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  /wwR = 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  /wwR = 0.0224/0.0415 for II). Both structures consist of one-dimensional [Sn2P4]6−∞1 chains separated by Ba2+ cations. The isolated [Sn2P4]6−∞1 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.