155Gd Mössbauer spectra of some Gd(III)-b-diketonato complexes

¹⁵⁵Gd Mössbauer spectra of some Gd(III)-b-diketonato complexes are reported. All of their ¹⁵⁵Gd Mössbauer isomer shift (d) values fall in a narrow range of +0.55-+0.65 mm^.s^-1, and are between those of GdF₃ and the cubic form of Gd₂O₃. This indicates that their Gd-O bonds have small covalent character. The value for quadrupole coupling constant (e²qQ) spread out from 1.67 to 7.56 mm^.s^-1 and reflects the difference well in symmetry of the coordination polyhedron around Gd(III) ions for those Gd(III)-b-diketonato complexes.     

4f-4f absorption spectra and hypersensitivity in nine-coordinate Ho(III) and Er(III) complexes in different environments

The effect of change in the environment upon 4f-4f absorption spectra of nine-coordinate Ho(III) and Er(III) complexes with thiocyanate and 2,2'-bipyridyl in methanol, DMSO, DMF and pyridine have been investigated. The oscillator strength for hypersensitive and non-hypersensitive transitions have been calculated and variation in the intensity and band shape with respect to solvent type is rationalized in terms of solvent structure and coordinating properties. A comparison with 1,10-phenanthroline complexes is investigated and has been found that phen has a larger impact on the transition intensities for these ions. Pyridine has been found most effective in promoting 4f-4f intensity. The results indicate that it is important to consider both the static and dynamic coupling mechanism while analysing the oscillator strength of hypersensitive transition.     

Extraction of Sm(III), Gd(III) and Ho(III) ions with picrolonic acid in methylisobutylketone

Summary Picrolonic acid (HPA) in methylisobutylketone (MIBK) (0.01 mol^. dm^-3) has been used for the extraction of lanthanide(III) ions such as Sm(III), Gd(III) and Ho(III) (Me) (~3^. 10^-6mol^. dm^-3) from pH 1-2 buffer solutions of 0.1 mol^. dm^-3(H⁺, Cl^-) ionic strength and quantitative extraction (>95%) was found at pH 2. Through slope analysis the composition of the organometallic adduct responsible for the extraction came out to be M(PA)₃. The conditional equilibrium constant values, log K_ex, were deduced to be 2.60±0.01, 2.09±0.01 and 1.44±0.03 for these lanthanide(III) ions, respectively. The metals in concentration up to ~2.5^. 10^-4mol^. dm^-3can be quantitatively extracted by the proposed system. Among the various anions, fluoride, oxalate and cyanide ions (~3.0^. 10^-4mol^. dm^-3) and, among the cations, Zn(II) Cu(II), Co(II) and Fe(III) reduced the lanthanide extraction. The extraction of various other metal ions at the optimized conditions of Me extraction for this series of lanthanide ions was also studied and high separation factors (10²-10³) were obtained showing the good selectivity of this extraction system.     

Luminescence of neodymium(III) carboxylate complexes with different ligands

The spectral and luminescent characteristics of neodymium(III) carboxylate complexes with different nitrogen- and phosphorus-containing neutral ligands were studied and the relationship between the intensity of luminescence and the composition of the coordination sphere was established. The most intensive luminescence of neodymium(III) compounds in the IR region was observed from the complexes with toluic and cinnamic acids.     

Photochemical behaviour of the Nd(III) and Ho(III) complexes of ethylenediaminetetraacetic acid

The photochemical decomposition of Nd³⁺/EDTA and Ho³⁺/EDTA has been carried out at 300 nm, and followed by changes within the hypersensitive absorption transitions of these ions. It was found that a single decarboxylation of the EDTA ligand occurred, and CO₂ gas was evolved. The reaction terminates after approx. 1 mol of CO₂ per mole of EDTA is produced, since the photoproduct absorbs strongly at 300 nm. Initial quantum yields were found to vary with pH, but averaged between 0.1 and 0.5 mol/Einstein.     

Studies on synthesis, infrared and fluorescence spectra of new europium (III) and terbium (III) complexes with an beta-diketonate-type ligand

A new beta-diketonate-type ligand, N-(2-amino-6-methyl-pyridinyl)ketoacetamide (L) and its complexes with europium (III) and terbium (III) were synthesized. The complexes were characterized by elemental analysis, infrared spectra and conductivity. The europium (III) and terbium (III)-ions were found to coordinate to the CO oxygen atoms and pyridine nitrogen atoms. The fluorescence properties of these complexes in solid, DMF and CH3OH were studied. The solvent factors influencing the fluorescent intensity are discussed.     

Synthesis,characterization and cytotoxic/cytostatic activity of Sm(III) and Gd(III) complexes

New Sm(III) and Gd(III) complexes of deprotonated 4-hydroxy-3[1-(4-nitrophenyl)-3-oxobutyl]-2H-1-benzopyran-2-one (Acenocoumarol) were synthesized and characterized using FT-IR, FT-Raman, NMR spectra, and elemental analyses. The vibrational study gave evidence for the coordination of ligand to lanthanide ions. The ligand and its lanthanide(III) complexes were tested for their cytotoxic/cytostatic activity against two tumor cell lines and peritoneal mouse macrophages. The Sm(III) and Gd(III) complexes exhibit good activity against melanoma B16 and fibrosarcoma L929 and are stronger inhibitors of tumor cell proliferation than the ligand. Besides their cytotoxicity to tumor cells, Acenocoumarol and its gadolinium(III) and samarium(III) complexes modulate NO generation in activated macrophages.     

EPR spectra and structures of spin-variable iron(III) complexes

The structures of the spin-variable iron(III) complexes Fe(4-OCH₃-SalEen)₂X and FeL′₂X (L′ is oxysalicylidene-N′-ethyl-N-ethylenediamine; X = PF₆, NO₃, and SCN) were examined from their EPR spectra. The coordination units (CUs) of these complexes are a high-symmetry octahedron with a slight tetrahedral distortion or a low-symmetry pseudooctahedron with considerable tetragonal and orthorhombic distortions. When the complex passes from the high-spin to low-spin state, its CU changes. The energy level splittings caused by various types of distortions were estimated from the EPR data. The distortion of the CU depends on the outer-sphere anion. The magnetic resonance parameters of the complexes were analyzed. The fine structure parameters of the EPR spectra of high-spin complexes (the ground-state term is $^6 A_{1_g }$ ) depend on the CU distortion and the covalent bonding. The spin-orbital coupling makes an appreciable second-order contribution to the expressions for the Zeeman coupling parameters of low-spin complexes (the ground-state term is $^2 T_{2_g }$ ).     

Unequivocal synthetic pathway to heterodinuclear (4f,4f') complexes: magnetic study of relevant (Ln(III), Gd(III)) and (Gd(III), Ln(III)) complexes

The tripodal ligand tris[4-(2-hydroxy-3-methoxyphenyl)-3-aza-3-buten]amine (LH(3)) is capable of coordinating to two different lanthanide ions to give complexes formulated as [LLnLn'(NO(3))(3)].x H(2)O. The stepwise synthetic procedure consists of introducing first a Ln(III) ion in the inner N(4)O(3) coordination site. The isolated neutral complex LLn is then allowed to react with a second and different Ln' ion that occupies the outer O(6) site, thus yielding a [LLnLn'(NO(3))(3)].x H(2)O complex. A FAB(+) study has confirmed the existence of (Ln, Ln') entities as genuine, when the Ln' ion in the outer site has a larger ionic radius than the Ln ion in the inner site. The qualitative magnetic study of the (Gd, Ln) and (Ln, Gd) complexes, based on the comparison of the magnetic properties of (Gd, Ln) (or (Ln, Gd)) pairs and (Y, Ln) (or (Ln, La)) pairs, is very informative. Indeed, these former complexes are governed by the thermal population of the Ln(III) Stark levels and the Ln-Gd interaction, while the latter are influenced by the thermal population of the Ln(III) Stark levels. We have been able to show that a ferromagnetic interaction exists at low temperature in the (Gd, Nd), (Gd, Ce), and (Yb, Gd) complexes. In contrast, an antiferromagnetic interaction occurs in the (Dy, Gd) and (Er, Gd) complexes. Although we cannot give a quantitative value to these interactions, we can affirm that their magnitudes are weak since they are only perceptible at very low temperature.     

Visible spectra of some chloropentakis(alkylamine)-cobalt(III) complexes

All four spin-allowed transitions in the visible spectra of the complexes [Co(RNH₂)₅Cl]²⁺, R = H, Me, Et, n-Pr, and n-Bu, have been resolved and the relevant crystal field and RACAH parameters determined with a method previously described. The results appear to be consistent within the series and agree well with those reported in the literature for structurally related systems.     

Electronic and infrared spectral studies of manganese(III) selenito complexes

Summary Selenito manganese(III) complexes of the type MMn(SeO₃)₂ · × H₂O (where M = H⁺, NH ₄ ⁺ , K⁺, Rb⁺ and Cs⁺) have been prepared, Magnetic measurements show all these complexes to be of high spin d⁴ type, On the basis of their i.r. and electronic spectral studies and other properties, a polymeric octahedral structure involving bridging oxygen atoms has been suggested.     

Molecular simulation of langmuir monolayer formation by Gd(III) stearate complexes

Clusters simulating the formation of Gd(III) stearate complex monolayers on the surface of an aqueous phase are studied by means of molecular mechanics. From a comparison of the calculated and experimental data, it concluded that Langmuir monolayers are produced by Gd(III) aqua complexes with one and two stearate anions.     

Synthesis of cationic gold(III) complexes using iodine(III)

Abstract

We report the synthesis and characterization of cationic Au(III) complexes supported by nitrogen-based ligands. The syntheses are achieved by reacting Au(I) complexes [Au(N-Me-imidazole)₂]⁺ and [Au(pyridine)(NHC)]⁺ with iodine(III) reagents PhI(OTf)(OAc) and [PhI(pyridine)₂]²⁺ yielding a series of cationic gold(III) complexes. In contrast, reactions of phosphine ligated gold(I) complexes with iodine(III) reagents results in the oxidation of the phosphine ligand.     

Single-crystal electronic spectra of some quadrate chromium(III) complexes

Polarised electronic spectra of trans-[Cr(tmd)₂F₂](ClO₄), trans-[Cr(en)₂(dma)₂](ClO₄)₃, trans-[Cr(en)₂(dmf)Cl](ClO₄)₂ and trans-[Cr(en)₂(dmf)Br](ClO₄)₂ have been measured at 77 K (tmd = trimethylenediamine; dma = N,N-dimethylacetamide; dmf = N,N-dimethylformamide; en = ethylenediamine, pn = propylenediamine). The observed quartet bands have been given definitive quadrate assignments based on polarisation characteristics. The four-component quadrate quartet bands have been uncovered and assigned also in the unpolarised crystal spectrum of trans-[Cr(en)₂(dmf)₂](ClO₄)₃ at 77 K and the solution spectrum of trans-[Cr(en)(pn)F₂]⁺. The band maxima derived by gaussian analysis in these spectra have been fitted with the theoretical energy equations of d³ configuration in quadrate ligand fields including full configuration interaction. The ligand field parameters Dq, Dt, and Ds and the election correlation parameter, B, extracted by such a fitting, have been compared with those obtained for other similar systems earlier. The significance of the ligand field symmetry parameters and the translated angular overlap model parameters is discussed.     

Structures and vibrational frequencies of vanadium (V) oligomers: An ab initio study using effective core potentials

Ab initio molecular geometries and vibrational frequencies of various isolated vanadate species (VO³⁻₄, HVO²⁻₄, H₂VO⁻₄, and V₂O⁴⁻₇) were calculated using different pseudopotentials. The relative merits of these were assessed by comparing the calculated molecular parameters with the corresponding values obtained from calculations at all-electron levels and, whenever available, from X-ray studies for the salts. The calculations were extended to higher oligomers (V₃O⁵⁻₁₀, V₄O⁶⁻₁₃, and V₄O⁴⁻₁₂) using the pseudopotential whose basis functions are (10s5p5d)/[2s1p1d] (55/5/5) on vanadium and (4s4p)/[2s2p] (31/31) on oxygen, which yielded the best compromise between accuracy and computational effort. The results indicate a linear centrosymmetric geometry for the isolated V₂O⁴⁻₇ anion. The higher oligomers have less than 180° V(SINGLE BOND)O(SINGLE BOND)V angles, except the noncyclic tetraoligomer which has a linear central V(SINGLE BOND)O(SINGLE BOND)V angle (180°). The cyclic V₄O⁴⁻₁₂ species presents a planar structure with all the vanadium and bridging oxygen atoms in the same plane. This structure was alrea dy reported for the [(CH₃)CNH₃][V₄O₁₂] salt. The results suggest a lower stability of the linear V₄O⁶⁻₁₃ species, in agreement with previous reports. © 1996 by John Wiley & Sons, Inc.     

氯冉酸阴离子桥联的Nd(III)-Nd(III), Dy(III)-Dy(III)和 Ho(III)-Ho(III)双 核配合物的合成与磁性

本文合成了三个以氯冉酸阴离子为桥基的稀土双核配合物,Ln~2(Phen)~4(CA)(NCS)~4(Ln=Nd,Dy,Ho;Phen=菲咯啉;CA=氯冉酸二价阴离子)。通过元素分析,红外光谱,电导,电子吸收光谱及变温(4-300K)磁化率表征了配合物,并由变温磁化率观察到的数据和理论方程通过最小二乘法拟合,得出分子内稀土离子间的相互作用参数:Z'J'=-0.79(Nd),-0.67(Dy),-0.63cm^-^1(Ho);表明稀土离子间存在极弱的反铁磁性交换相互作用。零场分裂参数Δ=-0.16(Nd),-0.76(Dy),-2.55cm^-^1(Ho);g=0.618(Nd),1.739(Dy),1.601(Ho),拟合因子≈10^-^4。