Syntheses, crystal structures, thermal stabilities and luminescence of six M(II)-hydroxyphosphonoacetate materials

Hydrothermal reactions of ZnII, BaII or CoII ion with 2-hydroxyphosphonoacetic acid (H3L) afforded six metal phosphonates, namely, [Zn5(O3PCH(OH)CO2)4(C6H9N2)2] (1), [(C4H12N2)Zn5(O3PCH(OH)CO2)4(H2O)2] (2), [(C3H12N2)0.5Zn5(HO3PCH(OH)CO2)(O3PCH(OH)CO2)3(H2O)2]·0.75H2O (3), [BaZn2(O3P CH(OH)CO2)2] (4), [Ba(HO3PCH(OH)CO2)] (5) and [(NH4)2Co7(HO3PCH(OH) CO2)6(HPO4)2(H2O)6]·4H2O (6). In 1, zinc tetrahedra ([ZnO4]) and octahedra ([ZnO5N], [ZnO6]) are bridged by 2-hydroxyphosphonoacetate with penta- and hexadendate modes into a hybrid layer, which is further pillared by the 3-picolylamines to form a 3D structure through Zn–N bonds and hydrogen bondings. Both 2 and 3 are 3D framework encapsulating piperazine and 1,2-propanediamine cations, respectively. In solids 4–6, the cross-linkages of [ZnO4], [BaO10] and [CoO6] polyhedral with 2-hydroxyphosphonoacetate form 3D frameworks. Solids 3 and 4 behave thermally stable up to 250 and 300 °C under air atmosphere, respectively. It is interesting that the peak emission of solid 3 displays a 10 nm red-shift after simple heat-treatment.