N-coordinated Complexes Research Articles

Synthesis and luminescent properties of five-six-membered bis(metallacyclic) platinum(II) complexes bearing polypyridine alkynes

A series of five-six-membered bis(metallacyclic) Pt(II) complexes bearing a 2,2′-bipyridine (BPY) or 2,2′:6′,2"-terpyridine (TPY) ethynyl ligand were synthesized and characterized. The structures of N^C*N-coordinated Pt(II) complexes (−)-1 and (−)-5 were confirmed by single crystal X-ray diffraction, displaying a slightly distorted square-planar coordination environment around the Pt(II) centers. Compared to N^N*C-coordinated Pt(II) derivatives ((−)-2, (−)-4 and (−)-6), N^C*N-coordinated complexes ((−)-1, (−)-3 and (−)-5) demonstrate a more significant AIE property with a sharp luminescence variation in response to water content. In addition, due to the existence of the pendent BPY or TPY unit, N^C*N-coordinated Pt(II) complexes show a luminescence response to Zn2+ ions. Cytotoxicity and cell imaging of luminescent five-six-membered bis(metallacyclic) Pt(II) complexes with polypyridine alkynes have been evaluated.

Mechanochromism and circularly polarized luminescence of chiral cyclometalated platinum(II) complexes with different configurations and aggregated forms

Using a new synthesis method, we have prepared two different coordination configurations of chiral cyclometalated N^C^N-coordinated and C^N-coordinated Pt(II) complexes by controlling the Cl− source. Single-crystal X-ray diffraction determines the tridentate and bidentate structures. All N^C^N-coordinated and C^N-coordinated Pt(II) complexes emit green-yellow light in CH2Cl2 solutions. Square-planar N^C^N-Coordinated complexes (−)-1 and (−)-2 show remarkable aggregation-induced emission behaviors in mixed CH2Cl2/n-hexane solutions with the emission quantum yield (Φem) intensified significantly. In addition, the luminescent color could change from green-yellow to red by varying the volumetric fraction of n-hexane. Complex (−)-2 grafted with long alkyl chains could form helical stacking aggregates, inducing enhanced ECD signals and measurable CPL activity. The yellow and orange solids of complex (−)-1 can be separated, and a high-contrast mechanochromic luminescence is found for the yellow form. Furthermore, the potential utility has been attempted in anti-counterfeiting applications based on the yellow solid of (−)-1. This study provides a new design strategy for the preparation of chiral cyclometalated Pt(II) complexes with specific configurations and aggregated forms that have various optical and electronic properties.

Photophysical Study on the Rigid Pt(II) Complex [Pt(naphen)(Cl)] (Hnaphen = Naphtho[1,2-b][1,10]Phenanthroline and Derivatives.

The electrochemistry and photophysics of the Pt(II) complexes [Pt(naphen)(X)] (Hnaphen = naphtho[1,2-b][1,10]phenanthroline, X = Cl or C≡CPh) containing the rigid tridentate C^N^N-coordinating pericyclic naphen ligand was studied alongside the complexes of the tetrahydro-derivative [Pt(thnaphen)(X)] (Hthnaphen = 5,6,8,9-tetrahydro-naphtho[1,2-b][1,10]phenanthroline) and the N^C^N-coordinated complex [Pt(bdq)(Cl)] (Hbdq = benzo[1,2-h:5,4-h’]diquinoline. The cyclic voltammetry showed reversible reductions for the C^N^N complexes, with markedly fewer negative potentials (around −1.6 V vs. ferrocene) for the complexes containing the naphen ligand compared with the thnaphen derivatives (around −1.9 V). With irreversible oxidations at around +0.3 V for all of the complexes, the naphen made a difference in the electrochemical gap of about 0.3 eV (1.9 vs. 2.2 eV) compared with thnaphen. The bdq complex was completely different, with an irreversible reduction at around −2 V caused by the N^C^N coordination pattern, which lacked a good electron acceptor such as the phenanthroline unit in the C^N^N ligand naphen. Long-wavelength UV-Vis absorption bands were found around 520 to 530 nm for the C^N^N complexes with the C≡CPh coligand and were red-shifted when compared with the Cl derivatives. The N^C^N-coordinated bdq complex was markedly blue-shifted (493 nm). The steady-state photoluminescence spectra showed poorly structured emission bands peaking at around 630 nm for the two naphen complexes and 570 nm for the thnaphen derivatives. The bdq complex showed a pronounced vibrational structure and an emission maximum at 586 nm. Assuming mixed 3LC/3MLCT excited states, the vibronic progression for the N^C^N bdq complex indicated a higher LC character than assumed for the C^N^N-coordinated naphen and thnaphen complexes. The blue-shift was a result of the different N^C^N vs. C^N^N coordination. The photoluminescence lifetimes and quantum yields ΦL massively increased from solutions at 298 K (0.06 to 0.24) to glassy frozen matrices at 77 K (0.80 to 0.95). The nanosecond time-resolved study on [Pt(naphen)(Cl)] showed a phosphorescence emission signal originating from the mixed 3LC/3MLCT with an emission lifetime of around 3 µs.

A DFT study of cis-[Ru(NO)(NO2)bpy(dye)2]n+ complexes as NO donors

The synthesis and characterization of a new complex, cis-[Ru(NO)(NO2)bpy(AO)2](PF6)2, was reported, and the release of NO from ruthenium-nitrosyl complexes with dye ligands was investigated using DFT and TDDFT methods. The complexes are cis-[Ru(NO)(NO2)bpy(dye)]n+, where the dye is either proflavine (1), acridine orange (2), neutral red (3), resorufin (4), thionol (5), or methylene violet (Bernthsen) (6). The optimized structures are in agreement with the experimental data of analogue complex from the literature. Simulated UV–Visible spectrum of complex 2 showed good agreement with the experimental results. The calculated electron affinities (EA) indicated that the N-coordinated complexes 1–3 should be more easily reduced and that this reduction weakens the Ru–NO bond, thus facilitating the NO release. Reduced complexes (Ru-NO0) presented lower bond dissociation energies (BDE) than the complexes (Ru-NO+). Complexes 1–3 showed the lowest BDE. This suggests a lower energy cost to release NO, and therefore, the N-coordinated complexes are the most promising NO donors among the investigated complexes.

Thermal Properties and Crystal Structures of Rhenium(I) Carbonyl Complexes with Tridentate Ligands: Preparation of Rhenium-Containing Ionic Liquids.

Although the coordination chemistry of rhenium complexes is a rapidly expanding research field, little is known about their thermal properties. In this study, we synthesized several rhenium tricarbonyl complexes with tridentate ligands (L) having S or N as donor atoms, fac-[Re(CO)3L]X (X = Tf2N [= bis(trifluoromethanesulfonyl)amide)], PF6) and fac-[Re(CO)3LCl], and investigated their thermal properties and crystal structures. The Tf2N salts were room temperature ionic liquids. The S-coordinated complexes, having longer coordination bonds, were less thermally stable than the N-coordinated complexes. Even though fac-[Re(CO)3LCl] are bidentate coordination complexes, they were thermally more stable than the isomeric tridentate complexes fac-[Re(CO)3L]Cl.

Chloropalladated tetranuclear and copper(I) complexes of propargylamines [RC≡CCH2NC4H8NCH2C≡CR

The reactions of propargylamines 1,4-bis(3-phenylprop-2-yn-1-yl)piperazine (1) and 1,4-bis(3-(trimethylsilyl)prop-2-yn-1-yl)piperazine (2) with PdCl2 and CuI is described. 1,4-Bis(3-phenylprop-2-yn-1-yl)piperazine reacts with one equivalent of PdCl2 to afford κ2-N,N-coordinated complexes [PdCl2{Me3SiCCCH2NC4H8NCH2C≡CSiMe3-κ2-N,N] (3) and [PdCl2{Me3SiCCCH2NC4H8NCH2C≡CSiMe3}-κ2-N,N] (4). The reactions of 1 and 2 with two equivalents of PdCl2 yielded rare chloropalladated tetranuclear complexes [Pd4(μ-Cl)4(PhC=C(Cl)CH2NC4H8NCH2(Cl)C=CPh)2] (5) and [Pd4(μ-Cl)4(Me3SiC=C(Cl)CH2NC4H8NCH2(Cl)C=CSiMe3)2] (6), respectively, resulting from the trans nucleophilic addition of chloride ion onto the electrophilic CC bond. The reactions of 1 and 2 with two equivalents of CuI produced 2-D coordination polymers [{Cu2(μ-I)}2(PhC≡C–CH2NC4H8NCH2C≡CPh)]n (7) and [{Cu2(μ-I)}2(Me3SiCCCH2NC4H8NCH2C≡CSiMe3)]n (8), respectively. Similar reactions in 1:1 M ratios produced dimeric complexes [Cu2(μ-I)2(PhC≡CCH2NC4H8NCH2C≡CPh)2] (9) and [Cu2(μ-I)2(Me3SiCCCH2NC4H8NCH2C≡CSiMe3)2] (10), respectively. The structures of compounds 3, 5 and 7 have been established by single crystal X-ray analysis.

Matrix isolation and ab initio study on HCN/CO2 system and its radiation-induced transformations: Spectroscopic evidence for HCN⋯CO2 and trans-HCNH⋯CO2 complexes.

Spectroscopic characteristics and X-ray induced transformations of the HCN⋯CO2 complex in solid Ar and Kr matrices were studied by FTIR spectroscopy and ab initio calculations at the CCSD(T) level. The complex was prepared by deposition of the HCN/CO2/Ng gas mixtures (Ng = Ar or Kr). The comparison of the experiment and calculations prove formation of a linear, H-bonded NCH⋯OCO complex with a substantial red shift of the C-H stretching band and a blue shift of the H-C-N bending band in respect to the monomer. This result is in contrast with the previous gas-phase observations, where only T-shape complex was found. Irradiation of deposited matrices leads to formation of CN radicals and HNC molecules and subsequent annealing results in appearance of H2CN and trans-HCNH in both matrices plus HKrCN in the case of Kr. In the presence of CO2, the strongest absorption of trans-HCNH radical demonstrates an additional blue-shifted (by 6.4 cm-1) feature, which was assigned to the N-coordinated complex of this radical with CO2 on the basis of comparison with calculations. To our knowledge, it is the first experimentally observed complex of this radical. No evidence was found for HKrCN⋯CO2 complex, which was explained tentatively by steric hindrance.

Platinum(II) as bifunctional linker in antibody-drug conjugate formation: coupling of a 4-nitrobenzo-2-oxa-1,3-diazole fluorophore to trastuzumab as a model.

The potential of platinum(II) as a bifunctional linker in the coordination of small molecules, such as imaging agents or (cytotoxic) drugs, to monoclonal antibodies (mAbs) was investigated with a 4-nitrobenzo-2-oxa-1,3-diazole (NBD) fluorophore and trastuzumab (Herceptin™) as a model antibody. The effect of ligand and reaction conditions on conjugation efficiency was explored for [Pt(en)(L-NBD)Cl](NO3 ) (en=ethylenediamine), with L=N-heteroaromatic, N-alkyl amine, or thioether. Conjugation proceeded most efficiently at pH 8.0 in the presence of NaClO4 or Na2 SO4 in tricine or HEPES buffer. Reaction of N-coordinated complexes (20 equiv) with trastuzumab at 37 °C for 2 h, followed by removal of weakly bound complexes with excess thiourea, afforded conjugates with an NBD/mAb ratio of 1.5-2.9 that were stable in phosphate-buffered saline at room temperature for at least 48 h. In contrast, thioether-coordinated complexes afforded unstable conjugates. Finally, surface plasmon resonance analysis showed no loss in binding affinity of trastuzumab after conjugation.

Heteroleptic ruthenium complexes with 6-(ortho-substituted phenyl)-2,2′-bipyridine derivatives

Coordination chemistry of 2,2′-bipyridine bearing an ortho-substituted phenyl group at the 6-position, i.e., 6-(o-X-phenyl)-2,2′-bipyridine (MeO-L: X = OMe; Me2N-L: X = NMe2) with [Ru(ttpy)Cl3] (ttpy = 4′-(4-tolyl)-2,2′;6′,2″-terpyridine) was investigated. The reaction of MeO-L and [Ru(ttpy)Cl3] in the presence of N-methylmorpholine afforded demethylated, O-coordinated complex [Ru(O-L)(ttpy)]+ (O-L: X = O) as well as the cyclometalated, C-coordinated complex [Ru(MeO-L)(ttpy)]+. On the other hand, reaction of Me2N-L and [Ru(ttpy)Cl3] in the presence of N-methylmorpholine afforded only N-coordinated complex [Ru(Me2N-L)(ttpy)]2+. The crystal structures, spectroscopic and redox properties were examined supplemented by DFT calculations. The spectroscopic and redox properties of RuN are more or less similar to those of [Ru(ttpy)Cl3]. On the other hand, the properties of RuC and RuO are mutually similar but significantly different from those of RuN. The anionic ligand in RuC and RuO raises the HOMO energy as compared to the neutral ligand in RuN, which is manifested in negatively shifted redox potentials, particularly the oxidation potentials, and thus, the red shift in the visible absorption band. Relevance of these complexes to sensitizers for dye-sensitized solar cells is briefly discussed.

Synthesis, Structure, Photophysics, and a DFT Study of Phosphorescent C*N∧N- and C∧N∧N-Coordinated Platinum Complexes

The reaction of N,N-diphenyl-2,2'-bipyridin-6-amine (L1) and N,N-diphenyl-6-(1H-pyrazol-1-yl)pyridin-2-amine (L2) with K2PtCl4 produced C*N(∧)N-coordinated cycloplatinated compounds with a five-six fused metallacycle 1a and 2a, respectively, which were then converted into their phenylacetylide derivatives 1b and 2b, respectively. Similar reactions starting from 2-phenyl-6-(1H-pyrazol-1-yl)pyridine (L3) produced C(∧)N(∧)N-coordinated platinum complexes 3a and 3b with a five-five-fused metallacycle. The structures of 1a, 1b, 2b, 3a, and 3b were determined by X-ray crystallography. The C*N(∧)N-coordinated platinum complexes are closer to a square geometry, whereas the C(∧)N(∧)N-coordinated complexes display a nearly perfect planar geometry. The π···π interactions were revealed in the crystal packing for 1a, 2b, and 3a with a π···π contact of 3.450, 3.422, and 3.414 Å, respectively. Two conformers were revealed in the crystal structure of 2b, one with the phenyl ring of the phenylacetylide being approximately parallel with the coordination plane and the other with the phenyl ring being approximately perpendicular to the coordination plane. Both 1a and 1b are weakly emissive in the red region. Complexes 2a and 3a are also weakly emissive, but their acetylide derivatives 2b and 3b emitted strongly green light at room temperature with quantum yields of 43 and 62%, respectively. DFT/TDDFT calculations were performed to elucidate the nature of their electronic transitions. The calculations suggested that lowest singlet and triplet excited states are characteristic of a mixed state involving one or more charge-transfer transitions such as ILCT, MLCT, and LLCT.

Highly Luminescent Tridentate N∧C*N Platinum(II) Complexes Featured in Fused Five–Six-Membered Metallacycle and Diminishing Concentration Quenching

A series of cyclometalating ligands, N-phenyl-N-(3-(pyridin-2-yl)phenyl)pyridin-2-amine (L1), N-(3-(1H-pyrazol-1-yl)phenyl)-N-phenylpyridin-2-amine (L2), N-phenyl-N-(3-(quinolin-2-yl)phenyl)pyridin-2-amine (L3), N-phenyl-N-(3-(pyridin-2-yl)phenyl)quinolin-2-amine (L4), N-(3-(isoquinolin-1-yl)phenyl)-N-phenylpyridin-2-amine (L5), and N-phenyl-N-(3-(pyridin-2-yl)phenyl)isoquinolin-1-amine (L6), were synthesized, which reacted with K(2)PtCl(4) in glacial acetic acid to produce N^C*N-coordinated platinum(II) complexes featured in a fused five-six-membered metallacycle, 1-6, respectively. The structures of 1, 3, 4, and 6 were determined by single crystal X-ray crystallography. The square geometries of the complexes are improved when compared with those of the N^C^N-coordinated complexes as the bite angles for the platinum in N^C*N-coordinated complexes 1, 3, and 4 are increased. The Pt-C bonds (1.94-1.95 Å) are shorter than those of C^N^N-coordinated platinum complexes but longer than those found for N^C^N-coordinated platinum complexes. With the increase of the steric interaction, the distortion of the molecules from a planar coordination geometry becomes more and more severe from 1 to 3 to 4 and 6, and in 6, the N-phenyl ring has to stand up on the coordination sphere to minimize the steric interaction with the N-isoquinolyl ring. The photophysical properties of the complexes were studied, and their absorption and emission spectra were interpreted by relating to the structural features revealed by the X-ray crystal structures and the orbital characters predicted by DFT calculations. All complexes are emissive in fluid at room temperature, and the quantum yields (up to 0.65) are comparable to those of highly emissive N^C^N-coordinated platinum complexes. Self-quenching was not observed in the concentration range of 10(-6) to 10(-4) M. Large rigidochromic shifts for the emissions of 2, 4, and 6 upon cooling from room temperature to rigid glass (77 K) were observed. Two different triplet states that control the emissions were proposed to account for the photophysical properties of 6.

The reactivity of TMSN 3 with ruthenium cyclopropenyl complexes containing different ligands and different substituent at Cγ

Ruthenium vinylidene complexes 2a– 2c containing indenyl and bidentate dppe ligands can be obtained in efficient yields. Treatment of the cationic ruthenium vinylidene complexes with n-Bu 4NOH in acetone yields the neutral cyclopropenyl products ( η 5-C 9H 7)(dppe)Ru–C C(Ph)CHR ( 3) ( 3a, R = Ph; 3b, R = CN; 3c, R = p-C 6H 4–CN) via the deprotonation reaction. Reaction of complexes 3a and 3c with Me 3SiN 3 (TMSN 3) the N-coordinated complexes 4a and 4c can be obtained as stable products. Complex 3b containing CN group at Cγ in the cyclopropenyl ring reacts with TMSN 3 yielded the tetrazolate complex 5b. Similar cyclopropenyl products containing indenyl and two triphenylphosphine ligands 3′ can also be synthesized. Reaction of complex 3b′ with TMSN 3 also yielded the tetrazolate complex as the major product. And the minor products are [Ru]–N 3 and organic compound 6b. Reaction of 3a′ and 3c′ with TMSN 3 yielded [Ru]–N 3. The corresponding organic products can also be obtained via the N 3 − attacking the metal center in the N-coordinated complexes 4a′ and 4c′.

Luminescent Platinum Complexes with Terdentate Ligands Forming 6-Membered Chelate Rings: Advantageous and Deleterious Effects in N∧N∧N and N∧C∧N-Coordinated Complexes

Platinum(II) complexes of the form [PtL(n)Cl](+) are reported, containing the N--N--N-coordinating ligands 2,6-di(8-quinolyl)pyridine (L(1)), 2,6-di(8-quinolyl)-4-methoxypyridine (L(2)), or 2,6-di(7-aza-indolyl)-pyridine (L(3)). Metathesis of the chloride co-ligand in [PtL(1)Cl](+) can be accomplished under mild conditions, as exemplified by the formation of the complexes [PtL(1)OMe](+) and [PtL(1)(C[triple bond]C-tfp)](+), in which L(1) remains bound as a terdentate ligand {HC[triple bond]C-tfp = 3,5-bis(trifluoromethyl)-phenylacetylene}. An N--C--N-coordinated, cyclometalated analogue of [PtL(1)Cl](+) has also been prepared, namely, PtL(4)Cl where HL(4) is 1,3-di(8-quinolyl)benzene. The common feature among the six new complexes described here is that they contain 6-membered chelate rings, rather than the usual 5-membered rings that form when more common N--N--N ligands, such as 2,2':6',2''-terpyridine (tpy), bind to Pt(II). All the quinolyl-based complexes are phosphorescent in solution at room temperature, with quantum yields up to 4%. This contrasts with the well-established lack of emission from [Pt(tpy)Cl](+) under these conditions. Density functional theory calculations suggest that the improvement may stem, at least in part, from the relief of ring strain associated with the larger chelate ring size, leading to a more optimal bite angle at the metal, close to 180 degrees , and hence to a stronger ligand field. Consideration of the luminescence parameters, including data at 77 K, together with absorption and electrochemical data and the results of TD-DFT calculations, suggests that the lowest-lying singlet states have metal-to-ligand charge-transfer (MLCT) character, but that the triplet state from which emission occurs has more predominant ligand-centered character. The azaindolyl complex [PtL(3)Cl](+) is not emissive at room temperature, apparently owing to a particularly small radiative rate constant. The cyclometalated complex PtL(4)Cl emits at lower energy than [PtL(1)Cl](+) but, in this case, the luminescence quantum yield is inferior to related complexes with 5-membered chelate rings.

Cyclometalated Platinum(II) Complexes of Pyrazole-Based, N∧C∧N-Coordinating, Terdentate Ligands: the Contrasting Influence of Pyrazolyl and Pyridyl Rings on Luminescence

1,3-Bis(1-pyrazolyl)-5-methyl-benzene, HL(2), undergoes cyclometalation at the C(2) position upon reaction with K(2)PtCl(4), to generate an N=C=N-coordinated complex, PtL(2)Cl. This compound is luminescent in degassed solution at 298 K, emitting in the blue region of the spectrum on the microsecond time scale (lambda(max) = 453 nm, tau = 4.0 micros, Phi(lum) = 0.02, in CH(2)Cl(2)). Compared to the analogous complex Pt(dpyb)Cl that incorporates pyridyl rather than pyrazole rings {dpybH = 1,3-di(2-pyridyl)-benzene}, the excited state is displaced to higher energy by 1700 cm(-1). This effect is rationalized in terms of the poorer pi-acceptor nature of pyrazolyl compared to pyridyl rings, leading to destabilization of the lowest unoccupied molecular orbital, which is largely localized on the heteroaromatic rings in both cases. Cyclic voltammetry and density functional theory calculations reinforce this interpretation, and suggest that the lowest-energy excited state is probably best described as heavily mixed pi(L)/d(Pt)/p(Cl) --> pi*(L) (IL/MLCT/LLCT) in character. 5-Aryl-substituted analogues of HL(2) are accessible in three steps from 1,3,5-tribromobenzene by Pd-catalyzed cross-coupling with aryl boronic acids, followed by copper-catalyzed bromo-iodo exchange, and subsequent amination with pyrazole under relatively mild conditions also catalyzed by copper. The corresponding Pt(II) complexes display red-shifted and more intense luminescence compared to PtL(2)Cl. Ligands incorporating one pyrazole and one pyridyl ring are also accessible; for example, 1-(1-pyrazolyl)-3-(2-pyridyl)benzene, HL(6). Their complexes are highly luminescent in solution; for example, for PtL(6)Cl, lambda(max) = 487 nm, tau = 6.9 micros, Phi(lum) = 0.55, in dilute solution in CH(2)Cl(2). At elevated concentrations, PtL(6)Cl displays an additional excimeric emission band that is substantially blue-shifted compared to that displayed by Pt(dpyb)Cl (bands centered at 645 and 695 nm, respectively), indicating that the presence of the pyrazole ring destabilizes the excimer. The introduction of a methyl substituent into the central aryl ring of such complexes is sufficient to eliminate the excimer emission.

Synthesis of Pd(II) 1-alkylperimidine complexes as efficient catalysts for Suzuki reactions involving arylchlorides

Three palladium(II) complexes of the type [PdCl2(PPh3)L] (L—1-alkylperimidine) have been prepared by reactions of [PdCl2(PPh3)]2 with 1-alkylperimidine. The complexes were characterized by conventional spectroscopic methods and elemental analyses. The incorporation of N-coordinated perimidine complexes of palladium(II) gave high catalytic activity in the Suzuki coupling deactivated aryl chloride substrates.

New neutral and cationic η 6-arene ruthenium complexes with phosphine and amine ligands: syntheses and molecular structures of [(η 6- p-cymene)Ru(NH 2CH 2C 6H 5)Cl 2], [(η 6-C 6Me 6)Ru(PPh 2Py)Cl 2] and [(η 6-C 6Me 6)Ru(PPh 2Py)Cl] +

The complex [{(η 6- p-cymene)Ru(μ-Cl)Cl} 2] ( 1) reacts with benzylamine to give a neutral N-coordinated complex of the type [(η 6- p-cymene)Ru(NH 2CH 2C 6H 5)Cl 2] ( 2). The complex [(η 6- p-cymene)Ru(PPh 3)Cl 2] ( 3) reacts with amine ligands to yield chiral complexes [(η 6- p-cymene)Ru(PPh 3)(NH 2-R)Cl] + [R = CH 2C 6H 5 ( 4a), p-ClC 6H 4 ( 4b), p-NO 2C 6H 4 ( 4c)]. Complexes 1 and 3 react with N,N-donor chelating 1,2-phenylenediamine (PDA) giving cationic complexes 5 and 6, respectively. The complex [(η 6-C 6Me 6)Ru(μ-Cl)Cl] 2 ( 7) reacts with diphenyl-2-pyridylphosphine to yield a neutral P-coordinated ruthenium(II) complex [(η 6-C 6Me 6)Ru(PPh 2Py)Cl 2] ( 8) as well as a cationic P,N-chelating complex [(η 6-C 6Me 6)Ru(PPh 2Py)Cl] + ( 9). The complex 9 undergoes substitution reactions with acetonitrile and 1,1-diphenyl-2-propyn-1-ol ligands. These complexes were characterized by FT-IR and FT-NMR spectroscopy as well as by analytical data. The molecular structures of the representative complexes [(η 6- p-cymene)Ru(NH 2CH 2C 6H 5)Cl 2] ( 2), [(η 6-C 6Me 6)Ru(PPh 2Py)Cl 2] ( 8) and [(η 6-C 6Me 6)Ru(PPh 2Py)Cl]BF 4 ( 9) were established by single-crystal X-ray diffraction studies.

Complexed nitrogen heterosuperbenzene: the coordinating properties of a remarkable ligand.

Tetra-peri-(tert-butyl-benzo)-di-peri-(pyrimidino)-coronene 1, the parent compound of the nitrogen heterosuperbenzene family N-HSB, is employed as a novel monotopic ligand in the formation of [Pd(eta3-C3H5)(1)]PF6 2 and [Ru(bpy)2(1)](PF6)2 (where bpy = 2,2'-bipyridine 3a and d8-2,2'-bipyridine 3b). These N-coordinated complexes are fully characterized by 1H NMR and IR spectroscopy and ESI-MS. Metal coordination has a profound effect on both the absorption and the emission properties of 1. Pd(II) coordination causes a red-shift in the low-energy absorptions, a decrease in the intensity of the n-pi absorptions, and a quenching of the emission. Ru(II) coordination causes absorption throughout the visible region and creates two new complexes that join an elite group of compounds known as "black" absorbers. 3a and 3b possess two discernible 1MLCT bands. The one of exceptionally low energy (lambda(max) = 615 nm) has an associated (3)MLCT emission (lambda(max) = 880 nm) due to the unprecedented electron delocalization and acceptor properties of the rigid aromatic N-HSB 1. Both Ru(II) complexes are near-IR emitters with unusually protracted emission lifetimes of 320 ns at 77 K. They are photochemically inert, and their electrochemical properties are consistent with the presence of a low-lying pi orbital on 1. The first two reversible reductions (E(1/2) (CH3CN), -0.54 V, -1.01 V vs SCE) are due to the stepwise reduction of 1 and are anodically shifted as compared to [Ru(bpy)3]2+. Temperature- and concentration-dependent NMR studies on 2 and 3a suggest extensive aggregation is occurring in solution.

Infrared Spectroscopic Investigation of Chemisorption on Chemically Synthesized Aluminum Nitride Nanopowders with 2-Pyrrolidinones

The chemical nature of a nanoparticle surface is of crucial importance in controlling the interparticle forces during powder processing. As a continuation of a FT-IR spectroscopy study on the surface chemical structure of the chemically synthesized aluminum nitride (AlN) nanopowders, the adsorption of two representative cyclic amides, i.e., N-methyl-2-pyrrolidinone (NMP) and 2-pyrrolidinone (NHP), have been investigated. Upon adsorption of these cyclic amides, strong hydrogen bonding between the amide carbonyl oxygen and the surface hydroxyl groups was evident. The unusual thermal stability for the hydrogen bonding observed with NMP was explained as being due to the enhancement by secondary interactions between the NMP amide carbonyl group and the surface Lewis acidic sites, such as Al3+. With the adsorption of NHP at room temperature, besides the formation of strong hydrogen bonding, a striking 100 cm-1 shift to higher wavenumbers was observed for both the carbonyl and amide C−N stretching bands. This has been interpreted as the formation of complex coordination between the amide nitrogen and the surface acidic sites. The amide N-coordinated complex plus the carbonyl O-coordinated hydrogen bonding promote a synergistic effect for strengthening the NHP adsorption on the AlN surface.

Superoxide dismutase mimetic activity of a cyclic tetrameric Schiff base N-coordinated Cu(II) complex

A pulse radiolytic study using the cyclic tetrameric Schiff base N-coordinated copper complex Cu(TAAB)2+ has been performed. The reaction of the Cu(TAAB)2+ complex with superoxide revealed pseudo first-order characteristics with the rate constant of k2 = (2.9 ± 0.5) × 108 mol−1 s−1 dm3. The complex survive presence of competing serum albumin in physiological concentrations. The complex stability constant K = 1.15 × 1018 (log K = 18.06) is two orders of magnitude higher than that of Cu(II)-serum albumin (log K = 16.2). Transient changes of the stability during the oxidation/reduction process and in the presence of 600 /μmol l−1 albumin did not affect significantly either the electronic absorption of the complex or its catalytic activity.

Structure and biological activity of nitrogen and oxygen coordinated nicotinic acid complexes of chromium

A series of N-coordinated M(II)(nic) 2(H 2O) 4 ≠ complexes, where M = Co, Ni, Mn or Cr and the O-coordinated species Cr(III)(nic) 2(H 2O) 4 + and Cr(III)(nic)(H 2O) 5 +2 have been prepared. A single crystal X-ray analysis of the complex Cr(II)(nic) 2(H 2O) 4 shows that the chromium ion is in the +2 oxidation state and that two nicotinic acid ligands are coordinated in a trans arrangement via the pyridine ring nitrogen atoms. The four equatorial positions are occupied by water molecules. Biological activity measurements with a yeast bioassay system however show that none of the N-coordinated complexes possess any glucose tolerance factor (GTF-type) activity. On the other hand, the O-coordinated chromium(III)-dinicotinic acid complex is biologically active which suggests that a trans arrangement of pyridine nitrogen atoms resembles that part of the GTF structure which is recognised by the receptors or enzymes which are involved in the expression of the biological effect.