The manganese(II) chloride tetrahydrate MnCl2·4H2O (α-form) crystallizes in the space group P21/n with a = 6.1918(4) Å, b = 9.5230(6) Å, c = 11.1918(6) Å, β = 99.757(3)°, and V = 650.37(7) Å3 (Z = 4). A second polymorph of MnCl2·4H2O (β-form) is mentioned in the literature to be isomorphous with FeCl2·4H2O 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, β-MnCl2·4H2O, using room temperature single-crystal X-ray diffraction. The β-form crystallizes in space group P21/c with a = 5.9893(5) Å, b = 7.2877(6) Å, c = 8.5838(7) Å, β = 110.952(4)°, and V = 349.89(5) Å3 (Z = 2), confirming that β-MnCl2·4H2O is isotype to Fe(II)Cl2·4H2O. To the best of our knowledge this is the first compound reported to crystallize in both MnCl2·4H2O-type (α-form) and FeCl2·4H2O-type (β-form) structures. The crystal structure of both α-form and β-form of MnCl2·4H2O consists of discrete octahedra complexes [MnCl2(H2O)4] linked by O–H⋅⋅⋅Cl− hydrogen bonds. However, chlorine atoms are in trans-configuration in the β-form (trans-[MnCl2(H2O)4] complexes) and in cis-configuration in the α-form (cis-[MnCl2(H2O)4] complexes). Moreover, the coordination polyhedra of the manganese(II) atoms are less distorted in the β-form. This leads to two different hydrogen bond networks and to a slightly more compact [MnCl2(H2O)4] complexes arrangement in the α-form. The title compound is the first representative among divalent metal tetrahydrate halogenides to present both the MnCl2·4H2O-type (α-form) and FeCl2·4H2O-type (β-form) structures, leading to different configuration of complexes [MnCl2(H2O)4], crystal packing, hydrogen bond networks, and possibly magnetic properties.

中文翻译：

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关于四水氯化锰多晶型物的晶体结构：α-MnCl2·4H2O和β-MnCl2·4H2O

四水合氯化锰 (II) MnCl2·4H2O（α 型）在空间群 P21/n 中结晶，a = 6.1918(4) Å, b = 9.5230(6) Å, c = 11.1918(6) Å, β = 99.757(3)°，V = 650.37(7) Å3 (Z = 4)。文献中提到 MnCl2·4H2O 的第二种多晶型物（β 型）与 FeCl2·4H2O 同晶，但其晶体结构从未得到证实。在这项研究中，我们首次使用室温单晶 X 射线衍射报告了四水合氯化锰 (II) 的第二种多晶型物 β-MnCl2·4H2O 的晶体结构。β-型在 P21/c 空间群中结晶，a = 5.9893(5) Å，b = 7.2877(6) Å，c = 8.5838(7) Å，β = 110.952(4)°，V = 349.89(5) ) Å3 (Z = 2)，证实 β-MnCl2·4H2O 与 Fe(II)Cl2·4H2O 是同种型的。据我们所知，这是第一个据报道同时以 MnCl2·4H2O 型（α 型）和 FeCl2·4H2O 型（β 型）结构结晶的化合物。MnCl2·4H2O 的 α 型和 β 型的晶体结构由离散的八面体配合物 [MnCl2(H2O)4] 组成，由 O-H⋅⋅⋅⋅Cl− 氢键连接。然而，氯原子在β-型（反式-[MnCl2(H2O)4]复合物）中呈反式构型，在α-型中呈顺式构型（顺式-[MnCl2(H2O)4]复合物）。此外，锰 (II) 原子的配位多面体在 β 型中变形较少。这导致了两个不同的氢键网络和一个稍微更紧凑的 [MnCl2(H2O)4] 配合物以 α 形式排列。