title: Crystal structure, physical properties and HRTEM investigation of the new oxonitridosilicate EuSi2O2N2.
abstract: 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.
authors.affiliation: Department Chemie und Biochemie, Lehrstuhl für Anorganische Festkörperchemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13 (D), 81377 Münich, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Stadler
authors.forename: Oliver
authors.initials: O
authors.lastname: Oeckler
authors.forename: Henning A
authors.initials: HA
authors.lastname: Höppe
authors.forename: Manfred H
authors.initials: MH
authors.lastname: Möller
authors.forename: Rainer
authors.initials: R
authors.lastname: Pöttgen
authors.forename: Bernd D
authors.initials: BD
authors.lastname: Mosel
authors.forename: Peter
authors.initials: P
authors.lastname: Schmidt
authors.forename: Viola
authors.initials: V
authors.lastname: Duppel
authors.forename: Arndt
authors.initials: A
authors.lastname: Simon
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schnick