Three of a kind? The non-isotypic triple CsCe[P2Se6], CsSm[P2Se6] and CsEr[P2Se6]

Abstract

Abstract Three new compounds of the CsLn[P2Se6] family with Ln = Ce, Sm and Er have been prepared and structurally characterized. Plate-shaped, amber-colored single crystals of these cesium lanthanoid(III) hexaselenodiphosphates(IV) were obtained by heating stoichiometric amounts of Ln, P and Se with CsCl as a reactive flux in fused silica ampoules at 800 °C for four days. CsCe[P2Se6] crystallizes monoclinically in space group P21/c with a = 1297.86(9), b = 776.24(5), c = 1198.43(8) pm, β = 106.589(3)° and Z = 4. The structure is isotypic with that of KLa[P2Se6], the Cs+ cations being ten-fold coordinated by selenium atoms to form double layers of condensed [CsSe10]19− polyhedra. Ce3+ resides in a nine-fold coordination and the [CeSe9]15− polyhedra also form double layers parallel to (100). CsSm[P2Se6] crystallizes in the orthorhombic space group P212121 with a = 688.67(5), b = 754.48(5), c = 2215.21(15) pm and Z = 4. Its structure is isotypic with that of KY[P2Se6] and the Cs+ cations reside in an eleven-fold coordination of selenium atoms constituting monolayers of condensed [CsSe11]21− polyhedra within the (001) plane. Sm3+ exhibits an eight-fold coordination sphere of selenium atoms and the [SmSe8]13− polyhedra are also linked to build up parallel monolayers. CsEr[P2Se6] crystallizes in the monoclinic space group P21/c again, but forms its own structure type with the lattice parameters a = 753.81(5), b = 1281.92(9), c = 1276.47(9) pm and β = 106.898(3)° and Z = 4. The Cs+ cations are twelve-fold coordinated by selenium atoms and erects a three-dimensional framework of condensed [CsSe12]23− polyhedra. The Er3+ cations show seven selenium atoms as neighbors and the [ErSe7]11− polyhedra are edge-connected to form discrete dimers [Er2Se12]18−. All three structures have similar ethane-like [P2Se6]4– anions in staggered conformation with bond lengths of 219–226 pm for d(P1–P2) and 213–222 pm for d(P–Se), which connect the Cs+ and Ln 3+ coordination polyhedra into three-dimensional crystal structures.