Abstract: | Ce3Cl5[SiO4] and Ce3Cl6[PO4]: A Chloride‐Rich Chloride Silicate of Cerium as Compared to the Phosphate By reacting CeCl3 with CeO2, cerium and SiO2, or P2O5, respectively, in molar ratios of 5 : 3 : 1 : 3 or 8 : 3 : 1 : 2, respectively, in sealed evacuated silica tubes (7 d, 850 °C) colorless, rod‐shaped single crystals of Ce3Cl5[SiO4] (orthorhombic, Pnma; a = 1619.7(2), b = 415.26(4), 1423.6(1) pm; Z = 4) and Ce3Cl6[PO4] (hexagonal, P63/m; a = 1246.36(9), c = 406.93(4) pm; Z = 2) are obtained as products insensitive to air and water. Excess cerium trichloride as flux promotes crystal growth and can be rinsed off again with water after the reaction. The crystal structures are determined by discrete [SiO4]4– or [PO4]3– tetrahedra as isolated units. Both, the chloride silicate Ce3Cl5[SiO4] and the chloride phosphate Ce3Cl6[PO4], exhibit structural similarities to CeCl3 (UCl3 type), when four or three Cl– anions are each substituted formally by one [SiO4]4– or [PO4]3– unit, respectively, in the tripled formula (Ce3Cl9). The coordination number for Ce3+ is thus raised from nine in CeCl3 to ten in Ce3Cl5[SiO4] and Ce3Cl6[PO4], along with a drastic reduction of the molar volume with the transition from Ce3Cl9 (Vm = 186.17 cm3/mol) to Ce3Cl5[SiO4] (Vm = 144.15 cm3/mol) and Ce3Cl6[PO4] (Vm = 164.84 cm3/mol). The polyhedra of coordination around Ce3+ can be described as quadruple‐capped trigonal prisms, which in addition to seven Cl– anions each also show another three oxygen atoms of two ortho‐silicate or ortho‐phosphate tetrahedra, respectively. |