Crystal structures of KM(AsF6)3 (M2+ = Mg, Co, Mn, Zn), KCu(SbF6)3 and [Co(HF)2]Sr[Sr(HF)]2[Sr(HF)2]2[AsF6]12

Abstract

Abstract The KM(AsF6)3 (M2+ = Mg, Co, Mn, Zn) and KCu(SbF6)3 compounds crystallize isotypically to previously known KNi(AsF6)3. The main features of the structure of these compounds are rings of MF6 octahedra sharing apexes with AsF6 octahedra connected into infinite tri-dimensional frameworks. In this arrangement cavities are formed where K+ cations are placed. Single crystals of CoSr5(AsF6)12·8HF were obtained as one of the products after the crystallization of 3KF/CoF2/SrF2 mixture in the presence of AsF5 in anhydrous HF. The CoSr5(AsF6)12·8HF is monoclinic, C/2c (No.15), with a = 26.773(5) Å, b = 10.087(2) Å, c = 21.141(5) Å, β = 93.296(13) °, V = 5699.9(19) Å3 at 200 K, and Z = 4. There are three crystallographically non-equivalent Sr2+ cations in the crystal structure of CoSr5(AsF6)12·8HF. The Sr1 is coordinated by ten fluorine atoms from eight different [AsF6]- anions, meanwhile Sr2 and Sr3 are bound to nine fluorine atoms provided by one HF and eight AsF6 units or by two HF and six AsF6 units, respectively. The Co2+ is coordinated distorted-octahedrally by six fluorine atoms from two HF molecules and four different AsF6 units. All those moieties in the crystal strucutre of [Co(HF)2]Sr[Sr(HF)]2[Sr(HF)2]2[AsF6]12 are connected into tridimensional framework. The CoSr5(AsF6)12·8HF is a unique example of compound where HF molecules are directly bound via fluorine atoms to two different metal centres.