New lead-free hybrid halometallates with dioctahedral anions synthesized using the template function of homopiperazine

Abstract New organic-inorganic hybrid halometallates of the general formula (HpipeH2)-[M2X10] · 2H2O, where M = Sb, Bi; X = Br, I; Hpipe is homopiperazine (C5N2H12), were synthesized. The crystal structures of three new compounds, α-(HpipeH2)2[Sb2I10] · 2H2O (1), β-(HpipeH2)2[Sb2I10)]-2H2O (2), and (HpipeH2)2[Bi2Br10] · 2H2O (3), were determined and analyzed in comparison with the previously synthesized analog (HpipeH2)2[Bi2I10] · 2H2O (4). All four compounds have similar crystal structures, in which inorganic dioctahedral [M2X10]4− anions alternate with organic (HpipeH2)2+ cations and water molecules to form 3D systems based on (N)H⋯X, (N)H⋯O, and (O)H⋯X hydrogen bonds. In all structures, the (HpipeH2)2+ cation serves the same template function, forming three (N)H⋯X hydrogen bonds with halogen atoms of the inorganic anion and one (N)H⋯O bond with a water molecule. In going from Sb to Bi and from I to Br, the band gap width increases and reaches 2.89 eV for compound 3.