A SINGLE-CRYSTAL X-RAY-INVESTIGATION OF THE STRUCTURES OF LA3(OH)(CRO4)4.3.5H2O AND LA2(CRO4)3.7H2O

The unit cell of La3(OH)(CrO4)4.(3.5)H2O (1) is monoclinic, space group C2/c (No. 15), with lattice parameters a = 33.187(6), b = 7.217(2), c = 14.327(3) angstrom, beta = 97.34(1)-degrees, Z = 8. La2(CrO4)3.(7)H2O (2) forms monoclinic crystals, space group P2(1)/n (No. 14), with lattice parameters a = 10.600(1), b = 19.317(2), c = 8.188(1) angstrom, beta = 90.88(1)-degrees, Z = 4. The structures of 1 and 2 were solved by direct methods from 2531 and 2911 independent diffractometer reflections and refined to R-values of 0.071 and 0.075, respectively. Both structures contain LaO9 coordination polyhedra. In 1 the structure contains three independent LaO9 coordination polyhedra forming alternating double and single layers of polyhedra parallel to the bc-plane. In 2 the structure contains two independent LaO9 coordination polyhedra each forming a layer parallel to the ac-plane. All the LaO9 coordination polyhedra in 1 and 2 are of the same type, a three-sided prism with the metal atom in the centre, six oxygen atoms in the corners and three oxygen atoms placed perpendicular to the three rectangular surfaces of the prism.