Crystal structures and properties of the thiostannates Eu2SnS4 and Sr2SnS4 and the selenogermanate γ-Sr2GeSe4

Eu2SnS4, Sr2SnS4, and Sr2GeSe4 have been synthesized by heating the elements or binary precursors at 1073 K and their crystal structures were determined by single crystal methods. Eu2SnS4 crystallizes with a new structure type (Pnma, a = 11.187(2), b = 8.768(2), c = 7.538(2) Angstrom, Z = 4), consisting of distorted [SnS4](4-) tetrahedra and sevenfold coordinated Eu2+ ions. Sr2SnS4 and gamma-Sr2GeSe4 are isostructural and form a new structure type likewise (Ama2, Z = 4, Sr2SnS4: a = 9.977(1), b = 10.311(2), c = 7.243(1) Angstrom, Sr2GeSe4: a = 10.284(2),b = 10.543(2), c = 7.41 (1) Angstrom) with more regular tetrahedral anions and strontium coordinated by seven and eight chalcogen atoms, respectively. Eu2SnS4 is a Curie-Weiss paramagnet (7.80(2) mu(B)/Eu; theta = 4.2(2) K) and orders antiferromagnetically at T-N = 5.5(2) K with a magnetization of 6.56(5) PB/Eu at 5.5 1 The divalent nature of europium is also evident from Eu-151 Mossbauer spectra which show a single signal at an isomer shift of - 12.2(l) mm/s at 78 K. Full magnetic hyperfine field splitting (19.5(2) T at the europium nuclei) is observed at 4.2 K. The Sn-119 spectrum shows one signal at 1.25(9) mm/s subject to quadrupole splitting of 0.76(2) mm/s. At 4.2 K a transferred hyperfine field of 3(1) T is detected at the tin site.