a central ruthenium ion coordinated to two neutral 2,2'-bipyridine (bpy) ligands and a third bpy ligand that is substituted at the 4' position with a methyl ester functionalized butanoate chain. The resulting cationic complex is balanced by a hexafluorophosphate (PF₆^-) counterion, which enhances solubility in organic solvents and helps crystallize the product for characterization and use.

The discovery of ruthenium(II) polypyridyl complexes dates back to the 1960s and 1970s, during which researchers investigated a range of transition metal-based chromophores for their photophysical properties. These complexes attracted considerable interest due to their long-lived metal-to-ligand charge transfer (MLCT) excited states, high photostability, and strong visible-light absorption. Functional derivatives such as ruthenium(II) bis(2,2'-bipyridine)(4'-methyl-4-butanoate-2,2'-bipyridine) were developed to introduce chemical reactivity and improve targeting capability in biological or materials systems.

The synthesis of this complex begins with the preparation of a substituted bipyridine ligand bearing the 4'-methyl-4-butanoate functionality. This is typically achieved by functionalizing 4'-methyl-2,2'-bipyridine via esterification reactions or coupling carboxylic acid derivatives with alcohol groups. The ligand is then reacted with the precursor compound \[Ru(bpy)₂Cl₂] under refluxing conditions, often in ethylene glycol or ethanol. The coordination process results in the displacement of the chloride ligands and formation of the tris-bipyridine complex. Final purification is performed by ion exchange or crystallization using NH₄PF₆, yielding the PF₆^- salt of the complex.

This ruthenium complex exhibits intense luminescence in the orange-red region of the visible spectrum, a result of its MLCT transition. Upon photoexcitation, an electron is transferred from a ruthenium-centered orbital to a π\*-orbital on one of the bipyridine ligands, generating a triplet excited state that has a relatively long lifetime (typically in the range of hundreds of nanoseconds in degassed solution). These photophysical properties make the complex an excellent candidate for use as a probe in time-resolved luminescence spectroscopy, biological imaging, and as a sensitizer in photodynamic therapy.

In biological applications, the ester group of the 4'-methyl-4-butanoate moiety can be hydrolyzed to expose a carboxylic acid, enabling covalent attachment to amine-functionalized biomolecules such as proteins, nucleic acids, or synthetic polymers. This facilitates the site-specific labeling of target molecules with the luminescent ruthenium center. Such modifications are useful for tracking biomolecular interactions, cellular uptake, or subcellular localization using fluorescence microscopy or lifetime imaging.

The complex is also studied in the context of electrochemical sensors and dye-sensitized solar cells (DSSCs). The electron-rich ruthenium core and delocalized π-system of the bipyridine ligands support efficient charge transfer processes when interfaced with semiconducting materials such as TiO₂. The ester functionality allows for anchoring to oxide surfaces through post-synthetic modification, enhancing adhesion and charge injection efficiency. Consequently, this compound and its analogues have been employed as light-absorbing dyes that convert visible light into electric current in DSSCs.

In addition to applications in energy and biology, ruthenium(II) polypyridyl complexes are explored in photocatalysis and supramolecular chemistry. Their predictable coordination geometry, tunable redox behavior, and strong luminescence make them useful building blocks for molecular assemblies, including cages, rotaxanes, and dendritic systems. The functionalized bipyridine ligand contributes both steric and electronic versatility, allowing the tailoring of properties through rational ligand design.

Overall, ruthenium(II) bis(2,2'-bipyridine)(4'-methyl-4-butanoate-2,2'-bipyridine) hexafluorophosphate exemplifies the multifunctional potential of transition metal complexes. Through careful modification of its ligand environment, researchers continue to expand its utility in diagnostics, therapeutics, energy conversion, and smart materials.