| Abstract: | Two Novel Sulfide Chlorides of the Lanthanides: Synthesis and Crystal Structure of Pr7S6Cl9 and Nd7S6Cl9 The reactions of the elemental lanthanides (M = Pr and Nd, resp.) with sulfur and the respective trichlorides (MCl3) in evacuated silica tubes (850 °C, 7 d) yield single-phase sulfide chlorides of the composition M7S6Cl9 when appropriate molar ratios (4 : 6 : 3) of the reactants (M : S : MCl3) are used. A slight excess of trichloride as a flux promotes the formation of lath-shaped transparent single crystals (Pr7S6Cl9: pale green, Nd7S6Cl9: pale violet) which prove to be water soluble and sensitive to hydrolysis. The crystal structure was determined from X-ray single-crystal data taking Nd7S6Cl9 (monoclinic, P2/c (no. 13); a = 2425.0(9), b = 664.2(2), c = 691.8(2) pm, β = 97.43(3)°, Z = 2; R = 0.060, Rw = 0.048) as an example. According to Guinier powder data, Pr7S6Cl9 crystallizes isotypically with a = 2441.6(9), b = 669.1(2), c = 696.3(2) pm, and β = 97.74(3)°. Thus four crystallographically independent cations (M3+) are present, each except for M2 coordinated by four S2– but differing in the number of their next Cl– neighbors. The figures of coordination are completed by four Cl– about M1 (square antiprism, CN = 8) and by three Cl– each about M3 and M4 (monocapped trigonal prisms, CN = 7, 2 Ç ). In contrast, M2 is coordinated by only two S2– but five (plus one) Cl– as bicapped trigonal prism (CN = 7 + 1). Eight crystallographically different anions, although indistinguishable by X-ray diffraction, exhibit coordination numbers of four (3 Ç S2– and 1 Ç Cl–) and three (4 Ç Cl–) with respect to the cations. So PbO-analogous layers of the composition 2∞{[(S6/7Cl1/7)M4/4]7}8+ parallel (010) are formed, consisting of 6/7 of S2– and only 1/7 of Cl– as centering anions for the edge-shared (M3+)4 tetrahedra for reasons of charge neutrality. These cationic layers are held together by alternatingly sheathed layers of Cl– with only threefold coordinated anions. |
