Two new quaternary thiophosphates with pseudo one-dimensional structures: Syntheses and crystal structures of Cs3Sm[PS4]2 and Rb3Sm[PS4]2

The new thiophosphates Rb3Sm[PS4]2 and Cs3Sm[PS4]2 were obtained as pale yellow needles using an in-situ formed thiophosphate flux. Rb3Sm[PS 4]2 crystallizes in the space group P21 with a = 9.7061(19) Å, b = 6.7517(14) Å, c = 11.395(2) Å, β = 90.63(3)°, (Z = 2); Cs3Sm[PS4]2 in space group P21/n with a = 15.311(3) Å, b = 6.8762(14) Å, c = 15.352(3) Å, β = 99.49(3)°, (Z = 4). The crystal structures are characterized by the formation of complex anionic chains, ∞1{(Sm[PS4]2)3-} which run along the [010] direction in both structures. One of the two independent thiophosphate groups connects three Sm3+ cations to form an infinite zigzag like arrangement, while the other acts as a terminal ligand to one Sm3+ions. Such a μ3 or face-grafting coordination mode of a [PS4]3- anion is not very common. The Sm3+ ions are in bicapped trigonal prismatic chalcogen coordination. The average Sm-S distances within the trigonal prisms are close to 2.88 Å, while the bonds to the capping atoms are distinctly longer. The chains are chiral yet their symmetry is close to 21/m. In contrast to the rubidium compound, Cs3Sm[PS4]2 contains both enantiomorphs. In both structures the chains are arranged as a distorted hexagonal rod packing.