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

Abstract

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][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 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][Zn-4(PO4)(2)(HPO4)(2)], VIII, and [C3N2H12][Zn-2(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)[Zn-5(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.