NOVEL TYPE OF OXONIUM SALTS H(3)OM(ASF6)(3) (M=MN, CO, NI) - SYNTHESES, STRUCTURES AND SOME PROPERTIES

H3OAsF6 reacts with M(AsF6)(2) (M=Mn,Co,Ni) in anhydrous hydrogen fluo ride (aHF) acidified with AsF5 at room temperature yielding novel oxon ium salts H(3)OM(AsF6)(3). If MF(2) is used instead of M(AsF6)(2) the aHF should be rich in AsF5 to synthesize M(AsF6), in situ. As source o f the oxonium cation water or the transition metal oxide can be used. X-ray powder diffraction at variable temperatures revealed for H3OCo(A sF6)(3) a phase transition at 120K. The high temperature (HT) form cry stallizes in the orthorhombic space group Pnma (No.62) with a=1037.6(1 ), b=1372.6(1), c=932.8(1) pm, V=1.3285(2) nm(3), Z=4 and d(c)=3.223 g /cm(3) at 150 K. The low temperature (LT) form crystallizes in the mon oclinic space group P2(1)/c (No.14) with a=1032.6(1), b=1370.2(2), c=1 867.1(2) pm, beta=90.036(9)degrees, V=2.6416(5) nm(3), Z=8, d(c)=3.242 g/cm(3) at 90 K. The structure was solved by direct methods using dif fractometer data sets and refined to conventional R1=0.039 for 2604 re flections (HT-form) and R1=0.053 for 9215 reflections (LT-form), respe ctively. One main feature of the H3OCo(AsF6)(3) structure is a ring of four AsF6 octahedra which are connected by four cobalt atoms. This ki nd of ring system is continued infinitely in the plane and also perpen dicular to the plane. In this arrangement open channels are created in which oxonium ions are placed below and above the plane.