Crystal Data for (NH4)3AsCr4O16 and K3AsCr4O16 the first examples of quaternary arsenic

We describe chemical preparations and give crystal data for two new arsenatochromates: (NH₄)₃AsCr₄O₁₆ and K₃AsCr₄O₁₆ isotypic with K₃PCr₄O₁₆. Both are monoclinic (Cc) with the following unit cells: a = 9.724(5), b = 11.98(5), c = 14.88(5)Å, β 105.82(5)º for the ammonium salt and a = 9.323(5), b = 12.03(5), c = 14.62(5) Å, β 105.25 (5)º for the potassium salt. The main feature of these salts is the geometrical configuration of the finite AsCr₄O₁₆ anion: a central AsO₄ tetrahedron sharing its four corners with CrO₄ tetrahedra. Up to now, these salts are the first example of a quaternary arsenic in a finite anion.     

Preparation and crystal structure of copper tetrasodium trimetaphosphate tetrahydrate: CuNa4(P3O9)2 · 4H2O

The preparation of copper-tetrasodium trimetaphosphate tetrahydrate: Na₄Cu(P₃O₉)₂ · 4H₂O is described. This salt is the first example of the occurence of Cu^II in a trimetaphosphate. The triclinic unit cell has the dimensions a = 7.907(5), b = 8.364(5), c = 7.122(5) Å, α = 102.46(5), β = 97.89(5), γ = 84.04(5)°. Crystal structure has been solved by using 2019 independent reflexions with a final R value 0.017. Both copper and sodium atoms are in octahedral coordination. NaO₆ octahedra form ribbons running in (011) planes. These ribbons are interconnected by CuO₆ octahedra as to form a three dimensional network. Hydrogen atoms have been located and refined. The hydrogen bond scheme is described.     

Preparation and Crystal Structure of Guanidinium Cyclododecaphosphate Hexahydrate: [C(NH2)3]12P12O36 · 6H2O

The title compound was prepared by ion exchange from the potassium salt, K₁₂P₁₂O₃₆ · 19/2H₂O. It represents a second new structural type of [P₁₂O₃₆]^12? ring anions. This sparingly water soluble salt is hexagonal, space group P6₃, with Z = 2 and the cell dimensions: a = 15.904(7), c = 16.67(2) Å. The crystal structure was solved by direct methods and refined to a final R value of 0.050. The ring anion is located around the threefold axis and hence has a threefold symmetry. The stacking of the rings creates large channels, parallel to the c direction, in which the guanidinium groups and the water molecules are located. Three of the six independent guanidinium groups are located on the threefold axes. The cohesion of the structure is performed by the numerous H-bonds generated by the organic cations and the water molecules.