Structural frustration and occupational disorder: the rare earth metal polysulfides Tb8S(14.8), Dy8S(14.9), Ho8S(14.9), and Y8S(14.8)

Dark red crystals of Y?S(14.8), Tb?S(14.8), Dy?S(14.9), and Ho?S(14.9) have been obtained following different reaction routes. The isostructural title compounds adopt the Gd?Se?? type, a 24-fold superstructure of the ZrSSi-type and can be described in space group A112 (non standard setting of C121, no. 5) with lattice parameter of a = 11.505(1) ?, b = 15.385(1) ?, c = 15.726(1) ?, and γ = 90.21(2)° for Y?S(15-x); a = 11.660(1) ?, b = 15.468(2) ?, c = 15.844(2) ?, and γ = 90.19(2)° for Tb?S(15-x); a = 11.584(1) ?, b = 15.340(2) ?, c = 15.789(2) ?, and γ = 90.34(2)° for Dy?S(15-x); and a = 11.538(1) ?, b = 15.288(2) ?, c = 15.740(2) ?, and γ = 90.23(1)° for Ho?S(15-x), respectively. The structure consists of an alternating stacking of puckered RES] (RE, rare-earth metals) double slabs and planar sulfur layers along 001]. The planar sulfur layers have a complex arrangement of S?2? dinuclear dianions, isolated S2? ions, and vacancies. All compounds contain trivalent rare-earth metal ions, for Tb?S(15-x) and Dy?S(15-x) antiferromagnetic order was found at T(N) = 5.4(2) K and 3.8(1) K, respectively. Short wavelength cutoff optical band gaps of 1.6 to 1.7 eV were determined.