Harald P. Fritzer

Hypersensitivity and nephelauxetic effect of Nd(III) in sodium borate glasses

Abstract An investigation of the optical absorption spectra of 1 mol% Nd2O2 in sodium borate glasses with Na2O contents varying from 7.5 to 40 mol% is presented. The glasses were obtained by quenching melts consisting of Na2CO3, H3BO3, and Nd2O3 (900 to 1100°C, 1.5–2 h) between steel plates. The optical absorption spectra were recorded at 300 and 20 K. Special emphasis is laid on the positions, half-widths, intensities and shapes of the 4 I 9 2 → 2 P 1 2 and the hypersensitive 4 I 9 2 → 4 G 5 2 , 2 G 7 2 transitions. The observed property versus composition variations are discussed in terms of the covalency of the neodynamium-oxygen bond and of changes induced into the crystalline field around the Nd3+ ions by structural changes of the glass matrix. The shape of the hypersensitive transition is used for comparison with existing models on the rare earth environment in oxide glasses.

Suitability of Nd(III) absorption spectroscopy to probe the structure of glasses from the ternary system Na2O–B2O3–SiO2

Abstract Optical absorption spectra of glasses from the ternary system Na 2 O–B 2 O 3 –SiO 2 with 20, 40, and 60 mol% SiO 2 and varying modifier contents containing 1 mol% Nd 2 O 3 were measured at cryogenic temperatures. The glasses were obtained by quenching the liquids of appropriate composition between steel plates. For comparison doped glasses from the binary systems Na 2 O–B 2 O 3 and Na 2 O–SiO 2 were included. The molar volumes and packing ratios of the doped ternary glasses were compared with those of undoped glasses with similar composition to make sure that the dopant ions do not affect the bulk glass properties. The position of the 4 I 9/2 → 2 P 1/2 transition was used to monitor the nephelauxetic effect and the hypersensitive 4 I 9/2 → 4 G 5/2 , 2 G 7/2 transition to monitor changes in the rare-earth environment with the glass composition. The observed changes of the spectral features are consistent with structural changes in the host glasses as proposed by models of these glasses derived from NMR and IR investigations on undoped glasses. Hence the suitability of Nd 3+ absorption spectroscopy to probe the structure of these glasses is established.

SYNTHESIS AND SPECTRAL AND STRUCTURAL CHARACTERIZATION OF A BRIDGING CHLOROPICOLINATOCOPPER(II) COMPLEX, CU(C5H4NCOO)CL

SummaryThe title complex of copper(II) chloride with picolinic acid was prepared and characterized by spectroscopic and X-ray crystallographic methods. The complex, Cu(C5H4NCOO)Cl, crystallizes tetragonal, space group P42/n (No. 86),a=976.4(1),c=1499.6(4) pm,N=8;Rw=0.048 for 543 observed MoKα diffractometer data. In the structure of the complex two μ-chloro bridges form only slightly bent Cu2Cl2 rings [Cu-Cl=224.2(4) and 275.6(4) pm] with Cu...Cu separation of 359.4(2) pm and Cl...Cl separation of 348.7(5) pm. These edge-sharing copper coordination polyhedra are further linked via the N and O donor atoms of the picolinato anions at Cu-N distances of 199.6(12) pm and Cu-O bond lengths of 195.7(8) and 200.6(10) pm, to form a two-dimensional layer structure in which these layers are arranged along theab plane. Each picolinate anion functions as a tetra-dentate ligand: N(1) and O(2) are coordinated to the same Cu(II) center whereas O(1) is bonded to a neighbouring Cu(II) center. O(2) is further bonded to the latter Cu(II) center at a long Cu-O distance of 256.5(8) pm. The electronic, infrared and Raman spectra of the solid complex are reported and discussed.ZusammenfassungDer Titelkomplex aus Kupfer(II)chlorid und Picolinsäure wurde dargestellt und mit spektroskopischen und Röntgen-Einkristall-Methoden charakterisiert. Cu(C5H4NCOO)Cl kristallisiert tetragonal, Raumgruppe P42/n (No. 86),a=976.4(1),c=1499.6(4) pm,N=8;Rw=0.048 für 543 beobachtete Mokα-Diffraktometerdaten. In der Kristallstruktur bilden zwei μ-chloro-Brücken nur wenig gewinkelte Cu2Cl2-Ringe aus [Cu-Cl=224.2(4) und 275.6(4) pm], mit Cu...Cu Abständen von 359.4(2) pm und Cl...Cl Abständen von 348.7(5) pm. Die kantenverknüpften Koordinationspolyeder der Kupferatome sind in Richtung derab-Ebene über die N- und O-Donoratome der Picolinat-Anionen [mit Cu-N Abständen von 199.6(12) pm und Cu-O Abständen von 195.7(8) und 200.6(10) pm] zu einer zweidimensionalen Schichtstruktur verknüpft. Jedes Picolinat-Anion fungiert als vierzähniger Ligand: N(1) und O(2) sind zum selben Cu(II)-Zentrum gebunden; O(1) ist zum benachbarten Cu(II)-Zentrum koordiniert, zu dem O(2) einen langen Cu-O-Abstand von 256.5(8) pm ausbildet. Die elektronischen, Infrarot- und Raman-Spektren des Festkörper-Komplexes werden berichtet und diskutiert.

Competitive cross-relaxation and energy transfer within the shell model: The case of Cs2NaSmxEuyY1 − x − yCl6

Abstract Electronic energy-transfer processes between Sm 3+ ( 4 G 5 2 ) donor ions and Eu 3+ ( 7 F 0 , 7 F 1 ) acceptor ions in the cubic hexachloroelpasolite crystals Cs 2 NaSm x Eu y Y 1 − x − y Cl 6 have been investigated over a wide range of Sm 3+ and Eu 3+ concentrations at temperatures of 80 and 300 K. In these systems the luminescence from the 4 G 5 2 state of Sm 3+ is strongly quenched by both cross-relaxation to nearby Sm 3+ ions and energy transfer to the 5 D 0 state of Eu 3+ . The lifetime of the 5 D 0 state is not affected by the presence of Sm 3+ . The rates of cross-relaxation and energy transfer are determined from luminescence decay curve measurements for the Sm 3+ 4 G 5 2 → 6 H 7 2 emission and the Eu 3+ 5 D 0 → 7 F 2 emission following excitation into the 4 G 5 2 state of Sm 3+ . The luminescence decay curves for the 4 G 5 2 state are analysed in terms of a recently developed discrete shell model for energy transfer assuming electric dipole vibronic-electric dipole vibronic and magnetic dipole-magnetic dipole interaction between Sm 3+ donor ions and Eu 3+ acceptor ions. Exact agreement is achieved for the energy transfer from Sm 3+ donor ions to Eu 3+ acceptors without curve fitting.

Fast cross relaxation in lanthanide hexachloroelpasolites: application of the shell model

Abstract Luminescence decay curves from the 4 G 5 2 state of Sm3+ in the cubic hexachloroelpasolite crystals Cs2 NaSmxY1−xCl6 (x = 0.005 to x = 1) have been measured in the temperature range 10–300 K. Energy transfer from the 4 G 5 2 to the 6FJ states occurs at all concentrations studied. At intermediate concentrations the decay curves are strongly non-exponential and are interpreted using a recently developed shell model. Extensions of the model which may provide a better description of the data are briefly discussed.

Paramagnetic conjugated polymers with stable radicals in side groups

SummaryPoly(1,3-dihydroxy-2-(4-ethynylphenyl)-4,4,5,5-tetramethylimidazolidine), poly(2-(4-ethynylphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-oxide), poly(4-(4-ethynylbenzylideneamino)-2,2,6,6-tetramethylpiperidine) and poly(4-(4-ethynylbenzylideneamino)-2,2,6,6-tetramethylpiperidine-1-oxyl) were prepared from poly(4-ethynyl-benzaldehyde). The products were characterized spectroscopically (IR, UV, 1H and 13C NMR) and with respect to the magnetic susceptibility. The polyradicals (1-oxyl compounds) showed paramagnetic properties obeying Curies law.

Molecular symmetry with quaternions

A new and relatively simple version of the quaternion calculus is offered which is especially suitable for applications in molecular symmetry and structure. After introducing the real quaternion algebra and its classical matrix representation in the group SO(4) the relations with vectors in 3-space and the connection with the rotation group SO(3) through automorphism properties of the algebra are discussed. The correlation of the unit quaternions with both the Cayley-Klein and the Euler parameters through the group SU(2) is presented. Besides rotations the extension of quaternions to other important symmetry operations, reflections and the spatial inversion, is given. Finally, the power of the quaternion calculus for molecular symmetry problems is revealed by treating some examples applied to icosahedral symmetry.

Spectroscopic studies and crystal field investigations on a complex neodymium(III) azide

Abstract Single crystals of Cs 4 Nd(N 3 ) 7 have been prepared by metathetical reactions and the optical spectra were recorded under high resolution. Since the crystals are inappropriate for conventional structure determinations due to radiation damage under the X-ray beam a method for finding the microsymmetry of the crystal field around the Nd(III) ion has been developed. By an investigation of the “hot band system” around 430 nm the splitting of the groundstate multiplet was determined with high accuracy. By a “truncated” crystal field calculation various coordination polyhedra have been tested in order to extract the most probable one. Evidence for dominantly hexagonal microsymmetry was found.

Investigation of phase separation in Nd3+ doped ternary sodium borosilicate glasses by optical spectroscopy.

Two glasses doped with 1 mol% Nd2O3 and batch compositions inside the miscibility gap of the ternary Na2O-B2O3-SiO2 system were prepared by rapid quenching of the 1,400 degrees C melts. Phase separation was induced by heat-treatment at 600 degrees C for different exposure times and monitored qualitatively by an observation of Rayleigh scattering. The 4I(9/2-->P(1/2) transition of Nd3+ around 23300 cm(-1) recorded for the quenched samples without heat-treatment was used to demonstrate that submicroscopic phase separation in the doped glasses occurs instantaneously upon quenching. The effect of the Nd3+ concentration on this submicroscopic phase separation was investigated.

Temperature dependence of luminescence decay from the 4G52 state of Sm3+ in Cs2NaSmxY1 − xCl6 and Cs2NaSmxEuyY1 − x − yCl6

Luminescence decay curves for the 4G52 → 6H72 emission of Sm3+ in the cubic hexachloroelpasolite crystals Cs2NaSmxY1 − xCl6 (x = 0.005–1) and Cs2NaSmxEuyY1 − x − yCl6 (x = 0.01–0.95, y = 0.05–0.99) have been measured over the temperature range 10–300 K using pulsed laser excitation into the (6H52)Γ7 → (4G52)Γ8 magnetic-dipole-allowed electronic transition of Sm3+. The luminescence from the 4G52 state is strongly quenched by both cross relaxation to nearby Sm3+ ions and energy transfer to the 5D0 state of Eu3+ acceptors. The temperature dependence of cross relaxation and energy transfer is discussed in terms of the involved mechanisms.