Luminescent properties of europium(III) and terbium(III) complexes with para- and ortho-ethoxybenzoic acids

The luminescent properties of europium(III) and terbium(III) complexes with para- and ortho-ethoxybenzoic acids are studied. The excitation energies of the triplet states of ligands are determined, a hypothesis is made about the efficient luminescence of europium(III) and terbium(III) complexes, the geometry of the coordination polyhedron of a europium complex is established, and the luminescence quantum yields of the complexes in solution are determined.     

Cyclometallated ruthenium(III) complexes: Synthesis,structure and properties

Reactions of Schiff bases (H₂apahR) derived from acetophenone and acid hydrazides, triethylamine and [Ru(PPh₃)₃Cl₂] (1:2:1 mole ratio) in methanol provide cyclometallated ruthenium(III) complexes of formula trans-[Ru(apahR)(PPh₃)₂Cl] in 74–81% yields. The complexes have been characterized by elemental analysis, magnetic susceptibility, spectroscopic (infrared, electronic and EPR) and electrochemical measurements. X-ray crystal structures of two representative complexes have been determined. In each complex, the metal centre is in distorted octahedral CNOClP₂ coordination sphere assembled by the C,N,O-donor meridionally spanning apahR^2?, the chloride and the two mutually trans-oriented PPh₃ molecules. All the complexes are one-electron paramagnetic (μ_eff. = 1.85–1.98 μ_B) and display rhombic EPR spectra in frozen (120 K) dichloromethane-toluene (1:1) solution. Electronic spectra of the complexes display several absorptions within 470–270 nm due to ligand-to-metal charge transfer and ligand centred transitions. The complexes are redox active and display a Ru(III) → Ru(II) reduction and a Ru(III) → Ru(IV) oxidation in the potential ranges ?0.66 to ?0.70 V and 0.75 to 0.80 V (vs. Ag/AgCl), respectively.     

Synthesis and structure of rhenium(IV) chloride complexes with acetonitrile

Cis and trans isomers of the tetrachlorodiacetonitrile rhenium(IV) complex were synthesized and isolated. The structure of cis-ReCl₄(N≡C-CH₃)₂ was studied by X-ray crystallography. It was shown that the coordination polyhedron of the central Re(IV) atom is formed by the four chlorine atoms and the nitrogen atoms of two coordinated acetonitrile molecules. The vibrational (IR and Raman) spectra of the cis isomer of the complex in solid state were interpreted by factor-group analysis. A comparison of the IR spectra of two isomers confirmed that they are cis and trans isomers.     

Synthesis and physicochemical properties of the Al(III), Ga(III) and In(III) complexes with chrysin

New solid compounds of Al(III), Ga(III) and In(III) with chrysin were obtained. Their composition and some physicochemical properties were studied by thermogravimetric analysis, UV-vis, infrared and solid state ¹³C NMR spectroscopies. Upon heating the hydrated compounds M(C₁₅H₉O₄)₃·nH₂O decomposed to the oxides. The structure of the compounds was elucidated on the basis of obtained results.     

Synthesis, reactivity, and properties of N-fused porphyrin rhenium(I) tricarbonyl complexes

The thermal reactions of N-fused tetraarylporphyrins or N-confused tetraarylporphyrins with Re2(CO)10 gave the rhenium(I) tricarbonyl complexes bearing N-fused porphyrinato ligands (4) in moderate to good yields. The rhenium complexes 4 are characterized by mass, IR, 1H, and 13C NMR spectroscopy, and the structures of tetraphenylporphynato complex 4a and its nitro derivative 15 are determined by X-ray single crystal analysis. The rhenium complexes 4 show excellent stability against heat, light, acids, bases, and oxidants. The aromatic substitution reactions of 4 proceed without a loss of the center metal to give the nitro (15), formyl (16), benzoyl (17), and cyano derivatives (19), regioselectively. In the electrochemical measurements for 4, one reversible oxidation wave and two reversible reduction waves are observed. Their redox potentials imply narrow HOMO-LUMO band gaps of 4 and are consistent with their electronic absorption spectra, in which the absorption edges exceed 1000 nm. Theoretical study reveals that the HOMO and LUMO of the rhenium complexes are exclusively composed of the N-fused porphyrin skeleton. Protonation of 4 takes place at the 21-position regioselectively, reflecting the high coefficient of the C21 atom in the HOMO orbital. The skeletal rearrangement reaction from N-confused porphyrin Re(I) complex (8) to N-fused porphyrin Re(I) complex (4) is suggested from the mechanistic study as well as DFT calculations.     

Mixed-ligand cyanide cobalt(III) complexes with 1,2-cyclohexanediaminetetraacetic acid: Synthesis and photochemical properties

[Co(CN)₂(H₃Cdta)] · 2H₂O (I) and Na₂[Co(CN)(Cdta)] · 3H₂O (II) (Cdta⁴⁻ is the 1,2-cyclohexanediaminetetraacetate) were synthesized. In I, the two cyanide ions and the Cdta nitrogen atoms are located in the equatorial plane, the carboxyl groups connected to different N atoms are in axial positions; in addition one of them, like two other uncoordinated carboxyl groups, is protonated. In II, Cdta is a pentadentate ligand coordinated in the cis-equatorial mode. UV excitation of the dicyano complexes at the ligand-to-metal charge transfer band gives organic derivatives of cobalt(III) stable enough for chromatographic isolation. Photolysis of II in neutral medium gives aqua(cyclohexanediaminetriacetato)cobalt (III) complexes as the final products.     

Synthesis and properties of cyano-bridged nickel(II)-iron(III) complexes

Summary Four kinds of novel CN-bridged Ni^II-Fe^III complexes, [NiLn(NC)Fe(CN)₅] ^–, have been synthesized and characterized by elemental analysis, i.r. and u.v.-vis. spectral analysis, and magnetic moments. The formation of cyanide bridges is evident from the i.r. and u.v.-vis. spectra by the appearance of v(CN) shifts and changes in _max with respect to the mononuclear parent complex [Fe(CN)₆]^3–. The magnetic properties indicate the existence of magnetic spin interactions between Ni^II and Fe^III through the cyanide bridge.     

Synthesis of N-heterocyclic carbene rhenium(I) carbonyl complexes

Reaction of aminophosphinimine [RHN(CH(2))(2)N[double bond, length as m-dash]PPh(3)] (R = H, Et) with Re(2)(CO)(10) provided the NH-functionalized carbene rhenium complex [Re(2)(CNHCH(2)CH(2)NR)(CO)(9)] (3a, R = H, 3b, R = Et). Treatment of 3 with Br(2) provided the mono nuclear [Re(CNHCH(2)CH(2)NR)(CO)(4)Br] (1, R = H, 2, R = Et). However, NH-functionalized carbene complexes 1-3 did not undergo N-alkylation with alkyl halides to yield the N-substituted NHC complexes. The direct ligand substitution of [Re(CO)(5)Br] with a carbene donor was employed to prepare [Re(IMes(2))(CO)(4)Br] (6a, IMes(2) = 1,3-di-mesitylimidazol-2-ylidene; 6b, IMes(2) = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene). Analyses of spectroscopic and crystal data of 6a and 6b show similar corresponding data among these complexes, suggesting the saturated and unsaturated NHCs have similar bonding with Re(I) metal centers. Reduction of 6a and 6b with LiEt(3)BH yielded the corresponding hydrido complexes 7a-b [ReH(CO)(4)(IMes(2))], but not 1 and 2. Ligand substitution of 1, 6a and 6b toward 2,2'-bipyridine (bipy) was investigated. Crystal structures of 1, 3a-b, 6a-b and 7b were determined for characterization and comparison.     

Unsaturated gold(III) tetraaza complexes: Synthesis,structures, and properties

Data on the synthesis and physicochemical study of polychelate gold(III) tetraaza complexes containing two five-membered and one or two six-membered unsaturated chelate rings were generalized.     

Synthesis and properties of some chromium(III) β-diketonate complexes

Summary Equimolar quantities of CrCl₃ · 3THF and-diketones, -dkH, react to yield CrCl₂(-dk) · 2THF and CrCl₂(-dk) · THF complexes in coordinating and noncoordinating solvents respectively. For 1 : 2 and 1 : 3 molar ratios of reactants, derivatives of general formulae CrCl(-dk)₂ and Cr(-dk)₃ (where-dkH = acerylacetrrnc, benzoylacetonc and dibenzoylmethane) have been isolated. All complexes have been characterized by elemental analysis, molecular weights and by i.r. spectra.     

Properties of fluoroantimonates(III) complexes with amino acids

Crystalline complex fluoroantimonates(III) with amino acids (glycine, β-alanine, DL-serine, DL-valine, L-leucine, and L-phenylalanine) have been prepared. The complexes stability in aqueous solutions has been studied with the cementation method. ¹H NMR studies of aqueous solutions of the amino acids complexes with SbF₃ at pH 1–6 and room temperature are reported. Preparation of polycrystalline metal antimony in aqueous solutions of tetrafluoroantimonates(III) complexes with the protonated amino acids has been demonstrated.     

Synthesis of Eu(III) and Tb(III) complexes with novel pyridine dicarboxamide derivatives and their luminescence properties

A novel ligand, N2,N6-bis[2-(3-methylpyridyl)]pyridine-2,6-dicarboxamide (L2) and the corresponding Eu(III) and Tb(III) hydrochlorate complexes have been synthesized and characterized in detail based on elemental analysis, IR and NMR. The crystal and molecular structure of the complexes was determined by X-ray crystallography. The Eu(III) and Tb(III) ions were found to coordinate to the amido nitrogen atoms and pyridine nitrogen atoms. The luminescence properties of lanthanide complexes in solid state, in different solutions and in different pH value were investigated. The result shows that Tb(III) complexes exhibit more efficient luminescence than Eu(III) complexes, and the ligand (L2) is an excellent sensitizer to Tb(III) ion.     

Mononuclear rhenium(III) and rhenium(II) complexes of 1,2-bis(diphenylphosphino)ethylene: The structure of trans-ReCl2(dppee)2

The mononuclear rhenium(III) complexes trans-[ReX₂(dppee)₂]X · nH₂O (X = Cl or Br, dppee = Ph₂PCHCHPPh₂) have been prepared by the reaction of (n-BU₄N)₂Re₂X₈ with dppee in methanol-conc. HX; in the case of X = Cl, ethanol may also be used as the reaction solvent. These salts undergo anion exchange reactions with ClO₄⁻ and/or PF₆⁻. The rhenium(II) complex trans-ReCl₂(dppee)₂ can be prepared by the cobaltocene reduction of trans-[ReCl₂(dppee)₂]Cl · 4H₂O and the reaction of Re₂Cl₆(PBu₃)ⁿ₂ with dppee in refluxing ethanol. The spectroscopic and electrochemical properties of [ReX₂(dppee)₂]⁺ have been investigated. Cyclic voltammetry (in 0.1 M tetra-n-butyl-ammonium hexafluorophosphate-CH₂Cl₂ with a Pt-bead electrode) shows reversible redox processes at E_1/2(ox) ca +1.5 V, E_1/2(red) ca −0.2 V, and E_1/2(red) ca −1.4 V vs Ag-AGCl that correspond to the Re(IV)-Re(III), Re(III)-Re(II) and Re(I)-Re(l) couples, respectively. The single-crystal X-ray crystal structure of trans-ReCl₂(dppee)₂ has confirmed its octahedral geometry. This complex crystallizes in the monoclinic space group P2₁/c with the following unit-cell dimensions: a = 11.321(2)Å, b = 13.011(2)Å, c = 17.242(3)Å, β = 95.79(2)°, V = 2527(1)ų, and Z = 2. The structure was refined to R = 0.041 (R_w = 0.070) for 2430 data with F² > 3.0σ(F²). The ReCl and ReP distances are 2.422(2) and 2.405(2)Å, respectively.     

Synthesis and properties of lanthanide(III) complexes with 4-hydroxy-3,5-dimethoxybenzoic acid

Complexes of yttrium(III) and lanthanides(III) with 4-hydroxy-3,5-dimethoxybenzoic (syringic) acid were obtained as solids with metal to ligand mole ratio of 1: 3. The compounds were characterized by elemental analysis, IR spectroscopy, X-ray diffraction patterns, solubility, and thermal studies. The complexes are sparingly soluble in water and stable at room temperature. Compounds of light lanthanides (from La to Nd) are hydrated and they crystallize in a triclinic system. When heated, they lose water molecules in one step and in the next step they decompose to oxides. Complexes of yttrium and other lanthanides are anhydrous and crystallize in a monoclinic system. They are stable up to 300°C and then decompose to oxides. As the coordination number of lanthanide ions is usually equal to 9 or 8, one can suppose that hydroxy or methoxy groups take part in the coordination of these metal ions.     

Photosensitized generation of singlet oxygen from rhenium(I) and iridium(III) complexes

Photophysical properties in dilute acetonitrile solution are reported for a number of iridium(III) and rhenium(I) complexes. The nature of the lowest excited state of the complexes under investigation is either metal-to-ligand charge transfer ((3)MLCT) or a ligand centred ((3)LC) state. Rate constants, k(q), for quenching of the lowest excited states by molecular oxygen are in the range 1.5 x 10(8) to 1.4 x 10(10) M(-1) s(-1). Efficiency of singlet oxygen production, f(Delta)(T), following oxygen quenching of the lowest excited states of these complexes, are in the range of 0.27-1.00. The rate constants and the efficiency of singlet oxygen formation are quantitatively reproduced by a model that assumes the competition between a non-charge transfer (nCT) and a CT deactivation channel. The balance between CT and nCT deactivation channels, which is described by the relative contribution p(CT) of CT induced deactivation, is discussed. The kinetic model is found to be successfully applied in the case of quenching of the excited triplet states of coordination compounds by oxygen in acetonitrile, as was proposed for the quenching of pi-pi* triplet states by oxygen.     

Synthesis and characterization of rhenium(VII) oxide complexes of phenothiazines

Summary Five complexes of rhenium(VII) oxide with N-alkylphenothiazines have been synthesized and characterized on the basis of elemental analyses, molar conductances, and u.v.-vis., i.r. and n.m.r. spectral data. The molecular formulas of the new ionic complexes are: [ReO₃(PTZ)₂(H₂O)][ReO₄], PTZ = chlorpromazine, promethazine or ethopropazine; [ReO₃(TF)(H₂O)][ReO₄], TF = trifluoperazine; and [ReO₃(TR)₃][ReO₄(H₂O)₂]·H₂O, TR = thioridazine. Tentative structures have been proposed.