The crystal structure of sinkankasite, a complex heteropolyhedral sheet mineral

Abstract

The crystal structure ofsinkankasite, Z = 2, MnH(H20).[Al(P030HMOH)](H20)2' triclinic, a = 9.590(2), b = 9.818(2), c = 6.860(1) A, a = 108.04(3), (3 = 99.63(3), 'Y = 98.87(3)°, V = 590.7(2) A3, space group pT, has been solved by direct methods and refined to an R index of 7.2% and an Rw index of 7.6% using 2170 unique observed reflections (iFo I 2: 50F)collected with MoKa X-ray radiation. The structure contains one distinct MnH position, which is octahedrally coordinated by two 0 atoms and four H20 groups. There are two distinct Al positions; each is octahedrally coordinated by four 0 atoms and two OH groups. The two distinct P positions are each tetrahedrally coordinated by three o atoms and one OH group. There are 15 unique H positions, which have been located and refined using soft constraints. The structure consists of corner-sharing chains of AI 6 octahedra, decorated on both sides by P . tetrahedra. These heteropolyhedral chains are linked through the Mn 6 octahedra to form continuous sheets of composition MnAIP206(OHk4H20. There are two interlayer anion positions, both of which are occupied by H20 groups. There are eight unique H bonds between the interlayer cations and the sheets on either side, and no other bonding occurs between the sheets. A total of seven unique H bonds occur between anions of the same heteropolyhedral sheet.