A Theoretical Probe for Structures, Metal–Metal Bonding, and Electronic Spectra of Paramagnetic Tetrapyrrolic RuII Complex

Dimeric complexes (RuIIPz)2 have been investigated using density functional theory (DFT), where Pz is a porphyrazine ligand that features a 16-atom, 18-π-electron cyclic polyene aromatic skeleton. Structural optimizations in various configurations and spin states indicate that (RuPz)2 favours a Pz–Pz staggered conformer over an eclipsed one; the paramagnetic triplet state with the staggered configuration is found as the global ground state. This agrees with experimental magnetic results of (RuOEPor)2 (OEPor = octaethylporphyrin) and (RuPc)2 (Pc = phthalocyanine). The Ru–Ru bond length was optimized to be 2.38 Å, close to the experimental bond length of 2.40–2.41 Å. The Ru2 doubly bonded nature has been evidenced by the Ru–Ru stretching vibrational frequency of 202 cm–1, bond energy of 30.7 kcal mol–1, and electronic arrangement of σ2π4(nonbonding-δ)4(π*)2. Further confirmation was obtained from high-level wave function theory calculations (complete active space self-consistent field and n-electron valence state second-order perturbation theory). Associated with the solvation of the explicit pyridine accounting for the first coordination sphere and the implicit continuum model for the long-range interaction, the electronic spectra of tetrapyrrolic ruthenium complex were calculated at the time-dependent DFT level.

Photocontrolled nitric oxide release from two nitrosylruthenium isomer complexes and their potential biomedical applications

Nitric oxide (NO) has key regulatory roles in various biological and medical processes. The control of its local concentration, which is crucial for obtaining the desired effect, can be achieved with exogenous NO donors. Release of NO from metal-nitrosyl complexes upon exposure to light is a strategy that could allow for the site-specific delivery of the reactive species NO to physiological targets. The photodissociation of NO from two nitrosylruthenium(II) isomer complexes {cis- and trans-[Ru(OAc)(2mqn)(2)NO]} was demonstrated by matrix-assisted laser desorption ionization time-of-flight mass spectrometry spectra, and electron paramagnetic resonance spectra further prove the photoinduced NO release by spin trapping of NO free radicals upon photoirradiation. Real-time NO release was quantitatively measured by electrochemistry with an NO-specific electrode. The quantitative control of NO release from [Ru(OAc)(2mqn)(2)NO] in aqueous solutions was done by photoirradiation at different wavelengths. Both isomers show photoinduced damage on plasmid DNA, but the trans isomer has higher cytotoxicity and photocytotoxicity activity against the HeLa tumor cell line than that of the cis isomer. Nitrosylruthenium(II) complex, with 8-quinolinol derivatives as ligands, has a great potential as a photoactivated NO donor reagent for biomedical applications.

Photoisomerization and structural dynamics of two nitrosylruthenium complexes: a joint study by NMR and nonlinear IR spectroscopies

In this work, the photoisomerization and structural dynamics of two isomeric nitrosylruthenium(ii) complexes [Ru(OAc)(2cqn)2NO] (H2cqn = 2-chloro-8-quinolinol) in CDCl3 and DMSO are examined using NMR and IR spectroscopic methods. The two N atoms in the 2cqn ligand are in trans position in the synthesized cis-1 isomer, while they are in cis position in the cis-2 isomer. Kinetics monitored by NMR spectroscopy shows that the rate constant of photoisomerization from cis-2 to cis-1 isomer depends on the wavelength of irradiation and solvent polarity; it proceeds faster on irradiating near the absorption peak in the UV-Vis region, and also in more polar solvents (DMSO). Density functional theory computation indicates that the peculiarity of [Ru(ii)-NO(+)] group affects the structure and reactivity of the nitrosylruthenium complexes. Using the nitrosyl stretching (νNO) to be vibrational probe, the structural dynamics and structural distributions of the cis-1 and cis-2 isomers are examined by steady-state linear infrared and ultrafast two-dimensional infrared (2D IR) spectroscopies. The structural and photochemical aspects of the observed spectroscopic parameters are discussed in terms of solute-solvent interactions for the two nitrosylruthenium complexes.

Structural, electronic, vibrational and NMR spectral analyses of [Ru(OAc)(2cqn)2NO] (H2cqn=2-chloro-8-quinolinol) isomers

Geometries of three [Ru(OAc)(2cqn)2NO] (H2cqn=2-chloro-8-quinolinol) isomers were fully optimized with density functional theory (DFT), and compared with their crystal structures. Their electronic spectra, infrared and NMR spectra were also calculated at the B3LYP level with Lanl2dz and 6-311G(d,p) as the basis set. And good agreement had been achieved between experimental and theoretical values of structural parameter, UV-vis absorption and scaled vibration frequency. With the gauge independent atomic orbital (GIAO) method, chemical shifts in (1)H and (13)C NMR of these isomers were also calculated, which could reasonably match with the experimental data. The calculated frontier molecular orbitals suggested that the electronic transition from a ligand-based orbital to an antibonding overlap of the Ru(d) and π(∗) NO(p) control the photo-induced reactivity of [Ru(OAc)(2cqn)2NO] complexes.

A simple synthetic route to obtain pure trans-ruthenium(II) complexes for dye-sensitized solar cell applications

We report a facile synthetic route to obtain functionalized quaterpyridine ligand and its trans-dithiocyanato ruthenium complex, based on a microwave-assisted procedure. The ruthenium complex has been purified using a silica chromatographic column by protecting carboxylic acid groups as iso-butyl ester, which are subsequently hydrolyzed. The highly pure complex exhibits panchromatic response throughout the visible region. DFT/time-dependent DFT calculations have been performed on the ruthenium complex in solution and adsorbed onto TiO2 to analyze relative electronic and optical properties. The ruthenium complex endowed with the functionalized quaterpyridine ligand was used as a sensitizer in dye-sensitized solar cell yielding a short-circuit photocurrent density of more than 19 mA cm(-2) with a broad incident photon to current conversion efficiency spectra ranging from 400 to 900 nm, exceeding 80 % at 700 nm.