New Lead-Free Hybrid Halometallates with Dioctahedral Anions Synthesized Using the Template Function of Homopiperazine

New organic-inorganic hybrid halometallates of the general formula (HpipeH 2 )-[M 2 X 10 ] · 2H 2 O, where M = Sb, Bi; X = Br, I; Hpipe is homopiperazine (C 5 N 2 H 12 ), were synthesized. The crystal structures of three new compounds, α-(HpipeH 2 ) 2 [Sb 2 I 10 ] · 2H 2 O (1) , β-(HpipeH 2 ) 2 [Sb 2 I 10 )]-2H 2 O (2) , and (HpipeH 2 ) 2 [Bi 2 Br 10 ] · 2H 2 O (3) , were determined and analyzed in comparison with the previously synthesized analog (HpipeH 2 ) 2 [Bi 2 I 10 ] · 2H 2 O (4). All four compounds have similar crystal structures, in which inorganic dioctahedral [M 2 X 10 ] 4− anions alternate with organic (HpipeH 2 ) 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 (HpipeH 2 ) 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 .