M. Gál

Vibrational spectroscopic studies of uranyl complexes in aqueous and non-aqueous solutions

Abstract Vibrational spectra have been obtained for aqueous solution of uranyl-perchlorates, -fluorides, -chlorides, -acetates and -sulphates over a range of solution composition with added anions. We have prepared [Bu n 4 N][UO 2 Cl 4 ], [Me 4 N][UO 2 Cl 4 ], [Pr n 4 N][[UO 2 (NO 3 ) 3 ], [Bu n 4 N][UO 2 (NO 3 ) 3 ], with the expectation that the large cation would give a better approximation to vibrational frequencies of the free anion and would allow measurements in non-coordinating solvents. As the perchlorate is not coordinated to [UO 2 ] 2+ in aqueous solution the expected structure is a solvated cation [UO 2 (OH 2 ) 5 ] 2+ with characteristic infrared 962.5, 253 and 160 cm −1 and Raman 874 and 198 cm −1 bands. The formation of weak, solvated [UO 2 X] + complexes (X=F, Cl) has been established with frequencies at 908, 827, 254, 380 cm −1 and 956, 871, 254 and 222 cm −1 for [UO 2 F] + and [UO 2 Cl] + , respectively. Bidentate NO 3 coordination has been established for solid and dissolved (in CH 2 Cl 2 ) [R 4 N][UO 2 (NO 3 ) 3 ] (R=Pr n , Bu n ). Aqueous solutions of UO 2 (NO 3 ) 2 and Cs[UO 2 (NO 3 ) 3 ] show no clear evidence that bidentate or monodentate nitrate is present. Both unidentate and bidentate linkage of acetate-uranyl were established for acetate complexes in aqueous solutions. For the uranyl sulphate system, monodentate sulphate coordination is the major mode at low SO 4 :U ratios, and even at a ratio of 3:1 there is very little free sulphate.

Mid-, far-infrared and raman spectra of uranyl complexes in aqueous solutions

Abstract Vibrational spectra have been obtained for aqueous solution of UO 2 C10 4 , Na 3 [UO 2 F 5 ], [NH 4 ] 3 [UO 2 F 5 ], UO 2 F 2 , [Bu 4 N] 2 [UO 2 Cl 4 ], UO 2 Cl 2 , UO(NO 3 ) 2 , Rb [UO 2 (NO 3 ) 3 ], [Pr 4 N] [UO 2 (NO 3 ) 3 ], UO 2 (O 2 CCH 3 ) 2 , [Pr 4 N] [UO 2 (O 2 CCH 3 ) 3 ] and UO 2 SO 4 over a range of solution composition. The residual absorptions of H 2 O after water subtraction suggest that some water molecules are bound to [UO 2 ] 2+ . There was no evidence of perchlorate coordination, but besides solvated [UO 2 ] 2+ ion formation of weak [UO 2 F] + and [UO 2 Cl] + complexes have been established. The four nitrate stretching features do not refer neither to bidentate nor to monodentate ligand, but both monodentate and bidentate linkage of acetate to uranyl were established for acetate complexes. The main species present in UO 2 SO 4 solution can be ascribed to a monodentate sulphate. From uranyl frequencies force constants and UO bond distances were calculated for solvated complexes.

Metastability in EuBa2(Cu1-xSnx)3O7-y studied by 119Sn and 151Eu Mössbauer spectroscopy.

The metallic oxide compound system EuBa/sub 2/(Cu/sub 1-//sub x/Sn/sub x/)/sub 3/O/sub 7-y/ (x = 0.05, 0.10, 0.20) was prepared for investigation with /sup 151/Eu and /sup 119/Sn Moessbauer spectroscopy. The best fits of the /sup 119/Sn Moessbauer lines reveal at least two different Sn/sup IV/ sites. The /sup 151/Eu spectra are characteristic for Eu/sup III/ state in these compounds. We have found a considerable difference between the shapes of /sup 119/Sn Moessbauer spectra recorded at room temperature and those recorded at the temperature of liquid nitrogen in the case of the sample having the highest tin content. Nevertheless, there is no evidence that this difference has a direct connection with the superconducting behavior.

Metastability in EuBa/sub 2/(Cu/sub 1-//sub x/Sn/sub x/)/sub 3/O/sub 7-y/ studied by /sup 119/Sn and /sup 151/Eu Moessbauer spectroscopy

The metallic oxide compound system EuBa/sub 2/(Cu/sub 1-//sub x/Sn/sub x/)/sub 3/O/sub 7-y/ (x = 0.05, 0.10, 0.20) was prepared for investigation with /sup 151/Eu and /sup 119/Sn Moessbauer spectroscopy. The best fits of the /sup 119/Sn Moessbauer lines reveal at least two different Sn/sup IV/ sites. The /sup 151/Eu spectra are characteristic for Eu/sup III/ state in these compounds. We have found a considerable difference between the shapes of /sup 119/Sn Moessbauer spectra recorded at room temperature and those recorded at the temperature of liquid nitrogen in the case of the sample having the highest tin content. Nevertheless, there is no evidence that this difference has a direct connection with the superconducting behavior.

Infrared, Raman and force field studies of tetrakis(anionomercuri)methanes

Abstract In order to throw light on the nature of the HgC bond in permecurated methanes, the infrared and Raman spectra of solid tetrakis(anionomercuri)methanes, C(HgX) 4 (X = CN − , HCOO − , CH 3 COO − and CF 3 COO − ) have been assigned in the range 4000−40 cm −1 . For these four as well as for other molecules of this type (X = F − , Cl − , Br − , I − and SCH 3 − ) the force fields for the CHg 4 tetrahedron have been calculated. The HgC force constants are 18 to 28% lower than in the related Hg(CH 3 )X compounds; since the HgC bond lengths are approximately the same in both linear and tetrahedral configuration, this can be explained in terms of the nonbonded interactions between mercury atoms.

Scaled quantum mechanical (SQM) force field and vibrational assignment for cyclohexane

Abstract The complete harmonic force field of cyclohexane has been calculated ab initio, using the split valence 4–21 Gaussian basis set. To account for systematic errors, the ab initio force constants were scaled empirically. Altogether seven scale factors were used in this procedure, whose values were mainly based on previous results on cyclobutane. The scaled quantum mechanical (SQM) force field obtained this way reproduces the fundamental frequencies of cyclohexane and several of its isotopomers with mean deviations of below 10 cm−1. The results are in excellent overall agreement with and support previous assignments and only a few minor modifications and additions are suggested.

Evolution of the coherence of vibrational states in a gradual disorder-order phase transition

Abstract The nematic liquid crystal compound n-p-methoxy-benzylidene-p-butylaniline (MBBA) may be induced to form a solid glassy liquid crystal state by fast cooling. Under heating this amorphous structure can be gradually transformed into real crystal through intermediate, not completely crystallized phases. Laser Raman spectra of all phases were recorded in the 3—1800 cm−1 frequency range. Analysing changes occuring in the intermolecular part of the spectra (3—160 cm−1) from one phase to another it can be shown that the coherence of vibrational states evolves gradually according to the different stages of the disorder-order structural transformation.

FT-IR, FT-FIR and computerized Raman studies of the vibrational spectra and structure of ethylene complexes.

Abstract Skeletal modes of [M(C 2 H 4 ) 3 ] (where M=Ni(O) or Pt(O)), and [Pt(C 2 H 4 Cl 3 ][NBu 4 ] have been measured and assigned. A new model for the normal coordinate treament of π-complexes has been adopted to calculate metal—ligand force constants. The Pt-ehtylene stretching force constants were 1.66, and 2.54 Ncm −1 , and the Pt-ehtylene tilting force constants were 2.04, and 2.84 Ncm −1 for [Pt(C 2 H 4 ) 3 ], and [Pt(C 2 H 4 )Cl 3 ] −1 respectively. These force constants suggest that the π-bonding dominates for tris(ethylene)platinum but that σ- and π-bonding are of almost equal importance for the Zeises salt analogue. The CC valence force constants of chemisorbed ehtylene suggest that C is rehybridised nearly to sp 3 on Ni(lll) and Pt(lll) surfaces but not on Pd(lll). The surface-ehtylene stretching force constants indicate that the bond strengths are in the order Pt>Ni>>Pd.

Mössbauer study of EuBa2Cu3O6+x material

Mössbauer spectra of a mixed EuBa2Cu3O6+x oxide where x>0.5 were recorded in temperature range of 76–300 K. Between 85–300 K temperature the parameters of the appearing line in the Mössbauer spectrum are consistent with an Eu(III) state. At 76 K, however, the spectrum of the freshly prepared material exhibits two separated lines.

High-Tc Superconductivity in La-Ba-Cu-O and Y-Ba-Cu-O Compounds

A high-critical-temperature superconducting transition in multiple-phase La-Ba-Cu-O and Y-Ba-Cu-O systems has been found with the aid of electrical and magnetic measurements. The possible causes of superconductivity is also considered. Among them the change of Fermi-surface topology is the most appreciated.