Synthesis and Crystal Structure from X-ray Powder Diffraction Data of Two Zirconium Diphosphonates Containing Piperazine Groups

Two new zirconium aminophosphonates have been obtained by reaction of Zr(IV) with piperazine-N,N′-bis(methylenephosphonate) building blocks. Their crystal structure has been determined ab initio from X-ray powder diffraction data collected with a conventional diffractometer. Although prepared in similar conditions, their composition and crystal structure is markedly different. Compound 1, of formula Zr2H4[(O3PCH2)2N2C4H8]3·9H2O, has a three-dimensional structure (trigonal, space group R3̅̅ (No. 148), a = 19.9400(9) Å, c = 9.5728(6) Å, Z = 3), made of infinite inorganic chains of ZrO6 octahedra and PO3C tetrahedra, running along the c-axis direction, connected by piperazine groups in the ab plane, and generating channels running along the c axis. Compound 2, of formula ZrF2(O3PCH2)2(NH)2C4H8, has a pillared-layered structure (monoclinic, space group P21/c (No. 14), a = 8.7148(2) Å, b = 8.1731(1) Å, c = 9.0134(2) Å, β = 105.175(1)° Z = 2) in which inorganic layers, made of the connectivity of Zr octahedra and P tetrahedra, are covalently connected by piperazine groups, that act as pillars. The effect of the various synthesis parameters is discussed. A probable structure directing parameter seems to be the pH value of the starting precipitation solution, that can influence the protonation of N atoms of piperazine moiety.