CRYSTAL STRUCTURE OF SODIUM 12-NIOBOMANGANATE(4) NA12MNNB12O38.50H2O

Sodium 12-niobomanganate(IV), Na12MnNb12O38 50H2O, is monoclinic, a = 24.18 ± 0.03 Å, b = 12.69 ± 0.02 Å, c = 14.14 ± 0.02 Å, β = 92.1 ± 0.2°, Z = 2, pexPtl = 2.31 g/cm3, pcaled = 2.26 g/cm3, space group P21/n, all at 24-25°. Data were collected photographically. The structure was refined by Fourier, difference Fourier, and full-matrix least-squares methods to an R value of 11.7% for 3263 observed reflections. The structure is composed of sodium ions, water molecules, and anions MnNb12O3812-. The anion consists of a manganese atom octahedrally coordinated by oxygen atoms from two Nb6O19 groups, the latter having first been found by Lindqvist in Na7HNb6O19. 15H2O. The anion has a crystallographic center of symmetry, but approximates D3d symmetry. The Mn-O distances are equal within experimental error (σ = 0.03 Å), averaging 1.87 Å, but the MnOe octahedron is stretched along the pseudo-threefold axis of the anion. The Nb-O distances range from 1.75 to 2.43 Å (σ = 0.03 Å), depending on the chemical environment of the oxygen atom. The packing of the anions correlates with the optical properties of the compound. The unit cell of trigonal Na2Li10MnNb12C38.44H2O was also determined. © 1969, American Chemical Society. All rights reserved.