Radical-ion salts obtained from tetraazaderivatives of nickel and copper and tetracyanoquinodimethane: structural and magnetic characterization

Several derivatives of formulae [M(N₄)(TCNQ)₂] and [M(N₄)(TCNQ)₂](TCNQ) (M = Ni, Cu; N₄ = 1,4,7,10-tetraazacyclododecane ([12] aneN₄), 1,4,8,11-tetraazacyclotetradecane ([14] aneN₄), 1,4,8,12-tetraazacyclopentadecane ([15] aneN₄), 1,4,7,10-tetraazadecane (trien), N,N,N-tris(2-aminoethyl)amine (tren), 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,14-diene (trans-dieneN₄)) have been obtained by metathesis reaction of the corresponding perchlorate or nitrate derivatives and LiTCNQ or (Et₃NH)(TCNQ)₂. The compounds [M(aneN₄)(TCNQ)₂] have a six coordinated metal atom surrounded by the four macrocyclic nitrogens and two nitrogens from σ coordinated TCNQ⁻. The overlap with a neighbouring 7,7,8,8-tetracyanoquinodimethane (TCNQ) forms the diamagnetic dianion [TCNQ]₂²⁻, and the whole structure can be seen as chains of metallomacrocyclic cations and TCNQ dianions alternating in the solid. The crystal structure of [Cu([15] aneN₄)(TCNQ)₂] confirms this fact. With open chain tetraamines the derivatives [Cu(trien)(TCNQ)₂] and [Cu(tren)(TCNQ)₂] are proposed to have the copper in a pentacoordinated environment, with only one coordinated TCNQ. In [M(trans-dieneN₄)](TCNQ)₂ both TCNQ⁻ are uncoordinated and dimerized, as the crystal structure of the nickel derivative confirms. The derivatives with three TCNQ [M(aneN₄)(TCNQ)₂](TCNQ) are proposed to have a structure derived from that of the analogous [M(aneN₄)(TCNQ)₂], based on the metallomacrocycle-[TCNQ]₂ chains connected through the extra TCNQ which remains uncoordinated and overlaps with the coordinated anions. This fact lowers the antiferromagnetic coupling inside the dimers and a small contribution for a thermally activated triplet state is observed in the magnetic susceptibility of these compounds.     

Effects of steric constraint on chromium(III) complexes of tetraazamacrocycles, 4: Comparison of the trans-difluoro-complexes of tet a, 1,4-C2-cyclam, and 1,11-C3-cyclam

The synthesis and characterization of the trans-difluorochromium(III) complexes of the constrained macrocyclic ligands 1,4-C₂-cyclam = 1,4,8,11-tetraazabicyclo[10.2.2]hexadecane and 1,11-C₃-cyclam = 1,4,8,11-tetraazabicyclo[9.3.3]heptadecane is reported. Only trans complexes are formed, and the structures of both trans-[Cr(1,4-C₂-cyclam)F₂]ClO₄ and trans-[Cr(1,11-C₃-cyclam)F₂]ClO₄ are presented. The photochemical and photophysical behavior of the 1,4-C₂-cyclam and 1,11-C₃-cyclam complexes is compared with that of the corresponding tet a (C-meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) complex. The constraint imposed by the additional bridging groups of 1,4-C₂-cyclam and 1,11-C₃-cyclam distorts the complexes away from both octahedral symmetry and centrosymmetry, as evidenced by the bond angles that deviate from ideal 90° and 180° values and by a significant distortion of the Cr(N₄) plane. This reduction in symmetry correlates with a monotonic increase in the extinction coefficients in going from the tet a to the 1,11-C₃-cyclam, to the 1,4-C₂-cyclam complex. These three complexes also exhibit large variations in their aqueous room-temperature excited state behavior; namely, the lifetimes of the ²T_1g (O_h) excited states are 30, 60, and 1.0 μs for the tet a, 1,11-C₃-cyclam, and 1,4-C₂-cyclam complexes, respectively. Studies of the excited-state lifetime of these complexes in acidified H₂O/dimethyl sulfoxide over the temperature range between −30 and +95 °C suggest that the 1,4-C₂-cyclam complex accesses a temperature-dependent relaxation mechanism at significantly lower temperatures than do the tet a or 1,11-C₃-cyclam complexes. The emission behavior of these complexes is also solvent-dependent, consistent with established theories that the degree of splitting of the emitting ²T_1g (O_h) state varies with the hydroxylic nature of the solvent.     

Crystal structure, magnetic and electrochemical properties of five-coordinate copper (II) complexes with 1,10-phenanthroline-5,6-dione

Three new five-coordinate Cu^II complexes, [Cu(tpy)(phen-dione)](PF₆)₂, [Cu(phen)(phen-dione)Cl]PF₆ and [Cu(bpy)(phen-dione)Cl]PF₆ (tpy = 2,2′;6′,2″-terpyridine, phen = 1,10-phenanthroline and phen-dione = 1,10-phenanthroline-5,6-dione) have been prepared and characterized by elemental analysis, IR and UV-Vis spectroscopies and cyclic voltammetry.The complex of [Cu(tpy)(phen-dione)](PF₆)₂ crystallized with one molecule of acetonitrile. The ortep drawing of [Cu(tpy)(phen-dione)](PF₆)₂ · CH₃CN shows that the coordination geometry around Cu^II is a distorted trigonal- bipyramid. Due to the steric hindrance of in the unit cell, the tpy ligands in each complex cation cannot interact in a π-π fashion. The effective magnetic moment (μ_eff) of the complexes was measured by the Evans method. The cyclic voltammograms at Pt disk electrode for these complexes display only one reversible Cu(II)/Cu(I) redox couple.     

Synthesis, characterization and reactivity of polypyridyl ruthenium(II) carbonyl complexes with phosphine derivatives: Ruthenium-carbon bond labilization based on steric and electronic effects

Ruthenium phosphine complexes with a CO ligand [Ru(tpy)(PR₃)(CO)Cl]⁺ (tpy = 2,2′:6′,2″-terpyridine, R = Ph or p-tolyl), were prepared by introduction of CO gas to the corresponding dichloro complexes at room temperature. New carbonyl complexes were characterized by various methods including structural analyses. They were shown to release CO following the addition of several N-donors to form the corresponding substituted complexes. The kinetic data and structural results observed in this study indicated that the CO release reactions proceeded in an interchange mechanism. The molecular structures of [Ru(tpy)(PPh₃)(CO)Cl]PF₆, [Ru(tpy)(P(p-tolyl)₃)(CO)Cl]PF₆ and [Ru(tpy)(PPh₃)(CH₃CN)Cl]PF₆ were determined by X-ray crystallography.     

Kinetics of the cis-to-planar interconversion of cis-diaqua(1,4,7,11-tetraazacyclotetradecane)nickel(II) ion

In order to examine the effects of coordinated hydroxide ion and free hydroxide ion in configurational conversion of a tetraamine macrocyclic ligand complex, the kinetics of the cis-to-planar interconversion of cis-[Ni(isocyclam)(H₂O)₂]²⁺ (isocyclam, 1,4,7,11-tetraazacyclotetradecane) has been studied spectrophotometrically in basic aqueous solution. The interconversion requires the inversion of one sec-NH center of the folded cis-complex to have the planar species. Kinetic data are satisfactorily fitted by the rate law, R = k_OH[OH⁻][cis-[Ni(isocyclam)(H₂O)₂]²⁺], where k_OH = 3.84 × 10³ dm³ mol⁻¹ s⁻¹ at 25.0 ± 0.1 °C with I = 0.10 mol dm⁻³ (NaClO₄). The large ΔH^≠, 61.7 ± 3.2 kJ mol⁻¹, and the large positive ΔS^≠, 30.2 ± 10.8 J K⁻¹ mol⁻¹, strongly support a free-base-catalyzed mechanism for the reaction.     

Synthesis, characterization and liquid-phase hydroxylation of phenol with hydrogen peroxide over host (nanopores of zeolite-Y)/guest (oxovanadium(IV) complexes of tetraaza macrocyclic ligands) nanocatalyst

Oxovanadium(IV) tetraaza complexes of [14]aneN₄: 1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane; [16]aneN₄: 1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane; Bzo₂[14]aneN₄: dibenzo-1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane and Bzo₂[16]aneN₄: dibenzo-1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane have been encapsulated in the nanopores of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of [bis(diamine)VO(IV)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, 1,3-diaminobenzene); [VO(N-N)₂]²⁺-NaY; in the nanopores of the zeolite-Y and (ii) in situ condensation of the oxovanadium(IV) precursor complex with ethylcinnamate. The new host-guest nanocatalysts were characterized by several techniques: chemical analysis and spectroscopic methods (FT-infrared (FT-IR), ultraviolet-visible (UV-Vis), X-ray diffraction (XRD), nitrogen adsorption and diffuse reflectance spectra (DRS)) technique. The analytical data indicated a composition corresponding to the mononuclear complex of tetraaza ligand. The characterization data showed the absence of extraneous complexes, retention of zeolite crystalline structure and encapsulation in the nanopores. Liquid-phase selective hydroxylation of phenol with H₂O₂ to a mixture of catechol and hydroquinone in CH₃CN have been reported using oxovanadium(IV) tetraaza complexes encapsulated in zeolite-Y as catalysts. All these catalysts are more selective toward catechol formation.     

Crystal structure and spectroscopic properties of trans-bis(nicotinato)(1,4,8,11-tetraazacyclotetradecane)chromium(III) perchlorate

The trans-[Cr(cyclam)(nic-O)₂]ClO₄ (cyclam = 1,4,8,11-tetraazacyclotetradecane; nic-O = O-coordinated nicotinate) has been prepared and structurally characterized by single-crystal X-ray diffraction at 150 K. The chromium atom is in a tetragonally compressed octahedral environment with four N atoms of the macrocyclic ligand in equatorial positions and two O-bonded nicotinates in trans axial positions. The macrocyclic cyclam adopts the centrosymmetric trans-III configuration with six- and five-membered chelate rings in chair and gauche conformation, respectively. The IR and visible spectral properties are consistent with the result of X-ray crystallography. The resolved band maxima of the electronic d-d spectrum are fitted with secular determinant for quartet state energy of d³ configuration in tetragonal field including configurational interaction. It is found that the nitrogen atoms of the cyclam ligand are a strong σ-donors and that O-bonded nicotinato group has strong σ- and π-donor characteristics toward the chromium(III) ion.     

Interfacial electron transfer on TiO2 sensitized with an axially anchored trans tetradentate Ru(II) compound

The ruthenium complexes, trans-[Ru(phen-NH-phen)(eina)₂](PF₆)₂ and trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ where phen-NH-phen = N,N-bis(1,10-phenanthroline-2-yl)amine, ina = isonicotinic acid and eina = ethyl isonicotinate, have been synthesized and characterized by ¹H NMR, elemental analysis, and IR spectroscopy. The compounds were non-emissive at room temperature, but displayed intense photoluminescence in 4:1 ethanol/methanol glasses at 77 K with corrected emission maximum at 570-580 nm. A quasi-reversible wave observed in cyclic voltammetry experiments was assigned to the Ru^III/II couple, E° (trans-[Ru(phen-NH-phen)(eina)₂)^3+/2+ = +1.22 V versus Ag/AgCl. The trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ compound was found to bind to nanocrystalline TiO₂ thin films from acetonitrile solution. Pulsed 532 nm excitation of trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ anchored to mesoporous nanocrystalline TiO₂ thin films resulted in an absorption difference spectra consistent with the formation of an interfacial charge separated state trans-[Ru^III (phen-NH-phen)(ina)₂]⁺/TiO₂ (e⁻). The formation of this state could not be time resolved, consistent with rapid excited state injection into the TiO₂, k_inj > 10⁸ s⁻¹. Comparative measurements with a thin film actinometer yielded an injection quantum yield (?_inj) of 0.8. Charge recombination required milliseconds for completion and followed a bi-second-order equal concentration kinetic model with k₁ = 1.0 × 10⁸ s⁻¹, and k₂ = 3.0 × 10⁵ s⁻¹. In regenerative solar cells with 0.5 M LiI and 0.005 M I₂ in acetonitrile, incident photon-to-current efficiencies were typically less than 10%.     

Enhanced DNA photocleavage properties of Ru(II) terpyridine complexes upon incorporation of methylphenyl substituted terpyridine and/or the polyazine bridging ligand dpp (2,3-bis(2-pyridyl)pyrazine)

The heteroleptic complexes, [(MePhtpy)RuCl(dpp)](PF₆) and [(tpy)RuCl(dpp)](PF₆), have been synthesized, characterized, and investigated with respect to their photophysical, redox, and DNA photocleavage properties (where MePhtpy = 4′-(4-methylphenyl)-2,2′:6′,2′′-terpyridine and dpp = 2,3-bis(2-pyridyl)pyrazine, tpy = 2,2′:6′,2′′-terpyridine). The X-ray crystal structure confirms the identity of the new [(MePhtpy)RuCl(dpp)](PF₆) complex. These heteroleptic complexes were found to photocleave DNA in the presence of oxygen, unlike the previously studied complex, [Ru(tpy)₂](PF₆)₂. The photophysical, redox, and DNA photocleavage properties of the heteroleptic complexes were compared with those of the homoleptic complexes, [Ru(MePhtpy)₂](PF₆)₂ and [Ru(tpy)₂](PF₆)₂. The heteroleptic complexes showed intense metal to ligand charge transfer (MLCT) transition at lower energy ([(MePhtpy)RuCl(dpp)](PF₆), 522 nm; [(tpy)RuCl(dpp)](PF₆), 516 nm) and longer excited state lifetimes as compared to the homoleptic complexes. The [Ru(MePhtpy)₂]²⁺ complex was found to photocleave DNA in contrast to [Ru(tpy)₂]²⁺. The introduction of a methylphenyl group on the tepyridine ligand not only enhances the ³MLCT excited state lifetime but also increases the lipophilicity and thereby the DNA binding ability of the molecule. An increase in lipophilicity upon addition of a methylphenyl group on the 2,2′:6′,2′′-terpyridine ligand was confirmed by determination of the partition coefficient ([(MePhtpy)RuCl(dpp)](PF₆), log P = +1.16; [(tpy)RuCl(dpp)](PF₆), log P = −1.27). The heteroleptic complexes photocleave DNA more efficiently than the homoleptic complexes, with the greatest activity being observed for the newly prepared [(MePhtpy)RuCl(dpp)](PF₆) complex.     

Synthesis, characterization and photophysical properties of mixed ligand tris(polypyridyl)chromium(III) complexes, [Cr(phen)2L]

A series of new heteroleptic, tris(polypyridyl)chromium(III) complexes, [Cr(phen)₂L]³⁺ (L = substituted phenanthrolines or bipyridines), has been prepared and characterized, and their photophyical properties in a number of solvents have been investigated. X-ray crystallography measurements confirmed that the cationic (3+) units contain only one ligand L plus two phenanthroline ligands. Electrochemical and photophysical data showed that both ground state potentials and lifetime decays are sensitive to ligand structure and the nature of the solvent with the exception of compounds containing L = 5-amino-1,10-phenanthroline (aphen) and 2,2′-bipyrimidine (bpm). Addition of electron-donating groups in the ligand structure shifts redox potentials to more negative values than those observed for the parent compound, [Cr(phen)₃]³⁺. Emission decays show a complex dependence with the solvent. The longest lifetime was observed for [Cr(phen)₂(dip)]³⁺ (dip = 4,7-diphenylphenanthroline) in air-free aqueous solutions, τ = 273 μs. Solvent effects are explained in terms of the affinity of hydrophobic complexes for non-polar solvent molecules and the solvent microstructure surrounding chromium units.     

Ruthenium(II) thiacrown complexes: Synthetic, spectroscopic, electrochemical, DFT, and single crystal X-ray structural studies of [Ru([15]aneS5)Cl](PF6)

We wish to report the synthesis of the Ru(II) crown thioether complex, (1,4,7,10,13-pentathiacyclopentadecane)chlororuthenium(II) hexafluorophosphate, [Ru([15]aneS₅)Cl](PF₆), and a study of its properties utilizing single crystal X-ray diffraction, electronic spectroscopy, NMR spectroscopy, density functional theory calculations and cyclic voltammetry. The crystal structure shows a single [15]aneS₅ macrocycle and a chloro ligand coordinated in a distorted octahedral fashion around the ruthenium(II) center. A significant shortening (0.15 Å) of the trans Ru-S bond length occurs in this complex compared to the related PPh₃ complex (2.4458(10) to 2.283(1) Å) due to the differences in the trans influence of the two ligands. ¹³C NMR spectroscopy demonstrates that the structure of [Ru([15]aneS₅)Cl]⁺ is retained in solution. As expected for a Ru(II) complex, the electronic absorption spectrum shows two d-d transitions at 402 and 331 nm. These are red-shifted compared to hexakis(thioether)ruthenium(II) complexes and consistent with the weaker ligand field effect of the chloro ligand. The electrochemical behavior of the complex in acetonitrile shows a single one-electron reversible oxidation-reduction at +0.722 V versus Fc/Fc⁺ which is assigned as the Ru(II)/Ru(III) couple. DFT calculations for [Ru([15]aneS₅)Cl]⁺ show a HOMO with orbital contributions from a t_2g type orbital of the Ru ion, a π component from a p orbital of the axial S atom of [15]aneS₅, and a p orbital of the chloro ligand while the LUMO consists of orbital contributions of d_x²-y² orbital of the Ru center and p orbitals of the four equatorial S donors.     

Preparation and structure of [Ru2(O2CMe)4]2[Fe(CN)5NO] and magnetically ordered Hx[Ru2(O2CMe)4]3−x[Cr(CN)5NO] possessing interpenetrating lattices

Reaction of [Ru₂(O₂CMe)₄]Cl with K₃[Cr(CN)₅NO] in water forms H_x[Ru^II/III₂(O₂CMe)₄]_3−x-[Cr(CN)₅NO]·zH₂O (x = 0.2) that magnetically orders at 4.0 K and possesses an interpenetrating body centered cubic [a = 13.2509(2) Å] structure with random locations of the bridging nitrosyl ligands, and x/3 vacant cation sites. Similarly, the aqueous reaction of [Ru₂(O₂CMe)₄]Cl with Na₂[Fe(CN)₅NO] forms paramagnetic [Ru₂(O₂CMe)₄]₂[Fe(CN)₅NO]·H₂O, which has a similar tetragonal interpenetrating structure [a = 13.0186(1) Å, c = 13.0699(2) Å] where the NO ligands are presumably nonbridging and 1/3 of the expected cation sites are unoccupied. The presence of uncoordinated NO sites in addition to missing neighboring [Ru₂(O₂CMe)₄]⁺ units, results in significant vacancies (or holes) in the lattice.     

Metal-metal stacking patterns between and with [Pt(tpy)X] cations

A comparative study of metallophilic interactions of [Pt(tpy)X]⁺ cations (tpy = 2,2′:6′,2″-terpyridine) in the presence of two different types of anions, (i) []⁻ anions that form double salts and (ii) simple p-block anions, is reported. Single-crystal X-ray diffraction data, solution-state ¹⁹⁵Pt NMR spectra, and variable temperature solid-state luminescence spectra are reported. Three [Pt(tpy)Cl]Y derivatives (Y = SbF₆, 1, SbF₆·CH₃CN, 4, PF₆, 2) and the [Pt(tpy)Br]PF₆ analog, 3, as well as two new double salts [Pt(tpy)CN][Au(CN)₂], 5, and [Pt(tpy)CN]₂[Au(C₆F₅)₂](PF₆), 6, have been synthesized and characterized. Structural analysis shows consistent patterns in Pt···Pt interactions that vary slightly depending on the coordinating halogen or pseudo-halogen X, counter anion Y, and lattice solvent. Metallophilic interactions are seen between [Pt(tpy)X]⁺ cations with all types of X ligands, but only with π-accepting X′ ligands from []⁻ anions are Pt?Au metallophilic interactions seen to be favored over Pt?Pt interactions. The [Au(CN)₂]⁻ anion consistently forms Pt···Au metallophilic contacts, unlike [Au(C₆F₅)₂]⁻. The ¹⁹⁵Pt NMR chemical shifts are ∼−2750 ppm for π-donor ligands and near −3120 ppm for π-acceptor ligands in [Pt(tpy)X]PF₆ compounds. Luminescence data show an unusual blue shift in [Pt(tpy)CCPh][Au(C₆F₅)₂] versus [Pt(tpy)CCPh]PF₆ ascribed to an intermolecular charge transfer.     

Crystal structure, optical, magnetic, and photochemical properties of the complex pentakis(dimethyl sulfoxide)nitrosylchromium(2+) hexafluorophosphate

The nitrosyl complex [Cr(dmso)₅(NO)](PF₆)₂ (1) (dmso = dimethyl sulfoxide) has been prepared by the solvolysis of [Cr(NCCH₃)₅(NO)](PF₆)₂ in neat dmso. The optical absorption spectrum of 1 in dmso shows maxima at 734, 567, 450, 413, and 337 nm. Continuous photolysis of 1 with λ = 365-580 nm light in dmso solution results in a release of NO with quantum yield, Φ, in the range 0.034-0.108 mol Einstein⁻¹. Irradiation of a deoxygenated CH₃CN solution of [Cr(NCCH₃)₅(NO)](PF₆)₂ in the presence of excess of [Fe(S₂CNEt₂)₂] results in a transfer of NO to the iron centre as shown from the characteristic EPR spectrum of [Fe(S₂CNEt₂)₂(NO)] with A_iso(¹⁴N) = 12.2 × 10⁻⁴ cm⁻¹. The EPR parameters of 1 were determined: g_iso, g_‖ and g_⊥ : 1.96725, 1.91881(4) and 1.992763(2); A_iso(⁵³Cr), A_‖ (⁵³Cr) and A_⊥(⁵³Cr): 22.8 × 10⁻⁴, 39 × 10⁻⁴ and 15.8 × 10⁻⁴ cm⁻¹; A_iso(¹⁴N), A_‖ (¹⁴N) and A_⊥(¹⁴N): 5.9 × 10⁻⁴, 2 × 10⁻⁴ and 7.540(4) × 10⁻⁴ cm⁻¹.     

Synthesis of cyclopentadienyl ruthenium(II) complexes containing tethered functionalities

The reaction of [C₅H₄(CH₂)_nX]Tl (1: n = 2, X = NMe₂, OMe, CN; n = 3, X = NMe₂) with [(η⁶-C₆H₆)RuCl(μ-Cl)]₂, 2, afforded the sandwich compounds [{η⁵-C₅H₄(CH₂)_nX}Ru(η⁶-C₆H₆)]PF₆, 3, and [η⁵-C₅H₄(CH₂)_nX]₂Ru, 4. Photolytic cleavage of 3 in acetonitrile afforded the tethered products [{η⁵:κN-C₅H₄(CH₂)_nX}Ru(CH₃CN)₂]PF₆, 5.     

Kinetic study of base-catalyzed asymmetric nitrogen conversion of cis-folded macrocyclic nickel(II) complex of 1,4,7,11-tetraazacyclotetradecane

In order to examine the effects of coordinated hydroxide ion and free hydroxide ion in configurational conversion of a tetraamine macrocyclic ligand complex, the kinetic of the cis-to-planar interconversion of cis-[Ni(isocyclam)(H₂O)₂]²⁺ (isocyclam = 1,4,7,11-tetraazacyclotetradecane) has been examined spectrophotometrically. All kinetic data have been satisfactorily fitted by the rate law, R = (k₁K_OH[OH⁻]² + k₂[OH⁻])(1 + K_OH[OH⁻])⁻¹(cis-[Ni(isocyclam)(H₂O)₂]²⁺ + [Ni(isocyclam)(OH)]⁺), where k₂ = (3.40 ± 0.12) × 10³ dm³ mol⁻¹ s⁻¹ is almost equal to k_OH determined in buffer solution (lowly basic media), K_OH = 22.7 ± 1.4 dm³ mol⁻¹ at I (ionic strength) = 0.10 mol dm⁻³ (NaClO₄ + NaOH) and 25.0 °C. Rate constants, k₂ and K_OH, are functions of ionic strength, giving a good evidence for an intermolecular pathway. The reaction follows a free-base-catalyzed mechanism where nitrogen inversion, solvation and ring conformational changes are occurred.     

DNA- and RNA-binding and enhanced DNA-photocleavage properties of a ferrocenyl-containing ruthenium(II) complex

The interaction of [Ru(bpy)₂(fip)](PF₆)₂ {bpy = 2,2′-bipyridine, fip = 2-ferrocenyl-1H-imidazo[4,5-f][1,10]-phenanthroline} with calf thymus DNA and yeast tRNA was investigated comparatively by UV-visible absorption and luminescence spectrophotometric titrations, steady-state emission quenching by [Fe(CN)₆]^4 −, ethidium bromide competition experiment, DNA thermal denaturation, viscosity measurements and salt effect studies. The results suggest that the complex binds to the DNA more strongly than to the RNA. The density functional theory calculations were also carried out in order to better understand the nucleic acid binding properties. Agarose gel electrophoresis showed that the complex exhibited enhanced DNA-photocleavage capacity on pUC 18 plasmid DNA under irradiation at 360 nm as compared with a ferrocenyl-free analogous complex.     

The bimolecular sensitization of nitric oxide release from weak interacting ruthenium units

This work reports on the bimolecular sensitization of nitric oxide release from cis-[Ru(bpy)₂(iso)NO](PF₆)₃ (1) (iso = isoquinoline and bpy = 2,2′-bipyridine) by irradiating the MLCT transition of the chloro analog cis-[Ru(bpy)₂(iso)Cl]PF₆ (2)_. The compounds displayed peaks in the ESI-MS spectra at m/z 749.1 and m/z 578.1 ascribed, respectively, to ([1(NO⁰)−2PF₆·CH₃OH]²⁺) and ([2−PF₆]⁺). In the cyclic voltammograms, the nitrosyl complex presented two redox waves related to the NO ligand at 0.48 and −0.37 V (versus Ag/AgCl, NO^+/0/−1 processes), while the sensitizer showed two reversible waves at 0.79 and −1.46 V (versus Ag/AgCl, Ru^2+/3+ and bpy ^0/−1, respectively). The most important feature of this system is that the nitrosyl compound does not have significant absorption in the visible region, while the sensitizer has an intense band centered at 496 nm. The irradiation of an equimolar mixture of the two compounds in an ethanol:water solution (v:v) with light of λ > 500 nm leads to NO release, as probed by amperometric measurements. The variational method was applied, showing that the two compounds self-assembly in solution with a 1:1 stoichiometry. Fluorescence spectra acquired at 77 K provided the E_0-0 for the system and, from the thermodynamic cycle it was estimated that the photoinduced electron transfer between the species has a ΔG value of −1.59 eV.     

Luminescent phosphinocrown-containing gold(I) complexes: Their syntheses, spectroscopic studies and host-guest chemistry

A series of phosphinocrown ether-containing gold(I) complexes, [Au(Ph₂P-b15c5)Cl] (1), [Au₂(μ-i-mnt)(Ph₂P-b15c5)₂] (2) and [Au₂(μ-dtc)(Ph₂P-b15c5)₂](PF₆) (3) (b15c5 = benzo-15-crown-5, i-mnt²⁻ = 1,1-dicyanoethylene-2,2-dithiolate, dtc⁻ = diethyldithiocarbamate) have been synthesized. Complexes 2 and 3 · NaPF₆ have also been structurally characterized. The emission bands at ca. 500-515 nm for 2 and 3 upon photo-excitation are tentatively assigned as derived from excited states of S → Au ligand-to-metal charge transfer (LMCT) origin. These complexes have been shown to serve as host for the specific binding of various metal cations.     

Dicopper(II) complexes showing DNA hydrolase activity and monomeric adduct formation with bis(4-nitrophenyl)phosphate

Ferromagnetic dicopper(II) complexes [Cu₂(μ-O₂CCH₃)(μ-OH)(L)₂(μ-L¹)](PF₆)₂, where L = 1,10-phenanthroline (phen), L¹ = H₂O in 1 and L = dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq), L¹ = CH₃CN in 2, are prepared and structurally characterized. Crystals of 1 and 2 belong to the monoclinic space group of P2₁/n and P2₁/m, respectively. The copper(II) centers display distorted square-pyramidal geometry having a phenanthroline base and two oxygen atoms of the bridging hydroxo and acetate group in the basal plane. The fifth coordination site has weak axially bound bridging solvent molecule H₂O in 1 and CH₃CN in 2. The Cu···Cu distances are 3.034 and 3.046 Å in 1 and 2, respectively. The complexes show efficient hydrolytic cleavage of supercoiled pUC19 DNA as evidenced from the mechanistic studies that include T4 DNA ligase experiments. The binuclear complexes form monomeric copper(II) adducts [Cu(L)₂(BNPP)](PF₆) (L = phen, 3; dpq, 4) with bis(4-nitrophenyl)phosphate (BNPP) as a model phosphodiester. The crystal structures of 3 and 4 reveal distorted trigonal bipyramidal geometry in which BNPP binds through the oxygen atom of the phosphate. The kinetic data of the DNA cleavage reactions of the binuclear complexes under pseudo- and true-Michaelis-Menten conditions indicate remarkable enhancement in the DNA hydrolysis rate in comparison to the control data.