LiCa₃As₂H and Ca₁₄As₆X₇ (X = C, H, N): Two new arsenide hydride phases grown from Ca/Li metal flux

The reaction of arsenic with sources of light elements in a Ca/Li melt leads to the formation of two new arsenide hydride phases. The predominant phase Ca₁₄As₆X₇ (X = C^4-, N^3-, H^-) exhibits a new tetragonal structure type in the space group P4/mbm (a = 15.749(1) Å, c = 9.1062(9) Å, Z = 4, R1 = 0.0150). The minor phase LiCa₃As₂H also has a new structure type in the orthorhombic space group Pnma (a = 11.4064(7) Å, b = 4.2702(3) Å, c = 11.8762(8)Å, Z = 4, R1 = 0.0135). Both phases feature hydride and arsenide anions separated by calcium cations. The red color of these compounds indicates they should be charge-balanced. DOS calculations on LiCa₃As₂H confirm a band gap of 1.4 eV; UV-vis spectroscopy on Ca₁₄As₆X₇ shows a band gap of 1.6 eV. Single-crystal neutron diffraction studies were necessary to determine the mixed occupancy of carbon, nitrogen, and hydrogen anions on the six light-element sites in Ca₁₄As₆X₇; these data indicated an overall stoichiometry of Ca₁₄As₆C_0.445N_1.135H_4.915.