Iridium Complexes with BIAN-Type Ligands: Synthesis, Structure and Redox Chemistry.

A series of iridium complexes with bis(diisopropylphenyl)iminoacenaphtene (dpp-bian) ligands, [Ir(cod)(dpp-bian)Cl] (1), [Ir(cod)(NO)(dpp-bian)](BF4)2 (2) and [Ir(cod)(dpp-bian)](BF4) (3), were prepared and characterized by spectroscopic techniques, elemental analysis, X-ray diffraction analysis and cyclic voltammetry (CV). The structures of 1-3 feature a square planar backbone consisting of two C = C π-bonds of 1,5-cyclooctadiene (cod) and two nitrogen atoms of dpp-bian supplemented with a chloride ion (for 1) or a NO group (for 2) to complete a square-pyramidal geometry. In the nitrosyl complex 2, the Ir-N-O group has a bent geometry (the angle is 125°). The CV data for 1 and 3 show two reversible waves between 0 and -1.6 V (vs. Ag/AgCl). Reversible oxidation was also found at E1/2 = 0.60 V for 1. Magnetochemical measurements for 2 in a range from 1.77 to 300 K revealed an increase in the magnetic moment with increasing temperature up to 1.2 µB (at 300 K). Nitrosyl complex 2 is unstable in solution and loses its NO group to yield [Ir(cod)(dpp-bian)](BF4) (3). A paramagnetic complex, [Ir(cod)(dpp-bian)](BF4)2 (4), was also detected in the solution of 2 as a result of its decomposition. The EPR spectrum of 4 in CH2Cl2 is described by the spin Hamiltonian H = gßHS with S = 1/2 and gxx = gyy = 2.393 and gzz = 1.88, which are characteristic of the low-spin 5d7-Ir(II) state. DFT calculations were carried out in order to rationalize the experimental results.

Novel Copper(II) Complexes with Dipinodiazafluorene Ligands: Synthesis, Structure, Magnetic and Catalytic Properties.

The reactions of CuX2 (X = Cl, Br) with dipinodiazafluorenes yielded four new complexes [CuX2L1]2 (X = Cl (1), Br (2), L1 = (1R,3R,8R,10R)-2,2,9,9-Tetramethyl-3,4,7,8,9,10-hexahydro-1H-1,3:8,10-dimethanocyclopenta [1,2-b:5,4-b']diquinolin-12(2H)-one) and [(CuX2)2L2]n (X = Cl (3), Br (4), L2 = (1R,3R,8R,10R,1'R,3'R,8'R,10'R)-2,2,2',2',9,9,9',9'-Octamethyl-1,1',2,2',3,3',4,4',7,7',8,8',9,9',10,10'-hexadecahydro-1,3:1',3':8,10:8',10'-tetramethano-12,12'-bi(cyclopenta [1,2-b:5,4-b']diquinolinylidene). The complexes were characterized by IR and EPR spectroscopy, HR-ESI-MS and elemental analysis. The crystal structures of compounds 1, 2 and 4 were determined by X-ray diffraction (XRD) analysis. Complexes 1-2 have a monomeric structure, while complex 4 has a polymeric structure due to additional coordinating N,N sites in L2. All complexes contain a binuclear fragment {Cu2(µ-X)2×2} (X = Cl, Br) in their structures. Each copper atom has a distorted square-pyramidal coordination environment formed by two nitrogen atoms and three halogen atoms. The Cu-Nax distance is elongated compared to Cu-Neq. The EPR spectra of compounds 1-4 in CH3CN confirm their paramagnetic nature due to the d9 electronic configuration of the copper(II) ion. The magnetic properties of all compounds were studied by the method of static magnetic susceptibility. For complexes 1 and 2, the effective magnetic moments are µeff ≈ 1.87 and 1.83 µB (per each Cu2+ ion), respectively, in the temperature range 50-300 K, which are close to the theoretical spin value (1.73 µB). Ferromagnetic exchange interactions between Cu(II) ions inside {Cu2(µ-X)2X2} (X = Cl, Br) dimers (J/kB ≈ 25 and 31 K for 1 and 2, respectively) or between dimers (θ' ≈ 0.30 and 0.47 K for 1 and 2, respectively) were found at low temperatures. For compounds 3 and 4, the magnetic susceptibility is well described by the Curie-Weiss law in the temperature range 1.77-300 K with µeff ≈ 1.72 and 1.70 µB for 3 and 4, respectively, and weak antiferromagnetic interactions (θ ≈ -0.4 K for 3 and -0.65 K for 4). Complexes 1-4 exhibit high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The maximum yield of cyclohexane oxidation products reached 50% (complex 3). Based on the data on the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play a decisive role in the oxidation reaction. The initial products in reactions with alkanes are alkyl hydroperoxides.

Synthesis, Structure, and Spectroscopic Study of Redox-Active Heterometallic Cluster-Based Complexes [Re5MoSe8(CN)6]n.

The heterometallic cluster-based compound K5[Re5MoSe8(CN)6] was obtained by high-temperature reaction from a mixture of ReSe2 and MoSe2 in molten potassium cyanide. The redox behavior of the [Re5MoSe8(CN)6]5- cluster anion was studied by cyclic voltammetry in aqueous and organic media showing two reversible one-electron-redox transitions with E1/2 of -0.462 and 0.357 V versus Ag/AgCl in CH3CN. Aqueous media potentials were found to be noticeably shifted to higher values because of solvation. Chemically accessible potentials allowed us to structurally isolate and characterize the [Re5MoSe8(CN)6]n (n = 3-, 4-, and 5-) cluster complex in several charge states with corresponding cluster skeletal electron (CSE) numbers ranging from 24 to 22. The electronic absorption of the [Re5MoSe8(CN)6]n cluster complex varies significantly upon a change of the CSE number, especially in the visible and near-IR regions. The local cluster core distortion upon electron removal was confirmed by density functional theory calculation, while the overall geometry of the cluster anion remained practically unaltered.

Paramagnetic Rhenium Iodide Cluster with N-Heterocyclic Carbene.

triangulo-Trirhenium nonaiodide Re3I9 reacts with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) to produce the novel 13-electron paramagnetic cluster Re3I8(IMes)2, which was characterized by means of X-ray diffraction analysis, ESR spectroscopy, magnetometry, and quantum chemistry.

Novel Oxidovanadium Complexes with Redox-Active R-Mian and R-Bian Ligands: Synthesis, Structure, Redox and Catalytic Properties.

A new monoiminoacenaphthenone 3,5-(CF3)2C6H3-mian (complex 2) was synthesized and further exploited, along with the already known monoiminoacenaphthenone dpp-mian, to obtain oxidovanadium(IV) complexes [VOCl2(dpp-mian)(CH3CN)] (3) and [VOCl(3,5-(CF3)2C6H3-bian)(H2O)][VOCl3(3,5-(CF3)2C6H3-bian)]·2.85DME (4) from [VOCl2(CH3CN)2(H2O)] (1) or [VCl3(THF)3]. The structure of all compounds was determined using X-ray structural analysis. The vanadium atom in these structures has an octahedral coordination environment. Complex 4 has an unexpected structure. Firstly, it contains 3,5-(CF3)2C6H3-bian instead of 3,5-(CF3)2C6H3-mian. Secondly, it has a binuclear structure, in contrast to 3, in which two oxovanadium parts are linked to each other through V=O···V interaction. This interaction is non-covalent in origin, according to DFT calculations. In structures 2 and 3, non-covalent π-π staking interactions between acenaphthene moieties of the neighboring molecules (distances are 3.36-3.40 Å) with an estimated energy of 3 kcal/mol were also found. The redox properties of the obtained compounds were studied using cyclic voltammetry in solution. In all cases, the reduction processes initiated by the redox-active nature of the mian or bian ligand were identified. The paramagnetic nature of complexes 3 and 4 has been proven by EPR spectroscopy. Complexes 3 and 4 exhibited high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The yields of products of cyclohexane oxidation were 43% (complex 3) and 27% (complex 4). Based on the data regarding the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play the most crucial role in the reaction. The initial products in the reactions with alkanes are alkyl hydroperoxides, which are easily reduced to their corresponding alcohols by the action of triphenylphosphine (PPh3). According to the DFT calculations, the difference in the catalytic activity of 3 and 4 is most likely associated with a different mechanism for the generation of ●OH radicals. For complex 4 with electron-withdrawing CF3 substituents at the diimine ligand, an alternative mechanism, different from Fenton's and involving a redox-active ligand, is assumed.

A Sterically Hindered Derivative of 2,1,3-Benzotelluradiazole: A Way to the First Structurally Characterised Monomeric Tellurium-Nitrogen Radical Anion.

Interaction of the tetradentate redox-active 6,6'-[1,2-phenylenebis(azanediyl)]bis(2,4-di-tert-butylphenol) (H4 L) with TeCl4 leads to neutral diamagnetic compound TeL (1) in high yield. The molecule of 1 has a nearly planar TeN2 O2 fragment, which suggests the formulation of 1 as TeII L2- , in agreement with the results of DFT calculations and QTAIM and NBO analyses. Reduction of 1 with one equivalent of [CoCp2 ] leads to quantitative formation of the paramagnetic salt [CoCp2 ]+ [1].- , which was characterised by single-crystal XRD. The solution EPR spectrum of [CoCp2 ]+ [1].- at room temperature features a quintet due to splitting on two equivalent 14 N nuclei. Below 150 K it turns into a broad singlet line with two weak satellites due to the splitting on the 125 Te nucleus. Two-component relativistic DFT calculations perfectly reproduce the a(14 N) HFI constants and A∥ (125 Te) value responsible for the low-temperature satellite splitting. Calculations predict that the additional electron in 1.- is localised mainly on L, while the spin density is delocalised over the whole molecule with significant localisation on the Te atom (≥30 %). All these data suggest that 1.- can be regarded as the first example of a structurally characterised monomeric tellurium-nitrogen radical anion.

23-Electron Octahedral Molybdenum Cluster Complex [{Mo6I8}Cl6].

Photoactive transition metal compounds that are prone to reversible redox reactions are important for myriad applications, including catalysis, optoelectronics, and sensing. This article describes chemical and electrochemical methods to prepare cluster complex (Bu4N)[{Mo6I8}Cl6], a rare example of a 23 e- cluster complex within the family of octahedral clusters of Mo, W, and Re. The low temperature and room temperature crystal structures; electronic structure; and the magnetic, optical, and electrochemical properties of this complex are described.

Formation of ordered films of axially bridged aluminum phthalocyanine [(tBu)4PcAl]2O via magnetic field-induced reaction.

The µ-(oxo)bis[tetra-tert-butylphthalocyaninato] aluminum(III) [(tBu)4PcAl]2O films with the crystallites oriented preferably in one direction were obtained via chemical transformation of tetra-tert-butylsubstituted chloroaluminum(III) phthalocyanine (tBu)4PcAlCl film upon its annealing in magnetic field. A comparative analysis of the influence of post-deposition annealing process without and under applied magnetic field of 1 T, on the orientation and morphology of (tBu)4PcAlCl and [(tBu)4PcAl]2O films, has been carried out by the methods of UV-vis, Infrared and Raman spectroscopies, XRD as well as atomic force microscopy. The formation of [(tBu)4PcAl]2O films with elongated crystallites having preferential orientation was observed upon heating of the films in magnetic field while annealing without magnetic field under the same conditions does not demonstrate any effect on the structure and morphology of these films. The reasons of the sensitivity of this reaction to the presence of such magnetic field is discussed and studied by electronic paramagnetic resonance spectroscopy.

Nitric oxide release and related light-induced cytotoxicity of ruthenium nitrosyls with coordinated nicotinate derivatives.

The synthetic approaches for the preparation of trans(NO,OH)-cis(NO2,NO2)-[RuNO(L)2(NO2)2OH], where L = ethyl nicotinate (I) and methyl nicotinate (II), are reported. The structures of the complexes are characterized by X-ray diffraction and analyzed by Hirshfeld surface analysis. Both compounds show a nitric oxide release reaction under 445 or 532 nm irradiation of dimethyl sulfoxide (DMSO) solutions, which is studied by combined ultraviolet-visible- (UV-vis), infrared- (IR), and electron paramagnetic resonance (EPR) spectroscopy and density functional theory (DFT) calculations. The charge transfer from the OH-Ru-NO chain and nitrite ligands to the antibonding orbitals of Ru-NO is responsible for the photo-cleavage of the ruthenium-nitrosyl bond. The elimination of NO leads to a side reaction, namely the protonation of the parent hydroxyl compound. The cytotoxicity and photo-induced cytotoxicity investigations of both compounds on the breast adenocarcinoma cell line MCF-7 reveal that (I) and (II) are cytotoxic with IC50 values of 27.5 ± 2.8 µM and 23.3 ± 0.3 µM, respectively. Moreover, (I) shows an increase of the toxicity after light irradiation by 7 times (IC50 = 4.1 ± 0.1), which makes it a prominent target for deeper biological investigations.

Temperature- and excitation wavelength-dependent emission in a manganese(ii) complex.

A mononuclear manganese(ii) complex with a chelating 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine ligand (L), [MnL2Cl2]·H2O, shows intriguing excitation wavelength-dependent emission. Depending on the excitation wavelength, the complex demonstrates three emission bands with the maxima at 380 nm, 440 nm and 495 nm. The 380 nm and 440 nm emissions originate from the π → π* and n → π* ligand-centered transitions. The long-wave 495 nm emission with microsecond lifetimes is related to the d-d transitions and/or metal-to-ligand and halogen-to-ligand charge transfer. The emission behavior of this complex is strongly temperature-dependent: upon cooling from 300 K down to 77 K, the intensity of emission considerably increases. The enhancement of the luminescence upon cooling is accompanied by the appearance of the vibrational structure. This complex is the first example of manganese(ii) complexes demonstrating excitation wavelength-dependent emission.

Bismuth germanate as a perspective material for dielectric resonators in EPR spectroscopy.

High purity bismuth germanate (Bi4(GeO4)3, BGO) is proposed and implemented as an alternative material for dielectric EPR resonators. A significant improvement of the absolute sensitivity can be readily achieved by substituting the alumina insert (ring) by BGO-made one in commercially available X-band EPR probeheads. Four BGO dielectric inserts of 2, 3, 4 and 5mm inner diameter (ID) were made for comparison with standard 5mm inner diameter alumina insert. All inserts were introduced into commercial Bruker EPR resonator ER 4118X-MD-5W1, and their performance was investigated. The Q-values of empty resonators, B1 saturation curves and continuous wave EPR spectra of DPPH (2,2-diphenyl-1-picrylhydrazyl) were measured and analyzed in a temperature range 6-300K. BGO-made resonators were found superior in several important aspects. The background signals arising from BGO are much weaker compared to those of alumina at B=0-0.6T and T=6-300K; this is especially useful for measuring weak signals in the half-field region, as well as those near the central field. Moreover, mechanical properties of BGO allow easy fabrication of dielectric bodies having various shapes and sizes; in particular, small BGO resonators (e.g. ID=2 or 3mm) strongly enhance sensitivity for small samples due to increase of the filling factor. All these advantages have been also inspected in the pulse mode, proving that higher B1 fields and better filling factors can be achieved, contributing to the overall enhancement of the performance.

Volatile Heterobimetallic Complexes from PdII and CuII ß-Diketonates: Structure, Magnetic Anisotropy, and Thermal Properties Related to the Chemical Vapor Deposition of CuPd Thin Films.

A novel approach for preparing volatile heterometallic complexes for use as precursors for the chemical vapor deposition of various materials is reported. New CuPd complexes based on ß-diketonate units were prepared, and their structures and compositions were determined. [PdL2 *CuL2 ] (1) and [PdL2 *Cu(tmhd)2 ] (2) (L=2-methoxy-2,6,6-trimethylheptane-3,5-dionate; tmhd=2,2,6,6- tetramethylheptane-3,5-dionate) are 1D coordination polymers with alternating metal complexes, which are connected through weak interactions between the Cu atoms and the OCH3 groups from the ligand of the Pd complexes. The volatility and thermal stability were studied using thermogravimetric and differential thermal analyses and mass spectrometry. Compound 1 vaporizes without decomposition into monometallic complexes. It exhibits magnetic anisotropy, which was revealed from the angular variations in the EPR spectrum of a single crystal. The vapor thermolysis process for 1 was investigated using mass spectrometry, allowing the process to be framed within the temperature range of 200-350 °C. The experimental data, supported by QTAIM calculations of the allowed intermolecular interactions, suggest that 1 likely exists in the gas phase as bimetallic molecules. Compound 1 proved to be suitable as a single-source precursor for the efficient preparation of CuPd alloy films with tunable Cu/Pd ratio. A possible mechanism for the film growth is proposed based on the reported data.

Heterometallic clusters with a new {Re3Mo3S8} core: direct synthesis, properties and DFT calculations.

We report the direct facile high-temperature synthesis and investigation of heterometallic rhenium-molybdenum cluster K6[Re3Mo3S8(CN)4(CN)2/2] (1) with a new {Re3Mo3S8} core. Dissolution of polymeric compound 1 resulted in subsequent oxidation and formation of stable 23e paramagnetic anionic cluster complex [Re3Mo3S8(CN)6](6-).