Nitrosyl Complexes Research Articles

Proton-transfer reactions of Re(II)-nitrosyl complexes: Potentiometric studies, DFT and TD-DFT calculations

In the present work, we investigated the proton-transfer reactions of Re(II)-nitrosyl complexes bearing halides and nicotinic acid (Hnic) or 6,6́-dinicotinic acid (H2dinic) trans-coordinated to the core {ReNO}3+ by potentiometry and UV − Vis absorption spectroscopy in a mixture DMSO:H2O (1:1; v:v). The presence of Hnic and H2dinic in title complexes promotes a marked decrease in the acidity (higher pK values) compared to the non-coordinated pyridine-derived ligands. The UV − Vis measurements indicate that the absorption spectra of complexes do not show any dependence on the acidity of the medium and the number of non-coordinated carboxylic units. Time-dependent Density Functional Theory (TD-DFT) calculations are performed to understand the optical properties of complexes and their response upon deprotonation. TD-DFT studies are conducted with PBE1PBE in combination with LANL2TZ on rhenium and 6–311++G(d,p) on non-metal atoms within the C-PCM approach. This methodology shows a reasonable match between the measured and simulated spectra keeping the computational cost low. The nature of all absorption bands is ascribed to a ligand-metal-to-ligand-metal charge transfer (LMLMCT), in which negligible contribution from carboxylic units is detected.

Characteristic vibrational frequencies of osmium(ii) nitrosyl complexes probed by Raman spectroscopy and DFT calculations

Raman spectroscopy at variable temperature provides experimental frequencies for osmium(ii) nitrosyl complexes. Vibrational transitions are assigned using DFT calculations.

Visible-light NO photolysis of ruthenium nitrosyl complexes with N2O2 ligands bearing π-extended rings and their photorelease dynamics.

NO photorelease and its dynamics for two {RuNO}6 complexes, Ru(salophen)(NO)Cl (1) and Ru(naphophen)(NO)Cl (2), with salen-type ligands bearing π-extended systems (salophenH2 = N,N'-(1,2-phenylene)-bis(salicylideneimine) and naphophenH2 = N,N'-1,2-phenylene-bis(2-hydroxy-1-naphthylmethyleneimine)) were investigated. NO photolysis was performed under white room light and monitored by UV/Vis, EPR, and NMR spectroscopies. NO photolysis was also performed under 459 and 489 nm irradiation for 1 and 2, respectively. The photochemical quantum yields of the NO photolysis (ΦNO) of both 1 and 2 were determined to be 9% at the irradiation wavelengths. The structural and spectroscopic characteristics of the complexes before and after the photolysis confirmed the conversion of diamagnetic Ru(II)(L)(Cl)-NO+ to paramagnetic S = ½ Ru(III)(L)(Cl)-solvent by photons (L = salophen2- and naphophen2-). The photoreleased NO radicals were detected by spin-trapping EPR. DFT and TDDFT calculations found that the photoactive bands are configured as mostly the ligand-to-ligand charge transfer (LLCT) of π(L) → π*(Ru-NO), suggesting that the NO photorelease was initiated by the LLCT. Dynamics of NO photorelease from the complexes in DMSO under 320 nm excitation were investigated by femtosecond (fs) time-resolved mid-IR spectroscopy. The primary photorelease of NO occurred for less than 0.32 ps after the excitation. The rate constants (k-1) of the geminate rebinding of NO to the photolyzed 1 and 2 were determined to be (15 ps)-1 and (13 ps)-1, respectively. The photochemical quantum yields of NO photolysis (ΦNO, λ = 320 nm) were estimated to be no higher than 14% for 1 and 11% for 2, based on the analysis of the fs time-resolved IR data. The results of fs time-resolved IR spectroscopy and theoretical calculations provided some insight into the overall kinetic reaction pathway, localized electron pathway or resonance pathway, of the NO photolysis of 1 and 2. Overall, our study found that the investigated {RuNO}6 complexes, 1 and 2, with planar N2O2 ligands bearing π-extended rings effectively released NO under visible light.

Ruthenium-nitrosyl complexes as NO-releasing molecules, potential anticancer drugs, and photoswitches based on linkage isomerism.

The synthesis of new types of mono- and polynuclear ruthenium nitrosyl complexes is driving progress in the field of NO generation for a variety of applications. Light-induced Ru-NO bond dissociation in solution may involve transient linkage isomers MS1 (Ru-ON) and MS2 (Ru-η2-NO), which can be detected spectroscopically and analyzed computationally. The investigation of photoisomerization processes in the solid state may be useful for potential application of such complexes for data storage, photochromic or photomagnetic materials or even non-linear optics. Herein we describe the major developments in the synthesis of ruthenium nitrosyl complexes, their photoinduced linkage isomerization (PLI) processes, their NO release both in the solid state and in solution, and their application as potential anticancer drugs. Illustrative examples of such innovations made mainly in the last decade are provided.

Computational Spectroscopic Investigation of the Effect of Nitrosyl Bonding Type on Molecular Properties in Iron Tetracarbonyl Nitrosyl Complex

Computational Spectroscopic Investigation of the Effect of Nitrosyl Bonding Type on Molecular Properties in Iron Tetracarbonyl Nitrosyl Complex

A Ruthenium(II) Nitrosyl Complex of N-Dehydroacetic Acid-Sulfadiazine: Synthesis, DFT Studies and in silico ADME Properties

A sulpha drug-derived Schiff base ligand N-dehydroacetic acid-sulfadiazine was synthesized by treatment of dehydroacetic acid and sulfadiazine. A mononuclear Ru(II) nitrosyl complex of the Schiff base ligand cis-[RuCl2(NO)(PPh3)(dha-sdz)] was synthesized. The complex was characterized by spectral (IR, 1H NMR and UV/visible) techniques and physico-chemical studies. A cyclic voltammetric technique observed the electrochemistry of the complex compound. Therefore, the Gaussian 09 programme has been used to optimized molecular structure, electronic surface analysis, NLO properties through DFT approaches via mixed basis set at B3LYP/LANL2DZ level of theory. The 1H NMR spectrum of complex compound was computed with the GIAO method and correlated to experimental chemical shift. The TD-DFT based electronic absorption spectrum was computed using the PCM model. Additionally, the synthesized compound was predicting its in silico ADME properties, showing good physico-chemical and bioactivity. Finally, the in vitro antioxidant activity of the studied compound was monitored via two radical scavenging inhibitors.

Two-photon absorption-based delivery of nitric oxide from ruthenium nitrosyl complexes

Since the discovery of the numerous physiological roles exhibited by nitric oxide (NO), ruthenium nitrosyl (RuNO) complexes have been regarded as one of the most promising NO donors, stable, well tolerated by the body and capable of releasing NO locally and quantitatively, under light irradiation. This release can be achieved by two-photon absorption (TPA) processes, which allow the irradiation to be performed in the near infrared domain, where light has its maximum depth of penetration in biological tissues. This review provides a short introduction on the biological properties of NO, on RuNO complexes with photo-releasing capabilities, and on the origin of TPA properties in molecules. Then, the RuNO complexes with TPA capabilities are thoroughly discussed either as monometallic or polymetallic species.

Metalloligand-based coordination polymer embedding the nitrosyl ruthenium complex for photoactive materials with bound nitric oxide.

The stability of a photoactivated isonitrosyl state was boosted by confining a pre-designed bicarboxylate ligand with a ruthenium nitrosyl fragment in a 2D metal-organic framework. The novel Zn/Ru-based MOF, {Zn[RuNO(H2O)(inic)2(OH)2]2}·12H2O (inic = isonicotinate), was obtained with enhanced isonitrosyl stability by 30 K (up to 200 K) compared to the related ruthenium-only complex.

A five-coordinate Ni(I) complex supported by 1,4,7-triisopropyl-1,4,7-triazacyclononane.

An isolated Ni(II)-nitrosyl complex supported by the bulky tridentate 1,4,7-triisopropyl-1,4,7-triazacyclononane (iPr3TACN) ligand was obtained from the reaction of a Ni(II) dimethyl complex with NOPF6, suggesting the in situ formation of a Ni(I) species that reacts with the resulting NO product. Use of a π-acceptor ancillary isocyanide ligand led to the isolation and characterization of an uncommon 5-coordinate Ni(I) complex supported by the iPr3TACN ligand and tert-butylisocyanide.

Reaction of a {Co(NO)}8 complex with superoxide: Formation of a six coordinated [CoII(NO)(O2[rad]–)] species followed by peroxynitrite intermediate

A nitrosyl complex of cobalt(II) porphyrinate, [Co(F20TPP2−)(NO)], (F20TPPH2 = 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin) having {Co(NO)}8 configuration was synthesized and characterized by means of spectroscopic and structural analyses. Single crystal X-ray structure of the complex revealed the square pyramidal geometry around the cobalt center with a bent nitrosyl group. It reacts with superoxide (O2–) ion in CH2Cl2 at −40 °C to result in the corresponding nitrite (NO2−) complex. Involvement of a cobalt(II)-peroxynitrite intermediate is proposed in the course of the reaction. Moreover, spectroscopic studies suggested the formation of a transient six-coordinated [CoII(NO)(O2–)] species.

A new photoactivable NO-releasing {Ru-NO}6 ruthenium nitrosyl complex with a tetradentate ligand containing aniline and pyridine moieties.

A new type of photoactivable NO-releasing ruthenium nitrosyl complex, [Ru(EPBP)Cl(NO)], with a tetradentate ligand, N,N'-(ethane-1,2-diyldi-o-phenylene)-bis(pyridine-2-carboxamide) (= H2 EPBP) was synthesized. Single crystal X-ray crystallography revealed that the complex has a distorted octahedral coordination geometry and NO is positioned at cis to Cl- ion. NO-photolysis was observed under a white room light. The photodissociation of Ru-NO bond was identified by various techniques including X-ray crystallography, IR, UV/Vis absorption, electron paramagnetic resonance (EPR), and NMR spectroscopies. Quantum yields for the NO-photolysis of the complex in CH3 OH, CHCl3 , DMSO, CH3 CN, and CH3 NO2 were measured to be 0.19-0.36 with 400 (±5) nm excitation. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were performed to understand the details of the photodissociation of the complex. The calculations suggest that the NO photolysis is most likely initiated by the electronic transition from the aniline moiety π MOs (π (aniline)) of the EPBP2- chelating ligand to the π-antibonding MO of Ru-NO (π*(Ru-NO)). Experimental and theoretical investigations indicate that the EPBP2- ligand provides an effective platform forming ruthenium nitrosyl complexes useful for NO-photoreleasing.

Photo controlled release of nitric oxide (NO) from amphiphilic and nanoscale vesicles based ruthenium nitrosyl complex: NO release and cytotoxicity studies

Nitric oxide (NO) is an important gaseous signaling molecule. Precise spatiotemporal control release of NO for therapeutic applications is still challenging. We report herein a new amphiphilic and nano scale vesicles based NO-delivery platform that is capable of light-controlled NO release. 1.Ru-NO was incorporated into the lipid bilayers to form nanoscale vesicles (Lip-1.Ru-NO) to make it bio-compatible and 100% water soluble. The liposome Lip-1.Ru-NO gradually released NO in blue light over a period of 120 min, with relatively high efficiency as compared to 1.Ru-NO in CH3CN-water mixture. Amount of NO release from liposomes could be easily controlled and modulated by changing the concentration of 1.Ru-NO in nano scale vesicles. Light triggered controlled NO release, water solubility, and non-toxic nature of the complex before and after NO release are fulfilled by incorporation of amphiphilic ruthenium complex in to the vesicles surface.

Can a Nitrosyl of a Mn(II)-Porphyrin Complex Release Nitroxyl/HNO?

In general, the nitrosyl complexes of Mn(II)-porphyrinate having the {Mn(NO)}6 configuration are not considered as HNO or nitroxyl (NO-) donors because of [MnI-NO+] nature. A nitrosyl complex of Mn(II)-porphyrin, [Mn(TMPP2-)(NO)], 1 [TMPPH2 = 5,10,15,20-tetrakis-4-methoxyphenylporphyrin], is shown to release HNO in the presence of HBF4. It is evidenced from the characteristic reaction of HNO with triphenylphosphine and isolation of the [(TMPP2-)MnIII(H2O)2](BF4), 2. This is attributed to the fact that H+ from HBF4 polarizes the NO group whereas the BF4- interacts with metal ion to stabilize the Mn(III) form. These two effects cooperatively result in the release of HNO from complex 1. In addition, complex 1 behaves as a nitroxyl (NO-) donor in the presence of [Fe(dtc)3] (dtc = diethyldithiocarbamate anion) and [Fe(TPP)(Cl)] (TPP = 5,10,15,20-tetraphenylporphyrinate) to result in [Fe(dtc)2(NO)] and [Fe(TPP)(NO)], respectively.

Blue-to-red light triggered nitric oxide release in cytotoxic/cytostatic ruthenium nitrosyl complexes bearing biomimetic ligands

The nitrosyl complexes trans(L,L)-[RuNO(L)2Cl3] (L = indazole (I) and imidazole (II)) were synthesized and comprehensively characterized including by single crystal X-ray diffraction. Both compounds exhibit light-induced NO release under blue or green light (445, 532 nm) irradiation of DMSO solutions, complex (I) also shows NO release under red 638 nm irradiation, which is in the range of phototherapeutic window (600–1100 nm). The photolysis was investigated by spectroscopic (UV–vis, IR, EPR) and electrochemical (CV) techniques, and it was shown that NO can be activated by both light excitation or electrochemically. Performed DFT calculations allow to reveal possible charge transfers responsible for the NO activation. The dynamics of ruthenium species after irradiation consists of a transformation of [Ru3+(DMSO)(L)2Cl3] complex to a more stable [Ru2+(DMSO)(L)2Cl3]− product. The cytotoxic test of both complexes against breast adenocarcinoma cell line MCF-7 shows, imidazole complex (II) exhibits cytostatic action at concentrations higher than 25 µM, while indazole complex (I) is highly cytotoxic with IC50 value of 3.1 ± 0.6 µM, which is an order of magnitude higher than the activity of cisplatin. New knowledge open the prospects for the design and synthesis of prominent compounds trans(L,L)-[RuNO(L)2Cl3], where the nature of L influences the photo-sensitive and cytotoxic properties of the resulted complexes.

Photoinduced linkage isomers in a model ruthenium nitrosyl complex: Identification and assignment of vibrational modes

Photoinduced NO-linkage isomers were investigated in the solid state of labelled trans-[Ru(14/15NO)(py4)F](ClO4)2 complex by combined IR-spectroscopy and DFT calculations. Based on the experimental data and the DFT calculations of this isotopically labelled 14/15NO nitrosyl compound, we present a complete assignment of the vibrational bands of three nitrosyl linkage isomers in a range from 4000 to 200 cm-1. The calculated IR-spectra match well with the experimental data allowing reliable assignment of the vibrational bands. The structural change from the Ru-NO (GS) to the Ru-ON (MS1) and Ru-η2-(NO) (MS2) linkage configuration leads to the downshift of the ν(NO) and ν(Ru-(NO)) bands, and a corresponding increase of the energy of the ν(Ru-F) band. The shift of the bands corresponds to the change of the Ru-(NO) and Ru-F bond lengths: increase of the Ru-(NO) bond length leads to the decrease of the energy of the ν(Ru-(NO)) band; decrease of the Ru-F bond length leads to the increase of the energy of the ν(Ru-F) band. These observations can be extrapolated to the family of related nitrosyl complexes and therefore be used for the qualitative prediction of the Ru-(NO) and Ru-Ltrans-to-NO bond lengths of different linkage isomers in the framework of one complex. While the formation of linkage isomers is a reversible process, long-time irradiation sometimes induces irreversible reactions such as the release of NO. Here, we show that the photolysis of trans-[Ru(14/15NO)(py4)F](ClO4)2 in KBr pellets may lead to the release of nitrous oxide N2O, conceivably through the formation of a {Ru-(κ2-ONNO)} intermediate.

Anomalous magnetism of uranium(IV)-oxo and -imido complexes reveals unusual doubly degenerate electronic ground states

Anomalous magnetism of uranium(IV)-oxo and -imido complexes reveals unusual doubly degenerate electronic ground states

Two‐Photon Absorption Properties in “Push‐Pull” Ruthenium Nitrosyl Complexes with various Fluorenylterpyridine‐Based Ligands

AbstractUsing the compound [RuII(FT)(bipy)(NO)](PF6)3 (FT is the electron‐rich 4’‐(2‐fluorenyl)‐2,2’:6’,2’’‐terpyridine ligand and bipy is 2–2’bipyridine) as a reference, two new compounds are presented in which carbon‐carbon double and triple bonds are inserted between the fluorenyl substituent and the terpyridine to provide an extended conjugation path. The electronic properties of the three complexes are compared experimentally by UV‐visible spectroscopy and computationally by means of the density functional theory. All of them exhibit a capability for NO release under irradiation on their low‐energy transition located in the 400–500 nm range, with a quantum yield around 0.01. Their two‐photon absorption (TPA) cross sections are investigated by the Z‐scan technique at λ=800 nm. While the reference compound exhibits a cross‐section equal to 108 GM, the introduction of double and triple bonds leads to increased cross‐sections equal to 131 GM and 150 GM, respectively. These values are discussed in reference to the two‐level model in use for “push‐pull” dipolar TPA chromophores.

In celebration of the 70thbirthday of Peter Klüfers

In celebration of the 70^thbirthday of Peter Klüfers

Catalytic reduction of nitrate by an oxidorhenium (V) complex

The previously published oxidorhenium(V) complex [ReOCl(L1)2] (2), equipped with the bidentate phenol-dimethyloxazoline ligand HL1 (2-(4,4-dimethyl-4,5-dihydro-1,3-oxazol-2-yl)-phenol), shows catalytic activity for the reduction of nitrate to nitrite under mild, ambient and aqueous conditions. The reaction operates under an oxygen atom transfer (OAT) mechanism, using dimethyl sulfide SMe2 (DMS) as oxygen acceptor. Experiments with catalytic amounts of 2 and labelled 15NO3– proved the full reduction of 15NO3– to 15NO2– by 15N NMR spectroscopy.For the second reduction step of nitrite NO2–, we have evidence for a single electron reduction to yield paramagnetic NO, as from one nitrate reduction experiment the paramagnetic cis-dioxidorhenium(VI) complex [Re(O)2(L1)2] (3) could be isolated and characterized by single-crystal X-ray diffraction analysis. Such a single electron reduction of nitrite NO2– would yield NO and complex 3 as the oxidation product.In a stoichiometric experiment of 2, 15NO3– and DMS, nitrous oxide 15N2O could be detected as the only 15N containing product by 15N NMR spectroscopy, proving that further reduction beyond NO is possible with pre-catalyst 2. The rhenium species responsible for the reduction to N2O is currently unknown. Most likely, N2O is formed via an intermediate rhenium nitrosyl complex. Experimental data was gathered by 1H and 15N NMR, IR- and UV–Vis spectroscopy, HR-ESI mass spectrometry, X-ray crystallography, and supported by theoretical computations (DFT).

Investigation of the interaction of the cationic nitrosyl iron complex [Fe(SC(NH2)2)2(NO)2]+ with molecular oxygen

The interaction of a nitrosyl iron complex with molecular oxygen was studied with Density Functional Theory. On the basis our analysis of the geometric and electronic structure of the complex, three variants of coordination of the oxygen molecule on it were investigated: the attachment of molecular oxygen to the iron center, an insertion of oxygen in between the Fe and NO and the bridging of two nitrosyl ligands. All of the coordination complexes require approximately the same amount of energy input to form. In all of the oxygen-enriched nitrosyl complexes we calculated, the doublet state was energetically below the quartet state. Next, we considered decomposition pathways since the products of all of these oxygen-attaching pathways may then decompose further. The result of this decomposition is either the release of nitrogen monoxide or the release of nitrogen dioxide. For all the three processes, transition and intermediate states were found, as well as the final products. The potential energy surfaces of the most important reactions were plotted. Finally, UV spectra of all the possible products of the oxidation of complex by molecular oxygen were calculated.