Ce2[MoO5][MoO4] and Ce5[MoO4]8: Two New Cerium Oxomolybdates, Each Exhibiting a Special Structural Feature

Abstract

Ce2[MoO5][MoO4] crystallizes monoclinically in space group P21/c (a = 2241.98(9), b = 712.95(3), c = 2044.19(8) pm, β = 116.936(2), Z = 16). Besides eight crystallographically different Ce3+ cations with coordination numbers ranging from seven plus one to ten, its structure contains two isolated oxomolybdate(VI) species, namely [MoO4]2− tetrahedra and [MoO5]4− trigonal bipyramids and square pyramids. The oxygen polyhedra around the Ce3+ cations build up a three-dimensional ∞ 3 {[Ce2O9]12−} network by vertex-, edge-, and face-connections with the Mo6+ cations residing in tetrahedral, square-pyramidal, and trigonal-bipyramidal voids therein. Ce5[MoO4]8 also crystallizes monoclinically in space group P21/c (a = 1133.14(5), b = 1704.96(7), c = 1406.21(6) pm, β = 90.749(2)° Z = 4). In its structure eight isolated [MoO4]2− tetrahedra are present, which display an overall negative charge of −16. To maintain electroneutrality, mixed-valency of the five crystallographically independent cerium cations must be considered. A thorough bond-valence analysis reveals cerium at the Ce1 site as tetravalent, while the other four cerium cations prove to be trivalent. The polyhedra around all cerium cations form chains with a V-shaped profile along [100] via vertex-, edge-, and face-connections to result in a sawblade pattern. These chains are interlocked into sheets parallel to the (001) plane and linked by the Mo6+ cations to form a three-dimensional network.