SYNTHESIS AND CRYSTAL STRUCTURE OF TWO NEW TETRAFLUOROBORATE CRYSTALLOHYDRATES M(BF4)2·3H2O, M = Sr, Ba.

Crystals of two new tetrafluoroborate crystallohydrates M(BF4)2·3H2O (M = Sr, Ba) are prepared by the evaporation of aqueous solutions. The compounds are studied by single crystal XRD and IR spectroscopy. Sr(BF4)2·3H2O crystallizes in the tetragonal crystal system (a = 6.9638(4) Å, c = 18.1671(12) Å, space group P42/mnm); Ba(BF4)2·3H2O crystallizes in the orthorhombic crystal system (a = 7.1996(2) Å, b = 18.0823(5) Å, c = 7.1860(2) Å, space group C2221). Their crystal structure is formed by isolated BF4 tetrahedra and water molecules with alkaline earth metal atoms in between. When cooled to 100 K, Ba(BF4)2·3H2O undergoes a polymorphic transition to the monoclinic modification accompanied by pseudo-merohedral twinning of crystals. [ABSTRACT FROM AUTHOR]