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 shown to transform, under simple reaction conditions, to two- and three-dimensional structures. Thus, the one-dimensional ladder, [C6N4H22]0.5[Zn(HPO4)2], I, on heating with piperazine in aqueous solution gives a layer phosphate, [C4N2H12][Zn2(PO4)2], III, and the three-dimensional phosphates [C2N2H10]0.5[Zn(PO4)], IV, [C6N4H22]0.5[Zn2(PO4)2], V and [C6N4H21]4[Zn21(PO4)18], VI. On heating in water in the absence of any amine, I transforms to a three-dimensional solid, [C6N4H22]0.5[Zn3(PO4)2(HPO4)], VII, with 16-membered channels. Of these, III and IV are the only new compounds. The phosphates formed by the transformations of I exhibit unique structural features. Thus, in III, the layers are formed only with 3- and 4-membered rings and have step-like features due to the presence of infinite Zn–O–Zn linkages. Compound IV has a structure similar to that of the naturally occurring aluminosilicate, gismondine, and VI possesses unusual Zn7O6 clusters. The ladder zinc phosphate, [C3N2H12][Zn(HPO4)2], II, transforms to two layered compounds, [C3N2H12][Zn4(PO4)2(HPO4)2], VIII, and [C3N2H12][Zn2(HPO4)3], IX, on heating with zinc acetate and water, respectively. 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[Zn5(H2O)(PO4)4(HPO4)], XI. The syntheses and structures of VIII–XI have already been reported. What is interesting is that the majority of the transformations seem to occur through the process of deprotonation of the phosphoryl group and elimination of the –HPO4 unit. The transformations of the ladder phosphates to higher dimensional structures reported in the present study not only demonstrate the seminal role of the one-dimensional structures as basic building units, but also the likely occurrence of self-assembly of these one-dimensional units in the building-up process.