On the Crystal Structures of the Polymorphs of Manganese(II) Chloride Tetrahydrate: alpha-MnCl2 center dot 4H(2)O and beta-MnCl2 center dot 4H(2)O

The manganese(II) chloride tetrahydrate MnCl2 center dot 4H(2)O (alpha-form) crystallizes in the space group P2(1)/n with a = 6.1918(4) angstrom,b = 9.5230(6) angstrom,c = 11.1918(6) angstrom, beta = 99.757(3)degrees, and V = 650.37(7) angstrom(3)(Z = 4). A second polymorph of MnCl2 center dot 4H(2)O (beta-form) is mentioned in the literature to be isomorphous with FeCl2 center dot 4H(2)O but its crystal structure was never confirmed. In this study, we report for the first time on the crystal structure of this second polymorph of manganese(II) chloride tetrahydrate, beta-MnCl2 center dot 4H(2)O, using room temperature single-crystal X-ray diffraction. The beta-form crystallizes in space group P2(1)/c with a = 5.9893(5) angstrom,b = 7.2877(6) angstrom,c = 8.5838(7) angstrom, beta = 110.952(4)degrees, and V = 349.89(5) angstrom(3)(Z = 2), confirming that beta-MnCl2 center dot 4H(2)O is isotype to Fe(II)Cl-2 center dot 4H(2)O. To the best of our knowledge this is the first compound reported to crystallize in both MnCl2 center dot 4H(2)O-type (alpha-form) and FeCl2 center dot 4H(2)O-type (beta-form) structures. The crystal structure of both alpha-form and beta-form of MnCl2 center dot 4H(2)O consists of discrete octahedra complexes [MnCl2(H2O)(4)] linked by O-H center dot center dot center dot Cl- hydrogen bonds. However, chlorine atoms are intrans-configuration in the beta-form (trans-[MnCl2(H2O)(4)] complexes) and incis-configuration in the alpha-form (cis-[MnCl2(H2O)(4)] complexes). Moreover, the coordination polyhedra of the manganese(II) atoms are less distorted in the beta-form. This leads to two different hydrogen bond networks and to a slightly more compact [MnCl2(H2O)(4)] complexes arrangement in the alpha-form [GRAPHICS] .