An investigation of microporous cetineite-type phases A6[B12O8][CX3]2[D x (H2O,OH,O)6−y ]

Abstract

Abstract The cetineite structure-type has the very general formula A 6[B 12O18][CX 3]2[D x Y 6−y ] with 0 ≤ x ≤ 2 and 0 ≤ y ≤ 6. In a preceding paper [Eur. J. Solid State Inorg. Chem. 35 (1998) 27–37] natural and synthetic cetineite-type phases with A = Na+, K+, Rb+, Sr2+, Ba2+; B = C = Sb; X = S2−, Se2−; D = Na+, Sb3+, C4+; and Y = H2O, OH−, O−2 have been described. In the present paper, the results of crystal structure determinations from single-crystal X-ray diffraction data of four of these phases are reported. K6[Sb12O18][SbS3]2[Sb0.12(H2O)5.64(OH)0.36]: P63/m, a = 14.318(3) Å, c = 5.633(1) Å, Z = 1; Sr6[Sb12O18][SbSe3]2[(OH)6]: P63/m, a = 14.320(3) Å, c = 5.515(1) Å, Z = 1; Ba6[Sb12O18][SbSe3]2[(CO3)1.5O1.5]: P63/m, a = 14.504(3) Å, c = 5.616(1) Å, Z = 1; K6[Sb12O18][SbSe3]2[(H2O)6]: P63, a = 29.260(7) Å, c = 5.6164(7) Å, Z = 4. In the first three phases 1-dimensional stacks of trigonal pyramids [SbX 3]3− are orientationally disordered between [Sb12O18] tubes stretching along [001]. Rotation of the tubes around their axes is governed by repulsive forces between lone-electron pairs of the Sb3+ of neighbouring tubes. The fourth phase has a 2a, 2b, c superstructure with an ordered arrangement of the stacks of [SbSe3] pyramids. Comparison of these four cetineite-type structures, with others described in the literature, reveal that the reported existence of subtypes with ordered and disordered [SbX 3] groups in a, b, c unit cells of P63 symmetry is doubtful. Changes in the structures are correlated with the length of the A–X bonds, the valence of the A cations, and the occupancy and size of the D cations, which are located along the tube axes and surrounded by Y ligands that form slightly elongated trigonal antiprisms. The extension of the cetineite structure field – r(B) = r(C) = 0.76 Å (Sb3+), 1.84 Å ≤ r(X) ≤ 1.98 Å (S2− and Se2−), 1.02 Å ≤ r(A [6]) ≤ 1.52 Å (Na+ to Rb+), and valence of A equal to +1 and +2 – is correlated with the strength and covalency of the various bonds between the atoms.