The crystal structure of jonesite, Ba 2 (K, Na) [Ti 2 (Si 5 Al)O 18 (H 2 O)](H 2 O) n : A first example of titanosilicate with porous double layers

The crystal structure of jonesite, Ba 2 (K,Na)[Ti 2 (Si 5 Al)O 18 (H 2 O)](H 2 O) n (monoclinic, P2 1 /m, a = 10.618(2), b = 25.918(4), c = 8.6945(14) Å, β = 127.633(3)°, V = 1894.8(6) Å 3 , Z = 4) from the Benitoite Gem Mine, San Benito County, California has been solved by direct methods from a crystal twinned on (001) and refined to R 1 = 0.045 (wR = 0.119, S = 1.028) using 3308 unique observed reflections (|F o | ≥ 4σ F ). The structure is based upon porous double layers of distorted TiΦ 6 octahedra (Φ = O, H 2 O) and TO 4 tetrahedra (T = Si, Al) parallel to (010). The layers consist of two sheets of corner-sharing TiΦ 6 octahedra and Si 2 O 7 groups each. The two adjacent sheets are linked along b by T 4 O 12 tetrahedral rings that are disordered over two positions. The double layer has an open structure characterized by eight-membered tetrahedral rings with apertures (free diameters) of 3.37 × 3.37 and 3.33 × 3.33 Å 2 , for two symmetrically non-equivalent rings. K + cations and H 2 O molecules are located in the pores of the double layers. Ba 2+ cations are between the double layers and provide their linkage into three-dimensional structure. Jonesite is a first example of titanosilicate with porous double-layer structure.