Band 217, Heft 1

Measurement of optical rotation in RbTiOAsO 4 (RTA) with the tilter method resulted in an optical rotation of ρ 12 = +17(3) o /mm at a wavelength of 670nm, when a (100) sample was tilted about [001]. A tilt about [010] showed no rotation, as expected from the directional dependence of optical rotation calculated from the tensor in point group mm 2. The absolute Miller-indices of the sam-les were found using X-ray anomalous scattering. The calculations with a dipole-dipole model show that the As 5+ -ions in RTA correlate with the main structural contribution of the optical rotation. However, there seems to be an even larger intrinsic contribution due to the Ti 4+ – ions as a result of the distorted octahedral co-ordination with oxygen.

The chemistry of nitrides and nitridometalates is a rapidly growing field in solid state chemistry. This short review is intended to give a brief but comprehensive over-view on the compounds and phases formed with manga-nese, which cover an especially broad range of oxidation states. Furthermore, the present paper tries to put the ob-served structures and properties of the compounds into a broader context.

The title compound [C 16 H 24 N 3 O 4 ] + [C 6 H 2 N 3 O 7 ] - resembles 18 membered macrocycle, which has two ether O atoms, two pairs of amide N and O atoms and an amine N as potential donor atoms. The macrocycle has undergone protonation at the amine N atom. The picrate ion interacts through its phenolic O atom with NH 2 + group via N-H⋅⋅⋅O hydrogen bond. NH 2 + also shows a strong intramolecular H bonding with one of the amide oxygens of the macrocyclic ring. This results in significant conformational changes in one half of the macrocyclic ring. Apart from it, an increased flexibility of the system and a -CH 2 ⋅⋅⋅ π interaction renders the cavity non-suitable for accepting small molecules like water or alcohol in it.

The crystal structures of Ln{[C(CH 3 )⋅(OH)(P 2 O 6 H 3 )][C(CH 3 )(OH)(P 2 O 6 H 2 )]}⋅5.5H 2 O, with Ln = Y (compound 1 ), Ln = Ho (compound 2 ) and Ln = Er (compound 3 ), have been determined by single crystal X-ray diffraction. The three compounds are isomorphous and crystallize in the monoclinic space group P 2 1 / n (n°14). The cell parameters of 1 are a = 10.451(2) Å, b = 11.395(3) Å, c = 17.173(3) Å, β = 94.28(1)°, those of 2 are a = 10.447(2) Å, b = 11.382(2) Å, c = 17.129(4) Å, β = 94.32(3)°, and those of 3 are a = 10.432(1) Å, b = 11.398(2) Å, c = 17.134(2) Å, β = 94.35(2)°.The coordination polyhedron around the lanthanide cations is a distorted monocapped trigonal prism with a slightly distorted C 2 v symmetry. The UV and visible light absorption spectrum was recorded for 3 . A detailed theoretical simulation of the energy level scheme of the 4f 11 configuration of Er 3+ was carried out. The angular parts were accurately calculated by group-theoretical and tensorial methods and the radial integrals were left as parameters to be determined semi-empirically. The C 2 v symmetry was described by free ion and crystal field parameters after refinement of these parameters on the absorption spectroscopic data of 3 .

The crystal structure of anhydrous ammonium acid oxalate, NH 4 HC 2 O 4 , obtained from the thermal decomposition of the related hemihydrate has been determined from powder diffraction data collected with monochromatic laboratory X-rays, using the capillary technique. The crystal structure is monoclinic, P 2 1 / c , Z = 4, a = 4.3629(1) Å, b = 13.5657(1) Å, c = 7.7100(1) Å, β = 102.602(1)° and V = 445.3(1) Å 3 . The structure has been solved with the direct methods and refined with the Rietveld method, from which the agreement factors R wp = 8.19% and R B = 5.18% have been obtained. The crystal structure consists of corrugated layers built from seven-fold ammonium coordination polyhedra and connected by oxalate groups. The hydrogen atom positions have been located and the hydrogen bond network is extensively discussed.