D.M Araújo Melo

Synthesis, properties and structure of hexaaquo-tris(N.N-dimethylformamide)- lanthanide trifluoromethanesulfonates

The compounds of general formula [Ln(DMF)3- (H2O)6](CF3SO3)3 (Ln = LaEu, Tb, Dy) were synthesized and characterized by microanalysis, conductance measurements, IR absorption (Nd3+) and emission (Eu3+) spectra. The crystal structure of the neodymium compound was determined by X-ray diffraction techniques. The compound crystallizes in the triclinic system, space group P1, a = 8.589(4), b = 11.222(2), c = 12.271(2) A, α = 56.83(2), β = 62.13(2), γ = 75.14(2)°, V = 875.2 A3, M = 918.4, Z = 1, Dc = 1.73 g cm−3, λ(Mo Kα) = 0.71073 A, μ = 1.65 mm−1, F(000) = 456, R = 0.056, Rw = 0.057, for 2979 independent reflections with I > 3σ(I). Nd3+ is coordinated to the oxygen atoms of six independent water molecules at a mean distance NdO = 2.52(1) A, and to the oxygen atoms of three independent DMF groups at a mean distance NdO = 2.40(2) A. The coordination polyhedron is a tricapped trigonal prism of point symmetry C3v.

Synthesis, characterization and structure of lanthanide nitrate complexes with 2-azacyclononanone (AZA)

Abstract Complexes with composition [Ln(NO3)3(AZA)3] (Ln=Nd, Eu, Gd, Tb, Ho and Er) were synthesized and characterized by CHN elemental analyses and lanthanide titration with EDTA. IR spectra show that they are anhydrous and the ligands (AZA) bonded through the carbonyl oxygen; nitrate counter-ions are bidentate, linked to the central ions. The emission spectrum of the europium complex was interpreted in terms of a D3h distorted to C3v symmetry. The structure, determined by X-ray single crystal studies is described as a distorted tricapped trigonal prism with the AZA ligands bonded to one of the bases of the prism and nitrates with one oxygen bonded to one of the bases of the prism and the other forming one of the caps.

Hydrated neodymium(III) and europium(III) picrate complexes with pyrazine-N-oxide

Abstract Compounds with composition Ln(pic)3·2pyzNO·7H2O (Ln=Nd, Eu; pic=picrate; pyzNO=pyrazine-N-oxide) were obtained by reaction of the hydrated lanthanide picrate with pyrazine-N-oxide in ethanol (molar ratio 1:4). The adducts were characterized by elemental analyses and IR spectra. X-ray single crystal data for the neodymium complex indicate that the crystal system is triclinic, space group P 1. Nd unit cell dimensions are: a=7.930(1) A; b=12.869(1) A; c=20.833(1) A; α=106.414(7) A; β=92.574(7) A; γ=92.202(9) A; V=2034.4(3) A; Z=2. Europium cell parameter are a=7.882(1) A, b=12.880(1) A, c=20.788(2) A, α=106.224(8)°, β=92.055(7)°, γ=93.140(7)°. One picrate is bidentate, coordinated through the phenoxo oxygen and one oxygen of an o-nitro group and two are not coordinated. One pyrazine-N-oxide is bonded through the oxygen and the other is out of sphere. Six water molecules are bonded and a seventh is not coordinated. The coordination polyhedron is a distorted tricapped trigonal prism.

Preparation and properties of complexes between rare earth trifluoroacetates and hexamethylphosphoramide (HMPA)

Abstract Complexes of composition [Ln(TFA) 3 (HMPA) 3 ] (Ln=La, Nd, Eu, Gd, Dy, Ho and Er, TFA=trifluoroacetate) were prepared and characterized by complexometric analyses with EDTA and CHN microanalytical procedures. IR spectra show that HMPA’s are linked to the central ions through the PO oxygen and that the trifluoroacetate ions are also coordinated. The visible absorption spectrum of the neodymium compound in a silicone mull, at room temperature, allows us to calculate the nephelauxetic parameter β =0.990, the covalent factor b 1/2 =0.070 and Sinha’s parameter δ =1.01. They are suggestive of an essentially electrostatic interaction between lanthanide and ligands. The emission spectra of the europium complex at room temperature and at 77 K were also determined. Thermogravimetry show that HMPA molecules are totally evaporated at ca. 260°C and that the residues are the corresponding rare earth oxyfluorides.

Bis(pentamethylene)urea complexes of the lanthanide nitrates: synthesis, characterization, properties

Lanthanide nitrate complexes of bis(pentamethylene)urea (BPMU) with general formula Ln(NO 3 ) 3 3BPMU, where Ln: La, Nd, Sm, Eu, Ho and Er have been prepared and characterized based on CHN elemental analyses, lanthanide titration with EDTA, molar conductivity, spectroscopic data and thermal studies. The infrared spectra show that ligands (BPMU) are bonded through the carbonyl oxygen, nitrate counter-ions are bidentate linked to the central ions. The structure of the neodymium complex was determined. The crystal is monoclinic, P2 1/c , Z = 4, with the following parameters: a = 10.148(1) A, b = 21.879(2), c = 19.154(2) A, β = 104.11(1)°, V = 4124.3(7) A 3 . The polyhedron is a distorted tricapped trigonal prism, coordination number nine.

Compounds of lanthanide picrates and 2-azacyclononanone (aza): synthesis, characterization and thermal study

Addition compounds between lanthanide(III) picrates and azacyclononanone(aza) were characterized by spectroscopic, microanalytical and X-ray data, with special emphasis on thermogravimetric techniques.

Kinetic study of the thermal decomposition of the compound of terbium(III) trifluoromethanesulfonate and hexamethylphosphoramide (HMPA) employing both Zsakó’s and nonlinear methods

Abstract Terbium trifluoromethanesulfonate compound with hexamethylphosphoramide was synthesized and characterized. Thermogravimetric data with three heating rates were used to obtain kinetic parameters such as activation energy (Ea), reaction order (n) and preexponential factor (k0). The results obtained by two different methods, Zsako’s and a nonlinear one, are compared.