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

Nonstoichiometric REEAl(2.07)(B(4)O(10))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 P (6) over bar 2m (n. 189), with the following unit cell parameters: a = 4.6060(6) angstrom, c = 9.3510(8) angstrom and V = 171.81(3) angstrom(3) (La, Ce); a = 4.5960(6) angstrom; c = 9.3170(10) angstrom and V = 170.44(4) angstrom(3) (Ce); a = 4.5830(7) angstrom, c = 9.2810(14) angstrom and V = 168.82(4) angstrom(3) (Nd). The REE cations are surrounded by six oxygen atoms, making up a trigonal prismatic coordination; Al cation is surrounded by five oxygen atoms, resembling a square pyramidal coordination, while the BO(4) group displays tetrahedral arrangement. The three-dimensional framework can be described as a mica-like structure packed down crystallographic axis c, with layers of six-membered rings of B tetrahedra alternated by inter-layers REE cations and layers of Al polyhedra. A complex network of REE center dot center dot center dot O and Al center dot center dot center dot O interactions concur to stabilize the framework.