Spectral and structural characterization of amidate-bridged platinum-thallium complexes with strong metal-metal bonds

The reactions of [Pt(NH3)2(NHCOtBu)2] and TlX3 (X = NO3-, Cl-, CF3CO2-) yielded dinuclear [{Pt(ONO2)(NH3)2(NHCOtBu)}Tl(ONO2)2(MeOH)] (2) and trinuclear complexes [{PtX(RNH2)2(NHCOtBu)2}2Tl]+ [X = NO3- (3), Cl- (5), CF3CO2- (6)], which were spectroscopically and structurally characterized. Strong Pt-Tl interaction in the complexes in solutions was indicated by both 195Pt and 205Tl NMR spectra, which exhibit very large one-bond spin-spin coupling constants between the heteronuclei (1J(PtTl)), 146.8 and 88.84 kHz for 2 and 3, respectively. Both the X-ray photoelectron spectra and the 195Pt chemical shifts reveal that the complexes have Pt centers whose oxidation states are close to that of Pt(III). Characterization of these complexes by X-ray diffraction analysis confirms that the Pt and Tl atoms are held together by very short Pt-Tl bonds and are supported by the bridging amidate ligands. The Pt-Tl bonds are shorter than 2.6 Angstrom, indicating a strong metal-metal attraction between these two metals. Compound 2 was found to activate the C-H bond of acetone to yield a platinum(IV) acetonate complex. This reactivity corresponds to the property of Pt(III) complexes. Density functional theory calculations were able to reproduce the large magnitude of the metal-metal spin-spin coupling constants. The couplings are sensitive to the computational model because of a delicate balance of metal 6s contributions in the frontier orbitals. The computational analysis reveals the role of the axial ligands in the magnitude of the coupling constants.     

Structural characterization and differentiation of modified isomeric tryptophans

Different mass spectrometry (MS) techniques have been applied to the study of modified tryptophan isomers obtained by photochemical reactions. The gas phase behavior of the molecular ions and the most abundant fragment ions produced under electron ionization has been selectively studied by MS/MS experiments. Both the fragmentation reactions occurring in the ion source, as well as those produced under collision-induced dissociation conditions have allowed to characterize and differentiate each isomer from the others. Investigation of a bisubstituted derivative has been useful in the rationalization of the gas phase behavior of this series of modified tryptophans. This study has allowed the evaluation of the role played by the substituents and their positions at the indolic ring on the gas phase decompositions that are distinctive and selective for each isomer. The occurrence of regiospecific reactions suggests that isomerization phenomena do not occur either in the molecular ions or in the main fragment ions in the gas phase.     

Microwave synthesis and characterization of europium complexes with cinnamic acid and phenanthroline

We report here the synthesis and characterization of a host of Eu(Phen)L₃ with cinnamic acid (C₆H₅CH = CHCOOH, HL) and phenanthroline (Phen), and employing microwave radiation, where the microwave radiation is used just for the uniform heating of the reaction mixture. Its IR absorption spectra, scanning electron microscopy (SEM), and fluorescence spectra were studied. The results show that the particles of Eu(Phen)L₃ phosphors are basically spherical in shape, with good dispersing. The mean particle size is 1–2 μm. The excitation spectrum is a broad band and the main peak is at 320.0 nm. Moreover, excitation peak at 396.0 nm was found in the excitation spectrum. The emission spectrum shows that Eu(Phen)L₃ has narrow emission peaks. The emission peaks are ascribed to Eu³⁺ ions transition from ⁵ D _J (J = 0) to ⁷ F _J (J = 1, 2, 4). However, the strongest main emission peak locates at 614.0 nm, which corresponds to the electric dipole transition of Eu³⁺(⁵ D ₀ → ⁷ F ₂) The article is published in the original.     

Heterodinuclear transition-metal complexes with multiple metal-metal bonds

Interactions between a pair of transition-metals can range from weak antiferromagnetic coupling to bonds of the highest multiplicity known in chemistry, for example, quadruple in isolatable compounds. Tremendous effort has been invested in studying homodinuclear transition-metal-metal bonds. In contrast, relatively little attention has been devoted to heterodinuclear analogues, as it is substantially more challenging to prepare and handle such entities. Yet, in this largely unexplored area of transition-metal chemistry, novel chemical interactions with unprecedented reactivities are likely to be found. Heterodinuclear analogues of diatomic transition-metal dimers being yet inaccessible, dinuclear complexes with Werner-type ligands provide examples of high-multiplicity bonds between different d elements in their least-perturbed form. Such compounds provide an opportunity to probe fundamental issues of chemical bonding between transition-metals, by revealing how and to what extent such bonds are affected by differences in the two metals. Complexes wherein electronically unsaturated heterodinuclear cores are stabilized by pi-acidic ligands (such as CO) hold the potential of new chemical reactions (including catalytic) that capitalize on the synergetic effect of two transition-metal centers.     

One-dimensionally extended paddlewheel dirhodium complexes from metal-metal bonds with diplatinum complexes

We have succeeded in obtaining unique one-dimensional (1D) chain complexes (1, 2, and 3) comprised of two types of metal species: rhodium and platinum. These compounds are constructed from a dinuclear rhodium complex (i.e., [Rh(2)]) and a pivalamidate-bridged platinum complex (i.e., [Pt(2)]), forming an attractive quasi-1D infinite chain, expressed as -{[Rh(2)]-[Pt(2)]-[Pt(2)]}(n)-. Interestingly, the bridging ligands of [Rh(2)] can be varied with trifluoroacetate, acetate, and acetamidate groups, indicating the possibility of electronic structure modulation in the 1D chain.     

Structural differentiation of isomeric N-oxides

The recently reported photochemical isomerization of 1-(2-pyridyl)benzotriazole 3-oxide to the 2-oxide created a need for a method of distinguishing between the structural isomers. Nmr experiments using Eu(fod)₃ established the position of the oxygen atoms and also yielded convincing evidence regarding attachment of the lanthanide shift reagent to these multi-functional compounds. Double irradiation experiments were used to resolve the structural problem while shift gradient considerations led to probable sites of coordination.     

The remarkable photochemistry of quadruply bonded metal-metal complexes

Quadruply bonded metal-metal (M⁴-M)comptexes in electronic excited stares exhibit a rich oxidation-reduction chemistry. The structural, electronic, and oxidation-reduction properties of M⁴-M complexes may be exploited to rationally design their excited state chemistry from conventional one-electron pathways to the first Iogical development of discrete multielectron pathways. As we commemorate the 30-year anniversary of the discovery of M⁴-M complexes by F. A. Cotton, this review shows that they currently provide chemistry with some of the most diverse and novel reactivity for transition metal complexes in the excited state.     

Structural characterization and catalytic activities of copper complexes with pyridine-amine-phosphine-oxide ligand

A new tetradentate containing pyridine, amine and phosphine oxide donor systems (1) was synthesized by the condensation of o-diphenylphosphinoaniline with 2-pyridinecarbaldehyde. Reaction of 1 with equal molar amount of CuCl₂ and Cu(ClO₄)₂ provided the formation of [CuCl₂(1)] (4) and [[Cu(1)(H₂O)](ClO₄)₂] (5), respectively. The ligand 1 behaves as a tridentate in 4, while as a tetradentate in 5. Both complexes were characterized by EPR, UV-Vis spectroscopy and X-ray diffraction. Both copper(II) complexes are in a square-pyramidal geometry. Single crystal structure of the copper complex reveals that the copper center is surrounded by three nitrogen donors and two chloride for 4; three nitrogen donors, water and oxygen donor from the moiety of phosphine oxide for 5. Complexation of 1 with CuCl in dichloromethane resulted in the formation of the corresponding copper(I) species, which catalyzed the oxidation of benzylic alcohols under aerobic conditions.     

Neodymium and europium complexes with amides and cyclic aminoxides

Complexes of neodymium and europium with amides and aminoxides were synthesized and characterized by complexometric analyses with EDTA, CHN microanalytical procedures, IR absorption spectra, absorption spectra of neodymium complexes, emission spectrum of europium compounds at 77 K, thermogravimetric analyses in N2 and differential scanning calorimetry (DSC) in N2. Infrared spectroscopy results revealed that the nitrate molecules are bound to the central ions as bidentate. Thermogravimetric plots indicated that the decomposition of the complexes occurs in the range 363-1163 K and resulted in the formation of Ln₂O₃ residues. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and characterization of nitrosyl diruthenium complexes. Interaction between NO and CO across the metal-metal bond

Two neutral diruthenium complexes and one anionic diruthenium complex, Ru2(dpf)4(NO), Ru2(dpf)4(NO)2, and [Ru2(dpf)4(NO)]-, where dpf is diphenylformamidinate anion, were synthesized and characterized as to their electrochemical and spectroscopic properties. Two of the compounds, Ru2(dpf)4(NO) and Ru2(dpf)4(NO)2, were also structurally characterized. Ru2(dpf)4(NO) undergoes reversible one-electron reductions under N2 at E1/2=0.06 and -1.24 V in CH2Cl2, 0.1 M TBABr. These processes are shifted to E1/2=0.18 and -0.78 V under CO due to the trans-coordination of a CO molecule which stabilizes the singly and doubly reduced forms of the metal-metal bonded complexes, thus leading to easier reductions. CO does not coordinate to Ru2(dpf)4(NO), but it does bind to the singly reduced species to generate [Ru2(dpf)4(NO)(CO)]- under a CO atmosphere in solution; characteristic NO and CO bands are seen for this compound at nuNO=1674 cm(-1) and nuCO=1954 cm(-1). Ru2(dpf)4(NO)2 displays a reversible one-electron reduction at E1/2=-1.24 V versus SCE and an irreversible reduction at Epc=-1.96 V in CH2Cl2, 0.1 M TBAP under N2. There are also two reversible one-electron oxidations at E1/2=0.24 and 1.15 V. Spectroelectrochemical monitoring of the Ru2(dpf)4(NO)2 oxidation processes in a thin-layer cell shows only a single NO vibration for each electrogenerated product and nuNO is located at 1726 (neutral), 1788 (singly oxidized), or 1834 (doubly oxidized) cm(-1). Finally, a labile CO complex, [Ru2(dpf)4(NO)(CO)]-, could be generated by passing CO into a solution of [Ru2(dpf)4(NO)]-. Formation of the mixed CO/NO adduct was confirmed by electrochemistry and infrared spectroscopy. Analysis of the NO and CO stretching vibration frequencies for [Ru2(dpf)4(NO)(CO)]- by in-situ FTIR spectroelectrochemistry and comparisons with data for Ru2(dpf)4(NO) and Ru2(dpf)4(CO) reveal the presence of a strong interaction between NO and CO across the Ru-Ru bond.     

Low-temperature biligand complexes of europium and samarium with mesogenic alkylcyanobiphenyls

For low-temperature cocondensates of europium and samarium (M) with a mesogenic ligand 4-pentyl-4-cyanobiphenyl (L), IR and UV spectroscopy studies have revealed the formation of two ML complexes (M/L = 1:2 and 1:1). Model calculations have been carried out in terms of density functional theory using the B3LYP exchange correlation potential. Biligand structures with an antiparallel arrangement of two ligand molecules including one and two metal atoms, respectively, are suggested. The values of the spectral shifts and the relative thermal stability of the complexes are discussed.Original Russian Text Copyright © 2004 by A. V. Vlasov, T. I. Shabatina, S. V. Konyukhov, A. Yu. Ermilov, A. V. Nemukhin, and G. B. SergeevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 406–411, May–June, 2004.     

Structural characterization of two copper(II) complexes with oxime-type ligands

Two new linear Cu^II complexes [Cu(L¹)₂] (I) (HL¹ = (E)-3,5-dichloro-2-hydroxy benzaldehyde O-methyl oxime) and [Cu(L²)₂] (II) (HL² = (E)-3,5-dichloro-2-hydroxy benzaldehyde O-ethyl oxime) are synthesized and characterized by elemental analysis, IR, UV-Vis, and X-ray diffraction methods. X-ray crystallographic analyses indicate that complexes I and II have a similar structure consisting of one Cu^II ion and two L⁻ units. In the complexes, the Cu^II ion lying on an inversion centre is four-coordinated in a trans-CuN₂O₂ square planar geometry by two phenolate O and two oxime N atoms from two symmetry-related N,O-bidentate oxime-type ligands. However, the crystal structure of the two complexes is different: complex I forms an infinite three-dimensional supramolecular network structure through intermolecular hydrogen bonding and π...π interaction, while complex II forms an infinite one-dimensional supramolecular structure through intermolecular hydrogen bonds.     

Photochemical properties of mixed-ligand complexes europium carboxylates

The photochemical behavior of mixed-ligand complexes of europium carboxylates with nitrogen-and phosphorus-containing neutral ligands of island and dimer types, Eu(L)₃ · xD · nH₂O and [Eu(L)₃ · xD]₂ · nH₂O (L is the trifluoroacetate, toluate, or cinnamate anion), was studied. During UV irradiation of the complexes of europium carboxylates with 1,10-phenanthroline and 2,2′-dipyridyl, a luminescence buildup was observed. EPR measurements demonstrated that the observed buildup of luminescence from europium occurs in parallel with the increase of the concentration of radical anions formed from neutral ligands.     

Electroluminescent properties of three ternary europium complexes with different phenanthroline derivatives

In the past decade a number of lanthanide com-plexes have been designed and synthesized for organic electroluminescent (EL) devices owing to their ex-tremely sharp emission bands and potentially high internal quantum efficiency[113]. This characteristic made the lanthanide complexes one kind of promising candidates for full color flat-panel displays which re-quire pure red, green and blue emissions. So far, how-ever, the devices based on lanthanide complexes as emitters have not demonstrated v…     

Extraction of europium complexes with 1,2,4,5-benzenetetracarboxylic acid and neutral ligands

Extraction of mixed-ligand europium complexes with 1,2,4,5-benzenetetracarboxylic (pyromellitic) acid and neutral ligands was studied. The complexation of europium with the ligands is discussed on the basis of data on europium distribution in extraction systems, as well as IR and luminescent spectroscopy data of extracts. Crystalline polynuclear europium complexes with pyromellitic acid and 1,10-phenanthroline and tris(hydroxymethyl)aminomethane were isolated from the extracts. The composition of pyrolysis products of extracts was studied. It was shown that nanosized bulk samples of europium oxide can be obtained by the pyrolysis of saturated extracts. Differences in the morphology of europium oxide nanoparticles were revealed in the samples obtained by pyrolysis of extracts differing in composition at the same temperature and time.     

Low-temperature complexes of europium atoms and dimers with cyanophenylpyridines and alkylcyanophenylpyridines

It is shown by IR-Fourier and UV-visible spectroscopy that two biligand complexes of different stoichiometric composition Ln·2L and 2Ln·2L (Ln = Eu; L = 4-pentyl-4′-cyanophenylpyridine) are formed in the course of low-temperature co-condensation of metal and ligand vapors on the surfaces cooled with liquid nitrogen. Quantum-chemical modeling of the equilibrium structures of the mono-and binuclear complexes of europium with unsubstituted cyanophenylpyridyl and para-ethylcyanophenylpyridyl ligands was carried out. The main geometrical parameters of these compounds were determined. For mononuclear complexes, there is a competition between two mechanisms of coordination of the metal atom: formation of sandwich π complexes by interactions with the π orbitals of the aromatic ligand system and σ coordination at the nitrogen atoms of the pyridine ring. The sandwich structures of the binuclear complexes with 4-ethylcyanophenylpyridine are stabilized by N…H intermolecular contacts between the N atom of the cyano group and the terminal H atom of the ethyl group. The spectral shifts and the relative thermal stability of complexes with varying nuclearity are discussed.     

The synthesis and characterisation of europium terpyridine-N-oxide complexes

Europium complexes of a series of terpyridine-N-oxide ligands have been prepared and structurally characterised by crystallographic studies. While the addition of three equivalents of terpyridine-1-oxide or terpyridine-1,1'-bisoxide results in complexes with nine co-ordinate tricapped trigonal prismatic or monocapped square antiprismatic geometries, respectively, three equivalents of the terpyridine-1,1',1'-trisoxide yields an unexpected 8 co-ordinate geometry. Luminescence studies of the three complexes in acetonitrile show a typical europium emission spectra, dominated by the (5)D(0)-(7)F(2) transition. While no simple trend in the relative quantum yields could be ascertained, the terpyridine-1-oxide complex was observed to have the most intense luminescence for this set of complexes.     

Synthesis and spectral properties of europium phthalocyanine complexes

Methods for the synthesis of europium complexes with phthalocyanine and thenoyltrifluoroacetonate (tta) or ferrocenoyltrifluoroacetonate (fta) ligands are discussed. The spectral characteristics of the complexes PcEu(tta)(ttaH) and PcEu(fta)(ftaH) (Pc is phthalocyanine) are studied.     

Synthesis and spectroscopic studies of europium chelate complexes

The synthesis of the mixed complexes of the europium ion with 2-pyridylcarbinol-N-oxide, and 2,2′-dipyridyl and 1,10-phenanthroline were prepared. The compounds, were characterized by means of chemical analyses, vibrational spectra, molar conductivities, and electronic spectra. The emission of the [EuL₃, phen] complex at 10 K is very intense and an assignment of the point symmetry of the Eu(III) ion has been made.