Controlling the In situ Decomposition of Chain-Type Polyamines To Direct the Crystal Growth of Cobalt−zinc Phosphates

The in situ decomposition of tetraethylene-pentamine, triethylenetetramine, or diethylenetriamine has been controlled to direct the synthesis of three open-framework cobalt−zinc phosphates, CoZnPO₄-I, CoZnPO₄-II, and CoZnPO₄-III. These phosphates can be synthesized as the intergrowth from a single gel at 200 °C in the presence of diethylenetriamine with propylamine as the assistant organic additive. Structure analysis reveals that species encapsulated in the structures of CoZnPO₄-I, CoZnPO₄-II, and CoZnPO₄-III are ammonium, ethylenediaminum, and diethylenetriaminum, respectively, which can be attributed to the in situ decomposition of diethylenetriamine molecules during the crystallization procedure. It has been found that the presence of second organic amine redound to controlling the decomposition of these linear polyamines, such as diethylenetriamine, to form these three CoZnPO₄ materials from a single gel. Pure phase of CoZnPO₄-I, CoZnPO₄-II, and CoZnPO₄-III have also been obtained by varying assistant amines, crystallizing at a lower temperature, or using other linear polyamines, such as triethylenetetramine or tetraethylene-pentamine instead of diethylenetriamine as the main organic additives. Single-crystal X-ray diffraction analysis has shown that CoZnPO₄-I is a novel metal phosphate. It crystallizes in hexagonal space group p6 ₃ (No.173), with a = 10.7207(5) Å, c = 8.7241(8) Å, V = 868.36(10) ų, and Z = 4. Its three-dimensional framework can be considered as the stacking of six-ring sheet with the combination of UDUDUD (U, upward; D, downward) and UUUDDD linkages in the proportion 1:3. Its negative framework is charge-compensated by NH₄ ⁺ cations, which are encapsulated in 6⁹4 cage of the structure. CoZnPO₄-II crystallizes in the tetragonal system, space group P4₂ bc (No. 106), with a = b = 14.694(2) Å, c = 8.936(2) Å, V = 1929.4(6) ų, and Z = 8, possesses DFT topology, and is built of ZnO₄ (or CoO₄), and PO₄ tetrahedra with ethylenediaminum cation resided in the 8-member ring channels to compensate the negative framework charge. The three-dimensional architecture of CoZnPO₄-III crystallizes in the trigonal system, space group R̅ (No. 148), with a = 13.5393(8) Å, c = 15.0443(10) Å, γ = 120°, V = 2388.3(3) ų, and Z = 3, is built up of ZnO₄(or CoO₄), PO₄ tetrahedra, and CoO₆ octahedra with diethylenetriaminums encapsulated in the channels.