Investigation of anhydrous metal(II) nitrates. I. Syntheses and crystal structures of Mg(NO3)2, Co(NO3)2 and Ni(NO3)2, with a stereochemical discussion

Abstract

Abstract Mg(NO3)2, Co(NO3)2 and Ni(NO3)2 were obtained as tiny crystals by dehydration of melts of the respective hydrates in the range 410–450 K. Structure determinations and refinements are based on single crystal X-ray data (CCD area detector) measured at 120–370 K. Crystal parameters at 120 K: Mg(NO3)2: R−3, a = 10.474(1), c = 38.782(4) Å, Z = 36, R 1 = 0.028; Co(NO3)2: R−3, a = 10.445(1), c = 12.769(2) Å, Z = 12, R 1 = 0.019; Ni(NO3)2: R−3, a = 10.332(1), c = 12.658(2) Å, Z = 12, R 1 = 0.025. Co(NO3)2 and Ni(NO3)2 are isotypic; the structure of Mg(NO3)2 is closely related, although it is not simply a stacking variant – it forms a new structure type. In all three compounds the MO6 octahedra share all corners with the NO3 groups to form framework structures; any edge sharing is thereby avoided. The geometries of the structures are also discussed in relation to a simple theoretical cubic structure (space group Pa−3) with the same connection pattern of the MO6 and NO3 building units. Neither X-ray single crystal and powder work nor differential thermoanalytical investigations indicated polymorphism in the temperature range investigated.