Crystal structure, physical properties and HRTEM investigation of the new oxonitridosilicate EuSi2O2N2.

The new layered oxonitridosilicate EuSi(2)O(2)N(2) has been synthesized in a radio-frequency furnace at temperatures of about 1400 degrees C starting from europium(III) oxide (Eu(2)O(3)) and silicon diimide (Si(NH)(2)). The structure of the yellow material has been determined by single-crystal X-ray diffraction analysis (space group P1 (no. 1), a=709.5(1), b=724.6(1), c=725.6(1) pm, alpha=88.69(2), beta=84.77(2), gamma=75.84(2) degrees ,V=360.19(9)x10(6) pm(3), Z=4, R1=0.0631, 4551 independent reflections, 175 parameters). Its anionic Si(2)O(2)N(2) (2-) layers consist of corner-sharing SiON(3) tetrahedra with threefold connecting nitrogen and terminal oxygen atoms. High-resolution transmission electron micrographs indicate both ordered and disordered crystallites as well as twinning. Magnetic susceptibility measurements of EuSi(2)O(2)N(2) exhibit Curie-Weiss behavior above 20 K with an effective magnetic moment of 7.80(5) mu(B) Eu(-1), indicating divalent europium. Antiferromagnetic ordering is detected at 4.5(2) K. EuSi(2)O(2)N(2) shows a field-induced transition with a critical field of 0.50(5) T. The four crystallographically different europium sites cannot be distinguished by (151)Eu Mössbauer spectroscopy. The room-temperature spectrum is fitted by one signal at an isomer shift of delta=-12.3(1) mm s(-1) subject to quadrupole splitting of DeltaE(Q)=-2.3(1) mm s(-1) and an asymmetry parameter of 0.46(3). Luminescence measurements show a narrow emission band with regard to the four crystallographic europium sites with an emission maximum at lambda=575 nm.

Structure and lithium dynamics of Li2AuSn2--a ternary stannide with condensed AuSn4/2 tetrahedra.

The new stannide Li(2)AuSn(2) was prepared by reaction of the elements in a sealed tantalum tube in a resistance furnace at 970 K followed by annealing at 720 K for five days. Li(2)AuSn(2) was investigated by X-ray diffraction on powders and single crystals and the structure was refined from single-crystal data: Z=4, I4(1)/amd, a=455.60(7), c=1957.4(4) pm, wR2=0.0681, 278 F(2) values, 10 parameters. The gold atoms display a slightly distorted tetrahedral tin coordination with Au-Sn distances of 273 pm. These tetrahedra are condensed through common corners leading to the formation of two-dimensional AuSn(4/2) layers. The latter are connected in the third dimension through Sn-Sn bonds (296 pm). The lithium atoms fill distorted hexagonal channels formed by the three-dimensional [AuSn(2)] network. Modestly small (7)Li Knight shifts are measured by solid-state NMR spectroscopy that are consistent with a nearly complete state of lithium ionization. The noncubic local symmetry at the tin site is reflected by a nuclear electric quadrupolar splitting in the (119)Sn Mössbauer spectra and a small chemical shift anisotropy evident from (119)Sn solid-state NMR spectroscopy. Variable-temperature static (7)Li solid-state NMR spectra reveal motional narrowing effects at temperatures above 200 K, revealing lithium atomic mobility on the kHz time scale. Detailed lineshape as well as temperature-dependent spin lattice relaxation time measurements indicate an activation energy of lithium motion of 27 kJ mol(-1).

Square-planar coordinated polyanions of palladium, platinum, and gold stannaborate [SnB11H11]2- coordination chemistry.

The tetrasubstituted polyanions of platinum, palladium, and gold [M(SnB(11)H(11))(4)](x-) (x=6, M=Pd, Pt; x=5, M=Au) have been prepared and characterized by single-crystal X-ray diffraction, elemental analysis, IR, Raman, (11)B, and (119)Sn heteronuclear NMR spectroscopy. In the case of the platinum derivative [Bu(3)MeN](6)[Pt(SnB(11)H(11))(4)] (2) (119)Sn Mössbauer spectroscopy has been carried out. The isolated salts are stable towards moisture and air and the complexes 2 and 3 were treated with 1,3-bis(diphenylphosphino)propane (dppp) to give the respective substitution products [Bu(3)MeN](2)[(dppp)M(SnB(11)H(11))(2)] (M=Pd, Pt).