X-ray crystal structure of synthetic REEAl2.07(B4O10)O0.60 (REE=(La,Ce); Ce; Nd) dimetaborates

Nonstoichiometric REEAL2.07(B4O10)O 0.60 (REE = (La, Ce); Ce; Nd) dimetaborates have been crystallized and analyzed by means of single crystal X-ray diffraction. The compounds resulted to be isostructural within hexagonal space group P62m (n. 189), with the following unit cell parameters: a = 4.6060(6) A, c = 9.3510(8) Å and V = 171.81(3)Å3 (La, Ce); a = 4.5960(6) Å c = 9.3170(10) A and V= 170.44(4) Å3 (Ce); a = 4.5830(7) Å, c = 9.2810(14) Å and V = 168.82(4) Å3 (Nd). The REE cations are surrounded by six oxygen atoms, making up a trigonal prismatic coordination; A1 cation is surrounded by five oxygen atoms, resembling a square pyramidal coordination, while the BO4 group displays tetrahedral arrangement. The three-dimensional framework can be described as a mica-like structure packed down crystallographic axis c, with layers of sixmembered rings of B tetrahedra alternated by inter-layers REE cations and layers of Al polyhedra. A complex network of REE... O and Al... O interactions concur to stabilize the framework.