Synthesis and average and incommensurately modulated crystal structure of 2D-K 3Ce 2P 3S 12

Abstract

K 3Ce 2P 3S 12, a new thiophosphate of cerium and potassium, has been synthesized for the first time and its average structure solved from single crystal data. A tentative solution for its weakly modulated, incommensurate structure has also been found within a (3+1)D formalism. The average structure of this new, yellow material has monoclinic symmetry, space group C2/ c with the following cell parameters a=20.595(3) Å, b=9.6453(10) Å, c=22.161(4) Å, β=97.360(13) and V=4366.0(19) Å 3 ( Z=8). Its crystal refinement yielded the residual factor R=4.77% for 187 parameters and 3117 independent reflections at a 2 σ( I) level. The two-dimensional structure can be viewed as built upon infinite 1 ∞[Ce 2P 2S 12] 8− chains connected to each other by [PS 4] tetrahedra to form 2 ∞[Ce 2P 3S 12] 3− layers. These corrugated slabs are electrostatically linked by potassium ions. K 3Ce 2P 3S 12 can be considered as a new member of the (K I 4(P 2) VIIIQ −II 6) l(K I 3P VQ −II 4) m(Ln III 4(P 2) VIII 3S −II 18) n(Ln IIIP VQ −II 4) o family (Ln=La, Ce; Q=S, Se) with l=0, m=1, n=0 and o=2 (K I 3Ce III 2P V 3S −II 12). The crystal refinement of the true modulated structure within the (3+1)D formalism (wavevector: q =−0.559(2) a ∗+0.589(3) c ∗ ) yielded the residual factor R=5.66% for 296 parameters and 3583 independent reflections (3117 main reflections and 466 first order satellites). In the aperiodic crystal, the modulation results from the rotation of the [PS 4] tetrahedra and the bicapped [CeS 8] trigonal prisms around the alkali metals.