Transformations of the low-dimensional zinc phosphates to complex open-framework structures. Part 2: one-dimensional ladder to two- and three-dimensional structures

Open-framework zinc phosphates with one-dimensional ladder structures are s hown to transform, under simple reaction conditions, to two- and three-dime nsional structures. Thus, the one-dimensional ladder, [C6N4H22](0.5)[Zn(HPO 4)(2)], I, on heating with piperazine in aqueous solution gives a layer pho sphate, [C4N2H12][Zn-2(PO4)(2)], III, and the three-dimensional phosphates [C2N2H10](0.5)[Zn(PO4)], IV, [C6N4H22](0.5)[Zn-2(PO4)(2)], V and [C6N4H21]( 4)[Zn-21(PO4)(18)], VI. On heating in water in the absence of any amine, I transforms to a three-dimensional solid, [C6N4H22](0.5)[Zn-3(PO4)(2)(HPO4)] , VII, with 16-membered channels. Of these, III and IV are the only new com pounds. The phosphates formed by the transformations of I exhibit unique st ructural features. Thus, in III, the layers are formed only with 3- and 4-m embered rings and have step-like features due to the presence of infinite Z n-O-Zn linkages. Compound IV has a structure similar to that of the natural ly occurring aluminosilicate, gismondine, and VI possesses unusual Zn7O6 cl usters. The ladder zinc phosphate, [C3N2H12][Zn(HPO4)(2)], II, transforms t o two layered compounds, [C3N2H12][Zn-4(PO4)(2)(HPO4)(2)], VIII, and [C3N2H 12][Zn-2(HPO4)(3)], IX, on heating with zinc acetate and water, respectivel y. II, on heating in water in the presence of other amines, forms a ladder, [C3N2H5][Zn(HPO4)], X, and a three-dimensional phosphate, [C3N2H12](2)[Zn- 5(H2O)(PO4)(4)(HPO4)], XI. The syntheses and structures of VIII-XI have alr eady been reported. What is interesting is that the majority of the transfo rmations seem to occur through the process of deprotonation of the phosphor yl group and elimination of the -HPO4 unit. The transformations of the ladd er phosphates to higher dimensional structures reported in the present stud y not only demonstrate the seminal role of the one-dimensional structures a s basic building units, but also the likely occurrence of self-assembly of these one-dimensional units in the building-up process.