Two polymorphs of Ba3Sn2P4: Single crystal and electronic structures

Two polymorphs (I and II) of Ba₃Sn₂P₄ have been found in the same preparative batch. Both compounds crystallize in the centrosymmetric monoclinic space group P2₁/c (#14, a = 7.8669(2) Å, b = 19.2378(5) Å, c = 7.8472(2) Å, β = 112.77(1)°, V = 1095.06(5) Å³, Z = 4, and R/wR = 0.0303/0.0710 for I; a = 7.8771(3) Å, b = 19.4099(7) Å, c = 7.7040(3) Å, β = 112.44(1)°, V = 1088.67(7) Å³, Z = 4, and R/wR = 0.0224/0.0415 for II). Both structures consist of one-dimensional chains separated by Ba²⁺ cations. The isolated chain consists of condensed ethane-like [Sn₂P₆] units. In polymorphs I and II, the condensation and connectivity of the [Sn₂P₆] units are quite different. While [Sn₂P₆] units form four- and six-membered rings in I, they form the five-membered rings in II. The electronic structure calculations indicate that semiconducting behavior is expected for both compounds.