Solid-State Syntheses, Crystallographic Spatial Disorders, Thermal Behavior, and Bandgaps of Hybrid Organic-Inorganic Manganese Halides: A2Mn(Cl/Br)4 (A = NH4, C(NH2)3, & C3H4N2).

By systematically optimizing solid-state synthesis via the concerted use of differential scanning calorimetry and in situ variable-temperature X-ray diffraction, we report the discovery of three new hybrid organic-inorganic halides A2Mn(Cl/Br)4 (A = NH4+, C3H4N2+) and demonstrate that (C(NH2)3)2MnBr4, previously reported from solution-based synthesis, can also be attained from solid-state methods. Overall, changing "A" based on its geometry, polarity, and resonance-stabilized charge delocation influences the crystallographic packing and spatial disorder, thermal behavior, and optical bandgap. With a dipole-free tetrahedral cation, as in (NH4)2MnBr4 (C2/c, mC180) or (NH4)2MnCl4 (P21/c, mP30), the direct optical bandgaps (4.28-4.36 eV) are wider than those with a trigonal planar dipole-free cation, as in (C(NH2)3)2MnBr4 (P21/c, mP300, 4.07 eV), or a planar dipolar cation geometry, as in (C3H4N2)2MnBr4 (I41/a, tI384, 4.05 eV). Furthermore, "A" affects the spatial arrangement and dimensionality of the inorganic frameworks comprised of spatially disordered MnBr4 tetrahedra and/or Mn(Cl/Br)6 octahedra with varying distortions. These resulting trends, coupled with the systematic investigation into the use of solid-state synthesis, and the motivation behind elucidating the nuanced role of the organic cation, altogether expand the phase space of hybrid materials.